Showing papers by "University of Maryland, Baltimore County published in 1996"

Cost-Benefit Analysis: Concepts and Practice

Abstract: Cost-Benefit Analysis provides accessible, comprehensive, authoritative, and practical treatments of the protocols for assessing the relative efficiency of public policies. Its review of essential concepts from microeconomics, and its sophisticated treatment of important topics with minimal use of mathematics helps students from a variety of backgrounds build solid conceptual foundations. It provides thorough treatments of time discounting, dealing with contingent uncertainty using expected surpluses and option prices, taking account of parameter uncertainties using Monte Carlo simulation and other types of sensitivity analyses, revealed preference approaches, stated preference methods including contingent valuation, and other related methods. Updated to cover contemporary research, this edition is considerably reorganized to aid in student and practitioner understanding, and includes eight new cases to demonstrate the actual practice of cost-benefit analysis. Widely cited, it is recognized as an authoritative source on cost-benefit analysis. Illustrations, exhibits, chapter exercises, and case studies help students master concepts and develop craft skills.

Revision of the Brief Visuospatial Memory Test: Studies of normal performance, reliability, and validity.

Abstract: There is an increasing demand for alternate-form neuropsychological tests that can be used in clinical trials with little risk of direct practice effect. Although the Brief Visuospatial Memory Test (BVMT) includes six equivalent alternate forms, its administration is limited to an immediate and 25-min delayed free-recall trial. We now present a revised version of the BVMT called the Brief Visuospatial Memory Test-Revised (BVMT-R) that includes three learning trials, a 25-min delayed recall trial, and a delayed yes/no recognition task. A new scoring system, which accounts for the location of test stimuli as well as the accuracy of recall, is also introduced. Using these new administration and scoring procedures, we administered the BVMT-R to 261 neuropsychiatric patients and 456 normal healthy adults. The results indicated that the test has excellent interform reliability, and the construct and criterion-related validity of the test were supported in studies using clinical samples. Although the BVMT-R is not without its limitations, the test's brevity and alternate-form capacity make it a valuable instrument for serial neuropsychological assessments.

Structure of the Amino-Terminal Core Domain of the HIV-1 Capsid Protein

Abstract: The three-dimensional structure of the amino-terminal core domain (residues 1 through 151) of the human immunodeficiency virus-type 1 (HIV-1) capsid protein has been solved by multidimensional heteronuclear magnetic resonance spectroscopy. The structure is unlike those of previously characterized viral coat proteins and is composed of seven alpha helices, two beta hairpins, and an exposed partially ordered loop. The domain is shaped like an arrowhead, with the beta hairpins and loop exposed at the trailing edge and the carboxyl-terminal helix projecting from the tip. The proline residue Pro1 forms a salt bridge with a conserved, buried aspartate residue (Asp51), which suggests that the amino terminus of the protein rearranges upon proteolytic maturation. The binding site for cyclophilin A, a cellular rotamase that is packaged into the HIV-1 virion, is located on the exposed loop and encompasses the essential proline residue Pro90. In the free monomeric domain, Pro90 adopts kinetically trapped cis and trans conformations, raising the possibility that cyclophilin A catalyzes interconversion of the cis- and trans-Pro90 loop structures.

On the formulation and theory of the Newton interior-point method for nonlinear programming

Abstract: In this work, we first study in detail the formulation of the primal-dual interior-point method for linear programming. We show that, contrary to popular belief, it cannot be viewed as a damped Newton method applied to the Karush-Kuhn-Tucker conditions for the logarithmic barrier function problem. Next, we extend the formulation to general nonlinear programming, and then validate this extension by demonstrating that this algorithm can be implemented so that it is locally and Q-quadratically convergent under only the standard Newton method assumptions. We also establish a global convergence theory for this algorithm and include promising numerical experimentation.

Crystal structure of dimeric HIV-1 capsid protein.

Abstract: X-ray diffraction analysis of a human immunodeficiency virus (HIV-1) capsid (CA) protein shows that each monomer within the dimer consists of seven alpha-helices, five of which are arranged in a coiled coil-like structure. Sequence assignments were made for two of the helices, and tentative connectivity of the remainder of the protein was confirmed by the recent solution structure of a monomeric N-terminal fragment. The C-terminal third of the protein is mostly disordered in the crystal. The longest helices in the coiled coil-like structure are separated by a long, highly antigenic peptide that includes the binding site of an antibody fragment complexed with CA in the crystal. The site of binding of the Fab, the position of the antigenic loop and the site of cleavage between the matrix protein and CA establish the side of the dimer that would be on the exterior of the retroviral core.

Identification of Ecdysis-Triggering Hormone from an Epitracheal Endocrine System

Abstract: Developing insects repeatedly shed their cuticle by means of a stereotyped behavior called ecdysis, thought to be initiated by the brain peptide eclosion hormone. Here an ecdysis-triggering hormone, Mas-ETH, is described from the tobacco hornworm Manduca sexta. Mas-ETH contains 26 amino acids and is produced by a segmentally distributed endocrine system of epitracheal glands (EGs). The EGs undergo a marked reduction in volume, appearance, and immunohistochemical staining during ecdysis, at which time Mas-ETH is found in the hemolymph. Injection of EGs extract or synthetic Mas-ETH into pharate larvae, pupae, or adults initiates preecdysis within 2 to 10 minutes, followed by ecdysis. Sensitivity to injected Mas-ETH appears much earlier before ecdysis and occurs with shorter latency than that reported for eclosion hormone. The isolated central nervous system responds to Mas-ETH, but not to eclosion hormone, with patterned motor bursting corresponding to in vivo preecdysis and ecdysis. Mas-ETH may be an immediate blood-borne trigger for ecdysis through a direct action on the nervous system.

Can Two-photon Interference be Considered the Interference of Two Photons?

Abstract: We report on a ``postponed compensation'' experiment in which the observed two-photon entangled state interference cannot be pictured in terms of the overlap of the two individual photon wave packets of a parametric down-conversion pair on a beam splitter. In the sense of a quantum eraser, the distinguishability of the different two-photon Feynman amplitudes leading to a coincidence detection is removed by delaying the compensation until after the output of an unbalanced two-photon interferometer.

Discrimination Comes in Many Forms Individual, Institutional, and Structural

Abstract: Three different types of discrimination are defined and analyzed. Individual and institutional discrimination refer to actions and/or policies that are intended to have a differential impact on minorities and women. Structural discrimination, on the other hand, refers to policies that are race or gender neutral in intent but that have negative effects on women, minorities, or both. Concrete examples of each type of discrimination are presented and pedagogical techniques for using these concepts are provided.

Identification and molecular characterization of a putative regulatory locus that affects autolysis in Staphylococcus aureus.

Abstract: Previously in our laboratory, a PCR-based strategy was used to isolate potential sensor gene fragments from the Staphyloccus aureus genome One DNA fragment was isolated that shared strong sequence similarity to genes encoding bacterial sensor proteins, indicating that it originated from within a potential staphylococcal sensor protein gene In this study, the DNA surrounding the PCR product origin was cloned and sequenced This analysis revealed the presence of two genes, termed lytS and lytR, whose deduced amino acid sequences were similar to those of members of the two-component regulatory system family of proteins S aureus cells containing an insertional disruption of lytS exhibited a marked propensity to form aggregates in liquid culture, suggesting that alterations in cell surface components exist in this strain Transmission electron microscopic examination of these cells revealed that the cell surface was rough and diffuse and that a large proportion of the cell population had lysed The lytS mutant also exhibited increased autolysis and an altered level of murein hydrolase activity produced compared with the parental strain, NCTC 8325-4 These data suggest that the lytS and lytR gene products control the rate of autolysis in S aureus by affecting the intrinsic murein hydrolase activity associated with the cell

Transverse correlation in optical spontaneous parametric down-conversion

Abstract: The transverse correlation between the pairs of photons produced in optical spontaneous parametric down-conversion is analyzed. The interesting features of the correlation arise from the form of the two-photon state generated in the process. The physics of the rings of radiation emerging from the crystal is described. We discuss the theory behind the recent experiments on two-photon geometric and physical optics. \textcopyright{} 1996 The American Physical Society.

Molecular recognition of pathogen attack occurs inside of plant cells in plant disease resistance specified by the Arabidopsis genes RPS2 and RPM1

Abstract: The Arabidopsis thaliana disease resistance genes RPS2 and RPM1 belong to a class of plant disease resistance genes that encode proteins that contain an N-terminal tripartite nucleotide binding site (NBS) and a C- terminal tandem array of leucine-rich repeats. RPS2 and RPM1 confer resistance to strains of the bacterial phytopathogen Pseudomonas syringae carrying the avirulence genes avrRpt2 and avrB, respectively. In these gene-for-gene relationships, it has been proposed that pathogen avirulence genes generate specific ligands that are recognized by cognate receptors encoded by the corresponding plant resistance genes. To test this hypothesis, it is crucial to know the site of the potential molecular recognition. Mutational analysis of RPS2 protein and in vitro translation/translocation studies indicated that RPS2 protein is localized in the plant cytoplasm. To determine whether avirulence gene products themselves are the ligands for resistance proteins, we expressed the avrRpt2 and avrB genes directly in plant cells using a novel quantitative transient expression assay, and found that expression of avrRpt2 and avrB elicited a resistance response in plants carrying the corresponding resistance genes. This observation indicates that no bacterial factors other than the avirulence gene products are required for the specific resistance response as long as the avirulence gene products are correctly localized. We propose that molecular recognition of P. syringae in RPS2- and RPM1-specified resistance occurs inside of plant cells.

Barrier functions in interior point methods

Abstract: We show that the universal barrier function of a convex cone introduced by Nesterov and Nemirovskii is the logarithm of the characteristic function of the cone. This interpretation demonstrates the invariance of the universal barrier under the automorphism group of the underlying cone. This provides a simple method for calculating the universal barrier for homogeneous cones. We identify some known barriers as the universal barrier scaled by an appropriate constant. We also calculate some new universal barrier functions. Our results connect the field of interior point methods to several branches of mathematics such as Lie groups, Jordan algebras, Siegel domains, differential geometry, complex analysis of several variables, etc.

The p and hp versions of the finite element method for problems with boundary layers

Abstract: We study the uniform approximation of boundary layer functions exp(-x/d) for x ∈ (0,1), d ∈ (0,1], by the p and hp versions of the finite element method. For the p version (with fixed mesh), we prove super-exponential convergence in the range p + 1/2 > e/(2d). We also establish, for this version, an overall convergence rate of O(p -1 √ln p) in the energy norm error which is uniform in d, and show that this rate is sharp (up to the √ln p term) when robust estimates uniform in d ∈ (0,1] are considered. For the p version with variable mesh (i.e., the hp version), we show that exponential convergence, uniform in d ∈ (0,1], is achieved by taking the first element at the boundary layer to be of size O(pd). Numerical experiments for a model elliptic singular perturbation problem show good agreement with our convergence estimates, even when few degrees of freedom are used and when d is as small as, e.g., 10 -8 . They also illustrate the superiority of the hp approach over other methods, including a low-order h version with optimal exponential mesh refinement. The estimates established in this paper are also applicable in the context of corresponding spectral element methods.

Two-photon geometric optics

Abstract: We report two-photon correlation experiments using spontaneous parametric down-conversion under a severe manipulation of the input pump field. Considering the case of passing the laser beam through a focusing lens before the down-conversion crystal, theoretical calculations and a series of imaging experiments demonstrate two-photon geometric optics effects. In particular, the imaging in coincidence counts of an aperture placed in one of the down-conversion beams is found to be the analog of a simple spherical mirror system, which displays a ``vacuum dispersion'' effect in that the object and image distances are wavelength weighted. \textcopyright{} 1996 The American Physical Society.

Generating uniformly distributed random latin squares

Abstract: By simulating an ergodic Markov chain whose stationary distribution is uniform over the space of n × n Latin squares, we can obtain squares that are (approximately) uniformly distributed; we offer two such chains. The central issue is the construction of “moves” that connect the squares. Our first approach uses the fact that an n × n Latin square is equivalent to an n × n × n contingency table in which each line sum equals 1. We relax the nonnegativity condition on the table's cells, allowing “improper” tables that have a single—1-cell. A simple set of moves connects this expanded space of tables [the diameter of the associated graph is bounded by 2(n − 1)3], and suggests a Markov chain whose subchain of proper tables has the desired uniform stationary distribution (with an average of approximately n steps between proper tables). By grouping these moves appropriately, we derive a class of moves that stay within the space of proper Latin squares [with graph diameter bounded by 4(n − 1)2]; these may also be used to form a suitable Markov chain. © 1996 John Wiley & Sons, Inc.

Identification of LytSR-regulated genes from Staphylococcus aureus.

Abstract: In this report, the characterization of a Staphylococcus aureus operon containing two LytSR-regulated genes, lrgA and lrgB, is described. Sequence and mutagenesis studies of these genes suggest that lrgA encodes a murein hydrolase exporter similar to bacteriophage holin proteins while lrgB may encode a protein having murein hydrolase activity.

Cannibalism Regulates Densities of Young Wolf Spiders: Evidence From Field and Laboratory Experiments

Abstract: We conducted field and laboratory experiments to examine the relative con- tributions of mortality from natural enemies and cannibalism to population regulation of the wolf spider Schizocosa ocreata. This cursorial spider is a common generalist predator in the leaf litter of forests of the eastern United States. In our study site in Maryland, densities of recently dispersed young S. ocreata can reach 60-90 individuals/M2, but decline to <15 spiders/M2 by early autumn. We investigated the cause of this rapid decline in spiderling density. We first performed a predator-exclusion field experiment to determine if natural enemies contributed significantly to spider mortality. Replicated enclosures with lip barriers to prevent emigration were stocked with newly dispersed S. ocreata spiderlings at either 0.75 X or 3x mean field density, or had no S. ocreata added (OX). Before spiderlings were intro- duced, we reduced potential enemies in half of the plots by sifting the litter and removing other spiders, centipedes and predaceous beetles, and by installing 3-mm mesh netting to exclude birds, wasps and other predators of S. ocreata. Over a period of 2.5 mo we measured effects of natural enemies and spider density on prey (Collembola), spider growth, and spider survival. Spider mortality was high (-"'80%) and strongly density dependent (DD). Survival in the 3x field-density plots was 50% lower than in the 0.75X plots. Increasing spiderling density did not significantly reduce Collembola density and resulted only in a minor DD reduction in spiderling growth (-"10%). Although overall spider mortality was high, excluding natural enemies did not significantly improve spider survival. The absence of emigration and the high spider mortality rates in the predator-reduction treatment strongly implicate cannibalism as the major DD mortality factor. We then conducted two laboratory experiments in order to obtain direct measurements of the rates of cannibalism. Rates of cannibalism were measured in 0.3-iM2 arenas stocked with S. ocreata at densities equivalent to those used in the field experiment. In Experiment 1, habitat complexity and prey availability were manipulated in arenas stocked with S. ocreata at 3 x mean field densities. In Experiment 2, we manipulated spider density (0.75 x and 3x) and prey density to evaluate the DD component of cannibalism. The laboratory experiments confirmed the importance of cannibalism as a DD mortality factor. DD mortality from cannibalism was influenced by both prey abundance and habitat complexity. The presence of prey significantly reduced rates of cannibalism, and there was a significant interaction between habitat complexity and prey availability. When prey were present, rates of cannibalism were higher in the complex habitat than the simple habitat. In the absence of prey, increasing habitat complexity had no effect on rates of cannibalism. Rates of cannibalism in the treatment that most closely mimicked field conditions-complex leaf- litter with prey at natural densities-did not differ significantly from the rate of mortality of S. ocreata in the field experiment. Considered together, the results of our field and laboratory experiments lead to the conclusion that cannibalism can act as a strong DD mortality factor for young instars of S. ocreata, with the potential to regulate densities of this abundant cursorial spider.

Parenting Sensitivity, Parental Depression and Child Health: The Mediational Role of Parental Self‐Efficacy

Abstract: This paper discusses the theoretical role of parental self-efficacy, or parents' beliefs in their competence and effectiveness in the parental role, as a mediator of relations between parent–child risk and parental sensitivity. Evidence is marshalled from studies of parenting in the contexts of maternal depression and child health risk to support the premise that parent–child characteristics affect parental sensitivity indirectly via their more direct impact on parental feelings of efficacy, and that parenting efficacy represents the ‘final common pathway’ in the prediction of parenting sensitivity. Also considered in this working model are specific social-contextual factors as independent contributors to parenting efficacy and as possible moderators of relations between parent–child characteristics and self-efficacy. Implications for intervention are discussed. © 1996 John Wiley & Sons, Ltd.

Transcriptional activation of promoters of the superoxide and multiple antibiotic resistance regulons by Rob, a binding protein of the Escherichia coli origin of chromosomal replication

Abstract: The Rob protein, isolated on the basis of its ability to bind to the right arm of the Escherichia coli origin of chromosomal replication, is about 50% identical in amino acid sequence to SoxS and MarA, the direct regulators of the superoxide (soxRS) and multiple antibiotic resistance (mar) regulons, respectively. Having previously demonstrated that SoxS (as a MalE-SoxS fusion protein) and MarA are essentially identical in their abilities to activate in vitro transcription of genes of the sox-mar regulons, we investigated the properties of Rob as a transcriptional activator. We found that Rob (i) activates the transcription of zwf,fpr,fumC, micF, nfo, and sodA, (ii) requires a 21-bp soxbox-marbox-robbox sequence to activate zwf transcription, (iii) protects the soxbox/marbox/robbox from attack by DNase 1, (iv) is ambidextrous, i.e., requires the C-terminal domain of the alpha subunit of RNA polymerase for activation of zwf but not fumC or micF, (v) bends zwf and fumC DNA, and (vi) binds zwf and fumC DNA as a monomer. Since these transcription activation properties of Rob are virtually identical to those of MalE-SoxS and MarA, it appears as if the E. coli genome encodes three genes with the same functional capacity. However, in contrast to SoxS and MarA, whose syntheses are induced by specific environmental stimuli and elicit a clear defense response, Rob is expressed constitutively and its normal function is unknown.

The N-terminal domain of TFIIB from Pyrococcus furiosus forms a zinc ribbon.

Abstract: The three-dimensional structure of the N-terminal domain of an archaeal TFIIB, which has high sequence homology with eucaryal analogues, is strikingly similar to that of the C-terminal zinc ribbon of the eucaryal transcription elongation factor TFIIB.

Sensitivity to inhibition by β-chemokines correlates with biological phenotypes of primary HIV-1 isolates

Abstract: Primary HIV-1 isolates were evaluated for their sensitivity to inhibition by β-chemokines RANTES (regulated upon activation, normal T-cell expressed and secreted), macrophage inflammatory protein 1α (MIP-1α), and MIP-1β. Virus isolates of both nonsyncytium-inducing (NSI) and syncytium-inducing (SI) biological phenotypes recovered from patients at various stages of HIV-1 infection were assessed, and the results indicated that only the isolates with the NSI phenotype were substantially inhibited by the β-chemokines. More important to note, these data demonstrate that resistance to inhibition by β-chemokines RANTES, MIP-1α, and MIP-1β is not restricted to T cell line-adapted SI isolates but is also a consistent property among primary SI isolates. Analysis of isolates obtained sequentially from infected individuals in whom viruses shifted from NSI to SI phenotype during clinical progression exhibited a parallel loss of sensitivity to β-chemokines. Loss of virus sensitivity to inhibition by β-chemokines RANTES, MIP-1α, and MIP-1β was furthermore associated with changes in the third variable (V3) region amino acid residues previously described to correlate with a shift of virus phenotype from NSI to SI. Of interest, an intermediate V3 genotype correlated with a partial inhibition by the β-chemokines. In addition, we also identified viruses sensitive to RANTES, MIP-1α, and MIP-1β of NSI phenotype that were isolated from individuals with AIDS manifestations, indicating that loss of sensitivity to β-chemokine inhibition and shift in viral phenotype are not necessarily prerequisites for the pathogenesis of HIV-1 infection.

Mixed \(hp\) finite element methods for problems in elasticity and Stokes flow

Abstract: We consider the mixed formulation for the elasticity problem and the limiting Stokes problem in ${\Bbb R}^d$ , $d=2,3$ . We derive a set of sufficient conditions under which families of mixed finite element spaces are simultaneously stable with respect to the mesh size $h$ and, subject to a maximum loss of $O (k^{\frac{d-1}{2}})$ , with respect to the polynomial degree $k$ . We obtain asymptotic rates of convergence that are optimal up to $O (k^\epsilon)$ in the displacement/velocity and up to $O (k^{\frac{d-1}{2}+\epsilon})$ in the "pressure", with $\epsilon >0$ arbitrary (both rates being optimal with respect to $h$ ). Several choices of elements are discussed with reference to properties desirable in the context of the $hp$ -version.

New directions in adaptive designs

Abstract: In any sequential medical experiment on a cohort of human beings, there is an ethical imperative to provide the best possible medical care for the individual patient. This ethical imperative may be compromised if a randomization scheme involving 50-50 allocation is used as accruing evidence begins to favor (albeit not yet conclusively) one experimental therapy over another. Adaptive designs have long been proposed to remedy this situation. An adaptive design seeks to skew assignment probabilities to favor the treatment performing best thus far in the study, proportionately to the magnitude of the treatment effect. Current researchers in adaptive designs are attempting to provide physicians with a wide choice of design options, and to address practical and ethical concerns within a rigorous mathematical framework. This paper focuses on several broad families of designs, including urn models, random walk rules and other rules. Numerous examples are given along with applications, dose-response studies, clinical trials for efficacy and combined toxicity-efficacy studies.

Polarization contrast vision in Octopus.

Abstract: While the ability to analyze polarized light is widespread among animals, its contribution to form vision has not yet been documented. We tested the hypothesis that polarization vision can be used for object discrimination, by training octopuses to distinguish between targets on the basis of the presence or absence of a pattern produced by a 90 degrees polarization contrast within the target. Octopuses recognized a 90 degrees contrast pattern within a single target, when presented either on a horizontal/vertical axis or on a 45 degrees/135 degrees axis. They were able to transfer their learning to new situations and to detect a polarization contrast when the orientations of the e-vector of light passing through the target center and background differed by as little as 20 degrees. Polarization vision may provide information similar to that available from color vision and thus serve to enhance the detection and recognition of objects.

Racial differences in body type preferences of men for women.

Abstract: Objective Research indicates that African-American women have a significantly higher prevalence of obesity, a markedly lower prevalence of eating disorders, and greater satisfaction with their bodies than Euro-American women. One potential contributing explanation for this difference may be differential body type preferences between the men in the two communities. Method: Sixty-three African-American and 116 Euro-American men were asked to rank, in order of attractiveness, a series of silhouettes of women of varying sizes. Additionally, they answered questions concerning their current relationships. Results: Euro-Americans chose significantly thinner figures, and reported wishing their girlfriends would lose weight significantly more often than African-Americans. Discussion: These differential preferences may translate into greater pressure within the Euro-American community for women to be thin than in the African-American community; however, a small effect size suggests that factors other than race contribute to men's body type preferences. © 1996 John Wiley & Sons, Inc.