The Discovery of Quasisoft and Supersoft Sources in External Galaxies

We apply a uniform procedure to select very soft sources from point sources observed by Chandra in 4 galaxies. This sample includes one elliptical galaxy (NGC 4967), 2 face-on spirals (M101 and M83), and an interacting galaxy (M51). We have found very soft X-ray sources (VSSs) in every galaxy. Some of these fit the criteria for canonical supersoft sources (SSSs), while others are somewhat harder. These latter have characteristic values of kT < 300 eV; we refer to them as quasisoft sources (QSSs). We found a combined total of 149 VSSs in the 4 galaxies we considered; 77 were SSSs and 72 were QSSs. (See the paper for the original long abstract)Comment: 20 pages, 6 figures. Accepted for publication in Ap

Liquid Drop Stability of a Superdeformed Prolate Semi-Spheroidal Atomic Cluster

Analytical relationships for the surface and curvature energies of oblate and prolate semi-spheroidal atomic clusters have been obtained. By modifying the cluster shape from a spheroid to a semi-spheroid the most stable shape was changed from a sphere to a superdeformed prolate semi-spheroid (including the flat surface of the end cap). Potential energy surfaces vs. deformation and the number of atoms, N, illustrate this property independent of N.Comment: 5 pages, 3 figurex, revtex

Solution of two-center time-dependent Dirac equation in spherical coordinates: Application of the multipole expansion of the electron-nuclei interaction

A non-perturbative approach to the solution of the time-dependent, two-center Dirac equation is presented with a special emphasis on the proper treatment of the potential of the nuclei. In order to account for the full multipole expansion of this potential, we express eigenfunctions of the two-center Hamiltonian in terms of well-known solutions of the "monopole" problem that employs solely the spherically-symmetric part of the interaction. When combined with the coupled-channel method, such a wavefunction-expansion technique allows for an accurate description of the electron dynamics in the field of moving ions for a wide range of internuclear distances. To illustrate the applicability of the proposed approach, the probabilities of the K- as well as L- shell ionization of hydrogen-like ions in the course of nuclear alpha-decay and slow ion-ion collisions have been calculated

Resonant Scattering and Recombination in CAL 87

The eclipsing supersoft X-ray binary CAL 87 has been observed with Chandra on August 13/14, 2001 for nearly 100 ksec, covering two full orbital cycles and three eclipses. The shape of the eclipse light curve derived from the zeroth-order photons indicates that the size of the X-ray emission region is about 1.5 solar radii. The ACIS/LETG spectrum is completely dominated by emission lines without any noticeable continuum. The brightest emission lines are significantly redshifted and double-peaked, suggestive of emanating in a 2000 km/s wind. We model the X-ray spectrum by a mixture of recombination and resonant scattering. This allows us to deduce the temperature and luminosity of the ionizing source to be kT = 50-100 eV and L_X = 5E37 erg/s.Comment: To appear in Proceedings of IAU Coll. 194 "Compact binaries in the Galaxy and beyond" (Rev. Mex. A&A Conf. Series), eds. G. Tovmassian and E. Sio

Modelling salinity management at farm and catchment scales in NSW and Thailand

The Spatial optimisation Model for Analysing Catchment Management (SMAC) has been developed to examine the relationship between groundwater accessions from agricultural land, land salinisation and its medium-term economic effects. This mathematical programming model represents the farm and catchment-scale aspects of land management. The model quantifies the relevant inter-relationships between socio-economic conditions, including the economic and policy environment affecting farms, and the biophysical condition of the catchment, including agronomy, hydrogeology and soil salinisation. The SMAC model was chosen as the catchment-modelling tool in an ACIAR project on salinisation to be carried out by a research team headed by the University of Technology, Sydney and, in Thailand, the project will involve Khon Kaen University, The Royal Forest Department and the Land Development Department of the Ministry of Agriculture and Cooperatives. SMAC will be applied for hydrological, economic and social modelling, at catchment and other scales to evaluate the impact of revegetation in Thailand (Lam Pao and Khorat and Australia (Liverpool Plains and Upper Macquarie Valley). This paper describes the SMAC model and discusses the methodological and other challenges of applying it in other regions with different land-use systems, economic conditions and hydrology, and a data-sparse environment

Strong electric fields induced on a sharp stellar boundary

Due to a first order phase transition, a compact star may have a discontinuous distribution of baryon as well as electric charge densities, as e.g. at the surface of a strange quark star. The induced separation of positive and negative charges may lead to generation of supercritical electric fields in the vicinity of such a discontinuity. We study this effect within a relativistic Thomas-Fermi approximation and demonstrate that the strength of the electric field depends strongly on the degree of sharpness of the surface. The influence of strong electric fields on the stability of compact stars is discussed. It is demonstrated that stable configurations appear only when the counter-pressure of degenerate fermions is taken into consideration.Comment: 13 pages, 2 figure

Pairs Emission in a Uniform Background Field: an Algebraic Approach

A fully algebraic general approach is developed to treat the pairs emission and absorption in the presence of some uniform external background field. In particular, it is shown that the pairs production and annihilation operators, together with the pairs number operator, do actually fulfill the SU(2) functional Lie algebra. As an example of application, the celebrated Schwinger formula is consistently and nicely recovered, within this novel approach, for a Dirac spinor field in the presence of a constant and homogeneous electric field in four spacetime dimensions.Comment: 26 pages, no figure

Particle Ratios and the QCD Critical Temperature

We show how the measured particle ratios at RHIC can be used to provide non-trivial information about the critical temperature of the QCD phase transition. This is obtained by including the effects of highly massive Hagedorn resonances on statistical models, which are used to describe hadronic yields. Hagedorn states are relevant close to $T_c$ and have been shown to decrease $\eta/s$ to the KSS limit and allow for quick chemical equilibrium times in dynamical calculations of hadrons. The inclusion of Hagedorn states creates a dependence of the thermal fits on the Hagedorn temperature, $T_H$, which is assumed to be equal to $T_c$, and leads to an overall improvement of thermal fits. We find that for Au+Au collisions at RHIC at $\sqrt{s_{NN}}=200$ GeV the best square fit measure, $\chi^2$, occurs at $T_c \sim 176$ MeV and produces a chemical freeze-out temperature of 170.4 MeV and a baryon chemical potential of 27.8 MeV.Comment: 6 pages, 2 figures, talk presented at the International Conference on Strangeness in Quark Matter, Buzios, Rio de Janeiro, Brazil, Sept. 27 - oct. 2, 200

Metastabilnost α-stabilnih jezgri bogatih neutroni!vla

Cluster radioactivities of nuclei far from beta-stability line in the neutron-rich region, where a-decay is not allowed, have been systematically studied within analytical superasymmetric fission model. Input mass tables calculated by various authors were used to determine the released energy. Half-lives shorter than 1030 seconds have been estimated for very neutron-rich parent nuclei with atomic numbers form 57 to 86. The emitted clusters are also proton-deficient nuclei, as for example 22O, 46S, 50Ar, 76Fe, 78Ni, etc.Sistematski je istraživana radioaktivnost atomskih jezgri s emisijom nukleonskih grozdova u području bogatom neutronima izvan linije beta stabilnosti, koristeći analitički supersimetrijski fisijski model. U određivanju oslobođene energije upotrebljavane su masene tablice različitih autora. Za jezgre bogate neutronima s atomskim brojevima između 57 i 86 procijenjena su vremena poluraspada na manje od 10 30 s. Emitirani grozdovi su također jezgre siromašne protonima, kao na primjer 2 20, 4 6S, 50Ar, 7 6Fe, 7 8Ni itd

Metastabilnost α-stabilnih jezgri bogatih neutroni!vla

Cluster radioactivities of nuclei far from beta-stability line in the neutron-rich region, where a-decay is not allowed, have been systematically studied within analytical superasymmetric fission model. Input mass tables calculated by various authors were used to determine the released energy. Half-lives shorter than 1030 seconds have been estimated for very neutron-rich parent nuclei with atomic numbers form 57 to 86. The emitted clusters are also proton-deficient nuclei, as for example 22O, 46S, 50Ar, 76Fe, 78Ni, etc.Sistematski je istraživana radioaktivnost atomskih jezgri s emisijom nukleonskih grozdova u području bogatom neutronima izvan linije beta stabilnosti, koristeći analitički supersimetrijski fisijski model. U određivanju oslobođene energije upotrebljavane su masene tablice različitih autora. Za jezgre bogate neutronima s atomskim brojevima između 57 i 86 procijenjena su vremena poluraspada na manje od 10 30 s. Emitirani grozdovi su također jezgre siromašne protonima, kao na primjer 2 20, 4 6S, 50Ar, 7 6Fe, 7 8Ni itd