Showing papers by "University of Maryland, Baltimore County published in 1992"

Nucleocapsid zinc fingers detected in retroviruses: EXAFS studies of intact viruses and the solution-state structure of the nucleocapsid protein from HIV-1.

Abstract: All retroviral nucleocapsid (NC) proteins contain one or two copies of an invariant 3Cys-1His array (CCHC = C-X2-C-X4-H-X4-C; C = Cys, H = His, X = variable amino acid) that are essential for RNA genome packaging and infectivity and have been proposed to function as zinc-binding domains. Although the arrays are capable of binding zinc in vitro, the physiological relevance of zinc coordination has not been firmly established. We have obtained zinc-edge extended X-ray absorption fine structure (EXAFS) spectra for intact retroviruses in order to determine if virus-bound zinc, which is present in quantities nearly stoichiometric with the CCHC arrays (Bess, J.W., Jr., Powell, P.J., Issaq, H.J., Schumack, L.J., Grimes, M.K., Henderson, L.E., & Arthur, L.O., 1992, J. Virol. 66, 840-847), exists in a unique coordination environment. The viral EXAFS spectra obtained are remarkably similar to the spectrum of a model CCHC zinc finger peptide with known 3Cys-1His zinc coordination structure. This finding, combined with other biochemical results, indicates that the majority of the viral zinc is coordinated to the NC CCHC arrays in mature retroviruses. Based on these findings, we have extended our NMR studies of the HIV-1 NC protein and have determined its three-dimensional solution-state structure. The CCHC arrays of HIV-1 NC exist as independently folded, noninteracting domains on a flexible polypeptide chain, with conservatively substituted aromatic residues forming hydrophobic patches on the zinc finger surfaces. These residues are essential for RNA genome recognition, and fluorescence measurements indicate that at least one residue (Trp37) participates directly in binding to nucleic acids in vitro. The NC is only the third HIV-1 protein to be structurally characterized, and the combined EXAFS, structural, and nucleic acid-binding results provide a basis for the rational design of new NC-targeted antiviral agents and vaccines for the control of AIDS.

Locking effects in the finite element approximation of elasticity problems

Abstract: We consider the finite element approximation of the 2D elasticity problem when the Poisson ratiov is close to 0.5. It is well-known that the performance of certain commonly used finite elements deteriorates asv?0, a phenomenon calledlocking. We analyze this phenomenon and characterize the strength of the locking androbustness of varioush-version schemes using triangular and rectangular elements. We prove that thep-andh-p versions are free of locking with respect to the error in the energy norm. A generalization of our theory to the 3D problem is also discussed.

Entropic Proximal Mappings with Applications to Nonlinear Programming

Abstract: We introduce a family of new transforms based on imitating the proximal mapping of Moreau and the associated Moreau-Yosida proximal approximation of a function. The transforms are constructed in terms of the AÂ†-divergence functional a generalization of the relative entropy and of Bregman's measure of distance. An analogue of Moreau's theorem associated with these entropy-like distances is proved. We show that the resulting Entropic Proximal Maps share properties similar to the proximal mapping and provide a fairly general framework for constructing approximation and smoothing schemes for optimization problems. Applications of the results to the construction of generalized augmented Lagrangians for nonlinear programs and the minimax problem are presented.

Resonances in electron scattering by molecules on surfaces

Abstract: This article reviews the discovery, exploration, and application of negative-ion resonances in inelastic electron scattering by molecules adsorbed on surfaces. A major theme of the review is the degree to which the properties of resonances in free molecules are perturbed by adsorption. The influence of the surface upon the energy, lifetime (width), symmetry, and decay channels of molecular resonances is discussed, in the light of both experimental and theoretical studies of a wide range (from diatomic molecules to polymers) of both weakly bound (physisorbed) and strongly bound (chemisorbed) molecules. The metallic image potential, electron scattering by the atoms of the surface, and chemical bonding in chemisorption systems are found to be key factors in determining the energy, width, and symmetry of resonances in molecular adsorbates. In the case of oriented adsorbed molecules, the angular distribution of scattered electrons is found to reflect not only the symmetry of the resonant state (as in the gas phase), but also the orientation of the molecular axis. Coherent elastic electron scattering by the surface can modulate the angular distributions, as well as the shape of the resonance profile. Selection rules that govern the observed resonance behavior are discussed. A further consequence of adsorption ismore » the enrichment of the range of channels into which resonances may decay, and the excitation of both molecule-surface and intermolecular vibrational modes has been established. The article concludes with an evaluation of future prospects for the investigation and application of resonances in adsorbed molecules.« less

Contagious laughter: Laughter is a sufficient stimulus for laughs and smiles

Abstract: The laugh- and/or smile-evoking potency of laughter was evaluated by observing responses of 128 subjects in three undergraduate psychology classes to laugh stimuli produced by a “laugh box.” Subjects recorded whether they laughed and/or smiled during each of 10 trials, each of which consisted of an 18-sec sample of laughter, followed by 42 sec of silence. Most subjects laughed and smiled in response to the first presentation of laughter. However, the polarity of the response changed quickly. By the 10th trial, few subjects laughed and/or smiled, and most found the stimulus “obnoxious.” Although other research has described canned-laughter effects, it did not consider the hypothesis confirmed here, that laughter itself evokes laughter, perhaps by activating a laughter-specific auditory-feature detector. This result is relevant to the neurological basis of social communication, human ethology, and theories of speech production and perception.

Evaluation of EPA's rapid bioassessment benthic metrics: Metric redundancy and variability among reference stream sites

Abstract: The data analysis scheme used in the U.S. Environmental Protection Agency's (EPA's) rapid bioassessment protocols (RBPs) integrates several community, population, and functional parameters (or metrics) into a single assessment of biological condition. A reference data base of macroinvertebrate data obtained from 10 ecoregions in Oregon, Colorado, and Kentucky was used to evaluate the appropriateness and variability of the benthic metrics and the similarities of results among ecoregions. Several statistical procedures, including principal component analysis, correlation coefficient, analysis of variance, and stepwise discriminant analysis, were used to test the efficacy of 17 community metrics. A general separation between the mountain ecoregions and the valley/plains ecoregions was determined to exist for the metrics. Two of the original eight metrics described in the EPA's RBPs for benthic macroinvertebrates were found to be highly variable and unreliable as measures of biological conditions in some ecoregions. Eleven metrics were determined as being valuable in discriminating between montane and valley/plains groupings of ecoregions.

Anger and post-traumatic stress disorder in female crime victims

Abstract: This study examined feelings of anger among female victims of crime and the relation of anger to the development of post-traumatic stress disorder (PTSD). One hundred and sixteen women who had been victims of sexual or nonsexual criminal assaults were compared to a matched comparison group of 50 nonvictimized women on measures of anger and anger expression. Results indicate that victims were angrier than nonvictims. The level of anger was related to various aspects of the assault, such as the use of a weapon and the victim's response to the attack. In addition, the results indicate that elevated anger is positively related to the development of PTSD. Results are discussed in relation to a cognitive/behavioral conceptualization of PTSD.

On numerical cubatures of singular surface integrals in boundary element methods

Abstract: We present and analyze methods for the accurate and efficient evaluation of weakly, Cauchy and hypersingular integrals over piecewise analytic curved surfaces in ?3. The class of admissible integrands includes all kernels arising in the numerical solution of elliptic boundary value problems in three-dimensional domains by the boundary integral equation method. The possibly not absolutely integrable kernels of boundary integral operators in local coordinates are pseudohomogeneous with analytic characteristics depending on the local geometry of the surface at the source point. This rules out weighted quadrature approaches with a fixed singular weight. For weakly singular integrals it is shown that Duffy's triangular coordinates leadalways to a removal of the kernel singularity. Also asymptotic estimates of the integration error are provided as the size of the boundary element patch tends to zero. These are based on the Rabinowitz-Richter estimates in connection with an asymptotic estimate of domains of analyticity in ?2. It is further shown that the modified extrapolation approach due to Lyness is in the weakly singular case always applicable. Corresponding error and asymptotic work estimates are presented. For the weakly singular as well as for Cauchy and hypersingular integrals which e.g. arise in the study of crack problems we analyze a family of product integration rules in local polar coordinates. These rules are hierarchically constructed from "finite part" integration formulas in radial and Gaussian formulas in angular direction. Again, we show how the Rabinowitz-Richter estimates can be applied providing asymptotic error estimates in terms of orders of the boundary element size.

Electrospray analysis of proteins: A comparison of positive-ion and negative-ion mass spectra at high and low pH

Abstract: Cationic and anionic electrospray mass spectra were measured for equine myoglobin, lactalbumin and hen egg white lysozyme from acidic and basic solutions. Both positive and negative ions were detected from all solutions in which the proteins were soluble. This was observed in both nebulization-assisted and thermally assisted electrospray. As in other studies, the distribution of the charge states reflected functional groups in the proteins, and also folding or extension of the protein.

Two-photon lithography for microelectronic application

Abstract: Two-photon excitation in laser scanning photolithography allows exposure of patterns not possible with conventional one-photon direct writing. In our experiments two red photons from a highly focused subpicosecond colliding pulse mode-locked dye laser are simultaneously absorbed by initiator molecules to affect a photochemical reaction that is normally driven by single-photon absorption using ultraviolet light. The quadratic dependence of the two-photon absorption rate on the incident intensity confines excitation to a submicron focal volume. By scanning this volume in a 3-d pattern through a thick layer of photoresist it is possible to expose arbitrary three dimensionally defined regions. Preliminary results showing half micron wide trenches of very high aspect ratio, and resist structures with undercutting edges, all produced with only a single development step, demonstrate. the potential utility of two-photon excitation in microfabrication.

Proton affinity of arginine measured by the kinetic approach

Abstract: The proton affinity of arginine is obtained from the kinetic method of dissociation of proton-bound dimers, as 245.2kcal/mol with an uncertainty of ±0.5 kcal/mol higher than that of histidine, the next most basic of the commonly occuring mammalian amino acids, in contrast to the average difference of 1 kcal/mol between the other 19 amino acids. The order of proton affinity of these 20 amino acids is also determined and discussed.

Tyrosinase Reaction/Chitosan Adsorption for Removing Phenols from Wastewater

Abstract: A two-step approach for removing phenols from aqueous solutions was investigated. In the first step, weakly adsorbable phenols are converted to quinones by the enzyme mushroom tyrosinase. The tyrosinase-generated quinones are then chemisorbed onto chitosan, a readily available waste product of the shellfish industry. In the absence of enzyme, quinone was observed to be rapidly adsorbed onto chitosan. Also, the enthalpy for quinone adsorption onto chitosan was observed to be −24.7 kcal/mol, which compares to enthalpies of -7 kcal/mol for adsorption of phenols and quinone onto activated charcoal. With the monophenol reactant cresol, the tyrosinase enzyme was observed to be somewhat stabilized in the presence of chitosan. This stabilization of tyrosinase is presumably due to the rapid adsorption of the reactive quinones onto chitosan. In contrast, tyrosinase was not stabilized by chitosan when the o-diphenol catechol was the reactant. The ability of chitosan to stabilize tyrosinase for monophenols but not for o-diphenols is discussed in terms of the relative rates of phenol oxidation by tyrosinase and quinone chemisorption onto chitosan. When mushroom tyrosinase and chitosan were added simultaneously to dilute, phenol-containing solutions, a nearly complete removal of UV-absorbing material was observed. This observation demonstrates the feasibility of removing phenols from dilute solutions using the tyrosinase reaction/chitosan adsorption approach.

Life-style and substance use among male African American urban adolescents: A cluster analytic approach

Abstract: University of Maryland Baltimore County Cluster analyzed four variables: school attendance, employment, church attendance, and delinquency, to develop life-style profiles. Data from 218 African-American urban adolescents were used in the study. Five meaningful clusters were retained and subjected to criterion validity analyses using measures of spirituality, participation in a voluntary organization, self-esteem, and friend's substance use. The five clusters were then compared on cigarette, alcohol, marijuana, and hard drug use. The results suggest that a life-style that includes an adaptive compensatory behavior component may be more adaptive than a life-style that does not include compensatory behavior. For example, youths who left high school before graduation but were involved in church reported less alcohol and substance use than youths who left school and were not involved in any meaningful instrumental activity. Implications for intervention and future research on high-risk behaviors are discussed.

Traveling salesman games

Abstract: In this paper we discuss the problem of how to divide the total cost of a round trip along several institutes among the institutes visited. We introduce two types of cooperative games—fixed-route traveling salesman games and traveling salesman games—as a tool to attack this problem. Under very mild conditions we prove that fixed-route traveling salesman games have non-empty cores if the fixed route is a solution of the classical traveling salesman problem. Core elements provide us with fair cost allocations. A traveling salesman game may have an empty core, even if the cost matrix satisfies the triangle inequality. In this paper we introduce a class of matrices defining TS-games with non-empty cores.

Work with Traumatized Children- Psychological Effects and Coping Strategies

Abstract: Work with traumatized children has a profound effect on emergency personnel and other health care providers. It is hypothesized that work with seriously ill or injured children potentiates motivating factors in the helper's personality, brakes down natural defenses and leads to strong identification with the victims. In this paper various psychological effects on the rescuer are outlined. Coping strategies used by health care personnel in the acute phase of an emergency are identified. Mental preparation, suppression of emotions, distancing from certain aspects of the event, and dehumanizing were frequently utilized coping strategies. Other coping mechanisms were regulating the amount of exposure, activities to restrict reflection, developing a sense of purpose, and self-reassuring comments. Postexposure response to child trauma include helplessness, fear and anxiety, existential insecurity, rage, sorrow and grief, intrusive images, self-reproach, shame and guilt, and changes in values. Emotional distancing and other self-protective strategies seem important at the scene; self-disclosure by talking about impressions and reactions is most helpful afterwards. However, carefully timed and executed interventions are necessary to break through the defensive barriers which are established by health care and other emergency personnel.

Solution structure of the Lewis x oligosaccharide determined by NMR spectroscopy and molecular dynamics simulations.

Abstract: The Lewis x (Lex) determinant is a trisaccharide fragment that has been implicated as a specific differentiation antigen, as a tumor antigen, and as a key component of the ligand for the endothelial leukocyte adhesion molecule, ELAM-1. High-resolution nuclear magnetic resonance spectroscopy shows it to have a relatively rigid structure. Only a small range of glycosidic dihedral angles in the trisaccharide produce simulated nuclear Overhauser effect spectra agreeing with data measured for the human milk pentasaccharide, lacto-N-fucopentaose-3, which contains the Lex determinant. Independently, the same average structure for the Lex determinant arises from in vacuo molecular dynamics simulations. The proposed conformation of the Lex trisaccharide is very similar to that recently determined for the closely related Lea trisaccharide. In agreement with the recent finding that both sialylated Lea and Lex react with ELAM-1, the results presented here show that the Lea and Lex determinants contain very similar carbohydrate domains.

Solution-state structure by NMR of zinc-substituted rubredoxin from the marine hyperthermophilic archaebacterium Pyrococcus furiosus.

Abstract: The three-dimensional solution-state structure is reported for the zinc-substituted form of rubredoxin (Rd) from the marine hyperthermophilic archaebacterium Pyrococcus furiosus, an organism that grows optimally at 100 degrees C. Structures were generated with DSPACE by a hybrid distance geometry (DG)-based simulated annealing (SA) approach that employed 403 nuclear Overhauser effect (NOE)-derived interproton distance restraints, including 67 interresidue, 124 sequential (i-j = 1), 75 medium-range (i-j = 2-5), and 137 long-range (i-j > 5) restraints. All lower interproton distance bounds were set at the sum of the van Der Waals radii (1.8 A), and upper bounds of 2.7 A, 3.3 A, and 5.0 A were employed to represent qualitatively observed strong, medium, and weak NOE cross peak intensities, respectively. Twenty-three backbone-backbone, six backbone-sulfur (Cys), two backbone-side chain, and two side chain-side chain hydrogen bond restraints were include for structure refinement, yielding a total of 436 nonbonded restraints, which averages to > 16 restraints per residue. A total of 10 structures generated from random atom positions and 30 structures generated by molecular replacement using the backbone coordinates of Clostridium pasteurianum Rd converged to a common conformation, with the average penalty (= sum of the square of the distance bounds violations; +/- standard deviation) of 0.024 +/- 0.003 A2 and a maximum total penalty of 0.035 A2. Superposition of the backbone atoms (C, C alpha, N) of residues A1-L51 for all 40 structures afforded an average pairwise root mean square (rms) deviation value (+/- SD) of 0.42 +/- 0.07 A. Superposition of all heavy atoms for residues A1-L51, including those of structurally undefined external side chains, afforded an average pairwise rms deviation of 0.72 +/- 0.08 A. Qualitative comparison of back-calculated and experimental two-dimensional NOESY spectra indicate that the DG/SA structures are consistent with the experimental spectra. The global folding of P. furiosus Zn(Rd) is remarkably similar to the folding observed by X-ray crystallography for native Rd from the mesophilic organism C. pasteurianum, with the average rms deviation value for backbone atoms of residues A1-L51 of P. furiosus Zn(Rd) superposed with respect to residues K2-V52 of C. pasteurianum Rd of 0.77 +/- 0.06 A. The conformations of aromatic residues that compose the hydrophobic cores of the two proteins are also similar. However, P. furiosus Rd contains several unique structural elements, including at least four additional hydrogen bonds and three potential electrostatic interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

An FEM study of the plastic deformation process of whisker reinforced SiC/Al composites

Abstract: The finite element method (FEM) was employed to investigate the matrix plastic flow in a whisker reinforced SiC/Al composite under external tensile load. It was found that the plastic zone induced by the plastic relaxation of thermal stresses expands under the external tensile load. The overall matrix plastic flow was characterized by the expansion and interconnection of the plastic zones around whiskers. This process can be divided into several characteristi stages, and related to the global stress-strain relationship. It also indicated that the strengthening was due mainly to the thermally induced matrix work hardening at the tip of the whisker. Finally, the initiation of plastic flow in an inhomogeneously reinforced composite was governed by the redistribution of the average stress and strength in the reinforcement clusters.

Purification and determination of the structure of capsular polysaccharide of Vibrio vulnificus M06-24.

Abstract: Virulence of Vibrio vulnificus has been strongly associated with encapsulation and an opaque colony morphology. Capsular polysaccharide was purified from a whole-cell, phosphate-buffered saline-extracted preparation of the opaque, virulent phase of V. vulnificus M06-24 (M06-24/O) by dialysis, centrifugation, enzymatic digestion, and phenol-chloroform extraction. Nuclear magnetic resonance spectroscopic analysis of the purified polysaccharide showed that the polymer was composed of a repeating structure with four sugar residues per repeating subunit: three residues of 2-acetamido-2,6-dideoxyhexopyranose in the alpha-gluco configuration (QuiNAc) and an additional residue of 2-acetamido hexouronate in the alpha-galactopyranose configuration (GalNAcA). The complete carbohydrate structure of the polysaccharide was determined by heteronuclear nuclear magnetic resonance spectroscopy and by high-performance anion-exchange chromatography. The 1H and 13C nuclear magnetic resonance spectra were completely assigned, and vicinal coupling relationships were used to establish the stereochemistry of each sugar residue, its anomeric configuration, and the positions of the glycosidic linkages. The complete structure is: [----3) QuipNAc alpha-(1----3)-GalpNAcA alpha-(1----3)-QuipNAc alpha-(1----]n QuipNAc alpha-(1----4)-increases The polysaccharide was produced by a translucent phase variant of M06-24 (M06-24/T) but not by a translucent, acapsular transposon mutant (CVD752). Antibodies to the polysaccharide were demonstrable in serum from rabbits inoculated with M06-24/O.

Bereavement support groups: who joins; who does not; and why.

Abstract: Compared widowed spouses who joined (n = 40) bereavement support groups (BSGs) during the first 13 months of bereavement with those who declined to join (n = 96). Controlling for gender, age, and socioeconomic status, no differences were found for perceived levels of social support, but joiners, compared with nonjoiners, reported experiencing more stressful events and scored significantly higher on measures of depression, anger, anxiety, and subjective stress. Nonjoiners and, to a lesser extent, joiners viewed those attending groups as less self-sufficient (e.g., need help, lonely), suggesting a mildly stigmatizing image of BSGs. A dialectical model is proposed in which BSG utilization rates are seen as the product of an avoidance-avoidance conflict involving the choice between suffering emotional distress on one's own or the perceived stigma of joining a BSG. Implications for future research on participation in self-help and mutual support groups are discussed.

Sequential expression of biomarkers in Bluegill Sunfish exposed to contaminated sediment.

Abstract: The temporal expression of various biological rsponses was determined in Bluegill SunfishLepomis macrochirus exposed under controlled laboratory conditions to sediment containing high concentrations of polynuclear aromatic hydrocarbons, polychlorinated biphenyls and heavy metals. Liver, gill, blood, kidney, brain, spleen and intestine were removed from Sunfish sampled at 1, 2, 4, 8, 16, and 40 weeks post-exposure. Biomarker data were recorded for specific proteins, enzymatic activities, DNA integrity, and histopathology. Biomarkers in the laboratory exposed fish were similar to those of indigenous Sunfish sampled from the site of origin of the contaminated sediment. Several patterns of development of biomarkers over time were also evident. For example, the responses of certain biomarkers are not time-dependent (i.e., intestine and gill ATPase activities) while that of others, such as brain ATPase activity, liver cytochrome P450 and NADPH content, stress proteins, chromatin proteins and DNA strand breaks, fluctuate over time. Still other biomarkers, such as EROD activity, zinc protoporphyrin content of the blood, and DNA adducts, showed marked increases over time. Such patterns need to be considered when comparing laboratory and field results and deciding which biomarkers to use for biomonitoring programs. Implications for natural selection and population/community level responses are also discussed.

Quantitative measurement of small through-hydrogen-bond and 'through-space' 1H-113Cd and 1H-199Hg J couplings in metal-substituted rubredoxin from Pyrococcus furiosus.

Abstract: A method is described for measurement of small unresolvable heteronuclear J couplings. The method is based on quantitative analysis of a phase-purged heteronuclear spin-echo difference spectrum, and is demonstrated for measuring 1H-113Cd and 1H-199Hg J couplings in metal-substituted rubredoxin (M(r) approximately 5.4 kDa) from Pyrococcus furiosus. Couplings from cadmium to backbone amide protons that are hydrogen bonded to the Cys-S atoms directly bonded to Cd vary from smaller than 0.3 to 1.8 Hz; a 'through-space' coupling between Cd and the protons of an alanine methyl group was measured to be 0.3 Hz. Couplings to 199Hg are significantly larger and fall in the 0.4-4 Hz range.

Intrinsic linewidths and radiative lifetimes of free excitons in GaAs quantum wells.

Abstract: The giant oscillator strength for radiative transitions of excitons in quantum wells is largely due to the macroscopic polarization of a two-dimensional system. At low temperatures the large oscillator strength leads to a short radiative lifetime of free excitons. We investigate the photoluminescence linewidths and lifetimes of free excitons in a series of extremely high-quality GaAs quantum wells as a function of lattice temperature, excitation intensity, and quantum-well width

The fracture toughness of titanium-fiber-reinforced bone cement.

Abstract: Fracture of the poly(methyl methacrylate) bone cement mantle can lead to the loosening and ultimate failure of cemented total joint prostheses. The addition of fibers to the bone cement increases fracture resistance and may reduce, if not eliminate, in vivo fracturing. This study discusses the effect of incorporating titanium (Ti) fibers on fracture toughness. Essential characteristics of the composite bone cement included a homogeneous and uniform fiber distribution, and a minimal increase in apparent viscosity of the polymerizing cement. Ti fiber contents of 1%, 2%, and 5% by volume increased the fracture toughness over non-reinforced bone cement by up to 56%. Bone cements of two different viscosities were used as matrix material, but when reinforced with the same fiber type and content, they showed no difference in fracture toughness. Four different fiber aspect ratios (68, 125, 227, 417) were tested. At 5% fiber content, there was no statistically significant dependence of fracture toughness on fiber aspect ratio. Scanning electron microscopy revealed important toughening mechanisms such as fiber/matrix debonding, local fracture path alteration, and ductile fiber deformation and fracture. Fiber fracture was evidence that the critical fiber length was exceeded. The surfaces of the Ti fibers were rough and irregular, indicating that a high degree of mechanical interlock between matrix and fiber was likely. The energy absorption contribution of plastic deformation and ductile fracture is absent in brittle fibers, like carbon, but is a distinction of the Ti fibers used in this study. © 1992 John Wiley & Sons, Inc.