Showing papers by "University of Pennsylvania published in 1989"
TL;DR: In this paper, the authors developed hypotheses about the continuity of relationships from the literature on social exchange, bargaining, and negotiation, which were framed as a simultaneous equation system and estimated via three-stage least squares on a sample of 690 relationships dyads involving manufacturers and their independent sales agents manufacturers' representatives.
Abstract: Recently, increasing attention has been paid to the question of how to build stable, long-term relationships between manufacturers and members of conventional channels. This descriptive field study concerns a basic requirement for building long-term relationships, which is the expectation by a marketing intermediary that the relationship will last. Hypotheses about the continuity of relationships are developed from the literature on social exchange, bargaining, and negotiation. These hypotheses are framed as a simultaneous equation system, which is estimated via three-stage least squares on a sample of 690 relationships dyads involving manufacturers and their independent sales agents manufacturers' representatives. Results substantially support the model, highlighting the importance of interpersonal relationships in insuring the continuity of the dyad.
2,428 citations
TL;DR: A simple model is developed, based on the diffusion approximation to radiative transfer theory, which yields analytic expressions for the pulse shape in terms of the interaction coefficients of a homogeneous slab.
Abstract: When a picosecond light pulse is incident on biological tissue, the temporal characteristics of the light backscattered from, or transmitted through, the sample carry information about the optical absorption and scattering coefficients of the tissue. We develop a simple model, based on the diffusion approximation to radiative transfer theory, which yields analytic expressions for the pulse shape in terms of the interaction coefficients of a homogeneous slab. The model predictions are in good agreement with the results of preliminary in vivo experiments and Monte Carlo simulations.
2,242 citations
TL;DR: In this paper, the authors surveyed consumers about their feelings toward their inputs to and outcomes from the sales transaction, as well as their perceptions of the inputs and outcomes of the salesperson.
Abstract: Automobile purchasers were surveyed about feelings toward their inputs to and outcomes from the sales transaction, as well as their perceptions of the inputs and outcomes of the salesperson. Struct...
1,983 citations
TL;DR: In this paper, the authors developed a model consistent with this observation, which assumes the firm itself best knows its prospects and found that firms with the most favorable prospects find it optimal to signal their type by underpricing their initial issue of shares, and investors know that only the best can recoup the cost of this signal from subsequent issues.
1,564 citations
TL;DR: Using 3H-thymidine labeling, a subpopulation of corneal epithelial basal cells are identified in the peripheral cornea in a region called limbus that are normally slow cycling, but can be stimulated to proliferate in response to wounding and to a tumor promotor, TPA.
1,383 citations
TL;DR: In this paper, the authors analyze economies in which individuals specialize in consumption and production and meet randomly over time in a way that implies that trade must be bilateral and quid pro quo Nash equilibria in trading strategies are characterized.
Abstract: We analyze economies in which individuals specialize in consumption and production and meet randomly over time in a way that implies that trade must be bilateral and quid pro quo Nash equilibria in trading strategies are characterized Certain goods emerge endogenously as media of exchange, or commodity money, depending both on their intrinsic properties and on extrinsic beliefs There are also equilibria with genuine fiat currency circulating as the general medium of exchange We find that equilibria are not generally Pareto optimal and that introducing fiat currency into a commodity money economy may unambiguously improve welfare Velocity, acceptability, and liquidity are discussed
1,353 citations
Journal Article•
TL;DR: The classical principles behind dielectric relaxation are summarized, as empirical correlations with tissue water content in other compositional variables, and a comprehensive table is presented of dielectrics properties.
Abstract: We critically review bulk electrical properties of tissues and other biological materials, from DC to 20 GHz, with emphasis on the underlying mechanisms responsible for the properties. We summarize the classical principles behind dielectric relaxation and critically review recent developments in this field. Special topics include a summary of the significant recent advances in theories of counterion polarization effects, dielectric properties of cancer vs. normal tissues, properties of low-water-content tissues, and macroscopic field-coupling considerations. Finally, the dielectric properties of tissues are summarized as empirical correlations with tissue water content in other compositional variables; in addition, a comprehensive table is presented of dielectric properties. The bulk electrical properties of tissues are needed for many bioengineering applications of electric fields or currents, and they provide insight into the basic mechanisms that govern the interaction of electric fields with tissue.
1,337 citations
TL;DR: Once inside a host cell, the infecting Listeria and their progeny can spread from cell to cell by remaining intracellular and thus bypass the humoral immune system of the organism.
Abstract: Listeria monocytogenes was used as a model intracellular parasite to study stages in the entry, growth, movement, and spread of bacteria in a macrophage cell line. The first step in infection is phagocytosis of the Listeria, followed by the dissolution of the membrane surrounding the phagosome presumably mediated by hemolysin secreted by Listeria as nonhemolytic mutants remain in intact vacuoles. Within 2 h after infection, each now cytoplasmic Listeria becomes encapsulated by actin filaments, identified as such by decoration of the actin filaments with subfragment 1 of myosin. These filaments are very short. The Listeria grow and divide and the actin filaments rearrange to form a long tail (often 5 microns in length) extending from only one end of the bacterium, a "comet's tail," in which the actin filaments appear randomly oriented. The Listeria "comet" moves to the cell surface with its tail oriented towards the cell center and becomes incorporated into a cell extension with the Listeria at the tip of the process and its tail trailing into the cytoplasm behind it. This extension contacts a neighboring macrophage that phagocytoses the extension of the first macrophage. Thus, within the cytoplasm of the second macrophage is a Listeria with its actin tail surrounded by a membrane that in turn is surrounded by the phagosome membrane of the new host. Both these membranes are then solubilized by the Listeria and the cycle is repeated. Thus, once inside a host cell, the infecting Listeria and their progeny can spread from cell to cell by remaining intracellular and thus bypass the humoral immune system of the organism. To establish if actin filaments are essential for the spread of Listeria from cell to cell, we treated infected macrophages with cytochalasin D. The Listeria not only failed to spread, but most were found deep within the cytoplasm, rather than near the periphery of the cell. Thin sections revealed that the net of actin filaments is not formed nor is a "comet" tail produced.
1,300 citations
01 Apr 1989-Graphical Models \/graphical Models and Image Processing \/computer Vision, Graphics, and Image Processing
TL;DR: Results show that all normal brains, at least at a certain level of representation, have the same topological structure, but may differ in shape details, and the matching process can account for these differences.
Abstract: Matching of locally variant data to an explicit 3-dimensional pictorial model is developed for X-ray computed tomography scans of the human brain, where the model is a voxel representation of an anatomical human brain atlas. The matching process is 3-dimensional without any preference given to the slicing plane. After global alignment the brain atlas is deformed like a piece of rubber, without tearing or folding. Deformation proceeds step-by-step in a coarse-to-fine strategy, increasing the local similarity and global coherence. The assumption underlying this approach is that all normal brains, at least at a certain level of representation, have the same topological structure, but may differ in shape details. Results show that we can account for these differences.
1,218 citations
TL;DR: A prognostic model for primary, clinical stage I cutaneous melanoma was developed using the lesional steps in tumor progression and multivariable logistic regression to develop a model that is 89% accurate in predicting survival.
Abstract: We used the lesional steps in tumor progression and multivariable logistic regression to develop a prognostic model for primary, clinical stage I cutaneous melanoma. This model is 89% accurate in predicting survival. Using histologic criteria, we assigned melanomas to tumor progression steps by ascertaining their particular growth phase. These phases were the in situ and invasive radial growth phase and the vertical growth phase (the focal formation of a dermal tumor nodule or dermal tumor plaque within the radial growth phase or such dermal growth without an evident radial growth phase). After a minimum follow-up of 100.6 months and a median follow-up of 150.2 months, 122 invasive radial-growth-phase tumors were found to be without metastases. Eight-year survival among the 264 patients whose tumors had entered the vertical growth phase was 71.2%. Survival prediction in these patients was enhanced by the use of a multivariable logistic regression model. Twenty-three attributes were tested for entry into this model. Six had independently predictive prognostic information: (a) mitotic rate per square millimeter, (b) tumor-infiltrating lymphocytes, (c) tumor thickness, (d) anatomic site of primary melanoma, (e) sex of the patient, and (f) histologic regression. When mitotic rate per square millimeter, tumor-infiltrating lymphocytes, primary site, sex, and histologic regression are added to a logistic regression model containing tumor thickness alone, they are independent predictors of 8-year survival (P less than .0005).
1,160 citations
TL;DR: Diffuse axonal injury was identified in 122 of a series of 434 fatal non‐missile head injuries–‐10 grade 1, 29 grade 2 and 83 grade 3; in 24 of these cases the diagnosis could not have been made without microscope examination, while in a further 31 microscopical examination was required to establish its severity.
Abstract: Diffuse axonal injury is one of the most important types of brain damage that can occur as a result of non-missile head injury, and it may be very difficult to diagnose post mortem unless the pathologist knows precisely what he is looking for. Increasing experience with fatal non-missile head injury in man has allowed the identification of three grades of diffuse axonal injury. In grade 1 there is histological evidence of axonal injury in the white matter of the cerebral hemispheres, the corpus callosum, the brain stem and, less commonly, the cerebellum; in grade 2 there is also a focal lesion in the corpus callosum; and in grade 3 there is in addition a focal lesion in the dorsolateral quadrant or quadrants of the rostral brain stem. The focal lesions can often only be identified microscopically. Diffuse axonal injury was identified in 122 of a series of 434 fatal non-missile head injuries--10 grade 1, 29 grade 2 and 83 grade 3. In 24 of these cases the diagnosis could not have been made without microscopical examination, while in a further 31 microscopical examination was required to establish its severity.
TL;DR: It is concluded that deletions of muscle mitochondrial DNA are associated with ophthalmoplegia and may result in impaired mitochondrial function, however, the precise relation between clinical and biochemical phenotypes and deletions remains to be defined.
Abstract: We investigated the correlations of deletions of mitochondrial DNA in skeletal muscle with clinical manifestations of mitochondrial myopathies, a group of disorders defined either by biochemical abnormalities of mitochondria or by morphologic changes causing a ragged red appearance of the muscle fibers histochemically. We performed genomic Southern blot analysis of muscle mitochondrial DNA from 123 patients with different mitochondrial myopathies or encephalomyopathies. Deletions were found in the mitochondrial DNA of 32 patients, all of whom had progressive external ophthalmoplegia. Some patients had only ocular myopathy, whereas others had Kearns-Sayre syndrome, a multisystem disorder characterized by ophthalmoplegia, pigmentary retinopathy, heart block, and cerebellar ataxia. The deletions ranged in size from 1.3 to 7.6 kilobases and were mapped to different sites in the mitochondrial DNA, but an identical 4.9-kilobase deletion was found in the same location in 11 patients. Biochemical analysis showed decreased activities of NADH dehydrogenase, rotenone-sensitive NADH-cytochrome c reductase, succinate-cytochrome c reductase, and cytochrome c oxidase, four enzymes of the mitochondrial respiratory chain containing subunits encoded by mitochondrial DNA. We conclude that deletions of muscle mitochondrial DNA are associated with ophthalmoplegia and may result in impaired mitochondrial function. However, the precise relation between clinical and biochemical phenotypes and deletions remains to be defined.
TL;DR: This article showed that change seems to proceed at the same rate in all contexts, at least for syntactic cases, and that the frequency of use of a new form across contexts reflect functional and stylistic factors, which are constant across time and independent of grammar.
Abstract: When one form replaces another over time in a changing language, the new form does not occur equally often in all linguistic contexts. Linguists have generally assumed that those contexts in which the new form is more common are those in which the form first appears and in which it advances most rapidly. However, evidence from several linguistic changes (most importantly the rise of the periphrastic auxiliary do in late Middle English) shows that the general assumption is false. Instead, at least for syntactic cases, change seems to proceed at the same rate in all contexts. Contexts change together because they are merely surface manifestations of a single underlying change in grammar. Differences in frequency of use of a new form across contexts reflect functional and stylistic factors, which are constant across time and independent of grammar.
TL;DR: In this paper, the authors used Tobin's Q ratios less than unity to designate overinvestors and found that the average return associated with announcements of large dividend changes is significantly larger for firms with Q's less-than-unity than for other firms.
TL;DR: In this paper, the role of expectations in servicing the public debt is discussed, and the important reasons for debt repudiation to be costly are the fact that not all individuals are alike and, therefore, the incidence of repudiation is not uniform.
Abstract: Publisher Summary This chapter discusses the role of expectations in servicing the public debt. Expectations may play a crucial role in the determination of equilibrium when the government debt is auctioned off to the public, and there is no attempt to manage expectations or to peg interest rates on the government debt. The nominal interest rate is not simply a passive reflection of people's inflationary expectations, but rather one of the main determinants of inflation. A credible anti-inflationary policy would have to implement rules to prevent nominal interest rates to become unduly high. However, the important reasons for debt repudiation to be costly are the fact that not all individuals are alike and, therefore, the incidence of repudiation is not uniform.
TL;DR: In the brain, the brain is one of the organs that is particularly sensitive to lack of oxygen and in humans at rest is responsible for 20% of total O2 consumption, even though it accounts for only 2% of the body weight.
Abstract: The importance of A TP as the main source of chemical energy in living matter and its involve ment in cellular processes has long been recog nized. The primary mechanism whereby higher or ganisms, including humans, generate ATP is through mitochondrial oxidative phosphorylation. For the majority of organs, the main metabolic fuel is glucose, which in the presence of oxygen under goes complete combustion to CO2 and H20: C6H1206 + 602 � 602 + 6H20 + energy ( 1) The free energy (.:lG) liberated in this exergonic re action is partially trapped as ATP in two consecu tive processes: glycolysis (cytosol) and oxidative phosphorylation (mitochondria). The first produces 2 mol of ATP per mol of glucose, and the second 36 mol of ATP per mol of glucose. In the latter case, 6 mol of ATP are contributed from the oxidation of 2 mol of NADH generated in the cytosol during gly colysis and transferred into the mitochondria indi rectly through various \"shuttle\" systems. (In the a-glycerophosphate shuttle, the yield of ATP per NADH is reduced from 3 to 2 because the relevant mitochondrial dehydrogenase is a flavoprotein linked enzyme). Thus, oxidative phosphorylation yields 1718 times as much useful energy in the form of ATP as can be obtained from the same amount of glucose by glycolysis alone. It is there fore not surprising that limitation of O2 supply pro duces very damaging effects on cellular function. The brain is one of the organs that is particularly sensitive to lack of oxygen and in humans at rest is responsible for 20% of total O2 consumption al though it accounts for only 2% of the body weight. The role of energy in the maintenance of central
TL;DR: By understanding economic analysis, physicians will be able to act as patient advocates and fulfill their responsibilities to society to manage resources prudently, Eisenberg believes.
Abstract: PUBLIC and professional concern about the cost of medical care has evoked a variety of proposed remedies. Professional societies have promulgated guidelines to help physicians provide the most appropriate services. 1,2 Government has begun to recognize the need for more research into clinical strategies in hopes of exploring the variations in medical practice and reducing federal health care outlays. 3 Insurance companies and businesses have desperately sought (and bought) consultants who promise to control beneficiaries' and employees' utilization of medical services. Underlying these cost-cutting solutions is a faith that medical care can be made cost-effective, that more value can be obtained for the money spent. The application of economics to medical practice does not necessarily mean that less should or can be spent, but rather that the use of resources might be more efficient. 4-21 To achieve more cost-effective medical practice, the attention of experts in health policy ultimately must
TL;DR: It is suggested that catastrophizing is a maladaptive coping strategy in RA patients and further research is needed to determine whether cognitive‐behavioral interventions designed to decrease catastrophize can reduce pain and improve the physical and psychological functioning of RA patients.
Abstract: The present study examined catastrophizing in rheumatoid arthritis (RA) patients. Subjects were 223 RA patients who were participants in a longitudinal study. Each patient completed the Catastrophizing scale of the Coping Strategies Questionnaire (CSQ) on 2 occasions separated by 6 months (time 1, time 2). The Catastrophizing scale is designed to measure negative self-statements, castastrophizing thoughts and ideation (sample items = 'I worry all the time about whether it will end,' 'It is awful and I feel that it overwhelms me'). Data analysis revealed that the Catastrophizing scale was internally reliable (alpha = 0.91) and had high test-retest reliability (r = 0.81) over a 6 month period. Correlational analyses revealed that catastrophizing recorded at time 1 was related to pain intensity ratings, functional impairment on the Arthritis Impact Measurement scale (AIMS), and depression at time 2. Predictive findings regarding catastrophizing while modest were obtained after controlling for initial scores on the dependent variables, demographic variables (age, sex, socioeconomic status), duration of pain, and disability support status. Taken together, these findings suggest that catastrophizing is a maladaptive coping strategy in RA patients. Further research is needed to determine whether cognitive-behavioral interventions designed to decrease catastrophizing can reduce pain and improve the physical and psychological functioning of RA patients.
TL;DR: The aim of this study was to map the viscerotopic representation of the upper alimentary tract in the sensory ganglia of the IXth and Xth cranial nerves and in the subnuclei of the solitary and spinal trigeminal tracts.
Abstract: The aim of this study was to map the viscerotopic representation of the upper alimentary tract in the sensory ganglia of the IXth and Xth cranial nerves and in the subnuclei of the solitary and spinal trigeminal tracts. Therefore, in 172 rats 0.5-65 microliters of horseradish peroxidase (HRP), wheat germ agglutinin-HRP, or cholera toxin-HRP were injected into the trunks and major branches of the IXth and Xth cranial nerves as well as into the musculature and mucosa of different levels of the upper alimentary and respiratory tracts. The results demonstrate that the sensory ganglia of the IXth and Xth nerves form a fused ganglionic mass with continuous bridges of cells connecting the proximal and distal portions of the ganglionic complex. Ganglionic perikarya were labeled in crude, overlapping topographical patterns after injections of tracers into nerves and different parts of the upper alimentary tract. After injections into the soft palate, pharynx, esophagus, and stomach, anterograde labeling was differentially distributed in distinct subnuclei in the nucleus of the tractus solitarius (NTS). Palatal and pharyngeal injections resulted primarily in labeling of the interstitial and intermediate subnuclei of the NTS and in the paratrigeminal islands (PTI) and spinal trigeminal complex. Esophageal and stomach wall injections resulted in labeling primarily of the subnucleus centralis and subnucleus gelatinosus, respectively. The distribution of upper alimentary tract vagal-glossopharyngeal afferents in the medulla oblongata has two primary groups of components, i.e., a viscerotopic distribution in the NTS involved in ingestive and respiratory reflexes and a distribution coextensive with fluoride-resistant acid-phosphatase-positive regions of the PTI and spinal trigeminal nucleus presumably involved in visceral reflexes mediated by nociceptive or chemosensitive C fibers.
09 Nov 1989
TL;DR: The basic chemistry and physics of polyacetylene, (CH)/sub x/, the prototype conducting polymer which is characteristic of most other conducting polymers, were described together with a description of the polyanilines, a large new class of conducting polymer.
Abstract: Summary form only given. The basic chemistry and physics of polyacetylene, (CH)/sub x/, the prototype conducting polymer which is characteristic of most other conducting polymers, were described together with a description of the polyanilines, a large new class of conducting polymers. Potential technological applications were discussed. Polyacetylene, (CH)/sub x/ is obtained in the form of silvery, flexible films by the polymerization of gaseous acetylene. >
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TL;DR: In this article, a stochastic model of nonsynchronous asset prices based on sampling with random censoring is developed to estimate the effects of infrequent trading on the time series properties of asset returns.
Abstract: We develop a stochastic model of nonsynchronous asset prices based on sampling with random censoring In addition to generalizing existing models of non-trading our framework allows the explicit calculation of the effects of infrequent trading on the time series properties of asset returns These are empirically testable implications for the variances, autocorrelations, and cross-autocorrelations of returns to individual stocks as well as to portfolios We construct estimators to quantify the magnitude of non-trading effects in commonly used stock returns data bases and show the extent to which this phenomenon is responsible for the recent rejections of the random walk hypothesis
TL;DR: In this paper, the authors provide an empirical test of the effects of competition on the adoption of technological innovations by organizations, based on the conceptualization developed in the model they prop...
Abstract: The authors provide an empirical test of the effects of competition on the adoption of technological innovations by organizations. They follow the conceptualization developed in the model they prop...
TL;DR: A new type of inflationary scenario based on metric formulations of gravity different from that of Einstein, e.g., Brans-Dicke theory of gravity is presented, which can be completed via bubble nucleation and fine tuning of an effective potential to obtain a slow-rollover transition.
Abstract: We present a new type of inflationary scenario based on metric formulations of gravity different from that of Einstein, e.g., a Brans-Dicke theory of gravity. Unlike previous inflation models, the inflationary phase transition can be completed via bubble nucleation. Hence, the fine tuning of an effective potential to obtain a slow-rollover transition is not required.
TL;DR: It is suggested that severe, prolonged cellular injury induces a preneoplastic proliferative response that fosters secondary genetic events that program the cell for unrestrained growth.
TL;DR: In this paper, optimal matched samples are obtained using network flow theory, which yields optimal constructions for several statistical matching problems that have not been studied previously, including the construction of matched samples with multiple controls, with a variable number of controls, and the balanced matched samples that combine features of pair matching and frequency matching.
Abstract: Matching is a common method of adjustment in observational studies. Currently, matched samples are constructed using greedy heuristics (or “stepwise” procedures) that produce, in general, suboptimal matchings. With respect to a particular criterion, a matched sample is suboptimal if it could be improved by changing the controls assigned to specific treated units, that is, if it could be improved with the data at hand. Here, optimal matched samples are obtained using network flow theory. In addition to providing optimal matched-pair samples, this approach yields optimal constructions for several statistical matching problems that have not been studied previously, including the construction of matched samples with multiple controls, with a variable number of controls, and the construction of balanced matched samples that combine features of pair matching and frequency matching. Computational efficiency is discussed. Extensive use is made of ideas from two essentially disjoint literatures, namely st...
TL;DR: In this paper, the authors study temporal volatility patterns in seven nominal dollar spot exchange rates, all of which display strong evidence of autoregressive conditional heteroskedasticity (ARCH).
Abstract: We study temporal volatility patterns in seven nominal dollar spot exchange rates, all of which display strong evidence of autoregressive conditional heteroskedasticity (ARCH). We first formulate and estimate univariate models, the results of which are subsequently used to guide specification of a multivariate model. The key element of our multivariate approach is exploitation of factor structure, which facilitates tractable estimation via a substantial reduction in the number of parameters to be estimated. Such a latent-variable model is shown to provide a good description of multivariate exchange rate movements: the ARCH effects capture volatility clustering, and the factor structure captures commonality in volatility movements across exchange rates.
TL;DR: This work analyzes a class of mathematical models the authors call NK models and shows that these models capture significant features of the maturation of the immune response, which is currently thought to share features with general protein evolution.
TL;DR: The authors examine persistence in U.S. aggregate output by estimating fractionally integrated ARIMA models, and find evidence of long memory, which induces persistence, though this long memory need not be associated with a unit root.
TL;DR: In this article, the relationship between adoption of administrative and technical innovations over time and its impact on organizational performance was studied. But the authors focused on the adoption of technical innovations rather than administrative innovations.
Abstract: The relationship between adoption of administrative and technical innovations over time and its impact on organizational performance was studied. A confirmatory analysis of the data from 85 public libraries showed that, over consecutive time periods, changes in the social structure, portrayed by the adoption of administrative innovations, lead to changes in the technical system, portrayed by the adoption of technical innovations. Empirical support was also provided for Daft's (1982) framework for organizational innovation that was found to be effective in separating organizations based on their performance levels.
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TL;DR: In this paper, the authors investigate pricing by Japanese manufacturing firms in export and domestic markets and find evidence that Japanese firms respond to changes in real exchange rates by "pricing to market", varying their export prices in yen relative to their domestic prices.
Abstract: This paper investigates pricing by Japanese manufacturing firms in export and domestic markets. The paper reports equations explaining the margin between export prices in yen and domestic prices for a wide range of final goods including many of the electronic and transport products which have figured so prominently in recent trade discussions. Evidence is presented showing that Japanese firms respond to changes in real exchange rates by "pricing to market", varying their export prices in yen relative to their domestic prices. The empirical specification makes it possible to disentangle planned changes in the margin between export and domestic prices from inadvertent changes in this margin due to unanticipated changes in exchange rates. The degree of pricing to market varies widely across products, but there is strong evidence that pricing to market occurs. The paper also investigates whether pricing to market has increased in scale in the period since 1985 when the yen began a sustained appreciation, but finds that only five of seventeen products experienced a shift in price behavior over that period.