Microwave Properties of Ba(0.6)K(0.4)BiO(3) Crystals

We report on field-induced variations of the microwave surface resistance at 9.6 GHz of Ba(0.6)K(0.4)BiO(3) crystals. Energy losses have been investigated as a function of the static magnetic field in the range of temperatures 4.2 K - Tc. By analyzing the experimental results in the framework of the Coffey and Clem model we determine the temperature dependence of the first-penetration field, upper critical field and depinning frequency. The results show that the pinning energy of this bismuthate superconductor is weaker than those of cuprates.Comment: 6 pages, 8 embedded figure

Exploring matrix effects on photochemistry of organic aerosols

This work explores the effect of the environment on the rate of photolysis of 2,4-dinitrophenol (24-DNP), an important environmental toxin. In stark contrast to the slow photolysis of 24-DNP in an aqueous solution, the photolysis rate is increased by more than an order of magnitude for 24-DNP dissolved in 1-octanol or embedded in secondary organic material (SOM) produced by ozonolysis of α-pinene. Lowering the temperature decreased the photolysis rate of 24-DNP in SOM much more significantly than that of 24-DNP in octanol, with effective activation energies of 53 kJ/mol and 12 kJ/mol, respectively. We discuss the possibility that the increasing viscosity of the SOM matrix constrains the molecular motion, thereby suppressing the hydrogen atom transfer reaction to the photo-excited 24-DNP. This is, to our knowledge, the first report of a significant effect of the matrix, and possibly viscosity, on the rate of an atmospheric photochemical reaction within SOM. It suggests that rates of photochemical processes in organic aerosols will depend on both relative humidity and temperature and thus altitude. The results further suggest that photochemistry in SOM may play a key role in transformations of atmospheric organics. For example, 24-DNP and other nitro-aromatic compounds should readily photodegrade in organic particulate matter, which has important consequences for predicting their environmental fates and impacts

Modification of Nanodiamonds by Xenon Implantation: A Molecular Dynamics Study

Xenon implantation into nanodiamonds is studied using molecular dynamics. The nanodiamonds range in size from 2-10 nm and the primary knock-on (PKA) energy extends up to 40 keV. For small nanodiamonds an energy-window effect occurs in which PKA energies of around 6 keV destroy the nanodiamond, while in larger nanodiamonds the radiation cascade is increasingly similar to those in bulk material. Destruction of the small nanodiamonds occurs due to thermal annealing associated with the small size of the particles and the absence of a heat-loss path. Simulations are also performed for a range of impact parameters, and for a series of double-nanodiamond systems in which a heat-loss path is present. The latter show that the thermal shock caused by the impact occurs on the timescale of a few picoseconds. These findings are relevant to ion-beam modification of nanoparticles by noble gases as well as meteoritic studies where implantation is proposed as the mechanism for xenon incorporation in pre-solar nanodiamonds

Muon spin rotation study of the magnetic penetration depth in the intercalated graphite superconductor CaC6

We report temperature- and magnetic field-dependent bulk muon spin rotation measurements in a c-axis oriented superconductor CaC6 in the mixed state. Using both a simple second moment analysis and the more precise analytical Ginzburg-Landau model, we obtained a field independent in-plane magnetic penetration depth {\lambda}ab (0) = 72(3) nm. The temperature dependencies of the normalized muon spin relaxation rate and of the normalized superfluid density result to be identical, and both are well represented by the clean limit BCS model with 2\Delta/kB Tc = 3.6(1), suggesting that CaC6 is a fully gapped BCS superconductor in the clean limit regime.Comment: Accepted for publication in PR

Association of the CCR5 gene with juvenile idiopathic arthritis

The CC chemokine receptor 5 (CCR5) has been shown to be important in the recruitment of T-helper cells to the synovium, where they accumulate, drive the inflammatory process and the consequent synovitis and joint destruction. A 32 base-pair insertion/deletion variant (CCR5Δ32) within the gene leads to a frame shift and a nonfunctional receptor. CCR5Δ32 has been investigated for its association with juvenile idiopathic arthritis (JIA), with conflicting results. The aim of this study was to investigate whether CCR5Δ32 is associated with JIA in an UK population. CCR5Δ32 was genotyped in JIA cases (n=1054) and healthy controls (n=3129) and genotype and allele frequencies were compared. A meta-analysis of our study combined with previously published studies was performed. CCR5Δ32 was significantly associated with protection from developing JIA, in this UK data set (P(trend)=0.006, odds ratio (OR) 0.79 95% confidence interval (95% CI): 0.66-0.94). The meta-analysis of all published case-control association studies confirmed the protective association with JIA (P=0.001 OR 0.82 95% CI: 0.73-0.93). CCR5Δ32 is a functional variant determining the number of receptors on the surface of T cells, and it is hypothesized that the level of CCR5 expression could influence the migration of proinflammatory T cells into the synovium and thus susceptibility to JIA