A phenomenological study of bottom-quark fragmentation in top-quark decay

Top-quark physics is one of the main fields of investigation at the Tevatron accelerator and, ultimately, at the LHC. We perform a phenomenological analysis of $t\bar{t}$ events at hadron colliders, with a focus on observables relying on bottom-quark fragmentation in top-quark decay. In particular, we investigate the B-lepton invariant-mass distribution in the dilepton channel and give an estimate of the contribution of bottom fragmentation to the Monte Carlo uncertainty on the top-quark mass reconstruction.     

Wavepacket models for subsonic twin jets using 3D parabolized stability equations

An extension of the classical parabolized stability equations to flows strongly dependent on the two cross-stream spatial directions and weakly dependent on the streamwise one is applied to model the large-scale structures present in twin-jet configurations. The existence of these unsteady flow structures, usually referred to as wavepackets, has been demonstrated in the literature for both subsonic and supersonic round jets, along with their relation to the generation of highly directional noise emitted in the aft direction. The present study considers twin-jet configurations with different separations at high Reynolds number and subsonic conditions. The existing instability modes for the twin-jet mean flow, their dependence on the separation of the two jets, and the interaction between the wavepackets originating from the two jets is investigated here. Arising from the axisymmetric mode for single round jets, two dominant modes are found for twin jets: a varicose one, relatively insensitive to jets' proximity, but likely to be efficient in radiating noise; a sinuous one, whose amplification is strongly dependent on the jets' distance, and which can be expected to produce weaker acoustic signatures.     

Radical anions containing the dioxidated 1,2,5‐thiadiazole heterocycle

Radical anions of 3,4‐aryl disubstituted 1,2,5‐thiadiazole 1,1‐dioxide were obtained by chemical and electrochemical reduction of their substrates, and characterized by ESR spectroscopy and cyclic voltammetry. The radical anion of the phenanthro[9,10‐c]‐1,2,5‐thiadiazole 1,1‐dioxide was found to be very stable in an aprotic solvent solution and did not react readily when water was added to the aprotic solvent, or the solution was saturated with oxygen gas. The radical formation chemical reaction competed with nucleophilic addition to the C?N bond of the thiadiazoles. A possible reaction mechanism, and a common reaction intermediate, supported by density functional theory calculations, is presented for the most stable radical. Copyright © 2009 John Wiley & Sons, Ltd.     

A historical perspective on location problems

Location problems represent a popular class of optimization problems in the field of logistics, and their applications play a key role in strategic planning activities related to both manufacturing and service industries. This paper presents a historical perspective of their evolution, from the historic challenge posed by Pierre de Fermat, through the contributions by Torricelli, Viviani, Simpson, Heinen, and other researchers, to Weber’s intuition about a practical use of the results of that challenge, and its subsequent developments. Modern developments of the discipline are also reviewed. There is particular emphasis on the work of pioneering researchers who provided seminal contributions to the field.     

Knight shifts in solid noble metals

The direct contribution to the Knight shift in solid noble metals is evaluated. The entire calculation is accomplished in the framework of the pseudopotential formalism and the effective shape of the Fermi surface is taken into account by using the simple “eight-cone” model by Ziman. The theoretical results are discussed and compared with the available experimental data.     

Mössbauer Investigation of FeSbO4

Mössbauer data are presented for FeSbO₄ at room temperature (RT) and liquid-nitrogen temperature (LNT). An interpretation of the relaxation phenomena in this compound at LNT is given which differs from previous conclusions (G. M. Bartenev et al. [9]) and shows a correlation with FeSbO₄ particle size. The results permit a more accurate evaluation of the phase composition of (Fe, Sb)O catalysts by means of Mössbauer spectroscopy.     

Oxidative degradation of food dye E133 Brilliant Blue FCF Liquid chromatography-electrospray mass spectrometry identification of the degradation pathway

This paper is devoted to the evaluation of the degradation pathway of the E133 Brilliant Blue FCF (C.I. 42090) that is largely used in the food industry. The degradation is studied in oxidation conditions obtained by addition of potassium persulfate at different persulfate to dye molar ratios under natural sunlight irradiation. The degradation pathway of the dye passes through a species coloured in dark blue and then gives rise to uncoloured species. Due to the low volatility and the poor thermal stability of the dye, reversed-phase liquid chromatography associated to mass spectrometry and tandom mass spectrometry was employed to follow the kinetics of degradation and identify some intermediates. The identification of organic species still present in the decoloured dye and the value of COD obtained in these conditions show evidence that complete decolorization does not correspond to complete mineralisation. No direct information of toxicity is available for the uncoloured degradation products but the further formation of aromatic amines can not be excluded.