Showing papers by "University of Massachusetts Amherst published in 1990"

Reflection groups and coxeter groups

Abstract: Part I. Finite and Affine Reflection Groups: 1. Finite reflection groups 2. Classification of finite reflection groups 3. Polynomial invariants of finite reflection groups 4. Affine reflection groups Part II. General Theory of Coxeter Groups: 5. Coxeter groups 6. Special case 7. Hecke algebras and Kazhdan-Lusztig polynomials 8. Complements Bibliography.

Progressive development of the rat osteoblast phenotype in vitro: Reciprocal relationships in expression of genes associated with osteoblast proliferation and differentiation during formation of the bone extracellular matrix

Abstract: The relationship of cell proliferation to the temporal expression of genes characterizing a developmental sequence associated with bone cell differentiation was examined in primary diploid cultures of fetal calvarial derived osteoblasts by the combined use of autoradiography, histochemistry, biochemistry, and mRNA assays of osteoblast cell growth and phenotypic genes. Modifications in gene expression define a developmental sequence that has 1) three principle periods–;proliferation, extracellular matrix maturation, and mineralization–;and 2) two restriction points to which the cells can progress but cannot pass without further signal–;the first when proliferation is down-regulated and gene expression associated with extracellular matrix maturation is induced, and the second when mineralization occurs. Initially, actively proliferating cells, expressing cell cycle-and cell growth-regulated genes, produce a fibronectin/type I collagen extracel-lular matrix. A reciprocal and functionally coupled relationship between the decline in proliferative activity and the subsequent induction of genes associated with matrix maturation and mineralization is supported by 1) a temporal sequence of events in which there is an enhanced expression of alkaline phos-phatase immediately following the proliferative period, and later, an increased expression of osteocalcin and osteopontin at the onset of mineralization; 2) increased expression of a specific subset of osteoblast phenotype markers, alkaline phosphatase and osteopontin, when proliferation is inhibited by hydroxyurea; and 3) enhanced levels of expression of the osteoblast markers as a function of ascorbic acid-induced collagen deposition, suggesting that the extracellular matrix contributes to both the shutdown of proliferation and the development of the osteoblast phenotype.

The Adolescent Outcome of Hyperactive Children Diagnosed by Research Criteria: I. An 8-Year Prospective Follow-up Study

Abstract: The psychiatric outcome is reported for a large sample of hyperactive children (N = 123), meeting research diagnostic criteria, and normal control children (N = 66) followed prospectively over an 8-year period into adolescence. Over 80% of the hyperactives were attention deficit hyperactivity disorder (ADHD) and 60% had either oppositional defiant disorder and/or conduct disorder at outcome. Rates of antisocial acts were considerably higher among hyperactives than normals, as were cigarette and marijuana use and negative academic outcomes. The presence of conduct disorder accounted for much though not all of these outcomes. Family status of hyperactives was much less stable over time than in the normal subjects. The use of research criteria for diagnosing children as hyperactive identifies a pattern of behavioral symptoms that is highly stable over time and associated with considerably greater risk for family disturbance and negative academic and social outcomes in adolescence than has been previously reported.

Detecting Differential Item Functioning Using Logistic Regression Procedures

Abstract: A logistic regression model for characterizing differential item functioning (DIF) between two groups is presented. A distinction is drawn between uniform and nonuniform DIF in terms of the parameters of the model. A statistic for testing the hypothesis of no DIF is developed. Through simulation studies, it is shown that the logistic regression procedure is more powerful than the Mantel-Haenszel procedure for detecting nonuniform DIF and as powerful in detecting uniform DIF.

Relationship of cell growth to the regulation of tissue-specific gene expression during osteoblast differentiation.

Abstract: The relationship of cell proliferation to the temporal expression of genes characterizing a developmental sequence associated with bone cell differentiation can be examined in primary diploid cultures of fetal calvarial-derived osteoblasts by the combination of molecular, biochemical, histochemical, and ultrastructural approaches. Modifications in gene expression define a developmental sequence that has 1) three principal periods: proliferation, extracellular matrix maturation, and mineralization; and 2) two restriction points to which the cells can progress but cannot pass without further signals. The first restriction point is when proliferation is down-regulated and gene expression associated with extracellular matrix maturation is induced, and the second when mineralization occurs. Initially, actively proliferating cells, expressing cell cycle and cell growth regulated genes, produce a fibronectin/type I collagen extracellular matrix. A reciprocal and functionally coupled relationship between the decl...

The strategy process, middle management involvement, and organizational performance

Abstract: This paper reports the results of a study investigating the strategic involvement of middlelevel managers in 20 organizations. The results suggest that involvement in the formation of strategy is associated with improved organizational performance. Consensus among middle-level managers, defined as strategic understanding and commitment, is related to involvement in the strategic process but not to organizational performance. Implications for research and the management of the strategic process are discussed.

Particle Production During Out-of-equilibrium Phase Transitions

Abstract: Techniques are developed to calculate the energy production in quantum fields which obtain a mass through the spontaneous symmetry breaking of a second field which is undergoing a phase transition. All fields are assumed to be out of thermal equilibrium and weakly coupled. The energy produced in a field, which is initially in its ground state, is computed for two generic types of time-dependent masses: a roughly monotonic turn on of the mass and an oscillatory mass. The formalism is applied to the questions of particle production and reheating in inflationary universe models. Requirements are found which the couplings in new-inflation-type models must satisfy for efficient reheating to occur.

Comprehensive Evaluation of Attention Deficit Disorder with and without Hyperactivity as Defined by Research Criteria.

Abstract: Children with attention deficit disorder with hyperactivity (ADD+H; N = 48) were compared with those without hyperactivity (ADD-H; N = 42), as well as with learning disabled and control children, on an extensive battery of interviews, behavior ratings, tests, and direct observations. ADD+H children had more externalizing and internalizing symptoms by parent and teacher report, were more off task during vigilance testing, and had more substance abuse, ADD+H, and aggression among their relatives than did the other groups. ADD-H children were more day-dreamy and lethargic by teacher report, more impaired in perceptual-motor speed, and had more anxiety disorders among their relatives than did ADD+H children. Results indicate that these 2 types of ADD may be separate, distinct childhood disorders rather than subtypes of a common attention deficit.

Human Motor Control

Abstract: Motor Control is a complex process that involves the brain, muscles, limbs, and often external objects. It underlies motion, balance, stability, coordination, and our interaction with others and technology. This book is a comprehensive introduction to motor control, covering a complex topic in an approachable way encompassing the psychological, physiological, and computational approaches to motor control. Human Motor Control, 2e cuts across all movement related disciplines: physical education, dance, physical therapy, robotics, etc. This second edition incorporates advances to the field, and integrates throughout the book how research harkens back to four critical questions: how do we select our actions of the many actions possible? How are these behaviors sequenced for appropriate order and timing between them? How does perception integrate with motor control? And how are perceptual-motor skills acquired? As before, the book retains its signature organization around activity systems. These activity systems include walking, looking, reaching, drawing and writing, keyboarding, speaking and singing, and smiling. Chapters here exemplify rather than encompass all the behaviors related to them. Hence smiling discusses physical and neural control of the face used in other expressions besides smiling, as well as the origins of emotional expression, and the importance of emotion expression in social interaction. These chapters on activity systems are preceded by chapters on basics, with an introduction and information on the physiological and psychological foundations of movement. The last section discusses integration of movements, individual differences, theories of motor control, and the contributions of both genetics and technology to motor control. Special features of the second edition: Organization by major activity systems New: brain imaging, social action, embodied cognition, advances in genetics and technology Detailed treatment of motor neuroscience Further Readings section added to each chapter * Retains unique organization of first edition: Part 1 on Preliminaries, Part 2 on Activity Systems, Part 3 on Principles and Prospects * Emphasizes exciting advances in the field and promising new directions * Well-illustrated with entertaining figures

Foot and word in prosodic morphology: The Arabic broken plural

Abstract: This article proposes a theory of prosodic domain circumscription, by means of which rules sensitive to morphological domain may be restricted to a prosodically characterized (sub-)domain in a word or stem. The theory is illustrated primarily by a comprehensive analysis of the Arabic broken plural; it is further supported by analysis of a number of processes from other languages, yielding a formal typology of domain-circumscription effects. The results obtained here depend on, and therefore confirm, two central principles of Prosodic Morphology: (1) the Prosodic Morphology Hypothesis, which requires that templates be expressed in prosodic, not segmental terms; and (2) the Template Satisfaction Condition, which requires that all elements in templates are satisfied obligatorily.

Boundary detection by constrained optimization

Abstract: A statistical framework is used for finding boundaries and for partitioning scenes into homogeneous regions. The model is a joint probability distribution for the array of pixel gray levels and an array of labels. In boundary finding, the labels are binary, zero, or one, representing the absence or presence of boundary elements. In partitioning, the label values are generic: two labels are the same when the corresponding scene locations are considered to belong to the same region. The distribution incorporates a measure of disparity between certain spatial features of block pairs of pixel gray levels, using the Kolmogorov-Smirnov nonparametric measures of difference between the distributions of these features. The number of model parameters is minimized by forbidding label configurations, which are assigned probability zero. The maximum a posteriori estimator of boundary placements and partitionings is examined. The forbidden states introduce constraints into the calculation of these configurations. Stochastic relaxation methods are extended to accommodate constrained optimization. >

A topological invariant arising in the stability analysis of travelling waves

Abstract: Travelling waves are special Solutions of partial differential equations in one space variable. They are characterized by their time invariant profile; indeed, s Solutions they evolve by translating at constant speed in the one spatial dimension. These Solutions are often the centerpiece of a physical System s they represent the transport of Information in a single direction. It is of fundamental importance for a given travelling wave to determine its stability relative to perturbations in the initial conditions for Solutions of the f ll partial differential equations. Stable Solutions are the most physically realistic since the external world provides enough perturbations that we can only expect to see waves which will dampen out these perturbations.

Side effects of methylphenidate in children with attention deficit hyperactivity disorder: a systemic, placebo-controlled evaluation.

Abstract: The frequency and severity of 17 side effects presumably associated with stimulant medication were assessed during a rigorous, triple-blind, placebo-controlled, crossover evaluation of methylphenidate, 0.3 and 0.5 mg/kg twice a day, in 83 children with attention deficit hyperactivity disorder. Side effects were rated by parents and teachers at the end of each weekly drug condition. Three children (3.6%) had side effects that were sufficiently serious to warrant immediate discontinuation of medication. Parent ratings indicated that only the side effects of decreased appetite, insomnia, stomachaches, and headaches increased significantly in frequency and severity during the two active medication doses as compared with the placebo condition. Fewer than half of the children experienced these side effects and among those who did, ratings of mean severity remained in the mild range. Teacher ratings showed little change over drug conditions, except on ratings of staring, sadness, and anxiety, which declined with increasing dose of medication. Parent ratings indicated that only the side effects of decreased appetite, insomnia, stomachaches, and headaches increased significantly in frequency and severity during the two active medication doses as compared with the placebo condition. Fewer than half of the children experienced these side effects and among those who did, ratings of mean severity remained in the mild range. Teacher ratings showed little change over drug conditions, except on ratings of staring, sadness, and anxiety, which declined with increasing dose of medication. Surprisingly, a high frequency of these behavior side effects were reported during the placebo condition. Stimulant medication within this therapeutic range, therefore, results in few, generally mild side effects.(ABSTRACT TRUNCATED AT 250 WORDS)

An IRAS Survey of the Taurus-Auriga Molecular Cloud

Abstract: IRAS data are used to search for young premain-sequence stars not previously associated with molecular cloud cores in the Taurus-Auriga region. NIR photometry and optical spectroscopy suggest that many of the objects are young stars. The sample includes six new embedded sources with luminosities comparable to that of the average T Tauri star, suggesting that surveys for premain-sequence stars in the cloud are essentially complete for luminosities greater than 0.5 solar luminosities. A disagreement is found between accretion rates derived from the duration of the embedded phase and those derived from the bolometric luminosity. It is found that this disagreement may be reconciled if a star accretes most of its mass in a time that is short compared to the duration of the embedded phase or if the ages of T Tauri stars have been underestimated.

Study of strong to ultratight protein interactions using differential scanning calorimetry

Abstract: Data from differential scanning calorimetry (DSC) may be used to estimate very large binding constants that cannot be conveniently measured by more conventional equilibrium techniques. Thermodynamic models have been formulated to describe interacting systems that involve either one thermal transition (protein-ligand) or two thermal transitions (protein-protein) and either 1:1 or higher binding stoichiometry. Methods are described for obtaining binding constants and heats of binding by two different methods: calculation or simulation fitting of data. Extensive DSC data on 2'CMP binding to RNase are presented and analyzed by the two methods. It is found that the methods agree when binding sites are completely saturated, but substantial errors arise in the calculation method when site saturation is incomplete and the transition of liganded molecules overlaps that of unliganded molecules. This arises primarily from an inability to determine TM (i.e., the temperature where concentrations of folded and unfolded protein are equal) under weak-binding conditions. Results from simulation show that the binding constants and heats of binding from the DSC method agree quantitatively with corresponding estimates obtained from equilibrium methods when extrapolated to the same temperature. It was also found from the DSC data that the binding constant decreases with increasing concentration of ligand, which might arise from nonideality effects associated with dimerization of 2'CMP. Simulations show that the DSC method is capable of estimating binding constants for ultratight interactions up to perhaps 10(40) M-1 or higher, while most equilibrium methods fail well below 10(10) M-1. DSC data from the literature on a number of interacting systems (trypsin-soybean trypsin inhibitor, trypsin-ovomucoid, trypsin-pancreatic trypsin inhibitor, chymotrypsin-subtilisin inhibitor, subtilisin BPN-subtilisin inhibitor, RNase S protein-RNase S peptide, avidin-biotin, ovotransferrin-Fe3+, superoxide dismutase-Zn2+, alkaline phosphatase-Zn2+, and assembly of regulatory and catalytic subunits of aspartate transcarbamoylase) were analyzed by simulation fitting or by calculation. Apparent single-site binding constants ranged from ca. 10(5) to 10(20) M-1, while the interaction constant for assembly of aspartate transcarbamoylase was estimated as 10(37) in molarity units. For most of these systems, the DSC interaction constants compared favorably with other literature estimates, for some it did not for reasons unknown, while for still others this represented the first estimate. Simulations show that for proteins having two binding sites for the same ligand within a single cooperative unit, ligand rearrangement will occur spontaneously during a DSC scan as the transition temperature of the unliganded protein is approached.(ABSTRACT TRUNCATED AT 400 WORDS)

An approximate analysis of the LRU and FIFO buffer replacement schemes

Abstract: In this paper, we develop approximate analytical models for predicting the buffer hit probability under the Least Recently Used (LRU) and First In First Out (FIFO) buffer replacement policies under the independent reference model In the case of the analysis of the LRU policy, the computational complexity for estimating the buffer hit probability is O(KB) where B is the size of the buffer and K denotes the number of items having distinct access probabilities In the case of the FIFO policy, the solution algorithm is iterative and the computational complexity of each iteration is O(K) Results from these models are compared to exact results for models originally developed by King [KING71] for small values of the buffer size, B, and the total number of items sharing the buffer, D Results are also compared with results from a simulation for large values of B and D In most cases, the error is extremely small (less than 01%) for both LRU and FIFO, and a maximum error of 3% is observed for very small buffer size (less than 5) when the access probabilities are extremely skewed To demonstrate the usefulness of the model, we consider two applications In our first application, we compare the LRU and FIFO policies to an optimal static buffer allocation policy for a database consisting of two classes of data items We observe that the performance of LRU is close to that of the optimal allocation As the optimal allocation requires knowledge of the access probabilities, the LRU policy is preferred when this information is unavailable We also observe that the LRU policy always performs better than the FIFO policy in our experiments In our second application, we show that if multiple independent reference streams on mutually disjoint sets of data compete for the same buffer, it is better to partition the buffer using an optimal allocation policy than to share a common buffer

Facilitated diffusion of glucose

Abstract: Article de synthese sur la diffusion facilite du glucose a travers les membranes cellulaires. Proteines de transport du glucose (identification et structure II re ), proprietes catalytiques de ces proteines (stereoselectivite, modele de transport dans l'erythrocyte humain et dans d'autres cellules mammiferes), regulation du transport facilite du glucose

Screening mammography: A missed clinical opportunity? Results of the NCI Breast Cancer Screening Consortium and National Health Interview Survey Studies

Abstract: Data from seven studies sponsored by the National Cancer Institute (NCI) were used to determine current rates of breast cancer screening and to identify the characteristics of and reasons for women not being screened. All seven studies were population-based surveys of women aged 50 to 74 years without breast cancer. While over 90% of non-Hispanic white respondents had regular sources of medical care, 46% to 76% had had a clinical breast examination within the previous year, and only 25% to 41% had had a mammogram. Less educated and poorer women had had fewer mammograms. The two most common reasons women gave for never having had a mammogram were that they did not know they needed it and that their physician had not recommended it. Many physicians may have overlooked the opportunity to recommend mammography for older women when performing a clinical breast examination and to educate their patients about the benefit of screening mammography.

Rules of hope

Abstract: Hope has been called the "life blood of the soul", an indispensable condition for human existence. Yet evidence in this book suggests that hope is neither a necessary nor a universal part of life. Rather, hope is constituted in accordance with cultural norms, and hence it may vary fundamentally from one society to another. In the first of four studies, Averill, Catlin, and Chon delineate four classes of rules that help constitute hope in Western societies. A second study examines the similarities and differences between hope and other, more prototypic emotions, such as anger and love. The third study uses content analyses of maxims and metaphors to clarify further the Western model of hope. In the fourth study, hope is compared with himang, its closest counterpart in Korea. The results of these studies provide the basis for an analysis of the functions of hope, on both the individual and social levels. But this book is not simply about hope. It is also about emotions in general. Current psychological theories focus on emotions that have distinct physiological components (e.g., fear and anger) and that can be investigated using animal models. As a consequence, our theories have a strong biological orientation. How would our theories change if they were to encompass more cognitively oriented emotions, such as hope? Rules of Hope provides some answers to this question.

Plastics from bacteria and for bacteria: Poly(β-hydroxyalkanoates) as natural, biocompatible, and biodegradable polyesters

Abstract: A wide variety of different types of microorganisms are known to produce intracellular energy and carbon storage products which have been generally described as being poly(β-hydroxybutyrate), PHB, but which are, more often than not, copolymers containing different alkyl groups at the β-position. Hence, PHB belongs to the family of poly(β-hydroxyalkanoates), PHA, all of which are usually formed as intracellular inclusions under unbalanced growth conditions. Recently, it became of industrial interest to evaluate PHA polyesters as natural, biodegradable, and biocompatible plastics for a wide range of possible applications such as surgical sutures or packaging containers. For industrial applications, the controlled incorporation of repeating units with different chain lengths into a series of copolymers is desirable in order to produce polyesters with a range of material properties because physical and chemical characteristics depend strongly on the polymer composition. Such “tailormade” copolymers can be produced under controlled growth conditions, in that if a defined mixture of substrates for a certain type of microorganisms is supplied, a well defined and reproducible copolymer is formed.

The strong halfspace theorem for minimal surfaces.

Abstract: D. Hoffman and W.H. Meeks, III Department of Mathematics, University of Massachusetts, Amherst, MA 01003, USA In [6] Jorge and Xavier constructed examples of complete nonplanar minimal surfaces contained between two parallel planes in •3. Recently Rosenberg and Toubiana have found complete minimally immersed annuli that are proper in an open slab 1-12]. On the basis of these and other results, the question has arisen as to whether or not there could exist a properly immersed minimal surface in ~3 that was contained between two parallel planes. The answer is negative, an immediate consequence of the following theorem.