Resistivity of non-Fermi liquid U2Pt2In under pressure

Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa). At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum develops in rho(T). A study of the field dependence of the minimum confirms its magnetic origin. The ratio c/a is proposed as the effective control parameter, rather than the unit cell volume.Comment: 5 pages (incl. 2 figures), submitted to SCES'99, Nagan

Proper identification of RR Lyrae Stars brighter than 12.5 mag

RR Lyrae stars are of great importance for investigations of Galactic structure. However, a complete compendium of all RR-Lyraes in the solar neighbourhood with accurate classifications and coordinates does not exist to this day. Here we present a catalogue of 561 local RR-Lyrae stars V_max less equal 12.5 mag according to the magnitudes given in the Combined General Catalogue of Variable Stars (GCVS) and 16 fainter ones. The Tycho2 catalogue contains about 100 RR Lyr stars. However, many objects have inaccurate coordinates in the GCVS, the primary source of variable star information, so that a reliable cross-identification is difficult. We identified RR Lyrae from both catalogues based on an intensive literature search. In dubious cases we carried out photometry of fields to identify the variable. Mennessier and Colome (2002) have published a paper with Tyc2-GCVS identifications, but we found that many of their identifications are wrong. Keywords: astrometry -- Stars: RR Lyrae stars -- Catalogues: Tycho-2 catalogue -- Catalogues: The HST Guide Star Catalogue, Version 1.2 -- Catalogues: Combined General Catalogue of Variable StarsComment: 5 pages with 2 figures; A and A accepted Online-Data are available under http://www.astro.uni-bonn.de/~gmaint

Chandra Detection of X-ray Absorption Associated with a Damped Lyman Alpha System

We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray absorption associated with intervening 21-cm and damped Ly$\alpha$ absorbers. For PKS 1127-145, we detect absorption which, if associated with an intervening z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption is not at z_{abs}=0.312, then the metallicity is still constrained to be less than 23% solar. The advantage of the X-ray measurement is that the derived metallicity is insensitive to ionization, inclusion of an atom in a molecule, or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is consistent with the oxygen abundance of 30% solar derived from optical nebular emission lines in a foreground galaxy at the redshift of the absorber. For Q1331+171 and Q 0054+144, only upper limits were obtained, although the exposure times were intentionally short, since for these two objects we were interested primarily in measuring flux levels to plan for future observations. The imaging results are presented in a companion paper.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical Journa

Constraints on Supersymmetry from Relic Density compared with future Higgs Searches at the LHC

Among the theories beyond the Standard Model (SM) of particle physics Supersymmetry (SUSY) provides an excellent dark matter (DM) candidate, the neutralino. One clear prediction of cosmology is the annihilation cross section of DM particles, assuming them to be a thermal relic from the early universe. In most of the parameter space of Supersymmetry the annihilation cross section is too small compared with the prediction of cosmology. However, for large values of the tan beta parameter the annihilation through s-channel pseudoscalar Higgs exchange yields the correct relic density in practically the whole range of possible SUSY masses up to the few TeV range. The required values of tan beta are typically around 50, i.e. of the order of top and bottom mass ratio, which happens to be also the range allowing for Yukawa unification in a Grand Unified Theory with gauge coupling unification. For such large values of tan beta the associated production of the heavier Higgses, which is enhanced by tan beta squared, becomes three orders of magnitude larger than the production of a simlar SM-like Higgs and could be observable as one of the first hints of new physics at the LHC.Comment: 12 pages, 5 figures, Published version in Phys. Lett. B with updated references and minor correction

Towards simultaneous electrical and optical investigation of BLMS using a novel microfluidic device

We firstly describe the influence of the phospholipid (PL) composition of bilayer lipid membrane on their electrical properties: (i) the more unsaturations in the tail, the earlier the BLM breakdown and (ii) the bulkier the head group, the less stable the membrane. Secondly, we design and fabricate novel devices that couple such electri-cal characterization to optical investigation and that enable the preparation of asym-metrical membranes: a “macro” device including a drilled PMMA plate as well as microfluidic device consisting of a glass-teflon foil-glass sandwich

A Deductive Proof System for Multithreaded Java with Exceptions

Besides the features of a class-based object-oriented language, Java integrates concurrency via its thread-classes, allowing for a multithreaded flow of control.Besides that, the language offers a flexible exception mechanism for handling errors or exceptional program conditions. To reason about safety-properties Java-programs and extending previous work on the proof theory for monitor synchronization, we introduce in this report an assertional proof method for JavaMT (Multi-Threaded Java), a small concurrent sublanguage of Java, covering concurrency and especially (exception handling). We show soundness and relative completeness of the proof method

A Formal, Resource Consumption-Preserving Translation of Actors to Haskell

We present a formal translation of an actor-based language with cooperative scheduling to the functional language Haskell. The translation is proven correct with respect to a formal semantics of the source language and a high-level operational semantics of the target, i.e. a subset of Haskell. The main correctness theorem is expressed in terms of a simulation relation between the operational semantics of actor programs and their translation. This allows us to then prove that the resource consumption is preserved over this translation, as we establish an equivalence of the cost of the original and Haskell-translated execution traces

A structural operational semantics of a concurrent class calculus

The concurrent $\nu$-calculus has been investigated as a core calculus for imperative, object-oriented languages with multithreading and heap-allocated objects. From an abstract point of view, the combination of this form of concurrency with objects corresponds to features known from the popular language Java. One distinctive feature, however, of the concurrent object calculus is that it is \emph{object-based}, where as the mainstream of object-oriented languages is \emph{class-based.} This technical report extends the concurrent $\nu$-calculus by introducing classes and explores some of the semantical consequences. The semantics will serve asthe basis for a proof of full abstraction wrt.\ to a may-testing based notion of observability