Showing papers by "University of Michigan published in 1995"

Posttraumatic stress disorder in the National Comorbidity Survey.

Abstract: Background: Data were obtained on the general population epidemiology of DSM-III-R posttraumatic stress disorder (PTSD), including information on estimated lifetime prevalence, the kinds of traumas most often associated with PTSD, sociodemographic correlates, the comorbidity of PTSD with other lifetime psychiatric disorders, and the duration of an index episode. Methods: Modified versions of the DSM-III-R PTSD module from the Diagnostic Interview Schedule and of the Composite International Diagnostic Interview were administered to a representative national sample of 5877 persons aged 15 to 54 years in the part II subsample of the National Comorbidity Survey. Results: The estimated lifetime prevalence of PTSD is 7.8%. Prevalence is elevated among women and the previously married. The traumas most commonly associated with PTSD are combat exposure and witnessing among men and rape and sexual molestation among women. Posttraumatic stress disorder is strongly comorbid with other lifetime DSM-III-R disorders. Survival analysis shows that more than one third of people with an index episode of PTSD fail to recover even after many years. Conclusions: Posttraumatic stress disorder is more prevalent than previously believed, and is often persistent. Progress in estimating age-at-onset distributions, cohort effects, and the conditional probabilities of PTSD from different types of trauma will require future epidemiologic studies to assess PTSD for all lifetime traumas rather than for only a small number of retrospectively reported "most serious" traumas. (Arch Gen Psychiatry. 1995;52:1048-1060)

A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase

Abstract: Hyperhomocysteinaemia has been identified as a risk factor for cerebrovascular, peripheral vascular and coronary heart disease. Elevated levels of plasma homocysteine can result from genetic or nutrient-related disturbances in the trans-sulphuration or re-methylation pathways for homocysteine metabolism. 5, 10-Methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the predominant circulatory form of folate and carbon donor for the re-methylation of homocysteine to methionine. Reduced MTHFR activity with a thermolabile enzyme has been reported in patients with coronary and peripheral artery disease. We have identified a common mutation in MTHFR which alters a highly-conserved amino acid; the substitution occurs at a frequency of approximately 38% of unselected chromosomes. The mutation in the heterozygous or homozygous state correlates with reduced enzyme activity and increased thermolability in lymphocyte extracts; in vitro expression of a mutagenized cDNA containing the mutation confirms its effect on thermolability of MTHFR. Finally, individuals homozygous for the mutation have significantly elevated plasma homocysteine levels. This mutation in MTHFR may represent an important genetic risk factor in vascular disease.

A Natural-Resource-Based View of the Firm

Abstract: Historically, management theory has ignored the constraints imposed by the biophysical (natural) environment. Building upon resource-based theory, this article attempts to fill this void by proposing a natural-resource-based view of the firm—a theory of competitive advantage based upon the firm's relationship to the natural environment. It is composed of three interconnected strategies: pollution prevention, product stewardship, and sustainable development. Propositions are advanced for each of these strategies regarding key resource requirements and their contributions to sustained competitive advantage.

A Theoretical Basis for a Biopharmaceutic Drug Classification: The Correlation of in Vitro Drug Product Dissolution and in Vivo Bioavailability

Abstract: A biopharmaceutics drug classification scheme for correlating in vitro drug product dissolution and in vivo bioavailability is proposed based on recognizing that drug dissolution and gastrointestinal permeability are the fundamental parameters controlling rate and extent of drug absorption. This analysis uses a transport model and human permeability results for estimating in vivo drug absorption to illustrate the primary importance of solubility and permeability on drug absorption. The fundamental parameters which define oral drug absorption in humans resulting from this analysis are discussed and used as a basis for this classification scheme. These Biopharmaceutic Drug Classes are defined as: Case 1. High solubility-high permeability drugs, Case 2. Low solubility-high permeability drugs, Case 3. High solubility-low permeability drugs, and Case 4. Low solubility-low permeability drugs. Based on this classification scheme, suggestions are made for setting standards for in vitro drug dissolution testing methodology which will correlate with the in vivo process. This methodology must be based on the physiological and physical chemical properties controlling drug absorption. This analysis points out conditions under which no in vitro-in vivo correlation may be expected e.g. rapidly dissolving low permeability drugs. Furthermore, it is suggested for example that for very rapidly dissolving high solubility drugs, e.g. 85% dissolution in less than 15 minutes, a simple one point dissolution test, is all that may be needed to insure bioavailability. For slowly dissolving drugs a dissolution profile is required with multiple time points in systems which would include low pH, physiological pH, and surfactants and the in vitro conditions should mimic the in vivo processes. This classification scheme provides a basis for establishing in vitro-in vivo correlations and for estimating the absorption of drugs based on the fundamental dissolution and permeability properties of physiologic importance.

Problems with Instrumental Variables Estimation when the Correlation between the Instruments and the Endogenous Explanatory Variable is Weak

Abstract: We draw attention to two problems associated with the use of instrumental variables (IV), the importance of which for empirical work has not been fully appreciated. First, the use of instruments that explain little of the variation in the endogenous explanatory variables can lead to large inconsistencies in the IV estimates even if only a weak relationship exists between the instruments and the error in the structural equation. Second, in finite samples, IV estimates are biased in the same direction as ordinary least squares (OLS) estimates. The magnitude of the bias of IV estimates approaches that of OLS estimates as the R 2 between the instruments and the endogenous explanatory variable approaches 0. To illustrate these problems, we reexamine the results of a recent paper by Angrist and Krueger, who used large samples from the U.S. Census to estimate wage equations in which quarter of birth is used as an instrument for educational attainment. We find evidence that, despite huge sample sizes, th...

Machine vision

Abstract: This text is intended to provide a balanced introduction to machine vision. Basic concepts are introduced with only essential mathematical elements. The details to allow implementation and use of vision algorithm in practical application are provided, and engineering aspects of techniques are emphasized. This text intentionally omits theories of machine vision that do not have sufficient practical applications at the time.

Trust: the connecting link between organizational theory and philosophical ethics

Abstract: Numerous researchers have proposed that trust is essential for understanding interpersonal and group behavior, managerial effectiveness, economic exchange and social or political stability, yet according to a majority of these scholars, this concept has never been precisely defined. This article reviews definitions from various approaches within organizational theory, examines the consistencies and differences, and proposes that trust is based upon an underlying assumption of an implicit moral duty. This moral duty—an anomaly in much of organizational theory—has made a precise definition problematic. Trust also is examined from philosophical ethics, and a synthesis of the organizational and philosophical definitions that emphasizes an explicit sense of moral duty and is based upon accepted ethical principles of analysis is proposed. This new definition has the potential to combine research from the two fields of study in important areas of inquiry.

Managerial and Organizational Cognition: Notes from a Trip Down Memory Lane

Abstract: The study of cognition in organizations has burgeoned in recent years. Top-down information processing theory suggests that individuals create knowledge structures to help them process information and make decisions. While the benefits of employing such knowledge structures are widely noted, there is a growing concern that they can limit decision makers' abilities to understand their information environments and thus, compromise their decision making. This issue has captured the imagination of managerial and organizational cognition researchers. To date, their inquiry has been eclectic in focus and method. To order and advance this work, the author reviews extant research on the developmental origins and decision consequences of both the content and structure of knowledge structures at multiple levels of analysis. A host of research challenges are identified to help develop a better understanding of knowledge structure representation, development, and use in organizations.

Toward a theory of organizational culture and effectiveness.

Abstract: his paper uses case studies and survey data to explore the relationship between organizational culture and effectiveness. The results provide evidence for the existence of four cultural traits—involvement, consistency, adaptability, and mission—and indicate that these characteristics are positively related to perceptions of performance as well as to objective measures such as return on assets and sales growth. Organizational culture is found to be measurable and to be related to important organizational outcomes. Richard L. Daft Abstract paper develops a model of organizational culture and effectiveness based on four traits of organizational cultures; involvement, consistency, adaptability, and mission. These traits are examined through two linked studies: In the first, qualitative case studies of five firms are used to identify the traits and the nature of their linkage to effectiveness; In the second, a quantitative study provides an exploratory analysis of CEO perceptions of these four traits and their relation to subjective and objective measures of effectiveness in a sample of 764 organizations. The results show support for the predic- tive value of the traits, and help to illustrate the complemen- tarity of qualitative and quantitative methods for studying organizational cultures. Two of the traits, involvement and adaptability, are indica- tors of flexibility, openness, and responsiveness, and were strong predictors of growth. The other two traits, consistency and mission, are indieators of integration, direction, and vision, and were better predictors of profitability. Each of the four traits were also significant predictors of other effective- ness criteria such as quality, employee satisfaction, and over- all performance. The results also showed that the four traits were strong predictors of subjectively-rated effectiveness cri- teria for the total sample of firms, but were strong predictors of objective criteria such as return-on-assets and sales growth only for larger firms. This paper suggests that culture can be studied as an integral part of the adaptation process of organizations and that specific eulture traits may be useful predictors of perfor- mance and effectiveness. The paper also illustrates how qual- itative case studies and inductive theory building can be combined with quantitative comparisons and theory-testing to make progress on specific aspects of organizational culture research.

Psychological empowerment: Issues and illustrations

Abstract: Discussed several issues related to psychological empowerment. The thesis of this paper is that the development of a universal and global measure of psychological empowerment may not be a feasible or appropriate goal. I begin by distinguishing between empowerment processes and outcomes. Underlying assumptions are discussed including the notion that empowerment differs across people, contexts, and times. A nomological network that includes intrapersonal, interactional, and behavioral components is also presented. Two examples of psychological empowerment for voluntary service organization members and members of a mutual help organization are described to help illustrate differences in the specific variables that may be used to measure psychological empowerment in different populations and settings.

Diagnosability of discrete-event systems

Abstract: Fault detection and isolation is a crucial and challenging task in the automatic control of large complex systems We propose a discrete-event system (DES) approach to the problem of failure diagnosis We introduce two related notions of diagnosability of DES's in the framework of formal languages and compare diagnosability with the related notions of observability and invertibility We present a systematic procedure for detection and isolation of failure events using diagnosers and provide necessary and sufficient conditions for a language to be diagnosable The diagnoser performs diagnostics using online observations of the system behavior; it is also used to state and verify off-line the necessary and sufficient conditions for diagnosability These conditions are stated on the diagnoser or variations thereof The approach to failure diagnosis presented in this paper is applicable to systems that fall naturally in the class of DES's; moreover, for the purpose of diagnosis, most continuous variable dynamic systems can be viewed as DES's at a higher level of abstraction >

Modeling the Drop-Out Mechanism in Repeated-Measures Studies

Abstract: Subjects often drop out of longitudinal studies prematurely, yielding unbalanced data with unequal numbers of measures for each subject. Modern software programs for handling unbalanced longitudinal data improve on methods that discard the incomplete cases by including all the data, but also yield biased inferences under plausible models for the drop-out process. This article discusses methods that simultaneously model the data and the drop-out process within a unified model-based framework. Models are classified into two broad classes—random-coefficient selection models and random-coefficient pattern-mixture models—depending on how the joint distribution of the data and drop-out mechanism is factored. Inference is likelihood-based, via maximum likelihood or Bayesian methods. A number of examples in the literature are placed in this framework, and possible extensions outlined. Data collection on the nature of the drop-out process is advocated to guide the choice of model. In cases where the drop-...

In the Mind of the Actor: The Structure of Adolescents' Achievement Task Values and Expectancy-Related Beliefs

Abstract: The authors assessed the dimensionality of and relations between adolescents' achievement-related beliefs and self perceptions, focusing on subjective valuing of achievement. Beliefs derived from expectancy-value theory (adolescents' valuing of achievement activities, expectancies for success and ability perceptions, and perceptions of task difficulty) were assessed. Adolescents completed questionnaires once a year for 2 years. Confirmatory factor analyses indicated that achievement-related beliefs separate into three task values factors (interest, perceived importance, and perceived utility), one expectancy/ability factor (comprising beliefs about one's competence, expectancies for success, and performance perceptions), and two task difficulty factors (perceptions of difficulty and perceptions of effort required to do well). Task values and ability perceptions factors were positively related to each other and negatively correlated to perceptions of task difficulty.

Textbook of Gastroenterology

Abstract: Textbook of gastroenterology , Textbook of gastroenterology , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

Social consequences of psychiatric disorders, I: Educational attainment.

Abstract: Objective This is the first in a series of investigations of the social consequences of psychiatric disorders based on the National Comorbidity Survey. Data on the relationship between preexisting psychiatric disorders and subsequent educational attainment are presented. Method The National Comorbidity Survey is a nationally representative survey of 8,098 respondents in the age range 15-54 years. A subsample of 5,877 respondents completed a structured psychiatric interview and a detailed risk factor battery. Diagnoses of DSM-III-R anxiety disorders, mood disorders, substance use disorders, and conduct disorder were generated, and survival analyses were used to project data on school terminations to the total U.S. population. Results Early-onset psychiatric disorders are present in more than 3.5 million people in the age range of the National Comorbidity Survey who did not complete high school and close to 4.3 million who did not complete college. The most important disorders are conduct disorder among men and anxiety disorders among women. The proportion of school dropouts with psychiatric disorders has increased dramatically in recent cohorts, and persons with psychiatric disorders currently account for 14.2% of high school dropouts and 4.7% of college dropouts. Conclusions Early-onset psychiatric disorders probably have a variety of adverse consequences. The results presented here show that truncated educational attainment is one of them. Debate concerning whether society can afford universal insurance coverage for the treatment of mental disorders needs to take these consequences into consideration.

The dominant logic: retrospective and extension

Abstract: This paper briefly reviews some history of the concept of dominant logic, and then elaborates some of the ways in which the authors have further developed this concept in recent years. Discussion focuses on the dominant logic as a filter, on the dominant logic as a level of strategic analysis, on the unlearning (forgetting) curve, on the dominant logic as an emergent property of organizations as complex adaptive systems, and on the relationship between organizational stability and the dominant logic. Throughout emphasis is given to the inherent nonlinear nature of organizations and the mental models that they create.

Developments in nonholonomic control problems

Abstract: Provides a summary of recent developments in control of nonholonomic systems. The published literature has grown enormously during the last six years, and it is now possible to give a tutorial presentation of many of these developments. The objective of this article is to provide a unified and accessible presentation, placing the various models, problem formulations, approaches, and results into a proper context. It is hoped that this overview will provide a good introduction to the subject for nonspecialists in the field, while perhaps providing specialists with a better perspective of the field as a whole. The paper is organized as follows: introduction to nonholonomic control systems and where they arise in applications, classification of models of nonholonomic control systems, control problem formulations, motion planning results, stabilization results, and current and future research topics.

Self-channeling of high-peak-power femtosecond laser pulses in air

Abstract: The self-channeling of ultrashort laser pulses through 20 m of air was demonstrated. The channeled pulse was measured to have 0.75 mJ of energy, a diameter of 80 microm FWHM, and a modulated spectrum. All these values were measured to be fairly constant during the propagation of the pulse. A preliminary model is shown to explain these results.

Empowerment theory, research, and application

Abstract: This introduction to the special issue briefly reviews the meaning and significance of the empowerment concept and problems associated with the proliferation of interest in empowerment. We identify some of the topics not included in this issue and relate those to the many broad and diverse areas of psychological empowerment theory and community-based research and intervention that are covered. We present synopses of each article along with some of the themes and lessons cutting across the frameworks, studies, and applications. These include a wide diversity of settings, fairly representative of empowerment interventions, and, at the same time, improved clarity (if not unanimity) of definitions and measurement, which has been a problem in much empowerment research and intervention.

High-Rate, Gas-Phase Growth of MoS2 Nested Inorganic Fullerenes and Nanotubes

Abstract: The gas-phase reaction between MoO3-x and H(2)S in a reducing atmosphere at elevated temperatures (800 degrees to 950 degrees C) has been used to synthesize large quantities of an almost pure nested inorganic fullerene (IF) phase of MoS(2). A uniform IF phase with a relatively narrow size distribution was obtained. The synthesis of IFs appears to require, in addition to careful control over the growth conditions, a specific turbulent flow regime. The x-ray spectra of the different samples show that, as the average size of the IF decreases, the van der Waals gap along the c axis increases, largely because of the strain involved in folding of the lamella. Large quantities of quite uniform nanotubes were obtained under modified preparation conditions.

Toward a better definition of the restless legs syndrome

Abstract: A large International Restless Legs Syndrome (RLS) Study Group has been formed. As its first task, the group has taken upon itself the role of definig the clinical features of the RLS. As minimal criteria for diagnosis, the group proposes the following four features: (a) desire to move the extremities, often associated with paresthesias/dysesthesias; (b) motor restlessness; (c) worsening of symptoms at rest with at least temporary relief by activity, and (d) worsening of symptoms in the evening or night. Other features commonly seen in RLS include sleep disturbance, periodic limb movements in sleep and similar involuntary movements while awake, a normal neurological examination in the idiopathic from, a tendency for the symptoms to be worse in middle to older age, and, in some cases, a family history suggestive of an autosomal dominant mode of inheritance.