Showing papers by "University of Pennsylvania published in 1987"
Posted Content•
TL;DR: In this paper, the random walk model is strongly rejected for the entire sample period (1962-1985) and for all sub-periods for a variety of aggregate returns indexes and size-sorted portfolios.
Abstract: In this paper, we test the random walk hypothesis for weekly stock market returns by comparing variance estimators derived from data sampled at different frequencies. The random walk model is strongly rejected for the entire sample period (1962-1985) and for all sub-periods for a variety of aggregate returns indexes and size-sorted portfolios. Although the rejections are largely due to the behavior of small stocks, they cannot be ascribed to either the effects of infrequent trading or time-varying volatilities. Moreover, the rejection of the random walk cannot be interpreted as supporting a mean-reverting stationary model of asset prices, but is more consistent with a specific nonstationary alternative hypothesis.
2,920 citations
01 Jan 1987
TL;DR: In this paper, the treatment of first-order phase transitions for standard grand unified theories is shown to break down for models with radiatively induced spontaneous symmetry breaking, leading to an explanation of the cosmological homogeneity, flatness, and monopole puzzles.
Abstract: The treatment of first-order phase transitions for standard grand unified theories is shown to break down for models with radiatively induced spontaneous symmetry breaking. It is argued that proper analysis of these transitions which would take place in the early history of the universe can lead to an explanation of the cosmological homogeneity, flatness, and monopole puzzles.
2,873 citations
TL;DR: Observations suggest that regional and historical processes, as well as unique events and circumstances, profoundly influence local community structure and ecologists must broaden their concepts of community processes and incorporate data from systematics, biogeography, and paleontology into analyses of ecological patterns and tests of community theory.
Abstract: The species richness (diversity) of local plant and animal assemblages—biological communities—balances regional processes of species formation and geographic dispersal, which add species to communities, against processes of predation, competitive exclusion, adaptation, and stochastic variation, which may promote local extinction During the past three decades, ecologists have sought to explain differences in local diversity by the influence of the physical environment on local interactions among species, interactions that are generally believed to limit the number of coexisting species But diversity of the biological community often fails to converge under similar physical conditions, and local diversity bears a demonstrable dependence upon regional diversity These observations suggest that regional and historical processes, as well as unique events and circumstances, profoundly influence local community structure Ecologists must broaden their concepts of community processes and incorporate data from systematics, biogeography, and paleontology into analyses of ecological patterns and tests of community theory
2,230 citations
TL;DR: In this paper, the effects of short-sale constraints on the speed of adjustment (to private information) of security prices are modeled. But short-sellers do not bias prices upward, while non-prohibitive costs have the reverse effect.
1,866 citations
TL;DR: It seems that an optimal strategy has evolved for sampling images simultaneously in the 2D spatial and spatial frequency domains and the Gabor function provides a useful and reasonably accurate description of most spatial aspects of simple receptive fields.
Abstract: 1. Using the two-dimensional (2D) spatial and spectral response profiles described in the previous two reports, we test Daugman's generalization of Marcelja's hypothesis that simple receptive fields belong to a class of linear spatial filters analogous to those described by Gabor and referred to here as 2D Gabor filters. 2. In the space domain, we found 2D Gabor filters that fit the 2D spatial response profile of each simple cell in the least-squared error sense (with a simplex algorithm), and we show that the residual error is devoid of spatial structure and statistically indistinguishable from random error. 3. Although a rigorous statistical approach was not possible with our spectral data, we also found a Gabor function that fit the 2D spectral response profile of each simple cell and observed that the residual errors are everywhere small and unstructured. 4. As an assay of spatial linearity in two dimensions, on which the applicability of Gabor theory is dependent, we compare the filter parameters estimated from the independent 2D spatial and spectral measurements described above. Estimates of most parameters from the two domains are highly correlated, indicating that assumptions about spatial linearity are valid. 5. Finally, we show that the functional form of the 2D Gabor filter provides a concise mathematical expression, which incorporates the important spatial characteristics of simple receptive fields demonstrated in the previous two reports. Prominent here are 1) Cartesian separable spatial response profiles, 2) spatial receptive fields with staggered subregion placement, 3) Cartesian separable spectral response profiles, 4) spectral response profiles with axes of symmetry not including the origin, and 5) the uniform distribution of spatial phase angles. 6. We conclude that the Gabor function provides a useful and reasonably accurate description of most spatial aspects of simple receptive fields. Thus it seems that an optimal strategy has evolved for sampling images simultaneously in the 2D spatial and spatial frequency domains.
1,723 citations
TL;DR: A neutrino burst was observed in the Kamiokande II detector on 23 February, 7:35:35 UT (7.1 min) during a time interval of 13 sec as mentioned in this paper.
Abstract: A neutrino burst was observed in the Kamiokande II detector on 23 February, 7:35:35 UT (\ifmmode\pm\else\textpm\fi{}1 min) during a time interval of 13 sec. The signal consisted of 11 electron events of energy 7.5 to 36 MeV, of which the first two point back to the Large Magellanic Cloud with angles 18\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}18\ifmmode^\circ\else\textdegree\fi{} and 15\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}27\ifmmode^\circ\else\textdegree\fi{}.
1,502 citations
TL;DR: This article develops parts of a universal theory of adaptation on correlated landscapes by adaptive processes that have sufficient numbers of mutations per individual to "jump beyond" the correlation lengths in the underlying landscape.
1,354 citations
TL;DR: In this paper, the emeraldine oxidation state of polyaniline was converted from an insulator to a metal by treatment with 1M aqueous HCl to form the corresponding salt, emeraldines hydrochloride.
1,286 citations
Posted Content•
TL;DR: In this article, the random walk model is strongly rejected for the entire sample period (1962-1985) and for all sub-periods for a variety of aggregate returns indexes and size-sorted portfolios.
Abstract: In this paper, we test the random walk hypothesis for weekly stock market returns by comparing variance estimators derived from data sampled at different frequencies. The random walk model is strongly rejected for the entire sample period (1962-1985) and for all sub-periods for a variety of aggregate returns indexes and size-sorted portfolios. Although the rejections are largely due to the behavior of small stocks, they cannot be ascribed to either the effects of infrequent trading or time-varying volatilities. Moreover, the rejection of the random walk cannot be interpreted as supporting a mean-reverting stationary model of asset prices, but is more consistent with a specific nonstationary alternative hypothesis.
1,060 citations
TL;DR: In this article, the use of the Beck Depression Inventory (BDI) for the self-report of depressive symptomatology is raised and considered, including the stability of depression and the need for multiple assessment periods.
Abstract: Issues concerning use of the Beck Depression Inventory (BDI) for the self-report of depressive symptomatology are raised and considered. Discussion includes the stability of depression and the need for multiple assessment periods, specificity and the need for multiple assessment measures, and selection cut scores and the need for terminological accuracy. Recommendations for the continued use of the BDI, designed to facilitate the integration of diverse studies and improve research on self-reported depression, are provided.
1,027 citations
TL;DR: In this article, the authors compare and contrast forms of control systems used in salesforce evaluation and based on the monitoring of outcomes or of behaviors in terms of emerging theories in economics.
Abstract: Forms of control systems used in salesforce evaluation and based on the monitoring of outcomes or of behaviors are described, contrasted, and evaluated in terms of emerging theories in economics, o...
TL;DR: The results indicate that sex and age have independent and interrelated effects on GH secretion, and an amplifying action of estradiol on the neuroendocrine regulation of pulsatile GH release is suggested.
Abstract: We undertook a study of the separate and combined effects of age and sex on the pulsatile pattern of GH secretion. The 24-h secretory profile of GH was generated by 20-min sampling in 10 young women (aged 18-33 yr), 10 young men (aged 18-33 yr), 8 postmenopausal women (aged greater than 55 yr), and 8 older men (aged greater than 55 yr). A computer-assisted pulse analysis program was used to assess both total GH secretion, as reflected in the 24-h integrated GH concentration (IGHC), and pulsatile secretion, as denoted by pulse frequency, duration, amplitude, and the fraction of GH secreted in pulses during the 24-h period (FGHP). IGHC was significantly greater in women than in men (P less than 0.025) and greater in the young than in the old (P less than 0.003). The mean pulse amplitude, duration, and FGHP were each greater in the young (P less than 0.006, P less than 0.03, and P less than 0.0001, respectively), but not significantly different between the sexes. The mean pulse frequency was not affected by sex or age. The serum concentration of free estradiol, but not free testosterone, correlated with IGHC (r = 0.46; P less than 0.005), pulse amplitude (r = 0.53; P less than 0.001), and FGHP (r = 0.59; P less than 0.0002). After correcting for the effects of estradiol, neither sex nor age influenced IGHC or mean pulse amplitude, while the effect of age on FGHP was reduced from 81% to 29%. Of the indices of GH secretion, FGHP had the strongest correlation (r = 0.43; P less than 0.006) with somatomedin-C. Somatomedin-C declined significantly with age in both sexes. Our results indicate that sex and age have independent and interrelated effects on GH secretion. These effects can be largely accounted for by corresponding variations in endogenous estradiol levels. These observations suggest an amplifying action of estradiol on the neuroendocrine regulation of pulsatile GH release.
TL;DR: The authors proposed a model-based direct adjustment method that preserves the attractive features of conventional direct adjustment while stabilizing the weights attached to small subclasses, which is a special case of model based direct adjustment under two different extreme models for the subclassspecific selection probabilities.
Abstract: Direct adjustment or standardization applies population weights to subclass means in an effort to estimate population quantities from a sample that is not representative of the population. Direct adjustment has several attractive features, but when there are many subclasses it can attach large weights to small quantities of data, often in a fairly erratic manner. In the extreme, direct adjustment can attach infinite weight to nonexistent data, a noticeable inconvenience in practice. This article proposes a method of model-based direct adjustment that preserves the attractive features of conventional direct adjustment while stabilizing the weights attached to small subclasses. The sample mean and conventional direct adjustment are both special cases of model-based direct adjustment under two different extreme models for the subclass-specific selection probabilities. The discussion of this method provides some insights into the behavior of true and estimated propensity scores: the estimated scores ...
TL;DR: The results suggest that superoxide dismutase plays the major role in protecting human spermatozoa against lipid peroxidation, and the superoxide Dismutase activity of a fresh sperm sample appears to be a good predictor of the lifetime (up to the complete loss of motility) of that particular sample, and so may prove useful in semen analysis.
Abstract: Spontaneous lipid peroxidation in washed human spermatozoa was induced by aerobic incubation at 32 C and measured by malonaldehyde production; loss of motility during the incubation was determined simultaneously. Malonaldehyde production at the point of complete loss of motility, defined as the lipoperoxidative lethal endpoint (LLE), was 0.10 +/- 0.03 nmol/10(8) cells (mean +/- SD, n = 40), and was independent of the time to complete loss of motility. Human spermatozoa produced both H2O2 and O2-. during aerobic incubation. Inhibition of superoxide dismutase in these cells with KCN showed that all the H2O2 production is due to action of the dismutase. The superoxide dismutase activity of individual human sperm samples varied between 1 and 10 U/10(8) cells, variations between samples from a single donor being nearly as great as those between different donors. The time to complete motility loss (tL) showed equal variation of 1 to 10 hours among samples. The rate of spontaneous lipid peroxidation, calculated as LLE/tL, for a given sperm sample and the superoxide dismutase activity of the same sample, determined prior to aerobic incubation, gave a good linear correlation (r = 0.97). Glutathione reductase, glutathione peroxidase, and glutathione were found to be present in human spermatozoa, but showed little variation among samples. These results suggest that superoxide dismutase plays the major role in protecting human spermatozoa against lipid peroxidation. In addition, the superoxide dismutase activity of a fresh sperm sample appears to be a good predictor of the lifetime (up to the complete loss of motility) of that particular sample, and so may prove useful in semen analysis.
TL;DR: A reverse correlation method is developed that allows quantitative determination of visual receptive-field structure in two spatial dimensions and it is demonstrated that thereverse correlation method yields results with several desirable properties, including convergence and reproducibility independent of modest changes in stimulus parameters.
Abstract: 1. A reverse correlation (6, 8, 25, 35) method is developed that allows quantitative determination of visual receptive-field structure in two spatial dimensions. This method is applied to simple cells in the cat striate cortex. 2. It is demonstrated that the reverse correlation method yields results with several desirable properties, including convergence and reproducibility independent of modest changes in stimulus parameters. 3. In contrast to results obtained with moving stimuli, we find that the bright and dark excitatory subregions in simple receptive fields do not overlap to any great extent. This difference in results may be attributed to confounding the independent variables space and time when using moving stimuli. 4. All simple receptive fields have subregions that vary smoothly in all directions in space. There are no sharp transitions either between excitatory subregions or between subregions and the area surrounding the receptive field. 5. Simple receptive fields vary both in the number of subregions observed, in the elongation of each subregion, and in the overall elongation of the field. In contrast with results obtained using moving stimuli, we find that subregions within a given receptive field need not be the same length. 6. The hypothesis that simple receptive fields can be modeled as either even symmetric or odd symmetric about a central axis is evaluated. This hypothesis is found to be false in general. Most simple receptive fields are neither even symmetric nor odd symmetric. 7. The hypothesis that simple receptive fields can be modeled as the product of a width response profile and an orthogonal length response profile (Cartesian separability) is evaluated. This hypothesis is found to be true for only approximately 50% of the cells in our sample.
TL;DR: The Analytic Hierarchy Process developed by Saaty (Saaty, T. L. 1980) has proven to be an extremely useful method for decision making and planning as discussed by the authors.
Abstract: The Analytic Hierarchy Process developed by Saaty (Saaty, T. L. 1980. The Analytic Hierarchy Process. McGraw-Hill, New York.) has proven to be an extremely useful method for decision making and planning. However, some researchers in these areas have raised concerns over the theoretical basis underlying this process. This paper addresses currently debated issues concerning the theoretical foundations of the Analytic Hierarchy Process. We also illustrate through proof and through examples the validity or fallaciousness of these criticisms.
TL;DR: In this article, the authors introduce an industrial product to a foreign market face a difficult decision. Should the product be marketed primarily by captive agents (company salesforce and company distributio-...
Abstract: Manufacturers introducing an industrial product to a foreign market face a difficult decision. Should the product be marketed primarily by captive agents (company salesforce and company distributio...
TL;DR: In this article, the authors use contingent claims analysis to derive optimal decision rules and to value such investments, and determine the effects of time to build, opportunity cost and uncertainty on the investment decision.
TL;DR: Investigation of the conceptual argument that acquisitions which are related in product/market or technological terms create higher value than unrelated acquisitions finds that related target firms benefit more from acquisition than unrelated target firms.
Abstract: This research investigates the conceptual argument that acquisitions which are related in productlmarket or technological terms create higher value than unrelated acquisitions. Related acquisitions are found to have greater total dollar gains than unrelated acquisitions. Acquired firms in related acquisitions have substantially higher gains than acquired firms in unrelated acquisitions. These findings indicate that related target firms benefit more from acquisition than unrelated target firms. Implications of these findings for managers are discussed. Research on corporate diversification is an important area in the strategic management literature. As this research has developed, some appealing operationalizations of diversification have emerged (Rumelt, 1974). These have resulted in generalizations about the linkage between diversification strategy and profitability. As the specificity of research on diversification has increased, corporate acquisitions have been researched as an exclusive focus. Notable among this research is Salter and Weinhold's (1979)
TL;DR: In this paper, the authors present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine.
Abstract: We present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed optical transitions. These results are in marked contrast with the electronic structure of other doped conducting polymers, in that only one single broad polaron band appears deep in the gap together with a very narrow band nearly degenerate with the conduction-band edge.
TL;DR: In this paper, the authors consider the perceived legitimacy of the school and its teachers and the development of oppositional culture by students and compare, critiqu, and re-consider these explanations in terms of critical social theory, more especially resistance theory.
Abstract: Various explanations for low school achievement of minority students include those of cultural differences between teacher and student and low motivation of students because of cynicism regarding their chances in the labor market. These explanations are compared, critiqued, and reconsidered in terms of critical social theory, more especially resistance theory. The article considers the perceived legitimacy of the school and its teachers and the development of oppositional culture by students. Transformation of routine educational practice is necessary, and culturally responsive pedagogy is one means of transformation. CULTURALLY RESPONSIVE PEDAGOGY, MINORITY STUDENT ACHIEVEMENT, RESISTANCE THEORY, OPPOSITIONAL CULTURE
TL;DR: It is demonstrated that activated platelets can be reliably detected in whole blood using activation-dependent monoclonal antibodies and flow cytometry and may be useful to assess the degree of platelet activation and the efficacy of antiplatelet therapy in clinical disorders.
TL;DR: The model appears to deal with the aperture problem as well as the human visual system since it extracts the correct velocity for patterns that have large differences in contrast at different spatial orientations, and it simulates psychophysical data on the coherence of sine-grating plaid patterns.
Abstract: A model is presented, consonant with current views regarding the neurophysiology and psychophysics of motion perception, that combines the outputs of a set of spatiotemporal motion-energy filters to extract optical flow. The output velocity is encoded as the peak in a distribution of velocity-tuned units that behave much like cells of the middle temporal area of the primate brain. The model appears to deal with the aperture problem as well as the human visual system since it extracts the correct velocity for patterns that have large differences in contrast at different spatial orientations, and it simulates psychophysical data on the coherence of sine-grating plaid patterns.
TL;DR: A model is developed based on the number and timing of the customers' previous transactions that allows computation of the probability that any particular customer is still active.
Abstract: This article is concerned with counting and identifying those customers who are still active. The issue is important in at least three settings: monitoring the size and growth rate of a firm's ongoing customer base, evaluating a new product's success based on the pattern of trial and repeat purchases, and targeting a subgroup of customers for advertising and promotions. We develop a model based on the number and timing of the customers' previous transactions. This approach allows computation of the probability that any particular customer is still active. Several numerical examples are used to illustrate applications of the model.
TL;DR: Two of four DNase hypersensitive sites found in the 5'-flanking region of the albumin gene map to the far-upstream and promoter regions; the others may reflect regions involved in developmental or environmental control of this gene.
Abstract: Transgenic mice were used to locate the cis-acting DNA elements that are important for efficient, tissue-specific expression of the mouse albumin gene in the adult. Chimeric genes with up to 12 kb of mouse albumin 5'-flanking region fused to a human growth hormone (hGH) reporter gene were tested. Remarkably, a region located 8.5-10.4 kb upstream of the albumin promoter was essential for high-level expression in adult liver and the region in between -8.5 and -0.3 kb was dispensable. The far-upstream region behaved like an enhancer in that its position and orientation relative to the albumin promoter were not critical; however, it did not function well with a heterologous promoter. Two of four DNase hypersensitive sites found in the 5'-flanking region of the albumin gene map to the far-upstream and promoter regions; the others may reflect regions involved in developmental or environmental control of this gene.
TL;DR: In this paper, the authors identify two major criteria that are predictors of venture success: the extent to which the venture is initially insulated from competition and the degree to which there is demonstrated market acceptance of the product.
TL;DR: The results indicate that TGF beta causes a marked enhancement of the production of types I and III collagens and fibronectin by cultured normal human dermal fibroblasts and may contribute to the development of pathological states of fibrosis.
Abstract: It has been previously shown that transforming growth factor beta (TGF beta) is capable of stimulating fibroblast collagen and fibronectin biosynthesis. The purpose of this study was to examine the mechanisms involved in TGF beta stimulation of fibroblast biosynthetic activity. Our results indicate that TGF beta causes a marked enhancement of the production of types I and III collagens and fibronectin by cultured normal human dermal fibroblasts. The rate of collagen production by fibroblasts exposed to TGF beta was 2-3-fold greater than that of control cells. These effects were associated with a 2-3-fold increase in the steady-state amounts of types I and III collagen mRNAs and a 5-8-fold increase in the amounts of fibronectin mRNAs as determined by dot-blot hybridization with specific cloned cDNA probes. In addition, the increased production of collagen and fibronectin and the increased amounts of their corresponding mRNAs remained elevated for at least 72 h after removal of TGF beta. These findings suggest that TGF beta may play a major role in the normal regulation of extracellular matrix production in vivo and may contribute to the development of pathological states of fibrosis.
TL;DR: In this article, the authors present an experimental examination of rank-order tournaments and piece rates and find that the mean effort levels chosen by subjects converged to their theoretical equilibrium levels in both the piece rate and symmetric tournament experiments.
Abstract: This paper presents an experimental examination of rank-order tournaments and piece rates. Ten experiments were run employing 225 paid undergraduate student volunteers. While, in general, the mean effort levels chosen by subjects converged to their theoretical equilibrium levels in both the piece rate and symmetric tournament experiments, a large variance was observed for all rank-order tournaments, and this variance persisted despite a number of different tournaments. The variance in the piece rate experiment was quite small. In the one asymmetric tournament, it was observed that while the mean effort level of "advantaged" subjects converged toward its theoretic equilibrium level, the mean effort level of disadvantaged subjects remained above their equilibrium level. In summation, while our results were supportive of the theory of tournaments, quite a number of puzzles were raised.
TL;DR: In this paper, the emeraldine base (EB) form of polyaniline can be varied from insulating ( σ −10 ohm −1 cm −1 ) through protonation.