Showing papers by "University of Maryland, College Park published in 2002"

An efficient k-means clustering algorithm: analysis and implementation

Abstract: In k-means clustering, we are given a set of n data points in d-dimensional space R/sup d/ and an integer k and the problem is to determine a set of k points in Rd, called centers, so as to minimize the mean squared distance from each data point to its nearest center. A popular heuristic for k-means clustering is Lloyd's (1982) algorithm. We present a simple and efficient implementation of Lloyd's k-means clustering algorithm, which we call the filtering algorithm. This algorithm is easy to implement, requiring a kd-tree as the only major data structure. We establish the practical efficiency of the filtering algorithm in two ways. First, we present a data-sensitive analysis of the algorithm's running time, which shows that the algorithm runs faster as the separation between clusters increases. Second, we present a number of empirical studies both on synthetically generated data and on real data sets from applications in color quantization, data compression, and image segmentation.

Building a practically useful theory of goal setting and task motivation. A 35-year odyssey.

Abstract: The authors summarize 35 years of empirical research on goal-setting theory. They describe the core findings of the theory, the mechanisms by which goals operate, moderators of goal effects, the relation of goals and satisfaction, and the role of goals as mediators of incentives. The external validity and practical significance of goal-setting theory are explained, and new directions in goal-setting research are discussed. The relationships of goal setting to other theories are described as are the theory's limitations.

A key-management scheme for distributed sensor networks

Abstract: Distributed Sensor Networks (DSNs) are ad-hoc mobile networks that include sensor nodes with limited computation and communication capabilities. DSNs are dynamic in the sense that they allow addition and deletion of sensor nodes after deployment to grow the network or replace failing and unreliable nodes. DSNs may be deployed in hostile areas where communication is monitored and nodes are subject to capture and surreptitious use by an adversary. Hence DSNs require cryptographic protection of communications, sensor-capture detection, key revocation and sensor disabling. In this paper, we present a key-management scheme designed to satisfy both operational and security requirements of DSNs. The scheme includes selective distribution and revocation of keys to sensor nodes as well as node re-keying without substantial computation and communication capabilities. It relies on probabilistic key sharing among the nodes of a random graph and uses simple protocols for shared-key discovery and path-key establishment, and for key revocation, re-keying, and incremental addition of nodes. The security and network connectivity characteristics supported by the key-management scheme are discussed and simulation experiments presented.

The Way We Think: Conceptual Blending And The Mind's Hidden Complexities

Abstract: A long-awaited synthesis that marks a major turning point in cognitive science. . Until recently, cognitive science focused on such mental functions as problem solving, grammar, and pattern-the functions in which the human mind most closely resembles a computer. But humans are more than computers: we invent new meanings, imagine wildly, and even have ideas that have never existed before. Today the cutting edge of cognitive science addresses precisely these mysterious, creative aspects of the mind. The Way We Think is a landmark analysis of the imaginative nature of the mind. Conceptual blending is already widely known in research laboratories throughout the world; this book, written to be accessible to both lay readers and interested scientists, is its definitive statement. Gilles Fauconnier and Mark Turner show that conceptual blending is the root of the cognitively modern human mind, and that conceptual blends themselves are continually combined and reblended to create the rich mental fabric in which we live. The Way We Think shows how this blending operates; how it is affected by (and gives rise to) language, identity, culture, and invention; and how we imagine what could be and what might have been. The result is a bold and exciting new view of how the mind works.

Sloan digital sky survey: Early data release

Abstract: The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of ≈106 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg2 of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux- and wavelength-calibrated, with 4096 pixels from 3800 to 9200 A at R ≈ 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.

The Moral Foundations of Trust

Abstract: The Moral Foundations of Trust seeks to explain why people place their faith in strangers, and why doing so matters. Trust is a moral value that does not depend upon personal experience or on interacting with people in civic groups or informal socializing. Instead, we learn to trust from our parents, and trust is stable over long periods of time. Trust depends on an optimistic world view: the world is a good place and we can make it better. Trusting people are more likely to give through charity and volunteering. Trusting societies are more likely to redistribute resources from the rich to the poor. Trust has been in decline in the United States for over 30 years. The roots of this decline are traceable to declining optimism and increasing economic inequality, which Uslaner supports by aggregate time series in the United States and cross-sectional data across market economies.

Atmospheric Modeling, Data Assimilation and Predictability

Abstract: This comprehensive text and reference work on numerical weather prediction, first published in 2002, covers not only methods for numerical modeling, but also the important related areas of data assimilation and predictability. It incorporates all aspects of environmental computer modeling including an historical overview of the subject, equations of motion and their approximations, a modern and clear description of numerical methods, and the determination of initial conditions using weather observations (an important science known as data assimilation). Finally, this book provides a clear discussion of the problems of predictability and chaos in dynamical systems and how they can be applied to atmospheric and oceanic systems. Professors and students in meteorology, atmospheric science, oceanography, hydrology and environmental science will find much to interest them in this book, which can also form the basis of one or more graduate-level courses.

Evaluation of a behavioral measure of risk taking: the Balloon Analogue Risk Task (BART).

Abstract: The present study (N 86) sought to evaluate a laboratory-based behavioral measure of risk taking (the Balloon Analogue Risk Task; BART) and to test associations between this measure and self-report measures of risk-related constructs as well as self-reported real-world risk behaviors. The BART evidenced sound experimental properties, and riskiness on the BART was correlated with scores on measures of sensation seeking, impulsivity, and deficiencies in behavioral constraint. Also, riskiness on the BART was correlated with the self-reported occurrence of addictive, health, and safety risk behaviors, with the task accounting for variance in these behaviors beyond that accounted for by demographics and self-report measures of risk-related constructs. These results indicate that the BART may be a useful tool in the assessment of risk taking.

Web Site Usability, Design, and Performance Metrics

Abstract: Web sites provide the key interface for consumer use of the Internet. This research reports on a series of three studies that developand validate Web site usability, design and performance metrics, including download delay, navigability, site content, interactivity, and responsiveness. The performance metric that was developed includes the subconstructs user satisfaction, the likelihood of return, and the frequency of use.Data was collected in 1997, 1999, and 2000 from corporate Web sites via three methods, namely, a jury, third-party ratings, and a software agent. Significant associations between Web site design elements and Web site performance indicate that the constructs demonstrate good nomological validity. Together, the three studies provide a set of measures with acceptable validity and reliability. The findings also suggest lack of significant common methods biases across the jury-collected data, third-party data, and agent-collected data.Results suggest that Web site success is a first-order construct. Moreover, Web site success is significantly associated with Web site download delay (speed of access and display rate within the Web site), navigation (organization, arrangement, layout, and sequencing), content (amount and variety of product information), interactivity (customization and interactivity), and responsiveness (feedback options and FAQs).

The draft genome of Ciona intestinalis : insights into chordate and vertebrate origins

Abstract: The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.

Network Ties, Reputation, and the Financing of New Ventures

Abstract: Explaining how entrepreneurs overcome information asymmetry between themselves and potential investors to obtain financing is an important issue for entrepreneurship research. Our premise is that economic explanations for venture finance, which do not consider how social ties influence this process, are undersocialized and incomplete. However, we also argue that organization theoretic arguments, which draw on the concept of social obligation, are oversocialized. Drawing on the organizational theory literature, and in-depth fieldwork with 50 high-technology ventures, we examine the effects of direct and indirect ties between entrepreneurs and 202 seed-stage investors on venture finance decisions. We show that these ties influence the selection of ventures to fund through a process of information transfer.

Changes in Children’s Self-Competence and Values: Gender and Domain Differences across Grades One through Twelve

Abstract: This study extended previous research on changes in children's self-beliefs by documenting domain-specific growth trajectories for 761 children across grades 1 through 12 in a longitudinal study of perceptions of self-competence and task values. Hierarchical Linear Modeling was used to (1) describe changes in beliefs across childhood and adolescence within the domains of mathematics, language arts, and sports; (2) examine the impact of changes in competence beliefs on changes in values over time in the same domains; and (3) describe gender differences in mean levels and trajectories of change in competence beliefs and values. The most striking finding across all domains was that self-perceptions of competence and subjective task values declined as children got older, although the extent and rate of decline varied across domains. For example, in language arts, competence beliefs declined rapidly during the elementary school years, but then leveled off or increased to some extent; whereas the decline in self-competence beliefs in sports accelerated during the high school years. Significant gender differences in beliefs were found in most domains; however, the gender differences in developmental trajectories appeared to be domain specific rather than global. Importantly, the gender differences between boys and girls did not systematically increase with age, as predicted by some socialization perspectives. Adding competence beliefs as an explanatory variable to the model for task values revealed that changes in competence beliefs accounted for much of the age-related decline in task values. In addition, competence beliefs accounted for most of the gender differences in task values for language arts and sports.

Scalable application layer multicast

Abstract: We describe a new scalable application-layer multicast protocol, specifically designed for low-bandwidth, data streaming applications with large receiver sets. Our scheme is based upon a hierarchical clustering of the application-layer multicast peers and can support a number of different data delivery trees with desirable properties.We present extensive simulations of both our protocol and the Narada application-layer multicast protocol over Internet-like topologies. Our results show that for groups of size 32 or more, our protocol has lower link stress (by about 25%), improved or similar end-to-end latencies and similar failure recovery properties. More importantly, it is able to achieve these results by using orders of magnitude lower control traffic.Finally, we present results from our wide-area testbed in which we experimented with 32-100 member groups distributed over 8 different sites. In our experiments, average group members established and maintained low-latency paths and incurred a maximum packet loss rate of less than 1% as members randomly joined and left the multicast group. The average control overhead during our experiments was less than 1 Kbps for groups of size 100.

Background and foreground modeling using nonparametric kernel density estimation for visual surveillance

Abstract: Automatic understanding of events happening at a site is the ultimate goal for many visual surveillance systems. Higher level understanding of events requires that certain lower level computer vision tasks be performed. These may include detection of unusual motion, tracking targets, labeling body parts, and understanding the interactions between people. To achieve many of these tasks, it is necessary to build representations of the appearance of objects in the scene. This paper focuses on two issues related to this problem. First, we construct a statistical representation of the scene background that supports sensitive detection of moving objects in the scene, but is robust to clutter arising out of natural scene variations. Second, we build statistical representations of the foreground regions (moving objects) that support their tracking and support occlusion reasoning. The probability density functions (pdfs) associated with the background and foreground are likely to vary from image to image and will not in general have a known parametric form. We accordingly utilize general nonparametric kernel density estimation techniques for building these statistical representations of the background and the foreground. These techniques estimate the pdf directly from the data without any assumptions about the underlying distributions. Example results from applications are presented.

Nonmonotonic Reasoning, Preferential Models and Cumulative Logics

Abstract: Many systems that exhibit nonmonotonic behavior have been described and studied already in the literature. The general notion of nonmonotonic reasoning, though, has almost always been described only negatively, by the property it does not enjoy, i.e. monotonicity. We study here general patterns of nonmonotonic reasoning and try to isolate properties that could help us map the field of nonmonotonic reasoning by reference to positive properties. We concentrate on a number of families of nonmonotonic consequence relations, defined in the style of Gentzen. Both proof-theoretic and semantic points of view are developed in parallel. The former point of view was pioneered by D. Gabbay, while the latter has been advocated by Y. Shoham in. Five such families are defined and characterized by representation theorems, relating the two points of view. One of the families of interest, that of preferential relations, turns out to have been studied by E. Adams. The "preferential" models proposed here are a much stronger tool than Adams' probabilistic semantics. The basic language used in this paper is that of propositional logic. The extension of our results to first order predicate calculi and the study of the computational complexity of the decision problems described in this paper will be treated in another paper.

Encouraging Knowledge Sharing: The Role of Organizational Reward Systems

Abstract: This article examines the role of monetary rewards in encouraging knowledge sharing in organizations through four mechanisms of knowledge sharing. We argue that the system of contributing knowledge to databases is the most amenable to rewards contingent on knowledge sharing behaviors because of opportunities for the reward allocator to measure the knowledge sharing behaviors. In the case of formal interactions within or across teams and work units, while rewards could be made partly contingent on knowledge sharing behaviors as in merit pay, rewards based on collective performance are also likely to be effective in creating a feeling of cooperation, ownership, and commitment among employees. In addition, we propose that team-based rewards and company wide incentives (profit sharing, gainsharing, and employee stock options) would be particularly instrumental in enhancing knowledge sharing within teams and across work units, respectively. In the case of knowledge sharing through informal interactions, the ke...

Is Information Risk a Determinant of Asset Returns

Abstract: We investigate the role of information-based trading in affecting asset returns. We show in a rational expectation example how private information affects equilibrium asset returns. Using a market microstructure model, we derive a measure of the probability of information-based trading, and we estimate this measure using data for individual NYSE-listed stocks for 1983 to 1998. We then incorporate our estimates into a Fama and French (1992) asset-pricing framework. Our main result is that information does affect asset prices. A difference of 10 percentage points in the probability of information-based trading between two stocks leads to a difference in their expected returns of 2.5 percent per year. ASSET PRICING IS FUNDAMENTAL to our understanding of the wealth dynamics of an economy. This central importance has resulted in an extensive literature on asset pricing, much of it focusing on the economic factors that influence asset prices. Despite the fact that virtually all assets trade in markets, one set of factors not typically considered in asset-pricing models are the features of the markets in which the assets trade. Instead, the literature on asset pricing abstracts from the mechanics of asset price evolution, leaving unsettled the underlying question of how equilibrium prices are actually attained. Market microstructure, conversely, focuses on how the mechanics of the trading process affect the evolution of trading prices. A major focus of this extensive literature is on the process by which information is incorporated into prices. The microstructure literature provides structural models of how prices become efficient, as well as models of volatility, both issues clearly of importance for asset pricing. But of perhaps more importance, microstructure models pro

A theory of goal systems.

Abstract: In this chapter, the authors describe a research program premised on the notion that the cognitive treatment affords conceptual and methodological advantages enabling new insights into problems of motivated action, self-regulation and self-control. They introduce placing their work in the broader historical context of social psychological theorizing about motivation and cognition. The authors present theoretical notions and trace their implications for a variety of psychological issues including activity experience, goal commitment, choice, and substitution. They also describe empirical research concerning a broad range of phenomena informed by the goal-systemic analysis. Two categories of cognitive properties play a major role in the behavior of goal systems: these are their structural and their allocational properties. The number of goals linked to a given means defines the multifinality set encapsulated in the notion of "many birds with one stone". Understanding the dynamics of commitment may improve our ability to foster commitment to realistic goals, and to reduce commitment to unattainable or unrealistic pursuits.

Single-walled carbon nanotube electronics

Abstract: Single-walled carbon nanotubes (SWNTs) have emerged as a very promising new class of electronic materials. The fabrication and electronic properties of devices based on individual SWNTs are reviewed. Both metallic and semiconducting SWNTs are found to possess electrical characteristics that compare favorably to the best electronic materials available. Manufacturability issues, however, remain a major challenge.

The role of children in the design of new technology

Abstract: This paper suggests a framework for understanding the roles that children can play in the technology design process, particularly in regards to designing technologies that support learning. Each role, user, tester, informant and design partner has been defined based upon a review of the literature and the author's own laboratory research experiences. This discussion does not suggest that any one role is appropriate for all research or development needs. Instead, by understanding this framework the reader may be able to make more informed decisions about the design processes they choose to use with children in creating new technologies. This paper will present for each role a historical overview, research and development methods, as well as the strengths, challenges and unique contributions associated with children in the design process.

Enterprise Restructuring in Transition: A Quantitative Survey

Abstract: We survey the empirical literature analyzing the process of enterprise restructuring in transition economies. The survey provides new insights into the relative effectiveness of different reform policies, and into how this effectiveness varies across regions. We study the effects of privatization, the importance of different types of owners, the effects of foreign and domestic competition, the consequences of soft budgets, and the role of managerial incentives and managerial human capital, on enterprise restructuring.

The economics of information security investment

Abstract: This article presents an economic model that determines the optimal amount to invest to protect a given set of information. The model takes into account the vulnerability of the information to a security breach and the potential loss should such a breach occur. It is shown that for a given potential loss, a firm should not necessarily focus its investments on information sets with the highest vulnerability. Since extremely vulnerable information sets may be inordinately expensive to protect, a firm may be better off concentrating its efforts on information sets with midrange vulnerabilities. The analysis further suggests that to maximize the expected benefit from investment to protect information, a firm should spend only a small fraction of the expected loss due to a security breach.