Showing papers by "University of California, Santa Barbara published in 1982"

Quantum Mechanics of Fractional-Spin Particles

Abstract: Composites formed from charged particles and vortices in (2+1)-dimensional models, or flux tubes in three-dimensional models, can have any (fractional) angular momentum. The statistics of these objects, like their spin, interpolates continuously between the usual boson and fermion cases. How this works for two-particle quantum mechanics is discussed here.

Magnetic Flux, Angular Momentum, and Statistics

Abstract: It is demonstrated that the orbital angular momentum ${l}_{z}$ of a particle of charge $q$ orbiting around a tube with magnetic flux $\ensuremath{\Phi}$ is quantized in units ${l}_{z}=\mathrm{integer}\ensuremath{-}\frac{q\ensuremath{\Phi}}{2\ensuremath{\pi}}$. A very simple physical argument for this is presented, and applied to understand the Dirac quantization condition and the charge-spin relation for particles bound to magnetic monopoles. The unusual statistics of flux-tube-charged-particle composites is discussed.

Heterostructure bipolar transistors and integrated circuits

Abstract: Two new epitaxial technologies have emerged in recent years (molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD)), which offer the promise of making highly advanced heterostructures routinely available. While many kinds of devices will benefit, the principal and first beneficiary will be bipolar transistors. The underlying central principle is the use of energy gap variations beside electric fields to control the forces acting on electrons and holes, separately and independently of each other. The resulting greater design freedom permits a re-optimization of doping levels and geometries, leading to higher speed devices. Microwave transistors with maximum oscillation frequencies above 100 GHz and digital switching transistors with switching times below 10 ps should become available. An inverted transistor strucure with a smaller collectors on top and a larger emitter on the bottom becomes possible, with speed advantages over the common "emitter-up" design. Double-heterostructure (DH) transistors with both wide-gap emitters and collectors offer additional advantages. They exhibit better performance under saturated operation. Their emitters and collectors may be interchanged by simply changing biasing conditions, greatly simplifying the architecture of bipolar IC's. Examples of heterostructure implementations of I2L and ECL are discussed. The present overwhelming dominance of the compound semiconductor device field by FET's is likely to come to an end, with bipolar devices assuming an at least equal role, and very likely a leading one.

Recruitment of marine invertebrates: the role of active larval choices and early mortality

Abstract: Spatial variation in the recruitment of sessile marine invertebrates with planktonic larvae may be derived from a number of sources: events within the plankton, choices made by larvae at the time of settlement, and mortality of juvenile organisms after settlement, but before a census by an observer. These sources usually are not distinguished. A study of the recruitment of four species of sessile invertebrates living on rock walls beneath a kelp canopy showed that both selection of microhabitats by settling larvae and predation by fish may be important. Two microhabitats were of interest; open, flat rock surfaces, and small pits and crevices that act as refuges from fish predators. The polychaete Spirorbis eximus and the cyclostome bryozoan Tubulipora spp. showed no preference for refuges, but settled apparently at random on the available substrata. Tubulipora was preyed upon heavily by fish, while Spirorbis was relatively unaffected. The bryozoans Celleporaria brunnea and Scrupocellaria bertholetti both recruited preferentially into refuges. Scrupocellaria were preyed upon, while Celleporaria juveniles seemed unaffected. Predation by fish modified the spatial distribution (Tubulipora), abundance (Tubulipora), or size distribution (Scrupocellaria) of the juvenile population, or had relatively little effect (Celleporaria, Spirorbis). All of the above events occur within three weeks of settlement. Since inferences about the effect of larval events on the population dynamics of adult organisms are often based on observations of the patterns of recruitment after one or two months, they are therefore likely to be misleading.

Reheating an inflationary universe

Abstract: A numerical analysis of the evolution of the Higgs expectation value and the temperature of the universe during the symmetry-breaking phase transition in an SU(5) theory with radiatively induced symmetry breaking is presented. It is shown that there is sufficient inflation (exponential expansion) to explain the cosmological homogeneity, isotropy, flatness, and monopole puzzles, and also that the universe reheats to a temperature $O({10}^{14} \mathrm{GeV})$ so that the usual scheme for baryogenesis can proceed.

Grazing-incidence diffraction and the distorted-wave approximation for the study of surfaces

Abstract: A method is developed for calculating the scattering of a beam of x rays striking the plane surface of a crystal at an angle below the critical angle for total external reflection The low penetration under this condition offers the possibility of determining the special structure of the surface layers, as has been pointed out by Marra, Eisenberger, and Cho A distorted-wave approach is developed whereby the crystal is first taken to be a homogeneous dielectric slab for the purpose of calculating the distorted wave The distorted wave is considered to illuminate the actual crystal, from which a scattering pattern can then be calculated The effects of absorption can be taken into account; in some cases absorption may offer the possibility of observing near-surface structures at angles of incidence larger than the critical angle Such illumination may also be useful for performing fluorescence analysis of the near-surface layers to determine their impurity content Synchrotron sources offer new opportunities for measurements of these kinds Thermal neutrons may also be used in place of x rays and offer unique opportunities for studying surface magnetization and, through inelastic scattering, surface phonons and, conceivably, surface magnons

Axions and family symmetry breaking

Abstract: Possible advantages of replacing the Peccei-Quinn U(1) quasisymmetry by a group of genuine flavor symmetries are pointed out. Characteristic neutral Nambu-Goldstone bosons will arise, which might be observed in rare $K$ or $\ensuremath{\mu}$ decays. The formulation of Lagrangians embodying these ideas is discussed schematically.

On the structure of vector quantizers

Abstract: Vector quantization is intrinsically superior to predictive coding, transform coding, and other suboptimal and {\em ad hoc} procedures since it achieves optimal rate distortion performance subject only to a constraint on memory or block length of the observable signal segment being encoded. The key limitation of existing techniques is the very large randomly generated code books which must be stored, and the computational complexity of the associated encoding procedures. The quantization operation is decomposed into its rudimentary structural components. This leads to a simple and elegant approach to derive analytical properties of optimal quantizers. Some useful properties of quantizers and algorithmic approaches are given, which are relevant to the complexity of both storage and processing in the encoding operation. Highly disordered quantizers, which have been designed using a clustering algorithm, are considered. Finally, lattice quantizers are examined which circumvent the need for a code book by using a highly structured code based on lattices. The code vectors are algorithmically generated in a simple manner rather than stored in a code book, and fast algorithms perform the encoding algorithm with negligible complexity.

Pathways to Participation

Abstract: The premise of this article is that adult participation in politics is affected by strong preadult forces in addition to the contemporaneous factors emphasized by recent studies. To test this premise, data are drawn from the 1965–1973 national socialization panel study of young Americans and their parents. Four causal models depicting pathways to participation among young adults are evaluated; each includes civic orientations as intervening variables. Three of the models assess the direct and indirect effects of parental characteristics—socioeconomic status, political activity, and civic orientations. The fourth model assesses the impact of adolescent involvement in high school activities. Taken individually, each pathway is shown to have an effect on adult participation, with parent socioeconomic status and high school activism having the most impact. When the four pathways are combined in a single model to reflect the connections among them, all remain important. The combined model illustrates the importance of a variety of methods of political learning. The combined model also demonstrates the crucial role of civic orientations in converting preadult experiences into later participation. Civic orientations are the primary carriers of preadult political learning. Overall, the results rebut the critics of socialization research who have questioned the existence of a linkage between early learning and adult political behavior.

One-Dimensional Ising Model and the Complete Devil's Staircase

Abstract: It is shown rigorously that the one-dimensional Ising model with long-range antiferromagnetic interactions exhibits a complete devil's staircase.

Monte Carlo Simulations of One-dimensional Fermion Systems

Abstract: We discuss a new method to perform numerical simulations of one-dimensional systems with fermion and boson degrees of freedom. The method is based on a direct-space, imaginary-time representation of the fermion field. It is fast so that systems having up to 100 sites can easily be simulated. In addition, the method provides an intuitive physical "picture" of the ground state of a one-dimensional many-body system. We discuss in detail how to implement the method and how to compute various physical quantities. In particular, we show how to extend the method to study averages of off-diagonal quantities in an occupation-number representation. To assess the accuracy of our procedure, we apply it to free fermions in one dimension and compare with exact results. We then study a model of spinless interacting fermions and obtain the expected phase structure and behavior of correlation functions. We also consider the extended Hubbard model at various points in its phase diagram and study the behavior of spin-density, charge-density, and pairing correlation functions. We then study the Gross-Neveu model and show how the behavior depends on the number of fermion flavors. Finally, we consider an electron-phonon model and study its behavior both in the one-particle polaron sector and in the half-filled-band case. Along the way we show pictures of the ground-state configurations that give physical insight into the properties of the systems, like charge-density-wave, spin-density-wave, and superconducting states, "fractional charges," and solitons. We conclude by comparing our method with other methods and discuss the possibility of extending it to higher dimensions.

Carbon dioxide hydration and dehydration kinetics in seawater1

Abstract: Rate constants for the hydration and dehydration reactions of carbon dioxide with water and with hydroxyl ion were measured in seawater by a pH-stat method at salinities (X lO:l) from 3.4 to 37.06 at 25°C and from 5” to 35°C at a salinity of 33.77. Transition state theory was used to extrapolate the rate constants to infinite dilution, with the following results at 25°C: kcoz = 0.037 ? 0.002. s-l, /COII-&~ = (7.1 + 0.7) x lo-l1 mol.dm-‘. s-‘, k,, = (7.6 + 1.1) x lo4 dm”* mol-’ * s-’ , and kIIcoB- = (1.8 f 0.3) x 10m4* s-l. The corresponding values in scawatcl of 33.77 salinity and 25°C calculated from equations fit to the experimental data are 0.036, 13.5 x 10 I’, 3.5 x 10d, and 1.40 x 10-4.

Theory of intermittency

Abstract: The aperiodic or chaotic behavior for one-dimensional maps just before a tangent bifurcation occurs appears as intermittency in which long laminarlike regions irregularly separated by bursts occur. Proceeding from the picture proposed by Pomeau and Manneville, numerical experiments and analytic calculations are carried out on various models exhibiting this behavior. The behavior in the presence of external noise is analyzed, and the case of a general power dependence of the curve near the tangent bifurcation is studied. Scaling relations for the average length of the laminar regions and deviations from scaling are determined. In addition, the probability distribution of path lengths, the stationary distribution of the maps, the correlation function and power spectrum of the map in the intermittent region, and the Lyapunov exponent are obtained.

Unconstrained frequency-domain adaptive filter

Abstract: An unconstrained frequency-domain least mean-squares (UFLMS) algorithm is presented. The algorithm is based on the "overlap-save" technique used in frequency-domain filtering. The proposed algorithm converges to the Wiener solution without the time-domain constraint on the impulse response as proposed by Ferrara. For a large number of taps ( \geq32 ), the UFLMS algorithm offers a significant reduction in computation. Another advantage is its fast convergence for highly correlated input signals. The performance of the algorithm is illustrated by a simulation.

A Translog Cost Function Analysis of U.S. Agriculture, 1939–77

Abstract: Over the past four decades major changes have occurred in U.S. agriculture. A new era in agricultural production in the United States began in 1939. World War II gave a boost to agriculture still bogged in the depression. Productivity increases over the period 1939-77 have been quite impressive. Measured crudely by the ratio of the indices of output and input, the productivity index (1967 = 100) increased from 59 in 1939 to 119 in 1977. To study this phenomenon, a multi-input translog cost function incorporating Hicks-neutral technical change (HNTC) was specified. Annual timeseries data for the United States was used to estimate the model. Neoclassical duality theory provides an approach for computing the pairwise elasticities of substitution between inputs for each year as well as the annual (own- and cross-) price elasticities of demand for inputs.

Daily otolith increments and recruitment in two coral-reef wrasses, Thalassoma bifasciatum and Halichoeres bivittatus

Abstract: Increments on the otoliths of two common coral reef fishes, the bluehead wrasse Thalassoma bifasciatum and the slippery dick Halichoeres bivittatus, were demonstrated by mark-recapture experiments to be daily. Otoliths were marked in two ways; by depriving fish of light, food, and temperature cycles and also by supplemental feeding in the field. Both experiments were performed in late 1980 in the San Blas Islands of Panama. A mark corresponding to settlement of the planktonic larva onto the reef was found on the otoliths of the bluehead wrasse. This settlement mark was used to calculate the dates of settlement of a collection of juveniles of this species taken from a patch reef in the San Blas Islands of Panama in 1981. Settlement occurred in short and irregular bursts. The number of daily increments before the settlement mark indicates a planktonic larval life of 40 to 72 d.

The stabilizing effect of a random environment

Abstract: It is shown that the lottery competition model permits coexistence in a stochastic environment, but not in a constant environment. Conditions for coexistence and competitive exclusion are determined. Analysis of these conditions shows that the essential requirements for coexistence are overlapping generations and fluctuating birth rates which ensure that each species has periods when it is increasing. It is found that a species may persist provided only that it is favored sufficiently by the environment during favorable periods independently of the extent to which the other species is favored during its favorable periods.

Liquid Water and Active Resurfacing on Europa.

Abstract: Arguments for recent resurfacing of Europa by H2O from a liquid layer are presented, based on new interpretations of recent spacecraft and earth-based observations and revised theoretical calculations. The heat flow in the core and shell due to tidal forces is discussed, and considerations of viscosity and convection in the interior are found to imply water retention in the outer 60 km or so of the silicates, forming a layer of water/ice many tens of km thick. The outer ice crust is considered to be too thin to support heat transport rates sufficient to freeze the underlying water. Observational evidence for the calculations would consist of an insulating layer of frosts derived from water boiling up between cracks in the surface crust. Evidence for the existence of such a frost layer, including the photometric function of Europa and the deposits of sulfur on the trailing hemisphere, is discussed.

Mechanisms of avian egg recognition: Which egg parameters elicit responses by rejecter species?

Abstract: Some species of North American passerines nearly always reject nonmimetic eggs placed in their nests and have apparently evolved this behavior in response to brood parasitism. Experiments presented here examined the specific egg parameters to which ‘rejecter species’ respond, the relative tolerances rejecters show towards nonmimetic eggs and the degree to which rejection is limited to eggs of the brown-headed cowbird (Molothrus ater), the only parasitic bird widespread in North America.