Showing papers by "Carnegie Mellon University published in 1994"

Dynamic Source Routing in Ad Hoc Wireless Networks.

Abstract: An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. In such an environment, it may be necessary for one mobile host to enlist the aid of other hosts in forwarding a packet to its destination, due to the limited range of each mobile host’s wireless transmissions. This paper presents a protocol for routing in ad hoc networks that uses dynamic source routing. The protocol adapts quickly to routing changes when host movement is frequent, yet requires little or no overhead during periods in which hosts move less frequently. Based on results from a packet-level simulation of mobile hosts operating in an ad hoc network, the protocol performs well over a variety of environmental conditions such as host density and movement rates. For all but the highest rates of host movement simulated, the overhead of the protocol is quite low, falling to just 1% of total data packets transmitted for moderate movement rates in a network of 24 mobile hosts. In all cases, the difference in length between the routes used and the optimal route lengths is negligible, and in most cases, route lengths are on average within a factor of 1.01 of optimal.

Distinguishing optimism from neuroticism (and trait anxiety, self-mastery, and self-esteem): a reevaluation of the Life Orientation Test

Abstract: Research on dispositional optimism as assessed by the Life Orientation Test (Scheier & Carver, 1985) has been challenged on the grounds that effects attributed to optimism are indistinguishable from those of unmeasured third variables, most notably, neuroticism. Data from 4,309 subjects show that associations between optimism and both depression and aspects of coping remain significant even when the effects of neuroticism, as well as the effects of trait anxiety, self-mastery, and self-esteem, are statistically controlled. Thus, the Life Orientation Test does appear to possess adequate predictive and discriminant validity. Examination of the scale on somewhat different grounds, however, does suggest that future applications can benefit from its revision. Thus, we also describe a minor modification to the Life Orientation Test, along with data bearing on the revised scale's psychometric properties.

Review of particle properties.

Abstract: This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 2205 new measurements from 667 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations. For the first time we cover searches for evidence of extra dimensions (both in the particle listings and in a new review). Another new review is on Grand Unified Theories. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.

The psychology of curiosity: A review and reinterpretation.

Abstract: Research on curiosity has undergone 2 waves of intense activity. The 1st, in the 1960s, focused mainly on curiosity's psychological underpinnings. The 2nd, in the 1970s and 1980s, was characterized by attempts to measure curiosity and assess its dimensionality. This article reviews these contributions with a concentration on the 1st wave. It is argued that theoretical accounts of curiosity proposed during the 1st period fell short in 2 areas: They did not offer an adequate explanation for why people voluntarily seek out curiosity, and they failed to delineate situational determinants of curiosity. Furthermore, these accounts did not draw attention to, and thus did not explain, certain salient characteristics of curiosity: its intensity, transience, association with impulsivity, and tendency to disappoint when satisfied. A new account of curiosity is offered that attempts to address these shortcomings. The new account interprets curiosity as a form of cognitively induced deprivation that arises from the perception of a gap in knowledge or understanding. Curiosity is the most superficial of all the affections; it changes its object perpetually; it has an appetite which is very sharp, but very easily satisfied; and it has always an appearance of giddiness, rest

Model checking and abstraction

Abstract: We describe a method for using abstraction to reduce the complexity of temporal-logic model checking. Using techniques similar to those involved in abstract interpretation, we construct an abstract model of a program without ever examining the corresponding unabstracted model. We show how this abstract model can be used to verify properties of the original program. We have implemented a system based on these techniques, and we demonstrate their practicality using a number of examples, including a program representing a pipelined ALU circuit with over 101300 states.

RAID: high-performance, reliable secondary storage

Abstract: Disk arrays were proposed in the 1980s as a way to use parallelism between multiple disks to improve aggregate I/O performance. Today they appear in the product lines of most major computer manufacturers. This article gives a comprehensive overview of disk arrays and provides a framework in which to organize current and future work. First, the article introduces disk technology and reviews the driving forces that have popularized disk arrays: performance and reliability. It discusses the two architectural techniques used in disk arrays: striping across multiple disks to improve performance and redundancy to improve reliability. Next, the article describes seven disk array architectures, called RAID (Redundant Arrays of Inexpensive Disks) levels 0–6 and compares their performance, cost, and reliability. It goes on to discuss advanced research and implementation topics such as refining the basic RAID levels to improve performance and designing algorithms to maintain data consistency. Last, the article describes six disk array prototypes of products and discusses future opportunities for research, with an annotated bibliography disk array-related literature.

A behavioral notion of subtyping

Abstract: The use of hierarchy is an important component of object-oriented design. Hierarchy allows the use of type families, in which higher level supertypes capture the behavior that all of their subtypes have in common. For this methodology to be effective, it is necessary to have a clear understanding of how subtypes and supertypes are related. This paper takes the position that the relationship should ensure that any property proved about supertype objects also holds for its subtype objects. It presents two ways of defining the subtype relation, each of which meets this criterion, and each of which is easy for programmers to use. The subtype relation is based on the specifications of the sub- and supertypes; the paper presents a way of specifying types that makes it convenient to define the subtype relation. The paper also discusses the ramifications of this notion of subtyping on the design of type families.

What's Mine Is Ours, or Is It? A Study of Attitudes about Information Sharing

Abstract: As technology for information access improves, people have more opportunities to share information. A theory of information sharing is advanced and we report the results of three experiments on attitudes about sharing technical work and expertise in organizations. Based on research on sensitive topics difficult to study in the field, we derived vignette-based measures of attitudes. Subjects read a description of an employee's encounter with a previously unhelpful coworker who subsequently requested help-in the form of a computer program or computer advice. The influence of prosocial attitudes and organizational norms is inferred from subjects' support of sharing despite the previous unhelpful behavior of the coworker. Experiments 1 and 3 demonstrated that greater self interest reduces support of sharing, but that a belief in organizational ownership of work encourages and mediates attitudes favoring sharing. Work experience and business schooling contribute to these attitudes. The theory asserts that information as expertise belongs to a special category of information that is part of people's identity and is self-expressive. Experiments 2 and 3 demonstrated that subjects felt computer expertise belonged more to its possessor than the computer program did but would share it more than the program. Hence, attitudes about information sharing depend on the form of the information. Sharing tangible information work may depend on prosocial attitudes and norms of organizational ownership; sharing expertise may depend on people's own self-expressive needs.

The role of emotion in believable agents

Abstract: Joseph Bates here is a notioti in the Arts of \"believable character.\" It does not mean an honest or reliable character, btit otie that provides the illtision of life, thtis permitting the atidience's stispension of disbelief The idea of believability has long been studied and explored in literatttre, theater, film, radio drama, and other media. Traditional character animators are among those artists who have sought to create believable characters, and the Disney animators of the 1930s made great strides toward this goal. The first page of the enormous classic reference work on Disney animaticjn [12] begins with these words:

Optimal and efficient path planning for partially-known environments

Abstract: The task of planning trajectories for a mobile robot has received considerable attention in the research literature. Most of the work assumes the robot has a complete and accurate model of its environment before it begins to move; less attention has been paid to the problem of partially known environments. This situation occurs for an exploratory robot or one that must move to a goal location without the benefit of a floorplan or terrain map. Existing approaches plan an initial path based on known information and then modify the plan locally or replan the entire path as the robot discovers obstacles with its sensors, sacrificing optimality or computational efficiency respectively. This paper introduces a new algorithm, D*, capable of planning paths in unknown, partially known, and changing environments in an efficient, optimal, and complete manner. >

A stereo matching algorithm with an adaptive window: theory and experiment

Abstract: A central problem in stereo matching by computing correlation or sum of squared differences (SSD) lies in selecting an appropriate window size. The window size must be large enough to include enough intensity variation for reliable matching, but small enough to avoid the effects of projective distortion. If the window is too small and does not cover enough intensity variation, it gives a poor disparity estimate, because the signal (intensity variation) to noise ratio is low. If, on the other hand, the window is too large and covers a region in which the depth of scene points (i.e., disparity) varies, then the position of maximum correlation or minimum SSD may not represent correct matching due to different projective distortions in the left and right images. For this reason, a window size must be selected adaptively depending on local variations of intensity and disparity. The authors present a method to select an appropriate window by evaluating the local variation of the intensity and the disparity. The authors employ a statistical model of the disparity distribution within the window. This modeling enables the authors to assess how disparity variation, as well as intensity variation, within a window affects the uncertainty of disparity estimate at the center point of the window. As a result, the authors devise a method which searches for a window that produces the estimate of disparity with the least uncertainty for each pixel of an image: the method controls not only the size but also the shape (rectangle) of the window. The authors have embedded this adaptive-window method in an iterative stereo matching algorithm: starting with an initial estimate of the disparity map, the algorithm iteratively updates the disparity estimate for each point by choosing the size and shape of a window till it converges. The stereo matching algorithm has been tested on both synthetic and real images, and the quality of the disparity maps obtained demonstrates the effectiveness of the adaptive window method. >

Hippocampal conjunctive encoding, storage, and recall: avoiding a trade-off.

Abstract: The hippocampus and related structures are thought to be capable of 1) representing cortical activity in a way that minimizes overlap of the representations assigned to different cortical patterns (pattern separation); and 2) modifying synaptic connections so that these representations can later be reinstated from partial or noisy versions of the cortical activity pattern that was present at the time of storage (pattern completion). We point out that there is a trade-off between pattern separation and completion and propose that the unique anatomical and physiological properties of the hippocampus might serve to minimize this trade-off. We use analytical methods to determine quantitative estimates of both separation and completion for specified parameterized models of the hippocampus. These estimates are then used to evaluate the role of various properties and of the hippocampus, such as the activity levels seen in different hippocampal regions, synaptic potentiation and depression, the multi-layer connectivity of the system, and the relatively focused and strong mossy fiber projections. This analysis is focused on the feedforward pathways from the entorhinal cortex (EC) to the dentate gyrus (DG) and region CA3. Among our results are the following: 1) Hebbian synaptic modification (LTP) facilitates completion but reduces separation, unless the strengths of synapses from inactive presynaptic units to active postsynaptic units are reduced (LTD). 2) Multiple layers, as in EC to DG to CA3, allow the compounding of pattern separation, but not pattern completion. 3) The variance of the input signal carried by the mossy fibers is important for separation, not the raw strength, which may explain why the mossy fiber inputs are few and relatively strong, rather than many and relatively weak like the other hippocampal pathways. 4) The EC projects to CA3 both directly and indirectly via the DG, which suggests that the two-stage pathway may dominate during pattern separation and the one-stage pathway may dominate during completion; methods the hippocampus may use to enhance this effect are discussed.

Situational coping and coping dispositions in a stressful transaction.

Abstract: After reporting dispositional coping styles, students reported situational coping and 4 classes of affect (from threat, challenge, harm, and benefit appraisals) 2 days before an exam, after the exam but before grades were posted, and after posting of grades. Coping did not predict lower levels of future distress; indeed, some coping seemed to induce feelings of threat. Feelings of harm before the exam induced several kinds of coping after the exam, mostly dysfunctional. Confidence about one's grade was a better predictor of emotions throughout than was coping. Dispositional coping predicted comparable situational coping at low-moderate levels in most cases. Coping dispositions did not reliably predict emotions, however, with these exceptions: Dispositional denial was related to threat, as was dispositional use of social support; dispositional use of alcohol was related to both threat and harm.

Routing in Ad Hoc Networks of Mobile Hosts

Abstract: An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration or standard support services. In such an environment, it may be necessary for one mobile host to enlist the aid of others in forwarding a packet to its destination due to the limited propagation range of each mobile host's wireless transmissions. Some previous attempts have been made to use conventional routing protocols for routing in ad hoc networks, treating each mobile host as a router. This position paper points out a number of problems with this design and suggests a new approach based on separate route discovery and route maintenance protocols.

The Geographic Sources of Innovation: Technological Infrastructure and Product Innovation in the United States

Abstract: The fate of regions and of nations increasingly depends upon ideas and innovations to facilitate growth. In recent years, geographers have made fundamental contributions to our understanding of the innovation process by exploring the diffusion of innovation, the location of R&D, and the geography of high-technology industry. This paper examines the geographic sources of innovation, focusing specifically on the relationship between product innovation and the underlying “technological infrastructure” of particular places. This infrastructure is comprised of agglomerations of firms in related manufacturing industries, geographic concentrations of industrial R&D, concentrations of university R&D, and business-service firms. Once in place, these geographic concentrations of infrastructure enhance the capacity for innovation, as regions come to specialize in particular technologies and industrial sectors. Geography organizes this infrastructure by bringing together the crucial resources and inputs for ...

House of Cards - Psychology and Psychotherapy Built on Myth

Abstract: In this book, Robyn Dawes critically examines some of the most cherished clinical assumptions and therapeutic methods now in use. He points out that we have all come under the sway of a "pop psych" view of the world, believing, for example, that self-esteem is an essential precursor to being a productive human being, that events in one's childhood determine one's fate as an adult, and that you have to love yourself before you can love another. Drawing on empirical research, Dawes systematically argues that none of the above is true and explores the debilitating effect these beliefs have on us. In addition, he takes issue with many of the treatment methods commonly used in therapy practices.

Optimal Investment and Consumption with Transaction Costs

Abstract: A complete solution is provided to the infinite-horizon, discounted problem of optimal consumption and investment in a market with one stock, one money market (sometimes called a "bond") and proportional transaction costs. The utility function may be of the form $c^p/p$, where $p < 0$ or $0 < p < 1$, or may be $\log c$. It is assumed that the interest rate for the money market is positive, the mean rate of return for the stock is larger than this interest rate, the stock volatility is positive and all these parameters are constant. The only other assumption is that the value function is finite; necessary conditions for this are given. In the Appendix (by S. Shreve), the sensitivity of the value function under the assumption $0 < p < 1$ is shown to be of the order of the transaction cost to the 2/3 power. This implies that the liquidity premium associated with small transaction costs is also of the order of the transaction cost to the 2/3 power. Because this power is less than 1, the marginal liquidity premium turns out to be infinite. The analysis of this paper and its Appendix relies on the concept of viscosity solutions to Hamilton-Jacobi-Bellman equations. A self-contained treatment of this subject, adequate for the present application, is provided.

Learning and Memory: An Integrated Approach

Abstract: CHAPTER 1: PERSPECTIVES ON LEARNING AND MEMORY: Learning and Adaptation Behaviourist and Cognitive Approaches CHAPTER 2: CLASSICAL CONDITIONING: Overview of Classical Conditioning Neural Basis of Classical Conditioning S-S or S-R Associations? CHAPTER 3: INSTRUMENTAL LEARNING: Overview of Instrumental Conditioning What is Associated? What is the Conditioned Stimulus? CHAPTER 4: REINFORCEMENT AND LEARNING: Overview Reward and Punishment Aversive Control of Behaviour CHAPTER 5: TRANSIENT MEMORIES: Conditioning Research versus Memory Research Sensory Memory CHAPTER 6: ACQUISITION OF MEMORIES: Introduction Practice and Trace Strength CHAPTER 7: RETENTION OF MEMORIES: Overview The Retention Function Spacing Effects Interference Retention of Emotionally Charged Material CHAPTER 8: RETRIEVAL OF MEMORIES: Overview of the Chapter CHAPTER 9: SKILL ACQUISITION: Overview of Skill Acquisition The Cognitive Stage CHAPTER 10: INDUCTIVE LEARNING: Overview of Inductive Learning Concept Acquisition Causal Inference CHAPTER 11: APPLICATIONS TO EDUCATION: The Goals of Education Psychology and Education Reading Instruction Mathematics Instruction.

Does the medium matter? The interaction of task type and technology on group performance and member reactions.

Abstract: The authors investigated the hypothesis that as group tasks pose greater requirements for member interdependence, communication media that transmit more social context cues will foster group performance and satisfaction. Seventy-two 3-person groups of undergraduate students worked in either computer-mediated or face-to-face meetings on 3 tasks with increasing levels of interdependence: an idea-generation task, an intellective task, and a judgment task. Results showed few differences between computer-mediated and face-to-face groups in the quality of the work completed but large differences in productivity favoring face-to-face groups. Analysis of productivity and of members' reactions supported the predicted interaction of tasks and media, with greater discrepancies between media conditions for tasks requiring higher levels of coordination. Results are discussed in terms of the implications of using computer-mediated communication systems for group work. In this study we tested the following general hypothesis: As group-member interdependence on tasks increases, communication media that transmit more social context cues will have a greater impact on group performance and satisfaction. For tasks with high needs for coordination, groups interacting face-toface will perform better and be more satisfied than will groups interacting in computer-medi ated discussions. For tasks with low needs for coordination, communication media will have little effect on group outcomes. We expected that these different media would be more or less effective for different types of tasks because both tasks and media affect the group-interaction process and the group-interaction process affects group outcomes (Hackman & Morris, 1975; McGrath, 1984). In the present study, we focused on the kinds of computermediated communication systems (CMCSs) in which the primary function is to foster information transfer through typed text (e.g., computer conferences and, to some extent, electronic mail). Many of the results of research on group decision support systems are excluded from this discussion. Because the primary

Bringing the Individual Back in: A Structural Analysis of the Internal Market for Reputation in Organizations

Abstract: We challenge the claimed incommensurability of individualism and structuralism by showing how a cognitive theory can guide the use of structural methods. According to balance theory, there is a str...

Model checking and modular verification

Abstract: We describe a framework for compositional verification of finite-state processes. The framework is based on two ideas: a subset of the logic CTL for which satisfaction is preserved under composition, and a preorder on structures which captures the relation between a component and a system containing the component. Satisfaction of a formula in the logic corresponds to being below a particular structure (a tableau for the formula) in the preorder. We show how to do assume-guarantee-style reasoning within this framework. Additionally, we demonstrate efficient methods for model checking in the logic and for checking the preorder in several special cases. We have implemented a system based on these methods, and we use it to give a compositional verification of a CPU controller.

What Do People Know About Global Climate Change? 1. Mental Models

Abstract: A set of exploratory studies and mental model interviews was conducted in order to characterize public understanding of climate change. In general, respondents regarded global warming as both bad and highly likely. Many believed that warming has already occurred. They tended to confuse stratospheric ozone depletion with the greenhouse effect and weather with climate. Automobile use, heat and emissions from industrial processes, aerosol spray cans, and pollution in general were frequently perceived as primary causes of global warming. Additionally, the [open quotes]greenhouse effect[close quotes] was often interpreted literally as the cause of a hot and steamy climate. The effects attributed to climate change often included increased skin cancer and changed agricultural yields. The mitigation and control strategies proposed by interviewees typically focused on general pollution control, with few specific links to carbon dioxide and energy use. Respondents appeared to be relatively unfamiliar with such regulatory developments as the ban on CFCs for nonessential uses. These beliefs must be considered by those designing risk communications or presenting climate-related policies to the public. 20 refs., 4 tabs.

Experimental Methods: A Primer for Economists

Abstract: List of figures and tables Preface Acknowledgments 1. Introduction 2. Principles of economics 3. Experimental design 4. Human subjects 5. Laboratory facilities 6. Conducting an experiment 7. Data analysis 8. Reporting your results 9. The emergence of experimental economics Appendices Glossary References Index.

Generalization in Reinforcement Learning: Safely Approximating the Value Function

Abstract: A straightforward approach to the curse of dimensionality in reinforcement learning and dynamic programming is to replace the lookup table with a generalizing function approximator such as a neural net. Although this has been successful in the domain of backgammon, there is no guarantee of convergence. In this paper, we show that the combination of dynamic programming and function approximation is not robust, and in even very benign cases, may produce an entirely wrong policy. We then introduce Grow-Support, a new algorithm which is safe from divergence yet can still reap the benefits of successful generalization.

Estimating Normal Means with a Dirichlet Process Prior

Abstract: In this article, the Dirichlet process prior is used to provide a nonparametric Bayesian estimate of a vector of normal means. In the past there have been computational difficulties with this model. This article solves the computational difficulties by developing a “Gibbs sampler” algorithm. The estimator developed in this article is then compared to parametric empirical Bayes estimators (PEB) and nonparametric empirical Bayes estimators (NPEB) in a Monte Carlo study. The Monte Carlo study demonstrates that in some conditions the PEB is better than the NPEB and in other conditions the NPEB is better than the PEB. The Monte Carlo study also shows that the estimator developed in this article produces estimates that are about as good as the PEB when the PEB is better and produces estimates that are as good as the NPEB estimator when that method is better.

Fast contact force computation for nonpenetrating rigid bodies

Abstract: A new algorithm for computing contact forces between solid objects with friction is presented. The algorithm allows a mix of contact points with static and dynamic friction. In contrast to previous approaches, the problem of computing contact forces is not transformed into an optimization problem. Because of this, the need for sophisticated optimization software packages is eliminated. For both systems with and without friction, the algorithm has proven to be considerably faster, simple, and more reliable than previous approaches to the problem. In particular, implementation of the algorithm by nonspecialists in numerical programming is quite feasible.

Symbolic model checking for sequential circuit verification

Abstract: The temporal logic model checking algorithm of Clarke, Emerson, and Sistla (1986) is modified to represent state graphs using binary decision diagrams (BDD's) and partitioned transition relations. Because this representation captures some of the regularity in the state space of circuits with data path logic, we are able to verify circuits with an extremely large number of states. We demonstrate this new technique on a synchronous pipelined design with approximately 5/spl times/10/sup 120/ states. Our model checking algorithm handles full CTL with fairness constraints. Consequently, we are able to express a number of important liveness and fairness properties, which would otherwise not be expressible in CTL. We give empirical results on the performance of the algorithm applied to both synchronous and asynchronous circuits with data path logic. >