Showing papers by "University of Illinois at Urbana–Champaign published in 1987"

Dynamics of the dissipative two-state system

Abstract: This paper presents the results of a functional-integral approach to the dynamics of a two-state system coupled to a dissipative environment. It is primarily an extended account of results obtained over the last four years by the authors; while they try to provide some background for orientation, it is emphatically not intended as a comprehensive review of the literature on the subject. Its contents include (1) an exact and general prescription for the reduction, under appropriate circumstances, of the problem of a system tunneling between two wells in the presence of a dissipative environment to the "spin-boson" problem; (2) the derivation of an exact formula for the dynamics of the latter problem; (3) the demonstration that there exists a simple approximation to this exact formula which is controlled, in the sense that we can put explicit bounds on the errors incurred in it, and that for almost all regions of the parameter space these errors are either very small in the limit of interest to us (the "slow-tunneling" limit) or can themselves be evaluated with satisfactory accuracy; (4) use of these results to obtain quantitative expressions for the dynamics of the system as a function of the spectral density $J(\ensuremath{\omega})$ of its coupling to the environment. If $J(\ensuremath{\omega})$ behaves as ${\ensuremath{\omega}}^{s}$ for frequencies of the order of the tunneling frequency or smaller, the authors find for the "unbiased" case the following results: For $sl1$ the system is localized at zero temperature, and at finite $T$ relaxes incoherently at a rate proportional to $\mathrm{exp}\ensuremath{-}{(\frac{{T}_{0}}{T})}^{1\ensuremath{-}s}$. For $sg2$ it undergoes underdamped coherent oscillations for all relevant temperatures, while for $1lsl2$ there is a crossover from coherent oscillation to overdamped relaxation as $T$ increases. Exact expressions for the oscillation and/or relaxation rates are presented in all these cases. For the "ohmic" case, $s=1$, the qualitative nature of the behavior depends critically on the dimensionless coupling strength $\ensuremath{\alpha}$ as well as the temperature $T$: over most of the ($\ensuremath{\alpha}$,$T$) plane (including the whole region $\ensuremath{\alpha}g1$) the behavior is an incoherent relaxation at a rate proportional to ${T}^{2\ensuremath{\alpha}\ensuremath{-}1}$, but for low $T$ and $0l\ensuremath{\alpha}l\frac{1}{2}$ the authors predict a combination of damped coherent oscillation and incoherent background which appears to disagree with the results of all previous approximations. The case of finite bias is also discussed.

Least-Squares Fitting of Two 3-D Point Sets

Abstract: Two point sets {pi} and {p'i}; i = 1, 2,..., N are related by p'i = Rpi + T + Ni, where R is a rotation matrix, T a translation vector, and Ni a noise vector. Given {pi} and {p'i}, we present an algorithm for finding the least-squares solution of R and T, which is based on the singular value decomposition (SVD) of a 3 × 3 matrix. This new algorithm is compared to two earlier algorithms with respect to computer time requirements.

Algorithms in Combinatorial Geometry

Abstract: This book offers a modern approach to computational geo- metry, an area thatstudies the computational complexity of geometric problems. Combinatorial investigations play an important role in this study.

Terms of empowerment/exemplars of prevention: toward a theory for community psychology.

Abstract: In order to develop theory any community of scientists must agree as to what constitutes its phenomena of interest. A distinction is made between phenomena of interest and exemplars. The concept "prevention" is viewed as an exemplar, whereas the concept "empowerment" is suggested as a leading candidate for the title "phenomena of interest" to Community Psychology. The ecological nature of empowerment theory is described, and some of the terms of empowerment (definitions, conditions, and periods of time) are explicated. Eleven assumptions, presuppositions, and hypotheses are offered as guidelines for theory development and empirical study.

Validity and reliability of the Experience-Sampling Method.

Abstract: To understand the dynamics of mental health, it is essential to develop measures for the frequency and the patterning of mental processes in every-day-life situations. The Experience-Sampling Method (ESM) is an attempt to provide a valid instrument to describe variations in self-reports of mental processes. It can be used to obtain empirical data on the following types of variables: (a) frequency and patterning of daily activity, social interaction, and changes in location; (b) frequency, intensity, and patterning of psychological states, i.e., emotional, cognitive, and conative dimensions of experience; (c) frequency and patterning of thoughts, including quality and intensity of thought disturbance. The article reviews practical and methodological issues of the ESM and presents evidence for its short-and long-term reliability when used as an instrument for assessing the variables outlined above.

Spin glasses and the statistical mechanics of protein folding

Abstract: The theory of spin glasses was used to study a simple model of protein folding. The phase diagram of the model was calculated, and the results of dynamics calculations are briefly reported. The relation of these results to folding experiments, the relation of these hypotheses to previous protein folding theories, and the implication of these hypotheses for protein folding prediction schemes are discussed.

The Use of Tensors to Describe and Predict Fiber Orientation in Short Fiber Composites

Abstract: The properties of a set of even‐order tensors, used to describe the probability distribution function of fiber orientation in suspensions and composites containing short rigid fibers, are reviewed These tensors are related to the coefficients of a Fourier series expansion of the probability distribution function If an n‐th‐order tensor property of a composite can be found from a linear average of a transversely isotropic tensor over the distribution function, then predicting that property only requires knowledge of the n‐th‐order orientation tensor Equations of change for the second‐ and fourth‐order tensors are derived; these can be used to predict the orientation of fibers by flow during processing A closure approximation is required in the equations of change A hybrid closure approximation, combining previous linear and quadratic forms, performs best in the equations of change for planar orientation The accuracy of closure approximations is also explored by calculating the mechanical properties o

Experience and brain development.

Abstract: This article considers how experience can influence the developing and mature brain and proposes a new categorization scheme based upon the type of information stored and the brain mechanisms that appear to be involved in storing it. In this scheme, experience-expectant information storage refers to incorporation of environmental information that is ubiquitous in the environment and common to all species members, such as the basic elements of pattern perception. Experience-expectant processes appear to have evolved as a neural preparation for incorporating specific information: in many sensory systems, synaptic connections between nerve cells are overproduced, and a subsequent selection process occurs in which aspects of sensory experience determine the pattern of connections that remains. Experience-dependent information storage refers to incorporation of environmental information that is idiosyncratic, or unique to the individual, such as learning about one's specific physical environment or vocabulary. The neural basis of experience-dependent processes appears to involve active formation of new synaptic connections in response to the events providing the information to be stored. Although these processes probably do not occur entirely independently of one another in development, the categories offer a new view more in accord with neural mechanisms than were terms like "critical" or "sensitive period."

The Endocrinology and Developmental Biology of the Prostate

Abstract: I. Introduction MALE accessory sex glands such as the prostate, seminal vesicle, and bulbourethral gland have served in various capacities as models for investigating the action of androgens in regulating epithelial growth, RNA and protein synthesis, and secretory activity. The most extensively studied gland of this group is the prostate. This gland is found exclusively in mammals and produces many components of semen such as fructose, zinc ions, and various proteins important for the formation of the copulatory plug in rodents. The impetus for investigating regulation of prostatic growth and function stems in part from the many pathological complications which affect this gland. The prostate is the site of various types of inflammatory and infectious conditions (1) as well as benign and malignant proliferative changes in aging males. Despite extensive research, little of the pathogenesis or natural history of these diseases has been elucidated (2). Benign prostatic hypertrophy (BPH), a disease in which t...

Learning Word Meanings From Context During Normal Reading

Abstract: This study investigated incidental learning of word meanings from context during normal reading. A total of 352 students in third, fifth, and seventh grades read either expository or narrative passages selected from grade-level textbooks, and after six days were tested on their knowledge of difficult words from the passages. Small but reliable gains in knowledge of words from the passages read were found at all grade and ability levels. Effects of word and text properties on learning from context were examined in some detail. Word properties investigated included length, morphological complexity, and part of speech. Text properties included the strength of contextual support for each word, readability as measured by standard formulas, and several measures of density of difficult words. Among the word properties, only conceptual difficulty was significantly related to learning from context. Among the text properties, learning from context was most strongly influenced by the proportion of unfamiliar words t...

Growth of single-crystal TiN/VN strained-layer superlattices with extremely high mechanical hardness

Abstract: Single‐crystal TiN/VN strained‐layer superlattices (SLS’s) with layer thicknesses lTiN =lVN =λ/2 (where λ is the period of the superlattice) ranging from 0.75 to 16 nm have been grown on MgO(100 ) substrates by reactive magnetron sputtering. Cross‐sectional transmission electron microscopy (TEM) and x‐ray diffraction examinations showed that the films were single crystals exhibiting coherent interfaces and several orders of superlattice reflections. There was no evidence in either plan‐view or cross‐sectional TEM analyses of misfit interfacial dislocation arrays. The primary defects observed were dislocation loops with a diameter of 8–10 nm extending through several layers and small defects with a diameter of 1–2 nm that were confined within single layers. Microindentation hardness values H, measured as a function of λ in films with a total thickness of 2.5 μm, increased from 2035±280 kg mm−2 for Ti0.5V0.5N alloys (i.e., λ=0) to reach a maximum of 5560±1000 kg mm−2 at λ=5.2 nm and then decreased rapidly t...

Guided Self-Scheduling: A Practical Scheduling Scheme for Parallel Supercomputers

Abstract: This paper proposes guided self-scheduling, a new approach for scheduling arbitrarily nested parallel program loops on shared memory multiprocessor systems. Utilizing loop parallelism is clearly most crucial in achieving high system and program performance. Because of its simplicity, guided self-scheduling is particularly suited for implementation on real parallel machines. This method achieves simultaneously the two most important objectives: load balancing and very low synchronization overhead. For certain types of loops we show analytically that guided self-scheduling uses minimal overhead and achieves optimal schedules. Two other interesting properties of this method are its insensitivity to the initial processor configuration (in time) and its parameterized nature which allows us to tune it for different systems. Finally we discuss experimental results that clearly show the advantage of guided self-scheduling over the most widely known dynamic methods.

D1 dopamine receptor--the search for a function: a critical evaluation of the D1/D2 dopamine receptor classification and its functional implications.

Abstract: The present review focuses on the hypothesized D1/D2 dopamine (DA) receptor classification, originally based on the form of receptor coupling to adenylate cyclase activity. The pharmacological effects of compounds exhibiting putative selective agonist or antagonist profiles at those DA receptors positively coupled to adenylate cyclase activity (D1 DA receptors) are extensively reviewed. Comparisons are made with the effects of putative selective D2 DA receptor agonists and antagonists, and on the basis of this work, the DA receptor classification is critically evaluated. A variety of biochemical, behavioral, and electrophysiological evidence is presented which supports the view that D1 and D2 DA receptors can interact in both an opposing and synergistic fashion. Particular attention is focused on the possibility that D1 receptor stimulation is required to enable the expression of certain D2 receptor-mediated effects, and the functional consequences of this form of interaction are considered. A hypothetical model is presented which considers how both the opposing and enabling forms of interaction between D1 and D2 DA receptors can control behavioral expression. Finally, the clinical relevance of this work is discussed and the potential use of selective D1 receptor agonists and antagonists in the treatment of psychotic states and Parkinson's disease is considered.

Audience Activity and Soap Opera Involvement: A Uses and Effects Investigation.

Abstract: This investigation examined the role of motives, attitudes, and audience activity in explaining the affective, cognitive, and behavioral involvement of 328 daytime soap opera viewers. Because inter correlations were found among motives, attitudes, activities, and involvement variables, canonical correlation analysis was used. There were two multivariate patterns. First, except for viewing to pass time, more salient viewing motivations (especially exciting entertainment and social utility), perceived realism, viewing intention, and attention were related to parasocial interaction, post viewing cognition, and post viewing discussion. Second, viewing for social utility, but not for voyeurism, and the lack of realism were related to post viewing discussion, but not to parasocial interaction. These audience orientations and the role of involvement in media uses and effects were discussed.

A New Model for the Equilibrium Shape of Raindrops

Abstract: The equilibrium shape of raindrops has been determined from Laplace's equation using an internal hydrostatic pressure with an external aerodynamic pressure based on measurements for a sphere but adjusted for the effect of distortion. The drop shape was calculated by integration from the upper pole with the initial curvature determined by iteration on the drop volume. The shape was closed at the lower pole by adjusting either the pressure drag or the drop weight to achieve an overall force balance. Model results provide bounds on the axis ratio of raindrops with an uncertainty of about 1% and very good agreement with extensive wind tunnel measurements for moderate to large water drops. The model yields the peculiar asymmetric shape of raindrops: a singly curved surface with a flattened base and a maximum curvature just below the major axis. A close match was found between model shapes and profiles obtained from photos of water drops for diameters up to 5 mm. Coefficients are provided for computing...

Critical Issues in Information Systems Research

Abstract: From the Publisher: Contains critical contributions by seventeen scholars, each writing on a different issue of major importance to information systems research. The book is divided into two sections. In Part I, chapters present a broad view of practice, including its sociology of knowledge, the responsibility of its professionals, and the effectiveness of its tools and procedures. In Part II, chapters focus on the social context of information systems. Contributors address the way we think about and research the organizational antecedents and consequences of information systems, their diffusion, and our ability to understand their repercussions in the wider network of changing social relations. Topics covered include semantics, systems analysis, system design, software engineering models, managerial expert systems, information systems in organization theory, a research agenda for a transaction cost approach to information systems, and much more.

Rapid change in the symbolic functioning of very young children

Abstract: A remarkable difference in the understanding of the symbolic relation between a scale model and the larger space that it represented was displayed by two age groups of young children. Three-year-old children who observed an object being hidden in a model knew where to find an analogous object hidden in the corresponding location in a room, but 2.5-year-old children did not. The success of the group of older children reveals an advance in their cognitive flexibility: they think of a model in two ways at the same time--both as the thing itself and as a symbol for something else.

Ribosomal RNA sequence suggests microsporidia are extremely ancient eukaryotes

Abstract: A comparative sequence analysis of the 18S small subunit ribosomal RNA (rRNA) of the microsporidium Vairimorpha necatrix is presented. The results show that this rRNA sequence is more unlike those of other eukaryotes than any known eukaryote rRNA sequence. It is concluded that the lineage leading to microsporidia branched very early from that leading to other eukaryotes.

A Nonparametric Approach for Assessing Latent Trait Unidimensionality.

Abstract: Assuming a nonparametric family of item response theory models, a theory-based procedure for testing the hypothesis of unidimensionality of the latent space is proposed. The asymptotic distribution of the test statistic is derived assuming unidimensionality, thereby establishing an asymptotically valid statistical test of the unidimensionality of the latent trait. Based upon a new notion of dimensionality, the test is shown to have asymptotic power 1. A 6300 trial Monte Carlo study using published item parameter estimates of widely used standardized tests indicates conservative adherence to the nominal level of significance and statistical power averaging 81 out of 100 rejections for examinee sample sizes and psychological test lengths often incurred in practice.

Social stereotypes and information-processing strategies: The impact of task complexity.

Abstract: Subjects read information about a defendant in a criminal trial with initial instructions to judge either his guilt (guilt judgment objective) or his aggressiveness (trait judgment objective). The defendant was either Hispanic or ethnically nondescript. After considering the evidence, subjects made both guilt and aggressiveness judgments (regardless of which type of judgment they were instructed to make at the time they read the information) and then recalled as much of the information they read as they could. Results favored the hypothesis that when subjects face a complex judgmental situation, they use stereotypes (when available and relevant) as a way of simplifying the judgment. Specifically, they use the stereotype as a central theme around which they organize presented evidence that is consistent with it, and they neglect inconsistent information. Subjects with a (complex) guilt judgment objective judged the defendant to be relatively more guilty and aggressive and recalled more negative information about him if he was Hispanic than if he was ethnically nondescript. In contrast, subjects with a (simple) trait judgment objective did not perceive either the guilt or aggressiveness of the two defendants to be appreciably different, and did not display any significant bias in their recall of the evidence. These and other results are discussed in terms of the information-processing strategies subjects are likely to use when they expect to make different types of judgments.

Feedback linearizing control of switched reluctance motors

Abstract: Motivated by technological advances in power electronics and signal processing, and by the interest in using direct drives for robot manipulators, we investigate the control problem of high-performance drives for switched reluctance motors (SRM's). SRM's are quite simple, low cost, and reliable motors as compared to the widely used dc motors. However, the SRM presents a coupled nonlinear multivariable control structure which calls for complex nonlinear control design in order to achieve high dynamic performances. We first develop a detailed nonlinear model which matches experimental data and establish an electronic commutation strategy. Then, on the basis of recent nonlinear control techniques, we design a state feedback control algorithm which compensates for all the nonlinearities and decouples the effect of stator phase currents in the torque production. The position dependent logic of the electronic commutator assigns control authority to one phase, which controls the motion, while the remaining phase currents are forced to decay to zero. Simulations for a direct drive, single link manipulator with the SRM are reported, which show the control performance of the algorithm we propose in nominal conditions and test its robustness versus the most critical parameter uncertainties of payload mass and stator resistance.

AIDS, homophobia and biomedical discourse: An epidemic of signification

Abstract: (1987). AIDS, homophobia and biomedical discourse: An epidemic of signification. Cultural Studies: Vol. 1, No. 3, pp. 263-305.

An integral manifold approach to the feedback control of flexible joint robots

Abstract: The control problem for robot manipulators with flexible joints is considered. The results are based on a recently developed singular perturbation formulation of the manipulator equations of motion where the singular perturbation parameter µ is the inverse of the joint stiffness. For this class of systems it is known that the reduced-order model corresponding to the mechanical system under the assumption of perfect rigidity is globally linearizable via nonlinear static-state feedback, but that the full-order flexible system is not, in general, linearizable in this manner. The concept of integral manifold is utilized to represent the dynamics of the slow subsystem. The slow subsystem reduces to the rigid model as the perturbation parameter µ tends to zero. It is shown that linearizability of the rigid model implies linearizability of the flexible system restricted to the integral manifold. Based on a power series expansion of the integral manifold around µ = 0, it is shown how to approximate the feedback linearizing control to any order in µ. The result is then an approximate feedback linearization which, assuming stability of the fast variables, linearizes the system for all practical purposes.