An Experimental Study On Load Carrying Capacity Of A Magnetic Bearing

The use of bearing is essential to all types of machines they provide the function of supporting heavier component in a desired position. These bearings have contact with the rotating part and causes surface wear which can be controlled by lubrication. The standards of performance for rotating equipment can be raised by providing robust, cost effective and easy to implement lsquoMagnetic bearingsrsquo. A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping and high axial instability. To enhance the radial load and radial stiffness and reduce the axial thrust, a theoretical and experimental study of various radial configurations, including hydrodynamic lubrication to improve dynamic performance of the magnetic bearing is made

The Roton Fermi Liquid

We introduce and analyze a novel metallic phase of two-dimensional (2d) electrons, the Roton Fermi Liquid (RFL), which, in contrast to the Landau Fermi liquid, supports both gapless fermionic and bosonic quasiparticle excitations. The RFL is accessed using a re-formulation of 2d electrons consisting of fermionic quasiparticles and $hc/2e$ vortices interacting with a mutual long-ranged statistical interaction. In the presence of a strong vortex-antivortex (i.e. roton) hopping term, the RFL phase emerges as an exotic yet eminently tractable new quantum ground state. The RFL phase exhibits a ``Bose surface'' of gapless roton excitations describing transverse current fluctuations, has off-diagonal quasi-long-ranged order (ODQLRO) at zero temperature (T=0), but is not superconducting, having zero superfluid density and no Meissner effect. The electrical resistance {\it vanishes} as $T \to 0$ with a power of temperature (and frequency), $R(T) \sim T^\gamma$ (with $\gamma >1$), independent of the impurity concentration. The RFL phase also has a full Fermi surface of quasiparticle excitations just as in a Landau Fermi liquid. Electrons can, however, scatter anomalously from rotonic "current fluctuations'' and "superconducting fluctuations'', leading to "hot" and "cold" spots. Fermionic quasiparticles dominate the Hall electrical transport. We also discuss instabilities of the RFL to a conventional Fermi liquid and a superconductor. Precisely {\it at} the instability into the Fermi liquid state, the exponent $\gamma =1$, so that $R(T) \sim T$. Upon entering the superconducting state the anomalous quasiparticle scattering is strongly suppressed. We discuss how the RFL phenomenology might apply to the cuprates.Comment: 43 page

The crystal structure of magnesium acetate-tetrahydrate Mg (CH<SUB>3</SUB>COO)<SUB>2</SUB>. 4 H<SUB>2</SUB>O

This article does not have an abstract

The crystal structure of p-azo-toluene (CH<SUB>3</SUB>-C<SUB>6</SUB>H<SUB>4</SUB>N)<SUB>2</SUB>

The crystal structure of p-azo-toluene has been determined by single crystal methods. The unit cell is monoclinic with a=12.01 &#197;, b=5.02 &#197;, c=9.32 &#197;, &#946;=90&#176;12'. The space-group is P21/a-C2h5 and there are two molecules per unit cell. Atomic positions were determined by electron density projections making use of 'trial and error' methods. Structure factors were obtained from visually estimated intensities on Weissenberg photographs taken with CuK&#945; radiation. The planar benzene rings are attached by zig-zag C-N=N-C bond with the bond distance -N=N-=1.27 &#197; and the angle N=N-C 134&#176;30'. The plane of the benzene ring makes an angle with the (ac) plane, its orientation is obtained by rotating it about the N-C bond by 10&#176;. The nearest distance between two molecules in the crystal is 3.92 &#197;

On the low energy properies of fermions with singular interactions

We calculate the fermion Green function and particle-hole susceptibilities for a degenerate two-dimensional fermion system with a singular gauge interaction. We show that this is a strong coupling problem, with no small parameter other than the fermion spin degeneracy, N. We consider two interactions, one arising in the context of the $t-J$ model and the other in the theory of half-filled Landau level. For the fermion self energy we show in contrast to previous claims that the qualitative behavior found in the leading order of perturbation theory is preserved to all orders in the interaction. The susceptibility $\chi_Q$ at a general wavevector $\bf{Q} \neq 2\bf{p_F}$ retains the fermi-liquid form. However the $2p_F$ susceptibility $\chi_{2p_F}$ either diverges as $T -> 0$ or remains finite but with nonanalytic wavevector, frequency and temperature dependence. We express our results in the language of recently discussed scaling theories, give the fixed-point action, and show that at this fixed point the fermion-gauge-field interaction is marginal in $d=2$, but irrelevant at low energies in $d \ge 2$.Comment: 21 pages, uuencoded LATEX file with included Postscript figures, R

Hall Effect in a Quasi-One-Dimensional System

We consider the Hall effect in a system of weakly coupled one-dimensional chains with Luttinger interaction within each chain. We construct a perturbation theory in the inter-chain hopping term and find that there is a power law dependence of the Hall conductivity on the magnetic field with an exponent depending on the interaction constant. We show that this perturbation theory becomes valid if the magnetic field is sufficiently large.Comment: 20 page

Fractional charge in transport through a 1D correlated insulator of finite length

Transport through a one channel wire of length $L$ confined between two leads is examined when the 1D electron system has an energy gap $2M$: $M > T_L \equiv v_c/L$ induced by the interaction in charge mode ($v_c$: charge velocity in the wire). In spinless case the transformation of the leads electrons into the charge density wave solitons of fractional charge $q$ entails a non-trivial low energy crossover from the Fermi liquid behavior below the crossover energy $T_x \propto \sqrt{T_L M} e^{-M /[T_L(1-q^2)]}$ to the insulator one with the fractional charge in current vs. voltage, conductance vs. temperature, and in shot noise. Similar behavior is predicted for the Mott insulator of filling factor $\nu = integer/(2 m')$.Comment: 5 twocolumn pages in RevTex, no figure

An Eddington ratio-driven origin for the LX- M∗relation in quiescent and star-forming active galaxies

A mild correlation exists in active galaxies between the mean black hole accretion, as traced by the mean X-ray luminosity and the host galaxy stellar mass M∗, characterised by a normalization steadily decreasing with cosmic time and lower in more quiescent galaxies. We create comprehensive semi-empirical mock catalogues of active black holes to pin down which parameters control the shape and evolution of the - M∗ relation of X-ray-detected active galaxies. We find that the normalization of the - M∗ relation is largely independent of the fraction of active galaxies (the duty cycle), but strongly dependent on the mean Eddington ratio, when adopting a constant underlying MBH - M∗ relation as suggested by observational studies. The data point to a decreasing mean Eddington ratio with cosmic time and with galaxy stellar mass at fixed redshift. Our data can be reproduced by black holes and galaxies evolving on similar MBH - M∗ relations but progressively decreasing their average Eddington ratios, mean X-ray luminosities, and specific star formation rates, when moving from the starburst to the quiescent phase. Models consistent with the observed - M∗ relation and independent measurements of the mean Eddington ratios are characterised by MBH - M∗ relations lower than those derived from dynamically measured local black holes. Our results point to the - M∗ relation as a powerful diagnostic to: (1) probe black hole-galaxy scaling relations and the level of accretion on to black holes; (2) efficiently break the degeneracies between duty cycles and accretion rates in cosmological models of black holes

The null energy condition and instability

We extend previous work showing that violation of the null energy condition implies instability in a broad class of models, including gauge theories with scalar and fermionic matter as well as any perfect fluid. Simple examples are given to illustrate these results. The role of causality in our results is discussed. Finally, we extend the fluid results to more general systems in thermal equilibrium. When applied to the dark energy, our results imply that w is unlikely to be less than -1.Comment: 11 pages, 5 figures, Revte

Beyond the random phase approximation in the Singwi-Sj\"olander theory of the half-filled Landau level

We study the $\nu=1/2$ Chern-Simons system and consider a self-consistent field theory of the Singwi-Sj\"olander type which goes beyond the random phase approximation (RPA). By considering the Heisenberg equation of motion for the longitudinal momentum operator, we are able to show that the zero-frequency density-density response function vanishes linearly in long wavelength limit independent of any approximation. From this analysis, we derive a consistency condition for a decoupling of the equal time density-density and density-momentum correlation functions. By using the Heisenberg equation of motion of the Wigner distribution function with a decoupling of the correlation functions which respects this consistency condition, we calculate the response functions of the $\nu=1/2$ system. In our scheme, we get a density-density response function which vanishes linearly in the Coulomb case for zero-frequency in the long wavelength limit. Furthermore, we derive the compressibility, and the Landau energy as well as the Coulomb energy. These energies are in better agreement to numerical and exact results, respectively, than the energies calculated in the RPA.Comment: 9 Revtex pages, 4 eps figures, typos correcte