271 research outputs found

    Phase Coexistence of a Stockmayer Fluid in an Applied Field

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    We examine two aspects of Stockmayer fluids which consists of point dipoles that additionally interact via an attractive Lennard-Jones potential. We perform Monte Carlo simulations to examine the effect of an applied field on the liquid-gas phase coexistence and show that a magnetic fluid phase does exist in the absence of an applied field. As part of the search for the magnetic fluid phase, we perform Gibbs ensemble simulations to determine phase coexistence curves at large dipole moments, μ\mu. The critical temperature is found to depend linearly on μ2\mu^2 for intermediate values of μ\mu beyond the initial nonlinear behavior near μ=0\mu=0 and less than the μ\mu where no liquid-gas phase coexistence has been found. For phase coexistence in an applied field, the critical temperatures as a function of the applied field for two different μ\mu are mapped onto a single curve. The critical densities hardly change as a function of applied field. We also verify that in an applied field the liquid droplets within the two phase coexistence region become elongated in the direction of the field.Comment: 23 pages, ReVTeX, 7 figure

    Pairing of Cooper Pairs in a Fully Frustrated Josephson Junction Chain

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    We study a one-dimensional Josephson junction chain embedded in a magnetic field. We show that when the magnetic flux per elementary loop equals half the superconducting flux quantum ϕ0=h/2e\phi_0=h/2e, a local \nbZ_2 symmetry arises. This symmetry is responsible for a nematic Luttinger liquid state associated to bound states of Cooper pairs. We analyze the phase diagram and we discuss some experimental possibilities to observe this exotic phase.Comment: 4 pages, 4 EPS figure

    Phase transitions in the one-dimensional frustrated quantum XY model and Josephson-junction ladders

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    A one-dimensional quantum version of the frustrated XY (planar rotor) model is considered which can be physically realized as a ladder of Josephson-junctions at half a flux quantum per plaquette. This system undergoes a superconductor to insulator transition at zero temperature as a function of charging energy. The critical behavior is studied using a Monte Carlo transfer matrix applied to the path-integral representation of the model and a finite-size-scaling analysis of data on small system sizes. Depending on the ratio between the interchain and intrachain couplings the system can have single or double transitions which is consistent with the prediction that its critical behavior should be described by the two-dimensional classical XY-Ising model.Comment: 13 pages, Revtex, J. Appl. Phys. (to appear), Inpe-las-00

    Selection of candidate container materials for the conceptual waste package design for a potential high level nuclear waste repository at Yucca Mountain

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    Preliminary selection criteria have been developed, peer-reviewed, and applied to a field of 41 candidate materials to choose three alloys for further consideration during the advanced conceptual design phase of waste package development for a potential high level nuclear waste repository at Yucca Mountain, Nevada. These three alloys are titanium grade 12, Alloy C-4, and Alloy 825. These selections are specific to the particular conceptual design outlined in the Site Characterization Plan. Other design concepts that may be considered in the advanced conceptual design phase may favor other materials choices

    Critical Exponents of the Fully Frustrated 2-D Xy Model

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    We present a detailed study of the critical properties of the 2-D XY model with maximal frustration in a square lattice. We use extensive Monte Carlo simulations to study the thermodynamics of the spin and chiral degrees of freedom, concentrating on their correlation functions. The gauge invariant spin-spin correlation functions are calculated close to the critical point for lattice sizes up to 240×240240\times 240; the chiral correlation functions are studied on lattices up to 96×9696\times 96. We find that the critical exponents of the spin phase transition are ν=0.3069\nu=0.3069, and η=0.1915\eta=0.1915, which are to be compared with the unfrustrated XY model exponents ν=1/2\nu=1/2 and η=0.25\eta=0.25. We also find that the critical exponents of the chiral transition are νχ=0.875\nu_{\chi}=0.875, 2β=0.19362\beta=0.1936, 2γ=1.822\gamma= 1.82, and 2γ=1.0252\gamma\>\prime=1.025, which are different from the expected 2-D Ising critical exponents. The spin-phase transition occurs at TU(1)=0.446T_{U(1)}=0.446 which is about 7\% above the estimated chiral critical temperature TZ2=0.4206T_{Z_{2}}= 0.4206. However, because of the size of the statistical errors, it is difficult to decide with certainty whether the transitions occur at the same or at slightly different temperatures. Finally, the jump in the helicity modulus in the fully frustrated system is found to be about 23\% below the unfrustrated universal value. The most important consequence of these results is that the fully frustrated XY model appears to be in a novel universality class. Recent successful comparisons of some of these results with experimental data are also briefly discussed. (TO APPEAR IN PRB)Comment: 47 pages (PHYZZX

    Vision and Foraging in Cormorants: More like Herons than Hawks?

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    Background Great cormorants (Phalacrocorax carbo L.) show the highest known foraging yield for a marine predator and they are often perceived to be in conflict with human economic interests. They are generally regarded as visually-guided, pursuit-dive foragers, so it would be expected that cormorants have excellent vision much like aerial predators, such as hawks which detect and pursue prey from a distance. Indeed cormorant eyes appear to show some specific adaptations to the amphibious life style. They are reported to have a highly pliable lens and powerful intraocular muscles which are thought to accommodate for the loss of corneal refractive power that accompanies immersion and ensures a well focussed image on the retina. However, nothing is known of the visual performance of these birds and how this might influence their prey capture technique. Methodology/Principal Findings We measured the aquatic visual acuity of great cormorants under a range of viewing conditions (illuminance, target contrast, viewing distance) and found it to be unexpectedly poor. Cormorant visual acuity under a range of viewing conditions is in fact comparable to unaided humans under water, and very inferior to that of aerial predators. We present a prey detectability model based upon the known acuity of cormorants at different illuminances, target contrasts and viewing distances. This shows that cormorants are able to detect individual prey only at close range (less than 1 m). Conclusions/Significance We conclude that cormorants are not the aquatic equivalent of hawks. Their efficient hunting involves the use of specialised foraging techniques which employ brief short-distance pursuit and/or rapid neck extension to capture prey that is visually detected or flushed only at short range. This technique appears to be driven proximately by the cormorant's limited visual capacities, and is analogous to the foraging techniques employed by herons

    Credentials, talent and cultural capital: a comparative study of educational elites in England and France

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    This article examines student accounts of credentials, talent and academic success, against a backdrop of the enduring liberal ideal of an education-based meritocracy. The article also examines Bourdieu’s account of academic qualifications as the dominant source of institutionalised cultural capital, and concludes that it does not adequately account for comparative differences in the social structure of competition and ideological shifts in class (re)production in different national contexts. This analysis is based on an empirical investigation of elite students at Oxford University and Sciences Po in Paris. We investigated how they understand the competition for a livelihood and whether they see themselves as more ‘talented’ than students from non-elite universities. This investigation revealed important similarities and differences between British and French students that have significant sociological implications for the (re)production and legitimation of educational and labour market inequalities

    Roughening Induced Deconstruction in (100) Facets of CsCl Type Crystals

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    The staggered 6-vertex model describes the competition between surface roughening and reconstruction in (100) facets of CsCl type crystals. Its phase diagram does not have the expected generic structure, due to the presence of a fully-packed loop-gas line. We prove that the reconstruction and roughening transitions cannot cross nor merge with this loop-gas line if these degrees of freedom interact weakly. However, our numerical finite size scaling analysis shows that the two critical lines merge along the loop-gas line, with strong coupling scaling properties. The central charge is much larger than 1.5 and roughening takes place at a surface roughness much larger than the conventional universal value. It seems that additional fluctuations become critical simultaneously.Comment: 31 pages, 9 figure

    Corporate environmental responsibility and criminology

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    This article addresses corporate environmental responsibility (CER) and aims to present a criminological analysis of it. We studied the opinion of a number of principle actors involved in CER in Europe in order to determine how they perceive it in terms of its definition, aetiology and approaches. For each of these dimensions we relate back to a criminological framework to ascertain how it is positioned in the green criminological debate. We start out by providing information on what corporate environmental responsibility is and how it relates to corporate social responsibility and sustainable development. Then we outline the theoretical framework in accordance with the three central themes for the criminological analysis of CER: definition, aetiology and approaches. We also explain the method that was used (semi-structured interviews). Next, we present the results according to the same threefold structure. Finally we discuss these results in a last part, which is divided in two. First, we look at the challenges that the criminological perspective poses for CER in terms of definition, aetiology and approaches. The second part of the discussion turns the question around and wonders how CER could contribute to greening criminology

    Null hypothesis significance testing: a short tutorial

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    Although thoroughly criticized, null hypothesis significance testing (NHST) remains the statistical method of choice used to provide evidence for an effect, in biological, biomedical and social sciences. In this short tutorial, I first summarize the concepts behind the method, distinguishing test of significance (Fisher) and test of acceptance (Newman-Pearson) and point to common interpretation errors regarding the p-value. I then present the related concepts of confidence intervals and again point to common interpretation errors. Finally, I discuss what should be reported in which context. The goal is to clarify concepts to avoid interpretation errors and propose reporting practices.</ns4:p
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