Improved measurement of the neutron absorption cross section for very low velocities

The absorption cross section of natural Gd and isotopic enriched 157Gd for ultra-cold neutrons (UCN) as a function of the velocity has been measured within a time-of-flight-experiment. Particular attention is paid to small velocities in the region of a few m/s. This is intended to determine the validity of the 1/v-law governing absorption cross sections in this region and the resulting divergence at v=0. The experiment does not show any significant violation of 1/v for v>3 m/s

Factors influencing the choice of treatment modality for individual patients with varicose veins.

INTRODUCTION There is evidence of effectiveness for a range of different treatment modalities for varicose veins but limited information about factors that influence treatment choice for individual patients. METHODS A postal survey was sent to 438 UK members of the Vascular Society of Great Britain and Ireland. RESULTS Overall, 251 responses were received (response rate 57%). A total of 222 respondents treated varicose veins using conventional surgery (84%), endothermal ablation (82%) and foam sclerotherapy (68%). The clinical pattern of veins appeared to have the greatest influence on treatment choice. This was followed by guidance from the National Institute for Health and Care Excellence, patient expectations, facilities, cost and whether treatment was carried out in the public or private sector. Respondents were asked to indicate whether each of 13 clinical 'scenarios' (eg very extensive varicose veins in both legs) would influence them towards or against using specified treatment modalities. 'Consensus' was defined as ≥80% of responses either towards or against any treatment modality; and disagreement as 41-59% both towards and against any modality (i.e. ∼50:50 split). There was consensus towards using endothermal ablation for truncal reflux, towards UGFS for localised varicose veins and towards conventional surgery for large, extensive, bilateral veins. There was consensus against UGFS for large truncal veins, and against surgery for obese patients and those with a history of venous thromboembolism. There were important disagreements about the influence of large or extensive veins, about whether patients were obese or slim and about a prior history of venous thromboembolism. CONCLUSIONS Conventional surgery is still widely available in the UK. Disagreements about treatment choice in different clinical scenarios suggest substantial variation in the treatments patients are offered. Attention to identifying subgroups in trials would help to guide treatment choice for individual patients

Effect of a strong magnetic field on the relaxation of a hot 2-D electron-hole plasma studied with picosecond photoluminescence

\u3cp\u3eWe present time-energy resolved picosecond photoluminescence measurements on a two-dimensional electron-hole plasma in a strong magnetic field. The temporal evolution of the temperature T\u3csub\u3ee,h\u3c/sub\u3e, the density n\u3csub\u3ee,h\u3c/sub\u3e and the Landau level broadening parameter Δ dre determined. At B=20T the cooling rate of the e-h plasma is increased by a factor of 7 with respect to B=0T.\u3c/p\u3

Relaxation of hot two dimensional carriers in a strong magnetic field studied with picosecond photoluminescence

\u3cp\u3eWe report the first investigations on the effect of a strong magnetic field on the energy relaxation of hot carriers in GaAs/AlGaAs quantum wells studied with picosecond time resolved photoluminescence. The energy relaxation is significantly increased at strong magnetic fields (20 T), while at lower field values (8 T) it is reduced with respect to B = 0 T. We discuss the possible origins of this dramatic change in energy relaxation.\u3c/p\u3

Bonding and Catalytic Application of Ruthenium N-Heterocyclic Carbene Complexes Featuring Triazole, Triazolylidene, and Imidazolylidene Ligands

The first mixed normal/abnormal NHC ruthenium(II) complexes bearing triazole/imidazole-based ligands are presented. The ruthenium complexes show differing coordination geometries depending on the ligand sphere and the coordination of the triazole. Two Ru(II) monocarbene complexes have been obtained, with a 2-imidazolylidene carbene and the 1,2,3-triazoles acting as neutral nitrogen donors. In addition, a tridentate Ru(II) complex featuring a normal 2-imidazolylidene as well as two abnormal 1,2,3-triazolylidene carbene moieties is described. Both structural motifs are evaluated in transfer hydrogenation of acetophenone, with the electron-rich Ru(II) tri-NHC exhibiting the highest conversion

Energy relaxation of lower-dimensional hot carriers studied with picosecond photoluminescence

\u3cp\u3eTo study the energy relaxation of lower-dimensional hot carriers, picosecond time- and energy-resolved photoluminescence measurements have been carried out on bulk GaAs and GaAs/AlxGa1-xAs quantum-well structures in the presence of magnetic fields up to B=20 T. For GaAs the results show that the energy-relaxation rate reduces with increasing strength of the magnetic field. This cooling behavior is adequately described by a model for energy relaxation containing the magnetic-field-dependent kinetics of the coupled carrier nonequilibrium-LO-phonon system. For the quantum-well structures, an increasing magnetic field normal to the quasi-two-dimensional layers reduces the carrier cooling up to B=8 T, while at higher field strengths an enhancement in cooling is observed up to B=20 T. We suggest this effect to be due to a reduction in energy relaxation rate by LO-phonon emission, so that at B>8 T carrier cooling is taken over by acoustic-phonon emission, which increases with magnetic field.\u3c/p\u3