Classical Nucleation Theory of the One-Component Plasma

We investigate the crystallization rate of a one-component plasma (OCP) in the context of classical nucleation theory. From our derivation of the free energy of an arbitrary distribution of solid clusters embedded in a liquid phase, we derive the steady-state nucleation rate of an OCP as a function of the Coulomb coupling parameter. Our result for the rate is in accord with recent molecular dynamics simulations, but it is greater than that of previous analytical estimates by many orders of magnitude. Further molecular dynamics simulations of the nucleation rate of a supercooled liquid OCP for several values of the coupling parameter would clarify the physics of this process.Comment: 6 pages, 1 figure, accepted by PR

The Visibility of Galactic Bars and Spiral Structure At High Redshifts

We investigate the visibility of galactic bars and spiral structure in the distant Universe by artificially redshifting 101 B-band CCD images of local spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our artificially redshifted images correspond to Hubble Space Telescope I-band observations of the local galaxy sample seen at z=0.7, with integration times matching those of both the very deep Northern Hubble Deep Field data, and the much shallower Flanking Field observations. The expected visibility of galactic bars is probed in two ways: (1) using traditional visual classification, and (2) by charting the changing shape of the galaxy distribution in "Hubble space", a quantitative two-parameter description of galactic structure that maps closely on to Hubble's original tuning fork. Both analyses suggest that over 2/3 of strongly barred luminous local spirals i.e. objects classified as SB in the Third Reference Catalog) would still be classified as strongly barred at z=0.7 in the Hubble Deep Field data. Under the same conditions, most weakly barred spirals (classified SAB in the Third Reference Catalog) would be classified as regular spirals. The corresponding visibility of spiral structure is assessed visually, by comparing luminosity classifications for the artificially redshifted sample with the corresponding luminosity classifications from the Revised Shapley Ames Catalog. We find that for exposures times similar to that of the Hubble Deep Field spiral structure should be detectable in most luminous low-inclination spiral galaxies at z=0.7 in which it is present. [ABRIDGED]Comment: Accepted for publication in The Astronomical Journa

The Pierre Auger Observatory: Results on Ultra-High Energy Cosmic Rays

The focus of this article is on recent results on ultra-high energy cosmic rays obtained with the Pierre Auger Observatory. The world's largest instrument of this type and its performance are described. The observations presented here include the energy spectrum, the primary particle composition, limits on the fluxes of photons and neutrinos and a discussion of the anisotropic distribution of the arrival directions of the most energetic particles. Finally, plans for the construction of a Northern Auger Observatory in Colorado, USA, are discussed.Comment: Proceedings of the International Workshop on Advances in Cosmic Ray Science, Waseda University, Shinjuku, Tokyo, Japan, March 2008; to be published in the Journal of the Physical Society of Japan (JPSJ) supplemen

Critical Exponents of the Metal-Insulator Transition in the Two-Dimensional Hubbard Model

We study the filling-controlled metal-insulator transition in the two-dimensional Hubbard model near half-filling with the use of zero temperature quantum Monte Carlo methods. In the metallic phase, the compressibility behaves as $\kappa \propto |\mu - \mu_c|^{-0.58\pm0.08}$ where $\mu_c$ is the critical chemical potential. In the insulating phase, the localization length follows $\xi_l \propto |\mu - \mu_c|^{-\nu_l}$ with $\nu_l = 0.26 \pm 0.05$. Under the assumption of hyperscaling, the compressibility data leads to a correlation length exponent $\nu_\kappa = 0.21 \pm 0.04$. Our results show that the exponents $\nu_\kappa$ and $\nu_l$ agree within statistical uncertainty. This confirms the assumption of hyperscaling with correlation length exponent $\nu = 1/4$ and dynamical exponent $z = 4$. In contrast the metal-insulator transition in the generic band insulators in all dimensions as well as in the one-dimensional Hubbard model satisfy the hyperscaling assumption with exponents $\nu = 1/2$ and $z = 2$.Comment: Two references added. The DVI file and PS figure files are also available at http://www.issp.u-tokyo.ac.jp/labs/riron/imada/furukawa/; to appear in J. Phys. Soc. Jpn 65 (1996) No.

Collective Effects in Linear Spectroscopy of Dipole-Coupled Molecular Arrays

We present a consistent analysis of linear spectroscopy for arrays of nearest neighbor dipole-coupled two-level molecules that reveals distinct signatures of weak and strong coupling regimes separated for infinite size arrays by a quantum critical point. In the weak coupling regime, the ground state of the molecular array is disordered, but in the strong coupling regime it has (anti)ferroelectric ordering. We show that multiple molecular excitations (odd/even in weak/strong coupling regime) can be accessed directly from the ground state. We analyze the scaling of absorption and emission with system size and find that the oscillator strengths show enhanced superradiant behavior in both ordered and disordered phases. As the coupling increases, the single excitation oscillator strength rapidly exceeds the well known Heitler-London value. In the strong coupling regime we show the existence of a unique spectral transition with excitation energy that can be tuned by varying the system size and that asymptotically approaches zero for large systems. The oscillator strength for this transition scales quadratically with system size, showing an anomalous one-photon superradiance. For systems of infinite size, we find a novel, singular spectroscopic signature of the quantum phase transition between disordered and ordered ground states. We outline how arrays of ultra cold dipolar molecules trapped in an optical lattice can be used to access the strong coupling regime and observe the anomalous superradiant effects associated with this regime.Comment: 12 pages, 7 figures main tex

Dust penetrated morphology in the high redshift Universe

Images from the Hubble Deep Field (HDF) North and South show a large percentage of dusty, high redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is not yet fully understood. Since the HDF preferentially samples restframe UV light, HDF morphologies are not dust or `mask' penetrated. The appearance of high redshift galaxies at near-infrared restframes remains a challenge for the New Millennium. The Next Generation Space Telescope (NGST) could routinely provide us with such images. In this contribution, we quantitatively determine the dust-penetrated structures of high redshift galaxies such as NGC 922 in their near-infrared restframes. We show that such optically peculiar objects may readily be classified using the dust penetrated z ~ 0 templates of Block and Puerari (1999) and Buta and Block (2001).Comment: 4 pages, 2 figures. Presented at the conference "The Link between Stars and Cosmology", 26-30 March, 2001, Puerto Vallarta, Mexico. To be published by Kluwer, eds. M. Chavez, A. Bressan, A. Buzzoni, and D. Mayya. High-resolution version of Figure 2 can be found at http://www.inaoep.mx/~puerari/conf_puertovallart

Scaling of Selfavoiding Tethered Membranes: 2-Loop Renormalization Group Results

The scaling properties of selfavoiding polymerized membranes are studied using renormalization group methods. The scaling exponent \nu is calculated for the first time at two loop order. \nu is found to agree with the Gaussian variational estimate for large space dimension d and to be close to the Flory estimate for d=3.Comment: 4 pages, RevTeX + 20 .eps file

A bias in optical observations of high redshift luminous infrared galaxies

We present evidence for the dramatically different morphology between the rest frame UV and 7micron mid-IR emission of VV114 and Arp299, two nearby (z~0) violently interacting infrared luminous galaxies (LIRGs). Nearly all LIRGs are interacting systems and it is currently accepted that they dominate the IR emission at z>1. Luminous IR galaxies located at z=1-2 could easily be detected as unresolved sources in deep optical/near-IR ground based surveys, as well as in upcoming 24micron surveys with the Space Infrared Telescope Facility. We demonstrate that the spatial resolution of these surveys will result in blending of the emission from unresolved interacting components. An increased scatter will thus be introduced in the observed optical to mid-IR colors of these galaxies, leading to a systematic underestimation of their dust content.Comment: To appear in the Astrophysical Journal Letters (4 pages 1 figure

Explorations in Hubble Space: A Quantitative Tuning Fork

In order to establish an objective framework for studying galaxy morphology, we have developed a quantitative two-parameter description of galactic structure that maps closely on to Hubble's original tuning fork. Any galaxy can be placed in this "Hubble space", where the x-coordinate measures position along the early-to-late sequence, while the y-coordinate measures in a quantitative way the degree to which the galaxy is barred. The parameters defining Hubble space are sufficiently robust to allow the formation of Hubble's tuning fork to be mapped out to high redshifts. In the present paper, we describe a preliminary investigation of the distribution of local galaxies in Hubble space, based on the CCD imaging atlas of Frei et al. (1996). We find that barred, weakly-barred, and unbarred galaxies are remarkably well-separated on this diagnostic diagram. The spiral sequence is clearly bimodal and indeed approximates a tuning fork: strongly-barred and unbarred spirals do not simply constitute the extrema of a smooth unimodal distribution of bar strength, but rather populate two parallel sequences. Strongly barred galaxies lie on a remarkably tight sequence, strongly suggesting the presence of an underlying unifying physical process. Rather surprisingly, weakly barred systems do not seem to correspond to objects bridging the parameter space between unbarred and strongly barred galaxies, but instead form an extension of the regular spiral sequence. This relation lends support to models in which the bulges of late-type spirals originate from secular processes driven by bars.Comment: Accepted for publication in The Astronomical Journal. Figure 2 is too large to be embedded in the paper, and has been included as a JPEG imag

Transport of heat and mass in a two-phase mixture. From a continuous to a discontinuous description

We present a theory which describes the transport properties of the interfacial region with respect to heat and mass transfer. Postulating the local Gibbs relation for a continuous description inside the interfacial region, we derive the description of the Gibbs surface in terms of excess densities and fluxes along the surface. We introduce overall interfacial resistances and conductances as the coefficients in the force-flux relations for the Gibbs surface. We derive relations between the local resistivities for the continuous description inside the interfacial region and the overall resistances of the surface for transport between the two phases for a mixture. It is shown that interfacial resistances depend among other things on the enthalpy profile across the interface. Since this variation is substantial the coupling between heat and mass flow across the surface are also substantial. In particular, the surface puts up much more resistance to the heat and mass transfer then the homogeneous phases over a distance comparable to the thickness of the surface. This is the case not only for the pure heat conduction and diffusion but also for the cross effects like thermal diffusion. For the excess fluxes along the surface and the corresponding thermodynamic forces we derive expressions for excess conductances as integrals over the local conductivities along the surface. We also show that the curvature of the surface affects only the overall resistances for transport across the surface and not the excess conductivities along the surface.Comment: 25 pages, 2 figure