bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diversity in the use of electronic mail: a preliminary inquiry
Authors: Mackay Wendy E. 
Published: July 2002

This paper describes a series of interviews that examine the ways that professional office workers use electronic mail to manage their daily work. The purpose is to generate hypotheses for future research. A number of implications for the design of flexible mail systems are discussed.
Two principal claims are made. First, the use of electronic mail is strikingly diverse, although not infinitely so. Individuals vary both in objective measures of mail use and in preferred strategies for managing work electronically. Feelings of control are similarly diverse and are related to the size of the user's inbox, numbers of folders, and subscriptions to distribution lists. This diversity implies that one's own experiences with electronic mail are unlikely to provide sufficient understanding of other's uses of mail. Mail designers should thus seek flexible primitives that capture the important dimensions of use and provide flexibility for a wide range of users.
The second claim is that electronic mail is more than just a communication system. Users archive messages for subject retrieval, prioritize messages to sequence work activities, and delegate tasks via mail. A taxonomy of work management is proposed in which mail is used for information management, time management, and task management activities. Directions for future research are suggested.
MODIFIED OLIGONUCLEOTIDES: Synthesis and Strategy for Users
Authors: Verma Sandeep , Eckstein Fritz 
Published: July 2002

Synthetic oligonucleotide analogs have greatly aided our understanding of several biochemical processes. Efficient solid-phase and enzyme-assisted synthetic methods and the availability of modified base analogs have added to the utility of such oligonucleotides. In this review, we discuss the applications of synthetic oligonucleotides that contain backbone, base, and sugar modifications to investigate the mechanism and stereochemical aspects of biochemical reactions. We also discuss interference mapping of nucleic acid–protein interactions; spectroscopic analysis of biochemical reactions and nucleic acid structures; and nucleic acid cross-linking studies.The automation of oligonucleotide synthesis, the development of versatile phosphoramidite reagents, and efficient scale-up have expanded the application of modified oligonucleotides to diverse areas of fundamental and applied biological research. Numerous reports have covered oligonucleotides for which modifications have been made of the phosphodiester backbone, of the purine and pyrimidine heterocyclic bases, and of the sugar moiety; these modifications serve as structural and mechanistic probes. In this chapter, we review the range, scope, and practical utility of such chemically modified oligonucleotides. Because of space limitations, we discuss only those oligonucleotides that contain phosphate and phosphate analogs as internucleotidic linkages.
LEWIS FRY RICHARDSON AND HIS CONTRIBUTIONS TO MATHEMATICS, METEOROLOGY, AND MODELS OF CONFLICT
Authors: Hunt J.C.R. 
Published: July 2002

[Figure: see text] ▪ Abstract  The life and major scientific contributions of Lewis Fry Richardson (1881–1953) are reviewed, with particular emphasis on his pioneering work in numerical analysis, meteorology, and numerical weather prediction. His later work on mathematical modeling of psychology, causes of conflict, and the statistics of wars is outlined in terms understandable to fluid dynamicists. It is included because it led to Richardson's discovery of one aspect of fractals, an analytical technique now recognized as valuable in the study of complex fluid motions.
Specificity and Degeneracy in Antigen Recognition: Yin and Yang in the Immune System
Authors: Eisen Herman N. 
Published: July 2002

One of the hallmarks of the immune system is specificity, a concept based on innumerable observations that antibodies react with the substance that elicited their production and only a few other structurally similar substances. The study of T cells has begun to suggest, however, that in responses mediated by their antibody-like receptors (T cell receptor or TCR) an individual T cell, expressing a singular TCR, can discriminate as exquisitely among antigens as the most specific antibodies but also exhibit “degeneracy”: i.e., it can react with many disparate antigens (peptide-MHC complexes). An explanation for this duality (specificity and degeneracy) can be found in (i) the powerful amplifying signal transduction cascades that allow a T cell to respond to the stable engagement of very few TCR molecules, initially perhaps only one or two out of around 100,000 per cell, by their natural ligands (peptide-MHC complexes or epitopes on antigen-presenting cells—or APC) and (ii) the inverse relationship between TCR affinity for epitopes and epitope density (the number of copies of an epitope per APC). Older observations on the excess of total globulin production over specific antibody production in response to conventional immunization procedures suggest that B cells also exhibit degeneracy, as well as specificity. These views are developed against a backdrop describing how the author became interested in the immune system and has pursued that interest. “…a concept of science drawn from … [textbooks] … is no more likely to fit the enterprise that produced them than an image of a national culture drawn from a tourist brochure.”      Thomas Kuhn, Structure Of Scientific Revolutions
Synaptic Modification by Correlated Activity: Hebb's Postulate Revisited
Authors: Bi Guo-qiang , Poo Mu-ming 
Published: July 2002

▪ Abstract  Correlated spiking of pre- and postsynaptic neurons can result in strengthening or weakening of synapses, depending on the temporal order of spiking. Recent findings indicate that there are narrow and cell type–specific temporal windows for such synaptic modification and that the generally accepted input- (or synapse-) specific rule for modification appears not to be strictly adhered to. Spike timing–dependent modifications, together with selective spread of synaptic changes, provide a set of cellular mechanisms that are likely to be important for the development and functioning of neural networks.When an axon of cell A is near enough to excite cell B or repeatedly or consistently takes part in firing it, some growth or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased.      Donald Hebb (1949)
Output Units of Motor Behavior: An Experimental and Modeling Study
Authors: Loeb E. P. , Giszter S. F. , Bizzi P. Saltiel and E. , Mussa-Ivaldi F. A. 
Published: July 2002

Abstract
Cognitive approaches to motor control typically concern sequences of discrete actions without taking into account the stunning complexity of the geometry and dynamics of the muscles. This begs the question: Does the brain convert the intricate, continuous-time dynamics of the muscles into simpler discrete units of actions, and if so, how? One way for the brain to form discrete units of behavior from muscles is through the synergistic co-activation of muscles. While this possibility has long been known, the composition of potential muscle synergies has remained elusive. In this paper, we have focused on a method that allowed us to examine and compare the limb stabilization properties of all possible muscle combinations. We found that a small set (as few as 23 out of 65,536) of all possible combinations of 16 limb muscles are robust with respect to activation noise: these muscle combinations could stabilize the limb at predictable, restricted portions of the workspace in spite of broad variations in the force output of their component muscles. The locations at which the robust synergies stabilize the limb are not uniformly distributed throughout the leg's workspace, but rather, they cluster at four workspace areas. The simulated robust synergies are similar to the actual synergies we have previously found to be generated by activation of the spinal cord. Thus, we have developed a new analytical method that enabled us to select a few muscle synergies with interesting properties out of the set of possible muscle combinations. Beyond this, the identification of robustness as a common property of the synergies in simple motor behaviors will open the way to the study of dynamic stability, which is an important and distinct property of the vertebrate motor-control system.
I. The Neurocognitive Profile of Williams Syndrome: A Complex Pattern of Strengths and Weaknesses
Authors: Bellugi Ursula , Lichtenberger Liz , Jones Wendy , Lai Zona , St. George Marie 
Published: July 2002

Abstract
The rare, genetically based disorder, Williams syndrome (WMS), produces a constellation of distinctive cognitive, neuroanatomical, and electrophysiological features which we explore through the series of studies reported here. In this paper, we focus primarily on the cognitive characteristics of WMS and begin to forge links among these characteristics, the brain, and the genetic basis of the disorder. The distinctive cognitive profile of individuals with WMS includes relative strengths in language and facial processing and profound impairment in spatial cognition. The cognitive profile of abilities, including what is ‘typical’ for individuals with WMS is discussed, but we also highlight areas of variability across the group of individuals with WMS that we have studied. Although the overall cognitive abilities (IQs) of individuals with WMS are typically in the mild-to-moderate range of mental retardation, the peaks and valleys within different cognitive domains make this syndrome especially intriguing to study across levels. Understanding the brain basis (and ultimately the genetic basis) for higher cognitive functioning is the goal we have begun to undertake with this line of interdisciplinary research.
The Psychophysiology of Real-Time Financial Risk Processing
Authors: Lo Andrew W. , Repin Dmitry V. 
Published: July 2002

Abstract
A longstanding controversy in economics and finance is whether financial markets are governed by rational forces or by emotional responses. We study the importance of emotion in the decision-making process of professional securities traders by measuring their physiological characteristics (e.g., skin conductance, blood volume pulse, etc.) during live trading sessions while simultaneously capturing real-time prices from which market events can be detected. In a sample of 10 traders, we find statistically significant differences in mean electrodermal responses during transient market events relative to no-event control periods, and statistically significant mean changes in cardiovascular variables during periods of heightened market volatility relative to normal-volatility control periods. We also observe significant differences in these physiological responses across the 10 traders that may be systematically related to the traders' levels of experience.
Patterns of Bimanual Interference Reveal Movement Encoding within a Radial Egocentric Reference Frame
Authors: Swinnen Stephan P. , Dounskaia Natalia , Duysens Jacques 
Published: July 2002

Abstract
Constraints on interlimb coordination have been studied intensively in past years with a primary focus on temporal features. The present study addressed spatial constraints or the degree of directional interference as a function of different line combinations between the upper limbs as well as the modulation of this interference as a result of different board orientations within the performer's workspace. This paradigm was used to address a prominent theme in motor neuroscience, namely whether (bimanual) movements are encoded within an allocentric reference frame (pattern of interference invariant with respect to extrinsic space) or within an egocentric reference frame (pattern of interference invariant relative to the center of the performer's action space, i.e., intrinsic). The observed patterns of interference revealed that movements are primarily encoded within a radial egocentric reference frame in which the performer is the center of action space. The present psychophysical findings converge with primate single-cell recording studies in which the direction has been identified as a primary movement parameter that is encoded in various brain regions, thereby constituting a principal determinant of bilateral interference.
Neuroanatomical Correlates of Human Reasoning
Authors: Goel Vinod , Gold Brian , Kapur Shitij , Houle Sylvain 
Published: July 2002

One of the important questions cognitive theories of reasoning must address is whether logical reasoning is inherently sentential or spatial. A sentential model would exploit nonspatial (linguistic) properties of representations whereas a spatial model would exploit spatial properties of representations. In general terms, the linguistic hypothesis predicts that the language processing regions underwrite human reasoning processes, and the spatial hypothesis suggests that the neural structures for perception and motor control contribute the basic representational building blocks used for high-level logical and linguistic reasoning. We carried out a [15O] H2O PET imaging study to address this issue. Twelve normal volunteers performed three types of deductive reasoning tasks (categorical syllogisms, three-term spatial relational items, and three-term nonspatial relational items) while their regional cerebral blood flow pattern was recorded using [15O] H2O PET imaging. In the control condition subjects semantically comprehended sets of three sentences. In the deductive reasoning conditions subjects determined whether the third sentence was entailed by the first two sentences. The areas of activation in each reasoning condition were confined to the left hemisphere and were similar to each other and to activation reported in previous studies. They included the left inferior frontal gyrus (Brodmann areas 45, 47), a portion of the left middle frontal gyrus (Brodmann area 46), the left middle temporal gyrus (Brodmann areas 21, 22), a region of the left lateral inferior temporal gyrus and superior temporal gyrus (Brodmann areas 22, 37), and a portion of the left cingulate gyrus (Brodmann areas 32, 24). There was no significant right- hemisphere or parietal activation. These results are consistent with previous neuroimaging studies and raise questions about the level of involvement of classic spatial regions in reasoning about linguistically presented spatial relations.
Graded Functional Activation in the Visuospatial System with the Amount of Task Demand
Authors: Carpenter P. A. , Just M. A. , Keller T. A. , Eddy W. , Thulborn K. 
Published: July 2002

Abstract
Two studies examined how the amount and type of computational demand are related to fMRI-measured activation in three bilateral cortical regions involved in the Shepard-Metzler (1971) mental-rotation paradigm. The amount of demand for the computation of visuospatial coordinates was manipulated by presenting mental rotation problems with increasing angular disparity (0, 40, 80, or 120°). Activation in both the left and right intraparietal sulcal regions increased linearly with angular disparity in two separate studies. Activation also occurred in the fusiform gyrus and inferior temporal regions, regions that are primarily associated with the processes of object and object-part identification. By contrast, the demand for object recognition and rotation processes was relatively low, and the demand for executing saccades was high in a control condition that required making a systematic visual scan of two grids. The grid-scanning condition resulted in relatively less activation in the parietal and inferior temporal regions but considerable activation in frontal areas that are associated with planning and executing saccades, including the precentral gyrus and sulcus into the posterior middle frontal region. These data suggest that the amount of activation in the various cortical regions that support visuospatial processing is related to the amount, as well as to the type, of computational demand.
Aging and Recognition Memory: Changes in Regional Cerebral Blood Flow Associated with Components of Reaction Time Distributions
Authors: Madden David J. , Gottlob Lawrence R. , Denny Laura L. , Turkington Timothy G. , Provenzale James M. , Hawk Thomas C. , Coleman R. Edward 
Published: July 2002

Abstract
We used H2 15O positron emission tomography (PET) to measure age-related changes in regional cerebral blood flow (rCBF) during a verbal recognition memory task. Twelve young adults (20 to 29 years) and 12 older adults (62 to 79 years) participated. Separate PET scans were conducted during Encoding, Baseline, and Retrieval conditions. Each of the conditions involved viewing a series of 64 words and making a two-choice response manually. The complete reaction time (RT) distributions in each task condition were characterized in terms of an ex-Gaussian model (convolution of exponential and Gaussian functions). Parameter estimates were obtained for the mean of the exponential component (τ), representing a task-specific decision process and the mean of the Gaussian component (μ), representing residual sensory coding and response processes. Independently of age group, both μ and τ were higher in the Encoding and Retrieval conditions than in the Baseline condition, and τ was higher during Retrieval than during Encoding. Age-related slowing in task performance was evident primarily in μ. For young adults, rCBF activation in the right prefrontal cortex, in the Retrieval condition, was correlated positively with μ but not with τ. For older adults, rCBF changes (both increases and decreases) in several cortical regions were correlated with both μ and τ. The data suggest that the attentional demands of this task are relatively greater for older adults and consequently lead to the recruitment of additional neural systems during task performance.
Target Selection for Pursuit and Saccadic Eye Movements in Humans
Authors: Krauzlis R. J. , Zivotofsky A. Z. , Miles F. A. 
Published: July 2002

Abstract
Eye movements were recorded from three subjects as they initiated tracking of a small circle (“target”) moving leftward or rightward, above or below the horizontal meridian, either alone or in the presence of a small square (“distractor”) moving leftward or rightward on the other side of the horizontal meridian. At the start of each trial, subjects were provided with either a “form” cue (always centrally positioned and having the circular shape and color of the upcoming moving target) or a “location” cue (a small white square positioned where the upcoming target would appear). The latency of pursuit increased in the presence of an oppositely moving distractor when subjects were provided the form cues but not when they were provided the location cues. The latency of saccades showed similar, but smaller, increases when subjects were given the form cues. On many trials with the form cues, pursuit started in the direction of the distractor and then reversed to follow the target. On these trials, the initial saccade often, but not always, also followed the distractor. These results indicate that the mechanisms of target selection for pursuit and saccades are tightly coordinated but not strictly yoked. The shared effects of the distractor on the latencies of pursuit and saccades probably reflect the common role of visual attention in filtering the inputs that guide these two types of eye movements. The differences in the details of the effects on pursuit and saccades suggest that the neural mechanisms that trigger these two movements can be independently regulated.
Learning Chaotic Attractors by Neural Networks
Authors: Bakker Rembrandt , Schouten Jaap C. , Giles C. Lee , Takens Floris , Bleek Cor M. van den 
Published: July 2002

An algorithm is introduced that trains a neural network to identify chaotic dynamics from a single measured time series. During training, the algorithm learns to short-term predict the time series. At the same time a criterion, developed by Diks, van Zwet, Takens, and de Goede (1996) is monitored that tests the hypothesis that the reconstructed attractors of model-generated and measured data are the same. Training is stopped when the prediction error is low and the model passes this test. Two other features of the algorithm are (1) the way the state of the system, consisting of delays from the time series, has its dimension reduced by weighted principal component analysis data reduction, and (2) the user-adjustable prediction horizon obtained by “error propagation”—partially propagating prediction errors to the next time step. The algorithm is first applied to data from an experimental-driven chaotic pendulum, of which two of the three state variables are known. This is a comprehensive example that shows how well the Diks test can distinguish between slightly different attractors. Second, the algorithm is applied to the same problem, but now one of the two known state variables is ignored. Finally, we present a model for the laser data from the Santa Fe time-series competition (set A). It is the first model for these data that is not only useful for short-term predictions but also generates time series with similar chaotic characteristics as the measured data.
Reinforcement Learning in Continuous Time and Space
Authors: Doya Kenji 
Published: July 2002

This article presents a reinforcement learning framework for continuous-time dynamical systems without a priori discretization of time, state, and action. Basedonthe Hamilton-Jacobi-Bellman (HJB) equation for infinite-horizon, discounted reward problems, we derive algorithms for estimating value functions and improving policies with the use of function approximators. The process of value function estimation is formulated as the minimization of a continuous-time form of the temporal difference (TD) error. Update methods based on backward Euler approximation and exponential eligibility traces are derived, and their correspondences with the conventional residual gradient, TD (0), and TD (λ) algorithms are shown. For policy improvement, two methods—a continuous actor-critic method and a value-gradient-based greedy policy—are formulated. As a special case of the latter, a nonlinear feedback control law using the value gradient and the model of the input gain is derived. The advantage updating, a model-free algorithm derived previously, is also formulated in the HJB-based framework. The performance of the proposed algorithms is first tested in a nonlinear control task of swinging a pendulum up with limited torque. It is shown in the simulations that (1) the task is accomplished by the continuous actor-critic method in a number of trials several times fewer than by the conventional discrete actor-critic method; (2) among the continuous policy update methods, the value-gradient-based policy with a known or learned dynamic model performs several times better than the actor-critic method; and (3) a value function update using exponential eligibility traces is more efficient and stable than that based on Euler approximation. The algorithms are then tested in a higher-dimensional task: cart-pole swing-up. This task is accomplished in several hundred trials using the value-gradient-based policy with a learned dynamic model.