bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer simulation—discussion of the technique and comparison of languages
Authors: Teichroew Daniel , Lubin John Francis
Published: July 2002

The purpose of this paper is to present a comparison of some computer simulation languages and of some of the packages by which each is implemented. Some considerations involved in comparing software packages for digital computers are discussed in Part I. The issue is obvious: users of digital computers must choose from available languages or write their own. Substantial costs can occur, particularly in training, implementation and computer time if an inappropriate language is chosen. More and more computer simulation languages are being developed: comparisons and evaluations of existing languages are useful for designers and implementers as well as users.

The second part is devoted to computer simulation and simulation languages. The computational characteristics of simulation are discussed with special attention being paid to a distinction between continuous and discrete change models. Part III presents a detailed comparison of six simulation languages and packages: SIMSCRIPT, CLP, CSL, GASP, GPSS and SOL. The characteristics of each are summarized in a series of tables. The implications of this analysis for designers of languages, for users, and for implementers are developed.

The conclusion of the paper is that the packages now available for computer simulation offer features which none of the more general-purpose packages do and that analysis of strengths and weaknesses of each suggests ways in which both current and future simulation languages and packages can be improved.
On synchronization in hard-real-time systems
Authors: Faulk Stuart R. , Parnas David L.
Published: July 2002

The design of software for hard-real-time systems is usually difficult to change because of the constraints imposed by the need to meet absolute real-time deadlines on processors with limited capacity. Nevertheless, a new approach involving a trio of ideas appears to be helpful for those who build software for such complex applications.
Dynamic hash tables
Authors: Larson Per-Ake
Published: July 2002

Linear hashing and spiral storage are two dynamic hashing schemes originally designed for external files. This paper shows how to adapt these two methods for hash tables stored in main memory. The necessary data structures and algorithms are described, the expected performance is analyzed mathematically, and actual execution times are obtained and compared with alternative techniques. Linear hashing is found to be both faster and easier to implement than spiral storage. Two alternative techniques are considered: a simple unbalanced binary tree and double hashing with periodic rehashing into a larger table. The retrieval time of linear hashing is similar to double hashing and substantially faster than a binary tree, except for very small trees. The loading times of double hashing (with periodic reorganization), a binary tree, and linear hashing are similar. Overall, linear hashing is a simple and efficient technique for applications where the cardinality of the key set is not known in advance.
Factors of success for end-user computing
Authors: Rivard Suzanne , Huff Sid L.
Published: July 2002

A two-phase study concerned with the factors of success associated with the development of computer applications by end users was conducted in 10 large organizations. During the first phase, in-depth interviews were used to refine a preliminary model of the factors of success for user development of computer applications (UDA). In the second phase, a questionnaire was administered to 272 end users experienced in developing applications. Statistical tests of the relationships in the model indicated that all but one of the derived hypotheses were substantiated. The result of this study is a field-verified model of the factors of success of UDA that provides a basis for implementation of UDA practices and policies in organizations, as well as for further research in end-user computing.
A methodology for creating user views in database design
Authors: Storey Veda C. , Goldstein Robert C.
Published: July 2002

The View Creation System (VCS) is an expert system that engages a user in a dialogue about the information requirements for some application, develops an Entity-Relationship model for the user's database view, and then converts the E-R model to a set of Fourth Normal Form relations. This paper describes the knowledge base of VCS. That is, it presents a formal methodology, capable of mechanization as a computer program, for accepting requirements from a user, identifying and resolving inconsistencies, redundancies, and ambiguities, and ultimately producing a normalized relational representation. Key aspects of the methodology are illustrated by applying VCS's knowledge base to an actual database design task.
Programming languages for computer music synthesis, performance, and composition
Authors: Loy Gareth , Abbott Curtis
Published: July 2002

The development of formal, descriptive, and procedural notations has become a practical concern within the field of music now that computers are being applied to musical tasks. Music combines the real-time demands of performance with the intellectual demands of highly developed symbolic systems that are quite different from natural language. The richness and variety of these demands makes the programming language paradigm a natural one in the musical application of computers. This paradigm provides musicians with a fresh perspective on their work. At the same time, music is a very advanced form of human endeavor, making computer music applications a worthy challenge for computer scientists. In this paper we outline the traditional tasks and forms of representation in music, then proceed with a survey of languages that deal with music programming.
Efficient table-free sampling methods for the exponential, Cauchy, and normal distributions
Authors: Ahrens Joachim H. , Dieter Ulrich
Published: July 2002

Three algorithms for sampling from exponential, Cauchy and normal distributions are developed. They are based on the "exact approximation" method, and their expected numbers of consumed uniform deviates are less than 1.04 per sample from the target distributions. The algorithms are simple and easily implemented in any desired precision. They require no space for long tables of auxiliary vectors, merely a few constants are needed. Nevertheless, their speed compares well with the performance of much more complex and table-aided sampling procedures.
3D Animation of Telecollaborative Anthropomorphic Avatars
Authors: Luciano Cristian , Banerjee Pat , Mehrotra Sanjay
Published: July 2002

A high-performance solution offers faster 3D representation of users by avatars without compromising real-time interactivity.
Performance analysis of several back-end database architectures
Authors: Hagmann Robert Brian , Ferrari Domenico
Published: July 2002

The growing acceptance of database systems makes their performance increasingly more important. One way to gain performance is to off-load some of the functions of the database system to aback-end computer. The problem is what functions should be off-loaded to maximize the benefits of distributed processing.

Our approach to this problem consisted of constructing several variants of an existing relational database system. INGRES, that partition the database system software into two parts, and assigning these two parts to two computers connected by a local area network. For the purposes of this experiment, six different variants of the database software were constructed to test the sir most interesting functional subdivisions. Each variant was then benchmarked using two different databases and query streams. The communication medium and the communication software were also benchmarked to measure their contribution to the performance of each configuration.

Combining the database and network measurement results, various conclusions were reached about the viability of the configurations, the desirable properties of the communications mechanisms to he used, the operating system interface and overhead, and the performance of the database system. The variants to be preferred depend on the hardware technology, operating system features, database system internal structure, and network software overhead.
The cost distribution of clustering in random probing
Authors: Bollobás Béla , Broder Andrei Z. , Simon Istvan
Published: July 2002

A new approach to the analysis of random probing hashing algorithms is presented. The probability-generating function in closed form for the asymptotic cost of insertion via random probing with secondary clustering is derived. For higher-order clustering, it is shown that all the moments of the probability distribution of the insertion cost exist and are asymptotically equal to the corresponding moments of the cost distribution under uniform hashing. The method in this paper also leads to simple derivations for the expected cost of insertion for random probing with secondary and higher-order clustering.
Performance of the Firefly RPC
Authors: Schroeder Michael D. , Burrows Michael
Published: July 2002

In this paper we report on the performance of the remote procedure call (RPC) implementation for the Firefly multiprocessor and analyze the implementation to account precisely for all measured latency. From the analysis and measurements, we estimate how much faster RPC could be if certain improvements were made. The elapsed time for an intermachine call to a remote procedure that accepts no arguments and produces no results is 2.66 ms. The elapsed time for an RPC that has a single 1440-byte result (the maximum result that will fit in a single packet) is 6.35 ms. Maximum intermachine throughput of application program data using RPC is 4.65 Mbits/s, achieved with four threads making parallel RPCs that return the maximum-size result that fits in a single RPC result packet. CPU utilization at maximum throughput is about 1.2 CPU seconds per second on the calling machine and a little less on the server. These measurements are for RPCs from user space on one machine to user space on another, using the installed system and a 10 Mbit/s Ethernet. The RPC packet exchange protocol is built on IP/UDP, and the times include calculating and verifying UDP checksums. The Fireflies used in the tests had 5 MicroVAX II processors and a DEQNA Ethernet controller.
SILICON
Authors: Epstein Emanuel
Published: July 2002

▪ Abstract  Silicon is present in plants in amounts equivalent to those of such macronutrient elements as calcium, magnesium, and phosphorus, and in grasses often at higher levels than any other inorganic constituent. Yet except for certain algae, including prominently the diatoms, and the Equisetaceae (horsetails or scouring rushes), it is not considered an essential element for plants. As a result it is routinely omitted from formulations of culture solutions and considered a nonentity in much of plant physiological research. But silicon-deprived plants grown in conventional nutrient solutions to which silicon has not been added are in many ways experimental artifacts. They are often structurally weaker than silicon-replete plants, abnormal in growth, development, viability, and reproduction, more susceptible to such abiotic stresses as metal toxicities, and easier prey to disease organisms and to herbivores ranging from phytophagous insects to mammals. Many of these same conditions afflict plants in silicon-poor soils—and there are such. Taken together, the evidence is overwhelming that silicon should be included among the elements having a major bearing on plant life.
CHLOROPHYLL DEGRADATION
Authors: Matile Philippe , Hörtensteiner Stefan , Thomas Howard
Published: July 2002

▪ Abstract  Although the loss of green color in senescent leaves and ripening fruits is a spectacular natural phenomenon, research on chlorophyll breakdown has been largely neglected until recently. This review summarizes knowledge about the fate of chlorophyll in degreening tissues that has been gained during the past few years. Structures of end- and intermediary products of degradation as well as the biochemistry of the porphyrin-cleaving reaction have been elucidated. The intracellular localization of the catabolic pathway is particularly important in the regulation of chlorophyll breakdown. None of the genes encoding the related catabolic enzymes has so far been isolated, which makes chlorophyll degradation an area of opportunity for future research.
THE SCIENTIFIC BASIS OF FORESTRY
Authors: Perry David A.
Published: July 2002

A sufficiently wise and flexible silvicultural art can be developed on the ground only by practitioners who understand the forest as a biological entity.

     F. S. Baker ( 10 )

…the existing level of knowledge about forests is inadequate to develop sound forest management policies.

     National Research Council ( 114 )

▪ Abstract  Over the past two decades forestry in the United States has diverged into two approaches with quite different objectives and scientific priorities. The management focus of most industrial lands is on increasing productivity of wood fiber via plantations and various cultural tools, especially genetic selection, fertilization, and control of noncrop vegetation. Federal forest management has shifted from a similar focus to greater emphasis on protecting diversity and water. Issues of long-term sustainability are important regardless of ownership. Science has played and continues to play a fundamental role in all aspects. Selection for fast-growing genotypes has increased yields on the order of 10% to 20% depending on species. Fertilization often increases growth significantly but responses are variable and difficult to predict. Significant questions remain concerning the sustainability of intensive forestry, particularly when practiced over wide areas. Soils are heavily impacted by some harvesting practices, and the degree to which damage can be repaired by fertilizers is an important scientific issue. Intensive forestry often results in increased pest problems. In at least one case (fusiform rust in southern pines), a pest has been contained by selecting resistant cultivars, a situation that may or may not be evolutionarily stable. Species diversity is clearly reduced under intensive management, raising questions about the functional role of species with no commercial value. Many of the questions facing forestry science—particularly those dealing with the relation between complexity and function—are precisely the ones confronting basic ecology. Over the past decade scientists have labored to develop ecosystem-based management approaches that maintain system complexity and function, and scientists have increasingly played nontraditional roles at the interface between biology, sociology, and policy.
Sequestration of Defensive Substances from Plants by Lepidoptera
Authors: Nishida Ritsuo
Published: July 2002

▪ Abstract  A number of aposematic butterfly and diurnal moth species sequester unpalatable or toxic substances from their host plants rather than manufacturing their own defensive substances. Despite a great diversity in their life histories, there are some general features in the selective utilization of plant secondary metabolites to achieve effective protection from predators. This review illustrates the biochemical, physiological, and ecological characteristics of phytochemical-based defense systems that can shed light on the evolution of the widely developed sequestering lifestyles among the Lepidoptera.
Strategies and Statistics of Sampling for Rare Individuals
Authors: Venette Robert C. , Moon Roger D. , Hutchison William D.
Published: July 2002

▪ Abstract  Diverse subdisciplines within entomology recognize the detection of rare individuals as the precursor to effective management of these individuals. Unfortunately, detection methods have often developed on a case-by-case basis, and advances in one subdiscipline have not carried over to similarly related fields. The biology of a particular organism will certainly affect sampling methods, but the underlying principles governing the power of a sampling strategy to detect rare individuals will apply across taxa. Our review of the sampling literature demonstrates the common problem of detecting rare individuals, reviews the fundamentals of probability theory as a foundation for any monitoring program, and discusses the inferences that can be drawn from samples, especially when resources limit sampling efforts. Particular emphasis is placed on binomial-, beta-binomial-, and hypergeometric-based sampling strategies as they pertain to quarantine inspections for exotic pests, veterinary/medical entomology, and insecticide resistance monitoring.
SHELTERBELTS ANDWINDBREAKS:Mathematical Modeling and Computer Simulations of Turbulent Flows
Authors: Wang Hao , Takle Eugene S , Shen Jinmei
Published: July 2002

▪ Abstract  Shelterbelts or windbreaks were used for centuries to reduce wind speed, to control heat and moisture transfer and pollutant diffusion, to improve climate and environment, and to increase crop yields; but only within the last few decades have systematic studies considered the aerodynamics and shelter mechanisms of shelterbelts and windbreaks. This review examines recent modeling and numerical simulation studies as well as the mechanisms that control flow and turbulence around shelterbelts and windbreaks. We compare numerical simulations with experimental data and explain the relationships between sheltering effects and the structure of shelterbelts and windbreaks. We discuss how and why the desired effects are achieved by using numerical analysis. This chapter begins with the derivation of a general equation set for porous shelterbelts and windbreaks; the numerical model and simulation procedure are developed; unseparated and separated flows are predicted and characterized; the momentum budget and shelter mechanisms are analyzed; the effects of wind direction, density, width, and three dimensionality of shelterbelt structure on flow and turbulence are systematically described. Recent modeling and simulation of heat flux and evapotranspiration are also summarized. Finally, we discuss the use of high-performance distributed and parallel computing as well as clusters of networked workstations to enhance performance of the model applied to simulations of shelterbelts and windbreaks.
Human Ehrlichioses: Newly Recognized Infections Transmitted by Ticks
Authors: Dumler J. Stephen , Bakken Johan S.
Published: July 2002

Human ehrlichioses are tick-borne infections caused by bacteria in the genus Ehrlichia. Human monocytic ehrlichiosis is caused by Ehrlichia chaffeensis and human granulocytic ehrlichiosis is caused by an agent similar to Ehrlichia equi. E. chaffeensis infects mononuclear phagocytes and is transmitted by Lone Star ticks (Amblyomma americanum) found in the south central and eastern United States. The agent of human granulocytic ehrlichiosis infects mostly neutrophils, is transmitted by Ixodes species ticks, and occurs mostly in the upper midwest and northeast United States. Despite the undifferentiated presentation of both ehrlichioses with fever, headache, myalgias, leukopenia, thrombocytopenia, and elevated liver enzyme activities, the diagnostic methods are distinct. Occasional severe complications include meningoencephalitis, adult respiratory distress syndrome, shock, and opportunistic infections. Immunocompromised patients are at high risk for death. An adverse outcome is associated with delayed diagnosis and therapy; thus, empirical treatment is advocated. Treatment with doxycycline usually results in prompt defervescence and cure.
BACTERIAL HEAVY METAL RESISTANCE: New Surprises
Authors: Silver Simon , Phung Le T.
Published: July 2002

Bacterial plasmids encode resistance systems for toxic metal ions including Ag+, AsO2−, AsO43−, Cd2+, Co2+, CrO42−, Cu2+, Hg2+, Ni2+, Pb2+, Sb3+, TeO32−, Tl+, and Zn2+. In addition to understanding of the molecular genetics and environmental roles of these resistances, studies during the last few years have provided surprises and new biochemical mechanisms. Chromosomal determinants of toxic metal resistances are known, and the distinction between plasmid resistances and those from chromosomal genes has blurred, because for some metals (notably mercury and arsenic), the plasmid and chromosomal determinants are basically the same. Other systems, such as copper transport ATPases and metallothionein cation-binding proteins, are only known from chromosomal genes. The largest group of metal resistance systems function by energy-dependent efflux of toxic ions. Some of the efflux systems are ATPases and others are chemiosmotic cation/proton antiporters. The CadA cadmium resistance ATPase of gram-positive bacteria and the CopB copper efflux system of Enterococcus hirae are homologous to P-type ATPases of animals and plants. The CadA ATPase protein has been labeled with32P from γ-32P-ATP and drives ATP-dependent Cd2+uptake by inside-out membrane vesicles. Recently isolated genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson's disease, encode P-type ATPases that are more similar to the bacterial CadA and CopB ATPases than to eukaryote ATPases that pump different cations. The arsenic resistance efflux system transports arsenite, using alternatively either a two-component (ArsA and ArsB) ATPase or a single polypeptide (ArsB) functioning as a chemiosmotic transporter. The third gene in the arsenic resistance system, arsC, encodes an enzyme that converts intracellular arsenate [As (V)] to arsenite [As (III)], the substrate of the efflux system. The three-component Czc (Cd2+, Zn2+, and Co2+) chemiosmotic efflux pump of soil microbes consists of inner membrane (CzcA), outer membrane (CzcC), and membrane-spanning (CzcB) proteins that together transport cations from the cytoplasm across the periplasmic space to the outside of the cell. Finally, the first bacterial metallothionein (which by definition is a small protein that binds metal cations by means of numerous cysteine thiolates) has been characterized in cyanobacteria.
A Community of Ants, Fungi, and Bacteria: A Multilateral Approach to Studying Symbiosis
Authors: Currie Cameron R.
Published: July 2002

▪ Abstract  The ancient and highly evolved mutualism between fungus-growing ants and their fungi is a textbook example of symbiosis. The ants carefully tend the fungus, which serves as their main food source, and traditionally are believed to be so successful at fungal cultivation that they are able to maintain the fungus free of microbial pathogens. This assumption is surprising in light of theories on the evolution of parasitism, especially for those species of ants that have been clonally propagating their cultivars for millions of years. Recent work has established that, as theoretically predicted, the gardens of fungus-growing ants are host to a specialized, virulent, and highly evolved fungal pathogen in the genus Escovopsis. In addition, the ants have evolved a mutualistic association with filamentous bacteria (actinomycetes) that produce antibiotics that suppress the growth of Escovopsis. Thus, the attine symbiosis appears to be a coevolutionary “arms race” between the garden parasite Escovopsis on the one hand and the ant-fungus-actinomycete tripartite mutualism on the other. These recent findings indicate that microbes may be key components in the regulation of other symbiotic associations between higher organisms.
Modular Organization of Frequency Integration in Primary Auditory Cortex
Authors: Schreiner Christoph E. , Read Heather L. , Sutter Mitchell L.
Published: July 2002

Two fundamental aspects of frequency analysis shape the functional organization of primary auditory cortex. For one, the decomposition of complex sounds into different frequency components is reflected in the tonotopic organization of auditory cortical fields. Second, recent findings suggest that this decomposition is carried out in parallel for a wide range of frequency resolutions by neurons with frequency receptive fields of different sizes (bandwidths). A systematic representation of the range of frequency resolution and, equivalently, spectral integration shapes the functional organization of the iso-frequency domain. Distinct subregions, or “modules,” along the iso-frequency domain can be demonstrated with various measures of spectral integration, including pure-tone tuning curves, noise masking, and electrical cochlear stimulation. This modularity in the representation of spectral integration is expressed by intrinsic cortical connections. This organization has implications for our understanding of psychophysical spectral integration measures such as the critical band and general cortical coding strategies.
THE USE OF SCINTILLATING FIBERS FOR CHARGED-PARTICLE TRACKING
Authors: Ruchti R. C.
Published: July 2002

▪ Abstract  The demand for instrumentation capable of detecting and triggering on ionizing radiation in high-rate particle physics experiments at colliding-beam and fixed-target accelerator facilities and for spacecraft-borne instrumentation in astrophysics has led to the development of new tracking technologies. One of these, scintillating fiber tracking, combines the speed and efficiency of a scintillation detector with the flexibility and hermeticity afforded by fiber technology. A paradigm for a fiber-tracking detector that utilizes organic plastic fibers read out with visible-light photon counters is presented and critiqued. Alternate strategies are considered, and an overview of recent experimental applications is provided.
ASPECTS OF HEAVY-QUARK THEORY
Authors: Bigi I. , Shifman M. , Uraltsev N.
Published: July 2002

▪ Abstract  Recent achievements in heavy-quark theory are critically reviewed. The emphasis is put on those aspects that either did not attract enough attention or cause heated debates in the current literature. Among other topics we discuss (a) basic parameters of the heavy-quark theory; (b) a class of exact QCD inequalities; (c) new heavy quark sum rules; (d) the virial theorem; (e) applications (|Vcb| from the total semileptonic width and from the B → D* transition at zero recoil). In some instances new derivations of previously known results are given, or new aspects addressed. In particular, we dwell on the exact QCD inequalities. Furthermore, a toy model is considered that may shed light on the controversy regarding the value of the kinetic energy of heavy quarks obtained by different methods.
CURRENT QUESTS IN NUCLEAR ASTROPHYSICS AND EXPERIMENTAL APPROACHES
Authors: Käppeler F. , Thielemann F.-K. , Wiescher M.
Published: July 2002

▪ Abstract  This review summarizes current problems and questions in experimental nuclear astrophysics. It focuses on the present need for experimental data, emphasizing novel methods and approaches. Starting with an overview on nuclear energy generation and nucleosynthesis in an astrophysical plasma, the discussion concentrates on crucial problems related to the various aspects of stellar evolution, from the hydrostatic stage through the advanced burning scenarios up to and including the supernova explosion mechanism. Innovative experimental approaches are needed to pursue the associated questions in stellar nucleosynthesis. Particular emphasis is given to the potential use of radioactive ion beams and their importance for characterizing explosive nucleosynthesis in X-ray bursts and supernovae.
NEWPHYSICS INCPVIOLATIONEXPERIMENTS
Authors: Masiero Antonio , Vives Oscar
Published: July 2002

▪ Abstract  CP violation plays a privileged role in our quest for new physics beyond the electroweak standard model. In the standard model, the violation of CP in the weak interactions has a single source: the phase of the quark mixing matrix (the CKM matrix, for Cabibbo-Kobayashi-Maskawa). Most extensions of the standard model exhibit new sources of CP violation. For instance, the truly minimal supersymmetric extension of the standard model has two new phases in addition to the CKM phase. Given that CP violation is so tiny in the kaon system, is still largely unexplored in B physics, and is negligibly small in the electric dipole moments, it is clear that new physics may have a good chance to manifest some departure from the standard model in this particularly challenging class of rare phenomena. On the other hand, it is also apparent that CP violation generally represents a major constraint on any attempt at model building beyond the standard model. In this review, we tackle these two sides of the relation between CP violation and new physics. Our focus will be on the potentialities to use CP violation as a probe on supersymmetric (SUSY) extensions of the standard model. We wish to clarify the extent to which such indirect signals for SUSY are linked to a fundamental theoretical issue: Is there a relation between the mechanism that originates the whole flavor structure and the mechanism that is responsible for the breaking of supersymmetry? Different ways to answer this question lead to quite different expectations for CP violation in B physics.
INFRARED AND RAMAN VIBRATIONAL OPTICAL ACTIVITY: Theoretical and Experimental Aspects
Authors: Nafie Laurence A.
Published: July 2002

▪ Abstract  Advances in the field of vibrational optical activity (VOA) are reviewed over the past decade. Topics are surveyed with an emphasis on the theoretical and instrumental progress in both vibrational circular dichroism (VCD) and Raman optical activity (ROA). Applications of VOA to stereochemical and biological problems are reviewed, with a bias toward new kinds of experiments made possible by theoretical and instrumental advances. In the field of VCD, the most notable advances have taken place in the quality and size of ab initio calculations of VOA intensities and in the quality of step-scan Fourier transform instrumentation. For ROA, the most dramatic progress has occurred in the areas of theoretical formulation and high-throughput instrumentation. Applications of VOA now include all major classes of biological and pharmaceutical molecules. VOA's importance as a diagnostic tool will likely grow as the control of molecular chirality increases in research and industrial areas.
Decoding the Dynamical Information Embedded in Highly Mixed Quantum States
Authors: Keske John C. , Pate Brooks H.
Published: July 2002

▪ Abstract  The standard description of the vibrational and rotational motion of polyatomic molecules, as expressed by the distortable rotor/harmonic oscillator approximation, provides an adequate description of the molecular quantum states only in regions of low total state density. When the total state density is large, exceeding 100 states/cm−1, the vibrational dynamics are “dissipative” and the fundamental process of intramolecular vibrational energy redistribution is operative. The presence of intramolecular vibrational energy redistribution leads to molecular quantum states of a qualitatively different nature. With respect to a normal-mode vibrational basis, these quantum states are “highly mixed” in their vibrational character and represent nuclear motion that is a combination of all the normal-mode motions. This review describes frequency domain spectroscopy techniques designed to probe the vibrational, rotational, and structural composition of these eigenstates. Recent work that investigates spectroscopy between highly mixed states is also reviewed.
Cellular Mechanism of Oxygen Sensing
Authors: López-Barneo José , Pardal Ricardo , Ortega-Sáenz Patricia
Published: July 2002

▪ Abstract  O2sensing is a fundamental biological process necessary for adaptation of living organisms to variable habitats and physiological situations. Cellular responses to hypoxia can be acute or chronic. Acute responses rely mainly on O2-regulated ion channels, which mediate adaptive changes in cell excitability, contractility, and secretory activity. Chronic responses depend on the modulation of hypoxia-inducible transcription factors, which determine the expression of numerous genes encoding enzymes, transporters and growth factors. O2-regulated ion channels and transcription factors are part of a widely operating signaling system that helps provide sufficient O2to the tissues and protect the cells against damage due to O2deficiency. Despite recent advances in the molecular characterization of O2-regulated ion channels and hypoxia-inducible factors, several unanswered questions remain regarding the nature of the O2sensor molecules and the mechanisms of interaction between the sensors and the effectors. Current models of O2sensing are based on either a heme protein capable of reversibly binding O2or the production of oxygen reactive species by NAD(P)H oxidases and mitochondria. Complete molecular characterization of the hypoxia signaling pathways will help elucidate the differential sensitivity to hypoxia of the various cell types and the gradation of the cellular responses to variable levels of PO2. A deeper understanding of the cellular mechanisms of O2sensing will facilitate the development of new pharmacological tools effective in the treatment of diseases such as stroke or myocardial ischemia caused by localized deficits of O2.
Trafficking of Canalicular ABC Transporters in Hepatocytes
Authors: Kipp Helmut , Arias Irwin M.
Published: July 2002

▪ Abstract  ATP-binding cassette (ABC) transporters located in the hepatocyte canalicular membrane of mammalian liver are critical players in bile formation and detoxification. Although ABC transporters have been well characterized functionally, only recently have several canalicular ABC transporters been cloned and their molecular nature revealed. Subsequently, development of specific antibodies has permitted a detailed investigation of ABC transporter intrahepatic distribution under varying physiological conditions. It is now apparent that there is a complex array of ABC transporters in hepatocytes. ABC transporter molecules reside in intrahepatic compartments and are delivered to the canalicular domain following increased physiological demand to secrete bile. Insufficient amounts of ABC transporters in the bile canalicular membrane result in cholestasis (i.e., bile secretory failure). Therefore, elucidation of the intrahepatic pathways and regulation of ABC transporters may help to understand the cause of cholestasis at a molecular level and provide clues for novel therapies.
STUDYING THE PRESIDENCY
Authors: Bowles Nigel
Published: July 2002

▪ Abstract  This essay identifies five schools of presidential study and argues that the presidency is better understood for the plurality of scholarly approaches embodied in them. The obstacles to the presidency's study notwithstanding, much more is now known about the presidency as an institution than was the case as recently as the mid-1970s. The essay argues that further research ought ideally to meet three conditions: It must be constitutionally informed and politically nuanced; it must be empirically rich, drawing on primary data in some form; and the investigation of particular cases should proceed with the cases' wider significance in mind, if not necessarily with the explicit intention of generating theory.
Food Intake and the Regulation of Body Weight
Authors: Woods Stephen C. , Schwartz Michael W. , Baskin Denis G. , Seeley Randy J.
Published: July 2002

This chapter reviews the recent literature on hormonal and neural signals critical to the regulation of individual meals and body fat. Rather than eating in response to acute energy deficits, animals eat when environmental conditions (social and learned factors, food availability, opportunity, etc.) are optimal. Hence, eating patterns are idiosyncratic. Energy homeostasis, the long-term matching of food intake to energy expenditure, is accomplished via controls over the size of meals. Individuals who have not eaten sufficient food to maintain their normal weight have lower levels of adiposity signals (leptin and insulin) in the blood and brain, and one consequence is that meal-generated signals (such as CCK) are less efficacious at reducing meal size. The converse is true if individuals are above their normal weight, when they tend to eat smaller meals. The final section reviews how these signals are received and integrated by the CNS, as well as the neural circuits and transmitters involved.
Psycholinguistics: A Cross-Language Perspective
Authors: Bates Elizabeth , Devescovi Antonella , Wulfeck Beverly
Published: July 2002

▪ Abstract  Cross-linguistic studies are essential to the identification of universal processes in language development, language use, and language breakdown. Comparative studies in all three areas are reviewed, demonstrating powerful differences across languages in the order in which specific structures are acquired by children, the sparing and impairment of those structures in aphasic patients, and the structures that normal adults rely upon most heavily in real-time word and sentence processing. It is proposed that these differences reflect a cost-benefit trade-off among universal mechanisms for learning and processing (perception, attention, motor planning, memory) that are critical for language, but are not unique to language.
Evolutionary Psychology: Toward a Unifying Theory and a Hybrid Science
Authors: Caporael Linnda R.
Published: July 2002

▪ Abstract  Although evolutionary psychology is typically associated with “selfish gene theory,” numerous other approaches to the study of mind and behavior provide a wealth of concepts for theorizing about psychology, culture, and development. These include general evolutionary approaches and theories focused on sociality, dual inheritance, multilevel selection, and developmental systems. Most evolutionary accounts use the same methods as Darwin—the “fit among facts”—to use natural selection as an explanation for behavior. Scientific standards for constraining and evaluating such accounts, research into the mutual influence of science and society on the understanding of evolution, and computational technologies for modeling species-typical processes are important considerations. Coevolutionary theories and developmental systems theories may eventually give rise to unification in a broad and general sense. Such a unification would be interdisciplinary and problem centered rather than discipline centered.
TIME-DEPENDENT COVARIATES IN THE COX PROPORTIONAL-HAZARDS REGRESSION MODEL
Authors: Fisher Lloyd D. , Lin D. Y.
Published: July 2002

▪ Abstract  The Cox proportional-hazards regression model has achieved widespread use in the analysis of time-to-event data with censoring and covariates. The covariates may change their values over time. This article discusses the use of such time-dependent covariates, which offer additional opportunities but must be used with caution. The interrelationships between the outcome and variable over time can lead to bias unless the relationships are well understood. The form of a time-dependent covariate is much more complex than in Cox models with fixed (non–time-dependent) covariates. It involves constructing a function of time. Further, the model does not have some of the properties of the fixed-covariate model; it cannot usually be used to predict the survival (time-to-event) curve over time. The estimated probability of an event over time is not related to the hazard function in the usual fashion. An appendix summarizes the mathematics of time-dependent covariates.
Understanding Changing Risk Factor Associations With Increasing Age in Adults
Authors: Kaplan G. A. , Haan Mary N. , Wallace Robert B.
Published: July 2002

▪ Abstract  With an increasingly older population, there is considerable interest in understanding the potential for risk factor interventions in order to prevent, postpone, or slow down the common diseases seen in older persons. However, it is often reported that the strength of association between risk factors and common disease outcomes decreases with increasing age. Actually, many different age-related patterns are observed. Understanding these patterns requires knowledge of issues related to the pathophysiology of aging, including age-related physiologic and metabolic alterations, detection and diagnosis of disease in the elderly, measurement of risk factors, sample selection, comorbidity, competing risks, selective survival, ceiling effects, and methods of analysis in aging populations.
Electrophysiology and Arrhythmogenic Activity of Single Cardiomyocytes From Canine Superior Vena Cava
Authors: Chen Yi-Jen , Chen Yao-Chang , Yeh Hung-I , Lin Cheng-I , Chen Shih-Ann
Published: July 2002

Background
—

The superior vena cava (SVC) has been proved to be a focal point in the initiation of paroxysmal atrial fibrillation. The autonomic nervous system plays an important role in the genesis of atrial fibrillation. However, the arrhythmogenic potentials of SVC and its responses to autonomic agents are not clear. The purpose of this study was to isolate single SVC cardiomyocytes and to investigate their electrophysiological characteristics, as well as the direct effects of autonomic agents.

Methods and Results
—

Canine SVC cardiomyocytes were isolated by perfusion with digestive enzymes. The action potentials and ionic currents were investigated in single SVC cardiomyocytes using the whole-cell clamp technique. Dissociation of the SVC yielded rod-shaped single cardiomyocytes with (n=74, 51%) or without (n=71, 49%) pacemaker activities. There were similar densities of inward Ca
2+
, delayed rectifier K
+
, transient inward, inward rectifier K
+
, and pacemaker currents between SVC cardiomyocytes with and without pacemaker activity. SVC cardiomyocytes with pacemaker activity have, however, greater transient outward currents than those without pacemaker activity. In SVC cardiomyocytes, acetylcholine (5.5 μmol/L) abolished the spontaneous activities, but isoproterenol (10 nmol/L), atropine (10 μmol/L), and phenylephrine (10 μmol/L) accelerated the spontaneous activity and induced the occurrences of early or delayed afterdepolarizations.

Conclusions
—

These findings suggest that SVC cardiomyocytes have distinct action potentials and ionic current profiles that may be responsible for the arrhythmogenic activity of the SVC.
One Step Forward: African-American Married Women in the South, 1950-1960
Authors: Heinicke Craig W.
Published: July 2002

The labor-force participation of African-American married women in the southern United States was increasing during a period of deteriorating labor markets when that of African-American men was decreasing. Although the effect of this development on the African-American family was complex, the trend was certainly a sign of limited progress for these women. The jobs that they were able to acquire were generally better than their customary work since the Civil War, despite the adverse labor-market shocks to which African-American families were subject.
Gene Culture: Molecular Metaphor in Visual Art
Authors: Anker Suzanne
Published: July 2002

This paper addresses visual art's relationship to genetics and its attendant metaphorical representation. By diagramming models of the ways in which DNA is visualized and comprehended as a system of signs, parallel conceptions between art history's engagement with abstraction, recontextualization, and duplication is compared to genetic process and laboratory experimentation.
Hypermedia, Eternal Life, and the Impermanence Agent
Authors: Wardrip-Fruin Noah
Published: July 2002

We look to media as memory, and a place to memorialize, when we have lost. Hypermedia pioneers such as Ted Nelson and Vannevar Bush envisioned the ultimate media within the ultimate archive—with each element in continual flux, and with constant new addition. Dynamism without loss. Instead we have the Web, where “Not Found” is a daily message. Projects such as the Internet Archive and Afterlife dream of fixing this uncomfortable impermanence. Marketeers promise that agents (indentured information servants that may be the humans of About.com or the software of “Ask Jeeves”) will make the Web comfortable through filtering—hiding the impermanence and overwhelming profluence that the Web's dynamism produces. The Impermanence Agent—a programmatic, esthetic, and critical project created by the author, Brion Moss, a.c. chapman, and Duane Whitehurst— operates differently. It begins as a storytelling agent, telling stories of impermanence, stories of preservation, memorial stories. It monitors each user's Web browsing, and starts customizing its storytelling by weaving in images and texts that the user has pulled from the Web. In time, the original stories are lost. New stories, collaboratively created, have taken their place.
Measuring the VC-Dimension Using Optimized Experimental Design
Authors: Shao Xuhui , Cherkassky Vladimir , Li William
Published: July 2002

VC-dimension is the measure of model complexity (capacity) used in VC-theory. The knowledge of the VC-dimension of an estimator is necessary for rigorous complexity control using analytic VC generalization bounds. Unfortunately, it is not possible to obtain the analytic estimates of the VC-dimension in most cases. Hence, a recent proposal is to measure the VC-dimension of an estimator experimentally by fitting the theoretical formula to a set of experimental measurements of the frequency of errors on artificially generated data sets of varying sizes (Vapnik, Levin, & Le Cun, 1994). However, it may be difficult to obtain an accurate estimate of the VC-dimension due to the variability of random samples in the experimental procedure proposed by Vapnik et al. (1994). We address this problem by proposing an improved design procedure for specifying the measurement points (i.e., the sample size and the number of repeated experiments at a given sample size). Our approach leads to a nonuniform design structure as opposed to the uniform design structure used in the original article (Vapnik et al., 1994). Our simulation results show that the proposed optimized design structure leads to a more accurate estimation of the VC-dimension using the experimental procedure. The results also show that a more accurate estimation of VC-dimension leads to improved complexity control using analytic VC-generalization bounds and, hence, better prediction accuracy.
Do Simple Cells in Primary Visual Cortex Form a Tight Frame?
Authors: Salinas Emilio , Abbott L. F.
Published: July 2002

Sets of neuronal tuning curves, which describe the responses of neurons as functions of a stimulus, can serve as a basis for approximating other functions of stimulus parameters. In a function-approximating network, synaptic weights determined by a correlation-based Hebbian rule are closely related to the coefficients that result when a function is expanded in an orthogonal basis. Although neuronal tuning curves typically are not orthogonal functions, the relationship between function approximation and correlation-based synaptic weights can be retained if the tuning curves satisfy the conditions of a tight frame. We examine whether the spatial receptive fields of simple cells in cat and monkey primary visual cortex (V1) form a tight frame, allowing them to serve as a basis for constructing more complicated extrastriate receptive fields using correlation-based synaptic weights. Our calculations show that the set of V1 simple cell receptive fields is not tight enough to account for the acuity observed psychophysically.
Differential Filtering of Two Presynaptic Depression Mechanisms
Authors: Bertram Richard
Published: July 2002

The filtering of input signals carried out at synapses is key to the information processing performed by networks of neurons. Two forms of presynaptic depression, vesicle depletion and G-protein inhibition of Ca2+ channels, can play important roles in the presynaptic processing of information. Using computational models, we demonstrate that these two forms of depression filter information in very different ways. G- protein inhibition acts as a high-pass filter, preferentially transmitting high-frequency input signals to the postsynaptic cell, while vesicle depletion acts as a low-pass filter. We examine how these forms of depression separately and together affect the steady-state postsynaptic responses to trains of stimuli over a range of frequencies. Finally, we demonstrate how differential filtering permits the multiplexing of information within a single impulse train.