A Matrix Model for AdS2

A matrix quantum mechanics with potential $V={q^2 \over r^2}$ and an SL(2,R) conformal symmetry is conjectured to be dual to two-dimensional type 0A string theory on AdS$_2$ with $q$ units of RR flux.Comment: 12 page

Influence of nonlocal electrodynamics on the anisotropic vortex pinning in YNi2B2CYNi_2B_2C

We have studied the pinning force density Fp of YNi_2B_2C superconductors for various field orientations. We observe anisotropies both between the c-axis and the basal plane and within the plane, that cannot be explained by usual mass anisotropy. For magnetic field $H \parallel c$, the reorientation structural transition in the vortex lattice due to nonlocality, which occurs at a field $H_1 \sim 1kOe$, manifests itself as a kink in Fp(H). When $H \bot c$, Fp is much larger and has a quite different H dependence, indicating that other pinning mechanisms are present. In this case the signature of nonlocal effects is the presence of a fourfold periodicity of Fp within the basal plane.Comment: 4 pages, 3 figure

The JCMT Gould Belt survey: Dense core clusters in Orion B

The James Clerk Maxwell Telescope Gould Belt Legacy Survey obtained SCUBA-2 observations of dense cores within three sub-regions of OrionB: LDN1622, NGC2023/2024, and NGC2068/2071, all of which contain clusters of cores. We present an analysis of the clustering properties of these cores, including the two-point correlation function and Cartwright’s Q parameter. We identify individual clusters of dense cores across all three regions using a minimal spanning tree technique, and find that in each cluster, the most massive cores tend to be centrally located. We also apply the independent M–Σ technique and find a strong correlation between core mass and the local surface density of cores. These two lines of evidence jointly suggest that some amount of mass segregation in clusters has happened already at the dense core stage

Relativistic Ring-Diagram Nuclear Matter Calculations

A relativistic extension of the particle-particle hole-hole ring-diagram many-body formalism is developed by using the Dirac equation for single-particle motion in the medium. Applying this new formalism, calculations are performed for nuclear matter. The results show that the saturation density is improved and the equation of state becomes softer as compared to corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A potential, nuclear matter is predicted to saturate at an energy per nucleon of --15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm$^{-1}$, in excellent agreement with empirical information. The compression modulus is 152 MeV at the saturation point.Comment: 23 pages text (LaTex) and 2 figures (paper, will be faxed upon request), UI-NTH-92-0

Understanding the Observed Evolution of the Galaxy Luminosity Function from z=6-10 in the Context of Hierarchical Structure Formation

Recent observations of the Lyman-break galaxy (LBG) luminosity function (LF) from z~6-10 show a steep decline in abundance with increasing redshift. However, the LF is a convolution of the mass function of dark matter halos (HMF)--which also declines sharply over this redshift range--and the galaxy-formation physics that maps halo mass to galaxy luminosity. We consider the strong observed evolution in the LF from z~6-10 in this context and determine whether it can be explained solely by the behavior of the HMF. From z~6-8, we find a residual change in the physics of galaxy formation corresponding to a ~0.5 dex increase in the average luminosity of a halo of fixed mass. On the other hand, our analysis of recent LF measurements at z~10 shows that the paucity of detected galaxies is consistent with almost no change in the average luminosity at fixed halo mass from z~8. The LF slope also constrains the variation about this mean such that the luminosity of galaxies hosted by halos of the same mass are all within about an order-of-magnitude of each other. We show that these results are well-described by a simple model of galaxy formation in which cold-flow accretion is balanced by star formation and momentum-driven outflows. If galaxy formation proceeds in halos with masses down to 10^8 Msun, then such a model predicts that LBGs at z~10 should be able to maintain an ionized intergalactic medium as long as the ratio of the clumping factor to the ionizing escape fraction is C/f_esc < 10.Comment: 15 pages, 2 figures; results unchanged; accepted by JCA

The McKean-Vlasov Equation in Finite Volume

We study the McKean--Vlasov equation on the finite tori of length scale $L$ in $d$--dimensions. We derive the necessary and sufficient conditions for the existence of a phase transition, which are based on the criteria first uncovered in \cite{GP} and \cite{KM}. Therein and in subsequent works, one finds indications pointing to critical transitions at a particular model dependent value, $\theta^{\sharp}$ of the interaction parameter. We show that the uniform density (which may be interpreted as the liquid phase) is dynamically stable for $\theta < \theta^{\sharp}$ and prove, abstractly, that a {\it critical} transition must occur at $\theta = \theta^{\sharp}$. However for this system we show that under generic conditions -- $L$ large, $d \geq 2$ and isotropic interactions -- the phase transition is in fact discontinuous and occurs at some \theta\t < \theta^{\sharp}. Finally, for H--stable, bounded interactions with discontinuous transitions we show that, with suitable scaling, the \theta\t(L) tend to a definitive non--trivial limit as $L\to\infty$

The James Clerk Maxwell Telescope Spectral Legacy Survey

Original article can be found at: http://www.journals.uchicago.edu/loi/pasp Copyright University of Chicago Press / AAS. DOI: 10.1086/511161Stars form in the densest, coldest, most quiescent regions of molecular clouds. Molecules provide the only probes that can reveal the dynamics, physics, chemistry, and evolution of these regions, but our understanding of the molecular inventory of sources and how this is related to their physical state and evolution is rudimentary and incomplete. The Spectral Legacy Survey (SLS) is one of seven surveys recently approved by the James Clerk Maxwell Telescope (JCMT) Board of Directors. Beginning in 2007, the SLS will produce a spectral imaging survey of the content and distribution of all the molecules detected in the 345 GHz atmospheric window (between 332 and 373 GHz) toward a sample of five sources. Our intended targets are a low-mass core (NGC 1333 IRAS 4), three high-mass cores spanning a range of star-forming environments and evolutionary states (W49, AFGL 2591, and IRAS 20126), and a photodissociation region (the Orion Bar). The SLS will use the unique spectral imaging capabilities of HARP-B/ACSIS (Heterodyne Array Receiver Programme B/Auto- Correlation Spectrometer and Imaging System) to study the molecular inventory and the physical structure of these objects, which span different evolutionary stages and physical environments and to probe their evolution during the star formation process. As its name suggests, the SLS will provide a lasting data legacy from the JCMT that is intended to benefit the entire astronomical community. As such, the entire data set (including calibrated spectral data cubes, maps of molecular emission, line identifications, and calculations of the gas temperature and column density) will be publicly available.Peer reviewe

Anomalous Superconducting Properties and Field Induced Magnetism in CeCoIn5

In the heavy fermion superconductor CeCoIn5 (Tc=2.3K) the critical field is large, anisotropic and displays hysteresis. The magnitude of the critical-field anisotropy in the a-c plane can be as large as 70 kOe and depends on orientation. Critical field measurements in the (110) plane suggest 2D superconductivity, whereas conventional effective mass anisotropy is observed in the (100) plane. Two distinct field-induced magnetic phases are observed: Ha appears deep in the superconducting phase, while Hb intersects Hc2 at T=1.4 K and extends well above Tc. These observations suggest the possible realization of a direct transition from ferromagnetism to Fulde-Ferrel-Larkin-Ovchinnikov superconductivity in CeCoIn5.Comment: 4 pages, 3 figure

Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere

A method for the full three-dimensional (3-D) reconstruction of the trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations Observatory (STEREO) data is presented. Four CMEs that were simultaneously observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and Behind STEREO satellites were analysed. These observations were used to derive CME trajectories in 3-D out to ~15Rsun. The reconstructions using COR1/2 data support a radial propagation model. Assuming pseudo-radial propagation at large distances from the Sun (15-240Rsun), the CME positions were extrapolated into the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in the different fields-of-view. It was found that CMEs slower than the solar wind were accelerated, while CMEs faster than the solar wind were decelerated, with both tending to the solar wind velocity.Comment: 17 pages, 10 figures, 1 appendi

Simulations of the Static Friction Due to Adsorbed Molecules

The static friction between crystalline surfaces separated by a molecularly thin layer of adsorbed molecules is calculated using molecular dynamics simulations. These molecules naturally lead to a finite static friction that is consistent with macroscopic friction laws. Crystalline alignment, sliding direction, and the number of adsorbed molecules are not controlled in most experiments and are shown to have little effect on the friction. Temperature, molecular geometry and interaction potentials can have larger effects on friction. The observed trends in friction can be understood in terms of a simple hard sphere model.Comment: 13 pages, 13 figure