Radial deformation of the earth by oceanic tidal loading

A high-degree spherical harmonic series is used to compute the radial deformation of the Earth by oceanic tidal loading. By exploiting fast numerical transforms, this approach is found to be much more efficient, but no less accurate, than the traditional Green's function approach. The method is used to derive an atlas of load tide maps for 10 constitutents of the NSWC ocean tide model

A Bethe Ansatz Study of Free Energy and Excitation Spectrum for Even Spin Fateev Zamolodchikov Model

A Bethe Ansatz study of a self dual Z_N spin model is undertaken for even spin system. One has to solve a coupled system of Bethe Ansatz Equations (BAE) involving zeroes of two families of transfer matrices. A numerical study on finite size lattices is done for identification of elementary excitations over the Ferromagnetic and Antiferromagnetic ground states. The free energies for both Ferromagnetic and Antiferromagnetic ground states and dispersion relation for elementary excitations are found.Comment: 25 pages, 4 figure

Counter-rotating Accretion Disks

We consider accretion disks consisting of counter-rotating gaseous components with an intervening shear layer. Configurations of this type may arise from the accretion of newly supplied counter-rotating gas onto an existing co-rotating gas disk. For simplicity we consider the case where the gas well above the disk midplane is rotating with angular rate $+\Omega$ and that well below has the same properties but is rotating with rate $-\Omega$. Using the Shakura-Sunyaev alpha turbulence model, we find self-similar solutions where a thin (relative to the full disk thickness) equatorial layer accretes very rapidly, essentially at free-fall speed. As a result the accretion speed is much larger than it would be for an alpha disk rotating in one direction. Counter-rotating accretion disks may be a transient stage in the formation of counter-rotating galaxies and in the accretion of matter onto compact objects.Comment: 7 pages, 3 figures, aas2pp4.sty, submitted to Ap

The SONYC survey: Towards a complete census of brown dwarfs in star forming regions

SONYC, short for "Substellar Objects in Nearby Young Clusters", is a survey program to provide a census of the substellar population in nearby star forming regions. We have conducted deep optical and near-infrared photometry in five young regions (NGC1333, rho Ophiuchi, Chamaeleon-I, Upper Sco, and Lupus-3), combined with proper motions, and followed by extensive spectroscopic campaigns with Subaru and VLT, in which we have obtained more than 700 spectra of candidate low-mass objects. We have identified and characterized more than 60 new substellar objects, among them a handful of objects with masses close to, or below the Deuterium burning limit. Through SONYC and surveys by other groups, the substellar IMF is now well characterized down to ~ 5 - 10 MJup, and we find that the ratio of the number of stars with respect to brown dwarfs lies between 2 and 6. A comprehensive survey of NGC 1333 reveals that, down to ~5MJup, free-floating objects with planetary masses are 20-50 times less numerous than stars, i.e. their total contribution to the mass budget of the clusters can be neglected.Comment: to appear in the proceedings of the conference 'Brown dwarfs come of age', May 20-24 2013, Memorie della Societa Astronomica Italian

Metric tensor as the dynamical variable for variable cell-shape molecular dynamics

We propose a new variable cell-shape molecular dynamics algorithm where the dynamical variables associated with the cell are the six independent dot products between the vectors defining the cell instead of the nine cartesian components of those vectors. Our choice of the metric tensor as the dynamical variable automatically eliminates the cell orientation from the dynamics. Furthermore, choosing for the cell kinetic energy a simple scalar that is quadratic in the time derivatives of the metric tensor, makes the dynamics invariant with respect to the choice of the simulation cell edges. Choosing the densitary character of that scalar allows us to have a dynamics that obeys the virial theorem. We derive the equations of motion for the two conditions of constant external pressure and constant thermodynamic tension. We also show that using the metric as variable is convenient for structural optimization under those two conditions. We use simulations for Ar with Lennard-Jones parameters and for Si with forces and stresses calculated from first-principles of density functional theory to illustrate the applications of the method.Comment: 10 pages + 6 figures, Latex, to be published in Physical Review

Detection of Pulsed X-ray Emission from PSR B1706-44

We report the first detection of pulsed X-ray emission from the young, energetic radio and Gamma-ray pulsar PSR B1706-44. We find a periodic signal at a frequency of f = 9.7588088 +/- 0.0000026 Hz (at epoch 51585.34104 MJD), consistent with the radio ephemeris, using data obtained with the High Resolution Camera on-board the Chandra X-ray Observatory}. The probability that this detection is a chance occurrence is 3.5E-5 as judged by the Rayleigh test. The folded light curve has a broad, single-peaked profile with a pulsed fraction of 23% +/- 6%. This result is consistent the ROSAT PSPC upper limit of < 18% after allowing for the ability of Chandra to resolve the pulsar from a surrounding synchrotron nebula. We also fitted Chandra spectroscopic data on PSR B1706-44, which require at least two components, e.g., a blackbody of temperature T(infinity) between 1.51E6 K and 1.83E6 K and a power-law of Gamma = 2.0 +/- 0.5. The blackbody radius at the nominal 2.5 kpc distance is only R(infinity) = 3.6 +/- 0.9 km, indicating either a hot region on a cooler surface, or the need for a realistic atmosphere model that would allow a lower temperature and larger area. Because the power-law and blackbody spectra each contribute more than 23% of the observed flux, it is not possible to decide which component is responsible for the modulation in the spectrally unresolved light curve.Comment: 6 pages, 4 figures, Latex, emulateapj. Published version. Includes an updated radio ephemeris and presents the absolute radio/X-ray phase alignmen

The Block Spin Renormalization Group Approach and Two-Dimensional Quantum Gravity

A block spin renormalization group approach is proposed for the dynamical triangulation formulation of two-dimensional quantum gravity. The idea is to update link flips on the block lattice in response to link flips on the original lattice. Just as the connectivity of the original lattice is meant to be a lattice representation of the metric, the block links are determined in such a way that the connectivity of the block lattice represents a block metric. As an illustration, this approach is applied to the Ising model coupled to two-dimensional quantum gravity. The correct critical coupling is reproduced, but the critical exponent is obscured by unusually large finite size effects.Comment: 10 page