Bubbling Calabi-Yau geometry from matrix models

We study bubbling geometry in topological string theory. Specifically, we analyse Chern-Simons theory on both the 3-sphere and lens spaces in the presence of a Wilson loop insertion of an arbitrary representation. For each of these three manifolds we formulate a multi-matrix model whose partition function is the vev of the Wilson loop and compute the spectral curve. This spectral curve is the reduction to two dimensions of the mirror to a Calabi-Yau threefold which is the gravitational dual of the Wilson loop insertion. For lens spaces the dual geometries are new. We comment on a similar matrix model which appears in the context of Wilson loops in AdS/CFT.Comment: 30 pages; v.2 reference added, minor correction

Large transconductance oscillations in a single-well vertical Aharonov-Bohm interferometer

Aharonov-Bohm (AB) interference is reported for the first time in the conductance of a vertical nanostructure based on a single GaAs/AlGaAs quantum well (QW). The two lowest subbands of the well are spatially separated by the Hartree barrier originating from electronic repulsion in the modulation-doped QW and provide AB two-path geometry. Split-gates control the in-plane electronic momentum dispersion. In our system, we have clearly demonstrated AB interference in both electrostatic and magnetic modes. In the latter case the magnetic field was applied parallel to the QW plane, and perpendicular to the 0.02 um^2 AB loop. In the electrostatic mode of operation the single-QW scheme adopted led to large transconductance oscillations with relative amplitudes exceeding 30 %. The relevance of the present design strategy for the implementation of coherent nanoelectronic devices is underlined.Comment: Accepted for publication on Physical Review B Rapid Communication

Shock oscillation model for quasi-periodic oscillations in stellar mass and supermassive black holes

We numerically examine centrifugally supported shock waves in 2D rotating accretion flows around a stellar mass (10 M) and a supermassive (106 M) black holes over a wide range of input accretion rates of 107 M\u2d9 /M\u2d9 E 10 124. The resultant 2D shocks are unstable with time and the luminosities show quasi-periodic oscillations (QPOs) with modulations of a factor of 2\u20133 and with periods of a tenth of a second to several hours, depending on the black hole masses. The shock oscillation model may explain the intermediate frequency QPOs with 1\u2013 10 Hz observed in the stellar mass black hole candidates and also suggest the existence of QPOs with the period of hours in active galactic nuclei. When the accretion rate M\u2d9 is low, the luminosity increases in proportion to the accretion rate. However, when M\u2d9 greatly exceeds the Eddington critical rate M\u2d9 E, the luminosity is insensitive to the accretion rate and is kept constantly around 3c3LE. On the other hand, the mass-outflow rate M\u2d9 loss increases in proportion to M\u2d9 and it amounts to about a few per cent of the input mass-flow rat

Radiative Shocks in Rotating Accretion Flows around Black Holes

It is well known that the rotating inviscid accretion flows with adequate injection parameters around black holes could form shock waves close to the black holes, after the flow passes through the outer sonic point and can be virtually stopped by the centrifugal force. We examine numerically such shock waves in 1D and 2D accretion flows, taking account of cooling and heating of the gas and radiation transport. The numerical results show that the shock location shifts outward compared with that in the adiabatic solutions and that the more rarefied ambient density leads to the more outward shock location. In the 2D-flow, we find an intermediate frequency QPO behavior of the shock location as is observed in the black hole candidate GRS 1915+105.Comment: 11pages, 5 Postscript figures, to appear in PASJ, Vol.56, No.3, 200

Structural and magnetic characterization of the complete delafossite solid solution (CuAlO2){1-x}(CuCrO2){x}

We have prepared the complete delafossite solid solution series between diamagnetic CuAlO2 and the t2g^3 frustrated antiferromagnet CuCrO2. The evolution with composition x in CuAl(1-x)Cr(x)O2 of the crystal structure and magnetic properties has been studied and is reported here. The room-temperature unit cell parameters follow the Vegard law and increase with x as expected. The effective moment is equal to the Cr^3+ spin-only S = 3/2 value throughout the entire solid solution. Theta is negative, indicating that the dominant interactions are antiferromagnetic, and its magnitude increases with Cr substitution. For dilute Cr compositions, J_BB was estimated by mean-field theory to be 2.0 meV. Despite the sizable Theta, long-range antiferromagnetic order does not develop until very large x, and is preceeded by glassy behavior. Data presented here, and that on dilute Al-substitution from Okuda et al., suggest that the reduction in magnetic frustration due to the presence of non-magnetic Al does not have as dominant an effect on magnetism as chemical disorder and dilution of the magnetic exchange. For all samples, the 5 K isothermal magnetization does not saturate in fields up to 5 T and minimal hysteresis is observed. The presence of antiferromagnetic interactions is clearly evident in the sub-Brillouin behavior with a reduced magnetization per Cr atom. An inspection of the scaled Curie plot reveals that significant short-range antiferromagnetic interactions occur in CuCrO2 above its Neel temperature, consistent with its magnetic frustration. Uncompensated short-range interactions are present in the Al-substituted samples and are likely a result of chemical disorder

Polaronic Heat Capacity in The Anderson - Hasegawa Model

An exact treatment of the Anderson - Hasegawa two - site model, incorporating the presence of superexchange and polarons, is used to compute the heat capacity. The calculated results point to the dominance of the lattice contribution, especially in the ferromagnetic regime. This behavior is in qualitative agreement with experimental findings.Comment: 9 pages, Revtex, 4 postscript figure

Effect of FK506 in experimental organ transplantation.

FK506 is the most potent immunosuppressive agent known. Its toxicity is substantial in dogs, minor in rats, and unknown in subhuman primates. In small doses that are nontoxic even in dogs, it can be used in synergistic combination with cyclosporine, steroids, and presumably in other drugs

BIons in topological string theory

When many fundamental strings are stacked together, they puff up into D-branes. BIons and giant gravitons are the examples of such D-brane configurations that arise from coincident strings. We propose and demonstrate analogous transitions in topological string theory. Such transitions can also be understood in terms of the Fourier transform of D-brane amplitudes.Comment: 21 pages; v.2 references added; v.3 reference added; v.4 minor corrections; v.5 substantial rewritin

Ultrafast heating and resolution of recorded crystalline marks in phase-change media

Copyright © 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics 104 (2008) and may be found at http://link.aip.org/link/?JAPIAU/104/104912/1This work presents an analytical study of the thermally activated amorphous-to-crystalline phase-change process when the heating source has a delta function temporal profile. This simulates the case of ultrafast heating where crystallization in the amorphous phase-change medium occurs during cooling. The study produced closed-form expressions that predict the necessary peak temperature, and hence energy density, in the phase-change medium for successful crystallization during ultrafast annealing as functions of the kinetic and thermal parameters of the medium. Closed-form expressions were also derived that provide estimates of the final crystalline mark widths and tail lengths when phase change has ceased. The analysis indicated the need to reduce the activation energy of crystallization and the thermal diffusivity of the medium to reduce the initial peak temperature, produced by the heating source, to avoid melting, to increase the crystallization rate, to achieve sufficient levels of crystalline fractions during cooling, and to reduce the size of recorded crystalline marks. Perturbation analysis was carried out to study the effects of latent heat of crystallization during the fast kinetics phase. The result was reductions in the cooling rate of the phase-change material, thus requiring lower peak temperatures to achieve higher volumes of crystalline fraction. Nevertheless, the effects of heat release during crystallization were found to be modest for the class of current phase-change material used in data storage