Non-Isotropic Angular Distribution for Very Short-Time Gamma-Ray Bursts

While most gamma-ray bursts (GRBs) are now believed to be from cosmological distances, the origin of very short-time GRBs is still not known. In the past, we have shown that GRBs with time duration (T90) less than 100 ms may form a separate class of GRBs based on the hardness and time distribution of these events. We have also shown that the ln N ln S distribution is consistent with the expectation of quasi-Euclidean distribution of sources. In this paper, we report the study of the angular location of these GRBs showing a strong deviation from isotropy within the Galactic coordinates of plus 180 degrees < longitude < 90 degrees and -30 degrees < latitude < 30 degrees. We have studied the rest of the GRBs and do not find a similar deviation. This further indicates that the very-short GRBs likely form a separate class of GRBs, most probably from sources of Galactic or near solar origin

On the origin of bimodal duration distribution of Gamma Ray Bursts

The modified version of a bullet model for gamma ray bursts is studied. The central engine of the source produces multiple sub-jets that are contained within a cone. The emission of photons in the source frame of a sub-jet either takes part in an infinitesimally thin shell, or during its expansion for a finite time. The analysis of the observed profiles of GRBs taken by BATSE leads us to the conclusion that the latter possibility is much more favored. We also study the statistical distribution of GRBs, in the context of their bimodality of durations, taking into account the detector's capability of observing the signal above a certain flux limit. The model with shells emitting for a finite time is able to reproduce only one class of bursts, short or long, depending on the adopted physical parameters. Therefore we suggest that the GRB bimodality is intrinsically connected with two separate classes of sources.Comment: 12 pages, 12 figures; accepted by MNRAS. Small changes to match the corre cted proof

Micro-cantilever testing of diamond - silicon carbide interfaces in silicon carbide bonded diamond materials produced by reactive silicon infiltration

SiC-bonded diamond materials produced by pressureless reactive infiltration of diamond preforms with silicon show high hardness and wear resistance. These properties are due to the relatively high diamond volume content of approximately 50 vol% and the mechanically strong interface between diamond and SiC. To determine the bending strength of individual interfaces between diamond and SiC, micro-cantilevers were prepared by focused ion beam milling at 13 grain boundaries and in-situ bending tests were carried out in a scanning electron microscope. The determined strength of cantilevers showing interface fracture was 10.4 ± 4.0 GPa. Fracture surfaces were analyzed to verify the fracture behavior and initiation. In addition to fracture at the interface diamond/SiC, fracture occurred inside the SiC grains and at the SiC/silicon interface at comparable strength values. The results prove the high diamond/SiC-interface bonding strength

Human anti-CD30 recombinant antibodies by guided phage antibody selection using cell panning

In various clinical studies, Hodgkin’s patients have been treated with anti-CD30 immunotherapeutic agents and have shown promising responses. One of the problems that appeared from these studies is the development of an immune response against the non-human therapeutics, which limits repeated administration and reduces efficacy. We have set out to make a recombinant, human anti-CD30 single-chain variable fragment (scFv) antibody, which may serve as a targeting moiety with reduced immunogenicity and more rapid tumour penetration in similar clinical applications. Rather than selecting a naive phage antibody library on recombinant CD30 antigen, we used guided selection of a murine antibody in combination with panning on the CD30-positive cell line L540. The murine monoclonal antibody Ki-4 was chosen as starting antibody, because it inhibits the shedding of the extracellular part of the CD30 antigen. This makes the antibody better suited for CD30-targeting than most other anti-CD30 antibodies. We have previously isolated the murine Ki-4 scFv by selecting a mini-library of hybridoma-derived phage scFv-antibodies via panning on L540 cells. Here, we report that phage display technology was successfully used to obtain a human Ki-4 scFv version by guided selection. The murine variable heavy (VH) and light (VL) chain genes of the Ki-4 scFv were sequentially replaced by human V gene repertoires, while retaining only the major determinant for epitope-specificity: the heavy-chain complementarity determining region 3 (CDR3) of murine Ki-4. After two rounds of chain shuffling and selection by panning on L540 cells, a fully human anti-CD30 scFv was selected. It competes with the parental monoclonal antibody Ki-4 for binding to CD30, inhibits the shedding of the extracellular part of the CD30 receptor from L540 cells and is thus a promising candidate for the generation of anti-CD30 immunotherapeutics. © 2000 Cancer Research Campaig

KO-Homology and Type I String Theory

We study the classification of D-branes and Ramond-Ramond fields in Type I string theory by developing a geometric description of KO-homology. We define an analytic version of KO-homology using KK-theory of real C*-algebras, and construct explicitly the isomorphism between geometric and analytic KO-homology. The construction involves recasting the Cl(n)-index theorem and a certain geometric invariant into a homological framework which is used, along with a definition of the real Chern character in KO-homology, to derive cohomological index formulas. We show that this invariant also naturally assigns torsion charges to non-BPS states in Type I string theory, in the construction of classes of D-branes in terms of topological KO-cycles. The formalism naturally captures the coupling of Ramond-Ramond fields to background D-branes which cancel global anomalies in the string theory path integral. We show that this is related to a physical interpretation of bivariant KK-theory in terms of decay processes on spacetime-filling branes. We also provide a construction of the holonomies of Ramond-Ramond fields in Type II string theory in terms of topological K-chains.Comment: 40 pages; v4: Clarifying comments added, more detailed proof of main isomorphism theorem given; Final version to be published in Reviews in Mathematical Physic