Suppression of Superconducting Critical Current Density by Small Flux Jumps in MgB2MgB_2 Thin Films

By doing magnetization measurements during magnetic field sweeps on thin films of the new superconductor $MgB_2$, it is found that in a low temperature and low field region small flux jumps are taking place. This effect strongly suppresses the central magnetization peak leading to reduced nominal superconducting critical current density at low temperatures. A borderline for this effect to occur is determined on the field-temperature (H-T) phase diagram. It is suggested that the small size of the flux jumps in films is due to the higher density of small defects and the relatively easy thermal diffusion in thin films in comparison with bulk samples.Comment: 7 figures Phys. Rev. B accepted scheduled issue: 01 Feb 200

CP Asymmetry for Inclusive Decay B→Xd+γB \to X_d + \gamma in the Minimal Supersymmetric Standard Model

We study the inclusive rare decay $B\to X_d+\gamma$ in the supergravity inspired Minimal Supersymmetric Standard Model and compute the CP-asymmetry in the decay rates. We show that there exist two phenomenologically acceptable sets of SUSY parameters: for one set the CP-asymmetry has the same (positive) sign as in the Standard Model and lies in the range (5-45)% while for the other set it is negative with values within -(2-21)%.Comment: 15 pages, uses axodraw.st

Simulating (electro)hydrodynamic effects in colloidal dispersions: smoothed profile method

Previously, we have proposed a direct simulation scheme for colloidal dispersions in a Newtonian solvent [Phys.Rev.E 71,036707 (2005)]. An improved formulation called the ``Smoothed Profile (SP) method'' is presented here in which simultaneous time-marching is used for the host fluid and colloids. The SP method is a direct numerical simulation of particulate flows and provides a coupling scheme between the continuum fluid dynamics and rigid-body dynamics through utilization of a smoothed profile for the colloidal particles. Moreover, the improved formulation includes an extension to incorporate multi-component fluids, allowing systems such as charged colloids in electrolyte solutions to be studied. The dynamics of the colloidal dispersions are solved with the same computational cost as required for solving non-particulate flows. Numerical results which assess the hydrodynamic interactions of colloidal dispersions are presented to validate the SP method. The SP method is not restricted to particular constitutive models of the host fluids and can hence be applied to colloidal dispersions in complex fluids

On the existence of supergravity duals to D1--D5 CFT states

We define a metric operator in the 1/2-BPS sector of the D1-D5 CFT, the eigenstates of which have a good semi-classical supergravity dual; the non-eigenstates cannot be mapped to semi-classical gravity duals. We also analyse how the data defining a CFT state manifests itself in the gravity side, and show that it is arranged into a set of multipoles. Interestingly, we find that quantum mechanical interference in the CFT can have observable manifestations in the semi-classical gravity dual. We also point out that the multipoles associated to the normal statistical ensemble fluctuate wildly, indicating that the mixed thermal state should not be associated to a semi-classical geometry.Comment: 22 pages, 2 figures. v2 : references added, typos correcte

Occurrences of mild compression wood in agathis borneensis and dacrydium elatum

Studies on the compression wood in tropical gymnosperms are uncommon due to their limited distribution and over-exploitation. Microscopic examination of the heartwood of two tropical gymnosperms, Agathis borneensis (local name: bindang, damar minyak) and Dacrydium elatum (local name: sempilor) growing on higher elevations in Sarawak, Malaysia showed the occurrence of mild compression wood. Intercellular spaces were present in the compression wood of A. borneensis, but not in D. elatum. Rounded shapes of tracheids, typical of severe compression wood, were not observed in any of the samples examined. In D. elatum helical cavities were present, which corresponded in location to cell wall checks seen in cross-sectional views. The S1 layer was relatively thick in both wood species but a distinct S3 layer was observable only in the mild compression wood of D. elatum. Although the main feature of the mild compression wood tracheids of both wood species was greater lignification of the outer S2 region, autofluorescence and KMnO4 staining showed the fluorescence and staining intensity in the corner middle lamella in some cases to be much stronger than that in the outer part of S2 layer