Showing papers by "University of Rochester published in 1990"

Introduction to WordNet: An On-line Lexical Database

Abstract: Standard alphabetical procedures for organizing lexical information put together words that are spelled alike and scatter words with similar or related meanings haphazardly through the list. Unfortunately, there is no obvious alternative, no other simple way for lexicographers to keep track of what has been done or for readers to find the word they are looking for. But a frequent objection to this solution is that finding things on an alphabetical list can be tedious and time-consuming. Many people who would like to refer to a dictionary decide not to bother with it because finding the information would interrupt their work and break their train of thought.

Financial Development, Growth, and the Distribution of Income

Abstract: A paradigm is presented in which both the extent of financial intermediation and the rate of economic growth are endogenously determined. Financial intermediation promotes growth because it allows a higher rate of return to be earned on capital, and growth in turn provides the means to implement costly financial structures. Thus financial intermediation and economic growth are inextricably linked in accord with the Goldsmith-McKinnon-Shaw view on economic development. The model also generates a development cycle reminiscent of the Kuznet hypothesis. In particular, in the transition from a primitive slow-growing economy to a developed fast-growing one, a nation passes through a stage in which the distribution of wealth across the rich and poor widens.

Mechanisms by which mitochondria transport calcium.

Abstract: It has been firmly established that the rapid uptake of Ca2+ by mitochondria from a wide range of sources is mediated by a uniporter which permits transport of the ion down its electrochemical gradient. Several mechanisms of Ca2+ efflux from mitochondria have also been extensively discussed in the literature. Energized mitochondria must expend a significant amount of energy to transport Ca2+ against its electrochemical gradient from the matrix space to the external space. Two separate mechanisms have been found to mediate this outward transport: a Ca2+/nNa+ exchanger and a Na(+)-independent efflux mechanism. These efflux mechanisms are considered from the perspective of available energy. In addition, a reversible Ca2(+)-induced increase in inner membrane permeability can also occur. The induction of this permeability transition is characterized by swelling of the mitochondria, leakiness to small ions such as K+, Mg2+, and Ca2+, and loss of the mitochondrial membrane potential. It has been suggested that the permeability transition and its reversal may also function as a mitochondrial Ca2+ efflux mechanism under some conditions. The characteristics of each of these mechanisms are discussed, as well as their possible physiological functions.

A Monte Carlo Implementation of the EM Algorithm and the Poor Man's Data Augmentation Algorithms

Abstract: The first part of this article presents the Monte Carlo implementation of the E step of the EM algorithm. Given the current guess to the maximizer of the posterior distribution, latent data patterns are generated from the conditional predictive distribution. The expected value of the augmented log-posterior is then updated as a mixture of augmented log-posteriors, mixed over the generated latent data patterns (multiple imputations). In the M step of the algorithm, this mixture is maximized to obtain the update to the maximizer of the observed posterior. The gradient and Hessian of the observed log posterior are also expressed as mixtures, mixed over the multiple imputations. The relation between the Monte Carlo EM (MCEM) algorithm and the data augmentation algorithm is noted. Two modifications to the MCEM algorithm (the poor man's data augmentation algorithms), which allow for the calculation of the entire posterior, are then presented. These approximations serve as diagnostics for the validity o...

Origin and evolution of retroelements based upon their reverse transcriptase sequences.

Abstract: To study the evolutionary relationship of reverse transcriptase (RT) containing genetic elements, a phylogenetic tree of 82 retroelements from animals, plants, protozoans and bacteria was constructed. The tree was based on seven amino acid domains totalling 178 residues identified in all RTs. We have also identified these seven domains in the RNA-directed RNA polymerases from various plus-strand RNA viruses. The sequence similarity of these RNA polymerases to RT suggests that these two enzymes evolved from a common ancestor, and thus RNA polymerase can be used as an outgroup to root the RT tree. A comparison of the genetic organization of the various RT containing elements and their position on the tree allows several inferences concerning the origin and evolution of these elements. The most probable ancestor of current retroelements was a retrotransposable element with both gag-like and pol-like genes. On one major branch of the tree, organelle and bacterial sequences (e.g. group II introns and bacterial msDNA) appear to have captured the RT sequences from retrotransposons which lack long terminal repeats (LTRs). On the other major branch, acquisition of LTRs gave rise to two distinct groups of LTR retrotransposons and three groups of viruses: retroviruses, hepadnaviruses and caulimoviruses.

Zidovudine in Asymptomatic Human Immunodeficiency Virus Infection: A Controlled Trial in Persons with Fewer Than 500 CD4-Positive Cells per Cubic Millimeter

Abstract: Zidovudine (AZT) is a potent inhibitor of the replication of the human immunodeficiency virus (HIV), and it has been shown to improve survival in advanced HIV disease. We conducted a randomized, double-blind trial in adults with asymptomatic HIV infection who had CD4+ cell counts of fewer than 500 per cubic millimeter on entry into the study. The subjects (92 percent male) were randomly assigned to one of three treatment groups: placebo (428 subjects); zidovudine, 500 mg per day (453); or zidovudine, 1500 mg per day (457). After a mean follow-up of 55 weeks (range, 19 to 107), 33 of the subjects assigned to placebo had the acquired immunodeficiency syndrome (AIDS), as compared with 11 of those assigned to receive 500 mg of zidovudine (P = 0.002; relative risk, 2.8; 95 percent confidence interval, 1.4 to 5.6) and 14 of those assigned to receive 1500 mg of zidovudine (P = 0.05; relative risk, 1.9; 95 percent confidence interval, 1.0 to 3.5). In the three treatment groups, the rates of progression (per 100 person-years) to either AIDS or advanced AIDS-related complex were 7.6, 3.6, and 4.3, respectively. As compared with those assigned to placebo, the subjects in the zidovudine groups had significant increases in the number of CD4+ cells and significant declines in p24 antigen levels. In the 1500-mg zidovudine group, severe hematologic toxicity (anemia or neutropenia) was more frequent than in the other groups (P less than 0.0001). In the 500-mg zidovudine group, nausea was the only toxicity that was significantly more frequent (in 3.3 percent) than in the placebo group (P = 0.001). We conclude that zidovudine is safe and effective in persons with asymptomatic HIV infection and fewer than 500 CD4+ cells per cubic millimeter. Additional study will be required to determine whether such treatment will ultimately improve survival for persons infected with HIV.

Tastes and Technology in a Two-Country Model of the Business Cycle: Explaining International Comovements

Abstract: Trade on international financial markets allows people to insure country-specific risk and smooth consumption intertemporally. Equilibrium models of business cycles with trade on global financial markets typically yield international consumption correlations near 1 and excessive volatility of investment. We incorporate nontraded goods in the model and find that the implications for aggregate consumption, investment, and the trade balance are consistent with business-cycle properties of industrialized countries. However, the model driven by technology shocks alone yields counterfactual implications for comovements between consumption and prices at the sectoral level. Taste shocks produce price - quantity relationships more consistent with the data. (JEL E30, F40)

What It Takes to Do Well in School and Whether I've Got It: A Process Model of Perceived Control and Children's Engagement and Achievement in School

Abstract: A new conceptualization of perceived control was used to test a process model describing the contribution of these perceptions to school achievement for students in elementary school (N = 220). Three sets of beliefs were distinguished: (a) expectations about whether one can influence success and failure in school (control beliefs); (b) expectations about the strategies that are effective in producing academic outcomes; and (c) expectations about one's own capacities to execute these strategies. Correlational and path analyses were consistent with a process model which predicted that children's perceived control (self-report) influences academic performance (grades and achievement test scores) by promoting or undermining active engagement in learning activities (as reported by teachers) and that teachers positively influence children's perceived control by provision of contingency and involvement (as reported by students). These results have implications for theories of perceived control and also suggest one pathway by which teachers can enhance children's motivation in school. Several decades of research have demonstrated that an important contributor to school performance is an individual's expectations about whether he or she has any control over academic successes and failures. A robust body of empirical findings has been produced using a variety of constructs, such as locus of control, causal attributions, learned helplessness, and self-efficacy. Beginning with the examination of beliefs about whether reinforcements are under internal or external control (Rotter, 1966), empirical evidence has accumulated indicating that children who believe that doing well in school is contingent on their own actions perform better than those who do not (Seligman, 1975). Similarly, children who believe that good grades are caused by internal and controllable causes (like effort; Weiner, 1979), who believe that they can produce the responses that lead to desired outcomes (Bandura, 1977), or who believe that they possess high ability (Harter, 1981; Stipek, 1980) perform better academically. These children score higher on tests of intelligence

Stock Volatility and the Crash of ’87

Abstract: This article analyzes the behavior of stock return volatility using daily data from 1885 through 1988. The October 1987 stock market crash was unusual in many ways. October 19 was the largest percentage change in market value in over 29,000 days. Stock volatility jumped dramatically during and after the crash. Nevertheless, it returned to lower, more normal levels more quickly than past experience predicted. The author uses data on implied volatilities from call option prices and estimates of volatility from futures contracts on stock indexes to confirm this result. Article published by Oxford University Press on behalf of the Society for Financial Studies in its journal, The Review of Financial Studies.

Identification of mutations in the COL4A5 collagen gene in Alport syndrome.

Abstract: X-linked Alport syndrome is a hereditary glomerulonephritis in which progressive loss of kidney function is often accompanied by progressive loss of hearing. Ultrastructural defects in glomerular basement membranes (GBM) of Alport syndrome patients implicate an altered structural protein as the cause of nephritis. The product of COL4A5, the alpha 5(IV) collagen chain, is a specific component of GBM within the kidney, and the gene maps to the same X chromosomal region as does Alport syndrome. Three structural aberrations were found in COL4A5, in intragenic deletion, a Pst I site variant, and an uncharacterized abnormality, which appear to cause nephritis and deafness, with allele-specific severity, in three Alport syndrome kindreds in Utah.

Eosinophilic gastroenteritis: a clinicopathological study of patients with disease of the mucosa, muscle layer, and subserosal tissues.

Abstract: The aim of this study was to evaluate the clinicopathological spectrum of eosinophilic gastroenteritis and identify possible difficulties in establishing the diagnosis. All patients with a diagnosis of eosinophilic gastroenteritis, defined by the presence of gastrointestinal symptoms and eosinophilic infiltration of the gut (38), or a radiological diagnosis with peripheral eosinophilia (two), were identified from the Mayo Clinic records; in none was there evidence of extraintestinal disease. Patients were divided into three groups according to the Klein classification: predominant mucosal (23), muscular (12), or subserosal disease (five). A fourth group of patients (10) for comparison had abdominal symptoms and unexplained peripheral eosinophilia but no proven eosinophilic infiltration of the gut. It was found that a history of allergy was reported by 20 of 40 patients with eosinophilic gastroenteritis. Peripheral eosinophilia was absent in nine of 40. The patients with subserosal disease were distinct from the other groups in presentation (abdominal bloating, ascites), higher eosinophil counts and in their dramatic responses to steroid therapy. Otherwise the patients were similar regarding demographic factors, presenting symptoms (abdominal pain, nausea, weight loss, diarrhoea), and laboratory parameters. The ESR was moderately raised in 10 of 40 patients. The disease may affect any area of the gastrointestinal tract; eosinophilic infiltration was documented in the oesophagus in one patient and in the colon in two cases. Endoscopic biopsies missed the diagnosis in five of 40 presumably because of patchy disease. Eosinophilic gastroenteritis should be considered in the differential diagnosis of unexplained gastrointestinal symptoms even in the absence of peripheral eosinophilia.

Political efficacy and trust: A report on the NES pilot study items

Abstract: Political efficacy and trust—among the most frequently used survey measures of general political attitudes—are often maligned for their lack of reliability and validity. This paper reports results from the National Election Studies 1987 pilot study, which included more than thirty-five efficacy and trust items. Five attitudinal dimensions were hypothesized; four emerged clearly. One scale, internal efficacy, is especially robust; a four- to six-item scale represents a considerable improvement on existing NES measures. External efficacy is distinguished from political trust, at least when the former is measured in terms of the fairness of political procedures and outcomes rather than in terms of elite responsiveness to popular demands. Though less decisive, there also is support for dividing trust into incumbent- and regime-based components. The failure to find a similar incumbent- and regime-based distinction for external efficacy is in accord with theoretical perspectives.

Preference for Infant-directed Speech in the First Month after Birth

Abstract: 2 experiments examined behavioral preferences for infant-directed (ID) speech over adult-directed (AD) speech in young infants. Using a modification of the visual-fixation-based auditory-preference procedure, Experiments 1 and 2 examined whether 12 1-month-old and 16 2-day-old infants looked longer at a visual stimulus when looking produced ID as opposed to AD speech. The results showed that both 1-month-olds and newborns preferrred ID over AD speech. Although the absolute magnitude of the ID speech preference was significantly greater, with the older infants showing longer looking durations than the younger infants, subsequent analyses showed no significant difference in the relative magnitude of this effect. Differences in overall looking times between the 2 groups apparently reflect task variables rather than differences in speech processing. These results suggest that infants' preference for the exaggerated prosodic features of ID speech is present from birth and may not depend on any specific postnatal experience. However, the possible role of prenatal auditory experience with speech is considered.

Chromatic mechanisms in striate cortex of macaque

Abstract: We measured the responses of 305 neurons in striate cortex to moving sinusoidal gratings modulated in chromaticity and luminance about a fixed white point. Stimuli were represented in a 3-dimensional color space defined by 2 chromatic axes and a third along which luminance varied. With rare exceptions the chromatic properties of cortical neurons were well described by a linear model in which the response of a cell is proportional to the sum (for complex cells, the rectified sum) of the signals from the 3 classes of cones. For each cell there is a vector passing through the white point along which modulation gives rise to a maximal response. The elevation (theta m) and azimuth (phi m) of this vector fully describe the chromatic properties of the cell. The linear model also describes neurons in l.g.n. (Derrington et al., 1984), so most neurons in striate cortex have the same chromatic selectivity as do neurons in l.g.n. However, the distributions of preferred vectors differed in cortex and l.g.n.: Most cortical neurons preferred modulation along vectors lying close to the achromatic axis and those showing overt chromatic opponency did not fall into the clearly defined chromatic groups seen in l.g.n. The neurons most responsive to chromatic modulation (found mainly in layers IVA, IVC beta, and VI) had poor orientation selectivity, and responded to chromatic modulation of a spatially uniform field at least as well as they did to any grating. We encountered neurons with band-pass spatial selectivity for chromatically modulated stimuli in layers II/III and VI. Most had complex receptive fields. Neurons in layer II/III did not fall into distinct groups according to their chromatic sensitivities, and the chromatic properties of neurons known to lie within regions rich in cytochrome oxidase appeared no different from those of neurons in the interstices. Six neurons, all of which resembled simple cells, showed unusually sharp chromatic selectivity.

“Sonoelasticity” images derived from ultrasound signals in mechanically vibrated tissues

Abstract: A method has been developed for detecting and imaging the relative "stiffness," or elasticity of tissues. Externally applied vibration at low frequencies (10-1000 Hz) is used to induce oscillations within soft tissues, and the motion is detected by Doppler ultrasound. The results are displayed in a format resembling conventional Doppler color flow mapping, and are termed "sonoelasticity images." Preliminary experiments indicate that these novel images may be useful for detecting hard tumors in the prostate, liver, breast, and other organs.

Optimal incentive-compatible priority pricing for the M/M/1 queue

Abstract: Consider a system that is modeled as an M/M/1 queueing system with multiple user classes. Each class is characterized by its delay cost per unit of time, its expected service time and its demand function. This paper derives a pricing mechanism which is optimal and incentive-compatible in the sense that the arrival rates and execution priorities jointly maximize the expected net value of the system while being determined, on a decentralized basis, by individual users. A closed-form expression for the resulting price structure is presented and studied.

Microorganisms associated with chromosome destruction and reproductive isolation between two insect species

Abstract: MICROORGANISMS have been implicated in causing cytoplasmic incompatibility in a variety of insect species, including mosquitoes, fruitflies, beetles and wasps1–17. The effect is typically unidirectional: incompatible crosses produce no progeny1–11 or sterile males12–14, whereas the reciprocal crosses produce normal progeny. The parasitic wasp Nasonia vitripennis is one of the few species in which the cytogenetic mechanism of incompatibility is known. In this species the paternal chromosome set forms a tangled mass in a fertilized egg and is eventually lost16. Here we report that cytoplasmic microorganisms are associated with complete bidirectional incompatibility between N. vitripennis and a closely related sympatric species, N. giraulti. Microorganisms can be seen in the eggs of both species. Hybrid offspring are normally not produced in crosses between the two species, but do occur after elimination of the microorganisms by antibiotic treatment. A cytogenetic and genetic study shows that bidirectional interspecific incompatibility is due to improper condensation of the paternal chromosomes. Microorganism-mediated reproductive isolation is of interest because it could provide a rapid mode of speciation18,19. The mechanism of incompatibility in Nasonia is also of interest as a potential tool for studying chromosome imprinting and chromosome condensation.

Tissue response to mechanical vibrations for “sonoelasticity imaging”

Abstract: The goal of "sonoelasticity imaging" is to differentiate between normal soft tissues and hard lesions. This is done by measuring and then displaying the ultrasound Doppler spectrum of regions within tissues which are mechanically forced with low frequency (20-1000 Hz) vibrations. The resolution and sensitivity of the technique ultimately rest on the spatial resolution of ultrasound Doppler detection, the low frequency mechanical properties of tissues, and the vibration response of layered, inhomogeneous regions with hard tumor inclusions and complicated boundary conditions set by the presence of skin, bones and other regions. An initial investigation has measured some tissue stiffness parameters, and applied these in a NASTRAN finite element analysis to simulate a prostate tumor in the pelvic cavity. The measurements show a wide separation between the elastic modulus of tumors and soft tissues such as muscle and prostate. NASTRAN analyses show the ability to delineate regions of different elasticity based on the pattern of vibration amplitudes. The ability to change vibration frequency within the 100-300 Hz band seems particularly helpful in simulations and experiments which visualize small stiff inclusions in tissues. Preliminary results support the postulate that sonoelasticity imaging can provide useful information concerning tissue properties that are not otherwise obtainable.

Indexing via color histograms

Abstract: This paper shows color histograms to be stable object representations over change in view, and demonstrates that they can differentiate among a large number of objects. The authors introduce a technique called histogram intersection for efficiently matching model and image histograms. Color can also be used to search for the location of an object. An algorithm called histogram backprojection performs this task efficiently in crowded scenes. >

Magnocellular and parvocellular contributions to responses in the middle temporal visual area (MT) of the macaque monkey

Abstract: Many lines of evidence suggest that the visual signals relayed through the magnocellular and parvocellular subdivisions of the primate dorsal LGN remain largely segregated through several levels of cortical processing. It has been suggested that this segregation persists through to the highest stages of the visual cortex, and that the pronounced differences between the neuronal response properties in the parietal cortex and inferotemporal cortex may be attributed to differential contributions from magnocellular and parvocellular signals. We have examined this hypothesis directly by recording the responses of cortical neurons while selectively blocking responses in the magnocellular or parvocellular layers of the LGN. Responses were recorded from single units or multiunit clusters in the middle temporal visual area (MT), which is part of the pathway leading to parietal cortex and thought to receive primarily magnocellular inputs. Responses in the MT were consistently reduced when the magnocellular subdivision of the LGN was inactivated. The reduction was almost always pronounced and often complete. In contrast, parvocellular block rarely produced striking changes in MT responses and typically had very little effect. Nevertheless, unequivocal parvocellular contributions could be demonstrated for a minority of MT responses. At a few MT sites, responses were recorded while magnocellular and parvocellular blocks were made simultaneously. Responses were essentially eliminated for all these paired blocks. These results provide direct evidence for segregation of magnocellular and parvocellular contributions in the extrastriate visual cortex and support the suggestion that these signals remain largely segregated through the highest levels of cortical processing.

Treating ordinal scales as interval scales: an attempt to resolve the controversy.

Abstract: Ever since the Harvard psychologist S. S. Stevens (1946) advanced his ideas concerning the connections between measurement scales and statistical analysis, there has been a continuing controversy regarding the use of traditional descriptive and inferential statistics for ordinal-level variables. The exchange in Nursing Research between Armstrong and this writer (Armstrong, 1981; Knapp, 1984, Armstrong, 1984) is illustrative of the competing positions. In this commentary, an attempt will be made to sort out the dimensions of the controversy summarize some recent contributions that help to clarify the issues, and suggest a possible solution to the problem. The reader who is interested in the earlier history of conflicting views about scales and statistics is referred to the excellent and balanced review by Gardner (1975).

Dispersal in the wood frog (rana sylvatica): implications for genetic population structure.

Abstract: Recapture of marked juvenile and adult wood frogs in five Appalachian Mountain ponds showed adults to be 100% faithful to the ponds in which they first bred, but approximately 18% of the juveniles dispersed to breed in ponds other than the one of origin. Effective population sizes were generally smaller than the population censuses and genetic neighborhoods had an average radius of 1,126 meters. Values of standardized genetic variance based on effective population size and mating success were relatively small. Genetic population structure estimated from the dispersal data suggested that ponds within about a 1,000 meter radius should show little genetic differentiation; ponds separated by a distance greater than 1,000 meters should experience little gene flow and show higher genetic differentiation. Wood frogs in these ponds do not show a meta-population structure as suggested for newts.