Showing papers by "University of California, Davis published in 1992"

Reactive Oxygen Species and the Central Nervous System

Abstract: Radicals are species containing one or more unpaired electrons. The oxygen radical superoxide (O 2 - ) and the non-radical oxidants hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) are produced during normal metabolism and perform several useful functions. Excessive production of O 2 - and H2O2 can result in tissue damage, which often involves generation of highly reactive hydroxy 1 radical (· OH) and other oxidants in the presence of “catalytic” iron or copper ions. A major form of antioxidant defence is the storage and transport of iron or copper ions in forms that will not catalyze formation of reactive radicals. Tissue injury, e. g., by ischaemia or trauma, can cause increased iron availability and accelerate free radical reactions. This may be especially important in the brain, since areas of this organ are rich in iron and cerebrospinal fluid cannot bind released iron ions. Oxidative stress upon nervous tissue can produce damage by several interacting mechanisms, including rises in intracellular free Ca2+ and, possibly, release of excitatory amino acids. Recent suggestions that free radical reactions are involved in the neurotoxicity of aluminium and in damage to the substantia nigra in Parkinson’s disease are reviewed. Finally, the nature of antioxidants is discussed, with a suggestion that antioxidant enzymes and chelators of iron ions may be more generally useful protective agents than chain-breaking antioxidants. Careful precautions must be taken in the design of antioxidants for therapeutic use.

A single-pool inositol 1,4,5-trisphosphate-receptor-based model for agonist-stimulated oscillations in Ca2+ concentration.

Abstract: Relying on quantitative measurements of Ca2+ activation and inhibition of the inositol 1,4,5-trisphosphate (IP3) receptor in the endoplasmic reticulum, we construct a simplified kinetic model to describe the properties of this channel. Selecting rate constants to fit key kinetic and equilibrium data, we find that the model reproduces a variety of in vivo and in vitro experiments. In combination with Ca(2+)-ATPase activity for Ca2+ uptake into the endoplasmic reticulum, the model leads to cytoplasmic oscillations in Ca2+ concentration at fixed IP3 concentration and only a single pool of releasable Ca2+, the endoplasmic reticulum. Incorporation of a positive-feedback mechanism of Ca2+ on IP3 production by phospholipase C enriches the properties of the oscillations and leads to oscillations in Ca2+ concentration accompanied by oscillations in IP3 concentration. We discuss the possible significance of these results for the interpretation of experiments.

WDM-based local lightwave networks. I. Single-hop systems

Abstract: An overview of emerging all-optical networks is given. The characteristics and alternative architectures for single-hop systems are discussed. The characteristics of lightwave technology that facilitate the design of wavelength-division-multiplexing (WDM) networks are reviewed, and it is explained how WDM local networks can be built based on the single-hop and multihop approaches. Various categories of single-hop systems are discussed: experimental systems, systems based on no pretransmission coordination, and systems based on pretransmission coordination, which also require a separate control channel. A simple classification for single-hop systems is provided. >

Attachment Styles and the "Big Five" Personality Traits: Their Connections with Each Other and with Romantic Relationship Outcomes

Abstract: Hazan and Shaver have identified three adult attachment styles corresponding to the infant-mother attachment patterns observed by Ainsworth and associates in the first year of life: secure, avoidant, and anxious-ambivalent. These three styles are related to a wide variety of close relationship processes and outcomes. To date, however; little research has focused on relations between attachment styles and major personality constructs. Such re-search can clarify, the nature of attachment styles and ensure that they are not simply redundant with existing constructs. The present research examined associations between attachment measures, relationship quality and outcome measures, and the 'Big Five"personality traits assessed by the NEO Personality Inventory. Attachment styles were related in theoretically predictable ways to the Big Five dimensions and especially to some of their 'facet' subscales but were not simply redundant with them. The NEO scales were generally not as powerful as the attachment style me...

Crop Ecology: Productivity and Management in Agricultural Systems

Abstract: Preface Part I. Farming Systems and Their Biological Components: 1. Agricultural systems 2. Trophic chains 3. Community concepts 4. Genetic resources 5. Development Part II. Physical and Chemical Environments: 6. Aerial environment 7. Soil resources Part III. Production Processes: 8. Nitrogen processes 9. Water relations 10. Photosynthesis 11. Respiration and partitioning Part IV. Resource Management: 12. Soil management 13. Strategies and tactics for rainfed agriculture 14. Water management in irrigated agriculture 15. Energy and labor Part V. Farming, Then, Now and in the Future: 16. Evolution of wheat farming systems in southern Australia 17. Technological change in high-yield agriculture 18. The future of agriculture Species list Conversions and constants useful in crop ecology Index.

Body size and proportions in early hominids.

Abstract: The discovery of several associated body parts of early hominids whose taxonomic identity is known inspires this study of body size and proportions in early hominids. The approach consists of finding the relationship between various measures of skeletal size and body mass in modern ape and human specimens of known body weight. This effort leads to 78 equations which predict body weight from 95 fossil specimens ranging in geological age between 4 and 1.4 mya. Predicted weights range from 10 kg to over 160 kg, but the partial associated skeletons provide the essential clues as to which predictions are most reliable. Measures of hindlimb joint size are the best and probably those equations based on the human samples are better than those based on all Hominoidea. Using hindlimb joint size of specimens of relatively certain taxonomy and assuming these measures were more like those of modern humans than of apes, the male and female averages are as follows: Australopithecus afarensis, 45 and 29 kg; A. africanus, 41 and 30 kg; A. robustus, 40 and 32 kg; A. boisei, 49 and 34 kg; H. habilis, 52 and 32 kg. These values appear to be consistent with the range of size variation seen in the entire postcranial samples that can be assigned to species. If hominoid (i.e., ape and human combined) proportions are assumed, the males would be 10 to 23 kg larger and the females 4 to 10 kg larger.

Slowing of mortality rates at older ages in large medfly cohorts.

Abstract: It is generally assumed for most species that mortality rates increase monotonically at advanced ages. Mortality rates were found to level off and decrease at older ages in a population of 1.2 million medflies maintained in cages of 7,200 and in a group of approximately 48,000 adults maintained in solitary confinement. Thus, life expectancy in older individuals increased rather than decreased with age. These results cast doubt on several central concepts in gerontology and the biology of aging: (i) that senescence can be characterized by an increase in age-specific mortality, (ii) that the basic pattern of mortality in nearly all species follows the same unitary pattern at older ages, and (iii) that species have absolute life-span limits.

State Infrastructure and Productive Performance

Abstract: The impact of public infrastructure investment on the productive performance of firms has been an important focus of the recent literature on productivity growth. The size of this impact has important implications for policymakers' decisions to invest in public capital, and productivity analysts' evaluation of productivity growth fluctuations and declines. However, detailed evaluation of the infrastructure impact is difficult using existing studies which rely on restricted models of firms' technology and behavior. In this paper we construct a more complete production theory model of firms' production and input decisions. We then apply our framework to state-level data on the output production and input (capital, nonproduction and production labor and energy) use of manufacturing firms to evaluate the contribution of infrastructure to firms' costs and productivity growth. We find that infrastructure investment does provide a significant direct benefit to manufacturing firms and thus augments productivity growth. We also show, however, that this evidence should be interpreted taking into account the social cost of such capital (which is not reflected in firms' costs), and the indirect impact resulting from scale effects.

WDM-based local lightwave networks. II. Multihop systems

Abstract: For pt.I see ibid., vol.6, no.3, p.12-27, 1992. A survey of wavelength-division-multiplexing (WDM)-based local lightwave networks is presented. The general characteristics of multihop systems are discussed, and various multihop approaches are reviewed. The construction of optimal structures based on minimizing the maximum link flow and optimizations based on minimization of the mean network packet delay are also reviewed. Regular topologies that have been studied as candidates for multihop lightwave networks, including the perfect shuffle, the de Bruijn graph, the toroid, and the hypercube, are discussed. Near-optimal node placement algorithms and shared-channel multihop systems are also discussed. >

Is there teaching in nonhuman animals

Abstract: We derive a simple operational definition of teaching that distinguishes it from other forms of social learning where there is no active participation of instructors, and then discuss the constituent parts of the definition in detail. From a functional perspective, it is argued that the instructor's sensitivity to the pupil's changing skills or knowledge, and the instructor's ability to attribute mental states to others, are not necessary conditions of teaching in nonhuman animals, as assumed by previous work, because guided instruction without these prerequisites could still be favored by natural selection. A number of cases of social interaction in several orders of mammals and birds that have been interpreted as evidence of teaching are then reviewed. These cases fall into two categories: situations where offspring are provided with opportunities to practice skills ("opportunity teaching"), and instances where the behavior of young is either encouraged or punished by adults ("coaching"). Although certain taxonomic orders appear to use one form of teaching more often than the other, this may have more to do with the quality of the current data set than with inherent species-specific constraints. We suggest several directions for future research on teaching in nonhuman animals that will lead to a more thorough understanding of this poorly documented phenomenon. We argue throughout that adherence to conventional, narrow definitions of teaching, generally derived from observations of human adult-infant interactions, has caused many related but simpler phenomena in other species to go unstudied or unrecorded, and severely limits further exploration of this topic.

Testifying in criminal court: emotional effects on child sexual assault victims.

Abstract: Child victims must cope not only with the emotional consequences of criminal acts but also with the potentially traumatizing effects of legal involvement. Dramatic increases in the reporting of child sexual abuse are bringing greater numbers of children into contact with the criminal justice system, raising fears that child victims of sex crimes will be further harmed by the courts. In the present study, the effects of criminal court testimony on child sexual assault victims were examined in a sample of 218 children. From this sample, the behavioral disturbance of a group of "testifiers" was compared to that of a matched control group of "nontestifiers" at three points following testimony: 3 months, 7 months, and after prosecution ended. At 7 months, testifiers evinced greater behavioral disturbance than nontestifiers, especially if the testifiers took the stand multiple times, were deprived of maternal support, and lacked corroboration of their claims. Once prosecution ended, adverse effects of testifying diminished. In courthouse interviews before and after testifying, the main fear expressed by children concerned having to face the defendant. Children who appeared more frightened of the defendant while testifying were less able to answer the prosecutors' questions; and later, after the cases were closed, they were more likely to say that testifying had affected them adversely. The two most pervasive predictors of children's experiences in the courtroom, however, were age and severity of abuse. Despite relevant laws, few innovative techniques were used to help the children testify. The results are discussed in relation to children's ability to cope with stressful situations, the interaction of the legal system with the child/family system, and debates about the need to protect child victims who testify in criminal court.

The Pretty Prudent Public: Post Post-Vietnam American Opinion on the Use of Military Force

Abstract: This article identifies a “post post-Vietnam” pattern in recent American public opinion on the use of military force. Data is drawn from eight cases of limited military force in the 1980s and the 1990–91 Persian Gulf war. Although other factors enter in, particularly the “halo effect” of quick-strike successes, the variations in public support are best explained by differences in principal policy objectives between force used to coerce foreign policy restraint by an aggressor state, and force used to influence or impose internal political change within another state. Distinctions are made both among and within the cases, showing the American public to have been much more supportive of the use of force when the principal objective was to restrain rather than remake governments. These findings have theoretical implications for the analysis of public opinion, prescriptive implications for U.S. foreign policy strategy, and normative implications for views of the role of the public in the foreign policy process.

Enzymatic and nonenzymatic cross-linking of collagen and elastin.

Abstract: Knowledge regarding the steps and mechanisms related to the intra- and interchain cross-linking of collagen and elastin has evolved steadily during the past 30 years. Recently, effort has been directed at identifying the location and types of cross-links that are found in collagen and elastin. There are two major groups of cross-links: those initiated by the enzyme lysyl oxidase and those derived from nonenzymatically glycated lysine and hydroxylysine residues. The formation of enzymatic cross-links depends on specific enzymes, amino acid sequences, and quaternary structural arrangements. The cross-links that are derived nonenzymatically occur more adventitiously and are important to pathobiological processes. Considerable progress has been made in elucidating the pathways of synthesis for several of the enzymatically mediated cross-links, as well as possible mechanisms regulating the specificity of cross-linking. Although less is known about the chemistry of cross-links arising from nonenzymatically glyc...

Large-eddy simulation of turbulent flow above and within a forest

Abstract: A large-eddy simulation has been performed of an atmospheric surface layer in which the lower third of the domain is occupied by a drag layer and heat sources to represent a forest. Subgridscale processes are treated using second-order closure techniques. Lateral boundaries are periodic, while the upper boundary is a frictionless fixed lid. Mean vertical profiles of wind velocity derived from the output are realistic in their shape and response to forest density. Similarly, vertical profiles of Reynolds stress, turbulent kinetic energy and velocity skewness match observations, at least in a qualitative sense. The limited vertical extent of the domain and the artificial upper boundary, however, cause some departures from measured turbulence profiles in real forests. Instantaneous turbulent velocity and scalar fields are presented which show some of the features obtained by tower instrumentation in the field and in wind tunnels, such as the vertical coherence of vertical velocity and the slope of structures revealed by temperature patterns.

Expression of an inward-rectifying potassium channel by the Arabidopsis KAT1 cDNA.

Abstract: Inward-rectifying potassium channels located in the plasma membrane of higher plant and animal cells contribute to cellular homeostasis and excitability. The genes encoding this specific class of K+ channels have not been functionally identified. This report shows that a single messenger RNA transcript from the Arabidopsis thaliana KAT1 complementary DNA confers the functional expression of a hyperpolarization-activated K+ channel in Xenopus oocytes. The channels encoded by KAT1 are highly selective for K+ over other monovalent cations, are blocked by tetraethylammonium and barium, and have a single channel conductance of 28 +/- 7 picosiemens with 118 millimolar K+ in the bathing solution. These functional characteristics, typical of inward-rectifying K+ channels in eukaryotic cells, demonstrate that KAT1 encodes an inward-rectifying K+ channel.

Root Respiration Associated with Ammonium and Nitrate Absorption and Assimilation by Barley

Abstract: We examined nitrate assimilation and root gas fluxes in a wild-type barley (Hordeum vulgare L. cv Steptoe), a mutant (nar1a) deficient in NADH nitrate reductase, and a mutant (nar1a;nar7w) deficient in both NADH and NAD(P)H nitrate reductases. Estimates of in vivo nitrate assimilation from excised roots and whole plants indicated that the nar1a mutation influences assimilation only in the shoot and that exposure to NO3− induced shoot nitrate reduction more slowly than root nitrate reduction in all three genotypes. When plants that had been deprived of nitrogen for several days were exposed to ammonium, root carbon dioxide evolution and oxygen consumption increased markedly, but respiratory quotient—the ratio of carbon dioxide evolved to oxygen consumed—did not change. A shift from ammonium to nitrate nutrition stimulated root carbon dioxide evolution slightly and inhibited oxygen consumption in the wild type and nar1a mutant, but had negligible effects on root gas fluxes in the nar1a;nar7w mutant. These results indicate that, under NH4+ nutrition, 14% of root carbon catabolism is coupled to NH4+ absorption and assimilation and that, under NO3− nutrition, 5% of root carbon catabolism is coupled to NO3− absorption, 15% to NO3− assimilation, and 3% to NH4+ assimilation. The additional energy requirements of NO3− assimilation appear to diminish root mitochondrial electron transport. Thus, the energy requirements of NH4+ and NO3− absorption and assimilation constitute a significant portion of root respiration.

Growth of breast-fed and formula-fed infants from 0 to 18 months: the DARLING Study

Abstract: Anthropometric data were collected monthly from birth to 18 months as part of the Davis Area Research on Lactation, Infant Nutrition and Growth study, which followed infants who were either breast-fed or formula-fed during the first 12 months. The two cohorts were matched for parental socioeconomic status, education, ethnic group, and anthropometric characteristics and for infant sex and birth weight, and neither group was given solid foods before 4 months. While mean weight of formula-fed infants remained at or above the National Center for Health Statistics median throughout the first 18 months, mean weight of breast-fed infants dropped below the median beginning at 6 to 8 months and was significantly lower than that of the formula-fed group between 6 and 18 months. In contrast, length and head circumference values were similar between groups. Weight-for-length z scores were significantly different between 4 and 18 months, suggesting that breast-fed infants were leaner. The groups had similar weight gain during the first 3 months, but breast-fed infants gained less rapidly during the remainder of the first year: cumulative weight gain in the first 12 months was 0.65 kg less in the breast-fed group. Length gain was similar between groups. These results indicate that weight patterns of breast-fed infants, even in a population of high socioeconomic status, differ from current reference data and from those of formula-fed infants. Thus, new growth charts based on breast-fed infants are needed.

Signal interception: performance advantages of cyclic-feature detectors

Abstract: The problem of detecting the presence of spread-spectrum phase-shift-keyed signals in variable noise and interference backgrounds is considered, and the performances of four detectors are evaluated and compared. The detectors include the optimum radiometer, the optimum modified radiometer that jointly estimates the noise level and detects the signal, and the maximum-SNR spectral-line regenerator for spectral-line frequencies equal to the chip rate and the doubled carrier frequency. It is concluded that the spectral-line regenerators can outperform both types of radiometers by a wide margin. The performance advantages are quantified in terms of receiver operating characteristics for several noise and interference environments and receiver collection times. >

High-resolution image reconstruction from lower-resolution image sequences and space-varying image restoration

Abstract: The authors address the problem of reconstruction of a high-resolution image from a number of lower-resolution (possibly noisy) frames of the same scene where the successive frames are uniformly based versions of each other at subpixel displacements. In particular, two previously proposed methods, a frequency-domain method and a method based on projections onto convex sets (POCSs), are extended to take into account the presence of both sensor blurring and observation noise. A new two-step procedure is proposed, and it is shown that the POCS formulation presented for the high-resolution image reconstruction problem can also be used as a new method for the restoration of spatially invariant blurred images. Some simulation results are provided. >

Aminopeptidase I of Saccharomyces cerevisiae is localized to the vacuole independent of the secretory pathway.

Abstract: The Saccharomyces cerevisiae APE1 gene product, aminopeptidase I (API), is a soluble hydrolase that has been shown to be localized to the vacuole. API lacks a standard signal sequence and contains an unusual amino-terminal propeptide. We have examined the biosynthesis of API in order to elucidate the mechanism of its delivery to the vacuole. API is synthesized as an inactive precursor that is matured in a PEP4-dependent manner. The half-time for processing is approximately 45 min. The API precursor remains in the cytoplasm after synthesis and does not enter the secretory pathway. The precursor does not receive glycosyl modifications, and removal of its propeptide occurs in a sec-independent manner. Neither the precursor nor mature form of API are secreted into the extracellular fraction in vps mutants or upon overproduction, two additional characteristics of soluble vacuolar proteins that transit through the secretory pathway. Overproduction of API results in both an increase in the half-time of processing and the stable accumulation of precursor protein. These results suggest that API enters the vacuole by a posttranslational process not used by most previously studied resident vacuolar proteins and will be a useful model protein to analyze this alternative mechanism of vacuolar localization.

Reversible histone modifications and the chromosome cell cycle.

Abstract: During the eukaryotic cell cycle, chromosomes undergo large structural transitions and spatial rearrangements that are associated with the major cell functions of genome replication, transcription and chromosome condensation to metaphase chromosomes. Eukaryotic cells have evolved cell cycle dependent processes that modulate histone:DNA interactions in chromosomes. These are; (i) acetylations of lysines; (ii) phosphorylations of serines and threonines and (iii) ubiquitinations of lysines. All of these reversible modifications are contained in the well-defined very basic N- and C- terminal domains of histones. Acetylations and phosphorylations markedly affect the charge densities of these domains whereas ubiquitination adds a bulky globular protein, ubiquitin, to lysines in the C-terminal tails of H2A and H2B. Histone acetylations are strictly associated with genome replication and transcription; histone H1 and H3 phosphorylations correlate with the process of chromosome condensation. The subunits of histone H1 kinase have now been shown to be cyclins and the p34CDC2 kinase product of the cell cycle control gene CDC2. It is probable that all of the processes that control chromosome structure:function relationships are also involved in the control of the cell cycle.

Ovule Development in Wild-Type Arabidopsis and Two Female-Sterile Mutants.

Abstract: Ovules are complex structures that are present in all seed bearing plants and are contained within the carpels in flowering plants. Ovules are the site of megasporogenesis and megagametogenesis and, following fertilization, develop into seeds. We combined genetic methods with anatomical and morphological analyses to dissect ovule development. Here, we present a detailed description of the morphological development of Arabidopsis ovules and report on the isolation of two chemically induced mutants, bell (bel1) and short integuments (sin1), with altered ovule development. Phenotypic analyses indicated that bel1 mutants initiate a single integument-like structure that develops aberrantly, sin1 mutants initiate two integuments, but growth of the integuments is disrupted such that cell division continues without normal cell elongation. Both mutants can differentiate archesporial cells, but neither forms a normal embryo sac. Genetic analyses indicated that bel1 segregates as a single recessive mutation, and complementation tests showed that the two mutants are not allelic. The phenotypes of the mutants indicate that normal morphological development of the integuments and proper embryo sac formation are interdependent or are governed in part by common pathways. The ovule mutants that we describe in Arabidopsis represent novel genetic tools for the study of this stage of reproductive development.

Applications of hysteresis switching in parameter adaptive control

Abstract: The hysteresis switching algorithm of R.H. Middleton et al. (ibid., vol.33, no.1, p.50-8, Jan. 1988) is reexamined in a broader context. To demonstrate its utility, the algorithm is applied to various families of identifier-based parameterized controllers of both the direct and indirect control types. Application to the direct control type results in a model reference adaptive controller capable of stabilizing, without excitation, any SISO process which can be modeled by a minimum phase linear system whose transfer function has relative and McMillan degrees not exceeding prescribing integers m and n, respectively. It is shown that such processes can also be adaptively stabilized with indirect adaptive controllers and hysteresis switching. A simple numerical example involving a non-minimum-phase process model is used to illustrate how hysteresis switching might be applied to implicitly tuned parameterized controllers to realize an adaptive controller with capabilities which might prove very difficult, if not impossible, to achieve without hysteresis switching or some other form of discontinuous control. >