Low mass πN enhancement in inelastic αp interaction

Evidence for an enhancement in the isospin $\text{I =}\text{1}\text{2}\text{π}\text{N}$ system at M = 1130 MeV/c² (Γ = 80 MeV/c²) has been found in the reaction αp → αx at an incident α-momentum of 4.00 and 5.08 GeV/c. A strong t-dependence of the cross section and a mass-slope correlation are seen as the main features of the data.     

Electronic resistivity and deffect structure of β-LiAl as a function of temperature and composition

The electrical resistivity of β-Li_xAl_1?x has been measured from 10 K to 290 K in single crystal samples for four different concentrations, x=0.480, 0.486, 0.500 and 0.525. An anomaly at 100 K is observed for the three lowest Li concentrations. This anomaly is associated with an ordering of constitutional Li vacancies. Above 100 K the temperature dependent part of the resistivity is independent of the Li concentration. However, the residual resistivity increases very rapidly with increasing Li concentration, becoming ～ 75 μΩ-cm for x=0.525. These results suggest that the two defect model of β-LiAl may be incomplete.     

Experimental magnetic form factor of platinum metal

The induced magnetic form factor of paramagnetic platinum was measured in an external field of 73 kOe at a temperature of 78 K. The data obtained for the six innermost Bragg reflections show that the spherically average magnetization density is in excellent agreement with that calculated by Watson-Yang. Freeman and Koelling. The result confirms the reliability of the present day band calculations, as well as assuring that the nontrivial orbital contribution to the form factor (g = 2.61) has been handled properly. The asphericity of the magnetization was more poorly determined, yielding at t_2g population of 70 ± 17%, to be compared with a calculated value of 93%. An attempt at a more direct determination of the role of the orbital contribution is described.     

Covering homology

We introduce the notion of covering homology of a commutative S-algebra with respect to certain families of coverings of topological spaces. The construction of covering homology is extracted from Bökstedt, Hsiang and Madsen's topological cyclic homology. In fact covering homology with respect to the family of orientation preserving isogenies of the circle is equal to topological cyclic homology. Our basic tool for the analysis of covering homology is a cofibration sequence involving homotopy orbits and a restriction map similar to the restriction map used in Bökstedt, Hsiang and Madsen's construction of topological cyclic homology.Covering homology with respect to families of isogenies of a torus is constructed from iterated topological Hochschild homology. It receives a trace map from iterated algebraic K-theory and there is a hope that the rich structure, and the calculability of covering homology will make it useful in the exploration of J. Rognes' “red shift conjecture”.     

Limits on an energy dependence of the speed of light from a flare of the active galaxy PKS 2155-304

In the past few decades, several models have predicted an energy dependence of the speed of light in the context of quantum gravity. For cosmological sources such as active galaxies, this minuscule effect can add up to measurable photon-energy dependent time lags. In this Letter a search for such time lags during the High Energy Stereoscopic System observations of the exceptional very high energy flare of the active galaxy PKS 2155-304 on 28 July 2006 is presented. Since no significant time lag is found, lower limits on the energy scale of speed of light modifications are derived.     

Fast X-ray scattering measurements on high temperature levitated liquids

We describe a new high temperature environment based on aerodynamic levitation and CO₂ laser heating designed for high energy X-ray diffraction at the ID11 beamline at ESRF. The use of two lasers simultaneously provides a homogeneous temperature and makes it possible to explore the supercooled state with a high degree of control (about 500 °C below the melting point in this work) and to work very close to T_g. The scattered beam is measured over a relatively wide Q-range of 0.5–19 Å^?1 with the ESRF Frelon 2D CDD camera. Using 1-min measurements we obtained good quality structure factors at various temperatures in the liquid and supercooled state of CaAl₂O₄. We also performed time-resolved measurements using an acquisition time of 100 ms and we obtained good statistics even at large Q. The Al–O and Ca–O bond lengths and coordination numbers derived from the calculated pair distribution functions are in good agreement with our previous X-ray and neutron works.     

Mass Spectrometric Identification of [4Fe–4S](NO)x Intermediates of Nitric Oxide Sensing by Regulatory Iron–Sulfur Cluster Proteins

Nitric oxide (NO) can function as both a cytotoxin and a signalling molecule. In both cases, reaction with iron–sulfur (Fe–S) cluster proteins plays an important role because Fe–S clusters are reactive towards NO and so are a primary site of general NO-induced damage (toxicity). This sensitivity to nitrosylation is harnessed in the growing group of regulatory proteins that function in sensing of NO via an Fe–S cluster. Although information about the products of cluster nitrosylation is now emerging, detection and identification of intermediates remains a major challenge, due to their transient nature and the difficulty in distinguishing spectroscopically similar iron-NO species. Here we report studies of the NO-sensing Fe–S cluster regulators NsrR and WhiD using non-denaturing mass spectrometry, in which non-covalent interactions between the protein and Fe/S/NO species are preserved. The data provide remarkable insight into the nitrosylation reactions, permitting identification, for the first time, of protein-bound mono-, di- and tetranitrosyl [4Fe–4S] cluster complexes ([4Fe–4S](NO), [4Fe–4S])(NO)₂ and [4Fe–4S](NO)₄) as intermediates along pathways to formation of product Roussin's red ester (RRE) and Roussin's black salt (RBS)-like species. The data allow the nitrosylation mechanisms of NsrR and WhiD to be elucidated and clearly distinguished.     

Diaryl sulfide-based inhibitors of trypanothione reductase: inhibition potency, revised binding mode and antiprotozoal activities

Trypanothione reductase (TR) is an essential enzyme of trypanosomatids and therefore a promising target for the development of new drugs against African sleeping sickness and Chagas' disease. Diaryl sulfides with a central anilino moiety, decorated with a flexible N-alkyl side chain bearing a terminal ammonium ion, are a known class of inhibitors. Using computer modelling, we revised the binding model for this class of TR inhibitors predicting simultaneous interactions of the ammonium ion-terminated N-alkyl chain with Glu18 as well as Glu465'/Glu466' of the second subunit of the homodimer, whereas the hydrophobic substituent of the aniline ring occupies the "mepacrine binding site" near Trp21 and Met113. Systematic alteration of the carboxylate-binding fragments and the diaryl sulfide core of the inhibitor scaffold provided evidence for the proposed binding mode. In vitro studies showed IC(50) values in the low micromolar to submicromolar range against Trypanosoma brucei rhodesiense as well as the malaria parasite Plasmodium falciparum.