Showing papers by "University of Massachusetts Amherst published in 1987"

Attitudes, Traits, and Actions: Dispositional Prediction of Behavior in Personality and Social Psychology

Abstract: Publisher Summary In the domain of personality psychology, the trait concept has carried the burden of dispositional explanation. A multitude of personality traits has been identified and new trait dimensions continue to join the growing list. In a similar fashion, the concept of attitude has been the focus of attention in the explanations of human behavior offered by social psychologists. Numerous attitudes have been assessed over the years and, as new social issues emerge, additional attitudinal domains are explored. The chapter provides little evidence to support the postulated existence of stable, underlying attitudes within the individual, which influence both verbal expressions and actions. It examines the relation between two or more actions that were assumed to reflect the same underlying disposition. The aggregation of responses across time, contexts, targets, or actions or across a combination of these elements permits the inferences of dispositions at varying levels of generality.

Modeling and Segmentation of Noisy and Textured Images Using Gibbs Random Fields

Abstract: This paper presents a new approach to the use of Gibbs distributions (GD) for modeling and segmentation of noisy and textured images. Specifically, the paper presents random field models for noisy and textured image data based upon a hierarchy of GD. It then presents dynamic programming based segmentation algorithms for noisy and textured images, considering a statistical maximum a posteriori (MAP) criterion. Due to computational concerns, however, sub-optimal versions of the algorithms are devised through simplifying approximations in the model. Since model parameters are needed for the segmentation algorithms, a new parameter estimation technique is developed for estimating the parameters in a GD. Finally, a number of examples are presented which show the usefulness of the Gibbsian model and the effectiveness of the segmentation algorithms and the parameter estimation procedures.

Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism

Abstract: The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2–4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits.

Can the gel point of a cross-linking polymer be detected by the G′ – G″ crossover?

Abstract: Dynamic mechanical measurements allow direct determination of the instant at which a network polymer gels. In such an experiment, the evolution of G′(t,ω0) and G″ (t,ω0) is measured in small amplitude oscillatory shear as a function of cross-linking time t. The frequency ω0 is kept constant throughout. At the beginning of the experiment, G″ is orders of magnitude larger than G′, and at completion of reaction, this order is reversed. It recently has been suggested by Tung and Dynes that the gel point (GP) might occur at the time at which G′ and G″ cross each other. However, there is much dispute whether GP occurs exactly at the crossover or just somewhere in its vicinity. This study resolves the dispute by modeling the rheological behavior at GP: There is only one class of network polymers for which GP coincides with the crossover. This class of polymers exhibits, when reaching GP, power law relaxation G(t) ∼ t−n with a specific exponent value n = 1/2. Examples are stoichiometrically balanced network polymers and networks with excess cross-linker, however, only at temperatures much above the glass transition. Otherwise, the power law behavior would be masked by vitrification. Power law relaxation seems to be property of polymers at GP in general. However, some polymers have a different exponent value, n ≠ 1/2, in which case the crossover occurs before GP (for n 1/2); i.e. the crossover cannot be used for detecting GP. While there are no networks known to us with n 1/2. A new method is suggested for measuring GP of these imbalanced networks.

Motivational Influences on Impression Formation: Outcome Dependency, Accuracy-Driven Attention, and Individuating Processes

Abstract: How might being outcome dependent on another person influence the processes that one uses to form impressions of that person? We designed three experiments to investigate this question with respect to short-term, task-oriented outcome dependency. In all three experiments, subjects expected to interact with a young man formerly hospitalized as a schizophrenic, and they received information about the person's attributes in either written profiles or videotapes. In Experiment 1, short-term, task-oriented outcome dependency led subjects to use relatively individuating processes (i.e., to base their impressions o f the patient on his particular attributes), even under conditions that typically lead subjects to use relatively category-based processes (i.e., to base their impressions on the patient's schizophrenic label). Moreover, in the conditions that elicited individuating processes, subjects spent more time attending to the patient's particular attribute information. Experiment 2 demonstrated that the attention effects in Experiment 1 were not merely a function of impression positivity and that outcome dependency did not influence the impression formation process when attribute information in addition to category-level information was unavailable. Finally, Experiment 3 manipulated not outcome dependency but theattentional goal of forming an accurate impression. We found that accuracy-driven attention to attribute information also led t o individuating processes. The results of the three experiments indicate that there are important influences of outcome dependency on impression formation. These results are consistent with a model in which the tendency for short-term, task-oriented outcome dependency to facilitate individuating impression formation processes is mediated by an increase in accuracy-driven attention to attribute information.

Motor schema based navigation for a mobile robot: An approach to programming by behavior

Abstract: Motor schemas are proposed as a basic unit of behavior specification for the navigation of a mobile robot. These are multiple concurrent processes which operate in conjunction with associated perceptual schemas and contribute independently to the overall concerted action of the vehicle. The motivation behind the use of schemas for this domain is drawn from neuroscientific, psychological and robotic sources. A variant of the potential field method is used to produce the appropriate velocity and steering commands for the robot. An implementation strategy based on available tools at UMASS is described. Simulation results show the feasibility of this approach.

Search for short-lived axions in an electron-beam-dump experiment.

Abstract: We report results of an electron-beam-dump search for neutral particles with masses in the range 1 to 15 MeV and lifetimes τ between 10^-14 and 10^-10 s. No evidence was found for such an object. We fule out the existence of any 1.8-MeV pseudoscalar boson with τ>8.2×10^-15 s and an absorption cross section in matter less than 1 mb per nucleon, and exclude τ>1×10^-14 s were its cross section to equal 50 mb per nucleon. In conjunction with measurements of the electron’s anomalous magnetic moment, this experiment shows that the narrow positron peaks observed in heavy-ion collisions at the Gessellschaft fur Schwerionenforschung are not due to an elementary pseudoscalar.

Radiation and scattering from a microstrip patch on a uniaxial substrate

Abstract: The problem of a rectangular microstrip antenna printed on a uniaxially anisotropic substrate is treated. The effect of anisotropy on the resonant frequency and surface wave excitation of the antenna is considered, and the radar cross section (RCS) of the antenna is calculated. The RCS calculation includes the effect of the load impedance (antenna mode scattering). Results for the resonant frequency of a patch on a uniaxial substrate are compared with measurements, and the RCS of a patch on an isotropic substrate is compared with measurements. The derivation of the uniaxial Green's function in spectral form, the associated moment method analysis for the input impedance and scattering of the microstrip patch, and the expressions for the far-zone fields of a source on a uniaxial substrate are presented.

Information retrieval by constrained spreading activation in semantic networks

Abstract: GRANT is an expert system for finding sources of funding given research proposals. Its search method-constrained spreading activation—makes inferences about the goals of the user and thus finds information that the user did not explicitly request but that is likely to be useful. The architecture of GRANT and the implementation of constrained spreading activation are described, and grant's performance is evaluated.

Fast area-efficient VLSI adders

Abstract: In this paper, we study area-time tradeoffs in VLSI for prefix computation using graph representations of this problem. Since the problem is intimately related to binary addition, the results we obtain lead to the design of area-time efficient VLSI adders. This is a major goal of our work: to design very low latency addition circuitry that is also area efficient. To this end, we present a new graph representation for prefix computation that leads to the design of a fast, area-efficient binary adder. The new graph is a combination of previously known graph representations for prefix computation, and its area is close to known lower bounds on the VLSI area of parallel prefix graphs. Using it, we are able to design VLSI adders having area A = 0(n log n) whose delay time is the lowest possible value, i. e. the fastest possible area-efficient VLSI adder.

I 3 R: a new approach to the design of document retrieval systems

Abstract: THE MOST EFFECTIVE METHOD OF IMPROVING THE RETRIEVAL PERFORMANCE OF A DOCUMENT RETRIEVAL SYSTEM IS TO ACQUIRE A DETAILED SPECIFICATION OF THE USER''S INFORMATION NEED. THE SYSTEM DESCRIBED IN THIS PAPER, (I(EXPONENT 3)R), PROVIDES A NUMBER OF FACILITIES AND SEARCH STRATEGIES BASED ON THIS APPROACH. THE SYSTEM USES A NOVEL ARCHITECTURE TO ALLOW MORE THAN ONE SYSTEM FACILITY TO BE USED AT A GIVEN STAGE OF A SEARCH SESSION. USERS INFLUENCE THE SYSTEM ACTIONS BY STATING GOALS THEY WISH TO ACHIEVE, BY EVALUATING SYSTEM OUTPUT, AND BY CHOOSING PARTICULAR FACILITIES DIRECT- LY. THE OTHER MAIN FEATURES OF (I(EXPONENT 3)R)) ARE AN EMPHASIS ON DOMAIN KNOWLEDGE USED FOR REFINING THE MODEL OF THE INFORMATION NEED, AND THE PROVISION OF A BROWSING MECHANISM THAT ALLOWS THE USER TO NAVIGATE THROUGH THE KNOWLEDGE BASE.

Cognitive Science: An Introduction

Abstract: Cognitive Science is a single-source undergraduate text that broadly surveys the theories and empirical results of cognitive science within a consistent computational perspective. In addition to covering the individual contributions of psychology, philosophy, linguistics, and artificial intelligence to cognitive science, the book has been revised to introduce the connectionist approach as well as the classical symbolic approach and adds a new chapter on cognitively related advances in neuroscience. Cognitive science is a rapidly evolving field that is characterized by considerable contention among different views and approaches. Cognitive Science presents these in a relatively neutral manner. It covers many new orientations theories and findings, embedding them in an integrated computational perspective and establishing a sense of continuity and contrast with more traditional work in cognitive science. The text assumes no prerequisite knowledge, introducing all topics in a uniform, accessible style. Many topics, such as natural language processing and vision, however, are developed in considerable depth, which allows the book to be used with more advanced undergraduates or even in beginning graduate settings. A Bradford Book

Precipitation Fluctuations over Northern Hemisphere Land Areas Since the Mid-19th Century.

Abstract: An extensive array of measurements extending back to the mid-19th century was used to investigate large-scale changes in precipitation over Northern Hemisphere land areas. Significant increases in mid-latitude precipitation and concurrent decreases in low-latitude precipitation have occurred over the last 30 to 40 years. Although these large-scale trends are consistent with general circulation model projections of precipitation changes associated with doubled concentrations of atmospheric carbon dioxide, they should be viewed as defining large-scale natural climatic variability. Additional work to refine regional variations and address potential network inhomogeneitics is needed. This study attempts to show secular precipitation fluctuations over hemispheric and continental-scale areas of the Northern Hemisphere.

Increasing the bandwidth of a microstrip antenna by proximity coupling

Abstract: The letter presents experimental results for a proximity-coupled microstrip patch antenna capable of 13% bandwidth. The impedance match (VSWR ≤ 2), copolarised radiation patterns and crosspolarised radiation were measured over this bandwidth to confirm operation. The construction is quite simple, consisting of a microstrip feedline on a substrate proximity-coupled to a rectangular microstrip patch on a covering superstrate; a small open-circuit tuning stub is connected in shunt with the feed line.

A Multivariate Analysis of Responses to Dissatisfaction

Abstract: Although consumer dissatisfaction is ubiquitous in the marketplace, empirical studies of dissatisfaction have been narrow in focus. This is especially true for studies of responses to dissatisfaction, for these investigations tend to ignore all dissatisfaction responses except complaint behavior. The study reported here replicates and extends an earlier investigation by concurrently examining three dissatisfaction responses—complaints, word of mouth, and brand switching intentions. Three sets of variables were examined in relationship to these responses: characteristics of the product problem, perceptions of the redress environment, and consumer characteristics. Complaint behavior and intention to switch brands showed strongest relationships with the first two types of variables. Word of mouth, on the other hand, seemed to be more heavily influenced by the consumer’s level of social interaction, a consumer characteristic. Findings indicate that the three dissatisfaction responses are independent in that they share little if any common variance and they seem to be influenced in different ways by the correlates studied.

The Urban Homeless: Estimating Composition and Size

Abstract: Although homelessness has been recognized as a serious and growing urban social problem, scientifically acceptable methods for estimating the composition and size of the homeless population have been lacking. A new research approach to estimating the size and composition of undomiciled urban populations is presented, and its utility is illustrated through a description of the literal homeless of Chicago. The homeless in the Chicago sample are unaffiliated persons living in extreme poverty, with high levels of physical and mental disability. Homelessness is interpreted as a manifestation of extreme poverty among persons without families in housing markets with declining stocks of inexpensive dwelling units suitable for single persons.

Using partial global plans to coordinate distributed problem solvers

Abstract: Communicating problem solvers can cooperate in various ways, such as negotiating over task assignments, exchanging partial solutions to converge on global results, and planning interactions that help each other perform their tasks better. We introduce a new framework that supports different styles of cooperation by using partial global plana to specify effective, coordinated actions for groups of problem solvers. In this framework, problem solvers summarise their local plans into node-plant that they selectively exchange to dynamically model network activity and to develop partial global plans. However, because network and problem characteristics can change and communication channels have delays and limited capacity, problem solvers' models and partial global plans may be incomplete, out-of-date, and inconsistent. Our mechanisms allow problem solvers to agree on consistent partial global plans when possible, and to locally form partial global plans that lead to satisfactory cooperation even in rapidly changing environments where complete agreement is impossible. In this paper, we describe the mechanisms, knowledge representations, and algorithms that we have developed for generating and maintaining partial global plans in a distributed system. We use experiments to illustrate how these mechanisms improve and promote cooperation in a variety of styles.

Scheduling Tasks with Resource Requirements in Hard Real-Time Systems

Abstract: This paper describes a heuristic approach for solving the problem of dynamically scheduling tasks in a real-time system where tasks have deadlines and general resource requirements. The crux of our approach lies in the heuristic function used to select the task to be scheduled next. The heuristic function is composed of three weighted factors. These factors explicitly consider information about real-time constraints of tasks and their utilization of resources. Simulation studies show that the weights for the various factors in the heuristic function have to be fine-tuned in order to obtain a degree of success in the range of 75-88 percent of that obtained via exhaustive search. However, modifying the approach to use limited backtracking improves the degree of success substantially to as high as 99.5 percent. This improvement is observed even when the initial set of weights are not tailored for a particular set of tasks. Simulation studies also show that in most cases the schedule determined by the heuristic algorithm is optimal or close to optimal.

Ultrastructure of the cytoskeleton in freeze-substituted pollen tubes ofNicotiana alata

Abstract: The ultrastructure of the cytoskeleton inNicotiana alata pollen tubes grownin vitro has been examined after rapid freeze fixation and freeze substitution (RF-FS). Whereas cytoplasmic microtubules (MTs) and especially microfilaments (MFs) are infrequently observed after conventional chemical fixation, they occur in all samples prepared by RF-FS. Cortical MTs are oriented parallel to the long axis of the pollen tube and usually appear evenly spaced around the circumference of the cell. They are always observed with other components in a structural complex that includes the following: 1. a system of MFs, in which individual elements are aligned along the sides of the MTs and crossbridged to them; 2. a system of cooriented tubular endoplasmic reticulum (ER) lying beneath the MTs, and 3. the plasma membrane (PM) to which the MTs appear to be extensively linked. The cortical cytoskeleton is thus structurally complex, and contains elements such as MFs and ER that must be considered together with the MTs in any attempt to elucidate cytoskeletal function. MTs are also observed within the vegetative cytoplasm either singly or in small groups. Observations reveal that some of these may be closely associated with the envelope of the vegetative nucleus. MTs of the generative cell, in contrast to those of the vegetative cytoplasm, occur tightly clustered in bundles and show extensive cross-bridging. These bundles, especially in the distal tail of the generative cell, are markedly undulated. MFs are observed commonly in the cytoplasm of the vegetative cell. They occur in bundles oriented predominantly parallel to the pollen tube axis. Although proof is not provided, we suggest that they are composed of actin and are responsible for generating the vigorous cytoplasmic streaming characteristic of living pollen tubes.

Coherent Cooperation Among Communicating Problem Solvers

Abstract: When two or more computing agents work on interacting tasks, their activities should be coordinated so that they cooperate coherently. Coherence is particularly problematic in domains where each agent has only a limited view of the overall task, where communication between agents is limited, and where there is no ``controller'' to coordinate the agents. Our approach to coherent cooperation in such domains is developed in the context of a distributed problem-solving network where agents cooperate to solve a single problem. The approach stresses the importance of sophisticated local control by which each problem-solving node integrates knowledge of the problem domain with (meta-level) knowledge about network coordination. This allows nodes to make rapid, intelligent local decisions based on changing problem characteristics with only a limited amount of intercommunication to coordinate these decisions. We describe three mechanisms that improve network coherence: 1) an organizational structure that provides a long-term framework for network coordination to guide each node's local control decisions; 2) a planner at each node that develops sequences of problem-solving activities based on the current situation; and 3) meta-level communication about the current state of local problem solving that enables nodes to dynamically refine the organization. We present a variety of problem-solving situations to show the benefits and limitations of these mechanisms, and we provide simulation results showing the mechanisms to be particularly cost effective in more complex problem-solving situations. We also discuss how these mechanisms might be of more general use in other distributed computing applications.

Synaptic circuits involving an individual retinogeniculate axon in the cat.

Abstract: In order to describe the circuitry of a single retinal X-cell axon in the lateral geniculate nucleus, we physiologically characterized such an axon in the optic tract and injected it intra-axonally with horseradish peroxidase. Subsequently, we recovered the axon and employed electron microscopic techniques to examine the distribution of synapses from 18% of its labeled terminals by reconstructing the unlabeled postsynaptic neurons through a series of 1,200 consecutive thin sections. We found remarkable selectivity for the axon's output, since only four of the 43 available neurons in a limited portion of the terminal arbor receive synapses from labeled terminals. Moreover, the distribution of these synapses on the four neurons, which we term cells 1 through 4, varies with respect to synapses from other classes of terminals that contact the same cells, including synapses from unlabeled retinal terminals. For cells 1 and 3, the labeled terminals provide 49% and 33%, respectively, of their retinal synapses, and these are located on both dendritic shafts and appendages. Synapses from the injected axon to these cells are thus integrated with those from other retinal axons. For cell 2, the labeled terminals provide 100% of its retinal synapses, but these synapses converge on clusters of dendritic appendages where they are integrated with convergent inhibitory inputs. Finally, for cell 4, the labeled terminals provide less than 2% of its retinal inputs, and these are distally located; we suggest that these synapses are remnants of physiologically inappropriate miswiring that occurs during development. The findings from this study support a concept of selectivity in neuronal circuitry in the mammalian central nervous system and also reveal some of the diverse integrative properties of neurons in the lateral geniculate nucleus.

A Generalized Spectral-Domain Green's Function for Multilayer Dielectric Substrates with Application to Multilayer Transmission Lines

Abstract: A generalized full-wave Green's function completely defining the field inside a multilayer dielectric structure due to a current element arbitrarily placed between any two layers is derived in two-dimensional spectral-domain form. It is derived by solving a "standard" form containing the current element with two substrates on either side of it, and using an iterative algorithm to take care of additional layers. Another iterative algorithm is then used to find the field in any layer in terms of the field expressions in the two layers of the "standard" form. The locations of the poles of the Green's function are predicted, and an asymptotic form is derived along with the asymptotic limit, by use of which the multilayer Green's function can be used in numerical methods as efficiently as the single-layer grounded-dielectric-substrate Green's function. This Green's function is then applied to a few multilayer transmission lines for which data are not found in the literature to date.