18,747 research outputs found

    Shear-stress controlled dynamics of nematic complex fluids

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    Based on a mesoscopic theory we investigate the non-equilibrium dynamics of a sheared nematic liquid, with the control parameter being the shear stress σxy\sigma_{\mathrm{xy}} (rather than the usual shear rate, γ˙\dot\gamma). To this end we supplement the equations of motion for the orientational order parameters by an equation for γ˙\dot\gamma, which then becomes time-dependent. Shearing the system from an isotropic state, the stress- controlled flow properties turn out to be essentially identical to those at fixed γ˙\dot\gamma. Pronounced differences when the equilibrium state is nematic. Here, shearing at controlled γ˙\dot\gamma yields several non-equilibrium transitions between different dynamic states, including chaotic regimes. The corresponding stress-controlled system has only one transition from a regular periodic into a stationary (shear-aligned) state. The position of this transition in the σxy\sigma_{\mathrm{xy}}-γ˙\dot\gamma plane turns out to be tunable by the delay time entering our control scheme for σxy\sigma_{\mathrm{xy}}. Moreover, a sudden change of the control method can {\it stabilize} the chaotic states appearing at fixed γ˙\dot\gamma.Comment: 10 pages, 11 figure

    Informational Warfare

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    Recent empirical and theoretical work suggests that reputation was an important mediator of access to resources in ancestral human environments. Reputations were built and maintained by the collection, analysis, and dissemination of information about the actions and capabilities of group members-that is, by gossiping. Strategic gossiping would have been an excellent strategy for manipulating reputations and thereby competing effectively for resources and for cooperative relationships with group members who could best provide such resources. Coalitions (cliques) may have increased members' abilities to manipulate reputations by gossiping. Because, over evolutionary time, women may have experienced more within-group competition than men, and because female reputations may have been more vulnerable than male reputations to gossip, gossiping may have been a more important strategy for women than men. Consequently, women may have evolved specializations for gossiping alone and in coalitions. We develop and partially test this theory

    Star-shaped Local Density of States around Vortices in a Type II Superconductor

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    The electronic structure of vortices in a type II superconductor is analyzed within the quasi-classical Eilenberger framework. The possible origin of a sixfold ``star'' shape of the local density of states, observed by scanning tunneling microscope experiments on NbSe2_2, is examined in the light of the three effects; the anisotropic pairing, the vortex lattice, and the anisotropic density of states at the Fermi surface. Outstanding features of split parallel rays of this star are well explained in terms of an anisotropic ss-wave pairing. This reveals a rich internal electronic structure associated with a vortex core.Comment: 4 pages, REVTeX, 3 figures available upon reques

    Method and apparatus for positioning a robotic end effector

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    A robotic end effector and operation protocol for a reliable grasp of a target object irrespective of the target's contours is disclosed. A robotic hand includes a plurality of jointed fingers, one of which, like a thumb, is in opposed relation to the other. Each finger is comprised of at least two jointed sections, and provided with reflective proximity sensors, one on the inner surface of each finger section. Each proximity sensor comprises a transmitter of a beam of radiant energy and means for receiving reflections of the transmitted energy when reflected by a target object and for generating electrical signals responsive thereto. On the fingers opposed to the thumb, the proximity sensors on the outermost finger sections are aligned in an outer sensor array and the sensors on the intermediate finger sections and sensors on the innermost finger sections are similarly arranged to form an intermediate sensor array and an inner sensor array, respectively. The invention includes a computer system with software and/or circuitry for a protocol comprising the steps in sequence of: (1) approach axis alignment to maximize the number of outer layer sensors which detect the target; (2) non-contact contour following the target by the robot fingers to minimize target escape potential; and (3) closing to rigidize the target including dynamically re-adjusting the end effector finger alignment to compensate for target motion. A signal conditioning circuit and gain adjustment means are included to maintain the dynamic range of low power reflection signals

    Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination

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    The magnon thermal conductivity κmag\kappa_{\mathrm{mag}} of the spin ladders in Sr14Cu24xZnxO41\rm Sr_{14}Cu_{24-x}Zn_xO_{41} has been investigated at low doping levels x=0x=0, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic defects which define an upper limit for lmagl_{\mathrm{mag}} and therefore allow a clear-cut relation between lmagl_{\mathrm{mag}} and κmag\kappa_{\mathrm{mag}} to be established independently of any model. Over a large temperature range we observe a progressive suppression of κmag\kappa_{\mathrm{mag}} with increasing Zn-content and find in particular that with respect to pure Sr14Cu24O41\rm Sr_{14}Cu_{24}O_{41} κmag\kappa_{\mathrm{mag}} is strongly suppressed even in the case of tiny impurity densities where lmag374l_{\mathrm{mag}}\lesssim 374~{\AA}. This shows unambiguously that large lmag3000l_{\mathrm{mag}}\approx 3000~{\AA} which have been reported for Sr14Cu24O41\rm Sr_{14}Cu_{24}O_{41} and La5Ca9Cu24O41\rm La_{5}Ca_9Cu_{24}O_{41} on basis of a kinetic model are in the correct order of magnitude

    Predictions of the pseudo-complex theory of Gravity for EHT observations- II. Theory and predictions

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    We present a resum\'e on the modified theory of gravity, called pseudo-complex General Relativity (pc-GR). It is the second in a series of papers, where the first one (Boller et al. 2019, referred to as paper I) discussed the observational consequences of pc-GR. In this paper, we concentrate on the underlying theory. PC-GR involves an algebraic extension of the standard theory of GR and it depends on two phenomenological parameters. An element included in pc-GR that is not present in standard GR is the energy-momentum tensor corresponding to an anisotropic ideal fluid, which we call dark energy. The two parameters are related to the coupling of mass to the dark energy and its fall-off as a function of r. The consequences and predictions of this theory will be discussed in the context of the observational results of the Even Horizon Telescope, expected soon. Our main result is that due to the accumulation of dark energy near a large mass, the modified theory predicts a dark ring followed by a bright ring in the emission profile of the accretion disc. We also discuss the light ring in the equatorial plane.Comment: 2 figure

    Hidden assumptions in the derivation of the Theorem of Bell

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    John Bell's inequalities have already been considered by Boole in 1862. Boole established a one-to-one correspondence between experimental outcomes and mathematical abstractions of his probability theory. His abstractions are two-valued functions that permit the logical operations AND, OR and NOT and are the elements of an algebra. Violation of the inequalities indicated to Boole an inconsistency of definition of the abstractions and/or the necessity to revise the algebra. It is demonstrated in this paper, that a violation of Bell's inequality by Einstein-Podolsky-Rosen type of experiments can be explained by Boole's ideas. Violations of Bell's inequality also call for a revision of the mathematical abstractions and corresponding algebra. It will be shown that this particular view of Bell's inequalities points toward an incompleteness of quantum mechanics, rather than to any superluminal propagation or influences at a distance
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