Evolution of Spatially Inhomogeneous Eco-Systems: An Unified Model Based Approach

Recently we have extended our the "unified" model of evolutionary ecology to incorporate the {\it spatial inhomogeneities} of the eco-system and the {\it migration} of individual organisms from one patch to another within the same eco-system. In this paper an extension of our recent model is investigated so as to describe the {\it migration} and {\it speciation} in a more realistic way.Comment: Latex, 10 pages, 8 figure

Cool Companions to White Dwarf Stars from the Two Micron All Sky Survey All Sky Data Release

We present the culmination of our near-infrared survey of the optically spectroscopically identified white dwarf stars from the McCook and Sion catalog, conducted using photometric data from the Two Micron All Sky Survey final All Sky Data Release. The color selection technique, which identifies candidate binaries containing a white dwarf and a low-mass stellar (or substellar) companion via their distinctive locus in the near-infrared color-color diagram, is demonstrated to be simple to apply and to yield candidates with a high rate of subsequent confirmation. We recover 105 confirmed binaries, and identify 27 firm candidates (19 of which are new to this work) and 21 tentative candidates (17 of which are new to this work) from the 2MASS data. Only a small number of candidates from our survey have likely companion spectral types later than M5, none of which is an obvious L-type (i.e., potential brown dwarf) companion. Only one previously known white dwarf + brown dwarf binary is detected. This result is discussed in the context of the 2MASS detection limits, as well as other recent observational surveys that suggest a very low rate of formation (or survival) for binary stars with extreme mass ratios

fMRI Response During Visual Motion Stimulation in Patients with Late Whiplash Syndrome

After whiplash trauma, up to one fourth of patients develop chronic symptoms including head and neck pain and cognitive disturbances. Resting perfusion single-pho ton-emission computed tomography (SPECT) found decreased temporoparietooccipi tal tracer uptake among these long-term symptomatic patients with late whiplash syn drome. As MT/MST (V5/V5a) are located in that area, this study addressed the question whether these patients show impairments in visual motion perception. We examined five symptomatic patients with late whiplash syndrome, five asymptomatic patients after whiplash trauma, and a control group of seven volunteers without the history of trauma. Tests for visual motion perception and functional magnetic resonance imaging (fMRI) measurements during visual motion stimulation were performed. Symptomatic patients showed a significant reduction in their ability to perceive coherent visual motion com pared with controls, whereas the asymptomatic patients did not show this effect. fMRI activation was similar during random dot motion in all three groups, but was signifi cantly decreased during coherent dot motion in the symptomatic patients compared with the other two groups. Reduced psychophysical motion performance and reduced fMRI responses in symptomatic patients with late whiplash syndrome both point to a functional impairment in cortical areas sensitive to coherent motion. Larger studies are needed to confirm these clinical and functional imaging results to provide a possible additional diagnostic criterion for the evaluation of patients with late whiplash syndrome

Evolution of population with sexual and asexual reproduction in changing environment

Using a lattice model based on Monte Carlo simulations, we study the role of the reproduction pattern on the fate of an evolving population. Each individual is under the selection pressure from the environment and random mutations. The habitat ("climate") is changing periodically. Evolutions of populations following two reproduction patterns are compared, asexual and sexual. We show, via Monte Carlo simulations, that sexual reproduction by keeping more diversified populations gives them better chances to adapt themselves to the changing environment. However, in order to obtain a greater chance to mate, the birth rate should be high. In the case of low birth rate and high mutation probability there is a preference for the asexual reproduction.Comment: 11 pages including figs., for Int. J. Mod. Phys. C 15, issue 2 (2004

Prediction of a surface state and a related surface insulator-metal transition for the (100) surface of stochiometric EuO

We calculate the temperature and layer-dependent electronic structure of a 20-layer EuO(100)-film using a combination of first-principles and model calculation based on the ferromagnetic Kondo-lattice model. The results suggest the existence of a EuO(100) surface state which can lead to a surface insulator-metal transition.Comment: 9 pages, 5 figures, Phys. Rev. Lett. (in press

The Mid-Infrared Spectrum of the Short Orbital Period Polar EF Eridani from the Spitzer Space Telescope

We present the first mid-infrared (5.5-14.5 micron) spectrum of a highly magnetic cataclysmic variable, EF Eridani, obtained with the Infrared Spectrograph on the Spitzer Space Telescope. The spectrum displays a relatively flat, featureless continuum. A spectral energy distribution model consisting of a 9500 K white dwarf, L5 secondary star, cyclotron emission corresponding to a B~13 MG white dwarf magnetic field, and an optically thin circumbinary dust disk is in reasonable agreement with the extant 2MASS, IRAC, and IRS observations of EF Eri. Cyclotron emission is ruled out as a dominant contributor to the infrared flux density at wavelengths >3 microns. The spectral energy distribution longward of ~5 microns is dominated by dust emission. Even longer wavelength observations would test the model's prediction of a continuing gradual decline in the circumbinary disk-dominated region of the spectral energy distribution.Comment: To be published in The Astrophysical Journa

Ferromagnetic Kondo-Lattice Model

We present a many-body approach to the electronic and magnetic properties of the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The coupling between itinerant conduction electrons and localized magnetic moments leads, on the one hand, to a distinct temperature-dependence of the electronic quasiparticle spectrum and, on the other hand, to magnetic properties, as e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly influenced by the band electron selfenergy and therewith in particular by the carrier density. We present results for the single-band Kondo-lattice model in terms of quasiparticle densities of states and quasiparticle band structures and demonstrate the density-dependence of the self-consistently derived Curie temperature. The transition from weak-coupling (RKKY) to strong-coupling (double exchange) behaviour is worked out. The multiband model is combined with a tight-binding-LMTO bandstructure calculation to describe real magnetic materials. As an example we present results for the archetypal ferromagnetic local-moment systems EuO and EuS. The proposed method avoids the double counting of relevant interactions and takes into account the correct symmetry of atomic orbitals.Comment: 15 pages, 10 figure

The Gibbs paradox, Black hole entropy and the thermodynamics of isolated horizons

This letter presents a new, solely thermodynamical argument for considering the states of the quantum isolated horizon of a black hole as distinguishable. We claim that only if the states are distinguishable, the thermodynamic entropy is an extensive quantity and can be well-defined. To show this, we make a comparison with a classical ideal gas system whose statistical description makes only sense if an additional 1/N!-factor is included in the state counting in order to cure the Gibbs paradox. The case of the statistical description of a quantum isolated horizon is elaborated, to make the claim evident.Comment: 8 pages, closest to the published version; taken from the author's diploma thesi

Recovery of the X-Ray Transient QX Nor (=X1608-52) in Outburst and Quiescence

We present optical and near-IR observations of QX Nor, the counterpart to the recurrent soft X-ray transient X1608-52, after its reappearance following the X-ray outburst in February 1996. The object has been seen only once before, during an X-ray outburst in 1977. Data from 3-5 months after the outburst show the counterpart at a mean magnitude of R=20.2 and variable on timescales of days. A comparison with identical observations in 1995 implies that the object has brightened by at least 1.8 mag in R following the X-ray outburst. We also detected QX Nor in the IR in both quiescence and outburst. A faint source is visible in the J but not the R band in May 1995. These first observations in the quiescent state yield magnitudes and colors consistent with optical emission from a low mass companion in the binary system, as is true in other soft X-ray transients.Comment: 10 pages including 4 figures and 2 tables; Uses AASTeX 4.0; Accepted for publication in The Astrophysical Journal, Volume 485, August 20, 199

Chandra HRC Localization of the Low Mass X-ray Binaries X1624-490 and X1702-429: The Infrared Counterparts

We report on the precise localization of the low mass X-ray binaries X1624-490 and X1702-429 with the Chandra HRC-I. We determine the best positions to be 16:28:02.825 -49:11:54.61 (J2000) and 17:06:15.314 -43:02:08.69 (J2000) for X1624-490 and X1702-429, respectively, with the nominal Chandra positional uncertainty of 0.6". We also obtained deep IR observations of the fields of these sources in an effort to identify the IR counterparts. A single, faint (Ks=18.3 +/- 0.1) source is visible inside the Chandra error circle of X1624-490, and we propose this source as its IR counterpart. For X1702-429, a Ks=16.5 +/- 0.07 source is visible at the edge of the Chandra error circle. The brightness of both counterpart candidates is comparable to that of other low mass X-ray binary IR counterparts when corrected for extinction and distance.Comment: 5 pages, 2 figures, accepted for publication in Ap