5,953 research outputs found

    Theory of magnetic oscillations in Weyl semimetals

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    Weyl semimetals are a new class of Dirac material that posses bulk energy nodes in three dimensions. In this paper, we study a Weyl semimetal subject to an applied magnetic field. We derive expressions for the density of states, electronic specific heat, and the quantum oscillations of the magnetization, DC conductivity, and thermal conductivity. We find phase shifts in the quantum oscillations that distinguish the Weyl semimetal from conventional three dimensional Schr\"odinger Fermions.Comment: 11 pages, 5 figure

    Study of the integration of wind tunnel and computational methods for aerodynamic configurations

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    A study was conducted to determine the effectiveness of using a low-order panel code to estimate wind tunnel wall corrections. The corrections were found by two computations. The first computation included the test model and the surrounding wind tunnel walls, while in the second computation the wind tunnel walls were removed. The difference between the force and moment coefficients obtained by comparing these two cases allowed the determination of the wall corrections. The technique was verified by matching the test-section, wall-pressure signature from a wind tunnel test with the signature predicted by the panel code. To prove the viability of the technique, two cases were considered. The first was a two-dimensional high-lift wing with a flap that was tested in the 7- by 10-foot wind tunnel at NASA Ames Research Center. The second was a 1/32-scale model of the F/A-18 aircraft which was tested in the low-speed wind tunnel at San Diego State University. The panel code used was PMARC (Panel Method Ames Research Center). Results of this study indicate that the proposed wind tunnel wall correction method is comparable to other methods and that it also inherently includes the corrections due to model blockage and wing lift

    Impact of Electron-Phonon Coupling on Near-Field Optical Spectra

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    The finite momentum transfer (q\boldsymbol{q}) longitudinal optical response σL(q,ω)\sigma^L(\boldsymbol{q},\omega) of graphene has a peak at an energy ω=vFq\omega=\hbar v_F q. This corresponds directly to a quasiparticle peak in the spectral density at momentum relative to the Fermi momentum kFqk_F -q. Inclusion of coupling to a phonon mode at ωE\omega_E results, for ω<ωE\omega<|\omega_E|, in a constant electron-phonon renormalization of the bare bands by a mass enhancement factor (1+λ)(1+\lambda) and this is followed by a phonon kink at ωE\omega_E where additional broadening begins. Here we study the corresponding changes in the optical quasiparticle peaks which we find to continue to directly track the renormalized quasiparticle energies until qq is large enough that the optical transitions begin to sample the phonon kink region of the dispersion curves where linearity in momentum is lost in the renormalized Dirac Fermion dispersion curves and the correspondence to a single quasiparticle energy is lost. Nevertheless there remains in σL(q,ω)\sigma^L(\boldsymbol{q},\omega) features analogous to the phonon kinks of the dispersion curves which are observable through variation of qq and ω\omega.Comment: 6 pages, 5 figure

    Notes on the Medical History of Key West, 1822-1832

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    The years 1818 to 1823 were unquiet times in the northern Caribbean. The Latin nations of the area were either stabilizing their newly gained independence or preparing for further expressions of defiance against their Iberian overlords. In any event there was neither time nor the resources for organizing a military patrol of the waters extending from Venezuela to Tampa Bay, from Yucatan to Puerto Rico. Piracy was virtually unrestrained, and wrecking, considered by some observers to have been an only slightly more honorable enterprise, went unregulated. Shortly after John W. Simonton had acquired the island, then known as Cayo Hueso, and Lieutenant Matthew C. Perry had planted the American flag there in March 1822, Congress was importuned to establish Key West as a port of entry and to provide such military support as might be necessary to protect it from the forays of outlaws and pirates. In a memorial to Congress, Simonton set the tone for innumerable subsequent publicity releases by praising the quality of the harbor, the heathful climate, and the excellence of the fresh spring water abounding there. President James Monroe was persuaded to consider the feasibility of fortifying the island, and, on February 1, 1823, Commodore David Porter was assigned the command of the West Indian Squadron, with instructions to “suppress piracy and protect American citizens and commerce in the West Indies and the Gulf of Mexico, and to establish a naval base for supplying the vessels of the squadron.

    Suppression of Spontaneous Supercurrents in a Chiral p-Wave Superconductor

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    The superconducting state of SRO is widely believed to have chiral p-wave order that breaks time reversal symmetry. Such a state is expected to have a spontaneous magnetization, both at sample edges and at domain walls between regions of different chirality. Indeed, muon spin resonance experiments are interpreted as evidence of spontaneous magnetization due to domain walls or defects in the bulk. However, recent magnetic microscopy experiments place upper limits on the magentic fields at the sample edge and surface which are as much as two orders of magnitude smaller than the fields predicted theoretically for a somewhat idealized chiral p-wave superconductor. We investigate the effects on the spontaneous supercurrents and magnetization of rough and pair breaking surfaces for a range of parameters within a Ginzburg-Landau formalism. The effects of competing orders nucleated at the surface are also considered. We find the conditions under which the edge currents are significantly reduced while leaving the bulk domain wall currents intact, are quite limited. The implications for interpreting the existing body of experimental results on superconducting SRO within a chiral p-wave model are discussed.Comment: Changes to section 3, typos remove

    Reclaiming human machine nature

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    Extending and modifying his domain of life by artifact production is one of the main characteristics of humankind. From the first hominid, who used a wood stick or a stone for extending his upper limbs and augmenting his gesture strength, to current systems engineers who used technologies for augmenting human cognition, perception and action, extending human body capabilities remains a big issue. From more than fifty years cybernetics, computer and cognitive sciences have imposed only one reductionist model of human machine systems: cognitive systems. Inspired by philosophy, behaviorist psychology and the information treatment metaphor, the cognitive system paradigm requires a function view and a functional analysis in human systems design process. According that design approach, human have been reduced to his metaphysical and functional properties in a new dualism. Human body requirements have been left to physical ergonomics or "physiology". With multidisciplinary convergence, the issues of "human-machine" systems and "human artifacts" evolve. The loss of biological and social boundaries between human organisms and interactive and informational physical artifact questions the current engineering methods and ergonomic design of cognitive systems. New developpment of human machine systems for intensive care, human space activities or bio-engineering sytems requires grounding human systems design on a renewed epistemological framework for future human systems model and evidence based "bio-engineering". In that context, reclaiming human factors, augmented human and human machine nature is a necessityComment: Published in HCI International 2014, Heraklion : Greece (2014

    Do Gender Differences in Perceived Prototypical Computer Scientists and Engineers Contribute to Gender Gaps in Computer Science and Engineering?

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    Women are vastly underrepresented in the fields of computer science and engineering (CS&E). We examined whether women might view the intellectual characteristics of prototypical individuals in CS&E in more stereotype-consistent ways than men might and, consequently, show less interest in CS&E. We asked 269 U.S. college students (187, 69.5% women) to describe the prototypical computer scientist (Study 1) or engineer (Study 2) through open-ended descriptions as well as through a set of trait ratings. Participants also rated themselves on the same set of traits and rated their similarity to the prototype. Finally, participants in both studies were asked to describe their likelihood of pursuing future college courses and careers in computer science (Study 1) or engineering (Study 2). Across both studies, we found that women offered more stereotype-consistent ratings than did men of the intellectual characteristics of prototypes in CS (Study 1) and engineering (Study 2). Women also perceived themselves as less similar to the prototype than men did. Further, the observed gender differences in prototype perceptions mediated the tendency for women to report lower interest in CS&E fields relative to men. Our work highlights the importance of prototype perceptions for understanding the gender gap in CS&E and suggests avenues for interventions that may increase women’s representation in these vital fields

    Letter from the Editors

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