A projective characterisation of ellipsoids by isotropy

In projective geometry, ellipsoids may be characterised by a property of isotropy about a single point. The author wishes to thank Rainer L?wen for advice on the presentation of the proof.     

Neutral meson production in relativistic heavy ion collisions

The production of ⁰ and mesons has been studied in the reactions²⁰Ne +Al at 350 MeV/u and⁴⁰Ar + Ca at 1.0 GeV/u. Rapidity distributions and transverse momentum spectra have been measured and are compared to thermal distributions.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Normal modes of a model radiating system

In order to gain insight into normal modes of realistic radiating systems, we study the simple model problem of a finite string and a semi-infinite string coupled by a spring. As expected there is a family of modes which are basically the modes of the finite string slowly damped by the radiation of energy to infinity on the semi-infinite string. But we also study another family of modes, found by Dyson in a different model problem, which are strongly damped modes of the semi-infinite string itself. These may be analogous to the modes of black holes, and they are likely to be present in relativistic stars as well. The question of whether the instability in these modes which Dyson found is present in realistic stars remains open.     

ExplorEnz: a MySQL database of the IUBMB enzyme nomenclature

Background  

We describe the database ExplorEnz, which is the primary repository for EC numbers and enzyme data that are being curated on behalf of the IUBMB. The enzyme nomenclature is incorporated into many other resources, including the ExPASy-ENZYME, BRENDA and KEGG bioinformatics databases.     

Observation of Δ+→ pπ0 decay in heavy-ion collisions

Proton-π⁰ coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-π⁰ invariant mass spectrum we observe a significant excess of strength above the background obtained by event mixing. We attribute this signal to the strength distribution N _Δ of the Δ baryonic resonance. No correlation is observed in the case of deuteron-π⁰ coincidences. Assuming isotropic emission of π⁰ and Δ⁺ from a midrapidity thermal source and isospin symmetry, we determined the global N _Δ/N _πratio of 0.79 ±0.30(stat) ±0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction are mediated by the Δ-resonance. Received: 7 April 2000 / Accepted: 29 August 2000     

Suppression of soft nuclear bremsstrahlung in proton-nucleus collisions

Photon energy spectra up to the kinematic limit have been measured in 190 MeV proton reactions with light and heavy nuclei to investigate the influence of the multiple-scattering process on the photon production. Relative to the predictions of models based on a quasifree production mechanism, a strong suppression of bremsstrahlung is observed in the low-energy region of the photon spectrum. We attribute this effect to the interference of photon amplitudes due to multiple scattering of nucleons in the nuclear medium.     

Origin of projectile-like fragments from40Ar +68Zn collisions between 15 and 35 MeV/nucleon: Direct transfer of nucleons and projectile fragmentation

The projectile-like fragments emitted in the⁴⁰Ar +⁶⁸Zn reaction performed at 14.6, 19.6, 27.6 and 35 MeV/nucleon are studied. Their energy spectra and angular distributions have been measured. Velocities, widths of the linear momentum distributions and cross sections have been deduced. The results are discussedi) in terms of transfer of a few nucleons and analysed with a diffractional model. They are consistent, for stripping reactions, with a direct transfer of nucleons and a target excitation yielding multiparticlemultihole configurations,ii) In terms of projectile fragmentation-like process with a modified abrasion model taking into account the energy separation of the participant nucleons. The projectile fragmentation-like process appears above 20 MeV/nucleon and strongly competes with transfer of nucleons at 35 MeV/nucleon. The evolution of the mechanisms with incident energy is discussed on the basis of the reduced widths of the linear momentum distributions and on those of velocities and cross sections.     

What can we learn from single molecule trajectories?

Diffusing membrane constituents are constantly exposed to a variety of forces that influence their stochastic path. Single molecule experiments allow for resolving trajectories at extremely high spatial and temporal accuracy, thereby offering insights into en route interactions of the tracer. In this review we discuss approaches to derive information about the underlying processes, based on single molecule tracking experiments. In particular, we focus on a new versatile way to analyze single molecule diffusion in the absence of a full analytical treatment. The method is based on comprehensive comparison of an experimental data set against the hypothetical outcome of multiple experiments performed on the computer. Since Monte Carlo simulations can be easily and rapidly performed even on state-of-the-art PCs, our method provides a simple way for testing various - even complicated - diffusion models. We describe the new method in detail, and show the applicability on two specific examples: firstly, kinetic rate constants can be derived for the transient interaction of mobile membrane proteins; secondly, residence time and corral size can be extracted for confined diffusion.     

High pt and photon physics with ALICE at LHC

ALICE,A Large Ion Collider Experiment,is dedicated to study the QCD matter at extreme high temperature and density to understand the Quark Gluon Plasma (QGP) and phase transition.High-transversemomentum photons and neutral mesons from the initial hard scattering of partons can be measured with ALICE calorimeters,PHOS (PHOton Spectrometer) and EMCAL (ElectroMagnetic CALorimeter).Combing the additional central tracking detectors,the γ-jet and π 0-jet measurements thus can be accessed.These measurements offer us a sensitive tomography probe of the hot-dense medium generated in the heavy ion collisions.In this paper,high p T and photon physics is discussed and the ALICE calorimeters capabilities of high-transverse-momentum neutral mesons and γ-jet measurements are presented.