Energy and centrality dependence of particle production at very low transverse momenta in Au+Au collisions

The PHOBOS experiment at RHIC has the unique capability of measuring particle production at very low transverse momenta. New results on low-transverse momentum invariant yields of pions, kaons, protons and antiprotons in 200 GeV Au+Au collisions are presented as a function of the collision centrality for the 50% most central events. In contrast to the results from d+Au collisions, no $m_{T}$ scaling is observed in the very low $p_{T}$ region. The low transverse momentum yields agree with extrapolations from intermediate transverse momentum measurements. For all collision centralities a flattening of the transverse momentum spectra is observed, consistent with a rapid transverse expansion of the system.Comment: 4 pages, 6 figures, presented at the 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur, India, February 4-10, 200

Surface properties of the clean and Au/Pd covered Fe3_3O4_4(111): a DFT and DFT+UU study

The spin-density functional theory (DFT) and DFT+$U$ with Hubbard $U$ term accounting for on-site Coulomb interactions were applied to investigate structure, stability, and electronic properties of different terminations of the Fe$_3$O$_4$(111) surface. All terminations of the ferrimagnetic Fe$_3$O$_4$(111) surface exhibit very large (up to 90%) relaxations of the first four interlayer distances, decreasing with the oxide layer depth. Our calculations predict the iron terminated surface to be most stable in a wide range of the accessible values of the oxygen chemical potential. The adsorption of Au and Pd on two stable Fe- and O-terminated surfaces is studied. Our results show that Pd binds stronger than Au both to the Fe- and O-terminated surface. DFT+$U$ gives stronger bonding than DFT. The bonding of both adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than to the Fe-terminated surface

Mean-field approaches to the Bose-Hubbard model with three-body local interaction

The zero temperature properties of the generalized Bose-Hubbard model including three-body interactions are studied on a mean-field level. We obtain analytical results using the so-called perturbative mean-field method and more detailed numerical results using the Gutzwiller product state variational Ansatz. These two approaches yield equivalent results which compare well on a qualitative level with recent exact results obtained in the literature.Comment: Proceedings of the CEWQO 201

The superconducting and magnetic states in RuSr2GdCu2O8, based on the magnetic, transport and magneto-caloric characteristics

The article discusses selected properties of the non- and superconducting polycrystalline samples of RuSr2GdCu2O8 and comments the consequences of introducing insignificant sub-stoichiometry of Ru into the nominal formula. The magneto-resistive and the magnetic characteristics are interpreted in favour of the formation of the intrinsically inhomogeneous superconducting phase, which seems to be stabilized along with the structural modifications likely enhanced with the modification of starting stoichiometry. The specific heat data reveals the shift of temperature of the magnetic ordering T_{m}, suggesting the dilution in magnetic sublattice of the Ru moments. The measurements of the magnetic field dependences of the isothermal magnetocaloric coefficient M_{T} show that there is no gain in magnetic entropy in a broad range of the accessed fields and temperatures. Whereas the multi-component character of the probed magnetic system precludes from concluding on the ground state for the Ru ordering, the maximum in M_{T}(H) which occurs at weak magnetic fields for temperature vicinity of T_{m} may reflect dominance of the ferromagnetic type interactions with a constrained correlation range. The literature explored models for the Ru magnetic ordering and possible phase separation in the RuSr2GdCu2O8 are brought into the discussion.Comment: Most of the discussed results conform to the first author's presentations given at XIV Polish National School for Superconductivity (XIV KSN) in October 2009, and at M2S-IX Conference in September 2009. Submitted to the proceedings of XIV KSN

Does Macro-Pru Leak? Evidence from a UK Policy Experiment

The regulation of bank capital as a means of smoothing the credit cycle is a central element of forthcoming macro-prudential regimes internationally. For such regulation to be effective in controlling the aggregate supply of credit it must be the case that: (i) changes in capital requirements affect loan supply by regulated banks, and (ii) unregulated substitute sources of credit are unable to offset changes in credit supply by affected banks. This paper examines micro evidence—lacking to date—on both questions, using a unique dataset. In the UK, regulators have imposed time-varying, bank-specific minimum capital requirements since Basel I. It is found that regulated banks (UK-owned banks and resident foreign subsidiaries) reduce lending in response to tighter capital requirements. But unregulated banks (resident foreign branches) increase lending in response to tighter capital requirements on a relevant reference group of regulated banks. This “leakage” is substantial, amounting to about one-third of the initial impulse from the regulatory change.

Electromagnetic form factors of the Delta baryon

We develop a methodology that enables us to extract accurately the electromagnetic Delta form factors and their momentum dependence. We test our approach in the quenched approximation as a preparation for a study using dynamical fermions. Our calculation of the four form factors covers pion masses between about 410 MeV and 560 MeV on lattices with a size of 2.9 fm and a lattice spacing 0.09 fm. From the form factors we are able to obtain estimates of the magnetic moment and the charge radius of the Delta, which we compare to existing experimental and theoretical results.Our non-zero result for the electric quadrupole form factor signals a deformation of the Delta, pointing to an oblate charge distribution

The Physics of Wind-Fed Accretion

We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-1. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.Comment: 9 pages including 5 color encapsulated postscript figures; accepted for inclusion in the proceedings of "Cool Discs, Hot Flows: The Varying Faces of Accreting Compact Objects," ed. M. Axelsson (New York: AIP); minor revision which addresses the referee's comments; added Fig. 1 and removed Fig. 3 and the associated tex

Quantum coherence and sensitivity of avian magnetoreception

Migratory birds and other species have the ability to navigate by sensing the geomagnetic field. Recent experiments indicate that the essential process in the navigation takes place in bird's eye and uses chemical reaction involving molecular ions with unpaired electron spins (radical pair). Sensing is achieved via geomagnetic-dependent dynamics of the spins of the unpaired electrons. Here we utilize the results of two behavioral experiments conducted on European Robins to argue that the average life-time of the radical pair is of the order of a microsecond and therefore agrees with experimental estimations of this parameter for cryptochrome --- a pigment believed to form the radical pairs. We also found a reasonable parameter regime where sensitivity of the avian compass is enhanced by environmental noise, showing that long coherence time is not required for navigation and may even spoil it.Comment: 6+ pages, 2+4 figures, new results adde

Double universality of a quantum phase transition in spinor condensates: the Kibble-\.Zurek mechanism and a conservation law

We consider a phase transition from antiferromagnetic to phase separated ground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We demonstrate the occurrence of two scaling laws, for the number of spin fluctuations just after the phase transition, and for the number of spin domains in the final, stable configuration. Only the first scaling can be explained by the standard Kibble-\.Zurek mechanism. We explain the occurrence of two scaling laws by a model including post-selection of spin domains due to the conservation of condensate magnetization