Showing papers by "University of Texas at Austin published in 1982"

A single quantum cannot be cloned

Abstract: If a photon of definite polarization encounters an excited atom, there is typically some nonvanishing probability that the atom will emit a second photon by stimulated emission. Such a photon is guaranteed to have the same polarization as the original photon. But is it possible by this or any other process to amplify a quantum state, that is, to produce several copies of a quantum system (the polarized photon in the present case) each having the same state as the original? If it were, the amplifying process could be used to ascertain the exact state of a quantum system: in the case of a photon, one could determine its polarization by first producing a beam of identically polarized copies and then measuring the Stokes parameters1. We show here that the linearity of quantum mechanics forbids such replication and that this conclusion holds for all quantum systems.

Efficacious Form for Model Pseudopotentials

Abstract: A simple way has been discovered to put model pseudopotentials, $V(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}})={\ensuremath{\Sigma}}_{\mathrm{lm}}|{Y}_{\mathrm{lm}}〉{V}_{l}(r)\ifmmode\times\else\texttimes\fi{}〈{Y}_{\mathrm{lm}}|$, into a form which reduces the number of integrals of $V(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}})$ required for an energyband calculation from $\frac{\mathrm{mn}(n+1)}{2}$ to $\mathrm{mn}$ for each $l$ in the sum (where $n$ is the number of plane waves used in the expansion and $m$ the number of points in the Brillouin zone at which the calculation is performed). The new form may be chosen to improve the accuracy of the pseudopotential when used in other chemical environments.

Performance Analysis Using Stochastic Petri Nets

Abstract: An isomorphism between the behavior of Petri nets with exponentially distributed transition rates and Markov processes is presented. In particular, k-bounded Petri nets are isomorphic to finite Markov processes and can be solved by standard techniques if k is not too large. As a practical example, we solve for the steady state average message delay and throughput on a communication link when the alternating bit protocol is used for error recovery.

Striate cortex of monkey and cat: contrast response function.

Abstract: 1. We measured the responses of 247 neurons recorded from the striate cortex of monkeys and cats as a function of the contrast intensity of luminance-modulated spatialtemporal sine-wave grating patterns to provide a qualitative description and a quantitative mathematical formulation of the contast response function (CRF). 2. Qualitatively, it is possible to provide a general description of the contrast response function for the majority of cells as follows: as the luminance contrast of a pattern increases, the response increases in a relatively linear fashion over approximately 50-607o of the response range (generally less than I log unit along the contrast range), the slope of the function then begins a rapid compression to an asymptotic maximum-saturation response level. There is, however, a great deal of variation. from cell to cell, in the exact shape and location of the CRF. 3. Quantitatively, the responses of each cell were analyzed in terms of the leastsquares (parameter optimized) best fit using four different mathematical functions: linear, logarithmic power, and hyperbolic ratio. The results of this procedure showed that, across the range of contrasts measured ( 1.4567o), the hypcrbolic ratio (H ratio) provided the best fit for the vast majority of striate cells: some 7O9o f the cells were best fitted by the H ratio and further, averaged across all cells, the H ratio produced the least average residual variance. 4. The contrast response function is an important factor when considering the spatial properties of cortical cells; nonlinearities in the CRF (compression and saturation) will necessarily influence the spatial tuning. We therefore measured the CRF at different spatial frequencies and used the parameters of the H ratio to test the predictions of two general classes of models. If the overall gain, compression, and saturation are set by the absolute response level (response-set gain), then the CRFs measured at different frequencies should shift horizontally along the contrast axis. Results show that the measured CRFs (tested on the same cell using different spatial frequencies) were shifted primarily vertically, suggesting that the gain, compression, and saturation were set by the absolute contrast level (contrast-set gain), relatively independent of spatial frequency; in terms of the H ratio, the semisaturation contrast and the exponent were relatively constant in comparison to the asymptotic saturation response. Thus, the spatial frequency response functions are relatively constant when measured at different stimulus contrasts. 5. There is a great deal of variation in the location of the dynamic response range, from cell to cell, along the contrast axis: some cells distribute their dynamic response range over the first lOVo of contrast, others the second, etc. (relatively independent of preferred spatial frequency). One might expect this range variation to be an important factor in behavioral contrast discrimination. To provide an indication of the average population response as a function of contrast, all cells were averaged together (percent response relative to each cell 's maximum): the slope of the bcst-fitt ing [nwer function (0.77) falls well within the range of estimates found for human psychophysical contrast discrimination functions.

Some Methods for Respecifying Measurement Models to Obtain Unidimensional Construct Measurement

Abstract: Lack of unidimensionality in structural equation models most often represents misspecification. The authors review the necessary conditions for unidimensional measurement of constructs. Two methods...

Computer rendering of stochastic models

Abstract: A recurrent problem in generating realistic pictures by computers is to represent natural irregular objects and phenomena without undue time or space overhead. We develop a new and powerful solution to this computer graphics problem by modeling objects as sample paths of stochastic processes. Of particular interest are those stochastic processes which previously have been found to be useful models of the natural phenomena to be represented. One such model applicable to the representation of terrains, known as “fractional Brownian motion,” has been developed by Mandelbrot.The value of a new approach to object modeling in computer graphics depends largely on the efficiency of the techniques used to implement the model. We introduce a new algorithm that computes a realistic, visually satisfactory approximation to fractional Brownian motion in faster time than with exact calculations. A major advantage of this technique is that it allows us to compute the surface to arbitrary levels of details without increasing the database. Thus objects with complex appearances can be displayed from a very small database. The character of the surface can be controlled by merely modifying a few parameters. A similar change allows complex motion to be created inexpensively.

Factors Affecting the Use of Market Research Information: A Path Analysis:

Abstract: The authors evaluate several factors affecting the attention given to or “use” of specific market research information by marketing managers. They apply path analysis to test a model of research us...

Supersymmetry at ordinary energies. Masses and conservation laws

Abstract: An assessment is made of the general problems encountered in formulating a realistic supersymmetric theory in which the spontaneous breakdown of supersymmetry occurs at ordinary energies accessible to accelerators. As a starting point, three problems are identified in SU(3)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}U(1) supersymmetric models with only quark and lepton chiral superfields: the up quarks get no masses, baryon and lepton ($B$ and $L$) conservation are violated by renormalizable and hence unsuppressed interactions, and the scalar counterparts of the quarks and leptons are too light. An interesting SU(3)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}U(1) model of Dimopoulos and Georgi that avoids these problems is considered; it is found that this model contains $B$- and $L$-nonconserving effective interactions of dimensionality 5 that lead to proton decay at too rapid a rate. To guarantee natural $B$ and $L$ conservation in effective interactions of dimensionality 4 and 5, it is suggested that the gauge group that describes physics at ordinary energies contains a factor, such as another U(1), in addition to SU(3)\ifmmode\times\else\texttimes\fi{}SU(2)\ifmmode\times\else\texttimes\fi{}U(1). Such theories do not contain dimension-5 $L$-nonconserving interactions which could produce an observable neutrino mass, but they do allow dimension-6 $B$- and $L$-nonconserving interactions that would lead to proton decay at an observable rate. Supersymmetry is found to constrain the matrix elements for proton decay in a phenomenologically interesting way. A general explanation is given of how such theories naturally avoid the problem of light scalars, as found by Fayet. The formalism is used to derive general approximate mass relations for the scalar superpartners of the quarks and leptons. The problem of anomalies in the new U(1) current is considered, and one attractive scheme for avoiding them is offered, in which the anomalies cancel for precisely three generations of quarks and leptons.

Life Span Study of SPF Fischer 344 Male Rats Fed AdLibitum or Restricted Diets: Longevity, Growth, Lean Body Mass and Disease

Abstract: A life-span study was carried out on longevity, pathologic lesions, growth, lean body mass and selected aspects of muscle of barrier-maintained SPF Fischer 344 rats fed either ad libitum (Group A) or 60% of the ad libitum intake (Group R). Food restriction was as effective in prolonging the life of already long-lived SPF rats as previously shown for rats maintained in conventional facilities. Food restriction not only increased the mean length of life but also acted to extend life span since more than 60% of the Group R rats lived longer than the longest lived Group A rat. Renal lesions occurred at an earlier age in Group A rats than in Group R rats and progressed more rapidly. Death of most Group A rats was associated with severe renal lesions while few Group R rats showed such lesions at death. Food restriction was also found to delay or prevent interstitial cell tumors of the testes, bile duct hyperplasia, myocardial fibrosis and myocardial degeneration. Gastrocnemius muscle mass declined in advanced age and food restriction delayed this decline. Interestingly, however, lean body mass did not progressively decline with increasing age but rather decline occurred only after the onset of the terminal disease process.

Perspective-taking and altruism.

Abstract: Reviews the evidence regarding the development of altruism and suggests that various forms of perspective-taking (perceptual, social, empathic, moral) might be the mediators of this development. Previous reviews in this area have generally concluded that the evidence relating perspective-taking and

Cosmological Constraints on the Scale of Supersymmetry Breaking

Abstract: The gravitino must be either light enough so that ambient gravitinos would not produce too large a cosmic deceleration, or heavy enough so that almost all gravitinos would have decayed before the time of helium synthesis. The second alternative is shown to allow supersymmetry-breaking scales above a model-dependent lower bound of ${10}^{11}$ to ${10}^{16}$ GeV.

When our identities are mistaken: Reaffirming self-conceptions through social interaction.

Abstract: Although those who have labored to change self-concepts in naturally occurring situations (jave often experienced difficulty, laboratory investigators have reported considerable success in this endeavor. This research sought to reconcile these contradictory findings by examining how people respond behaviorally and psychologically when they receive feedback that disconfirms their self-conceptions. The results showed that self-discrepant feedback produced changes in selfratings only when recipients had no opportunity to reject and refute it. If participants had opportunity to behaviorally discredit discrepant feedback, they did so and subsequently displayed minimal self-rating change. The discussion proposes some important differences between transitory fluctuations and enduring changes in self-ratings and suggests some conditions that must be met before lasting self-concept changes will occur.

Rapid 13C/12C turnover during growth of brown shrimp (Penaeus aztecus)

Abstract: Using natural-abundance 13C/12C ratios as tracers, carbon turnover rates were determined for postlarval brown shrimp, Penaeus aztecus, in five laboratory growth experiments. Although tissue turnover in adult animals generally occurs during maintenance metabolism and is a function of time, turnover for young postlarval shrimp was accelerated during growth, and was primarily a function of weight gained rather than time. Metabolic loss of tissue carbon during growth was usually approximated by the function, Fraction lost=1-(initial weight/final weight). For shrimp that switch diets in the sea, model calculations show that this high turnover rate coupled with a four-fold weight increase suffices for shrimp to achieve a close isotopic resemblance of 1‰ or less (δ13C units) to the new diet.

Crypts are the site of intestinal fluid and electrolyte secretion

Abstract: The site of adenosine 3',5'-monophosphate-mediated fluid and electrolyte secretion across mammalian large intestine was found to be the crypts of Lieberkuhn by means of two techniques. First, the formation of fluid droplets was visualized on the oil-covered mucosal surface directly over crypt duct openings when secretion was stimulated. Second, microelectrode impalement of individual surface and crypt cells revealed that only crypts cells produced a pattern of secretagogue induced alterations in membrane potential and resistance that was characteristic of secretory epithelia.

Adsorption of surfactants on mineral oxide surfaces from aqueous solutions

Abstract: Adsorption isotherms for three isomerically pure alkylbenzene sulfonates were measured on alumina and kaolinite from aqueous solutions. A patchwise adsorption model, which incorporates bilayer adsorption, lateral interactions, and two-dimensional phase transitions, is developed and shown to describe the observed isotherms below the CMC. As expected, Henry's Law describes the adsorption at sufficiently low surfactant concentrations. In this region, only unassociated, first-layer, surfactant molecules are present on the surface and at least the terminal 10th through the 12th carbons in the alkyl chain interact strongly with the surface, in addition to the charged head-surface electrostatic attraction. The adsorption increases rapidly beyond a certain concentration. At this concentration, hemimicelles resulting from lateral interaction between adsorbed surfactants first appear on the most energetic surface patches. At still higher concentrations, successively less energetic patches are sites for two-dimensional phase transitions forming hemimicelles. The environment for methylene groups in the hemimicelle is more favorable than that in a micelle. Above the CMC, adsorption is independent of concentration. This indicates that micelles do not adsorb significantly and that the pseudo-phase separation model is a good approximation for these systems.

Polymer films on electrodes. 9. Electron and mass transfer in Nafion films containing tris(2,2'-bipyridine)ruthenium(2+)

Abstract: The electrochemical behavior of Ru(bpy),2+ (bpy = 2,2'-bipyridine) contained in 2-"thick films of the perfluorosulfonate polymer Nafion on glassy carbon is described. The apparent diffusion coefficient, D, , for the 2+ and 3+ forms was determined by potential-step chronoamperometric measurements to be (5 & 2) X cm*s-l. Dapp for the 2+ form was independent of loading of R ~ ( b p y ) , ~ + in the film. The shapes of the cyclic voltammetric (current-potential) waves for the system were fit by digital simulation techniques with a model involving interactions between the electroactive groups as well as interconversions of different forms of the 2+ and 3+ species. Recent reports from this labora t~ry l -~ have described polymer electrodes based on the ion-containing polymer Nafion.4 Because (CF2 C Fz )I (C FC F21? I O-GF~) G C F ~ C F ~ SGCN:

Polymer Films on Electrodes. 8. Investigation of Charge-Transport Mechanisms in Nafion Polymer Modified Electrodes

Abstract: The mechanism of charge transport through Nafion polymers coated on glassy carbon electrodes and containing Cp2FeTMA+, R~(bpy),~+, and O~(bpy),~+ (where Cp2FeTMA+ is ((trimethylammonio)methyl)ferrocene, bpy = 2,2'-bipyridine) is described. The apparent diffusion coefficients, Dam,, of polymer modified electrodes, as measured by conventional electrochemical methods and which can include contributions from intermolecular electron transfer, are compared to the diffusion coefficients of actual mass transport of the electroactive species through the polymer, D,, as measured from the rate of permeation of the electroactive material. The results indicate that Dapp = D, for Cp2FeTMA+, Dapp 20, for Os(bpy),*+, and DaP4 = 15D, for Ru(bpy)t+. These results are discussed in terms of the Dahms-Ruff model, where the observed diffusional behavior is due to both physical diffusion of the electroactive species and an electron-transfer component that can contribute to the observed behavior. The contribution of the electron-exchange mechanism toward the value of Dapp decreases in the order of electroactive species, Ru(bpy),*+ >> O~(bpy),~+ 2 Cp2FeTMA+. A key question in the behavior of "polymer electrodes" (elec- trodes coated with a thin layer of polymer1-*) involves the mechanism of charge transport through the layers. The rate of charge transport frequently governs the rate of electrochemical and catalytic processes at such electrodes and has been the subject of numerous recent inve~tigations.~,~.~-" Charge can be trans- ported through the layer by electron transfer between redox centers, counterion diffusion, and diffusion of the electroactive species; the relative contribution of these effects is probably different for different kinds of polymer coatings.

Tactile extinction: distinguishing between sensorimotor and motor asymmetries in rats with unilateral nigrostriatal damage

Abstract: We describe and demonstrate the usefulness of a reliable procedure for quantifying “sensorimotor” asymmetries in rats with nigrostriatal damage. Conventional tests, such as the popular Von Frey hair technique are sometimes inadequate in that positive responses are difficult to quantify, they are susceptible to subjective interpretation, and they require that the animal make head movements. Circling behavior has become established as a measure of asymmetrical nigrostriatal activity, but it does not measure stimulus-directed movement. One group of rats was given unilateral microinfusions of 6-OHDA into the nigrostriatal system which decreased levels of dopamine in the ipsilateral striatum and yieded an ipsilateral turning bias. Another group was given electrolytic lesions in the substantia nigra area, which yielded a severe contralateral circling bias. Small pieces of adhesive paper were applied to various parts of the limbs or snout and latencies to remove the stimuli were recorded. Because head and body movements were not required, assessment of stimulus-directed movement asymmetries could be quantified rapidly without the interference of stimulus-independent (“spontaneous”) postural and motor asymmetries. In the 6-OHDA-treated rats there was ipsilateral bias in stimulus-directed activity. Indeed, there was ipsilateral hyper-reactivity relative to sham controls. In rats with electrolytic nigra lesions, despite a strong contralateral “spontaneous” motor bias, there likewise was an ipsilateral bias in stimulus-directed movement, which could only be detected using the adhesive removal test. This similarity in stimulus-directed movement asymmetry between the two groups may reflect a common asymmetry in ascending dopaminergic pathways. The opposite circling bias following electrolytic nigra lesions may reflect differential damage to non-dopaminergic efferent projections. The bilateral adhesive removal (tactile extinction) test appears to permit the separate quantification of stimulus-directed and stimulus-independent movement asymmetries.

Toward a Theory of Infant Temperament

Abstract: Why do we have a chapter on temperament in a volume primarily devoted to the concepts of attachment and affiliation? Years ago, such a chapter would have been unthinkable because attachment and temperament appeared to refer to different phenomena. Classic theories of mother-infant relations such as those of Spitz (1965) and Bowlby (1951) leaned in the direction of a “tabula rasa” model of the human infant by proposing that emotional and drive-regulating experiences provided by the mother were crucial for the formation and maintenance of ego functions. The individual differences these theorists were interested in were those resulting from successes and failures of maternal interaction, although on occasion they did invoke genetic and constitutional factors to account for unusual tolerances or susceptibilities to the ill effects of maternal separation. Individual differences in temperament, then, were relegated to a shorthand description of the susceptibility of the “tabula rasa” to experience—how hard or soft the tablet was, so to speak. Little speculation took place about how such differences in the infant could be assessed or whether they played a role in attachment.

Electrogenerated chemiluminescence. 41. Electrogenerated chemiluminescence and chemiluminescence of the Ru(2,21 - bpy)32+-S2O82- system in acetonitrile-water solutions

Abstract: The electrogenerated chemiluminescence (ecl) produced in acetonitrile-water solutions (1:1 by volume) by the reaction of electrogenerated Ru(bpy)/sub 3//sup +/ with the strongly oxidizing intermediate, SO/sub 4//sup -/, generated during reduction of S/sub 2/O/sub 8//sup 2 -/ is described The orange luminescence (lambda/sub max/ = 625 nm) corresponds to emission from Ru(bpy)/sub 3//sup 2 +/* The relative ecl intensity is a function of S/sub 2/O/sub 8//sup 2 -/ concentration, and for a 1 mM Ru(bpy)/sub 3//sup 2 +/ solution the maximum ecl intensity was obtained at 15-20 mM S/sub 2/O/sub 8//sup 2 -/ Slightly higher concentrations (>30 mM S/sub 2/O/sub 8//sup 2 -/) effectively quench light emission because of the Ru(bpy)/sub 3//sup 2 +/*-S/sub 2/O/sub 8//sup 2 -/ reaction The ecl efficiency (photons produced/electrons consumed) was approx 5% and was insensitive to dissolved O/sub 2/ A chemiluminescence based on reduction with Mg metal is also described

An Application of Mathematical Programming to Assess Productivity in the Houston Independent School District

Abstract: A school may be viewed as an enterprise in which the professional staff provide the operating conditions for converting quantifiable resources or inputs into pupil learning outputs. The resources are determined by budgets, teacher assignments, and student assignments while learning is determined by various outputs scored according to standardized tests such as the Iowa Test of Basic Skills. Following the work of Charnes, Cooper, and Rhodes Charnes, A., W. W. Cooper, E. Rhodes. 1981. Evaluating program and managerial efficiency: an application of data envelopment analysis to program follow through. Management Sci.27 6 668-697., we use a ratio definition of efficiency that takes account of all outputs and inputs without requiring a priori specification of weights. Instead a series of mathematical programs are applied to determine "virtual multipliers" from actual data. The multipliers produce values that can be regarded as the "most favorable weights" for each school being evaluated. If the resulting optimum virtual multipliers for a given school yield an efficiency ratio of one, then that school is said to be efficient. If the ratio is less than one then that school is said to be inefficient relative to the other schools in the analysis. The ratio is also accorded operational significance-it is not merely an index number-so that the resulting values and the associated virtual multipliers make it possible to locate where improvements may be made along with their relative magnitudes. This analysis was applied to 167 elementary schools in the Houston Independent School District. Of these schools, 78 were found to be inefficiently utilizing their resources as compared to the 89 efficient schools. Based on this pilot study, an Educational Productivity Council has been formed at the University of Texas at Austin to provide an annual analysis for all of its member schools. At present 285 Texas schools in 22 districts are scheduled for participation in the annual analysis as described in this investigation.

Application of an extended RISM equation to dipolar and quadrupolar fluids

Abstract: A generalization of the RISM integral equation for site–site pair correlation functions previously proposed by us is discussed and applied to model liquids composed of strongly polar diatomic molecules. The nonuniform molecular charge distribution is represented by the introduction of charged interaction sites. The generalization consists of applying closure conditions analogous to those which are known to be reasonable for the description of atomic ionic fluids, and the corresponding renormalization of the contributions arising from long range forces. We discuss both the symmetry properties of the pair correlation functions in special cases and the dielectric properties implied by theory. Applications are presented for three two‐site models which differ substantially in the degree of asymmetry of the non‐Coulombic potential between the two sites, and for three three‐site models for Br2. The two sites models are compared to computer simulation results, and those for Br2 to experimental results. The analysis shows that the integral equation is well balanced in that in every case the qualitative features of the liquids structure which are introduced by polarity are well represented, even in cases where the site–site potentials are individually much larger than kBT. In cases where the molecular shape and polar forces are in competition, the results are of comparable accuracy to the corresponding theory for nonpolar systems. In the extreme case where changes in orientational structure can occur without interfering with packing requirements, the results appear quantitatively less reliable.

Integral equation predictions of liquid state structure for waterlike intermolecular potentials

Abstract: An application of our recently developed extended RISM equation formulation to several three‐site models of water is presented. The site–site correlation functions are obtained and compared to available computer simulation results. Further, the variation of liquid state structure with the model site charge is examined. The analysis of these results has demonstrated that the integral equation approach provides a correct qualitative description of the liquid structure, although the amplitudes of most structural features are somewhat less accurate that their positions. Comparison to our earlier results for simpler models suggests that the nature of the quantitative deficiencies of the approach is predictable. The charging study has shown that the development of waterlike structure with increasing site charge follows a qualitatively different pattern for oxygen–oxygen pairs, compared to those involving hydrogen. This is attributed to interference between the amplitudes characteristic of liquid water and of simple liquids. These results suggest that this is the origin of a relatively flat 0–0 correlation function for several models studied in the past, and, further, that such results should not be properly characterized as ’’unstructured.’’

A multiplicative model for efficiency analysis

Abstract: This paper develops theory and algorithms for a “multiplicative” Data Envelopment Analysis (DEA) model employing virtual outputs and inputs as does the CCR ratio method for efficiency analysis. The frontier production function results here are of piecewise log-linear rather than piecewise linear form.

Children and Marital Happiness: A Further Specification of the Relationship.

Abstract: The effects of the presence of children on their parents' marital happiness were estimated, with data from six U. S. national surveys conducted from 1973 through 1978, for subpopulations delineated on the basis of sex, race, level of education, religious preference, employment status, and stated ideal number of children for a ,family. No evidence for distinctly positive mean effects was found for any subpopulation, the estimated mean effects ranging from distinctly negative (for most of the subpopulations) to near zero for whites who said that the ideal number of children for a family is four or more. The findings contribute to a rather large body of accumulating evidence which indicates that on the average children adversely affect marital quality, both in the total population of married persons in the U. S. and in several large and important subpopulations. Some implications of the findings are discussed.