Showing papers by "University of Pennsylvania published in 1999"

Starburst99: Synthesis Models for Galaxies with Active Star Formation

Abstract: Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman. We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 106—109 yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at a Web site, which allows users to run specific models with nonstandard parameters as well. We also make the source code available to the community.

Why Differences Make a Difference: A Field Study of Diversity, Conflict and Performance in Workgroups:

Abstract: A multimethod field study of 92 workgroups explored the influence of three types of workgroup diversity (social category diversity, value diversity, and informational diversity) and two moderators ...

Quintessence, cosmic coincidence, and the cosmological constant

Abstract: Recent observations suggest that a large fraction of the energy density of the Universe has negative pressure. One explanation is vacuum energy density; another is quintessence in the form of a scalar field slowly evolving down a potential. In either case, a key problem is to explain why the energy density nearly coincides with the matter density today. The densities decrease at different rates as the Universe expands, so coincidence today appears to require that their ratio be set to a specific, infinitesimal value in the early Universe. In this paper, we introduce the notion of a ``tracker field,'' a form of quintessence, and show how it may explain the coincidence, adding new motivation for the quintessence scenario.

Polymersomes: tough vesicles made from diblock copolymers.

Abstract: Vesicles were made from amphiphilic diblock copolymers and characterized by micromanipulation. The average molecular weight of the specific polymer studied, polyethyleneoxide-polyethylethylene (EO40-EE37), is several times greater than that of typical phospholipids in natural membranes. Both the membrane bending and area expansion moduli of electroformed polymersomes (polymer-based liposomes) fell within the range of lipid membrane measurements, but the giant polymersomes proved to be almost an order of magnitude tougher and sustained far greater areal strain before rupture. The polymersome membrane was also at least 10 times less permeable to water than common phospholipid bilayers. The results suggest a new class of synthetic thin-shelled capsules based on block copolymer chemistry.

A Resource-Based Framework for Assessing the Strategic Advantages of Family Firms

Abstract: The Resource-Based View (RBV) of competitive advantage provides a theoretical framework from the field of strategic management for assessing the competitive advantages of family firms. The RBV isolates idiosyncratic resources that are complex, intangible, and dynamic within a particular firm. The bundle of resources that are distinctive to a firm as a result of family involvement are identified as the “familiness” of the firm. This approach provides a research and practice method for assessing the specific behavioral and social phenomena within a firm that provide an advantage. Using a familiness model for assessing competitive advantage overcomes many of the problems associated with the generic claim that family companies have an advantage over nonfamily companies. It also provides a unified systems perspective of family firm performance.

The Influence of Institutional Investors on Myopic R&D Investment Behavior

Abstract: This paper examines whether institutional investors create or reduce incentives for corporate managers to reduce investment in research and development (RD otherwise, institutional ownership serves to reduce pressures on managers for myopic investment behavior.

Natural engineering principles of electron tunnelling in biological oxidation-reduction.

Abstract: We have surveyed proteins with known atomic structure whose function involves electron transfer; in these, electrons can travel up to 14 A between redox centres through the protein medium. Transfer over longer distances always involves a chain of cofactors. This redox centre proximity alone is sufficient to allow tunnelling of electrons at rates far faster than the substrate redox reactions it supports. Consequently, there has been no necessity for proteins to evolve optimized routes between redox centres. Instead, simple geometry enables rapid tunnelling to high-energy intermediate states. This greatly simplifies any analysis of redox protein mechanisms and challenges the need to postulate mechanisms of superexchange through redox centres or the maintenance of charge neutrality when investigating electron-transfer reactions. Such tunnelling also allows sequential electron transfer in catalytic sites to surmount radical transition states without involving the movement of hydride ions, as is generally assumed. The 14 A or less spacing of redox centres provides highly robust engineering for electron transfer, and may reflect selection against designs that have proved more vulnerable to mutations during the course of evolution.

Comprehensive discharge planning and home follow-up of hospitalized elders: a randomized clinical trial

Abstract: ContextComprehensive discharge planning by advanced practice nurses has demonstrated short-term reductions in readmissions of elderly patients, but the benefits of more intensive follow-up of hospitalized elders at risk for poor outcomes after discharge has not been studied.ObjectiveTo examine the effectiveness of an advanced practice nurse–centered discharge planning and home follow-up intervention for elders at risk for hospital readmissions.DesignRandomized clinical trial with follow-up at 2, 6, 12, and 24 weeks after index hospital discharge.SettingTwo urban, academically affiliated hospitals in Philadelphia, Pa.ParticipantsEligible patients were 65 years or older, hospitalized between August 1992 and March 1996, and had 1 of several medical and surgical reasons for admission.InterventionIntervention group patients received a comprehensive discharge planning and home follow-up protocol designed specifically for elders at risk for poor outcomes after discharge and implemented by advanced practice nurses.Main Outcome MeasuresReadmissions, time to first readmission, acute care visits after discharge, costs, functional status, depression, and patient satisfaction.ResultsA total of 363 patients (186 in the control group and 177 in the intervention group) were enrolled in the study; 70% of intervention and 74% of control subjects completed the trial. Mean age of sample was 75 years; 50% were men and 45% were black. By week 24 after the index hospital discharge, control group patients were more likely than intervention group patients to be readmitted at least once (37.1% vs 20.3%; P<.001). Fewer intervention group patients had multiple readmissions (6.2% vs 14.5%;P = .01) and the intervention group had fewer hospital days per patient (1.53 vs 4.09 days; P<.001). Time to first readmission was increased in the intervention group (P<.001). At 24 weeks after discharge, total Medicare reimbursements for health services were about $1.2 million in the control group vs about $0.6 million in the intervention group (P<.001). There were no significant group differences in postdischarge acute care visits, functional status, depression, or patient satisfaction.ConclusionsAn advanced practice nurse–centered discharge planning and home care intervention for at-risk hospitalized elders reduced readmissions, lengthened the time between discharge and readmission, and decreased the costs of providing health care. Thus, the intervention demonstrated great potential in promoting positive outcomes for hospitalized elders at high risk for rehospitalization while reducing costs.

Limbic Activation During Cue-Induced Cocaine Craving

Abstract: OBJECTIVE: Since signals for cocaine induce limbic brain activation in animals and cocaine craving in humans, the objective of this study was to test whether limbic activation occurs during cue-induced craving in humans. METHOD: Using positron emission tomography, the researchers measured relative regional cerebral blood flow (CBF) in limbic and comparison brain regions of 14 detoxified male cocaine users and six cocaine-naive comparison subjects during exposure to both non-drug-related and cocaine-related videos and during resting baseline conditions. RESULTS: During the cocaine video, the cocaine users experienced craving and showed a pattern of increases in limbic (amygdala and anterior cingulate) CBF and decreases in basal ganglia CBF relative to their responses to the nondrug video. This pattern did not occur in the cocaine-naive comparison subjects, and the two groups did not differ in their responses in the comparison regions (i.e., the dorsolateral prefrontal cortex, cerebellum, thalamus, and visu...

Experience‐weighted Attraction Learning in Normal Form Games

Abstract: In ‘experience-weighted attraction’ (EWA) learning, strategies have attractions that reflect initial predispositions, are updated based on payoff experience, and determine choice probabilities according to some rule (e.g., logit). A key feature is a parameter δ that weights the strength of hypothetical reinforcement of strategies that were not chosen according to the payoff they would have yielded, relative to reinforcement of chosen strategies according to received payoffs. The other key features are two discount rates, φ and ρ, which separately discount previous attractions, and an experience weight. EWA includes reinforcement learning and weighted fictitious play (belief learning) as special cases, and hybridizes their key elements. When δ= 0 and ρ= 0, cumulative choice reinforcement results. When δ= 1 and ρ=φ, levels of reinforcement of strategies are exactly the same as expected payoffs given weighted fictitious play beliefs. Using three sets of experimental data, parameter estimates of the model were calibrated on part of the data and used to predict a holdout sample. Estimates of δ are generally around .50, φ around .8 − 1, and ρ varies from 0 to φ. Reinforcement and belief-learning special cases are generally rejected in favor of EWA, though belief models do better in some constant-sum games. EWA is able to combine the best features of previous approaches, allowing attractions to begin and grow flexibly as choice reinforcement does, but reinforcing unchosen strategies substantially as belief-based models implicitly do.

Cosmological tracking solutions

Abstract: A substantial fraction of the energy density of the universe may consist of quintessence in the form of a slowly rolling scalar field. Since the energy density of the scalar field generally decreases more slowly than the matter energy density, it appears that the ratio of the two densities must be set to a special, infinitesimal value in the early universe in order to have the two densities nearly coincide today. Recently, we introduced the notion of tracker fields to avoid this initial conditions problem. In the paper, we address the following questions: What is the general condition to have tracker fields? What is the relation between the matter energy density and the equation-of-state of the universe imposed by tracker solutions? And can tracker solutions help to explain why quintessence is becoming important today rather than during the early universe?

Systemic biosynthesis of prostacyclin by cyclooxygenase (COX)-2: the human pharmacology of a selective inhibitor of COX-2.

Abstract: Prostaglandins (PG) are synthesized by two isoforms of the enzyme PG G/H synthase [cyclooxygenase (COX)]. To examine selectivity of tolerated doses of an inhibitor of the inducible COX-2 in humans, we examined the effects of celecoxib on indices of COX-1-dependent platelet thromboxane (Tx) A2 and on systemic biosynthesis of prostacyclin in vivo. Volunteers received doses of 100, 400, or 800 mg of celecoxib or 800 mg of a nonselective inhibitor, ibuprofen. Ibuprofen, but not celecoxib, significantly inhibited TxA2-dependent aggregation, induced ex vivo by arachidonic acid (83 +/- 11% vs. 11. 9 +/- 2.2%; P < 0.005) and by collagen. Neither agent altered aggregation induced by thromboxane mimetic, U46619. Ibuprofen reduced serum TxB2 (-95 +/- 2% vs. -6.9 +/- 4.2%; P < 0.001) and urinary excretion of the major Tx metabolite, 11-dehydro TxB2 (-70 +/- 9.9% vs. -20.3 +/- 5.3%; P < 0.05) when compared with placebo. Despite a failure to suppress TxA2-dependant platelet aggregation, celecoxib had a modest but significant inhibitory effect on serum TxB2 4 hr after dosing. By contrast, both ibuprofen and celecoxib suppressed a biochemical index of COX-2 activity (endotoxin induced PGE2 in whole blood ex vivo) to a comparable degree (-93.3 +/- 2% vs. -83 +/- 6.1%). There was no significant difference between the doses of celecoxib on COX-2 inhibition. Celecoxib and ibuprofen suppressed urinary excretion of the prostacyclin metabolite 2,3 dinor 6-keto PGF1alpha. These data suggest that (i) platelet COX-1-dependent aggregation is not inhibited by up to 800 mg of celecoxib; (ii) comparable COX-2 inhibition is attained by celecoxib (100-800 mg) and ibuprofen (800 mg) after acute dosing; and (iii) COX-2 is a major source of systemic prostacyclin biosynthesis in healthy humans.

The consolidation of the financial services industry: Causes, consequences, and implications for the future

Abstract: This article designs a framework for evaluating the causes, consequences, and future implications of financial services industry consolidation, reviews the extant research literature within the context of this framework (over 250 references), and suggests fruitful avenues for future research. The evidence is consistent with increases in market power from some types of consolidation; improvements in profit eAciency and diversification of risks, but little or no cost eAciency improvement on average; relatively little eAect on the availability of services to small customers; potential improvements in payments system eAciency; and potential costs on the financial system from increases in systemic risk or expansion of the financial safety net. ” 1999 Elsevier Science B.V. All rights reserved.

EIN2, a bifunctional transducer of ethylene and stress responses in Arabidopsis.

Abstract: Ethylene regulates plant growth, development, and responsiveness to a variety of stresses. Cloning of the Arabidopsis EIN2 gene identifies a central component of the ethylene signaling pathway. The amino-terminal integral membrane domain of EIN2 shows similarity to the disease-related Nramp family of metal-ion transporters. Expression of the EIN2 CEND is sufficient to constitutively activate ethylene responses and restores responsiveness to jasmonic acid and paraquat-induced oxygen radicals to mutant plants. EIN2 is thus recognized as a molecular link between previously distinct hormone response pathways. Plants may use a combinatorial mechanism for assessing various stresses by enlisting a common set of signaling molecules.

Culture specific and cross-culturally generalizable implicit leadership theories: Are attributes of charismatic/transformational leadership universally endorsed?

Abstract: This study focuses on culturally endorsed implicit theories of leadership (CLTs). Although cross-cultural research emphasizes that different cultural groups likely have different conceptions of what leadership should entail, a controversial position is argued here: namely that attributes associated with charismatic/transformational leadership will be universally endorsed as contributing to outstanding leadership. This hypothesis was tested in 62 cultures as part of the Global Leadership and Organizational Behavior Effectiveness (GLOBE) Research Program. Universally endorsed leader attributes, as well as attributes that are universally seen as impediments to outstanding leadership and culturally contingent attributes are presented here. The results support the hypothesis that specific aspects of charismatic/transformational leadership are strongly and universally endorsed across cultures.

The Use of Equity Grants to Manage Optimal Equity Incentive Levels

Abstract: We predict and find that firms use annual grants of options and restricted stock to CEOs to manage the optimal level of equity incentives. We model optimal equity incentive levels for CEOs, and use the residuals from this model to measure deviations between CEOs’ holdings of equity incentives and optimal levels. We find that grants of new incentives from options and restricted stock are negatively related to these deviations. Overall, our evidence suggests that firms set optimal equity incentive levels and grant new equity incentives in a manner that is consistent with economic theory.

Data on the Web: From Relations to Semistructured Data and XML

Abstract: 1 Introduction 2 A Syntax for Data 3 XML 4 Query Languages 5 Query Languages for XML 6 Interpretation and advanced features 7 Typing semistructured data 8 Query Processing 9 The Lore system 10 Strudel 11 Database products supporting XML

The biology of hair follicles.

Abstract: Hair has many useful biologic functions, including protection from the elements and dispersion of sweat-gland products (e.g., pheromones). It also has psychosocial importance in our society, and patients with hair loss (alopecia) (Table 1) or excessive hair growth often suffer tremendously. Not surprisingly, the demand for drugs that alter hair growth and appearance has led to a multibillion-dollar industry, yet few drugs that are effective for these purposes are available. However, recent progress in our understanding of the biology and pathology of hair follicles should lead to more effective therapies for disorders of hair growth. Structure and Function of Hair . . .

Prevention of graft versus host disease by inactivation of host antigen-presenting cells.

Abstract: Graft versus host disease, an alloimmune attack on host tissues mounted by donor T cells, is the most important toxicity of allogeneic bone marrow transplantation. The mechanism by which allogeneic T cells are initially stimulated is unknown. In a murine allogeneic bone marrow transplantation model it was found that, despite the presence of numerous donor antigen-presenting cells, only host-derived antigen-presenting cells initiated graft versus host disease. Thus, strategies for preventing graft versus host disease could be developed that are based on inactivating host antigen-presenting cells. Such strategies could expand the safety and application of allogeneic bone marrow transplantation in treatment of common genetic and neoplastic diseases.

Do Institutional Investors Prefer Near-Term Earnings over Long-Run Value?

Abstract: Critics often argue that institutional investors have an excessive focus on short-term firm performance that leads corporate managers to make decisions to boost short-term earnings at the expense of long-run value. This paper examines whether institutional investors exhibit preferences for near-term earnings over long-run value and whether such preferences have implications for firms' stock prices. Using the Ohlson [1995] model, I separate firm value into three components-book value, expected near-term earnings, and expected long-term (terminal) value-and test whether institutions prefer firms for which more of firm value is expected to be realized as near-term earnings rather than as long-term earnings. The results indicate that the level of ownership by institutions with short investment horizons (transient institutions) and by institutions held to stringent fiduciary standards (banks) is positively (negatively) associated with the amount of value in near-term (long-term) earnings. This evidence indicates that institutions with the strongest incentives to favor firms with a high proportion of value in near-term earnings exhibit such preferences. This evidence that banks and transient institutions prefer near-term earnings over long-run value raises the question of whether such institutions myopically price firms, overweighting short-term earnings potential and underweighting long-term earnings potential. Evidence of such myopic pricing would establish a link through which institutional investors could pressure managers into a short-term focus. The results provide no evidence that high levels of ownership by banks translate into myopic mispricing. However, high levels of transient ownership are associated with an over- (under-) weighting of near-term (long-term) expected earnings and a trading strategy based on this finding generates significant abnormal returns. This finding supports the concerns that many corporate managers have about the adverse effects of an ownership base dominated by short-term-focused institutional investors.

Liposomal Amphotericin B for Empirical Therapy in Patients with Persistent Fever and Neutropenia

Abstract: Background In patients with persistent fever and neutropenia, amphotericin B is administered empirically for the early treatment and prevention of clinically occult invasive fungal infections. However, breakthrough fungal infections can develop despite treatment, and amphotericin B has substantial toxicity. Methods We conducted a randomized, double-blind, multicenter trial comparing liposomal amphotericin B with conventional amphotericin B as empirical antifungal therapy. Results The mean duration of therapy was 10.8 days for liposomal amphotericin B (343 patients) and 10.3 days for conventional amphotericin B (344 patients). The composite rates of successful treatment were similar (50 percent for liposomal amphotericin B and 49 percent for conventional amphotericin B) and were independent of the use of antifungal prophylaxis or colony-stimulating factors. The outcomes were similar with liposomal amphotericin B and conventional amphotericin B with respect to survival (93 percent and 90 percent, respectively), resolution of fever (58 percent and 58 percent), and discontinuation of the study drug because of toxic effects or lack of efficacy (14 percent and 19 percent). There were fewer proved breakthrough fungal infections among patients treated with liposomal amphotericin B (11 patients [3.2 percent]) than among those treated with conventional amphotericin B (27 patients [7.8 percent], P=0.009). With the liposomal preparation significantly fewer patients had infusion-related fever (17 percent vs. 44 percent), chills or rigors (18 percent vs. 54 percent), and other reactions, including hypotension, hypertension, and hypoxia. Nephrotoxic effects (defined by a serum creatinine level two times the upper limit of normal) were significantly less frequent among patients treated with liposomal amphotericin B (19 percent) than among those treated with conventional amphotericin B (34 percent, P Conclusions Liposomal amphotericin B is as effective as conventional amphotericin B for empirical antifungal therapy in patients with fever and neutropenia, and it is associated with fewer breakthrough fungal infections, less infusion-related toxicity, and less nephrotoxicity.

The DNA sequence of human chromosome 22

Abstract: Knowledge of the complete genomic DNA sequence of an organism allows a systematic approach to defining its genetic components. The genomic sequence provides access to the complete structures of all genes, including those without known function, their control elements, and, by inference, the proteins they encode, as well as all other biologically important sequences. Furthermore, the sequence is a rich and permanent source of information for the design of further biological studies of the organism and for the study of evolution through cross-species sequence comparison. The power of this approach has been amply demonstrated by the determination of the sequences of a number of microbial and model organisms. The next step is to obtain the complete sequence of the entire human genome. Here we report the sequence of the euchromatic part of human chromosome 22. The sequence obtained consists of 12 contiguous segments spanning 33.4 megabases, contains at least 545 genes and 134 pseudogenes, and provides the first view of the complex chromosomal landscapes that will be found in the rest of the genome.

Invited Commentary: Propensity Scores

Abstract: The propensity score is the conditional probability of exposure to a treatment given observed covariates. In a cohort study, matching or stratifying treated and control subjects on a single variable, the propensity score, tends to balance all of the observed covariates; however, unlike random assignment of treatments, the propensity score may not also balance unobserved covariates. The authors review the uses and limitations of propensity scores and provide a brief outline of associated statistical theory. They also present a new result of using propensity scores in case-cohort studies.

The Teacher Research Movement: A Decade Later

Abstract: In this article, we discuss the latest renewal of interest in the U.S. in teacher research and other forms of practitioner inquiry, a movement that is now a little more than a decade old. We argue that part of what makes the current wave of interest a movement and not just the latest educational fad is that teacher research stems from several different, but in some ways compatible, intellectual traditions and educational projects. We identify five major trends that characterize the current U.S. movement: (a) the prominence of teacher research in teacher education, professional development, and school reform; (b) the development of conceptual frameworks and theories of teacher research; (c) the dissemination of teacher research beyond the local level; (d) the emergence of critique of teacher research and the teacher research movement; and (e) the transformative potential of teacher research on some aspects of university culture. Based on our own teacher research experiences and understandings of teacher re...

Serum amyloid A, the major vertebrate acute-phase reactant.

Abstract: The serum amyloid A (SAA) family comprises a number of differentially expressed apolipoproteins, acute-phase SAAs (A-SAAs) and constitutive SAAs (C-SAAs). A-SAAs are major acute-phase reactants, the in vivo concentrations of which increase by as much as 1000-fold during inflammation. A-SAA mRNAs or proteins have been identified in all vertebrates investigated to date and are highly conserved. In contrast, C-SAAs are induced minimally, if at all, during the acute-phase response and have only been found in human and mouse. Although the liver is the primary site of synthesis of both A-SAA and C-SAA, extrahepatic production has been reported for most family members in most of the mammalian species studied. In vitro, the dramatic induction of A-SAA mRNA in response to pro-inflammatory stimuli is due largely to the synergistic effects of cytokine signaling pathways, principally those of the interleukin-1 and interleukin-6 type cytokines. This induction can be enhanced by glucocorticoids. Studies of the A-SAA promoters in several mammalian species have identified a range of transcription factors that are variously involved in defining both cytokine responsiveness and cell specificity. These include NF-κB, C/EBP, YY1, AP-2, SAF and Sp1. A-SAA is also post-transcriptionally regulated. Although the precise role of A-SAA in host defense during inflammation has not been defined, many potential clinically important functions have been proposed for individual SAA family members. These include involvement in lipid metabolism/transport, induction of extracellular-matrix-degrading enzymes, and chemotactic recruitment of inflammatory cells to sites of inflammation. A-SAA is potentially involved in the pathogenesis of several chronic inflammatory diseases: it is the precursor of the amyloid A protein deposited in amyloid A amyloidosis, and it has also been implicated in the pathogenesis of atheroscelerosis and rheumatoid arthritis.