Showing papers by "University of Illinois at Urbana–Champaign published in 2001"

A New Approach to Linear Filtering and Prediction Problems

Abstract: The clssical filleting and prediclion problem is re-examined using the Bode-Shannon representation of random processes and the ?stat-tran-sition? method of analysis of dynamic systems. New result are: (1) The formulation and Methods of solution of the problm apply, without modification to stationary and nonstationary stalistics end to growing-memory and infinile -memory filters. (2) A nonlinear difference (or differential) equalion is dericed for the covariance matrix of the optimal estimalion error. From the solution of this equation the coefficients of the difference, (or differential) equation of the optimal linear filter are obtained without further caleulations. (3) Tke fillering problem is shoum to be the dual of the nois-free regulator problem. The new method developed here, is applied to do well-known problems, confirming and extending, earlier results. The discussion is largely, self-contatained, and proceeds from first principles; basic concepts of the theory of random processes are reviewed in the Appendix.

Factor graphs and the sum-product algorithm

Abstract: Algorithms that must deal with complicated global functions of many variables often exploit the manner in which the given functions factor as a product of "local" functions, each of which depends on a subset of the variables. Such a factorization can be visualized with a bipartite graph that we call a factor graph, In this tutorial paper, we present a generic message-passing algorithm, the sum-product algorithm, that operates in a factor graph. Following a single, simple computational rule, the sum-product algorithm computes-either exactly or approximately-various marginal functions derived from the global function. A wide variety of algorithms developed in artificial intelligence, signal processing, and digital communications can be derived as specific instances of the sum-product algorithm, including the forward/backward algorithm, the Viterbi algorithm, the iterative "turbo" decoding algorithm, Pearl's (1988) belief propagation algorithm for Bayesian networks, the Kalman filter, and certain fast Fourier transform (FFT) algorithms.

From few to many: illumination cone models for face recognition under variable lighting and pose

Abstract: We present a generative appearance-based method for recognizing human faces under variation in lighting and viewpoint. Our method exploits the fact that the set of images of an object in fixed pose, but under all possible illumination conditions, is a convex cone in the space of images. Using a small number of training images of each face taken with different lighting directions, the shape and albedo of the face can be reconstructed. In turn, this reconstruction serves as a generative model that can be used to render (or synthesize) images of the face under novel poses and illumination conditions. The pose space is then sampled and, for each pose, the corresponding illumination cone is approximated by a low-dimensional linear subspace whose basis vectors are estimated using the generative model. Our recognition algorithm assigns to a test image the identity of the closest approximated illumination cone. Test results show that the method performs almost without error, except on the most extreme lighting directions.

Autonomic healing of polymer composites

Abstract: Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).

Chemoradiotherapy after Surgery Compared with Surgery Alone for Adenocarcinoma of the Stomach or Gastroesophageal Junction

Abstract: Background Surgical resection of adenocarcinoma of the stomach is curative in less than 40 percent of cases. We investigated the effect of surgery plus postoperative (adjuvant) chemoradiotherapy on the survival of patients with resectable adenocarcinoma of the stomach or gastroesophageal junction. Methods A total of 556 patients with resected adenocarcinoma of the stomach or gastroesophageal junction were randomly assigned to surgery plus postoperative chemoradiotherapy or surgery alone. The adjuvant treatment consisted of 425 mg of fluorouracil per square meter of body-surface area per day, plus 20 mg of leucovorin per square meter per day, for five days, followed by 4500 cGy of radiation at 180 cGy per day, given five days per week for five weeks, with modified doses of fluorouracil and leucovorin on the first four and the last three days of radiotherapy. One month after the completion of radiotherapy, two five-day cycles of fluorouracil (425 mg per square meter per day) plus leucovorin (20 mg per squar...

Spectrofluorometric characterization of dissolved organic matter for indication of precursor organic material and aromaticity

Abstract: We studied the fluorescence properties of fulvic acids isolated from streams and rivers receiving predominantly terrestrial sources of organic material and from lakes with microbial sources of organic material. Microbially derived fulvic acids have fluorophores with a more sharply defined emission peak occurring at lower wavelengths than fluorophores in terrestrially derived fulvic acids. We show that the ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm, obtained with an excitation of 370 nm, can serve as a simple index to distinguish sources of isolated aquatic fulvic acids. In our study, this index has a value of ;1.9 for microbially derived fulvic acids and a value of ;1.4 for terrestrially derived fulvic acids. Fulvic acids isolated from four large rivers in the United States have fluorescence index values of 1.4‐1.5, consistent with predominantly terrestrial sources. For fulvic acid samples isolated from a river, lakes, and groundwaters in a forested watershed, the fluorescence index varied in a manner suggesting different sources for the seepage and streamfed lakes. Furthermore, we identified these distinctive fluorophores in filtered whole water samples from lakes in a desert oasis in Antarctica and in filtered whole water samples collected during snowmelt from a Rocky Mountain stream. The fluorescence index measurement in filtered whole water samples in field studies may augment the interpretation of dissolved organic carbon sources for understanding carbon cycling in aquatic ecosystems.

The physics of manganites: Structure and transport

Abstract: The fundamental physical properties of doped ${\mathrm{LaMnO}}_{3},$ generically termed ``manganites,'' and much of the underlying physics, were known more than 40 years ago. This article first reviews progress made at that time, the concept of double exchange in particular, and points out the missing elements that have led to a massive resurgence of interest in these and related materials. More recent research is then described, treating first the ground states that emerge as divalent atoms are substituted for trivalent La. A wide range of ground states appear, including ferromagnetic metals, orbital- and charge-ordered antiferromagnets, and more complex stripe and spin-glass states. Because of the interest in so-called colossal magnetoresistance that occurs in the ferromagnetic/metallic composition range, a section is devoted to reviewing the atypical properties of that phase. Next the high-temperature phase is examined, in particular, evidence for the formation of self-trapped small polarons and the importance of Jahn-Teller coupling in this process. The transitions between the high-temperature polaronic phase and the ferromagnetic and charge-ordered states are treated in a fourth section. In each section, the authors stress the competition among charge, spin, and lattice coupling and review the current state of theoretical understanding. They conclude with some comments on the impact that research on these materials has on our understanding of doped oxides and other strongly correlated electronic materials.

Misunderstanding analysis of covariance.

Abstract: Despite numerous technical treatments in many venues, analysis of covariance (ANCOVA) remains a widely misused approach to dealing with substantive group differences on potential covariates, particularly in psychopathology research. Published articles reach unfounded conclusions, and some statistics texts neglect the issue. The problem with ANCOVA in such cases is reviewed. In many cases, there is no means of achieving the superficially appealing goal of "correcting" or "controlling for" real group differences on a potential covariate. In hopes of curtailing misuse of ANCOVA and promoting appropriate use, a nontechnical discussion is provided, emphasizing a substantive confound rarely articulated in textbooks and other general presentations, to complement the mathematical critiques already available. Some alternatives are discussed for contexts in which ANCOVA is inappropriate or questionable. In research comparing groups of participants, classical experimental design (Campbell & Stanley, 1963) relies, whenever possible, on random assignment of participants to groups. Observed differences between such groups, prior to experimental treatments, are due to chance rather than being meaningfully related to the

Individualism-Collectivism and Personality

Abstract: This paper provides a review of the main findings concerning the relationship between the cultural syndromes of individualism and collectivism and personality. People in collectivist cultures, compared to people in individualist cultures, are likely to define themselves as aspects of groups, to give priority to in-group goals, to focus on context more than the content in making attributions and in communicating, to pay less attention to internal than to external processes as determinants of social behavior, to define most relationships with ingroup members as communal, to make more situational attributions, and tend to be self-effacing.

Quantum Monte Carlo simulations of solids

Abstract: This article describes the variational and fixed-node diffusion quantum Monte Carlo methods and how they may be used to calculate the properties of many-electron systems. These stochastic wave-function-based approaches provide a very direct treatment of quantum many-body effects and serve as benchmarks against which other techniques may be compared. They complement the less demanding density-functional approach by providing more accurate results and a deeper understanding of the physics of electronic correlation in real materials. The algorithms are intrinsically parallel, and currently available high-performance computers allow applications to systems containing a thousand or more electrons. With these tools one can study complicated problems such as the properties of surfaces and defects, while including electron correlation effects with high precision. The authors provide a pedagogical overview of the techniques and describe a selection of applications to ground and excited states of solids and clusters.

Profitability of Momentum Strategies: An Evaluation of Alternative Explanations

Abstract: This paper evaluates various explanations for the profitability of momentum strategies documented in Jegadeesh and Titman ~1993!. The evidence indicates that momentum profits have continued in the 1990s, suggesting that the original results were not a product of data snooping bias. The paper also examines the predictions of recent behavioral models that propose that momentum profits are due to delayed overreactions that are eventually reversed. Our evidence provides support for the behavioral models, but this support should be tempered with caution. Many portfolio managers and stock analysts subscribe to the view that momentum strategies yield significant profits. Jegadeesh and Titman ~1993! examine a variety of momentum strategies and document that strategies that buy stocks with high returns over the previous 3 to 12 months and sell stocks with poor returns over the same time period earn profits of about one percent per month for the following year. 1 Although these results have been well accepted, the source of the profits and the interpretation of the evidence are widely debated. Although some have argued that the results provide strong evidence of “market inefficiency,” others have argued that the returns from these strategies are either compensation for risk, or alternatively, the product of data mining. The criticism that observed empirical regularities arise because of data mining is typically the hardest to address because empirical research in nonexperimental settings is limited by data availability. Fortunately, with

A field guide to foldamers.

Abstract: III. Foldamer Research 3910 A. Overview 3910 B. Motivation 3910 C. Methods 3910 D. General Scope 3912 IV. Peptidomimetic Foldamers 3912 A. The R-Peptide Family 3913 1. Peptoids 3913 2. N,N-Linked Oligoureas 3914 3. Oligopyrrolinones 3915 4. Oxazolidin-2-ones 3916 5. Azatides and Azapeptides 3916 B. The â-Peptide Family 3917 1. â-Peptide Foldamers 3917 2. R-Aminoxy Acids 3937 3. Sulfur-Containing â-Peptide Analogues 3937 4. Hydrazino Peptides 3938 C. The γ-Peptide Family 3938 1. γ-Peptide Foldamers 3938 2. Other Members of the γ-Peptide Family 3941 D. The δ-Peptide Family 3941 1. Alkene-Based δ-Amino Acids 3941 2. Carbopeptoids 3941 V. Single-Stranded Abiotic Foldamers 3944 A. Overview 3944 B. Backbones Utilizing Bipyridine Segments 3944 1. Pyridine−Pyrimidines 3944 2. Pyridine−Pyrimidines with Hydrazal Linkers 3945

Measurement of qubits

Abstract: We describe in detail the theory underpinning the measurement of density matrices of a pair of quantum two-level systems ~‘‘qubits’’ !. Our particular emphasis is on qubits realized by the two polarization degrees of freedom of a pair of entangled photons generated in a down-conversion experiment; however, the discussion applies in general, regardless of the actual physical realization. Two techniques are discussed, namely, a tomographic reconstruction ~in which the density matrix is linearly related to a set of measured quantities ! and a maximum likelihood technique which requires numerical optimization ~but has the advantage of producing density matrices that are always non-negative definite!. In addition, a detailed error analysis is presented, allowing errors in quantities derived from the density matrix, such as the entropy or entanglement of formation, to be estimated. Examples based on down-conversion experiments are used to illustrate our results.

Bose-Einstein condensation in the alkali gases: Some fundamental concepts

Abstract: The author presents a tutorial review of some ideas that are basic to our current understanding of the phenomenon of Bose-Einstein condensation (BEC) in the dilute atomic alkali gases, with special emphasis on the case of two or more coexisting hyperfine species. Topics covered include the definition of and conditions for BEC in an interacting system, the replacement of the true interatomic potential by a zero-range pseudopotential, the time-independent and time-dependent Gross-Pitaevskii equations, superfluidity and rotational properties, the Josephson effect and related phenomena, and the Bogoliubov approximation.

Incivility in the workplace: Incidence and impact.

Abstract: This study extends the literature on interpersonal mistreatment in the workplace by examining the incidence, targets, instigators, and impact of incivility (eg, disrespect, condescension, degradation) Data were collected from 1,180 public-sector employees, 71% of whom reported some experience of workplace incivility in the previous 5 years As many as one third of the most powerful individuals within the organization instigated these uncivil acts Although women endured greater frequencies of incivility than did men, both genders experienced similarly negative effects on job satisfaction, job withdrawal, and career salience Uncivil workplace experiences were also associated with greater psychological distress; however, indices of psychological and physical health were relatively unaffected The authors discuss these findings in the context of organizational and cognitive stress theories

Dimensionality reduction for fast similarity search in large time series databases

Abstract: The problem of similarity search in large time series databases has attracted much attention recently. It is a non-trivial problem because of the inherent high dimensionality of the data. The most promising solutions involve first performing dimensionality reduction on the data, and then indexing the reduced data with a spatial access method. Three major dimensionality reduction techniques have been proposed: Singular Value Decomposition (SVD), the Discrete Fourier transform (DFT), and more recently the Discrete Wavelet Transform (DWT). In this work we introduce a new dimensionality reduction technique which we call Piecewise Aggregate Approximation (PAA). We theoretically and empirically compare it to the other techniques and demonstrate its superiority. In addition to being competitive with or faster than the other methods, our approach has numerous other advantages. It is simple to understand and to implement, it allows more flexible distance measures, including weighted Euclidean queries, and the index can be built in linear time.

Biofilm formation by the fungal pathogen Candida albicans: development, architecture, and drug resistance.

Abstract: Biofilms are a protected niche for microorganisms, where they are safe from antibiotic treatment and can create a source of persistent infection. Using two clinically relevant Candida albicans biofilm models formed on bioprosthetic materials, we demonstrated that biofilm formation proceeds through three distinct developmental phases. These growth phases transform adherent blastospores to well-defined cellular communities encased in a polysaccharide matrix. Fluorescence and confocal scanning laser microscopy revealed that C. albicans biofilms have a highly heterogeneous architecture composed of cellular and noncellular elements. In both models, antifungal resistance of biofilm-grown cells increased in conjunction with biofilm formation. The expression of agglutinin-like (ALS) genes, which encode a family of proteins implicated in adhesion to host surfaces, was differentially regulated between planktonic and biofilm-grown cells. The ability of C. albicans to form biofilms contrasts sharply with that of Saccharomyces cerevisiae, which adhered to bioprosthetic surfaces but failed to form a mature biofilm. The studies described here form the basis for investigations into the molecular mechanisms of Candida biofilm biology and antifungal resistance and provide the means to design novel therapies for biofilm-based infections.

Control of nitrogen export from watersheds by headwater streams

Abstract: A comparative 15 N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.

Building the Virtual State: Information Technology and Institutional Change

Abstract: From the Publisher: "In Building the Virtual State, Jane Fountain explains how government must evolve to become part of the Internet revolution. Fountain calls on government agencies to abandon outmoded bureaucratic tendencies in favor of a less centralized approach to providing services. This requires a change not only in the way government executives think, but also in the way they view their relationships with citizens. They must answer questions regarding costs and maintenance of Internet portals, and at the same time assure citizens that their privacy will be protected." The creation of this "virtual state," Fountain argues, will not be easy, exposing much of the structural obsolescence of our current bureaucracy. However, if our government is to serve its central purpose - to work for its citizens and provide them with the opportunity to excel - it must embrace this change. It must negotiate the solutions to the internal questions of management, as well as external questions of protection of privacy and capability of use by all citizens. The outcome of this struggle will likely determine the extent to which the American government will be recast in the Information Age and whether its citizens will emerge as winners or losers.

The Stock Market Valuation of Research and Development Expenditures

Abstract: We examine whether stock prices fully value firms’ intangible assets, specifically research and development ~R&D!. Under current U.S. accounting standards, financial statements do not report intangible assets and R&D spending is expensed. Nonetheless, the average historical stock returns of firms doing R&D matches the returns of firms without R&D. However, the market is apparently too pessimistic about beaten-down R&D-intensive technology stocks’ prospects. Companies with high R&D to equity market value ~which tend to have poor past returns! earn large excess returns. A similar relation exists between advertising and stock returns. R&D intensity is positively associated with return volatility.

Cooperative Networks and Competitive Dynamics: a Structural Embeddedness Perspective

Abstract: Firms are embedded in networks of cooperative relationships that influence the flow of resources among them. Dynamic resource flows and differentiated structural positions lead to asymmetries and influence firms' competitive behavior toward others in the network. We develop a multilevel conceptual model relating key network properties to competitive action and response. A structural embeddedness perspective with a focus on simultaneous cooperation and competition advances our understanding of competitive dynamics and provides intriguing possibilities for future research.

The mispricing of abnormal accruals

Abstract: This paper examines the market pricing of Jones (1991) modelestimated abnormal accruals (often termed “discretionary accruals” in the prior literature) to test whether stock prices rationally reflect the one‐year‐ahead earnings implications of these accruals. Using the Mishkin (1983) and hedge‐portfolio test methods Sloan (1996) employs, I find that the market overestimates the persistence, or one‐year‐ahead earnings implications, of abnormal accruals, and consequently overprices these accruals. These results extend Subramanyam (1996) by demonstrating that the market not only prices, but also overprices abnormal accruals. They also suggest that the overpricing of total accruals that Sloan (1996) documents is due largely to abnormal accruals. The results are robust to five alternative measures of abnormal accruals, and still hold when I estimate abnormal accruals after controlling for major unusual but largely nondiscretionary accruals. The latter finding is consistent with the notion that the market overp...

The Classroom Social Environment and Changes in Adolescents’ Motivation and Engagement During Middle School

Abstract: The authors investigated how students’ (N = 233) perceptions of the social environment of their eighth-grade classroom related to changes in motivation and engagement when they moved from seventh to eighth grade. In general, prior motivation and engagement were strong predictors of subsequent motivation and engagement, whereas gender, race, and prior achievement were not related to changes in motivation or engagement. A higher-order classroom social environment factor accounted for significant changes in all motivation and engagement outcomes. Four distinct dimensions of the social environment were differentially important in explaining changes in various indices of motivation and engagement. In general, however, students’ perceptions of teacher support, and the teacher as promoting interaction and mutual respect were related to positive changes in their motivation and engagement. Students’ perceptions of the teacher as promoting performance goals were related to negative changes in student motivation and...

Communication and Uncertainty Management.

Abstract: The fundamental challenge for refining theories of communication and uncertainty is to abandon the assumption that uncertainty will produce anxiety. To better explain processes of communication and uncertainty management the authors must answer questions about a) the experience and meaning of uncertainty b) the role of appraisal and emotion in uncertainty management and c) the range of behavioral and psychological responses to uncertainty. This paper outlines and extends a theory of uncertainty management and reviews current theory and research in this area. In addition to the theoretical advances promised by this perspective the paper describes applications to health communication practice. The drive in disease prevention to reduce uncertainty about the state of health and illness has led to a "culture of chronic illness". Constant surveillance of peoples health combined with improved methods for screening and monitoring virtually guarantee finding something wrong with every person creating a society divided into the chronically ill and the worried well (i.e. those waiting to be diagnosed). (authors)

A unified equation of state of dense matter and neutron star structure

Abstract: An equation of state (EOS) of neutron star matter, describing both the neutron star crust and the liquid core, is calculated. It is based on the eective nuclear interaction SLy of the Skyrme type, which is particularly suitable for the application to the calculation of the properties of very neutron rich matter (Chabanat et al. 1997, 1998). The structure of the crust, and its EOS, is calculated in the T = 0 approximation, and under the assumption of the ground state composition. The crust-core transition is a very weakly rst-order phase transition, with relative density jump of about one percent. The EOS of the liquid core is calculated assuming (minimal) npe composition. Parameters of static neutron stars are calculated and compared with existing observational data on neutron stars. The minimum and maximum masses of static neutron stars are 0:094 M and 2:05 M, respectively. Eects of rotation on the minimum and the maximum mass of neutron stars are briefly discussed.