1,870 research outputs found

    Random anisotropy disorder in superfluid 3He-A in aerogel

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    The anisotropic superfluid 3He-A in aerogel provides an interesting example of a system with continuous symmetry in the presence of random anisotropy disorder. Recent NMR experiments allow us to discuss two regimes of the orientational disorder, which have different NMR properties. One of them, the (s)-state, is identified as the pure Larkin-Imry-Ma state. The structure of another state, the (f)-state, is not very clear: probably it is the Larkin-Imry-Ma state contaminated by the network of the topological defects pinned by aerogel.Comment: JETP Lett. style, 6 pages, no figures, discussion extended, references added, version to be published in JETP Letter

    Unstable states of the superfluid confined between rotating spheres

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    The unstable states (including those related to self-accelerations of pulsars) in which the mutual friction causes an irreversible motion of vortices is considered

    Orbital glass and spin glass states of 3He-A in aerogel

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    Glass states of superfluid A-like phase of 3He in aerogel induced by random orientations of aerogel strands are investigated theoretically and experimentally. In anisotropic aerogel with stretching deformation two glass phases are observed. Both phases represent the anisotropic glass of the orbital ferromagnetic vector l -- the orbital glass (OG). The phases differ by the spin structure: the spin nematic vector d can be either in the ordered spin nematic (SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN) is formed under conventional cooling from normal 3He. The second phase (OG-SG) is metastable, being obtained by cooling through the superfluid transition temperature, when large enough resonant continuous radio-frequency excitation are applied. NMR signature of different phases allows us to measure the parameter of the global anisotropy of the orbital glass induced by deformation.Comment: 7 pages, 6 figures, Submitted to Pis'ma v ZhETF (JETP Letters

    Alignment and resolution studies of a MARS CT scanner

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    This paper describes a procedure of alignment of MARS CT scanner with cone beam geometry. The position of the xray source relative to the detector, the tilt of the detector are measured during alignment. The mechanical precision of gantry movement is determined. Significant improvement in the quality of image reconstruction has been achieved as a result of the calibration. Spatial resolution (PTF) of the scanner is confirmed to be about 30 μm

    Attachment of Rod-Like (BAR) Proteins and Membrane Shape

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    Previous studies have shown that cellular function depends on rod-like membrane proteins, among them Bin/Amphiphysin/Rvs (BAR) proteins may curve the membrane leading to physiologically important membrane invaginations and membrane protrusions. The membrane shaping induced by BAR proteins has a major role in various biological processes such as cell motility and cell growth. Different models of binding of BAR domains to the lipid bilayer are described. The binding includes hydrophobic insertion loops and electrostatic interactions between basic amino acids at the concave region of the BAR domain and negatively charged lipids. To shed light on the elusive binding dynamics, a novel experiment is proposed to expand the technique of single-molecule AFM for the traction of binding energy of a single BAR domain

    Impact of transition from permanent pasture to new swards on the nitrogen use efficiency, nitrogen and carbon budgets of beef and sheep production

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    There is currently much debate around the environmental implications of ruminant farming and a need for robust data on nitrogen (N) and carbon (C) fluxes from beef and sheep grazing systems. Here we use data collected from the North Wyke Farm Platform along with the SPACSYS model to examine the N and C budgets and the N use efficiency (NUE) of grassland swards at different stages of establishment. We assessed the transition from permanent pasture (PP) to a high-sugar grass (HSG), and a mixed sward of HSG with white clover (HSGC), identifying data specifically for the reseed (RS) years and the first year following RS (HSG-T and HSGC-T). Dominant fluxes for the N budget were N offtake as cut herbage and via livestock grazing, chemical-N fertiliser and N leaching at 88-280, 15–177, and 36–92 kg N ha−1 a−1, respectively. Net primary productivity, soil respiration and C offtake as cut herbage and via livestock grazing at 1.9 –15.9, 1.74–12.5, and 0.34–11.7 t C ha−1 a−1, respectively, were the major C fluxes. No significant differences were found between the productivity of any of the swards apart from in the RS year of establishment. However, NUE of the livestock production system was significantly greater for the HSGC and HSGC-T swards at 32 and 42% compared to all other swards, associated with the low chemical-N fertiliser inputs to these clover-containing swards. Our findings demonstrate opportunities for improving NUE in grazing systems, but also the importance of setting realistic NUE targets for these systems to provide achievable goals for land-managers