Showing papers by "University of California published in 1987"

How brains make chaos in order to make sense of the world

Abstract: Recent “connectionist” models provide a new explanatory alternative to the digital computer as a model for brain function. Evidence from our EEG research on the olfactory bulb suggests that the brain may indeed use computational mechanisms like those found in connectionist models. In the present paper we discuss our data and develop a model to describe the neural dynamics responsible for odor recognition and discrimination. The results indicate the existence of sensory- and motor-specific information in the spatial dimension of EEG activity and call for new physiological metaphors and techniques of analysis. Special emphasis is placed in our model on chaotic neural activity. We hypothesize that chaotic behavior serves as the essential ground state for the neural perceptual apparatus, and we propose a mechanism for acquiring new forms of patterned activity corresponding to new learned odors. Finally, some of the implications of our neural model for behavioral theories are briefly discussed. Our research, in concert with the connectionist work, encourages a reevaluation of explanatory models that are based only on the digital computer metaphor.

Choice under Uncertainty: Problems Solved and Unsolved

Abstract: Ffifteen years ago, the theory of choice under uncertainty could be considered one of the “success stories” of economic analysis: it rested on solid axiomatic foundations, it had seen important breakthroughs in the analytics of risk, risk aversion and their applications to economic issues, and it stood ready to provide the theoretical underpinnings for the newly emerging “information revolution” in economics.1 Today choice under uncertainty is a field in flux: the standard theory is being challenged on several grounds from both within and outside economics. The nature of these challenges, and of our profession’s responses to them, is the topic of this paper.

Relaxation in complex systems

Abstract: The phenomenon of slow relaxation is discussed with emphasis on finding a general explanation of its ubiquity After a review of the phenomenon, possible causes are considered both at the microscopic level and from a configuration space viewpoint Quenched randomness and strongly constrained dynamics appear most important microscopically In configuration space the central requirement seems to be the existence of many valleys connected sparsely in a hierarchical way Recent toy models are shown to fit into this overall picture

The Role of Risk in Explaining Differences in Profitability

Abstract: This study examined the role of risk in explaining cross-sectional differences in the profitability of business units. Applying suggestions of financial theory, we disaggregated risk into two components-systematic and unsystematic-that are thought to have different effects on return. Drawing on the PIMS data base, we found each component of risk to have a substantial, significant, and different impact on return on investment (ROI). The research and strategy implications of the roles of risk are discussed. The two key factors in any investment decision are return and risk. Under the assumption that investors are risk-averse and seek to minimize the risk for any level of expected return, intuition suggests that additional return must compensate investors for assuming additional risk. Scholars in finance and other disciplines have devoted a great deal of work to refining and formalizing this intuition. This same logic applies in the context of strategy, as Wensley (1981), Bettis and Mahajan (1985), and others have observed. A strategic investment decision should explicitly consider risk-decision makers should demand a higher return for an investment involving high risk. Yet, in typical practice, strategic investment decisions are adjusted for risk ad hoc, if at all. Firms typically set relatively high hurdle rates in making go/no go investment decisions and apply these rates to all investments, regardless of their riskiness (Hayes & Gavin, 1982). Further, historical evaluation of existing strategies, whether it concerns evaluating present management or attempting to place values on businesses to be divested or acquired, focuses almost exclusively on return and rarely attempts to quantify risk. These failures to account for risk adequately will unquestionably lead to inappropriate decisions. All else being equal, if firms judge business performance only in terms of return, regardless of risk, they will place more resources than warranted in risky strategies, forgo profitable opportunities, and apply misguided performance evaluations. Further, if researchers do not control for risk in studies assessing the effects of strategic factors on We would like to thank the Strategic Planning Institute for providing access to the data used in this study.

Ethylene in Plant Growth, Development, and Senescence

Abstract: Amongst hormones in both plant and animal kingdoms, ethylene, a gaseous hydrocarbon, is unique. Despite its chemical simplicity, it is a potent growth regulator, affecting the growth, differentiation, and senescence of plants, in concentrations as little as 0.01 µl/1. As recently as twenty years ago, plant physiologists were divided as to whether this gas, which had been shown to have a range of striking effects on plant tissues, could properly be called a hormone. Since then, the advent of gas chromatographic means of detecting and measuring ethylene, the elucidation of its biosynthetic pathway, and the discovery of potent regulators of its production and action, have provided powerful tools for physiologists to explore the role of ethylene in plant growth and development. Ethylene is now considered to be one of the important natural plant growth regulators, and the literature abounds with reports of its effects on almost every phase of the life of plants. Although the majority of studies have concentrated on particular processes, particularly fruit ripening, flower senescence, and abscission, many other reported responses of plants to ethylene may be important parts of normal growth and development.

Biosynthesis and Metabolism of Ethylene

Abstract: Ethylene is a plant hormone that is involved in the regulation of many physiological responses (2). In addition to its recognition as a “ripening hormone”, ethylene is involved in other developmental processes from germination of seeds to senescence of various organs and in many responses to environmental stresses.

Pharmacodynamic modeling of the EEG effects of ketamine and its enantiomers in man

Abstract: The pharmacodynamics of a racemic mixture of ketamine R,S (±)-ketamine and of each enantiomer, S(+)-ketamine and R(−)-ketamine, were studied in five volunteers. The median frequency of the electroencephalogram (EEG) power spectrum, a continuous noninvasive measure of the degree of central nervous system (CNS) depression (pharmacodynamics), was related to measured serum concentrations of drug (pharmacokinetics). The concentration-effect relationship was described by an inhibitory sigmoid Emax pharmacodynamic model, yielding estimates of both maximal effect (Emax) and sensitivity (IC50) to the racemic and enantiomeric forms of ketamine. R(−)-ketamine was not as effective as R,S(±)-ketamine or S(+)-ketamine in causing EEG slowing. The maximal decrease (mean±SD) of the median frequency (Emax)for R(−)-ketamine was 4.4±0.5 Hz and was significantly different fromR,S (±)-ketamine (7.6 ±1.7 Hz) and S(+)-ketamine (8.3±1.9Hz). The ketamine serum concentration that caused one-half of the maximal median frequency decrease (IC50) was 1.8±0.5Μg/mL for R(−)-ketamine; 2.0±0.5 Μg/mL for R,S(±)-ketamine; and 0.8±0.4 Μg/mL for S(+)-ketamine. Because the maximal effect (Emax) of the R(−)-ketamine was different from that of S(+)-ketamine and R,S(±)-ketamine, it was not possible to directly compare the potency (i.e., IC50) of these compounds. Accordingly, a classical agonist/partial-agonist interaction model was examined, using the separate enantiomer results to predict racemate results. Although the model did not predict racemate results well, its failure was not so great as to provide clear evidence of synergism (or excess antagonism) of the enantiomers.

Infant Predictors of the Longitudinal Course of Schizophrenic Development

Abstract: This study was begun in 1952 to test the hypothesis that specific neurointegrative disorders in infancy predict vulnerability to later schizophrenia and schizotypal disorder. Twelve offspring of chronic schizophrenic mothers and 12 controls from similar low socioeconomic status (SES) backgrounds have been studied since their births in 1952-53 and 1959-60. The infants were ranked according to the severity of their neurointegrative disorder, or "pandysmaturation" (PDM), based on analysis of Gesell tests and physical growth measures repeated 10 times between birth and 2 years. Twenty-three subjects (96 percent) completed all 10-, 15- and 20/22-year followup examinations. PDM was significantly related to maternal schizophrenia but not to obstetrical complications, SES, sex, or ethnic background. The severity of PDM was significantly related to the blind evaluations of the severity of psychopathology at 10 years. One 26-year risk subject has been chronically schizophrenic since age 17. The author, nonblind, provisionally diagnosed six other risk subjects as schizotypal or paranoid personality. All seven had PDM; six required 6 to 18+ years of treatment; four with "negative" symptoms remain severely impaired. All six sick subjects had severe social-affective symptoms by 3-6 years of age; four had perceptual deficits by 2 years. Some social-affective, cognitive, academic, and vocational impairments included in the "negative" symptoms and "process" traits of schizophrenia had antecedents before 2 years of age. Primary prevention requires research into the mechanisms underlying these dysfunctions in infancy.

Stochastic modeling of the independent roles of particle size and grain size in transgranular cleavage fracture

Abstract: The independent roles of grain size and particle size on sharp crack and rounded notch toughness are investigated over a range of temperatures from the lower shelf into the early ductile/brittle transition region. The results are interpreted in terms of a weakest link statistical model wherein the onset of failure coincides with the critical propagation of a particle microcrack into the matrix. It is shown that, for a fixed particle size distribution, both sharp-crack and rounded-notch toughness decrease with increasing grain size. However, at fixed grain size, the sharp-crack toughness increases, while the rounded-notch toughness decreases with increasing particle size. Such effects result primarily from the difference in the number of activated particles in the plastic zone.

Chronic low-level lead exposure. Its role in the pathogenesis of hypertension.

Abstract: Lead is a common element in the earth's crust, serving useful purposes in industry, but serving no purpose in the human body. Increase in blood pressure is an important public health problem with numerous factors contributing to many facets of the disease. The relationship of lead exposure and increased blood pressure has long been considered, but only recently critically investigated. Reports of subtle changes in calcium metabolism and renal function, as well as in vitro studies examining end-arteriolar smooth muscle contractility, link lead exposure and increased blood pressure. This paper critically examines the evidence associating chronic low-level lead exposure and increased blood pressure. The review focuses on epidemiological, clinical, and toxicological data. The epidemiological evidence is consistent with low-level exposure to lead causing an elevation in blood pressure. The strength of that association, and the dose-response characteristics, are less certain. Individual resistance and susceptibility could affect the degree of blood pressure elevation. The results of animal and in vitro studies are consistent with the epidemiological evidence, and suggest biologically plausible mechanisms for the association. The most probable mechanisms are intracellular perturbations in calcium metabolism mediated by direct lead effects at the end-arteriole, and indirect effects via renal dysfunction. Better indices of lead exposure and lead activity are needed to quantify these effects in humans. New and safer methods of chelating lead suggest interesting approaches for studying the relationship between lead and hypertension. This link could have significant implications in determining what constitutes a 'safe' level of environmental lead exposure, and whether a proportion of essential hypertension could be 'cured' by chelation therapy.

The Evolution of Deterrent Responses in Plant­ Feeding Insects

Abstract: A plant deterrent may be defined as “a chemical which inhibits feeding or ovi-position when present in a place where insects would, in its absence, feed or oviposit” (Dethier et al. 1960). In general, we believe that behavioral deterrence caused by such chemicals in plants plays a major role in host selection (Dethier 1954; Jermy 1966; Bernays and Chapman 1977), and the chemicals effectively protect most plants from most insects. All plants have a complex profile of secondary compounds ranging in number from a few to hundreds and there are an estimated 100,000–400,000 different secondary compounds in terrestrial plant species (Swain 1977). Most that have been investigated are deterrent to one or other of the insect species tested. The more restricted the insect’s host range, the more compounds that are found deterrent and the lower the threshold for rejection of such deterrents (Jermy 1983).

Natural Products Chemistry and Chemical Defense in Tropical Marine Algae of the Phylum Chlorophyta

Abstract: This article reviews the natural products chemistry of marine green algae (Chlorophyta), including investigations to December, 1986 The natural products chemistry is presented with an emphasis on chemical ecology, and in particular upon the natural biological functions of algal metabolites in the marine environment The results of biological testing of the metabolites in laboratory assays designed to examine antimicrobial activity, cytotoxicity, larval toxicity, and ichthyotoxicity are summarized Results of laboratory and field experiments designed to identify the deterrent effects of the metabolites toward herbivores are also reviewed Recent studies, documenting chemical variation in the production of secondary metabolites within plants, among individual plants, and among populations of algae are discussed, with a focus on the ecological factors which may produce this phenomenon

Transport and transformations of organic chemicals in the soil-air-water ecosystem

Abstract: The dissemination of soil-applied organic compounds through the environment stems in large part from the old concept of soil as a safe waste repository. The early conventional wisdom assumed that organic chemicals would either degrade into harmless byproducts as a result of microbial or chemical reactions, immobilize completely by binding to soil solids, or volatilize to the atmosphere where dilution to harmless levels was assured. This false assurance led to years of agricultural chemical use and chemical waste disposal with no monitoring of soil, atmosphere, or groundwater in the vicinity of application or storage sites.

Calluses and callus-like growth in seaweeds: Induction and culture

Abstract: Calluses of plants are masses of unorganized tissues formed as a result of injury. Some callus masses are soft, others are of harder consistency, and all are lumps of undifferentiated cells, an abnormal growth-form of the plant. This paper describes seaweed calluses, and similar abnormal growth-forms of seaweeds which produce mounds of undifferentiated tissues referred to here as callus-like growth.

Late Pleistocene Refugia in Europe

Abstract: In the archaeological record of Paleolithic Europe, southwestern France stands out as a region of exceptional richness and complexity, known for its abundance of sites, detailed sequence of archaeological cultures, and rich inventory of parietal and portable art. In order to explain the extraordinary developments in this area, attention must be given to the unique combination of factors that set this region apart from the rest of western Europe. Some of these factors are local and will be mentioned briefly. Others, however, are regional, in that they may be discovered only by examining southwestern France in the context of a larger area. It is these latter factors that are the main focus of this discussion. Southwestern France will be viewed as a refugium for European populations during the last glacial maximum, and the implications of this view will be explored.

Apparatus and method of preserving the viability of animal organs

Abstract: An apparatus and method of maintaining the viability of animal organs, and in particular human organs, by controlling the storage temperature of the organ and providing the organ with sufficient nutrients and oxygen, while also monitoring and maintaining the organ's transmembrane potential within a predefined range.

The relationship between toughness and microstructure in Fe-high Mn binary alloys

Abstract: The influence of Mn content on the ductile-brittle transition in 16 to 36 wt pct Mn steels was investigated and interpreted in light of the evolving microstructure. It was found that when hcp e martensite is present in the as-quenched condition or forms during deformation, it lowers the toughness. In 25Mn steel, the stress concentrations at e plate intersections result in the formation of planar void sheets along the {111}γ planes. The deformation-induced α’ martensite in 16 to 20 pct Mn alloys enhances the toughness, but leads to a ductile-to-brittle transition at low temperatures that is due to the intrusion of an intergranular fracture mode. Binary alloys with greater than 31 pct Mn also fracture in an intergranular mode at 77 K although the impact energy remains quite high. Auger spectroscopy of the fracture surfaces shows no evidence of significant impurity segregation, which suggests the importance of slip heterogeneity in controlling intergranular fracture in these alloys.

Dimensions and Components of Individual Differences in Spatial Abilities

Abstract: The goal of this chapter is to review advances in the study of individual differences in spatial abilities and to consider some of the practical implications of this work. There are many reasons for the study of spatial cognition in general and spatial ability in particular. First, it is of theoretical and practical significance to understand how individuals represent the physical world in which they operate. Evidence exists for a theoretical separation of spatial representations and semantic representations. Second, there is a substantial literature suggesting the existence of several spatial abilities which are differentiable from general ability and from verbal abilities. Third, there appear to be important sex differences in some spatial abilities. Fourth, measures of spatial ability frequently add unique variance to the prediction of performance in certain courses such as engineering design or graphics and occupations such as mechanic, architect, or pilot.

Comparison of esmolol and nitroprusside for acute post-cardiac surgical hypertension.

Abstract: Because acute systemic hypertension early after cardiac surgery has been linked to catecholamine elevation, an open-label, randomized, crossover study was performed to compare the efficacy of esmolol, a new ultra-short-acting intravenous β-blocking agent, to nitroprusside, the standard therapy. Controlled drug infusions to maximal dosage (esmolol, 300 μg/kg/min, and nltroprusside, 10 μg/kg/min) were titrated to achieve at least a 15% reduction in systolic pressure. The blood pressure (BP) endpoint was achieved with esmolol (within 29 ± 14 minutes) in 18 of 20 patients (90%), compared with 19 of 20 (95%) with nitroprusside infusion (within 21 ± 15 minutes, difference not significant [NS]). Systolic BP decreased from 170 ± 13 to 136 ± 12 mm Hg (mean ± standard deviation) with esmolol and from 170 ± 13 to 141 ± 13 mm Hg with nitr roprusside infusion (both p

Interstellar Magnetic Fields

Abstract: Methods to observe magnetic fields are considered. Next, results for external galaxies are reviewed; I conclude that most results are questionable. Next, the Galactic field is reviewed. The large-scale field decreases slowly with Galactic radius and z, and has a strength ~ 4 µG near the Sun. It is a roughly circular field, which may reverse one or more times inside the Solar circle. The local value of the uniform component is ≳1.6 µG. The Galactic field is not uniform. A few ‘magnetic bubbles’ of diameter ~ 100 pc stand out quite prominently, and statistical analyses show that the nonuniform component of the field is at least as strong as the uniform component. Finally, observations of the field on small scales are reviewed. There is no evidence for an increase in field strength with volume density for densities ≲ 100 cm-3, except behind interstellar shocks and near some dark clouds and star-forming regions. For larger densities the data are consistent with the field increasing as a fairly weak power of the volume density. The field is often morphologically related to the interstellar gas — e.g. parallel or perpendicular to filaments, and systematically oriented in large shells. This can also be true on smaller scales; for example, bipolar flows tend to be aligned with the large-scale, ambient magnetic field.

Conquest and Consolidation: A Comparison of the Wari and Inka Occupations of a Highland Peruvian Valley

Abstract: A recent archaeological survey was conducted of a highland Peruvian valley in order to evaluate the effect on a local culture of the expansion of empires. The strategy employed in the consolidation of a region under an imperial administrative structure is the result of two general factors: the needs of the empire, and the level of extant local political organization. Evidence of Wari and Inka imperial facilities in the Carahuarazo Valley is interpreted in light of changes in the local culture during each occupation to provide a more complete picture of this process. A relatively greater Wari presence and lesser Inka presence are interpreted as the result of differing administrative needs on the part of the respective empires, as well as differing local systems at the time of each conquest. Similarities in goods and services extracted by each empire serve to indicate that although imperial strategies differed, the end result of consolidation of the area into each empire was roughly similar.

A Packet Radio Network for Library Automation

Abstract: The progress of libraries towards establishing online databases and automated search and retrieval tools allows them to share their resources and provide access to remote users Unfortunately, the steady increase in the cost of leased lines makes them very undesirable as the media for access networks for budget-constrained libraries An alternative approach-a packet switching radio network-is therefore presented here Low-cost, commercially available radio transceivers and standard personal computers are the hardware building blocks of the system The resulting network employs a suite of protocols, including channel access, routing, congestion control, and the higher-level TCP/IP This network, which is planned to cover a large part of northern California, will provide remote access to University of California's automated library online catalog system It will also support communication between any two end-points, provide for alternative routes in cases of link or nodal failure, and monitor its own performance This paper, then, presents the network's topology, its architecture, its basic elements, and the functions it performs

Fitting Cosines: Some Procedures and Some Physical Examples

Abstract: The paper is concerned with a variety of time series models that in some sense lead to the fitting of a cosine function of unknown frequency. Both linear and nonlinear models are considered, including both decaying cosines and sustained ones. The discussion is illustrated with examples from seismology (free oscillations of the Earth), geophysics (the Chandler wobble), nuclear magnetic resonance, laser Doppler velocimetry and oceanography (dispersion). The paper ends by surveying a variety of results developed for specific models by various authors. A variety of open problems are indicated.