Showing papers by "University of California, Davis published in 1985"

Nonlinear observers with linearizable error dynamics

Abstract: A new method for designing asymptotic observers for a class of nonlinear systems is presented. The error between the state of the systems and the state of the observer in appropriate coordinates evolves linearly and can be made to decay aribtrarily exponentially fast.

Displacement of ca by na from the plasmalemma of root cells : a primary response to salt stress?

Abstract: A microfluorometric assay using chlorotetracycline (CTC) as a probe for membrane-associated Ca(2+) in intact cotton (Gossypium hirsutum L. cv Acala SJ-2) root hairs indicated displacement of Ca(2+) by Na(+) from membrane sites with increasing levels of NaCl (0 to 250 millimolar). K(+)((86)Rb) efflux increased dramatically at high salinity. An increase in external Ca(2+) concentration (10 millimolar) mitigated both responses. Other cations and mannitol, which did not affect Ca(2+)-CTC chelation properties, were found to have no effect on Ca(2+)-CTC fluorescence, indicating a Na(+)-specific effect. Reduction of Ca(2+)-CTC fluorescence by ethyleneglycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid, which does not cross membranes, provided an indication that reduction by Na(+) of Ca(2+)-CTC fluorescence may be occurring primarily at the plasmalemma. The findings support prior proposals that Ca(2+) protects membranes from adverse effects of Na(+) thereby maintaining membrane integrity and minimizing leakage of cytosolic K(+).

Computer generation of structural models of amorphous Si and Ge.

Abstract: We have developed and applied a computer algorithm that generates realistic random-network models of $a$-Si with periodic boundary conditions. These are the first models to have correlation functions that show no serious discrepancy with experiment. The algorithm provides a much-needed systematic approach to model construction that can be used to generate models of a large class of amorphous materials.

The missing feminist revolution in sociology

Abstract: Feminists have made important contributions to sociology, but we have yet to transform the basic conceptual frameworks of the field. A comparison of sociology with anthropology, history, and literature–disciplines which have been more deeply transformed–suggests factors that may facilitate or inhibit feminist paradigm shifts. The traditional subject matter of sociology fell into a co-optable middle ground, neither as thoroughly male centered as in history or literature, nor as deeply gendered as in anthropology. In addition, feminist perspectives have been contained in sociology by functionalist conceptualizations of gender, by the inclusion of gender as a variable rather than as a theoretical category, and by being ghettoized, especially in Marxist sociology. Feminist rethinking is also affected by underlying epistemologies (proceeding more rapidly in fields based on interpretive rather than positivist understanding), and by the status and nature of theory within a discipline.

Rise of the grassland biome, central North America

Abstract: Fossil floras and mammalian faunas from the Great Plains indicate that as aridity increased during the Miocene and Pliocene, forests and woodlands were confined gradually to moister valleys as grassland spread on the interfluves which were covered earlier with park-like openings. The initial rise of extensive grasslands probably commenced in the Miocene-Pliocene transition (7-5 m.y. ago), the driest part of the Tertiary, which restricted forests and woodlands and encouraged the explosive evolution of grasses and forbs. Following the fluctuation of Pleistocene climatevegetation zones, warm, dry Altithermal climate restricted wooded tracts at the expense of spreading grasslands. The rise of the grassland biome was thus due to occasional periods of increased aridity that restricted forests and woodlands and favored grasses and forbs; to increasing drought west of the 100th meridian which created a flammable source (dry grass); to natural and man-made fires on the relatively flat plains over which fire could spread uninterruptedly; to fire that destroyed relict trees and groves on the flat grasslands, restricting them to rocky ridges removed from fire; and probably also to large browsing mammals (many now extinct) that may have destroyed scattered trees and shrubs on the interfluves during the Altithermal. Youthfulness of the grassland biome agrees with a) the occurrence of most of its species in the bordering forests and woodlands, b) the presence of few endemic plants in it, a relation shown also by insects and birds, c) the relict occurrence of diverse trees over the region, and d) the invasion of grassland by woody vegetation.

Shoot multiplication from mature trees of Douglas-fir ( Pseudotsuga menziesii ) and sugar pine ( Pinus lambertiana )

Abstract: Opening of apical and axillary buds of mature Douglas-fir and sugar pine trees was obtained on a newly formulated basal medium (DCR) without growth regulators. Elongation of buds was observed on 1/2 strength DCR with 0.3% activated charcoal (DCR-1). In sugar pine, multiple shoots were obtained when explants on DCR with 0.5 mg/1 BAP for 5–6 weeks were transferred to DCR-1 medium. On subculture, axillary buds again developed when shoots were cultured on DCR with 0.2 mg/1 BAP for Douglas-fir and 0.5 mg/1 BAP for sugar pine. These buds were again elongated on DCR-1 medium. By subculturing 7–10 shoots of Douglas-fir and 2–3 shoots of sugar pine, over 100 shoots can be obtained in a year.

Slip correction measurements of spherical solid aerosol particles in an improved Millikan apparatus

Abstract: A slip correction factor is used to correct Stokes' law for the fact that the no-slip boundary condition is violated for small aerosol particles moving with respect to the gaseous medium. The Knuds...

A prospective, randomized study of the management of severe ankle fractures.

Abstract: One hundred and thirty-eight patients with a closed grade-4 supination-external rotation or pronation-external rotation ankle fracture (Lauge-Hansen classification) who were seen in the emergency room of the University of Chicago Hospitals were entered into a randomized study of the results of various methods of treatment. Ninety-six patients with satisfactory initial closed reduction were randomized between continued closed treatment in a plaster cast and open reduction with rigid internal fixation according to the techniques of the Association for the Study of Internal Fixation (ASIF). Forty-two patients with unsatisfactory closed reduction were randomized between open reduction with internal fixation of only the medial malleolus and open reduction with rigid internal fixation according to the ASIF techniques. Of the 138 patients who were admitted to the study, only seventy-one (51 per cent) could be followed for an average of 3.5 years (a typical return rate of urban trauma centers). The outcomes were evaluated by a scoring system that included clinical, anatomical, and arthritis scores. Statistical analysis of the data showed that, of the patients with initial satisfactory closed reduction, the ones treated by open reduction and rigid internal fixation had significantly higher total scores, particularly the patients who were more than fifty years old and those with a medial malleolar fracture. The small number of patients with unsatisfactory closed reduction who were treated by one of the two types of open reduction and internal fixation and were available for follow-up precluded drawing any conclusions about the superiority of one method of internal fixation over the other in that group. The difference in the talocrural angle between the injured and normal sides was the only statistically significant radiographic indicator of a good prognosis.

The Plastic Spin

Abstract: On presente une formulation macroscopique des grandes deformations elastoplastiques avec des variables de structure tensorielles

Expression, Glycosylation, and Secretion of an Aspergillus Glucoamylase by Saccharomyces cerevisiae

Abstract: A strain of Saccharomyces cerevisiae capable of simultaneous hydrolysis and fermentation of highly polymerized starch oligosaccharides was constructed. The Aspergillus awamori glucoamylase enzyme, form GAI, was expressed in Saccharomyces cerevisiae by means of the promoter and termination regions from a yeast enolase gene. Yeast transformed with plasmids containing an intron-free recombinant glucoamylase gene efficiently secreted glucoamylase into the medium, permitting growth of the transformants on starch as the sole carbon source. The natural leader sequence of the precursor of glucoamylase (preglucoamylase) was processed correctly by yeast, and the secreted enzyme was glycosylated through both N- and O-linkages at levels comparable to the native Aspergillus enzyme. The data provide evidence for the utility of yeast as an organism for the production, glycosylation, and secretion of heterologous proteins.

The MRFIT behavior pattern study. II. Type A behavior and incidence of coronary heart disease.

Abstract: Behavior pattern was assessed by interview for 3,110 men at eight centers in the Multiple Risk Factor Intervention Trial (1973-1976). The Type A pattern was not significantly associated with risk of first major coronary events (coronary death and definite nonfatal myocardial infarction) after a mean follow-up of 7.1 years. Crude relative risks for Types A1-A2 versus X-B were 1.08 in usual care, 0.82 in special intervention, and 0.92 overall. Adjustment for age, blood pressure, cigarette smoking, serum cholesterol, consumption of alcohol, and educational attainment yielded relative risks of 0.99 in usual care, 0.81 in special intervention, and 0.87 overall (95% confidence interval = 0.59-1.28). The Jenkins Activity Survey Type A score, obtained for 12,772 men at all 22 centers, was also not significantly associated with risk of first major coronary events. Overall, crude risks in the lowest (Type B) through highest (Type A) quintiles of the score's distribution were 5.0%, 4.4%, 4.0%, 4.3%, and 4.1%, respectively. The proportional hazards regression coefficient, adjusted for the variables listed above, was -0.006 (95% confidence interval = -0.015-0.003). These results raise questions regarding the robustness of the Type A hypothesis in its present form. Further studies are needed to investigate these questions and to evaluate the validity of procedures used to assess behavior patterns.

Specific alteration of NCAM-mediated cell adhesion by an endoneuraminidase.

Abstract: A phage endoneuraminidase that specifically cleaves alpha-2, 8-linked polysialic acid has been found to be a useful probe for examining the biological role of this sugar moiety on the neural cell adhesion molecule (NCAM). The enzyme caused a 3.3-fold increase in the rate of NCAM-dependent aggregation of membrane vesicles from chicken embryonic brain, without the nonspecific effects previously encountered with the use of exoneuraminidases. The enhancement of aggregation was closely correlated with removal of sialic acid as assessed by electrophoretic mobility. Extension of this analysis to cultures of spinal ganglia indicated that removal of sialic acid by the endoneuraminidase results in an increase in the thickness of neurite bundles. This enhancement of fasciculation was reversed by addition of anti-NCAM Fab, suggesting that the enzyme treatment was not toxic and did not produce nonspecific effects on adhesion. Injection of the enzyme into the eyes of 3.5-d chicken embryos consistently produced a striking array of abnormalities in those parts of the neural retina that contained the highest concentrations of NCAM at the time of injection. These perturbations included a dramatic thickening of the neural epithelium in the posterior eye, a failure of cells in this region to elongate radially, formation of an ectopic optic fiber layer, and an incomplete association of the presumptive pigmented epithelium with the neural retina. These results provide the first direct evidence that the polysialic acid on NCAM has a regulatory effect on adhesion between living cells, and that the amount of this carbohydrate is critical for the normal morphogenesis of nerve tissue.

Complications of tension-band wiring of olecranon fractures.

Abstract: We encountered a high incidence of complications related to the technique of tension-band wire fixation of displaced fractures of the olecranon in a five-year retrospective study of twenty patients (twenty fractures). All had been treated with primary open reduction using the AO technique of tension-band wiring. Twenty patients were followed at least to union as determined radiographically. The most frequent complication was symptomatic prominence of the Kirschner wires at the elbow in sixteen patients. There was skin breakdown in four patients, and infection developed in one. Measurable proximal migration of the Kirschner wires, however, occurred in only three patients. Prominence of the Kirschner wires usually was due to improper seating at the time of surgery (twelve of sixteen patients). Most complications that are related to this method of fixation may be avoided by careful attention to surgical technique.

Antibodies against metal chelates

Abstract: Because monoclonal antibodies can recognize and bind to specific groups of atoms such as tumour antigens, they have promise for use in vivo as carriers of radionuclides, drugs or other appended molecules for diagnosis and treatment of disease. Attachment of metal ions to antibodies by means of bifunctional chelating agents can add the diverse nuclear, physical and chemical properties of the metallic elements to these specific binding proteins (ref. 4 and refs therein). With the ultimate aim of engineering probe-binding properties into the antibodies themselves, we have now prepared monoclonal antibodies against the EDTA chelate of indium. These antibodies show a remarkable preference for indium chelates; changing to another metal such as scandium or gallium can decrease the antibody-binding constant by more than three orders of magnitude. These antibodies also introduce a new degree of control over the biological distributions of chelated radionuclides, markedly altering their uptake in tumours and normal organs.

Germination and seedling growth of cotton: salinity‐calcium interactions

Abstract: . The effects of NaCl salinity on germination and early seedling growth of cotton were studied. Germination was both delayed and reduced by 200 mol m−3 NaCl in the presence of a complete nutrient medium. Seedlings, 7–9 d old, were greatly reduced in fresh weight by salinity. The addition of supplemental Ca2+ (10 mol m−3 as SO42− or Cl−) to the medium did not improve germination but, to a large degree, offset the reduction in root growth caused by NaCl. Roots growing in the high salt medium without supplemental Ca2+ appeared infected by microbes. The cation specificity of the beneficial Ca2+ effect on growth was ascertained by testing additions of MgSO4 or KCl to the NaCl treatments. The contents of K4 and Ca2+ were reduced in both roots and shoots by the NaCl treatments. Supplemental Ca2+ partially offset this effect for K4 in the roots and for Ca2+ in both roots and shoots. Sodium contents were not affected by the supplemental Ca2+. It is concluded that the beneficial effect of high Ca2+ concentrations on root growth of cotton seedlings in a saline environment may be due to maintenance of K/Na-selectivity and adequate Ca status in the root.

Boundary structures are formed by organic components of the Murchison carbonaceous chondrite

Abstract: The first cellular systems to appear on the Earth were presumably assembled from three molecular species: information-storing molecules capable of replication, enzyme-like catalysts structurally encoded by that information and able to enhance replication rates, and boundary-forming molecules which could encapsulate the system represented by the first two molecular species. Encapsulation would provide a microenvironment conducive to interaction of the molecular species involved, and would further serve to differentiate such systems according to their reproductive success. Boundary structures could also provide permeability properties useful for the directed transport of nutrient molecules required for growth and replication. The experiments reported here focused on non-polar molecules extracted from carbonaceous chrondrites. Such molecules represent plausible models for the mixture of organic substances present on the early Earth. We found that certain components in the extract have physical properties which lead to the formation of boundary structures.

Parent-Offspring Conflict in Budgerigars

Abstract: Despite widespread theoretical interest in genetic conflict between parents and offspring, there is little empirical evidence that it exists in nature. Theoretical models suggest two outcomes of conflict not predicted by alternate theories: (1) offspring that control the allocation of parental investment might show escalated demand behaviours (e.g., begging) and demand more resources than they could efficiently use and (2) parents might evolve behavioural counterstrategies which prevented offspring from obtaining extra resources, but which were more costly than a "laissez-faire" parental strategy allowing offspring control. These predictions were tested in budgerigars, (Melopsittacus undulatus) in large flight cages at Davis, California. Budgerigar clutches hatch extremely asynchronously, yet all nestlings grew at similar rates and fledged at similar sizes and ages. This independence of hatch order and performance seemed due primarily to the mother budgerigar's allofeeding strategy: females allofed offspring mainly on the basis of size, and only secondarily attended to begging rate. Offspring of a given age and size were treated the same by their mothers regardless of hatch order, and offspring undersized for their age were fed as if they were younger. In contrast, male budgerigars attended to offspring begging rates. Males tended to initiate feeding bouts when offspring begged, and to allofeed vigorous beggers more often. Variance in male allofeeding behaviour allowed comparisons of size-matched families in which females performed nearly all of the allofeeds to nestlings (= female-fed families) with families in which males and females both allofed nestlings (= male-aided families). The parent controlled the allocation of food in female-fed families, while offspring had greater control over food allocation in male-fed families. As was predicted by conflict theory, the female counterstrategy was effective but potentially costly: the food delivery rate of females was only half as fast as males'. Conversely, offspring control resulted in an escalation of beg rate for the same degree of need (as measured by size and growth), and male-aided offspring obtained nearly three times more regurgitations than female-fed nestlings, yet grew at comparable rates and fledged at comparable sizes and ages. Hence, offspring demanded and obtained more food than they could effectively use. Other avian parents also seem to use effective but potentially costly counterstrategies, and other avian offspring may demand more food than they require. Even if initial hatch asynchronies functioned in brood reduction, the parental strategies described here would allow parents to retain control over the timing and conditions for offspring loss.

Identification of an inducible catabolic system for sialic acids (nan) in Escherichia coli.

Abstract: Escherichia coli K-12 and K-12 hybrid strains constructed to express a polysialic acid capsule, the K1 antigen, were able to efficiently use sialic acid as a sole carbon source. This ability was dependent on induction of at least two activities: a sialic acid-specific transport activity, and an aldolase activity specific for cleaving sialic acids. Induction over basal levels required sialic acid as the apparent inducer, and induction of both activities was repressed by glucose. Induction also required the intracellular accumulation of sialic acid, which could be either added exogenously to the medium or accumulated intracellularly through biosynthesis. Exogenous sialic acid appeared to be transported by an active mechanism that did not involve covalent modification of the sugar. Mutations affecting either the transport or degradation of sialic acid prevented its use as a carbon source and have been designated nanT and nanA, respectively. These mutations were located by transduction near min 69 on the E. coli K-12 genetic map, between argG and glnF. In addition to being unable to use sialic acid as a carbon source, aldolase-negative mutants were growth-inhibited by this sugar. Therefore, the intracellularly accumulated sialic acid was toxic in aldolase-deficient E. coli strains. The dual role of aldolase in dissimilating and detoxifying sialic acids is consistent with the apparent multiple controls on expression of this enzyme. Images

Seasonal relationships between leaf nitrogen content (photosynthetic capacity) and leaf canopy light exposure in peach (Prunus persica)

Abstract: Field gas exchange measurements on intact peach (Prunus persica (L.) Batsch) leaves indicate that leaf nitrogen content (NL) and leaf weight per unit leaf area (Wa) are highly correlated with CO2 assimilation rate (A) and mesophyll conductance (gm). Therefore, NL and Wa were used to study seasonal relationships between leaf carboxylation capacity and natural light exposure in tree canopies. From mid-season onwards, NL and Wa were linearly correlated with light exposure expressed as the amount of time during a clear day that a leaf was exposed to a photosynthetic photon flux density (Q) of ≥ 100 μmol m−2 s−1. The data support the hypothesis that whole-tree photosynthesis is optimized by partitioning of photosynthetic capacity among leaves in deciduous tree canopies with respect to natural light exposure.