Showing papers by "University of Texas at Austin published in 1976"

Completely Positive Dynamical Semigroups of N Level Systems

Abstract: We establish the general form of the generator of a completely positive dynamical semigroup of an N‐level quantum system, and we apply the result to derive explicit inequalities among the physical parameters characterizing the Markovian evolution of a 2‐level system.

Theory of plasma transport in toroidal confinement systems

Abstract: The dissipation induced by coulomb-collisional scattering provides an irreducible minimum, and thus a useful standard for comparison, for transport processes in a hot, magnetically confined plasma. The kinetic description of this dissipation is provided by an equation of the Fokker-Planck form. As in the standard transport theory for a neutral gas, approximate solution of the Fokker-Planck equation permits the calculation of transport coefficients, which linearly relate the fluxes of particles, energy, and electric charge, to the density and temperature gradients, and to the electric field. The transport relations are useful in studying the confinement properties of present and future experimental devices for research in controlled thermonuclear fusion. The transport theory for a magnetized plasma (in which the Larmor radius is much smaller than gradient scale lengths describing the plasma fluid) departs from the theory for a neutral gas in several fundamental ways. Thus, transport coefficients for a magnetized plasma can be calculated even when the collisional mean free path is much longer than the gradient scale length (as would pertain in thermonuclear regimes). Such transport coefficients are generally nonlocal, being defined in terms of averages over surfaces with macroscopic dimensions. Furthermore, when the mean free path is long, the magnetized-plasma transport coefficients depend crucially upon the magnetic field geometry, the effects of which must be treated at the kinetic level of the Fokker-Planck equation. The results display several novel couplings between collisional dissipation and the electromagnetic field. The present review of magnetized-plasma transport theory is intended to be as widely accessible as possible. Thus the relevant features of magnetic confinement in closed (toroidal) systems, and of charged particles in spatially varying fields, are derived, at least in outline, from first principles. Although consideration is given to "classical" transport in which most field geometric effects are omitted, major emphasis is placed on the "neoclassical" theory which has been developed over the last decade. Neoclassical transport coefficients are specifically relevant to a magnetically confined plasma, rather than to just a magnetized plasma; their unusual features, such as nonlocality and geometry dependence, become particularly important in the high temperature regime of proposed thermonuclear reactors. The area of neoclassical theory which seems most complete---its application to axisymmetric tokamak-type confinement systems---is correspondingly stressed.

Perspectives on cognitive dissonance

Abstract: Published in 1976, Perspectives on Cognitive Dissonance is a valuable contribution to the field of Social Psychology.

Effect of partially immobilizing sorption on permeability and the diffusion time lag

Abstract: The gas permeability and diffusion time lag may exhibit varying degrees of pressure dependence for glassy polymers. The sorption isotherm appears to consist of contributions from both Langmuir and Henry's law terms in such systems. This “dual sorption” theory advanced in the literature pictures gas held by the Langmuir mode as being completely immobilized. In the present paper, this model is extended to accommodate different degrees of partial immobilization of gas sorbed by this mode using two different formulations. One uses a transport expression based on concentration gradients while the other is based on chemical potential gradients. The predictions are that: (1) total immobilization results in a constant permeability with a time lag which strongly decreases with pressure; (2) no immobilization results in a constant time lag with a permeability which decreases strongly with pressure; and (3) incomplete immobilization results in both the permeability and time lag decreasing with pressure but neither as strongly as in the other limiting cases. The differences which may arise by the two formulations of the model are discussed.

Vacuum expectation value of the stress tensor in an arbitrary curved background: The covariant point-separation method

Abstract: A method known as covariant geodesic point separation is developed to calculate the vacuum expectation value of the stress tensor for a massive scalar field in an arbitrary gravitational field. The vacuum expectation value will diverge because the stress-tensor operator is constructed from products of field operators evaluated at the same space-time point. To remedy this problem, one of the field operators is taken to a nearby point. The resultant vacuum expectation value is finite and may be expressed in terms of the Hadamard elementary function. This function is calculated using a curved-space generalization of Schwinger's proper-time method for calculating the Feynman Green's function. The expression for the Hadamard function is written in terms of the biscalar of geodetic interval which gives a measure of the square of the geodesic distance between the separated points. Next, using a covariant expansion in terms of the tangent to the geodesic, the stress tensor may be expanded in powers of the length of the geodesic. Covariant expressions for each divergent term and for certain terms in the finite portion of the vacuum expectation value of the stress tensor are found. The properties, uses, and limitations of the results are discussed.

A contour integral computation of mixed-mode stress intensity factors

Abstract: A path independent contour integral formula for the distinct calculation of combined mode stress intensity factors in linear plane elasticity problems is presented. The method is based on a Somigliana type singular integral representation and is easily appended to existing finite element computer codes. Numerical results to three problems with known perturbation solutions are given and demonstrate the accuracy and stability of the method.

Secretion of an FSH-Inhibiting Factor by Cultured Sertoli Cells

Abstract: Levels of LH and FSH released in vitro by rat anterior pituitary cells which were either co-cultured with isolated rat Sertoli cells or were grown with spent media recovered from the cultured Sertoli cells were measured by radioimmunoassay. The amounts of FSH released by pituitary cells grown for three days with Sertoli cells isolated from 31-36 day old rats or spent media from the cultured Sertoli cells, were significantly (P less than 0.01) lower compared to control pituitary cultures grown with fresh chemically defined medium. In contrast, the levels of LH were similar to the controls. The selective inhibition of FSH release was not observed when pituitary cells were co-cultured with rat spleen or kidney cells or with ruptured Sertoli cells. The FSH-inhibiting Sertoli-cell factor (SCF) was found to be a heat-labile macromolecule. It is suggested that the SCF may be secreted by the Sertoli cells in vivo, and regulate FSH secretion via negative feedback mechanism at the pituitary level.

Changes in the shape of the developing vertebrate nervous system analyzed experimentally, mathematically and by computer simulation.

Abstract: Two forces are necessary and sufficient to produce the transformation of the newt neural plate from a hemispheric sheet of cells one cell thick to a keyhole shape. These forces are: (1) a regionally programmed shrinkage of the surface of the neural plate (accomplished by contraction of the apical surfaces of the neural plate cells and elongation of these cells perpendicular to the plate); and (2) displacement of the whole sheet caused by elongation of either the notochord or the overlying neural plate cells in the antero-posterior direction. A computer simulation and mathematical analysis ("morphodynamics"), together with experiments and observations on embryos, were used to deduce the morphogenesis of the neural plate from these forces.

Efficient generation of the binary reflected gray code and its applications

Abstract: Algorithms are presented to generate the n-bit binary reflected Gray code and codewords of fixed weight in that code. Both algorithms are efficient in that the time required to generate the next element from the current one is constant. Applications to the generation of the combinations of n things taken k at a time, the compositions of integers, and the permutations of a multiset are discussed.

Semiconductor Electrodes: V. The Application of Chemically Vapor Deposited Iron Oxide Films to Photosensitized Electrolysis

Abstract: The preparation of polycrystalline n-type Fe203 electrodes by the chemical vapor deposition (CVD) of iron oxide onto Ti and Pt substrates is reported. The behavior of these electrodes in aqueous solutions of different pH in the absence and presence of illumination is shown. Photoassisted electrolysis of water occurs at wavelengths longer than 400 nm and the current vs. wavelength curve for this process is compared to that of a CVD TiO2 electrode.

Special Escherichia coli serotypes among enterotoxigenic strains from diarrhoea in adults and children.

Abstract: 106 enterotoxigenicEscherichia coli strains from children and adults from many parts of the world were serotyped for O and H antigens. Some O∶H types,i.e. O6∶H16, O8∶H9, O15∶H11, O25∶H42, O78∶H11 and O78∶H12, were found repeatedly from different geographical locations. Some of these O∶H serotypes were only found rarely among more than 20000E. coli strains collected over many years from different locations and sources. It is suggested that these special O∶H serotypes represent clones which have been selected to the special conditions in the small intestine and selected to carry the plasmids necessary to provoke diarrhoea.

The origin of deuterium

Abstract: General nuclear constraints are used to show that deuterium is most likely of pregalactic origin. Big-bang nucleosynthesis is the most plausible source for significant amounts of this isotope, but other, more speculative, sources are not ruled out.

Role of chloride transport in regulation of intracellular pH

Abstract: IT is well known that introducing acid into a cell causes a rapid fall in intracellular pH (pHi) which is followed by a slower rise1–5. Since this return of pHi towards its original value could not be accounted for by the passive transmembrane movement of H+, OH−, or HCO3−, it was ascribed to the active removal of acid from the cell1,2. In the squid giant axon, this acid extrusion is reversibly blocked by cyanide and greatly enhanced by HCO3−/CO2 (ref. 3). More recently, it has been found that acid extrusion in the snail neurone also is stimulated by HCO3−/CO2 (ref. 4), and that, in addition, it is inhibited by 4-acetamido-4′-isothiocyano-stilbene-2,2′-disulphonic acid (SITS)5, a known inhibitor of anion fluxes in erythrocytes6. In this respect it is interesting to note that a component of Cl− efflux in barnacle muscle also is stimulated by HCO3−/CO2 and blocked by SITS7. We now report that acid extrusion in the squid axon requires internal Cl− and ATP, that it is blocked by SITS, and that it is accompanied by the SITS-sensitive efflux of an equivalent amount of Cl−. These observations suggest that acid extrusion actually involves the neutral exchange of external HCO3− for internal Cl−.

The equivalence of generalized least squares and maximum likelihood estimates in the exponential family.

Abstract: The method of iterative weighted least squares can be used to estimate the parameters in a nonlinear regression model. If the dependent variables are observations from a member of the regular exponential family, then under mild conditions it is shown that the IWLS estimates are identical to those obtained using the maximum likelihood principle. An application is provided to illustrate the results.

Radiation‐induced xerostomia in cancer patients. Effect on salivary and serum electrolytes

Abstract: Saliva and serum electrolyte concentrations were monitored in 30 patients given a course of xerostomia-producing cancer radiotherapy. The mean flow rate of stimulated whole saliva decreased 83.3% during a 6-week treatment period. The striking reduction in saliva output was accompanied by significant increases in saliva Na+, Cl-, Ca++, Mg++ and Prot.- concentrations and by a decrease in saliva HCO3- content. The xerostomic saliva was more concentrated and had a greater salinity than the pretreatment saliva in each instance. In contrast, none of the serum electrolytes measured was significantly altered by the subtotal salivary shutdown.

A Sensitive Radioenzymatic Assay for Dopamine,Norepinephrine, and Epinephrine inPlasma and Tissue

Abstract: A double-isotope, radioenzymatic assayfor measuring dopamine, norepinephrine, and epi-nephrine in one sample is described. The assayprocedure includes incubation, solvent extraction,and thin-layer chromatography. Dopamine, norepi-nephrine, and epinephrine were incubated withcatechol-O-methyl transferase (COMT) and [3H]S-adenosyl methionine ([3H]SAM) and were convertedto the O-methylated tritiated derivatives: [3H]meth-oxytyramine, [3H]normetanephrine, and [3H]meta-nephrine, respectively. After several extractionsteps, the O-methylated products were purified bymeans of two-dimensional, thin-layer chromatogra-phy using silica gel. The thin-layer chromatographicsystem resulted in complete separation of the threeO-methylated compounds with an overlap of only1-2%. The assay was linear from 0 to 5 ng for eachcatecholamine and had a sensitivity of 10-30 pg. Theaddition of large amounts of plasma reduced theactivity of COMT, but increasing the magnesiumconcentration in the incubation mixture and the addition of E...

Postmating female odor in Heliconius butterflies: a male-contributed antiaphrodisiac?

Abstract: Genetic crosses between races of Heliconius erato that differ in the odor of female abdominal glands show that the odor originates in the male and is transferred to the female at mating. Behavioral observations strongly suggest that the odor is an antiaphrodisiac that helps to enforce monogamy among females.

Resource availability and population density in primates: A socio-bioenergetic analysis of the energy budgets of Guatemalan howler and spider monkeys

Abstract: This paper presents data on the food and energy utilization budgets of two sympatric species of nonhuman primates living in the quasi-rain forest of Tikal, Guatemala. Seven researchers working in teams obtained approximately 1200 hours of animal-observer contact time, representing approximately 2400 hours in the field. The following information is herein presented: (1) data on the estimated energy expenditure of the cebidae population living in the study site; (2) the nutritional composition of some foods eaten by Tikal's howler and spider population; (3) an estimate of the nutritional intake of howlers and spiders; and (4) an estimate of the carrying capacity of the habitat. The above types of data were combined in an attempt to answer the following question: To what extent are population density and size an indication of the carrying capacity of the habitat either in terms of food availability or quality? Data presented in this paper suggest that low population density and small group size are not necessarily the result of a nutritionally poor environment. The Tikal study site is capable of supporting 8,500 animal/km2. In the absence of other comparable quantitative socio-bioenergetic surveys it is herein suggested that the concept of food resource limitation is largely a myth among primatologists.

Methodological Considerations in Cross-national Consumer Research

Abstract: The field of consumer behavior has evolved rapidly in a relatively brief perod of time. The depth as well as the breadth of the research on consumer behavior has been impressive. However, most of the research in the area has one common limitation: it is culture bound. Nearly all consumer studies have been conducted in the United States. Thus, the principles which have been developed are associated only with U.S. consumer behavior; the theories which have been derived can legitimately be used to describe, predict, or understand consumer behavior only in the United States.

Melatonin: Effects on the circadian locomotor rhythm of sparrows

Abstract: The continuous administration of low levels of melatonin via intraperitoneally placed Silastic capsules either (i) shortened the free-running period of activity or (ii) induced continuous activity in house sparrows (Passer domesticus) maintained in constant darkness. After the melatonin-filled capsules were removed, the period of the circadian rhythm of activity lengthened in rhythmic birds and normal rhythmicity was restored in continuously active birds. The results suggest that melatonin is involved in the physiological control of circadian rhythmicity in sparrows.

The Self-Consciousness Scale: A Discriminant Validity Study.

Abstract: A recent Self-Consciousness Scale (SCS) measures Private and Public Self-Consciousness and Social Anxiety. The present research was intended to establish discriminant validity for the two Self-consciousness components with respect to several other variables. 105 male undergraduates completed the SCS, the Otis Test of Mental Ability, an abbreviated Edwards Personal Preference Schedule (measuring need for achievement), a Test Anxiety Questionnaire, and the EASI Temperament Survey. Private Self-consciousness did not correlate significantly with any other measure. Public Self-consciousness correlated weakly with the temperaments of Sociability and Emotionality. The Self-consciousness components of the SCS thus appear to be relatively independent of the other measures tested.

Some New Results on Compromise Solutions for Group Decision Problems

Abstract: We report some new results on compromise solutions studied by Yu [Yu, P. L. 1973. A class of decisions for group decision problems. Management Sci.19 8, April 936--946]. The following article focuses on the relation between the compromise solution and its parameter. In particular, we show that, under some nice conditions, the compromise solution is a continuous function of its parameter. A fundamental monotonicity result Theorem 3.1 concerning compromise solutions is derived. The result enables us to generate the bounds of all compromise solutions. When n = 2, two monotonicity results are derived. These yield a good interpretation of the parameter p. When p is small the “group utility” is emphasized; and when p increases the individual regrets receive more weight. Finally we construct an example to illustrate that the monotonicity results for n = 2 are almost impossible to be generated for n > 2.