Showing papers by "University of Pennsylvania published in 1980"

On the Impossibility of Informationally Efficient Markets

Abstract: If competitive equilibrium is defined as a situation in which prices are such that all arbitrage profits are eliminated, is it possible that a competitive economy always be in equilibrium? Clearly not, for then those who arbitrage make no (private) return from their (privately) costly activity. Hence the assumptions that all markets, including that for information, are always in equilibrium and always perfectly arbitraged are inconsistent when arbitrage is costly. We propose here a model in which there is an equilibrium degree of disequilibrium: prices reflect the information of informed individuals (arbitrageurs) but only partially, so that those who expend resources to obtain information do receive compensation. How informative the price system is depends on the number of individuals who are informed; but the number of individuals who are informed is itself an endogenous variable in the model. The model is the simplest one in which prices perform a well-articulated role in conveying information from the informed to the uninformed. When informed individuals observe information that the return to a security is going to be high, they bid its price up, and conversely when they observe information that the return is going to be low. Thus the price system makes publicly available the information obtained by informed individuals to the uninformed. In general, however, it does this imperfectly; this is perhaps lucky, for were it to do it perfectly , an equilibrium would not exist. In the introduction, we shall discuss the general methodology and present some conjectures concerning certain properties of the equilibrium. The remaining analytic sections of the paper are devoted to analyzing in detail an important example of our general model, in which our conjectures concerning the nature of the equilibrium can be shown to be correct. We conclude with a discussion of the implications of our approach and results, with particular emphasis on the relationship of our results to the literature on "efficient capital markets."

An improved diagnostic evaluation instrument for substance abuse patients. The Addiction Severity Index.

Abstract: The Addiction Severity Index (ASI) is a structured clinical interview developed to fill the need for a reliable, valid, and standardized diagnostic and evaluative instrument in the field of alcohol and drug abuse. The ASI may be administered by a technician in 20 to 30 minutes producing 10-point problem severity ratings in each of six areas commonly affected by addiction. Analyses of these problem severity ratings on 524 male veteran alcoholics and drug addicts showed them to be highly reliable and valid. Correlational analyses using the severity ratings indicated considerable independence between the problem areas, suggesting that the treatment problems of patients are not necessarily related to the severity of their chemical abuse. Cluster analyses using these ratings revealed the presence of six subgroups having distinctly different patterns of treatment problems. The authors suggest the use of the ASI to match patients with treatments and to promote greater comparability of research findings.

Soliton excitations in polyacetylene

Abstract: A theoretical analysis of the excitation spectrum of long-chain polyenes is presented. Because of the twofold degeneracy of the ground state of the dimerized chain, elementary excitations corresponding to topological solitons are obtained. The solitons can have three charge states $Q=0$. $\ifmmode\pm\else\textpm\fi{}e$. The neutral soliton has spin one-half while the charged solitons have spin zero. One electronic state is localized at the gap center for each soliton or antisoliton present. The soliton's energy of formation, length, mass, activation energy for motion, and electronic properties are calculated. These results are compared with experiment.

A spatial processor model for object colour perception

Abstract: A comprehensive mathematical model to account for colour constancy is formulated. Since the visual system is able to measure true object colour in complex scenes under a broad range of spectral compositions, for the illumination; it is assumed that the visual system must implicitly estimate and illuminant. The basic hypothesis is that the estimate of the illuminant is made on the basis of spatial information from the entire visual field. This estimate is then used by the visual system to arrive at an estimate of the (object) reflectance of the various subfields in the complex visual scene. The estimates are made by matching the inputs to the system to linear combinations of fixed bases and standards in the colour space. The model provides a general unified mathematical framework for related psychophysical phenomenology.

Image reconstruction from projections

Abstract: This article covers the problem of reconstruction of structures from data collected based on transmitted or emitted radiation. The problem occurs in a wide range of areas, such as X-ray CT, emission tomography, photon migration imaging, electron microscopic reconstruction, etc. The article addresses the design, implementation, evaluation, and application of computer algorithms for solving the reconstruction problem in various biomedical areas and emphasizes the essential role of computers, which is due to the fact that the underlying biomedical problems result in mathematical problems in which the number of unknowns is in the millions.

A random pore model for fluid‐solid reactions: I. Isothermal, kinetic control

Abstract: For fluid-solid reactions, a random pore model is developed which allows for arbitrary pore size distributions in the reacting solid. The model can represent the behavior of a system that shows a maximum in reaction rate as well as one that does not, and it identifies an optimal pore structure for either of such systems. It is demonstrated that the new model subsumes several earlier treatments as special cases. By comparison with the grain model, a relationship is derived between the effective grain shape factor and a pore structure parameter defined here. When the variance of the pore size distribution is effectively zero, the new results approach those predicted by the Petersen (1957) model over a large range of conversions. The char gasification data of Hashimoto et al. (1979) are shown to produce correlations consistent with the expectations of the new model.

Marketing Applications of the Analytic Hierarchy Process

Abstract: Several marketing applications of the Analytic Hierarchy Process AHP are reviewed. The paper starts with a brief description of this process, which was developed by Thomas Saaty in 1971, including an eight-point outline of how to apply it. The thrust of the paper is a discussion of a number of illustrative applications of the AHP covering the following areas: the portfolio decisions of a firm whose management is concerned with the determination of the desired target portfolio and allocation of resources among its components, determination of the directions for new product development, and generation and evaluation of marketing mix strategies. Various suggestions for additional research on the AHP and its marketing applications are highlighted.

When Is It Coevolution

Abstract: 'Coevolution' may be usefully defined as an evolutionary change in a trait of the individuals in one population in response to a trait of the individuals of a second population, followed by an evolutionary response by the second population to the change in the first. 'Diffuse coevolution' occurs when either or both populations in the above definition are represented by an array of populations that generate a selective pressure as a group. Ehrlich and Raven's (1964) classic paper on the interactions of butterflies and plants was the first essay explicitly focused on coevolution. However, they did not define coevolution, and butterflies were neither stated nor implied to have been the single populations or array of herbivores that have generated the plant traits that they discuss as causing butterfly distributions on host plants. I believe that the lack of an original definition of 'coevolution,' the inapplicability of the example chosen by the original advocates of the use of the term, and the obvious commonplace nature of coevolutionary events in the history of plant-animal interactions have led to misleading uses of the term in contemporary evolutionary thought and studies. Here, I wish to call for more careful attention to the use of 'coevolution' as a word and concept. There are three conspicuous misuses at present: 1) It is commonly assumed that a pair of species whose traits are mutualistically congruent have coevolved. For example, it is quite possible that the fruit traits of a mammal-dispersed seed coevolved with the mammal's dietary needs. However, it is also quite possible that the mammal entered the plant's habitat with its dietary preferences already established and simply began feeding on the fruits of the species that fulfilled them. When this occurs, it is those species that are most exactly congruent which will appear most coevolved yet are likely to be the least coevolved. Are the hard seeds of those aridland trees dispersed by passage through a contemporary mammal gut coevolved with the mammal? Not necessarily. 2) In similar manner, a herbivore parasitic on a plant is often thought of as coevolved with the defense timing, chemistry, morphology, etc. However, when a parasite arrives in a new habitat, it will feed on those species whose defense traits it can circumvent because of the abilities it carries at the time. Such a parasite cannot be distinguished from one that evolved the ability to circumvent a defense while in trophic contact with its host. 3) When other evidence makes it clear that a parasite has evolved traits to circumvent the defenses of its host, it is frequently automatically assumed that coevolution has occurred. However, it is not necessary to conclude that the defense trait circumvented was evolutionarily produced in response to the parasite in question. In fact, it is likely that many defense traits of plants were produced through coevolution with animals no longer present in their habitat or no longer parasitizing them if present. Strongly coevolved parasite-host systems probably as often proceed to ecological independence of the participants as to relatively benign parasitism. In summary, I plead for the retention of the usefulness of 'coevolution' by removing it from synonymy of usage with 'interaction, '"symbiosis, '"mutualism,' and 'animal-plant interaction.' A bee is not necessarily coevolved with the flower it pollinates, a caterpillar is not necessarily

The Determinants of the Variability of Stock Market Prices

Abstract: The most familiar interpretation for the large and unpredictable swings that characterize common stock price indices is that price changes represent the efficient discounting of "new information." It is remarkable given the popularity of this interpretation that it has never been established what this information is about. Recent work by Shiller, and Stephen LeRoy and Richard Porter, has shown evidence that the variability of stock price indices cannot be accounted for by information regarding future dividends since dividends just do not seem to vary enough to justify the price

Density-functional approach to local-field effects in finite systems: Photoabsorption in the rare gases

Abstract: We present a formalism based on density-functional theory capable of describing polarization-type many-body effects influencing the photoresponse of small electronic systems. The self-consistent field approach we describe incorporates correlations into a local, effective single-particle potential which takes account of the time-dependent fields induced by an external radiation field. In this paper we present calculations of the static polarizabilities, total photoabsorption cross sections, and selected partial photoabsorption cross sections of the rare gases which yield results in good agreement with experiment. A study of the energy and spatial dependence of the local field leads to a clear physical picture of the dielectric properties of these systems.

Technology Transfer to Overseas Subsidiaries by U. S.-Based Firms

Abstract: Although economists and policymakers have devoted considerable attention to the transfer of technology by US-based multinational firms to their overseas subsidiaries, very little is known about the nature of the technology that is being transferred overseas in this way, the extent to which it leaks out to non-US competitors, the size of the benefits it confers on the host (and other non-US) countries, and the sorts of non-US firms that receive the largest benefits of this sort. The findings presented shed new light on each of these topics, but are only a beginning. 18 references, 5 tables.

Improved separation of phospholipids in thin layer chromatography

Abstract: The mobile phases described permit separation of the six major phospholipids of amniotic fluid in one dimension with either conventional or high performance thin layer chromatography. An example of this separation with an extract of amniotic fluid is given.

Nifedipine therapy for coronary-artery spasm. Experience in 127 patients

Abstract: We report clinical experience with the coronary vasodilator nifedipine in 127 patients with symptoms of myocardial ischemia associated with electrocardiographic or angiographic evidence, or both, of coronary-artery spasm. In the majority of patients conventional antianginal therapy including nitrates and beta-adrenergic blockers failed, and in one third of the patients at least one episode of ventricular tachycardia developed during an attack of angina. Nifedipine (40 to 160 mg every 24 hours) significantly reduced the mean weekly rate of anginal attacks from 16 to two (P less than 0.001). Similar marked reductions in the nitroglycerin requirement were noted. In 63 per cent of the patients complete control of anginal attacks was achieved, and in 87 per cent the frequency of angina was reduced by at least 50 per cent. Nifedipine was generally well tolerated, with only 5 per cent of the patients requiring termination of the drug because of intolerable side effects. This experience with nifedipine suggests that it is a highly effective drug for the treatment of coronary-artery spasm and variant angina.

RF-field interactions with biological systems: Electrical properties and biophysical mechanisms

Abstract: Electrical properties of tissues, macromolecular solutions, and cell membranes are summarized at frequencies from the extra low frequency (ELF) to microwave range. Previously presented dielectric data are supplemented by new results and a more detailed discussion of the physical mechanisms for the observed temperature coefficients of the dielectric properties. The dielectric data are discussed in terms of the interaction mechanisms which give rise to observed relaxational effects. Possible mechanisms for nonthermal weak interactions between radio-frequency (RF) energy and tissues are discussed and evaluated.

Nature of the open state in long polynucleotide double helices: possibility of soliton excitations

Abstract: The existence of transiently open states in DNA and synthetic polynucleotide double helices has been demonstrated by hydrogen exchange measurements; base pairs reversibly separate and reclose, exposing nucleotide protons to exchange with solvent protons. Recently it has been possible to define the equilibrium, kinetic, and activation parameters of the major open state that determines base pair hydrogen exchange. However, there is no direct information at the moment about the conformation of the open form. Here we consider the possibility that the low energy and slow opening and closing rates observed reflect a deformation involving several adjacent base pairs. Assuming a mobile open unit capable of diffusing along the double helix, we find that available data are consistent with structures of 10 or so adjacent open pairs. It is further suggested that these structures correspond to thermally induced soliton excitations of the double helix, which retain coherence by sharing the energy of a twist deformation among several base pairs. Solitons are nonlinear excitations that can travel as coherent solitary waves, and have been recognized as an important mechanism for mediating conformational changes in polymers and condensed systems generally. Comparison of the double helix with simple mechanical analogs suggests that soliton excitations may well exist within DNA chains, and the present analysis shows that the hydrogen exchange open state is consistent with these.

Dysplastic nevus syndrome: A phenotypic association of sporadic cutaneous melanoma

Abstract: Clinical photographs of 79 prospectively studied cases of non-familial cutaneous malignant melanoma were reviewed; special attention was directed to the distribution pattern of coexistent melanocytic lesions. A group of 15 patients had moles on the covered buttock area. Seven of these patients had large clinically atypical nevi, and biopsies of these nevi showed severe melanocytic dysplasia. Residual elements of melanocytic dysplasia were identified in five of the primary melanomas in this group of patients. It is suggested that these patients represent a distinctive syndrome, the Dysplastic Nevus Syndrome (DNS) and that they are at increased risk for development of primary cutaneous malignant melanoma. The clinically and histologically distinctive dysplastic nevi of these patients are identical to the precursor lesion for melanoma that we have previously described in a familial context, the B-K mole syndrome. This paper represents the first description of this form of dysplasia in non-familial melanoma.

Periodontal probing: What does it mean?

Abstract: The periodontal probe has been and continues to be used as an important diagnostic instrument by the dental profession. The measurements recorded with the probe have generally been considered to represent a reasonably accurate estimate of sulcus or pocket depth. Recent reports on the histopathology of the periodontal lesion and the histological features of a healing lesion, together with histological studies on the relationship of the probe to periodontal tissues, have shed some new light on periodontal probing. It is now apparent that probing depth measured from the gingival margin seldom corresponds to sulcus or pocket depth. The discrepancy is least in the absence of inflammatory changes and increases with increasing degrees of inflammation. In the presence of periodontitis the probe tip passes through the inflamed tissues to stop at the level of the most coronal intact dento-gingival fibers, approximately 0.3-0.5 mm apical to the apical termination of the junctional epithelium. Decreased probing depth measurements following periodontal therapy may be due in part to decreased penetrability of the gingival tissues by the probe. Following treatment aimed at obtaining new attachment in periodontal defects, wider variations may occur between the location of the probe tip and the most coronal dento-gingival fibers than in the case of untreated sites. This is due in part to the formation of a so-called "long" junctional epithelium. In the absence of inflammation this epithelium may not be penetrable during ordinary probing, but could account for a rapid increase in probing depth measurements when inflammatory changes allow the probe to traverse the epithelium and/or the adjacent infiltrated connective tissue. In view of the difficulty inherent in relating periodontal probing measurements to actual sulcus or pocket depth, the interpretation of periodontal probing in the practice of periodontics may need reappraisal.

The Location of Overseas Production and Production for Export by U.S. Multinational Firms

Abstract: The location of overseas manufacturing production by U.S. firms seems to have been strongly influenced by common factors that operate in all industries: notably proximity to the United States and to other markets. Within industries, the choices made by parent firms among locations appear to show a tendency of "opposites attract," with low-wage and low-capital-intensity parents choosing high-wage, high-capital intensity countries and high-wage, high-capital-intensity parents making the opposite choice. Production for export seems to have been most strongly attracted by large internal markets in host countries. Economies of scale in production presumably made large markets also economical as export bases. Another factor was high trade propensities of host countries, which we interpret as representing access to imported materials at low world prices or better transport, finance, and other trade facilities. Labor cost seems to have been a weak influence on location choices. U.S. firms tended to export from high-wage countries but the high productivity in such countries more than offset the high wages. However, labor cost, to the extent we could measure it, was not in general a major influence on the location of export production.

Structural defects in amorphous solids A computer simulation study

Abstract: A definition of structural defects in amorphous solids in terms of the distribution of the internal stresses on the atomic level and of the symmetry of the environment of individual atoms is introduced. This definition does not require an ideal reference structure. The concept of the internal stresses on the atomic scale has been previously applied to describe the core structure of crystalline dislocations. In this paper it has been applied to the model amorphous structure generated by a computer simulation. It was found that there is a significant variation in the magnitude and direction of internal stresses, and that there are regions of 10 to 20 atoms over which the stresses remain either high or low. A method of calculating the symmetry coefficients at atomic sites has been proposed, and applied to the same system. It has been shown that there are significant correlations between the internal stresses and the local symmetry. The low-stress, high-symmetry regions resemble microcrystalline clus...

Organizational Symbolism: A Topic To Expand Organizational Analysis

Abstract: Our basic purpose in this paper is twofold: (1) to call attention to “organizational symbolism,” an important aspect of all institutions that has been virtually ignored, and (2) to suggest questions for a comprehensive research program for studying this topic.

Deleterious effect of glucose pretreatment on recovery from diffuse cerebral ischemia in the cat. I. Local cerebral blood flow and glucose utilization.

Abstract: Diffuse cerebral ischemia was created in pentobarbital-anesthetized cats by basilar and bilateral carotid artery occlusions and hypotension. Local cerebral blood flow (ICBF) was assessed autoradiographically with 14C-antipyrine, and local cerebral glucose utilization with 14C-2-deoxyglucose. In animals without glucose pretreatment, 15 min of ischemia led to a homogeneous reduction of post-ischemic cerebral perfusion to 31% of control; ischemia of 30 min produced post-ischemic perfusion heterogeneities in the cerebral cortex and deep gray structures. In animals pretreated with dextrose, 1.5 gm/kg intravenously, heterogeneous cerebral perfusion was observed following only 15 min of ischemia, and a severe global impairment of cerebral reperfusion occurred after the 30 min insult. Deoxyglucose autoradiograms in the latter animals were remarkable for a complete suppression of tracer uptake in the cerebral cortex and a paradoxically increased tracer concentration in the cerebral white matter. Mean plasma glucose in the treated animals exceeded 1000 mg/100 ml. Large glucose loads prior to ischemia dramatically impair post-ischemic cerebral perfusion.

Effect of scaling and root planing on the composition of the human subgingival microbial flora

Abstract: The effect of a single session of scaling and root planing on the subgingival periodontal flora of 14 adult human subjects was investigated by darkfield microscopy At baseline, one randomly selected periodontally diseased site in each subject was assessed for GI and P1I scores, probing depth and the percentage distribution in subgingival debris of coccoid cells, spirochetes, motile cells and other microorganisms Following a single full mouth scaling and root planing session, these criteria were reevaluated at other initially diseased sites, one per subject and time interval The intervals tested were days 3, 7, 14, 21, 28, 35, 42, 49, 56, 70 and 90 The P1I and GI scores tended to decrease during the first 14 days, returning to baseline around days 21–28 After another transient decline around 35–42 days the values stabilized around baseline levels till the end of the experiment Probing depth decreased below baseline during the first 7 days and with the exception of day 28, remained below baseline level till the end of the experiment Coccoid cells increased from 251 % at baseline to 761 % on day 3 Return to the baseline level occurred by day 21 Spirochetes did not return to baseline until day 42 The percentage of motile cells decreased significantly from baseline on day 3 only (148 % to 38 %) The results indicated that a single session of scaling and root planing is capable of disturbing the proportions of certain bacterial forms in the subgingival periodontal flora, and that it may require approximately 42 days for the proportions to return to baseline levels Probing depth was significantly decreased by the debridement throughout most of the 90-day experimental period The proportion of coccoid cells was negatively correlated with both GI and P1I scores, while the percentage of spirochetes was positively correlated with GI and P1I scores as well as probing depth measurements

Equilibrium land use patterns in a nonmonocentric city

Abstract: In the 1970's, a new genre of mathematical urban land use theory, called the new urban economics (Mills and MacKinnon [S]), was developed. The principal characteristics of those models are the monocentricity of the city, the uniform transportation system, the homogeneity of households and production firms, and so forth (Richardson [ 161). Among these, the assumption of monocentricity seems t o be very crucial to the formulation of the models. By monocentricity, we assume that the city has a single, pre-specified center, the CBD, which has a fixed size and employs the city's entire labor force. This assumption greatly simplifies the analysis: for example, commuting trips can be exactly specified if the residential locations are known, and with the assumption of a linear or circular city, the spatial characteristics of each location in the city can be described simply by the distance from the CBD. However, from the viewpoint of theoretical completeness, the centrality or noncentrality of a city should be explained within the framework of the model, which incorporates interdependences among economic activities, without prespecified locations of employment activities. And, if the model succeeds in clarifying the conditions for the existence of the CBD, we can not only judge the adequacy of the monocentric assumption adopted by the current urban land use models but also step forward to a more fruitful theory which is capable of explaining various kinds of nonmonocentric phenomena. Moreover, from the viewpoint of reality, monocentricity is an implausible assumption. In the face of the tendency of increasing decentralization and a decline of the role of the CBD as a single focus of employment activity (Mills [9]), urban land use models based on the monocentric assumption are clearly inadequate for analyzing recent cities.' Thus, both from the viewpoints of theoretical completeness and practical usefulness, the development of nonmonocentric models of urban land use is needed. There have been a few works which attempt to relax the monocentric assumption in two different ways. One approach is to introduce pre-specified

The UHF and microwave dielectric properties of normal and tumour tissues: variation in dielectric properties with tissue water content

Abstract: Dielectric measurements have been made on various soft tumour and normal tissues between 0.01 and 17 GHz at body temperature. At microwave frequencies above 1-5 GHz, the tissue dielectric properties can be fitted to Debye equations with the same relaxation frequency (25 GHz) as found for pure water at 37 degrees C. The tissue dielectric properties correlate well with their water contents. The conductivity of the tissue at 0.1 GHz (which is close to that of the cytoplasm itself) increases with the volume fraction of water in the tissue, in a manner consistent with that previously observed in proteins suspended in electrolyte solution. The contribution of the tissue water to the tissue dielectric permittivity at frequencies below 1 GHz is fitted by a function of water content different to that describing the conductivity data. Empirical equations that may be used to predict the dielectric properties of other soft tissues within this wide frequency range are suggested.

Deleterious effect of glucose pretreatment on recovery from diffuse cerebral ischemia in the cat. II. Regional metabolite levels.

Abstract: Glucose was infused intravenously into cats prior to cerebral ischemia. Brain concentrations of glucose, measured in 7 regions, were elevated 2.5-fold compared to those of non-infused animals. Ischemia of 15 or 30 minutes duration caused a greater accumulation of lactic acid in the brain of glucose-infused animals. Post-ischemic restitution of cerebral ATP, phosphocreatine, and lactate during 90 minutes of recirculation was severely impaired in the brain of animals pretreated with glucose compared to untreated animals. Thus, excess lactic acidosis may be a major factor interfering with metabolic restitution following cerebral ischemia.