Tracer studies on f-actin fluctuations

We present a study on the fluctuations of semiflexible actin filaments using fluorescence videomicroscopy, focusing on the end-to-end fluctuations of single filaments. In order to specifically measure the position of the polymer's ends, we developed a novel noninvasive method that consists of annealing short end tags to the filaments. This allows us to probe polymer fluctuations to a very high accuracy. We compared the distribution of the end-to-end distance with recent theoretical results, and found excellent agreement. We also studied the dynamics of the mean-square end-to-end distance deltaR2(t) and orientation of the ends, deltaTheta(2)(t), finding power laws t(3/4) and t(1/4), respectively. Scaling behavior for deltaR2(t) is observed over several decades in relaxation time in agreement with theoretical results.     

Universal pion freeze-out in heavy-ion collisions

Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.     

Complete one-loop calculation of the <Emphasis Type="Italic">T</Emphasis>-violating <Emphasis Type="Italic">D</Emphasis>-parameter in neutron decay in the MSSM

We investigate the violation of time reversal invariance in the decay of the free neutron in the framework of the minimal supersymmetric standard model (MSSM). The coefficient of the triple product of the neutron spin and the momenta of electron and neutrino, the so-called D parameter, is computed at one-loop order including all diagrams. We find that D is mainly sensitive to the trilinear A coupling in the squark sector and to the phase of the coefficient which mixes the two Higgs superfields. The maximal MSSM contribution using parameters still allowed by experiment is however at , while QED final state interactions give a value of . Explicit expressions for all relevant diagrams are given in an appendix.Received: 3 March 2003, Revised: 16 May 2003, Published online: 3 July 2003     

Signals of very high energy neutralinos in future cosmic ray detectors

“Top–down” models explain the observation of ultra-high energy cosmic rays (UHECR; E5×10¹⁹ eV) through the decay of very massive, long-lived “X particles”. If superparticles with masses near a TeV exist, X decays also lead to a significant flux of very energetic neutralinos, assumed to be the (stable or long-lived) lightest superparticles. There is a range of energies where neutrinos get absorbed in the Earth, but neutralinos can still traverse it. These neutralinos could in principle be detected. We calculate the detection rate in planned experiments such as OWL and EUSO. For bino-like neutralinos, which have been considered previously, we find detection rates below 1 event per Teraton of target and year in all cases; often the rates are much smaller. In contrast, if the neutralino is higgsino-like, more than ten events per year per Teraton might be observed, if the mass of the X particle is near its lower bound of 10¹² GeV.     

The chemistry of 2H-3,1-benzoxazine-2,4(1H)dione (isatoic anhydrides) 1. The synthesis of N-substituted 2H-3,1-benzoxazine-2,4(1H)diones

Three methods for the preparation of N-substituted 2H-3,1-benzoxazine-2,4(1H)diones (isatoic anhydrides) (1) utilizing 2-chloro-, 2-nitrobenzoic acids and N-unsubstituted isatoic anhydrides as starting materials, are described.     

Ruthenium tetraoxide oxidations of alkanes: DFT calculations of barrier heights and kinetic isotope effects

The oxidation of C-H and C-C bonds by metal-oxo compounds is of general interest. We studied the RuO4-mediated catalytic oxidation of several cycloalkanes such as adamantane and cis- and trans-decalin as well as methane. B3LYP/6-31G(d) calculations on the experimentally proposed (3+2) mechanism are in good agreement with known experimental results. Comparison of experimental and theoretical kinetic isotope effects confirms the proposed mechanism. Besides RuO4, we also looked at RuO4(OH)- as a potential active species to account for ruthenium tetraoxide oxidations under strong basic conditions.     

Ein neues Verfahren zur Bestimmung des Stickstoffs in Kohle und Koks

Ohne Zusammenfassung     

Arraying Cell Cultures Using PEG‐DMA Micromolding in Standard Culture Dishes

A robust and effortless procedure is presented, which allows for the microstructuring of standard cell culture dishes. Cell adhesion and proliferation are controlled by three‐dimensional poly(ethylene glycol)‐dimethacrylate (PEG‐DMA) microstructures. The spacing between microwells can be extended to millimeter size in order to enable the combination with robotic workstations. Cell arrays of microcolonies can be studied under boundary‐free growth conditions by lift‐off of the PEG‐DMA layer in which the growth rate is accessible via the evolution of patch areas. Alternatively, PEG‐DMA stencils can be used as templates for plasma‐induced patterning.