974 research outputs found

    Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau Levels

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    We observe density induced 90∘^{\circ} rotations of the anisotropy axes in transport measurements at half-filled high Landau levels in the two dimensional electron system, where stripe states are proposed (ν\nu=9/2, 11/2, etc). Using a field effect transistor, we find the transition density to be 2.9×10112.9\times10^{11}cm−2^{-2} at ν\nu=9/2. Hysteresis is observed in the vicinity of the transition. We construct a phase boundary in the filling factor-magnetic field plane in the regime 4.4<ν<4.64.4<\nu<4.6. An in-plane magnetic field applied along either anisotropy axis always stabilizes the low density orientation of the stripes.Comment: 1 revtex file, 3 eps figure

    Calcium phosphate nanoparticles as intrinsic inorganic antimicrobials: In search of the key particle property

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    One of the main goals of materials science in the 21st century is the development of materials with rationally designed properties as substitutes for traditional pharmacotherapies. At the same time, there is a lack of understanding of the exact material properties that induce therapeutic effects in biological systems, which limits their rational optimization for the related medical applications. This study sets the foundation for a general approach for elucidating nanoparticle properties as determinants of antibacterial activity, with a particular focus on calcium phosphate nanoparticles. To that end, nine physicochemical effects were studied and a number of them were refuted, thus putting an end to frequently erred hypotheses in the literature. Rather than having one key particle property responsible for eliciting the antibacterial effect, a complex synergy of factors is shown to be at work, including (a) nanoscopic size; (b) elevated intracellular free calcium levels due to nanoparticle solubility; (c) diffusivity and favorable electrostatic properties of the nanoparticle surface, primarily low net charge and high charge density; and (d) the dynamics of perpetual exchange of ultrafine clusters across the particle/solution interface. On the positive side, this multifaceted mechanism is less prone to induce bacterial resistance to the therapy and can be a gateway to the sphere of personalized medicine. On a more problematic side, it implies a less intense effect compared to single-target molecular therapies and a difficulty of elucidating the exact mechanisms of action, while also making the rational design of theirs for this type of medical application a challenge

    Orientation of the Stripe Formed by the Two-Dimensional Electrons in Higher Landau Levels

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    Effect of periodic potential on the stripe phase realized in the higher Landau levels is investigated by the Hartree-Fock approximation. The period of the potential is chosen to be two to six times of the fundamental period of the stripe phase. It is found that the stripe aligns perpendicularly to the external potential in contrast to a naive expectation and hydrodynamic theory. Charge modulation towards the Wigner crystallization along the stripe is essential for the present unexpected new result.Comment: 5 pages, RevTex, two figures included in the tex

    Anisotropic States of Two-Dimensional Electron Systems in High Landau Levels: Effect of an In-Plane Magnetic Field

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    We report the observation of an acute sensitivity of the anisotropic longitudinal resistivity of two-dimensional electron systems in half-filled high Landau levels to the magnitude and orientation of an in-plane magnetic field. In the third and higher Landau levels, at filling fractions nu=9/2, 11/2, etc., the in-plane field can lead to a striking interchange of the "hard" and "easy" transport directions. In the second Landau level the normally isotropic resistivity and the weak nu=5/2 quantized Hall state are destroyed by a large in-plane field and the transport becomes highly anisotropic.Comment: 5 pages, 4 figures, minor errors correcte

    Comments on "the interpretation of the EPR and Mossbauer spectra of two-iron, one-electron iron-sulfur proteins"

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    Evidence is presented indicating that the note mentioned in the title is incorrect in two important aspects. 1.) According to our results of ENDOR spectroscopy and computer simulations of Mossbauer spectra, the conclusions drawn are based on an erroneous interpretation of the Mossbauer spectra. 2.) According to quotations from the literature, previous interpretations of experimental data on iron-sulfur proteins are incorrectly represented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33508/1/0000005.pd

    The two-iron ferredoxins in spinach, parsley, pig adrenal cortex, Azotobacter vinelandii, and Clostridium pasteurianum: Studies by magnetic field Mossbauer spectroscopy

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    The two-iron ferredoxins from spinach, parsley, Azotobacter vinelandii, Clostridium pasteurianum and the pig adrenal cortex were investigated by Mossbauer spectroscopy at temperatures from 4 to 256[deg]K and in magnetic fields up to 46 kGauss. Computational programs were devised to allow comparison of the experimental data with computer-simulated spectra in order to facilitate identification of the experimental spectral detail with specific Mossbauer spectroscopic parameters (quadrupole splittings, isomer shifts and nuclear hyperfine and nuclear Zeeman interactions). The results of the analysis permit the following properties of the active center to be established directly as the result of these experiments: 1. 1. In the oxidized forms of the proteins, each iron is in the high spin (S = 5/2) ferric state, spin-coupled to produce a resultant molecular diamagnetism for the protein at temperatures below 100[deg]K.2. 2. In the reduced state of the protein, the active center contains a single ferric site, retaining many properties of the ferric iron in the oxidized protein, but spincoupled to a high spin (S = 2) ferrous site, producing a molecular paramagnetism due to a net electron spin of one half at low temperatures (S = 1/2).3. 3. In spinach and parsley ferredoxins, the ligand symmetry around the ferrous site in the reduced form of the proteins is tetrahedral with measurable axial and rhombic distortions.4. 4. The iron sites in both the oxidized and reduced forms of all the proteins studied are similar, with the possible exception that the ligand symmetry at the ferrous site in the reduced form of the two-iron ferredoxins from C. pasteurianum, A. vinelandii (Azotobacter I and II), and pig adrenal cortex has not been characterized as being square planar or tetrahedral, although octahedral symmetry has been excluded.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33534/1/0000033.pd

    Measurement of inclusive charged current interactions on carbon in a few-GeV neutrino beam

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    The SciBooNE Collaboration reports a measurement of inclusive charged current interactions of muon neutrinos on carbon with an average energy of 0.8 GeV using the Fermilab Booster Neutrino Beam. We compare our measurement with two neutrino interaction simulations: NEUT and NUANCE. The charged current interaction rates (product of flux and cross section) are extracted by fitting the muon kinematics, with a precision of 6-15% for the energy dependent and 3% for the energy integrated analyses. We also extract CC inclusive interaction cross sections from the observed rates, with a precision of 10-30% for the energy dependent and 8% for the energy integrated analyses. This is the first measurement of the CC inclusive cross section on carbon around 1 GeV. These results can be used to convert previous SciBooNE cross section ratio measurements to absolute cross section values.Comment: 21 pages, 16 figures. Accepted by Phys. Rev. D. Minor revisions to match the accepted versio
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