25,434 research outputs found
The statistical origins of quantum mechanics
It is shown that Schroedinger's equation may be derived from three
postulates. The first is a kind of statistical metamorphosis of classical
mechanics, a set of two relations which are obtained from the canonical
equations of particle mechanics by replacing all observables by statistical
averages. The second is a local conservation law of probability with a
probability current which takes the form of a gradient. The third is a
principle of maximal disorder as realized by the requirement of minimal Fisher
information. The rule for calculating expectation values is obtained from a
fourth postulate, the requirement of energy conservation in the mean. The fact
that all these basic relations of quantum theory may be derived from premises
which are statistical in character is interpreted as a strong argument in favor
of the statistical interpretation of quantum mechanics. The structures of
quantum theory and classical statistical theories are compared and some
fundamental differences are identified.Comment: slightly modified version, 24 pages, no figure
A Search for CO in the Local Group Dwarf Irregular Galaxy WLM
We present 12CO J = 1-0 and J = 2-1 observations of the low metallicity (12 +
log(O/H) = 7.74) Local Group dwarf irregular galaxy WLM made with the 15 m SEST
and 14 m FCRAO telescopes. Despite the presence a number of HII regions, we
find no CO emission. We obtain low upper limits on the integrated intensity
(I(CO) >= 0.18 K km/s for CO (1-0)). The non-detection is consistent with the
result of Taylor, Kobulnicky and Skillman (1998), that dwarf galaxies below a
metallicity of ~ 7.9 are not detected in CO emission. WLM shows that this trend
continues for low metallicity galaxies even as their metallicities approach
7.9. These results are consistent with the models of the metal poor ISM by
Norman and Spaans (1997). By comparing our CO data with observations of star
formation in WLM, we find evidence for a high CO to H conversion factor.Comment: 11 pages, 3 figures, accepted by A&
The radio-far infrared correlation: Spiral and blue compact dwarf galaxies opposed
The recently established correlation between radio continuum and far infrared emission in galaxies was further investigated by comparing normal spiral and blue compact dwarf galaxies. The puzzling result is that the ratio of radio to far infrared luminosity and its dispersion is the same for both samples, although their ratios of blue to far infrared luminosity, their radio spectral indices and their dust temperatures exhibit markedly different mean values and dispersions. This suggests that the amount of energy radiated in the two regimes is enhanced in the same way although the mechanisms responsible for the two components are rather different and complex. The fact that the blue light does not increase at the same proportion shows that both the radio and the far infrared emission are connected with the recent star formation history
Interplay of Fulde-Ferrell-Larkin-Ovchinnikov and Vortex states in two-dimensional Superconductors
Clean superconductors with weakly coupled conducting planes have been
suggested as promising candidates for observing the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We consider here a layered
superconductor in a magnetic field of arbitrary orientation with respect to the
conducting plane. In this case there is competition of spin-pair-breaking and
orbital-pair-breaking effects. In previous work, phase boundaries characterized
by Landau quantum numbers n > 0 have been predicted. Here, we calculate the
actual structure of the stable states below Hc2 by minimizing the free energy.
We find several new order parameter structures differing from both the
traditional Abrikosov and FFLO solutions. Some interesting unsolved questions
appear in the limit of large n.Comment: 13 pages, 3 figure
Antivortices due to competing orbital and paramagnetic pair-breaking effects
Thermodynamically stable vortex-antivortex structures in a
quasi-two-dimensional superconductor in a tilted magnetic field are predicted.
For this geometry, both orbital and spin pair-breaking effects exist, with
their relative strength depending on the tilt angle \Theta. The spectrum of
possible states contains as limits the ordinary vortex state (for large \Theta)
and the Fulde-Ferrell-Larkin-Ovchinnikov state (for \Theta=0). The
quasiclassical equations are solved near H_{c2} for arbitrary \Theta and it is
shown that stable states with coexisting vortices and antivortices exist in a
small interval close to \Theta=0. The results are compared with recent
predictions of antivortices in mesoscopic samples.Comment: 11 pages, 3 figure
Large-Scale Radio Structure in the Universe: Giant Radio Galaxies
Giant radio galaxies (GRGs), with linear sizes larger than 1 Mpc (H0=50
km/s/Mpc), represent the biggest single objects in the Universe. GRGs are rare
among the entire population of radio galaxies (RGs) and their physical
evolution is not well understood though for many years they have been of
special interest for several reasons. The lobes of radio sources can compress
cold gas clumps and trigger star or even dwarf galaxy formation, they can also
transport gas from a host galaxy to large distances and seed the IGM with
magnetic fields. Since GRGs have about 10 to 100 times larger sizes than normal
RGs, their influence on the ambient medium is correspondingly wider and is
pronounced on scales comparable to those of clusters of galaxies or larger.
Therefore `giants' could play an important role in the process of large-scale
structure formation in the Universe. Recently, thanks to the new all sky radio
surveys, significant progress in searching for new GRGs has been made.Comment: To appear in Multiwavelength AGN Surveys, ed. R. Maiolino and R.
Mujica, Singapore: World Scientific, 2004, 2 page
Improved Templates for Photometric Redshifts of Submm Sources
There is growing evidence that some star-forming galaxies at z>1 are
characterized by high efficiencies and specific star formation rates. In the
local universe, these traits are shared by ``active'' Blue Compact Dwarf
galaxies (BCDs) with compact and dense star-forming regions. The Spectral
Energy Distributions (SEDs) of these BCDs are dominated by young massive star
clusters, embedded in a cocoon of dust. In this Letter, we incorporate these
BCD SEDs as templates for two samples of high-redshift galaxy populations
selected at submm wavelengths. Because of the severe absorption of the optical
light, the featureless mid-infrared spectrum, and the relatively flat radio
continuum, the dusty star-cluster SEDs are good approximations to most of the
submm sources in our samples. In most cases, the active BCD SEDs fit the
observed photometric points better than the ``standard'' templates, M 82 and
Arp 220, and predict photometric redshifts significantly closer to the
spectroscopic ones. Our results strongly suggest that the embedded dusty star
clusters in BCD galaxies are superior to other local templates such as M 82 and
Arp 220 in fitting distant submm starburst galaxies.Comment: Accepted by ApJL: 4 pages, 2 figures, 2 table
- …