FACULTY PUBLICATIONS

Properties of the Observed Lyα Forest
M. Demianski, A.G. Doroshkevich, and V. Turchaninov

Mon. Not. R.A.S., 318, 1189, 2000

The main observed properties of Lyα absorbers are investigated on the basis of a theoretical model of formation and evolution of dark matter (DM) structure elements. This model is generally consistent with simulations of absorber formation and with the statistical description of structure evolution based on the Zel’dovich theory. The analysis of redshift variations of comoving linear number density of absorbers was performed in our previous paper. We show that the observed characteristics of the Doppler parameter can be related to the size of DM structure elements that allow us to explain the observed distribution of the Doppler parameter. This distribution is found to be consistent with the Gaussian initial perturbations. The observed characteristics of entropy and column density N_HI confirm that the merging of pancakes is the main evolutionary process at redshifts z ≥ 2. The observed sample of absorbers mainly characterizes the matter distribution within large low-density regions and therefore it is difficult to reconstruct the density field from the distribution of absorbers.

Redshift Distribution of Lyα Lines and Metal Systems
M. Demianski, A.G. Doroshkevich, and V. Turchaninov

Mon. Not. R.A.S. 318, 1177, 2000

The observed redshift distribution of Lyα lines and metal systems is examined in order to discriminate and to trace the evolution of structure elements observed in the galaxy distribution, at small redshifts, and to test the theoretical description of structure evolution. We show that the expected evolution of a filamentary component of structure describes quite well the redshift distribution of metal systems and stronger Lyα lines with log (N_HI) ≥ 14, at z ≤ 3. The redshift distribution of weaker Lyα lines can be attributed to the population of poorer structure elements (Zel’dovich pancakes), which were formed at high redshifts from the invisible dark matter and non-luminous baryonic matter, and which at lower redshifts are mainly merged and dispersed.

Statistical Characteristics of Simulated Walls
M. Demianski, A.G. Doroshkevich, V. Müller, and V. Turchaninov

Mon. Not. R.A.S., 318, 665, 2000

The large-scale matter distribution in three different simulations of CDM models is investigated and compared with corresponding results of the Zel’dovich theory of non-linear gravitational instability. We show that the basic characteristics of wall-like structure elements are well described by this theory, and that they can be expressed by the cosmological parameters and a few spectral moments of the perturbation spectrum. Therefore, the characteristics of such elements provide reasonable estimates of these parameters. We show that the compressed matter is relaxed and gravitationally confirmed and manifests itself in the existence of walls as (quasi-) stationary structure elements with a lifetime restricted by their disruption into high-density clouds. The matter distribution is investigated in both real and redshift spaces. In both cases, almost the same particles form the walls, and we estimate differences in corresponding wall characteristics. The same methods are applied to several mock catalogues of “galaxies,” which allows us to characterize a large-scale bias between the spatial distribution of dark matter and of simulated “galaxies.”

Sulfur and Argon Abundances in Type II Planetary Nebulae
Milingo, J.B., Henry, R.B.C., and Kwitter, K.B.

Rev. Mex de Astron. y Astrofis. Conference Series, Vol. 10, p. 230, (2001)

Sulfur and argon gradients for the Milky Way are presented based on newly-acquired spectrophotometry of Type II planetary nebulae (PN). These spectra extend from 3600 Å to 9600 Å allowing us to use the [S III] lines at 9069 Å and 9532 Å to improve upon earlier sulfur abundance estimates. Considering that a significant portion of sulfur in PN exists in the S+2 ionization state, this method should allow us to extrapolate more reliable total element abundances from ionic abundances. Given the progenitor mass and location of Type II PN (close to the Galactic disk), objects in this sample are free of nucleosynthetic self-contamination and thus their S and Ar abundances in particular are expected to reflect levels of these elements in the interstellar medium at the time of PN progenitor formation. Sulfur and argon abundances also provide important information for studying massive star yields of these two elements, as well as their distribution across the Milky Way disk.

SECIS: The Solar Eclipse Coronal Eclipse Imaging System
Phillips, K.J.H., P.D. Read, P.T. Gallagher, F.P. Keenan, P. Rudawy, B. Rompolt, A. Berlicki, A. Buczylko, F. Diego, R. Barnsley, R.N. Smartt, J.M. Pasachoff, and B.A. Babcock

Solar Physics, 193, 259, (2000)

Further Evidence for Increasing Pressure in Triton’s Atmosphere
Elliot, J.L., M.J. Person, S.W. McDonald, M.W. Buie, E.W. Dunham, R.L. Millis, R.A. Nye, C.B. Olkin, L.H. Wasserman, L.A. Young, W.B. Hubbard, R. Hill, H.J. Reitsema, J.M. Pasachoff, T.H. McConnochie, B.A. Babcock, R.C. Stone, P. Francis

Icarus, 148, 347 (2000)

A Search at Two Eclipses for Short-Period Waves that Heat the Corona
Pasachoff, J.M., B.A. Babcock, K.D. Russell, T.H. McConnochie, and S. Diaz

Solar Physics, 195, #2 (2000)

Further Evidence for Increasing Pressure and a Non-spherical Shape in Triton’s Atmosphere
Person, J.M., J.L. Elliot, S.W. McDonald, M.W. Buie, E.W. Dunham, R.L. Millis, R.A. Nye, C.B. Olkin,
L.H. Waserman, L.A. Young, W.B. Hubbard, R. Hill, H.J. Reitsema, J.M. Pasachoff, B.A. Babcock,
T.M. McConnochie, R.C. Stone

AAS Division of Planetary Science, abstract 32.4502 (2000)

Solar-Eclipse Science: Still Going Strong (including) Early Eclipse Science and Pro-am Solar-Eclipse Conference
Pasachoff, J.M.

Sky & Telescope, 101, 46 (2001)

Eclipse
J.M. Pasachoff

Encyclopedia of Astronomy and Astrophysics, Institute of Physics and Macmillan (2001)

Sun
Pasachoff, Jay M., and Leon Golub

World Book (2000)

Nine Ways to Look at a Comet
Pasachoff, Jay M. and Roberta J.M. Olson

Muse, September, pp. 33-38 (2000)

The chvH Locus of Agrobacterium tumefaciens Encodes a Homolog of the Elongation Factor P
E.-T. Peng, L.M. Banta, Visiting Associate Professor of Biology, T.C. Charles, and E.W. Nester

J.Bacteriol., 183, 36-45 (2001)

The virulence of Agrobacterium tumefaciens depends on both chromosome- and Ti plasmid-encoded gene products. In this study, we characterize a chromosomal locus, chvH, previously identified by TnphoA mutagenesis and shown to be required for tumor formation. Through DNA sequencing and comparison of the sequence with identified sequences in the database, we show that this locus encodes a protein similar in sequence to elongation factor P, a protein thought to be involved in peptide bond synthesis in Escherichia coli. The analysis of vir-lacZ and vir-phoA translational fusions as well as Western immunoblotting revealed that the expression of Vir proteins such as VirE2 was significantly reduced in the chvH mutant compared with the wild-type strain. The E. coli efp gene complemented detergent sensitivity, virulence, and expression of VirE2 in the chvH mutant, suggesting that chvH and efp are functionally homologous. As expected, ChvH exerts its activity at the posttranscriptional level. Southern analysis suggests that the gene encoding this elongation factor is present as a single copy in A. tumefaciens. We constructed a chvH deletion mutant in which a 445-bp fragment within its coding sequence was deleted and replaced with an omega fragment. On complex medium, this mutant grew more slowly than the wild-type strain, indicating that elongation factor P is important but not essential for the growth of Agrobacterium.

Genetic and Environmental Factors Affecting T-pilus Formation
E.-M. Lai, O Chesnokova, L.M. Banta, Visiting Associate Professor of Biology, and C.I. Kado

J. Bacteriol. 182, 3705-3716 (2000)

The T pilus, primarily composed of cyclic T-pilin subunits, is essential for the transmission of the Ti-plasmid T-DNA from Agrobacterium tumefaciens to plant cells. Although the virB2 gene of the 11-gene virB operon was previously demonstrated to encode the full-length propilin, and other genes of this operon have been implicated as members of a conserved transmembrane transport apparatus, the role of each virB gene in T-pilin synthesis and transport and T-pilus biogenesis remained undefined. In the present study, each virB gene was examined and was found to be unessential for T-pilin biosynthesis, except virB2, but was determined to be essential for the export of the T-pilin subunits and for T-pilus formation. We also find that the genes of the virD operon are neither involved in T-pilin export nor T-pilus formation. Critical analysis of three different virD4 mutants also showed that they are not involved in T-pilus biogenesis irrespective of the A. tumefaciens strains used. With respect to the environmental effects on T-pilus biogenesis, we find that T pili are produced both on agar and in liquid culture and are produced at one end of the A. tumefaciens rod-shaped cell in a polar manner. We also report a novel phenomenon whereby flagellum production is shut down under conditions which turn on T-pilus formation. These conditions are the usual induction with acetosyringone at pH 5.5 of Ti-plasmid vir genes. A search of the vir genes involved in controlling this biphasic reaction in induced A. tumefaciens cells revealed that virA on the Ti plasmid is involved and that neither virB nor virD genes are needed for this reaction. The biphasic reaction therefore appears to be mediated through a two-component signal transducing system likely involving an unidentified vir gene in A tumefaciens.

K.A Schmidt, Visiting Assistant Professor of Biology

Ecology 81, 2077-2085 (2000)

Habitat Selection under Temporal Heterogeneity: Exorcising the Ghost of Competition Past
K.A. Schmidt, Visiting Assistant Professor of Biology

Ecology 81, 2622-2630 (2000)

Linking Consumer-Resource Theory and Digestive Physiology: Application to Seasonal Diet Shifts
C.J. Whelan, J.S. Brown, K.A. Schmidt, Visiting Assistant Professor of Biology, B.B. Steele, and M.F. Wilson

Evol. Ecol. Res. 2, 911-934 (2000)

The Calcineurin-NFAT Pathway and Muscle Fiber-Type Gene Expression
S.J. Swoap, Assistant Professor of Biology, E.J. Stevenson, R.B. Hunter, H. Mitchell-Felton, N.V. Kansagra,
J.M. Lang, K.Å. Esser, and S.C. Kandarian

Amer. J. Physiol. 279(4), C915-C924 (2000)

The bHLH Transcription Factor MyoD is Required for the Appropriate Regulation of Myosin Heavy Chain IIB Expression
D.J. Seward, J.C. Haney, M.A. Rudnicki, and S.J. Swoap, Assistant Professor of Biology

Amer. J. Physiol. 280(2), C408-C413 (2001)

Altered Leptin Signaling is Sufficient, but not Necessary, for Blood Pressure Reduction Following Caloric Restriction
S.J. Swoap, Assistant Professor of Biology, A. Belfield, A Brophy, and S. Normyle

FASEB Journal 154(4), A78 (2001)

ESR Isochron Exercises: How Accurately Do Modern Dose Rate Measurements Reflect Paleodose Rates?
B.A.B. Blackwell, Research Scientist, A.R. Skinner, Senior Lecturer of Chemistry, J.I.B. Blickstein

Quarternary Science Reviews, 20, 1031-1039 (2001)

In electron spin resonance (ESR) dating tooth enamel, after selecting the appropriate U uptake model, the most significant uncertainty lies in the external dose rate, D_ext(t), which can vary with time. Unlike standard ESR which measures the external dose rate in the modern context, D_ext(t₀), assuming that it reflects the actual external dose rate over the millennia, the isochron method calculates the time-averaged dose rate, D_ext(t) experienced by the tooth without such assumptions. In 45 teeth ranging from 30 ka to 4.5 Ma from 17 sites, D_ext(t) determined by EU or LU isochrons only equaled D_ext(t₀) about 50% of the time. In several sites, geologic evidence indicates that secondary sedimentary processes have significantly altered sedimentary compositions and/or water concentrations, and hence, D_ext(t), over time, accounting for 60-80% of D_ext(t)–D_ext(t₀) disagreements. Simulated isochrons suggest that at least seven teeth, whose isochrons had negative ages or D_ext(t) probably had lost U, while five, with accurate ages but very large D_ext(t) have likely experienced a second U uptake event.

External Dose Rate Determinations for ESR Dating at Bau de l’Aubesier, Provence, France
Bonnie A.B. Blackwell, Research Scientist, Helen Y. Leung, Anne R. Skinner, Senior Lecturer of Chemistry,
Henry P. Schwarcz, Serge Lebel, Hélène Valladas, Joel I.B. Blickstein, Mimi N. Divjak

Quarternary International, 68-71, 345-361 (2000)

At Bau de l’Aubesier, Provence, France, Mousterian artifacts and human teeth occur in inhomogeneous (“lumpy”) sedimentary deposits that include bone and tooth fragments. Due to uranium (U) uptake by the bones and teeth, the external dose rate experienced by the teeth has changed over time. Such changes must be considered when calculating thermoluminescence (TL) ages for burnt flint artifacts or electron spin resonance (ESR) ages for the teeth therein. Here, we assess the external dose rates using three methods: in situ TL dosimetry gives the modern dose rate, whereas volumetrically averaged geochemical analysis is used to estimate time-averaged dose rates that consider U uptake by U-rich sedimentary components. In ESR isochron analysis multiple subsamples with variable U concentrations measure the external dose rates experienced by the tooth regardless of reworking, but do depend on the uptake model assumed.

The methods each suggest significantly different dose rates. TL dosimetry for two combustion horizons measured external γ dose rates at 0.143 ± 0.012 mGray/y in Layer IV and 0.184 ± 0.016 mGray/y in Layer H. Geochemical analysis when volumetrically averaged to account for the influence from different sedimentary components indicates external γ dose rates ranging from as low as 0.094 ± 0.024 mGray/y assuming RU for U-rich sedimentary components to a maximum of 0.251 ± 0.048 mGray/y assuming EU for the U-rich components. Isochron analyses suggest more variable dose rates, ranging from a minimum of 0.009 ± 0.040 mGray/y (LU) in the lower layers to a high of 1.103 ± 0.160 mGray/y (EU) in Layer H1. Three isochrons indicated that the tooth had experienced U leaching or a second uptake event which would affect the accuracy of the dose rate determinations for those teeth. Other teeth may have experiences similar processes. Quaternary researchers who want reliable dates in the age ranges for ESR or TL must carefully consider both the nature of the sediment, especially U-rich bone fragments, and its geometric arrangement around the samples to be dated. Corresponding results using more than one analytic method may be required for a reasonable confidence level.

Origin of Mitochondria in Relation to Evolutionary History of Eukaryotic Alanyl-tRNA Synthetase
J.W. Chihade, Assistant Professor of Chemistry, J.R. Brown, P.R. Schimmel, and L. Ribas de Pouplana

Proceedings of the National Academy of Sciences, 97, 12153-12157 (2000)

The origin of the eukaryotic cell remains an unsolved question. Numerous experimental and phylogenetic observations support the symbiotic origin of the modern eukaryotic cell, with its nucleus and (typically) mitochondria. Incorporation of mitochondria has been proposed to precede development of the nucleus, but it is still unclear whether mitochondria were initially part of basal eukaryotes. Data on alanyl-tRNA synthetase from an early eukaryote and other sources are presented and analyzed here. These data are consistent with the notion that mitochondrial genesis did not significantly precede nucleus formation. Moreover, the data raise the possibility that diplomonads are primary amitochondriates that radiated from the eukaryotic lineage before mitochondria became fully integrated as a cellular organelle.

Asymmetric Synthesis of Phorboxazole B, Part I: Synthesis of the C₂₀–C₃₈ and C₃₉–C₄₆ Subunits
David A. Evans, Victor J. Cee, Thomas E. Smith, Assistant Professor of Chemistry,
Duke M. Fitch, and Patricia S. Cho

Angewandte Chemie, International Edition, 39, 2533-2536 (2000)

Application of Complex Aldol Reactions to the Total Synthesis of Phorboxazole B
David A. Evans, Duke M. Fitch, Thomas E. Smith, Assistant Professor of Chemistry, and Victor J. Cee

Journal of the American Chemical Society, 122, 10033-10046 (2000)

The synthesis of phorboxazole B has been accomplished in 27 linear steps and an overall yield of 12.6%. The absolute stereochemistry of the C₄–C₁₂, C₃₃–C₃₈, and C₁₃–C₁₉ fragments was established utilizing catalytic asymmetric aldol methodology, while the absolute stereochemistry of the C₂–C₃₂ fragment was derived from an auxiliary-based asymmetric aldol reaction. All remaining chirality was incorporated through internal asymmetric induction, with the exception of the C₄₃ stereocenter which was derived from (R)-trityl glycidol. Key fragment couplings include a stereoselective double stereodifferentiating aldol reaction, a metalated oxazole alkylation, an oxazole-stabilized Wittig olefination, and a chelation-controlled addition of the fully elaborated alkenyl metal side chain.

Kinetic Studies of the Evaporation of Model Polar Stratospheric Cloud Films Using FTIR and TPD
Birgit G. Koehler, Assistant Professor of Chemistry

International Journal of Chemical Kinetics, 33, 295-309 (2001)

This study combines Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption to examine the evaporation kinetics of thin films of crystalline nitric acid hydrates, solid amorphous H₂O/HNO₃ mixtures, H₂O–ice, ice coated with HCl, and solid HNO₃. IR spectroscopy measured the thickness of each film as it evaporated, either at constant temperature or during a linear temperature ramp (temperature programmed infrared, TPIR). Simultaneously, a mass spectrometer measured the rate of evaporation directly by monitoring the evolution of the molecules into the gas phase (temperature programmed desorption, TPD). Both TPIR and TPD data provide a measurement of the desorption rate and yield the activation energy and preexponential factor for desorption. TPD measurements have the advantage of producing many data points, but are subject to interference from experimental difficulties such as uneven heating from the edge of a sample and sample support as well as pumping speed limitations. TPIR experiments give clean but fewer data points. Evaporation occurred between 170 and 215 K for the various films. Ice evaporates with an activation energy of 12.9 ±1 kcal/mol and a preexponential factor of 1 × 1032±1.5 molec/cm2sec, in good agreement with the literature. The beta form of nitric acid trihydrate, β–NAT, has an E_des of 15.6 ±2 kcal/mol with log A = 34.3±2.3; the alpha form of nitric acid trihydrate, α–NAT, is around 17.7 ± 3 kcal/mol with log A = 37.2±4. For nitric acid dihydrate, NAD, E_des is 17.3 ±2 kcal/mol with log A = 35.9±2.6; for nitric acid monohydrate, NAM, E_des is 13.0 ± 3 kcal/mol with log A = 31.4±3. The α–NAT converts to β–NAT during evaporation, and the amorphous solid H₂O/HNO₃ mixtures crystallize during evaporation. The barrier to evaporation for pure nitric acid is 14.6±3 kcal/mol with log A = 34.4±3.

The Adsorption of Ammonia on n-Hexane Soot at Low Temperatures
Annabel H. Muenter ’99 and Birgit G. Koehler, Assistant Professor of Chemistry

Journal of Physical Chemistry A, 104, 8527-8534 (2000)

Ammonia is arguably the most important alkaline trace species in the atmosphere. In addition to major ammonia sources at the ground, ammonium has been observed in aircraft exhaust that injects ammonia or ammonium directly into the upper troposphere. If ammonia adsorbs to a soot surface, then reactions in the troposphere between ammonia and other trace gases may be facilitated by soot particles. We examined the uptake of ammonia on n-hexane soot using transmission Fourier transform infrared spectroscopy to quantify the uptake of the gas on soot particles between 115 and 173 K and up to 0.1 Pa (10–3 Torr) NH₃. At temperatures above 173 K, we see virtually no adsorption of ammonia on soot for NH₃ pressures up to 0.1 Pa (10–3 Torr). Between 115 and 173 K we find that upon exposure to the soot, some ammonia sticks rapidly while additional ammonia adsorbs more slowly to the soot. For fast adsorption, the uptake coefficient ranges from ~0.02 ±0.01 at 115 K to ≥1.5(±0.8) × 10–4 at 153 K. The amount of rapid uptake of NH₃ on soot follows the shape of a Langmuir adsorption isotherm. On the heterogeneous soot surface, this simple uptake behavior implies that ammonia adsorbs to soot onto a group of sites with similar binding characteristics. Between 123 and 153 K the saturation coverage is roughly 0.1 monolayer with a binding energy of 24 ± 1 kJ/mole. At 115 K up to a full monolayer adsorbs with roughly 21 kJ/mole binding energy. Ammonia adsorption on soot is not likely to be significant at temperatures and ammonia partial pressures found in the troposphere.

Introduction to Chemical Oscillations Using a Modified Lotka Model
Enrique Peacock-López, Associate Professor of Chemistry

The Chemical Educator, 5, 216-222 (2000)

In teaching chemical kinetics, most textbooks use the Lotka-Volterra Model to introduce the concept of chemical oscillations. Unfortunately, the Lotka-Volterra yields neutrally stable limit cycles for any initial conditions, which is a nonphysical property not observed in chemical kinetics. A more physical, two-variable model with simple linear stability analysis is therefore desirable. Here we consider a Modified Lotka-Volterra Model which shows multiple physical steady states, and both damped and stable oscillations. We can also study a stable node bifurcation to a saddle point and a stable node bifurcation to a stable limit cycle. This dynamically richer model can be analyzed through a simple linear stability analysis and numerical integration of the system of ordinary differential equations. Both methods, in particular the analytical analysis, are accessible to undergraduate students.

Chemical Oscillations: The Templator Model
Enrique Peacock-López, Associate Professor of Chemistry

The Chemical Educator, 6, 202-209 (2001)

Recently, Rebek has synthesized self-replicating molecules in the laboratory. Given the importance of such molecules, we are introducing a simple model of self-replicating molecules for the first time. The model mimics the experimental template mechanism and is an important new dynamical model with cubic nonlinearity. This nonlinearity is modeled after the self-replicating mechanism recently reported in the literature. Here we consider the full Templator Model and a minimal model, which disregard the uncatalized step in the mechanism. For the minimal model, we find exact analytical expression for the locations of the bifurcation points. For the full model, however, we obtain analytical approximations for the bifurcation points that compare very well with the exact numerical solutions.

Q-band Studies of the ESR Signal in Tooth Enamel
A.R. Skinner, Senior Lecturer of Chemistry, D.E. Chasteen, J.M. Shao, B.A.B. Blackwell

Quarternary Science Reviews, 20, 1027-1030 (2001)

Tooth enamel is one of the most promising materials for ESR dating because the X-band signal is large, easy to measure, and extremely stable. The mean lifetime at ambient temperature has been measured at greater than the age of the earth! However, the X-band spectrum in fossil teeth is, in fact, a composite of two signals that can be resolved if the sample is examined in the Q-band region. The relative size of the two signals appears to be a function of degree of fossilization; older teeth have a better-defined second signal. A study of the dependence of these signals on radiation dose, microwave power, and temperature strongly suggests that both signals are located in the hydroxyapatite crystal structures. As such, then, the X-band spectrum, measured at moderate modulation amplitude, is suitable for determining the age of fossil teeth.

Intramolecular Hetero Diels-Alder Routes to Carboline Alkaloids
Scott A. Snyder ’99, David A. Vosburg ’97, Matthew G. Jarvis ’96,
and J. Hodge Markgraf, Professor of Chemistry emeritus

Tetrahedron, 56, 5329-5335 (2000)

Concise and efficient routes to the carboline alkaloids isocanthine, isocanthin-6-one, 1-methylisocanthine, and 1-methylisocanthin-6-one are reported. In each case, the key synthetic step is an intramolecular hetero Diels-Alder reaction of a 1-aza-1,3-diene with an acetylenic dienophile.

Strained Heterocyclic Systems. Part 21. The Menschutkin Reaction
J. Hodge Markgraf, Professor of Chemistry emeritus, Poorab K. Sangani ’97, Ryan J. Manalansan,
Scott A. Snyder ’99, and Randolph P. Thummel

Journal of Chemical Research (Synopsis), 561-563 (2000)

Rate constants are reported for the methyl iodide quarternizations of six 2-substituted quinolines and pyridines. Relative rates are interpreted in terms of steric effects, electronic effects, strain effects, and calculated geometries.

Software for Parallel Adaptive Computation
Joseph E. Flaherty and James D. Teresco, Assistant Professor of Computer Science

Proc. 16th IMACS World Congress on Scientific Computation, Applied Mathematics and Simulation, Paper 174-6 (2000)

Reusable software tools for the solution of partial differential equations using parallel adaptive finite element methods have been developed. We describe the design and implementation of the object-oriented parallel mesh structures within the Rensselaer Partition Model (RPM). This hierarchical model is used to distribute finite element meshes and associated data on a parallel computer. It represents heterogeneous processor and network speeds, and may be used to represent processes in any parallel computing environment, including an SMP, a distributed-memory sizes, and the corresponding interconnection network can be useful in a dynamic load balancing algorithm which seeks to achieve a good balance with minimal interprocessor communication penalties when a slow interconnection network is involved. An example of a partitioning scheme which takes advantage of this information is given.

A Hierarchical Partition Model for Adaptive Finite Element Computation
James D. Teresco, Assistant Professor of Computer Science, Mark W. Beall, Joseph E. Flaherty and Mark S. Shephard

Computational Methods in Applied Mechanical Engineering, 184, 269-285 (2000)

Software tools for the solution of partial differential equations using parallel adaptive finite element methods have been developed. We describe the design and implementation of the parallel mesh structures within an adaptive framework. The most fundamental concept is that of a hierarchical partition model used to distribute finite element meshes and associated data on a parallel computer. The hierarchical model represents heterogeneous processor and network speeds, and may be used to represent processes in any parallel computing environment, including an SMP, a distribute-memory computer, a network of workstations, or some combination of these. Using this model to segment the computation into chunks that can fit into cache memory provides a potential efficiency gain from an increased cache hit rate, even in a single processor environment. The information about different processor speeds, memory sizes, and the corresponding interconnection network can be useful in a dynamic load balancing algorithm which seeks to achieve a good balance with minimal interprocessor communication penalties when a slow interconnection network is involved.

Software for the Parallel Adaptive Solution of Conservation Laws by Discontinuous Galerkin Methods
Joseph E. Flaherty, Mark S. Shepard, Raymond M. Loy, and James D. Teresco,
Assistant Professor of Computer Science

Discontinuous Galerkin Methods Theory, Computation, and Applications, Lecture Notes in Computational Science and Engineering, 11, 113-124, (2000)

We develop software tools for the solution of conservation laws using parallel adaptive discontinuous Galerkin methods. In particular, the Rensselaer Partition Model (RPM) provides parallel mesh structures within an adaptive framework to solve the Euler equations of compressible flow by a discontinuous Galerkin method (LOCO). Results are presented for a Rayleigh-Taylor flow instability for computations performed on 128 processors of an IMB SP computer. In addition to managing the distributed data and maintaining a load balance, RPM provides information about the parallel environment that can be used to tailor partitions to a specific computational environment.

A Library to Support a Graphics Based Object-First Approach to CS 1
Kim B. Bruce, Andrea Danyluk and Thomas Murtagh

SIGCSE Proceedings, pp. 6-10, 2001

In this paper, we describe a library we have developed that supports an “OO-from-the-beginning” approach to CS 1. The design of interactive graphical programs helps students to both use objects and write methods early while designing and implementing interesting graphical programs. The use of real graphics “objects and write methods early while designing and implementing interesting programs. The use of real graphics “objects” and event-driven programming are important components of this approach.

Our Curriculum Has Become Math-Phobic!
Kim B. Bruce, Charles Keleman and Allen Tucker

SIGCSE Proceedings, pp. 243-247, 2001

An earlier paper by the authors argued that mathematical ideas play an important role in the computer science curriculum, and that Discrete Mathematics needs to be taught early in the computer science curriculum. In this follow-up paper, we present evidence that computer science curricula are drifting away from a fundamental commitment to theoretical and mathematical ideas. We propose some actions that can be taken to help reverse this drift.

The Drawability Problem for Minimum Weight Triangulation
Bill Lenhart, Giuseppe Liotta

Theoretical Computer Science (To appear)

A graph is minimum weight drawable if it admits a straight-line drawing that is a minimum weight triangulation of the set of points representing the vertices of the graph. We study the problem of characterizing those graphs that are minimum weight drawable. Our contribution is twofold: We show that there exist infinitely many triangulations that are not minimum weight drawable. Furthermore, we present non-trivial classes of triangulations that are minimum weight drawable, along with corresponding linear time algorithms that take as input any graph from one of these classes and produce as output such a drawing. One consequence of our work is the construction of triangulations that are minimum weight drawable but not Delaunay drawable – that is, not drawable as a Delaunay triangulation.

Proceedings of the Eighteenth International Conference on Machine Learning
Carla E. Brodley, Purdue University
Andrea Danyluk, Associate Professor of Computer Science

Morgan Kaufmann, (2001)

This volume contains the papers presented at the Eighteenth International Conference on Machine Learning (ICML-2001) held June 28 – July 2, 2001 in Williamstown, Massachusetts. ICML-2001 is an annual international forum for the presentation, discussion and dissemination of new algorithms, theoretical results, and applications of machine learning. The conference received 249 paper submissions, from which the 80 papers that appear here were selected by the program committee.

SHRIMP Data from Detrital Zircons with Metamorphic Overgrowths Reveal Tectonic History of the Proterozoic Itremo Group, Central Madagascar
Rónadh Cox, Assistant Professor of Geosciences, Drew S. Coleman, Boston University
Joseph L. Wooden, U. S. Geological Survey, and Carla B. Chokel ’00

Geological Society of America Abstracts with Programs, 32 (7), A-248 (2000)

The Itremo Group in central Madagascar is a continental shelf sequence of quartzites, pelites and marbles that was metamorphosed and deformed during Gondwana assembly. The quartzites are compositionally mature quartz arenites with little petrologic variability, but detrital zircons are commonly quite abundant. The data presented here represent 235 grains (40 of which were dated twice or thrice) from 10 samples collected at widely separated localities throughout the Itremo Group outcrop belt. U-Pb ages of rounded detrital grains range from 1720 to 2900 Ma, indicating that these sediments were derived from a varied mid-Proterozoic to Archean source terrane. There is no statistically significant inter-sample variation in the detrital grain populations, indicating either a single source area for all the sediment, or thorough mixing in the depositional environment of sediment from multiple sources. Because of the regional extent of the sedimentary sequence, and the fact that the quartzites were deposited in a high-energy shallow-marine environment, the latter interpretation is preferred. The age distribution of the population has several distinct modes, and mixture modeling (method of Sambridge and Compston, 1994) using only Pb-Pb ages that are less than 6% discordant (N=97), confirms that there are four discrete populations.

These populations have average ages of 1875 Ma (35% of data points); 2135 Ma (18%); 2500 Ma (37%); and 2670 Ma (10%). Errors on these averages range from 2 to 5 Ma. The detrital zircons experienced late Proterozoic Pb-loss and, in some areas of the outcrop belt, metamorphic overgrowth. Analysis of the thin, faceted rims indicates that they grew at approximately 600 Ma. The metamorphism is related to regional deformation of the sedimentary package during the assembly of Gondwana. Large-scale recumbent nappes and myloritic shear zones record disruption of the stable continental environment and tectonic transport of the shelf sediments at that time. Analyses at the edges of some grains record Mesozoic lead-loss, probably related to Cretaceous uplift and volcanism associated with Madagascar’s passage over the Marion hot spot.

Applied Hydrogeology in the Arlington Quadrangle
David J. DeSimone, Lecturer in Geosciences
Alan P. Baldivieso ’01

Geological Society of America Abstracts with Programs, 33 (1), A-26 (2001)

An evaluation of the hydrogeologic resources of the Arlington 7.5 minute quadrangle, VT, was carried out for the Vermont Geology Survey under contract with the Vermont Geology Division. We have delineated the extent of carbonate bedrock and glacial overburden aquifers in the valley portion of the quadrangle. Overburden thickness and aquifer recharge potential maps were generated, as were three stratigraphic cross sections of the quadrangle. A technical report prepared for the Vermont Survey will examine the aquifer systems and will determine ground water flow to and through the aquifers.

1793 well driller logs were initially examined from computerized records obtained from the Vermont Survey. Of these, 286 wells could be confidently correlated to an existing house and placed on a map using Arcview. A large carbonate bedrock aquifer underlies the inhabited valley portions of the quadrangle and its extent was revealed by subsurface data from 255 wells. The aquifer ranges from 100 to 300 ft in depth and is confined from above by overburden units of till and/or clay. A piezometric surface map for this aquifer was constructed and indicates that areas surrounding topographic highs where there are gaps or thinning in the confining layer might have an enhanced aquifer recharge potential.

A smaller unconfined sand and gravel aquifer, tapped by 17 wells, lies in the central valley portion of the quadrangle where overburden deposits are thickest. This aquifer rests above the layer of till confining the carbonate aquifer and ranges from 50-150 ft in depth. Recharge is by direct infiltration through the permeable gravel and sand unit and the aquifer consequently has the highest recharge potential.

In addition to the technical report, we plan to present a cohesive summary of the surface geology and hydrogeology of the quadrangle that is accessible to the non-geologist and useful in land management decisions. It is hoped that the report will promote environmentally informed decisions on land use in the quadrangle.

Glacier Movement over a Bedrock Ridge as Seen at Mendenhall Glacier, Juneau, Alaska
Marlene F. Duffy ’01
David J. DeSimone, Lecturer in Geosciences

Geological Society of America Abstracts with Programs, 33 (1), A-64 (2001)

Over the past decade, the rapid retreat of the Mendenhall Glacier, Juneau, Alaska has exposed a large schist ridge or “rib” striking approximately 160 (an 82 degree angle to the valley wall). The relatively unweathered stoss face of this rib offers the opportunity to develop a mathematical model to approximate the changing ice flow as a function of ice thickness through abundant striations trending from 140 to 230 degrees. The stoss face of this rib consists of a series of stoss and lee features. The striations reveal a repetitive pattern of changing ice flow up each of these features.

Using a tape and compass method, striation and joint plane data were collected along numerous transects approximately perpendicular to the strike of the form. Using this data, a physical model was developed to explain the plastic flow of the glacier over the ridge. More importantly, this data was used to develop and check a simple mathematical model of the affects of such an obstacle on glacier flow. This model utilizes velocity equations previously developed by others and the properties of adding vectors to crudely predict direction of flow at any point of one of these smaller stoss and lee features.

The Cosmogenic Isotope Record of Late Pleistocene Incision, Boulder Canyon, Colorado
David P. Dethier, Professor of Geosciences, Taylor F. Schildgen ’00
Paul Bierman ’85, Univ. of Vermont, and Marc Caffee, Lawrence Livermore National Laboratory

Geological Society of America Abstracts with Programs, 32 (7), A- 473 (2000)

Geomorphic relations and cosmogenic 26Al, 10Be, and 14C dating link late Pleistocene terraces along Boulder Canyon, Colorado with Front Range moraines and surfaces on the adjacent High Plains. Bull Lake moraines along upper Boulder Creek have minimum average 10Be and 26Al ages of 101 ± 21 ka and 122 ± 26 ka and Pinedale moraines have average model ages of 16.9 ± 3.5 and 17.5 ± 3.6 ka. Isolated terrace remnants 20 to 15 m above grade give a model age of 130 ± 27.5 ka. More extensive fill terraces 15 to 4 m above grade have average model ages from ~30 to 10.5 ka (early to late Pinedale). Low terraces and fans built from tributary catchments show that Boulder Creek has been within 4 m of grade throughout Holocene time. Inset, closely spaced Pinedale-age terraces record multiple pulses of local aggradation and incision 5 to 20 km downstream from Pinedale moraines, implying that glacial events controlled terrace formation. Relative soil development and sparse radiometric ages suggest that the Louviers, Broadway and Piney Creek Alluviums downstream on the High Plains correlate with the three groups of terraces along Boulder Creek. Louviers and Broadway surfaces are only 7 and 4 m, respectively, above grade, indicating downstream convergence of terrace profiles, and slower net incision in the High Plains in late Pleistocene time. Since ~600 ka, net incision rates on the High Plains near Boulder Creek have been ~0.04 m/ka, whereas rates in Boulder Canyon have averaged ~0.15 m/ka since about 130 ka. Extrapolating late Pleistocene rates to middle Pliocene time gives 375 m of net incision in Boulder Canyon, deeper than the modern canyon. Downcutting rates along Boulder Canyon must have increased since early Pleistocene time, perhaps as bedrock knickpoints migrated upstream in response to increases in snowmelt discharge.

Fire and Ice: Using Isotopic Dating Techniques to Interpret the Geomorphic History of Middle Boulder Creek, Colorado
Taylor F. Schildgen ’00
David P. Dethier, Professor of Geosciences

Geological Society of America Abstracts with Programs, 32 (7), A-18 (2000)

Cosmogenic 26Al, 10Be, 14C, and 36Cl dating of geomorphic surfaces along Colorado Front Range canyons provides a framework for analyzing fluvial response to late Pleistocene sediment budget perturbations. Incision rates measured from these surfaces constrain long-term evolution of Front Range canyons. Cosmogenic exposure ages of moraines near Boulder Canyon are consistent with regional glacial chronologies. Bull Lake moraines have minimum average 10Be and 26Al ages of 101 ± 21 ka and 122 ± 26 ka. Pinedale moraines near Nederland have average model 10Be and 26Al ages of 16.9 ± 3.5 and 17.5 ± 3.6 ka, consistent with other cosmogenic exposure and 14C age estimates. Our ages and field relationships suggest that late Pinedale glaciers were nearly as extensive as those active during earlier Pinedale and Bull Lake advances. Fill terraces downstream in Boulder Canyon record fluvial responses to glaciation in the Front Range. Terrace heights above grade can be divided into: (1) Bull Lake (> ~100 ka; at 15 to 20 m); (2) Pinedale (30 to 10 ka; at 4 to 15 m); and (3) Holocene (< 10 ka; at < 4 m). Height ranges record short-term fluctuations in the river profile superimposed on long-term river incision. Limited cosmogenic and 14C dating and soil development suggest that ~ 130 ka terraces in Boulder Canyon correlate with the Louviers Alluvium and that the 32 to 10 ka fills correlate with the Broadway Alluvium on the adjacent High Plains. Terraces < 4 m above grade and alluvial fans in Boulder Canyon record Holocene deposition resulting from forest fires related to climate change. Alluvial fans accumulated at the mouths of 0.5-1.0 sq. km tributary catchments; deposition and associated forest fires correlate with relatively dry late Holocene climate and with the warm, moist early Holocene.

Understanding Glacier Sliding from Subglacially Deposited Silt Skins
Carissa L. Carter ’01
David P. Dethier, Professor of Geosciences

Geological Society of America Abstracts with Programs, 33 (1), A-65 (2001)

In the past two decades, the retreating Mendenhall Glacier in Juneau, Alaska has exposed a bedrock ridge spotted with patchy coatings of calcite-cemented silt to sand-sized lithic grains that can aid our understanding of subglacial processes. These coatings, referred to here as “silt skins”, range from 0.5 to 20 mm in thickness and display two distinct morphologies: striated and corrugated. Striated silt skins are thin, located mainly on stoss slopes, and preserve local striation direction. Thicker, corrugated skins form on lee slopes and consist of parallel micro-ridges elongated in the local down-dip direction. Micro-ridges are constructional features enhanced by erosional processes; wavelengths generally range from 1 to 10 mm.

Thin sections, SEM images, and hand specimens demonstrate that matrix/cement ratios, average grain size, and micro-ridge height and wavelength vary with position on the rock ridge. Highest, thickest skin populations are concentrated on lee slopes in topographic depressions on the rock ridge. Dirty basal ice samples have a relatively high concentration of dissolved calcium to magnesium despite the low concentration of carbonate in the garnet-staurolite grade meta-sediments of the area.

Features morphologically similar to silt skins have been described by Hallet (1976) at temperate glaciers in Alberta and the northern United States, and attributed to subglacial precipitation of CaCO₃ on limestone bedrock. Silt skins at the Mendenhall Glacier formed in the subglacial cavity system from processes likely related to regelation flow and cyclical fluctuations in subglacial hydrology. While they do not persist in subaerial exposures for longer than ~ 20 years near the Mendenhall Glacier, silt skins may provide a useful tool for understanding the dynamics of glacier flow over bedrock.

Sediment Budgets and Stream Terraces: Reconstructing the Effects of Historic Land-use on Sediment Transport in the Birch Brook Catchment, Massachusetts
William B. Ouimet ’01
David P. Dethier, Professor of Geosciences

Geological Society of America Abstracts with Programs, 33 (1), A-64 (2001)

Sediment budgets for the South Branch of Birch Brook, NW Massachusetts, indicate that annual bedload discharge (1.6 tons/sq. km/year) is a function of the number of peak events above bankfull (0.34 cu. meters/sec.) and sediment supply. Sediment availability in the South Branch, a small, forested mountain stream draining 1.25 sq. km, is limited due to low erosion rates on hill slopes. Significant sediment storage occurs behind organic debris dams, in pools associated with bedrock reaches, and along the channel. When annual storms events are < 80 to 90 percent of bankfull, relatively little sediment is available for transport. Because sediment storage along the channel is substantial, the relationship between discharge and sediment delivery shifts after high discharge events, such as the 15-year flood, flush out significant debris dams and transport sediment downstream.

Deforestation, grazing and cultivation within the Birch Brook catchment throughout the 19th century resulted in increased erosion on hill slopes and stream aggradation. We studied stream terraces <1.2 meters above the stream channel along 3.4 km of channel length in the Birch Brook catchment. Stream terraces record increased sediment load and account for aggradation and redistribution of sediment within stream channels of the Birch Brook catchment during this period of high sediment yield. Based on our analysis of modern sediment storage and annual bedload discharge, we estimate that sediment load was potentially three to ten times greater than modern load during this period of increased erosion and fewer organic debris dams. The widespread distribution, volume, and composition of these terraces suggest deposition from continuous aggradation rather than a single storm event such as the 500 or 1000-year flood. Tree core dates frame the stabilization of these terrace surfaces between 60-80 years before present, correlating with major reforestation in the catchment.

Geologic Framework of the Northern Santo Domingo Basin: Structural Overlap of the La Bajada and Pajarito Fault Zones
David A. Sawyer, U.S. Geological Survey
David P. Dethier, Professor of Geosciences et al.

Geological Society of America Abstracts with Programs, 33 (5), 2001

Recent detailed geologic mapping and aeromagnetic data in the vicinity of Cochiti Pueblo elucidate the structural relationship of the La Bajada and Pajarito fault zones in the northern Santo Domingo basin, Rio Grande rift, New Mexico. The La Bajada fault is the principal down-to-the west boundary structure along the NE margin of the Santo Domingo accommodation basin. To the NW, the down-to-east Pajarito fault zone forms the principal western boundary of the asymmetric Española basin. An eastern branch fault splays SE from the Pajarito fault zone near St. Peters Dome. This east Pajarito branch continues for 20 km to the SE where it lies adjacent to and parallels the northern 16 km of the La Bajada fault zone. At the surface these overlapping fault zones offset the Cerros del Rio basalts (2.7-2.2 Ma) and the upper Bandelier Tuff (1.22 Ma), but may represent only the latest displacements on these fault systems. The region of fault zone overlap is characterized by inward-arcing, oblique-slip, fault segments and splays that suggest coeval propagation and mechanical interaction of the Pajarito and La Bajada fault zones. Based on detailed aeromagnetic data, we interpret the east Pajarito fault zone to project at least 10 km south parallel to the northern La Bajada fault in the subsurface of Santo Domingo basin. This projected fault segment displaces Cerros del Rio basalts at shallow depth down to the east to form a narrow (3 km) graben adjoining the La Bajada escarpment. Recognition of the east Pajarito fault zone allows subdivision of the northern Santo Domingo basin into three Pliocene-Quaternary tectonic and stratigraphic domains: a western graben, between the main Pajarito fault zone exposed at Tent Rocks and the Cochiti fault; a central horst exhibiting shallow Cerros del Rio basalts between the Cochiti and east Pajarito faults; and the narrow eastern graben adjoining the La Bajada fault described above.

Pliocene Incision of the Rio Grande in Northeastern New Mexico
James C. Cole, U. S. Geological Survey
David P. Dethier, Professor of Geosciences et al.

Geological Society of America Abstracts with Programs, 33 (5), (2001)

Stratigraphic and geomorphic features of the Rio Grande rift between Española and Socorro indicate the river system began to cut into basin-fill in late Pliocene time, not middle Pleistocene as previously held (e.g., Connell et al., 2000). Between 2.8-2.2 Ma, extensive basalt flows buried a low-relief landscape across the rift. The earliest magmas at Cerros del Rio, Santa Ana Mesa, and Isleta in the basin centers produced hydromagmatic eruptions (Kelley and Kudo, 1978), indicating little incision has taken place at this time (high water table). No thick or extensive fluvial deposits accumulated in this part of the Rio Grande rift during and immediately following eruptions despite continued subsidence (except near very active Pajarito and La Bajada faults; e.g., Sawyer et al., 2001). The widespread hiatus in deposition indicates the drainage system had begun to erode into the upper Santa Fe Group, perhaps as early as 2.5 Ma. The oldest significant post-basalt fluvial deposits are coarse sand and gravel beds restricted to a narrow tract along the eastern side of the modern Rio Grande (e.g. Maldonado et al., 1999). They are younger than 1.6 Ma (contain clasts of older Bandelier Tuff) and locally as young as 1.2 Ma (contain tephra of the younger Bandelier eruption) and overlie tilted and eroded upper Santa Fe. We interpret these deposits as the oldest, highest inset river terrace fill in the rift, underlying the Sunport geomorphic surface of central Albuquerque about 300 feet above grade. Twenty miles south at Los Lunas, basalt erupted at about 1.1 Ma over upper Santa Fe deposits (capped by a thick calcic soil) and flowed 400 feet down toward the Rio Grande where it buried a topographic bench slightly higher than the Sunport surface. The Los Lunas relationships indicate that the Rio Grande had deeply incised the Santa Fe Group by 1.1 Ma and that Santa Fe deposition by the ancestral Rio Grande-Rio Puerco fluvial system had ceased long before.

Influence of Seasonal Winds on Coastal Carbonate Dunes from the Recent and Plio-Pleistocene at Punta Chivato (Baja California Sur, Mexico)
Patrick Russell ’97
Markes E. Johnson, Professor of Geosciences

Journal of Coastal Research, 16, 709-723 (2000)

Distribution of calcium-carbonate sand in the lower Gulf of California is regulated by seasonal winds that preferentially transfer materials to dunes from windward beaches. In order to document the strong onshore flow of winter winds, salt-pruned plants (krummholz) were surveyed at 168 locations on the exposed north side of the Punta Chivato promontory in Baja California Sur (Mexico). Growth deformation is characteristic among leatherplant (Jatropha cuneata) and copal (Bursea hindsinia) trees, which are up to 45 years old. Extensive Recent dunes are well developed almost exclusively along the windward north coast of the promontory, where they reach elevations 60 m above sea level. Sediment samples were collected along two transects from beach or subtidal stations across coastal dunes and from one cliff-perched locality on the northeast tip of the promontory. The calcium-carbonate component of the dunes varies between 50-75% by volume, as determined by point counts on thin sections cut from epoxy-cemented samples. The volcaniclastic content varies locally depending on extent of igneous bedrock exposed intertidally. Mollusk-shell fragments account for the dominant share of dune bioclasts, out-numbering particles derived from coralline red algae by ratios between 25:1 and 50:1. Lithified paleodunes of Pleistocene to possible Pliocene age on the north shore also reveal a large calcium-carbonate component in which particles of molluscan origin out-number coralline algae by ratios as high as 27:1. These results contrast with other regional data on Recent and Pleistocene beach sediments in more protected settings, where crushed debris from rhodoliths, or circumrotatory coralline red algae, are the dominant component. The overall biological provenance of calcium carbonate materials appears to be a consequence of different optimum growing areas for mollusk beds as opposed to rhodolith beds.

Pliocene-Pleistocene Rocky Shorelines Trace Coastal Development of Bahía Concepción, Gulf Coast of Baja California Sur (Mexico)
Markes E. Johnson, Professor of Geosciences
J. Ledesma-Vázquez, Univ. Autonoma de Baja California

Palaeogeography, Palaeoclimatology, Palaeoecology, 166, 65-88 (2001)

Pliocene rocky-shore deposits on the east coast of Baja California Sur (Mexico) formed under the influence of tectonic events and changing relative sea level in the Gulf of California. Depositional patterns are represented by two distinct styles of marine transgression. Level-bedded deposits in semi-enclosed basins form steep buttress unconformities similar in profile to basin fill detected through seismic stratigraphy. Such deposits are typical of sheltered rocky shores, where erosion of terrestrial materials is limited by low wave energy and/or slow rates of changing sea level. Ramp deposits form low-angle (5º to 9º) unconformities on exposed rocky shores, where erosion is enhanced by high wave energy and/or rapid rates of changing sea level. These conform to the pattern of coastal or marine onlap in seismic stratigraphy.

With an area of 270 km2, Bahía Concepción is one of the largest fault-bound bays in the Gulf of California. It occupies a half-graben structure that opens on the gulf to the north. An additional 100 km of coastline was formed after Pliocene flooding of the Bahía Concepción graben. Sheltered rocky shores are represented by buttress unconformities between Miocene volcanics (Comondú Group) and Upper Pliocene strata in small, connected basins at the southeast end of the bay. Dating is based on Clypeaster marquerensis (sand dollar) and associated mollusks in limestones from the Bahía Concepción Member of the Infierno Formation. Other unconformities with the Comondú on the open gulf coast adjacent to Bahía Concepción take the form of carbonate ramps. At Punta Chivato, 20 km north of the bay mouth, the San Marcos Formation is traditionally considered Early Pliocene in age based on Clypeaster bowersi (echinoid) and Solenastrea fairbanksi (coral). At San Nicolas, 15 km east from the southern terminus of the bay, C. bowersi likewise dates the basal Pliocene. Parallel to the axis of the bay, the Bahía Concepción fault zone is no older than the Miocene, because it cuts through the Comondú Group. The main expansion zone for the protogulf jumped over this zone to the east, where Lower Pliocene conglomerates were deposited on a faulted coast between Punta Chivato and San Nicolas. Along this front, eroded andesite cobbles predominate as a component of the basal Pliocene, but rare granodiorite cobbles indicate a Cretaceous source brought to the surface from considerable depth.

Punta Chivato, Bahía Concepción, and the San Nicolas areas retain widespread Upper Pleistocene rocky-shore deposits unconformable with Pliocene strata or the Miocene Comondú. Granodiorites eroded from Punta San Antonio also form the basis for an Upper Pleistocene rocky-shore. These deposits usually are near the 12-m elevation regionally associated with substage 5e terraces (120-135 Ka). Their uniformity in elevation inside and outside Bahía Concepción indicates that minor tectonic uplift was locked in step throughout the immediate region by that time.

Continental Island from the Upper Silurian (Ludlow) Sino-Korean Plate
Rong, Jia-Yu, Nanjing Inst. of Geology and Palaeontology
Markes E. Johnson, Professor of Geosciences

Chinese Science Bulletin, 46, 238-241 (2001)

Recent field studies on Upper Silurian stratigraphy and paleontology in the Inner Mongolia Autonomous Region near Bater Obo resulted in the discovery of a small continental island with fossil invertebrates preserved as encrusters (stromatoporoids and corals) attached directly to a rocky shore surface and buried by silty clay mud. The Bater island (named herein) is 610 m x 200 m in size and composed of Ordovician igneous rock (diorite). Limestone strata dating from the Ludlow Epoch (about 420 Ma) surround the island and dip away from the igneous core in a radial pattern. The encrusting fossils occur on the sheltered (south and southeast) side of the island, whereas the north side was exposed to stronger wave activity based on a basal conglomerate unit composed of diorite boulders. This is the first record of an ancient island in China and the first report worldwide of stromatoporoids as members of a rocky-shore community. The island clearly shows distinct windward and leeward deposits comparable to geologically younger islands from the Mesozoic and Cenozoic outside China.

Tectonic Significance of Textural Unconformities in Garnet from the New England Appalachians
Paul Karabinos, Professor of Geosciences

Geological Society of America Abstracts with Programs, 32 (7), A-31 (2000)

Distinctive, Al-rich metasediments from Vermont contain garnet porphyroblasts whose textures record an undisputed history of multi-stage growth. Rosenfeld (1968) suggested that the garnet cores grew during the Ordovician Taconian orogeny and that the rims grew during the Devonian Acadian orogeny. Karabinos (1985) used zoning patterns to argue that incomplete garnet resorption separated the two growth stages. A different interpretation proposed by Thompson et al. (1977) is that these unconformities were produced during a single prograde Acadian metamorphism in which two or more garnet producing reactions were separated by an intermediate garnet consuming reaction. This last interpretation is inconsistent with regional observations that textural unconformity are found in rocks over a wide range of metamorphic conditions, including some for which no prograde garnet consuming reactions are plausible. The hiatus in garnet growth throughout southern Vermont is texturally correlated with the development of a crenulation cleavage, pointing to a tectonic cause for the regional change in metamorphic conditions. A strong spatial correlation in intensity between an early set of isograds defined by mineral inclusions in garnet cores and a late set of isograds defined by matrix assemblages argues against two prograde events separated by 80 million years. The prograde dehydration reactions in these rocks could be interrupted and/or reversed by (1) an increase in the activity of water (fluid infiltration along faults), (2) an increase in P (loading by thrust sheets), or (3) a decrease in T (tectonic unroofing by low-angle normal faults). Fluid infiltration along low-angle normal faults during the Acadian orogeny is supported by the observation that these rocks are found in domes structurally below faults characterized by omission or dramatic thinning of the lithologic units. Further, rutile is found only in garnet cores whereas ilmenite is present in garnet rims and the matrix, suggesting that P decreased from the first to second stage of garnet growth. An important problem is explaining why prograde reactions resumed after tectonic unroofing. The widespread occurrence of late granitoid intrusions in the domes suggests that decompression melting and advective heat transfer may have caused an increase in T.

Acadian Extension in Western New England
Paul Karabinos, Professor of Geosciences

Geological Society of America Abstracts with Programs, 33 (1), A4-A5 (2001)

A dramatic feature of the geology of western New England is the thinness of some Paleozoic units east of the Green Mountain and Berkshire massifs in southeastern Vt. and western Mass. compared to equivalent units north, west, and south of the massifs. These structurally thinned units are widely interpreted as preserving a Taconian accretionary wedge and arc complex. The attenuation of these units is most compelling around the Chester dome where rocks lithologically equivalent to the Pinney Hollow, Ottauquechee, Stowe, and Missisquoi Formations are locally one to two orders of magnitude thinner than they are elsewhere. P-T paths for rocks structurally below the attenuated zone in the Chester dome suggest 2.5 kbar of decompression during Acadian metamorphism (Vance and Holland, 1993), equivalent to approx. 10 km of denudation. Boudinaged layers and stretched porphyroblasts within the attenuated zone also indicate extension. Rosenfeld (1968) recognized west-southwest directed layer-parallel extension and layer-perpendicular shortening in stretched pebble conglomerates of the Silurian Shaw Mountain Formation showing that extension is not restricted to pre-Silurian rocks. Thus, extension and crustal thinning were accomplished by internal strain as well as displacement on multiple faults distributed throughout a significant crustal section. Assuming that decompression resulted entirely from tectonic denudation and that average fault dips were 10 to 30 degrees, the relative displacement of rocks above and below the attenuated zone during extension was between 60 to 20 km. Early Acadian crustal thickening led to metamorphism at pressures up to approx. 10 kbar around the Chester dome (Kohn and Spear, 1990). Below the attenuated zone, garnet cores record this higher-pressure metamorphism and contain abundant rutile inclusions. Garnet growth was interrupted by a temperature decrease accompanying extension and decompression. A second lower-pressure prograde metamorphism and garnet growth stage, lacking rutile inclusions, produced unconformity textures and reflects a temperature increase caused by enhanced heat flow. Peak metamorphic temperatures were reached after extension but prior to later, dome-stage Acadian folding.

Competing Models for the Origin of the Shelburne Falls and Bronson Hill Arcs, New England Appalachians
Paul Karabinos, Professor of Geosciences

Geological Society of America Abstracts with Programs, 33 (1), A-20 (2001)

Recent studies show that arc magmatism was widespread in the Appalachians and Caledonides between 480-470 Ma, coeval with the Shelburne Falls arc (SFA) in western New England. Paleomagnetic and fossil evidence from Newfoundland, however, demonstrates that coeval arcs developed near Laurentia, near Avalonia, and within Iapetus (MacNiocaill and others, 1997); thus correlations based on age alone are tenuous. Karabinos and others (1998) argued that the SFA formed above an east-dipping subduction zone and collided with Laurentia during the Taconian orogeny (470-455 Ma). The younger Bronson Hill arc (BHA) (454-442 Ma, Tucker and Robinson, 1990) may have formed (1) above the same east-dipping subduction zone as the SFA (Ratcliffe and others, 1998), (2) above a new west-dipping subduction zone following the Taconian orogeny (Karabinos and others, 1998), or (3) far from Laurentia near the Avalonian margin (Van Staal and others, 1998). Because arc rocks in western New England range in age from 496 to 436 Ma, the first model requires subduction for 30 m.y. after initial collision of Laurentia and the SFA. It seems impossible to generate arc magmas for so long after closure of the ocean basin that separated Laurentia and the SFA. Furthermore, work in the Canadian Appalachians provides clear evidence for multiple Ordovician arcs as opposed to a single long-lived arc. A lack of paleomagnetic and fossil data make it difficult to rule out either the second or third model. The following observations favor the second model: (1) In western Conn. arc rocks coeval with the BHA intruded deformed and metamorphosed rocks correlated with the SFA. (2) In northern New Hampshire two sequences containing volcanics coeval with the SFA and BHA are separated by an unconformity (R.H. Moench, personal com.), (3) The Connecticut Valley trough, which separates the SFA and BHA, contains rift volcanics that began to form soon after arc magmatism in the BHA ceased, consistent with both having formed above a west-dipping subduction zone.

Landscape Evolution in the City of Rocks National Reserve, Southern Idaho
Kevin Pogue, Whitman College
Paul Karabinos, Professor of Geosciences

The Fourteenth Keck Research Symposium in Geology, 14, 158-161 (2001)

The City of Rocks National Reserve lies within the core of the Albion Range metamorphic core complex, part of the belt of highly extended Cordilleran core complexes within the Basin and Range province. Rocks exposed in the Albion Range record most of the major tectonic events that affected the western United States. The oldest rocks are basement gneiss and schist of the Green Creek Complex, part of the Archean Wyoming Province (Armstrong and Hills, 1967; Armstrong, 1968). These are overlain by low-grade Proterozoic metasediments deposited during the rifting event that led to the formation of the Cordilleran passive margin. Shallow water sedimentary units were deposited along the new margin during the Paleozoic and Mesozoic, prior to Late Jurassic to Cretaceous compressional deformation associated with the Sevier orogeny. This part of Idaho was in the hinterland of the Sevier thrust belt and shows evidence of both compression and extension during the late Mesozoic (Wells, 1977). In the Oligocene, the Almo pluton was emplaced as the region was dramatically uplifted and extended. Before and after emplacement, the rocks overlying the pluton were extended along large-scale low-angle normal faults (Miller and Bedford, 1999). Extension continued throughout the Cenozoic and the rocks were uplifted to form three large-scale structural domes (Miller, 1980). Bimodal volcanics associated with the passage of the Yellowstone hotspot blanketed the region during the Miocene. The most recent extension is along high-angle late Quaternary range-bounding normal faults. The highest points of the Albion Range, Mt. Harrison (9,600’) and Cache Peak (10,200’) hosted alpine glaciers during the Pleistocene. Deep erosion by streams and glaciers along the crest of the range has exposed the Archean Green Creek Complex and the Almo pluton in the core of the structural domes. The granitic rocks of these units have been eroded into a spectacular landscape of fins and spires.

Precambrian Igneous and Metamorphic Rocks in the Florissant Region, Central Colorado: Their Topographic Influence, Past and Present
R. A. Wobus, Professor of Geosciences

Bulletin No. 5, Pikes Peak Research Station, 9 p. (2001)

The Late Eocene lake deposits with their world-famous fossils at Florissant, central Colorado, lie in a paleovalley incised into the Pikes Peak Granite, ca. 1.08 Ga (Ga = “billion years”), within a few kilometers of the western edge of the 3000 km2 Pikes Peak batholith. A prominent NNW-trending ridge of highly resistant sillimanitic schists and gneisses (ca. 1.75 Ga) bounds the batholith on the west, and relatively more resistant granite of the 1.46 Ga Cripple Creek batholith is in contact with the Pikes Peak Granite southwest of the lake deposits. Smaller plutons of older gneissic tonalite and granodiorite correlated with the Routt (Boulder Creek) plutonic suite (ca. 1.70-1.67 Ga) also occur just west of the Pikes Peak batholith.

The anorogenic Pikes Peak batholith typically consists of reddish, coarse-grained, easily weathered biotite- and hornblende-biotite granite. A fine-grained, often porphyritic variant locally forms a chilled margin along the western edge of the batholith and is found in many small stocks scattered through it. With a more resistant texture than the coarse-grained Pikes Peak Granite, this rock underlies many of the promontories that rise above the extensive Eocene erosion surface which was developed across most of the batholith and upon which the Florissant lake deposits lie. Late sodic plutons of the Pikes Peak batholith, such as the syenite stock and fayalite granite ring dikes of the Lake George intrusive center immediately north of the lake beds, also have greater resistance to erosion than the typical coarse-grained Pikes Peak Granite.

Geochemical studies by student and faculty participants in the Keck Undergraduate Geology Consortium (Smith and others, 1999) conclude that the Pikes Peak Granite is an A-type granite that was emplaced during a time of crustal extension, perhaps associated with continental epeirogenic uplift and doming, and that the late sodic plutons may owe their alignment to a rifting event. Nd-Sm isotopic studies indicate that the granitic rocks represent crustal melts and that the late sodic plutons are fractionation products of mantle-derived mafic rocks with only minor contamination by continental crust (Smith and others, 1999).

Geochemistry of Volcanic Units of the Bonanza Caldera, Central Colorado: Implications for Magma Sources and Vent Locations
D. R. Smith, Trinity University, Rebecca B. Atkinson ’00
R. A. Wobus, Professor of Geosciences, and others

Geological Society of America Abstracts with Programs, 33 (5), A-6 (2001)

The ~38-33 Ma Bonanza volcanic center is located north of the Rio Grande Rift and along a NNW alignment with the Mt. Aetna and Grizzly Peak calderas to the north. Bonanza has been considered part of the San Juan volcanic field, but the relatively early timing of caldera collapse and onset of silicic activity distinguishes it from calderas of the western and central parts of the San Juan field. Prior to caldera formation, Bonanza was a composite cone built of high-potassium andesite and dacite lavas. Explosive eruptions of <50 cubic kilometers of felsic magma led to trapdoor-style caldera collapse. Pyroclastic units include the dacitic lower Bonanza Tuff (LBT) and rhyolitic upper Bonanza Tuff (UBT). Activity resumed to andesitic and dacitic lavas, followed by intrusion of silicic stocks along the caldera margin.

Petrologic and new geochemical data exhibit similarities between the LBT and the andesitic/dacitic lavas that occur above and below the pyroclastic units, whereas the UBT is geochemically distinct from other Bonanza volcanic units. Major and trace element compositions are inconsistent with derivation of UBT rhyolitic magma by fractionation involving intermediate parental magmas represented by the LBT and Bonanza lavas. The UBT is interpreted as a crustal melt, involving a source distinct from those that supplied intermediate magmas.

The distinctive nature of the UBT relative to other Bonanza volcanic units raises the question whether UBT magma was erupted from local vents or from vents distal from the Bonanza caldera. However, the UBT shares geochemical characteristics with late silicic stocks emplaced at vents along the caldera margin, suggesting that UBT rhyolitic magma was erupted from those (or other) vents proximal to the caldera.

The Pepsi Putnam Challenge
Colin C. Adams, Mark Hopkins Professor of Mathematics

Mathematical Intelligencer, 22, No. 3, 37-38 (2000)

The Putnam exam with product placement.

The S.S. Riemann
Colin C. Adams, Mark Hopkins Professor of Mathematics

Mathematical Intelligencer, 22, No. 4, 41-42 (2000)

A theorem meets its iceberg.

Overcoming Math Anxiety
Colin C. Adams, Mark Hopkins Professor of Mathematics

Mathematical Intelligencer, 23, No. 1, 45-50 (2001)

Math anxiety as a disease.

U-Substitution
Colin C. Adams, Mark Hopkins Professor of Mathematics

Mathematical Intelligencer, 23, No. 2, 29 (2001)

A technique of integration on the basketball court.

How to Ace the Rest of Calculus: The Streetwise Guide
Colin C. Adams, Mark Hopkins Professor of Mathematics, J. Hass and A. Thompson

W.H. Freeman and Company (April, 2001)

The second in the humorous How to Ace Series, covering the rest of calculus.

The Knot Book
Colin C. Adams, Mark Hopkins Professor of Mathematics

W.H. Freeman and Company (January, 2001)

Updated paperback edition.

Exploring the Number Jungle: A Journey into Diophantine Analysis
Edward B. Burger, Associate Professor of Mathematics

The American Mathematical Society, 155 (2000)

In this text, the reader is led through a journey of discovery to the high points of diophantine analysis and related areas of number theory.

On Periods of Elements from Real Quadratic Number Fields
Edward B. Burger, Associate Professor of Mathematics, and A.J. van der Poorten

Canadian Math. Soc. Proceedings Series, 27, 35-43 (2000)

Here we provide another proof of a theorem of E. Burger regarding a necessary and sufficient condition on the partial quotients of two real quadratic irrational numbers to insure that they are elements of the same quadratic number field over Q.

Diophantine Olympics and World Champions: Polynomials and Primes Down Under
Edward B. Burger, Associate Professor of Mathematics

The American Mathematical Monthly, 107, 822-829 (2000)

Using a lighthearted Olympic theme, we prove that there exist transcendental numbers whose best approximates have denominators that are values of certain non-constant polynomials evaluated at integers and transcendental numbers whose approximates have denominators who are all primes.

Abandoning Dead Ends: Embracing Lively Beginnings
Edward B. Burger, Associate Professor of Mathematics, and Michael Starbird

Mathematical Association of America Focus, 9, 10-11 (2000)

Here we examine what mathematics can add to the life of the mind far beyond the discipline itself.

On a Question of Mordell and a Spectrum of Linear Forms
Edward B. Burger, Associate Professor of Mathematics

Journal of the London Mathematical Society, 62, 701-715 (2000)

Here we consider a question raised by Mordell regarding lattice point-free parallelepipeds and find a spectrum of optimal regions in dimension 2.

Global Structures on CR Manifolds via Nash Blow-ups
Thomas Garrity, Professor of Mathematics

Michigan Math. J., 48, 281-294 (2000)

A generic compact real codimension two submanifold X of complex (n+2) space will have a CR structure at all but a finite number of points (failing at the complex jump points J). The main theorem of this paper gives a method of extending the CR structure on the non-jump points X-J to the jump points. We examine a Gauss map from X-J to an appropriate flag manifold F and take the closure of the graph of this map in X x F. This is a version of a Nash blow-up. We give a clean criterion for when this closure is a smooth manifold and see that the local differential properties at the points X-J can now be naturally extended to this new smooth manifold, allowing global techniques from differential geometry to be applied to compact CR manifolds. As an example, we find topological obstructions for the manifold to be Levi nondegenerate.

On Periodic Sequences for Algebraic Numbers
Thomas Garrity, Professor of Mathematics

J. of Number Theory, 88, no. 1, 86-103 (2001)

For each positive integer n > 1, a new approach to expressing real numbers as sequences of nonnegative integers is given. The N = 2 case is equivalent to the standard continued fraction algorithm. For n = 3, it reduces to a new iteration of the triangle. Cubic irrationals that are roots of x3 + k x2 + x - 1 are shown to be precisely those numbers with purely periodic expansions of period length one. For general positive integers n, it reduces to a new iteration of an n dimensional simplex.

Riemannian Geometry: A Beginner’s Guide
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics

A.K. Peters, revised printing (2001)

Starting with an extrinsic approach to curvature, this book provides a short, intuitive, direct introduction to Riemannian geometry, including topics from general relativity, global geometry, and current research on norms more general than area. The second edition includes many new problems and new sections on the isoperimetric problem and on double Wulff crystals.

Calculus Lite
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics

A.K. Peters, Third Edition, (2001)

This lean text covers single-variable calculus in under 300 pages by (1) getting right to the point, and stopping there, and (2) introducing some standard preliminary topics, such as trigonometry and limits, by using them in the calculus.

Math Chat
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics

MAA Web Page, Semi-Monthly, (1998)

Column with questions, answers, and prizes. Available at the Mathematical Association of America web page at www.maa.org.

Perimeter-minimizing Curves and Surfaces in Rn Enclosing Prescribed Multi-volume
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics

Asian J. Math., 4, 373-382, (2000)

Planar curves minimizing length for given area are classically characterized as circular arcs. We give a new generalization to Rn of such area constraints and characterize the minimizing curves. We also consider surfaces satisfying new generalized volume constraints.

The Isoperimetric Problem on Surfaces of Revolution of Decreasing Gauss Curvature
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics,
Hugh Howards and Michael Hutchings

Trans. AMS, 352, 4889-4909, (2000)

We prove that the least-perimeter way to enclose prescribed area in the plane with smooth, rotationally symmetric, complete metric of strictly decreasing Gauss curvature consists of one or two circles, bounding a disc, the complement of a disc, or an annulus. We also provide a new isoperimetric inequality in general surfaces with boundary.

Some Sharp Isoperimetric Theorems for Riemannian Manifolds
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics,
David L. Johnson

Indiana U. Math J., 49, 1017-1041 (2000)

We prove that a region of small prescribed volume in a smooth, compact Riemannian manifold has at least as much perimeter as a round ball in the model space form, using differential inequalities and the Gauss-Bonnet-Chern theorem with boundary term. First we show that a minimizer is a nearly round sphere. We also provide some new isoperimetric inequalities in surfaces.

Proof of the Double Bubble Conjecture
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics,
Michael Hutchings, Manuel Ritore, and Antonio Ros

ERA AMS, 6, 45-49 (2000)

We prove that the standard double bubble provides the least-area way to enclose and separate two regions of prescribed volume in R3.

Hales’s Proof of the Hexagonal Honeycomb Conjecture and Related Recent Results and Open Problems
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics
Pacelli Zitha, John Banhard, and Guy Verbist, eds.

Proc. 3rd EuroConference on Foams, Emulsions and Applications, (2000)

A write-up of my talk at the Eurofoam Conference in Delft, The Netherlands.

Proof of the Double Bubble Conjecture
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics

The Amer. Math. Monthly, 108, 193-205 (March 2001)

An expository account of our proof that the standard double bubble provides the least-area way to enclose and separate two regions of prescribed volume in R3.

Double Bubble No More Trouble
Frank Morgan, Dennis Meenan (’54) Centennial Professor of Mathematics

Math Horizons, 2, 30-31 (November 2000)

A popular account with color illustrations of our proof that the standard double bubble provides the least-area way to enclose and separate two regions of prescribed volume in R3.

On Nonsingular Chacon Transformations
Cesar E. Silva, Professor of Mathematics, and T. Hamachi

Illinois Journal of Math, Vol. 44, 868-883 (2000)

We construct nonsingular Chacon transformations with 2-cuts of type III lambda, for every 0 < lambda < 1, and type II infinity and show that their 2-fold Cartesian product is ergodic.

A Quasiperiodic Route to Chaos in the Kerr Lens Modelocked Ti:Sapphire Laser
S.R. Bolton and Mark R. Acton ’00

Physical Review A, 62, 063803 (2000)

We have performed an experimental study of the nonlinear dynamics in a Kerr-lens model-locked Ti:Sapphire laser producing ~25 fs pulses. Grassberger-Procaccia and false nearest-neighbors analyses indicate that the pulse trains follow a quasiperiodic route to low-dimensional chaos. The experimental results agree quite well with a simulation based on the Gaussian four-by-four matrix formalism. Pulse resolved measurements show that the instability in pulse energy is associated with instabilities in the pulse spectral and spatial profiles.

Evidence of Six-Particle Coulomb Correlations in Six-wave-mixing Signals from a Semiconductor Quantum Well
V.M. Axt, S.R. Bolton, U. Neukirch, L.J. Sham, and D.S. Chemla

Physical Review B, 63, 115303 (2000)

Six-wave-mixing signals from a ZnSe quantum well are analyzed experimentally and with a microscopic density-matrix description using the dynamics-controlled truncation scheme. For each physically distinct combination of polarizations of the exciting pulses, the spectrum of six wave mixing emission is measured as a function of time delay. The experimental results are compared with calculations performed at different levels of approximations. Although the leading order contributions to six wave mixing signal are of fifth order in the laser field, we show that there are significant signal components, which are due to at least χ7 processes. The sensitivity of the six wave mixing signals to high-order Coulomb correlations is demonstrated. Six point density matrices are found to be indispensable for the interpretation of our experiments, while some details seem to indicate the involvement of even higher order correlation functions. Furthermore, we find a remarkable dynamical decoupling of spectral signatures and the delay-time behavior after excitation with linearly polarized light.

Demonstration of Sixth-order Coulomb Correlations in a Semiconductor Single Quantum Well
S.R. Bolton, U. Neukirch, L.J. Sham, D.S. Chemla and V.M. Axt

Physical Review B, 85, 2002 (2000)

Six-wave mixing in a ZnSe quantum well is investigated and compared with microscopic theory. We demonstrate that sixth-order Coulomb correlations have a significant qualitative impact on the nonlinear optical response. Six-wave mixing is shown to be a uniquely sensitive tool for investigation of correlations beyond the four-point level.

Effects of Higher-order Correlations on the Pump-probe Response of Semiconductors
U. Neukirch, S.R. Bolton, L.J. Sham and D.S. Chemla

Physica Status Solidi, October (2000)

The pump-and-probe response of a ZnSe quantum well is investigated in which the biexciton binding energy exceeds both the exciton damping and inhomogeneous broadening by far. A comparison between experimental data and model calculations shows, that with co-circularly polarized beams the nonlinear mean field contributions dominate those induced by four-particle correlations. In contrast, only the four-particle correlations contribute to the signal in counter-circular configuration. Here it turns out that the exciton-biexciton interaction dominates the response for resonant excitation of the exciton. The Occurrence of exciton-biexciton transitions leads to a renormalization of the period of coherent oscillations at negative pulse delay.

Polariton-Biexciton Transitions in a ZnSe-based Microcavity
U. Neukirch, S.R. Bolton, N.A. Fromer, L.J. Sham, D.S. Chemla

Journal of Crystal Growth, 214, 1010 (2000)

The optical third-order nonlinearity of a ZnSe-based microcavity is investigated by the pump and probe method. In the specially designed non-monolithic sample the biexciton binding energy exceeds all damping constants and the normal-mode splitting between exciton and cavity photon. For counter-circular polarized beams the nonlinear response exhibits strong oscillatory structures in the spectral vicinity of the polariton-biexciton transition. Comparison to model calculations shows that in this case the coherent nonlinearity is completely dominated by biexciton-exciton interactions beyond the Hartree-Fock approximation.

Observation of Optically Induced Feshbach Resonances in Collisions of Cold Atoms
F.K. Fatemi, K.M. Jones and P.D. Lett

Physical Review Letters, 85, 4462 (2000)

We have observed optically induced Feshbach resonances in a cold (<1mK) sodium vapor. The optical coupling of the ground and excited-state potentials changes the scattering properties of an ultracold gas in much the same way as recently observed magnetically-induced Feshbach resonances, but allows for some experimental conveniences associated with using lasers rather than magnetic fields. The scattering properties can be varied by changing either the intensity or the detuning of a laser tuned near a photoassociation transition to a molecular state in the dimer. In principle, this method allows the scattering length of any atomic species to be altered. A simple model is used to fit the dispersive resonance lineshapes.

Entangled Rings
Kevin M. O’Connor ’00 and William K. Wootters, Professor of Physics

Physical Review A, 63, 052302 (2001)

Consider a ring of N qubits in a translationally invariant quantum state. We ask to what extent each pair of nearest neighbors can be entangled. Under certain assumptions about the form of the state, we find a formula for the maximum possible nearest-neighbor entanglement. We then compare this maximum with the entanglement achieved by the ground state of an antiferromagnetic ring consisting of an even number of spin-1/2 particles. We find that, though the antiferromagnetic ground state typically does not maximize the nearest-neighbor entanglement relative to all other states, it does so relative to other states having zero z component of spin.

Entanglement of Formation and Concurrence
William K. Wootters, Prof. of Physics

Journal of Quantum Information and Computation, 1, 27-44 (2001)

Entanglement of formation is one of three widely studied measures of entanglement of a general bipartite system. This paper reviews our current understanding of entanglement of formation and the related concept of concurrence, including discussions of additivity, the problem of finding explicit formulas, and connections between concurrence and other properties of bipartite systems.

The Thematic Apperception Test
Phebe Cramer, Professor of Psychology

In Encyclopedia of Psychology, (2000)

Development of Identity: Gender Makes a Difference
Phebe Cramer, Professor of Psychology

Journal of Research in Personality, 34, 42-72 (2000)

Gender-based differences in the relation between Identity status and personality configurations of 200 male and female college students were studied. For statuses based on commitment (the Achieved and Foreclosed identities), the personality configuration of males and females was more similar than that of males and females in statuses lacking commitment (Moratorium and Diffused). Further, the importance of four personality dimensions that had been hypothesized (Grotevant, 1987) to promote identity development (ego-resilience, openness to experience, self-esteem, and self-monitoring) was found to vary as a function of gender, as did the self-descriptions of males and females in each identity status.

Defense Mechanisms in Psychology Today: Further Processes for Adaptation
Phebe Cramer, Professor of Psychology

American Psychologist, 55, 637-646 (2000)

Although the concept of the defense mechanism was rejected from academic psychology for a number of years, recent empirical studies show renewed interest in defenses. Cognitive psychologists have confirmed the existence of unconscious psychological processes, a requisite for defenses. Developmental, personality, and social psychologists have all found evidence for defense mechanisms that explicate psychological functioning. The relevance of this new information for clinical practice is discussed.

Defense Use and Defense Understanding in Children
Phebe Cramer, Professor of Psychology and Melissa Brilliant ’99

Journal of Personality, 69, 297-322 (2001)

This study investigated the relation between children's use of defense mechanisms and their understanding of those defenses. We hypothesized that, once a child understands how a particular defense functions, the use of that defense will no longer be successful and will be replaced by another defense mechanism that is not yet understood. Defense use was assessed from the Thematic Apperception Test (TAT) stories told by 122 children; defense understanding was determined from the children's understanding of stories portraying defenses. The results indicated that younger children (mean age = 7–8) used the defense of denial more than the older children (mean age = 9–11). Older children understood the functioning of denial and projection better than the younger children. A comparison of children who did and did not understand a defense showed that younger children who understood the functioning of denial were less likely to themselves use denial. Likewise, older children who understood the functioning of projection were less likely to use this defense.

Beyond the Fundamental Attribution Era?
Steven Fein, Associate Professor of Psychology

Psychological Inquiry, 12, 16-21 (2001)

Comments on the article by J. Sabini et al (see record 2001-14918-001), which reviewed and critiqued classic studies on social influence and the fundamental attribution error. The present author believes that Sabini et al raise important concerns about cracks in the foundation that underlie the prototypical understanding of the correspondence bias (also known as fundamental attribution error). However, Sabini et al may have gone too far in their critiques. Some of the ways in which the present author's work on the effects of suspicion on the correspondence bias can aid in highlighting problems in the article by Sabini et al.

Prejudice as Self-Image Maintenance: Affirming the Self through Derogating Others
Steven Fein, Associate Professor of Psychology and Steven Spencer

Stereotypes and Prejudice: Essential Readings. Key Readings in Social Psychology, 172-190 (2000)

The authors argue that self-image maintenance processes play an important role in stereotyping and prejudice. Three studies demonstrated that when individuals evaluated a member of a stereotyped group, they were less likely to evaluate that person negatively if their self-images had been bolstered through a self-affirmation procedure, and they were more likely to evaluate that person stereotypically if their self-images had been threatened by negative feedback. Moreover, among those individuals whose self-image had been threatened, derogating a stereotyped target mediated an increase in their self-esteem. The authors suggest that stereotyping and prejudice may be a common means to maintain one's self-image, and they discuss the role of self-image-maintenance processes in the context of motivational, sociocultural, and cognitive approaches to stereotyping and prejudice.

Central CRH Suppresses Specific Antibody Responses: Effects of beta-Adrenoceptor Antagonism and Adrenalectomy
Elliot M. Friedman, Assistant Professor of Psychology and Michael Irwin

Brain, Behavior, and Immunity, 15, 65-77 (2001)

Central corticotropin releasing hormone (CRH)-induced activation of the sympathetic nervous system and/or the pituitary-adrenal axis is hypothesized to mediate suppression of in vivo specific antibody responses. To test whether -adrenergic receptor activation is involved in the immunosuppressive effects of central CRH, rats were pretreated with propranolol or saline before intracerebroventricular infusion of CRH and immunization with keyhole limpet hemocyanin (KLH). KLH (3 µg/kg) immunization induced significant increases in circulating levels of antigen-specific IgM and IgG. Central infusion of CRH (200 pmol) suppressed both IgM and IgG responses. Pretreatment with propranolol (20 mg/kg IP) reversed CRH-induced suppression of IgG responses but had no effect on IgM levels. To test whether adrenal activation also plays a role in the effects of KLH on specific antibody responses, a separate group of animals underwent adrenalectomy prior to CRH infusion and immunization with KLH. As compared to nonadrenalectomized control rats, adrenalectomized rats showed a reduction of antibody responses, and CRH failed to induce a further suppression of IgM or IgG responses in adrenalectomized animals. Collectively, these data suggest that beta-adrenoceptors mediate the suppression of primary antibody responses induced by central CRH. Moreover, the adrenals may promote optimal primary antibody responses after exposure to physiological levels of antigen.

“Interpreting and Inventing Social Reality: Attributional and Constructive Elements in Social Comparison”
George R. Goethals, II, Professor of Psychology and William M.P. Klein

Handbook of Social Comparison: Theory and Research, 23-44 (2000)

This chapter discusses a facet of social comparison: the balance between the careful logic and rationale that people sometimes bring to social comparison vs. the seemingly irrational and biased thinking that just as often affects the way they compare to others. The authors begin by discussing the way social comparison has been integrated into highly rational models of attribution processes that became central to social psychology in the 1970s. This integration imagined a social comparer who was generally thoughtful, logical, and rational. Next, they consider the way models of a much lazier, self-protective and self-enhancing social thinker suggested a less logical but no less clever social comparer who constructed a view of his standing in relation to others that supported a self-satisfied appraisal of important personal characteristics.

Responding to Blame in Family Therapy: A Constructionist/Narrative Perspective
M. L. Friedlander, Laurie Heatherington, Professor of Psychology, and Abbe L. Marrs ’93

The American Journal of Family Therapy, 28, 133-146 (2000)

Blaming events (N=25) were identified in seven interviews conducted by prominent theorists who espouse a constructionist or narrative approach to family treatment. Congruent with this perspective, we used conversation analysis (Gale, 1996) and the grounded theory method of constant comparison (Corbin & Strauss, 1990) to identify the therapists’ behaviors and strategies following blame expressed by family members. Results indicated three core categories or themes of therapists’ responses to blame – Ignoring/Diverting, Acknowledging/Challenging, and Reframing – subsuming 17 individual codes (e.g., challenging all-or-none thinking, highlighting neutral information, interrupting, focusing on competence). The most frequent code was focusing on the positive.

Confessions: Psychological and Forensic Aspects
Saul M. Kassin, Professor of Psychology

In International Encyclopedia of the Social and Behavioral Sciences, (2001)

Throughout history, confessions have played an important role in three domains of human interaction: (1) most religions oblige adherents to confess their transgressions as a means of moral cleansing; (2) most psychotherapies are founded on the empirically supported belief that self-disclosure – including about past misdeeds – promotes mental and physical health; (3) most criminal justice systems seek confessions to the police as potent evidence of guilt. In contrast to the religious and therapeutic settings, where it easy to understand why people exhibit an “urge to confess,” police confessions yield harmful consequences to the confessor, making this aspect of human behavior more difficult to understand. In fact, however, such confessions are often elicited through psychologically coercive methods of interrogation. These methods sometimes lead people to confess to crimes they did not commit. Yet when confessions are presented in court, juries are uncritically accepting, inferring guilt even from statements that are coerced. Increasingly, psychological experts are called to testify in court about the psychology of interrogations and confessions.

On the “General Acceptance” of Eyewitness Testimony Research: A New Survey of the Experts
Saul M. Kassin, Professor of Psychology

American Psychologist, 56, 405-416 (2001)

In light of recent advances in eyewitness research and applications, the present study updated a prior survey of eyewitness experts (Kassin, Ellsworth, & Smith, 1989). Sixty-four psychologists were questioned about their courtroom experiences and opinions on 30 eyewitness phenomena. As indicated by an agreement rate of at least 80%, there was a strong consensus that the following phenomena are sufficiently reliable to be presented in court: the wording of questions, lineup instructions, confidence malleability, mugshot-induced bias, post-event information, child witness suggestibility, attitudes and expectations, hypnotic suggestibility, alcoholic intoxication, the cross-race bias, weapon focus, the accuracy-confidence correlation, the forgetting curve, exposure time, presentation format, and unconscious transference. At least two-thirds of respondents also endorsed items on showups, description-matched foils, child witness accuracy, lineup fairness, and false memories. Various results indicate that eyewitness experts set high standards before agreeing to testify and that the main objective is to educate the jury, not assist a particular party. Despite certain limitations, these results should help to shape the content of expert testimony so that it more accurately represents opinions within the scientific community.

Memory Retention is Modulated by Acute Estradiol and Progesterone Replacement
Noah J. Sandstrom, & Christina L. Williams

Behavioral Neuroscience, 115, 384-393 (2001)

Ovarian hormones alter spine density of hippocampal granule and pyramidal cells in young adult and aging female rats (Miranda, Williams, & Einstein, 1999; Woolley, 1998). The present study investigates a behavioral correlate of these hormone-induced changes in hippocampal connectivity in 3- and 8-month-old female rats using a delayed matching-to-place version of the water maze. When primed with 10-µg injections of estradiol 72 and 48 hr prior to testing, the memory retention of ovariectomized rats was improved relative to retention following priming with oil. A single injection of progesterone maintained this enhancement if testing occurred within 8 hr of the progesterone injection but not if testing occurred more than 24 hr following the progesterone injection. These findings indicate that estradiol and progesterone alter memory retention and suggest that these changes may be the result of hormone-induced increases in hippocampal connectivity.

Do Others Judge Us as Harshly as We Think? Overestimating the Impact of Our Failures, Shortcomings, and Mishaps
Kenneth Savitsky, Assistant Professor of Psychology, N. Epley and T. Gilovich

Journal of Personality and Social Psychology, 81, 44–56 (2001)

When people suffer an embarrassing blunder, social mishap, or public failure, they often feel that their image has been severely tarnished in the eyes of others. Four studies demonstrate that these fears are commonly exaggerated. Actors who imagined committing one of several social blunders (Study 1), who experienced a public intellectual failure (Studies 2 and 3), or who were described in an embarrassing way (Study 4) anticipated being judged more harshly by others than they actually were. These exaggerated fears were produced, in part, by the actors’ tendency to be inordinately focused on their misfortunes and by their resulting failure to consider the wider range of situational factors that tend to moderate onlookers’ impressions. Discussion focuses on additional mechanisms that may contribute to overly pessimistic expectations as well as the role of such expectations in producing unnecessary social anxiety.

Clinical Implications of “Subthreshold” Depressive Symptoms
P. M. Lewinsohn, Ari Solomon, Assistant Professor of Psychology, A. Zeiss, and J. Seeley

Journal of Abnormal Psychology, 109, 345-351 (2000)

There is active debate regarding whether diagnosable depression exists on a continuum with subthreshold depressive symptoms or represents a categorically distinct phenomenon. To address this question, multiple indexes of dysfunction (psychosocial difficulties, mental health treatment history, and future incidence of major depression and substance abuse/dependence) were examined as a function of the extent of depressive symptoms in 3 large community samples (adolescent, adult, and older adult; N = 3,003). Increasing levels of depressive symptoms were associated with increasing levels of psychosocial dysfunction and incidence of major depression and substance use disorders. These findings suggest that (a) the clinical significance of depressive symptoms does not depend on crossing the major depressive diagnostic threshold and (b) depression may best be conceptualized as a continuum. Limitations of the present study are discussed.

Perceptions of Depression Among Never Depressed and Recovered-Depressed People
L. Kirk, D. A. F. Haaga, Ari Solomon, Assistant Professor of Psychology, and C. Brody

Cognitive Therapy and Research, 24, 585-594 (2000)

Assessed perceptions of the impact of depression among two groups of currently nondepressed adults. The 25 recovered-depressed (RD) participants (mean age 37.28 yrs) had a history of major depressive disorder but had been recovered for at least 2 mo since the most recent depressive episode. The 25 never-depressed (ND) participants (mean age 40.04 yrs) had no history of major depressive disorder. Participants completed the Self-Appraisal Questionnaire (J. C. Coyne and M. M. Calarco, 1992) as an assessment of beliefs about the experience of having been depressed. RDs rated depression as having more severe after-effects than did the NDs. They reported feeling more loss of energy, being a burden on others, need to hide depression symptoms, strength drawn from depression, need to maintain a balance in life, fear of relationships, fear of taking risks, fear of recurrence of depression, and sense of stigma. These results replicated the findings of Coyne and Calarco (1995), and extended them to a more fully recovered population. It is suggested that these perceptions are important to understand because a person's ideas about depression may influence treatment outcome and susceptibility to future episodes.