Showing papers by "University of Maryland, Baltimore County published in 1998"

Hopkins Verbal Learning Test—Revised: Normative data and analysis of inter-form and test–retest reliability.

Abstract: The Hopkins Verbal Learning Test (HVLT) is a brief verbal learning and memory test with six alternate forms. The HVLT is ideal in situations calling for repeated neuropsychological examinations, but it lacks a delayed recall trial which is essential for the assessment of abnormal forgetting. We present a revised version of the HVLT which includes a delayed recall trial, and therefore delays the yes/no recognition trial. The equivalence of test forms was examined in two separate studies using between-groups and within-subjects research designs. In both studies, the six forms of the revised HVLT (HVLT-R) were found to be equivalent with respect to the recall trials, but there were some modest differences in recognition. Recommendations for the use of the HVLT-R in serial neuropsychological examinations are provided, as well as normative data tables from a sample of 541 subjects, spanning ages 17 to 88 years.

Structure of the HIV-1 Nucleocapsid Protein Bound to the SL3 Ψ-RNA Recognition Element

Abstract: The three-dimensional structure of the human immunodeficiency virus–type 1 (HIV-1) nucleocapsid protein (NC) bound to the SL3 stem-loop recognition element of the genomic Ψ RNA packaging signal has been determined by heteronuclear magnetic resonance spectroscopy. Tight binding (dissociation constant, ∼100 nM) is mediated by specific interactions between the amino- and carboxyl-terminal CCHC-type zinc knuckles of the NC protein and the G7 and G9 nucleotide bases, respectively, of the G6-G7-A8-G9 RNA tetraloop. A8 packs against the amino-terminal knuckle and forms a hydrogen bond with conserved Arg32, and residues Lys3 to Arg10 of NC form a 310helix that binds to the major groove of the RNA stem and also packs against the amino-terminal zinc knuckle. The structure provides insights into the mechanism of viral genome recognition, explains extensive amino acid conservation within NC, and serves as a basis for the development of inhibitors designed to interfere with genome encapsidation.

Statistics of cone responses to natural images: implications for visual coding

Abstract: We gathered hyperspectral images of natural, foliage-dominated scenes and converted them to human cone quantal catches to characterize the second-order redundancy present within the retinal photoreceptor array under natural conditions. The data are expressed most simply in a logarithmic response space, wherein an orthogonal decorrelation robustly produces three principal axes, one corresponding to simple changes in radiance and two that are reminiscent of the blue–yellow and red–green chromatic-opponent mechanisms found in the primate visual system. Further inclusion of spatial stimulus dimensions demonstrates a complete spatial decorrelation of these three cone-space axes in natural cone responses.

How effective are neural networks at forecasting and prediction? A review and evaluation

Abstract: Despite increasing applications of artificial neural networks (NNs) to forecasting over the past decade, opinions regarding their contribution are mixed. Evaluating research in this area has been difficult, due to lack of clear criteria. We identified eleven guidelines that could be used in evaluating this literature. Using these, we examined applications of NNs to business forecasting and prediction. We located 48 studies done between 1988 and 1994. For each, we evaluated how effectively the proposed technique was compared with alternatives (effectiveness of validation) and how well the technique was implemented (effectiveness of implementation). We found that eleven of the studies were both effectively validated and implemented. Another eleven studies were effectively validated and produced positive results, even though there were some problems with respect to the quality of their NN implementations. Of these 22 studies, 18 supported the potential of NNs for forecasting and prediction. Copyright © 1998 John Wiley & Sons, Ltd.

Reduction of Established Spontaneous Mammary Carcinoma Metastases following Immunotherapy with Major Histocompatibility Complex Class II and B7.1 Cell-based Tumor Vaccines

Abstract: For many cancer patients, removal of primary tumor is curative; however, if metastatic lesions exist and are not responsive to treatment, survival is limited. Although immunotherapy is actively being tested in animal models against primary tumors and experimental metastases (i.v. induced), very few studies have examined immunotherapy of spontaneous, established metastatic disease. The shortage of such studies can be attributed to the paucity of adequate animal models and to the concern that multiple metastatic lesions may be more resistant to immunotherapy than a localized primary tumor. Here, we use the BALB/c-derived mouse mammary carcinoma, 4T1, and show that this tumor very closely models human breast cancer in its immunogenicity, metastatic properties, and growth characteristics. Therapy studies demonstrate that treatment of mice with established primary and metastatic disease with MHC class II and B7.1-transfected tumor cells reduces or eliminates established spontaneous metastases but has no impact on primary tumor growth. These studies indicate that cell-based vaccines targeting the activation of CD4+ and CD8+ T cells may be effective agents for the treatment of malignancies, such as breast cancer, where the primary tumor is curable by conventional methods, but metastatic lesions remain refractile to current treatment modalities.

Coming out for lesbian women: its relation to anxiety, positive affectivity, self-esteem, and social support.

Abstract: The present study investigated relations between lesbians' disclosure of their sexual orientation and psychological adjustment. The 499 participants responded to a questionnaire assessing level of self-disclosure, sources of social support, forms of socializing, self-description of sexual orientation, and length of self-identification as a lesbian. The more widely a woman disclosed her sexual orientation the less anxiety, more positive affectivity, and greater self-esteem she reported. Degree of disclosure to family, gay and lesbian friends, straight friends, and co-workers was related to overall level of social support, with those who more widely disclosed reporting greater levels of support. Participants who more widely disclosed their sexual orientation were less likely to engage in anonymous socializing, had a larger percentage of lesbian friends, and were more involved in the gay and lesbian community. Path analyses revealed a mediating effect of social reactions (both initial and current) o...

C-C Chemokines, Pivotal in Protection Against HIV Type 1 Infection

Abstract: Exposure to HIV type 1 (HIV-1) does not usually lead to infection. Although this could be because of insufficient virus titer, there is now abundant evidence that some individuals resist infection even when directly exposed to a high titer of HIV. This protection recently has been correlated with homozygous mutations of an HIV-1 coreceptor, namely CCR5, the receptor for the β-chemokines. Moreover, earlier results already had shown that the same chemokines markedly suppress the nonsyncitial inducing variants of HIV-1, the chief virus type transmitted from person to person. CCR5 mutation, as a unique mechanism of protection, is, however, suspect because HIV-1 variants can use other chemokine receptors as their coreceptor. Moreover, recent results have established that infection can indeed sometimes occur with such mutations. Here, we report on transient natural resistance over time of most of 128 hemophiliacs who were inoculated repeatedly with HIV-1-contaminated Factor VIII concentrate from plasma during 1980–1985 before the development of the HIV blood test. Furthermore, and remarkably, 14 subjects remain uninfected to this date, and in these subjects we found homozygous CCR5 mutations in none but in most of them overproduction of β chemokines. In vitro experiments confirmed the potent anti-HIV suppressive effect of these chemokines.

Personal security agent: KQML-based PKI

Abstract: Certificate management infrastructure, a.k.a. PKI (Public Key Infrastructure), which issues and provides access to public key certificates to preserve the integrity of a public key, is fundamental for electronic commerce and business across the Internet. To satisfy the requirements of various applications, PKI should demonstrate customization to user needs, interoperability and flexibility in its implementations so it can satisfy the needs of various applications. Particularly, due to the popularity of software agent-based applications over the Internet, security will be urgently needed by the “agent society”. We propose to implement the authority of authentication verification service systems as personal autonomous software agents, called security agents. In this paper, we present two aspects of KQML-based PKI: 1. the security agent concept and its functional modules; 2. an extension of KQML, which is needed for public key management and secure communications among security agents and application agents.

Internal validity of project MATCH treatments: Discriminability and integrity.

Abstract: Project MATCH (Matching Alcoholism Treatments to Client Heterogeneity) is a multisite collaborative project designed to evaluate patient-treatment interactions in alcoholism treatment. To evaluate whether major threats to the internal validity of the independent (treatment) variable in Project MATCH could be ruled out, we investigated several aspects of treatment integrity and discriminability. In this study, 1,726 alcohol-dependent participants at 10 sites were randomized to 3 treatments: cognitive-behavioral treatment (CBT), motivational enhancement therapy (MET), and 12-step facilitation (TSF). Participants received treatment either as outpatients or as aftercare following a more intensive inpatient or day hospital treatment. For both the outpatient and aftercare arms of the study, treatments were discriminable in that therapists implemented each of the treatments according to manual guidelines and rarely used techniques associated with comparison approaches. Participants received a high level of exposure to their study treatments, and the intended contrast in treatment dose between MET and the 2 more intensive treatments (CBT and TSF) was obtained. Alcoholics Anonymous involvement was significantly higher for participants assigned to TSF versus MET or CBT, whereas the treatments did not differ in utilization of other nonstudy treatments. Nonspecific aspects of treatment such as therapist skillfulness and level of the therapeutic alliance were comparable across treatment conditions.

Relational transducers for electronic commerce

Abstract: Electronic commerce is emerging as one of the major Web-supported applications requiring database support. We introduce and study high-level declarative specifications of business models, using an approach in the spirit of active databases. More precisely, business models are specified as relational transducers that map sequences of input relations into sequences of output relations. The semantically meaningful trace of an input?output exchange is kept as a sequence of log relations. We consider problems motivated by electronic commerce applications, such as log validation, verifying temporal properties of transducers, and comparing two relational transducers. Positive results are obtained for a restricted class of relational transducers called Spocus transducers (for semi-positive outputs and cumulative state). We argue that despite the restrictions, these capture a wide range of practically significant business models.

Green Fluorescent Protein as a Real Time Quantitative Reporter of Heterologous Protein Production

Abstract: Since its cloning and commercial availability, applications of green fluorescent protein (GFP) as a reporter gene have become prevalent in many aspects of science. The attributes of GFP could also be applied to the area of heterologous protein production. The work described here represents the first experiments to use GFP as a generic tool to monitor protein production in bioprocess development. We have constructed a plasmid containing an operon fusion of the two reporter genes GFP and chloramphenicol acetyl transferase (CAT) . CAT served as a “model” recombinant protein product to demonstrate the in situ quantifiable reporting mechanism of GFP. Our results indicate there is a direct correlation between the fluorescence intensity of GFP and the functional activity of the downstream CAT protein. In addition, there is a quantitative relationship between the level of CAT protein concentration and GFP fluorescence. These experiments provide the groundwork for using GFP as an in situ reporter gene for scale-up and process optimization of recombinant protein production.

Self-similarity in file systems

Abstract: We demonstrate that high-level file system events exhibit self-similar behaviour, but only for short-term time scales of approximately under a day. We do so through the analysis of four sets of traces that span time scales of milliseconds through months, and that differ in the trace collection method, the filesystems being traced, and the chronological times of the tracing. Two sets of detailed, short-term file system trace data are analyzed; both are shown to have self-similar like behaviour, with consistent Hurst parameters (a measure of self-similarity) for all file system traffic as well as individual classes of file system events. Long-term file system trace data is then analyzed, and we discover that the traces' high variability and self-similar behaviour does not persist across time scales of days, weeks, and months. Using the short-term trace data, we show that sources of file system traffic exhibit ON/OFF source behaviour, which is characterized by highly variably lengthed bursts of activity, followed by similarly variably lengthed periods of inactivity. This ON/OFF behaviour is used to motivate a simple technique for synthesizing a stream of events that exhibit the same self-similar short-term behaviour as was observed in the file system traces.

Internal validity of Project MATCH treatments: discriminability and integrity.

Abstract: Project MATCH (Matching Alcoholism Treatments to Client Heterogeneity) is a multisite collaborative project designed to evaluate patient-treatment interactions in alcoholism treatment. To evaluate whether major threats to the internal validity of the independent (treatment) variable in Project MATCH could be ruled out, we investigated several aspects of treatment integrity and discriminability. In this study, 1,726 alcohol-dependent participants at 10 sites were randomized to 3 treatments: cognitive-behavioral treatment (CBT), motivational enhancement therapy (MET), and 12-step facilitation (TSF). Participants received treatment either as outpatients or as aftercare following a more intensive inpatient or day hospital treatment. For both the outpatient and aftercare arms of the study, treatments were discriminable in that therapists implemented each of the treatments according to manual guidelines and rarely used techniques associated with comparison approaches. Participants received a high level of exposure to their study treatments, and the intended contrast in treatment dose between MET and the 2 more intensive treatments (CBT and TSF) was obtained. Alcoholics Anonymous involvement was significantly higher for participants assigned to TSF versus MET or CBT, whereas the treatments did not differ in utilization of other nonstudy treatments. Nonspecific aspects of treatment such as therapist skillfulness and level of the therapeutic alliance were comparable across treatment conditions.

Estimation of a Common Mean and Weighted Means Statistics

Abstract: Measurements made by several laboratories may exhibit nonnegligible between-laboratory variability, as well as different within-laboratory variances. Also, the number of measurements made at each laboratory often differ. Questions of fundamental importance in the analysis of such data are how to form a best consensus mean, and what uncertainty to attach to this estimate. An estimation equation approach due to Mandel and Paule is often used at the National Institute of Standards and Technology (NIST), particularly when certifying standard reference materials. Primary goals of this article are to study the theoretical properties of this method, and to compare it with some alternative methods, in particular to the maximum likelihood estimator (MLE). Toward this end, we show that the Mandel-Paule solution can be interpreted as a simplified version of the maximum likelihood method. A class of weighted means statistics is investigated for situations where the number of laboratories is large. This class...

Preparing the Way: A Qualitative Study of High-Achieving African American Males and the Role of the Family

Abstract: Employed qualitative methods to examine the role of the family in the academic success of very high-achieving African American males. Findings revealed a complex tapestry of family processes and contexts involved in each youth's journey to outstanding academic achievement. Specifically, the combined importance of parental-determined academic engagement, strict discipline, nurturance, and community connectedness appeared to counteract potentially negative contextual influences of neighborhood, peers, schools, and society. The qualitative findings tell a multifaceted, rich, and compelling story of the pathways to academic success for Black males, and highlight the need for culture-specific and ecologically based conceptualization, research, and intervention approaches.

Migratory Behavior of Ovigerous Blue Crabs Callinectes sapidus: Evidence for Selective Tidal-Stream Transport

Abstract: In the late summer and early fall, newly inseminated female blue crabs (Callinectes sapidus) leave low-salinity areas of estuaries and migrate seaward to spawn near the entrance. We tested the hypothesis that migration of female C. sapidus to spawning grounds is facilitated by selective tidal-stream transport (STST). We monitored the swimming direction of adult crabs from a stationary platform located about I km inside the entrance to the Newport River Estuary (Beaufort, North Carolina). Swimming activity near the sur$ace occurred primarily at night and most crabs avoided swimming against tidal currents. Eighty-one percent of the crabs observed moving downestuary toward the inlet during ebb tide were ovigerous females. Of the 36 gravid females captured traveling in ebb currents, 97% possessed dark egg masses containing late-stage embryos. Conversely, nearly all (98%) adult crabs observed traveling in flood currents lacked egg masses, and all the females captured while migrating upestuary exhibited signs of recent spawning. These observations indicate that ovigerous blue crabs use ebb-tide transport to migrate seaward to spawn and flood-tide transport to reenter the estuary shortly after larval release. Atlantic blue crabs (Cullinectes supidus Rathbun), like many brachyuran crabs, possess a complex life cycle that includes both estuarine and coastal migratory phases, making them ideal models for studying the intricacies of hydrodynamic transport, dispersal, and recruitment [see

Mechanism of Spectral Tuning in the Dolphin Visual Pigments

Abstract: The absorption maxima of both rod and cone visual pigments of the bottlenose dolphin (Tursiops truncatus) are blue-shifted relative to those of terrestrial mammals. A comparison of the sequence of the dolphin rod photopigment gene with that of the bovine rod suggests that, of the 28 nonidentical amino acids, three amino acid substitutions at positions 83, 292, and 299 in the dolphin rod pigment are responsible for the 10 nm blue shift in absorption maxima. A similar comparison of the dolphin long-wavelength sensitive (LWS) cone photopigment gene with those of the human LWS cones suggests that a single substitution at position 292 (using the convention of rhodopsin numbering) in the dolphin LWS cone pigment results in a blue shift in absorption maxima. A mutagenesis study reveals that the combination of the three dolphin specific substitutions in the bovine rod pigment (83D to 83N, 292A to 292S, and 299A to 299S) causes a blue shift from the wild-type λmax of 499 nm to 489 nm. The single substitution in th...

Quantification and segmentation of brain tissues from MR images: a probabilistic neural network approach

Abstract: This paper presents a probabilistic neural network based technique for unsupervised quantification and segmentation of brain tissues from magnetic resonance images. It is shown that this problem can be solved by distribution learning and relaxation labeling, resulting in an efficient method that may be particularly useful in quantifying and segmenting abnormal brain tissues where the number of tissue types is unknown and the distributions of tissue types heavily overlap. The new technique uses suitable statistical models for both the pixel and context images and formulates the problem in terms of model-histogram fitting and global consistency labeling. The quantification is achieved by probabilistic self-organizing mixtures and the segmentation by a probabilistic constraint relaxation network. The experimental results show the efficient and robust performance of the new algorithm and that it outperforms the conventional classification based approaches.

The visual pigments of the bottlenose dolphin (Tursiops truncatus).

Abstract: To assess the dolphin's capacity for color vision and determine the absorption maxima of the dolphin visual pigments, we have cloned and expressed the dolphin opsin genes. On the basis of sequence homology with other mammalian opsins, a dolphin rod and long-wavelength sensitive (LWS) cone opsin cDNAs were identified. Both dolphin opsin cDNAs were expressed in mammalian COS-7 cells. The resulting proteins were reconstituted with the chromophore 11-cis-retinal resulting in functional pigments with absorption maxima (lambdamax) of 488 and 524 nm for the rod and cone pigments respectively. These lambdamax values are considerably blue shifted compared to those of many terrestrial mammals. Although the dolphin possesses a gene homologous to other mammalian short-wavelength sensitive (SWS) opsins, it is not expressed in vivo and has accumulated a number of deletions, including a frame-shift mutation at nucleotide position 31. The dolphin therefore lacks the common dichromatic form of color vision typical of most terrestrial mammals.

What is a Central City in the United States? Applying a Statistical Technique for Developing Taxonomies

Abstract: We test the null hypothesis that municipalities defined as central cities by the US Bureau of the Census in 1990 are homogeneous-a hypothesis we reject. Rather, we find that US central cities consist of 2 distinct subsets of municipalities that are aggregated from 13 cluster groupings. The article has two purposes. The first is methodological. We develop a method that uses cluster analysis to group US central cities; then we employ discriminant analysis to establish the statistical validity of those groups. We also develop techniques to minimise the role of judgement in selecting the appropriate cluster solution. The second purpose of the article is to test the substantive null hypothesis. Our rejection of the homogeneity assumption raises the spectre of specification error in research and public policies that assume homogeneity among central cities.

Inclusion of local structure effects in theoretical x-ray resonant scattering amplitudes using ab initio x-ray-absorption spectra calculations

Abstract: Improved calculations of Bragg peak intensities near atomic resonance are obtained by including the effect of the local environment around the resonant atoms on the resonant scattering amplitudes $\ensuremath{\Delta}{f=f}^{\ensuremath{'}}{+if}^{\ensuremath{''}}.$ Theoretical absorption cross sections calculated by the ab initio x-ray-absorption code FEFF are used to obtain the imaginary part ${f}^{\ensuremath{''}}$ by extension of the optical theorem to nonforward scattering under the dipole approximation. The real part ${f}^{\ensuremath{'}}$ is obtained by a limited range Kramers-Kronig transform of the difference between ${f}^{\ensuremath{''}}$ based on FEFF and existing theoretical calculations of ${f}^{\ensuremath{''}}$ based on an isolated-atom model. The atomic part of $\ensuremath{\Delta}f$ calculated by FEFF for the resonant atom embedded in the local potential is assumed to have spherical symmetry; however, no restriction is placed on the spectral features due to multiple scattering of the intermediate-state virtual photoelectron. Bragg peak intensities calculated in the kinematic approximation using the FEFF-based $\ensuremath{\Delta}f$ are compared to intensities calculated using the isolated-atom $\ensuremath{\Delta}f$ and to experimental data for Cu metal and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.8}$ at the Cu K absorption edge, and for ${\mathrm{UO}}_{2}$ at the U ${M}_{\mathrm{IV}}$ absorption edge.

A direct way of specifying flow‐dependent background error correlations for meteorological analysis systems

Abstract: Identifying a viable strategy for specifying the background error covariance remains an importantproblem in meteorological data assimilation. From a formal point of view the number ofindependent parameters needed for this is n 2 /2 where n is the dimension of the model statespace. In most analysis systems used in operational mode at the present time, the error covarianceis modeled using assumptions about homogeneity and isotropy, and the resulting backgrounderror covariance matrix thus does not depend on the state of the atmosphere. In thispaper, we propose a simple and inexpensive method for specifying univariate background errorcorrelations in terms of the background field itself. We illustrate the positive impact of theimplementation of this model by a simple example in which we reconstruct a total ozone fieldfrom a sparse set of observations. We finally discuss the generalization of the basic idea involvedto univariate correlations for general meteorological models. DOI: 10.1034/j.1600-0870.1998.00004.x

The Bacillus subtilis DinR Binding Site: Redefinition of the Consensus Sequence

Abstract: Recently, the DinR protein was established as the cellular repressor of the SOS response in the bacterium Bacillus subtilis. It is believed that DinR functions as the repressor by binding to a consensus sequence located in the promoter region of each SOS gene. The binding site for DinR is believed to be synonymous with the formerly identified Cheo box, a region of 12 bp displaying dyad symmetry (GAAC-N4-GTTC). Electrophoretic mobility shift assays revealed that highly purified DinR does bind to such sites located upstream of the dinA, dinB, dinC, and dinR genes. Furthermore, detailed mutational analysis of the B. subtilis recA operator indicates that some nucleotides are more important than others for maintaining efficient DinR binding. For example, nucleotide substitutions immediately 5′ and 3′ of the Cheo box as well as those in the N4 region appear to affect DinR binding. This data, combined with computational analyses of potential binding sites in other gram-positive organisms, yields a new consensus (DinR box) of 5′-CGAACRNRYGTTYC-3′. DNA footprint analysis of the B. subtilis dinR and recA DinR boxes revealed that the DinR box is centrally located within a DNA region of 31 bp that is protected from hydroxyl radical cleavage in the presence of DinR. Furthermore, while DinR is predominantly monomeric in solution, it apparently binds to the DinR box in a dimeric state.

Electronic Commerce: Technical, Business, and Legal Issues

Abstract: 1. Introduction. Overview. EC Statistics. Objectives of EC. Requirements and Services. 2. EC Components. Electronic Data Interchange. Digital Currency. Electronic Catalogs. Intranets and Extranets. 3. EC in Business. The Business Case. Business Uses of Electronic Commerce. Business Models and Business Functions. Industrial Applications. EC Use within Government. 4. Technical Issues for Electronic Commerce. Telecommunication Infrastructure. Decision Support Systems for EC. Interoperability. Storage and Retrieval of Multimedia Information. Workflow Management. Markup Languages. 5. Security for Electronic Commerce. Functions and Requirements. Security Management and Business Controls. User Perceptions and Trust. Security Technologies. The Cryptography Debate. Legal Validity of Digital Signatures. 6. Legal Frameworks: Policy & Regulatory Issues for Electronic Commerce. Intellectual Property. Legal Issues for Electronic Payment Systems. Contractual and Legal Settlements. Regulatory Framework for Electronic Commerce. 7. Conclusions and Future Directions. Interoperability. Automated Interactions. Information Overload. Mobile Computing. Multimedia Information. Matchmaking Services. Economic, Social, and Cultural Issues. References. Index.

Dispersion-managed solitons at normal average dispersion

Abstract: We find that in a dispersion-managed fiber, in which the strength of the dispersion management is above some threshold, solitons can exist with normal average dispersion. When the normal average dispersion is below some limiting value there exist two soliton solutions with the same pulse duration and different pulse energies. When the normal average dispersion is above this limiting value, no soliton exists. Both higher-energy and lower-energy solitons are dynamically stable in the parameter range that we considered.