Showing papers by "University of California, Santa Barbara published in 1985"
TL;DR: In this article, the results of numerical simulations of nonlinear gravitational clustering in universes dominated by weakly interacting, cold dark matter are presented and the evolution of the fundamental statistical properties of the models is described and their comparability with observation is discussed.
Abstract: The results of numerical simulations of nonlinear gravitational clustering in universes dominated by weakly interacting, 'cold' dark matter are presented. The numerical methods used and the way in which initial conditions were generated are described, and the simulations performed are catalogued. The evolution of the fundamental statistical properties of the models is described and their comparability with observation is discussed. Graphical comparisons of these open models with the observed galaxy distribution in a large redshift survey are made. It is concluded that a model with a cosmological density parameter omega equal to one is quite unacceptable if galaxies trace the mass distribution, and that models with omega of roughly two, while better, still do not provide a fully acceptable match with observation. Finally, a situation in which galaxy formation is suppressed except in sufficiently dense regions is modelled which leads to models which can agree with observation quite well even for omega equal to one.
3,037 citations
TL;DR: In this paper, the authors studied candidate vacuum configurations in ten-dimensional O(32) and E 8 × E 8 supergravity and superstring theory that have unbroken N = 1 supersymmetry in four dimensions.
2,447 citations
TL;DR: In this paper, a growth model with shocks to technology is studied, and it is shown that, unlike previous equilibrium models of the business cycle, this economy displays large fluctuations in hours worked and relatively small fluctuations in productivity.
2,238 citations
TL;DR: In this article, a new isotopy invariant of oriented links of tamely embedded circles in 3-space is presented, where the image of the link is a union of transversely intersecting immersed curves, each provided with an orientation, and undercrossings are indicated by broken lines.
Abstract: The purpose of this note is to announce a new isotopy invariant of oriented links of tamely embedded circles in 3-space. We represent links by plane projections, using the customary conventions that the image of the link is a union of transversely intersecting immersed curves, each provided with an orientation, and undercrossings are indicated by broken lines. Following Conway [6], we use the symbols L+, Lo, L_ to denote links having plane projections which agree except in a small disk, and inside that disk are represented by the pictures of Figure 1. Conway showed that the one-variable Alexander polynomials of L+, Lo, L_ (when suitably normalized) satisfy the relation
1,225 citations
TL;DR: Site consistency argues that either settlement or early post-settlement mortality is determined by specific local physical conditions at a site, such as coastal morphology, internal waves, shore waves, currents, or by consistent abundances of natural enemies.
847 citations
TL;DR: In this paper, the linear density response of inhomogeneous electronic systems is discussed from a density-functional point of view, and a local density approximation for the frequency-dependent exchange-correlation potential is derived.
Abstract: The linear density response of inhomogeneous electronic systems is discussed from a density-functional point of view. We derive a local density approximation for the frequency-dependent exchange-correlation potential which is compared with the ``adiabatic'' expression used in former work.
840 citations
TL;DR: The storage mechanism is capable of independently maintaining species coexistence, and some suggestions on how to distinguish qualitatively the operation of storage from alternative mechanisms are provided.
Abstract: For most species, a changeable environment creates a situation in which recruitment varies considerably from one breeding season to the next. If adults survive well, an occasional favorable recruitment can sustain population numbers over long periods. In effect, the gains made in favorable periods are stored in the adult population. Storage is particularly important when the species is at low densities, because then the potential population growth rate is very high if a favorable period occurs. Our past work showed that the storage mechanism could lead to coexistence of two species in lottery competition for space, as long as generations overlapped and there was sufficient variation in recruitment (Chesson and Warner 1981). This was true even if one species had an average competitive advantage. The storage model also operates when more than two species are competing, when resources renew independently of population sizes, and when not all the resource is used. It also operates in simple Lotka-Volterra sys...
726 citations
TL;DR: In this paper, the authors present a new approach called atheoretical macroeconometrics that is less dependent on prior theoretical restrictions of the sort that were central to the approach of the Cowles Commission.
701 citations
TL;DR: In this article, the authors considered the problem of normal faults whose normal lies in the σ1′σ3′ plane of a stress field with effective principal compressive stresses σ 1′ >σ 2′ > σ 3′ for the simplest frictional failure criterion, τ = μσn′ = μ(σn − P), where τ and σn are respectively the shear and normal stresses to the existing fault, P is fluid pressure and μ is the static friction.
687 citations
TL;DR: In this paper, a simple, fully quantum mechanical model for electron transfer using a one mode treatment which incorporates this coupling is studied, and the limits of the moderate and the high friction are analyzed in detail.
Abstract: In biological and chemical electron transfer, a nuclear reaction coordinate is coupled to other nuclear and/or ‘‘solvent’’ coordinates. This coupling, or friction, if strong enough, may substantially slow down motion along the reaction coordinate, and thus vitiate the assumption of electron transfer being nonadiabatic with respect to the nuclei. Here, a simple, fully quantum mechanical model for electron transfer using a one mode treatment which incorporates this coupling is studied. Path integral methods are used to study the dependence of the reaction rate on friction, and the limits of the moderate and the high friction are analyzed in detail. The first limit will prevail if the reaction coordinate is, e.g., an underdamped nuclear vibration, whereas the second limit will prevail if it corresponds to a slow or diffusive degree of freedom. In the high‐friction limit, the reaction rate is explicitly shown to vary between the nonadiabatic and adiabatic expressions as the tunneling matrix element and/or the friction are varied. Starting from a path integral expression for the time evolution of the reduced density matrix for the electron and reaction coordinate, a Fokker–Planck equation is obtained which reduces in the high‐friction limit to a Smoluchowski equation similar to one solved by Zusman.
672 citations
TL;DR: In this paper, the quadrature-phase amplitudes and two-mode squeezed states were introduced for analyzing two-photon devices, in which photons in the output modes are created or destroyed two at a time.
Abstract: This paper introduces a new formalism for analyzing two-photon devices (e.g., parametric amplifiers and phase-conjugate mirrors), in which photons in the output modes are created or destroyed two at a time. The key property of a two-photon device is that it excites pairs of output modes independently. Thus our new formalism deals with two modes at a time; a continuum multimode description can be built by integrating over independently excited pairs of modes. For a pair of modes at frequencies \ensuremath{\Omega}\ifmmode\pm\else\textpm\fi{}\ensuremath{\epsilon}, we define (i) quadrature-phase amplitudes, which are complex-amplitude operators for modulation at frequency \ensuremath{\epsilon} of waves ``cos[\ensuremath{\Omega}(t-x/c)]'' and ``sin[\ensuremath{\Omega}(t-x/c)]'' and (ii) two-mode squeezed states, which are the output states of an ideal two-photon device. The quadrature-phase amplitudes and the two-mode squeezed states serve as the building blocks for our formalism; their properties and their physical interpretation are extensively investigated.
TL;DR: This article reviewed the most recent and sometimes controversial estimates of deforestation in developing countries and analyzed the relationship between deforestation and its probable causes, and compared three recent estimates of the rate of deforestation between 1968 and 1978 using rank order correlation.
Abstract: Developing nations are faced with a two-edged sword in the field of energy. On the one hand the rising price of oil has reduced the potential for fossil fuel energy and eroded foreign exchange reserves in oil-importing countries. At the same time deforestation may be causing increased prices or shortages of fuels such as fuelwood and charcoal. This paper reviews the most recent and sometimes controversial estimates of deforestation in developing countries and analyzes the relationship between deforestation and its probable causes. Three recent estimates of the rate of deforestation in developing countries between 1968 and 1978 are compared using rank order correlation. Two of the estimates, of closed forest and moist tropical forest, are in significant agreement but differ from a third estimate that includes open woodland and regenerating forest. Agreement is strong among all three sources for a restricted group of countries. A cross-national analysis confirms the most frequently cited causes of ...
TL;DR: It is suggested that a stable pest equilibrium is neither a necessary nor a sufficient condition for control, and it is shown that satisfactory control in model systems is compatible with both local extinction of the pest and polyphagy in the natural enemy.
Abstract: The conventional wisdom of biological control of insect pests, and its related ecological theory, is that successful natural enemies in long-lived ecosystems (1) impose a low, stable pest equilibrium, and (2) share the following properties: (a) host-specific; (b) synchronous with the pest; (c) can increase in density rapidly when the pest does; (d) need only one pest individual to complete their life cycle; (e) have a high search rate for the pest; (f) aggregate at areas of high pest density, which is thought to stabilize the interaction. These features are more characteristic of parasitoids than predators. We suggest that a stable pest equilibrium is neither a necessary nor a sufficient condition for control. We show that satisfactory control in model systems is compatible with both local extinction of the pest and polyphagy in the natural enemy. Only one of nine real examples of successful control is convincingly a stable interaction; the remainder show either strong evidence for instability and local e...
TL;DR: The invariant vacuum state appropriate for inflationary models of the early universe is identified and shown to decay due to the Hawking effect, and a mechanism for dynamically relaxing ..lambda../sub eff/..-->..0 is thereby suggested.
Abstract: In this, the first of a series of papers on quantum field theory in de Sitter spacetime, the invariant vacuum state appropriate for inflationary models of the early universe is identified and shown to decay due to the Hawking effect. The created pairs have an energy-momentum which leads to a first-order decrease of the effective cosmological constant, independently of any matter phase transition. A mechanism for dynamically relaxing ..lambda../sub eff/..-->..0 is thereby suggested.
TL;DR: The present study provides a baseline measure of recognition under those circumstances, and it indicates that haptic object recognition can be both rapid and accurate.
Abstract: How good are we at recognizing objects by touch? Intuition may suggest that the haptic system is a poor recognition device, and previous research with nonsense shapes and tangible-graphics displays supports this opinion. We argue that the recognition capabilities of touch are best assessed with three-dimensional, familiar objects. The present study provides a baseline measure of recognition under those circumstances, and it indicates that haptic object recognition can be both rapid and accurate.
TL;DR: In this article, the stability of first-order dissipative relativistic fluid theories including the theories of Eckart and of Landau and Lifshitz as special cases is studied.
Abstract: We consider the stability of a general class of first-order dissipative relativistic fluid theories which includes the theories of Eckart and of Landau and Lifshitz as special cases. We show that all of these theories are unstable in the sense that small spatially bounded departures from equilibrium at one instant of time will diverge exponentially with time. The time scales for these instabilities are very short; for example, water at room temperature and pressure has an instability with a growth time scale of about ${10}^{\mathrm{\ensuremath{-}}34}$ seconds in these theories. These results provide overwhelming motivation (we believe) for abandoning these theories in favor of the second-order (Israel) theories which are free of these difficulties.
TL;DR: In this paper, it was shown that a localized fluid which is initially compressed and outgoing, on average, will develop singularities regardless of the size of the initial disturbance, regardless of its initial disturbance.
Abstract: Presented are several results on the formation of singularities in solutions to the three-dimensional Euler equations for a polytropic, ideal fluid under various assumptions on the initial data. In particular, it is shown that a localized fluid which is initially compressed and outgoing, on average, will develop singularities regardless of the size of the initial disturbance.
TL;DR: A generalization of the cell-space principle is presented, based on discrete model theory, and then applied to a hypothetical but fairly complex problem of individual decision and large-scale urban change.
Abstract: Cellular spaces have recently received a lot of attention in computer science and elsewhere as models capable of bridging the gap between disaggregate and aggregate description. Despite their obvious spatial interpretation, standard cell-space models are too constrained by their background conventions to be useful in realistic geographic applications. In this paper, a generalization of the cell-space principle is presented, based on discrete model theory, and then applied to a hypothetical but fairly complex problem of individual decision and large-scale urban change. The paper ends with a discussion of the wider import of this methodology, which has close links with, among other things, bifurcation theory, cognitive science modeling of individual decision and behavior, and other issues of actual or potential interest to geographers.
TL;DR: For instance, the authors of as mentioned in this paper show that the path of ice-center migration in the Gondwana supercontinent follows the published paleomagnetic wander paths, and that ice centers migrated from south polar regions to south-polar regions, where the pole lies in oceanic or coastal regions.
Abstract: Continental glaciation, as recorded by sedimentary facies and by pavements scoured into underlying rocks, affected northern Africa at the end of the Proterozoic Era. This glaciation was followed in the Cambrian Period by a long, warmer interval without recorded ice sheets upon the Gondwana supercontinent. Strong glaciation ensued in Late Ordovician time in central northern Africa, and centers moved into then adjoining northern Brazil and on westward into southern Brazil, southern Africa, and Bolivia and into northern Argentina by the Early Silurian. From Middle Silurian time, world-wide and Gondwanan climate ameliorated until Late Devonian (Famennian) time, when glaciation again affected Brazil and perhaps parts of Africa. Glacial centers apparently waned after the late Famennian (latest Devonian) but waxed again in Andean regions and northern Brazil in Early and mid-Early Carboniferous times to begin the strong Late Paleozoic Ice Age. Many ice caps and ice sheets came and went across the wide reaches of Gondwana during the late Paleozoic, beginning on the west, culminating in southern Africa in the Late Carboniferous, continuing strongly in India and Australia in the Permian, and dying out in eastern Australia and in Antarctica in early Late Permian time. The path of ice-center migration closely follows published paleomagnetic wander paths. The record suggests that, among other terrestrial factors which cause ice ages, glaciation flourished when Gondwana lay in south polar regions and that glaciation disappeared when Gondwana glided, so that the pole lay in oceanic or coastal regions.
TL;DR: The influence-functional method is used and it is shown that quantum-interference effects are severely diminished by the presence of damping even when its influence on the system is only light.
Abstract: This paper reports the result of a calculation which shows the effect of damping on the quantum interference of two Gaussian wave packets in a harmonic potential. The influence-functional method, which seems to be the most appropriate one for this kind of calculation, is used. It is shown that quantum-interference effects are severely diminished by the presence of damping even when its influence on the system is only light. The corrections to the undamped formulas are always expressible in terms of the phenomenological damping constant, the temperature (in the high-temperature limit), the cutoff frequency of the reservoir oscillators, and the mean number of quanta of energy intially present in the system. Both weakly and strongly damped systems are analyzed in the regime of low and high temperatures.
TL;DR: A review of the theory of inflationary universe models, giving particular emphasis to the question of origin and growth of energy-density fluctuations in these new cosmologies is given in this paper.
Abstract: This paper reviews the theory of inflationary universe models, giving particular emphasis to the question of origin and growth of energy-density fluctuations in these new cosmologies. The first four sections constitute a pedagogical introduction to some of the important quantum field theory methods used in inflationary universe scenarios: calculation of the effective potential, finite-temperature quantum field theory, analysis of the decay of a metastable quantum state, and free field theory in curved space-time.
TL;DR: If the Universe contains a nearly critical density of photinos which are also assumed to constitute the dark matter in the authors' galactic halo, then gravitational trapping by the Sun and ensuing annihilation in the solar core yields a significant flux of approx.250-MeV neutrinos which results in about 2 neutrino-induced events per kiloton-year in an underground proton-decay detector.
Abstract: If the Universe contains a nearly critical density of photinos which are also assumed to constitute the dark matter in our galactic halo, then gravitational trapping by the Sun and ensuing annihilation in the solar core yields a significant flux of \ensuremath{\sim}250-MeV neutrinos. This results in about 2 neutrino-induced events per kiloton-year in an underground proton-decay detector.
TL;DR: In this article, the authors introduce an econometric technique to analyze the factors affecting the land shares of alternative irrigation technologies in agriculture, and they estimate the likelihood of use of drip, sprinkler, and surface irrigation by fruit growers in the Central Valley of California.
Abstract: This paper introduces an econometric technique to analyze the factors affecting the land shares of alternative irrigation technologies in agriculture. It estimates the likelihood of use of drip, sprinkler, and surface irrigation by fruit growers in the Central Valley of California. Higher water costs, the use of groundwater, the production of nuts, and location are found to increase the likelihood of using drip and sprinkler irrigation. The results are used to demonstrate the effectiveness of water price increases in inducing water conservation.
TL;DR: The physical and electronic properties of poly(isothianaphthene) are reported in this paper, including initial characterization, electrochemical cyclic voltammetry, spectroscopy, and transport properties.
Abstract: The physical and electronic properties of poly(isothianaphthene) PITN, are reported, including initial characterization, electrochemical cyclic voltammetry, spectroscopy, and transport properties. PITN has the smallest energy gap of any known conjugated organic polymer, Eg≂1 eV. This novel conjugated polymer exhibits reversible chemical and electrochemical p‐type doping with an associated high contrast color change. After doping, thin films of PITN have very low optical density in the visible portion of the spectrum. Thus, PITN is the first example of a transparent highly conducting polymer (σ∼50 Ω−1 cm−1).
TL;DR: On montre que des caracteristiques tres generales de the theorie critique de la singularite d'arete de Yang-Lee a 2 dimensions determine completement la facon dont la theorie realise l'invariance conforme.
Abstract: It is shown that very general features of the critical theory of the Yang-Lee edge singularity in two dimensions completely determine the way in which the theory realizes conformal invariance. This leads to the value $\ensuremath{\sigma}=\ensuremath{-}\frac{1}{6}$ for the edge exponent, and makes possible the calculation of the correlation functions.
TL;DR: It is shown that a superposition of two states is reduced to a mixture at a rate proportional to the separation between the two states, which underlines the difficulty of observing asuperposition of macroscopic quantum states in practice.
Abstract: The effect of dissipation on a macroscopic superposition of quantum states is studied with use of a Markovian master-equation approach. It is shown that a superposition of two states is reduced to a mixture at a rate proportional to the separation between the two states. This underlines the difficulty of observing a superposition of macroscopic quantum states in practice.
TL;DR: Polar wander paths for the North and South China blocks suggest that both were parts of Gondwana in the Palaeozoic, and the North China block accreted to Siberia in the late Permian.
Abstract: Polar wander paths for the North and South China blocks suggest that (1) both were parts of Gondwana in the Palaeozoic, (2) the North China block accreted to Siberia in the late Permian and (3) the South China block accreted to the North China block in the middle Triassic to the early Jurassic. Comparison of the polar wander path for the South China block with that for northern Eurasia suggests that relative motion of over 4,000 km has occurred between them.
TL;DR: This article showed that rapid opening of linking extensional fracture systems to allow passage of earthquake ruptures through dilational fault jogs in fluid-saturated crusts is opposed by transient suctional forces induced near the rupture tips.
Abstract: Palaeoseismic studies over the past several years have indicated that segments of certain major faults tend to rupture at fairly regular intervals in characteristic earthquakes of about the same size1. This implies the presence of local structural controls which govern the nucleation and stopping of ruptures. Understanding rupture arrest is important, not only because it governs the size of characteristic earthquakes, but also because deceleration of ruptures results in the radiation of high-frequency energy leading to strong ground motion2. I show here that rapid opening of linking extensional fracture systems to allow passage of earthquake ruptures through dilational fault jogs in fluid-saturated crusts is opposed by transient suctional forces induced near the rupture tips3. Rupture arrest may then be followed by delayed slip transfer as fluid pressures re-equilibrate by diffusion.
TL;DR: Regular observations made over a period of 5 yr in four permanent transects provided data on plant, sea urchin, and fish densities which indicate that two unusually severe winter storms in 1980 and 1983 had different effects on a southern California kelp-forest community.
Abstract: Regular observations made over a period of 5 yr in four permanent transects provided data on plant, sea urchin, and fish densities which indicate that two unusually severe winter storms in 1980 (“Storm I”) and 1983 (“Storm II”) had different effects on a southern California kelp-forest community. Storm I removed all canopies of the giant kelp Macrocystis pyrifera, but spared most understory kelps, mainly Pterygophora californica. Hence, the previously large accumulation of detached drift kelp, mostly M. pyrifera, disappeared. Denied their preferred diet of drift kelp, the sea urchins Strongylocentrotus franciscanus and S. purpuratus then emerged from shelters to find alternative food. Without effective predators, they consumed most living plants, including the surviving understory kelps. This weakened the important detritus-based food chain, as indicated indirectly by declining abundances of algal turf and fish (Embiotocidae) that eat small animals living in turf. In 1983, Storm II reversed the process by eliminating exposed urchins, while clearing rock surfaces for widespread kelp settlement and growth. By summer 1984, the kelp grew to maturity to form extensive canopies despite elevated water temperatures during summer and fall of 1983. Thus, severe storms may have vastly different effects on community structure, depending on the state of the community before the disturbance.
TL;DR: In this article, the CP-conserving couplings of axions to photons, electrons, and nucleons were derived for an arbitrary axion model and the relevance of the results to proposed axion search experiments was briefly discussed.