Annealing study of A1/GaSb contact with the use of doppler broadening technique

Using a monoenergetic positron beam, annealing study of the Al/n-GaSb system was performed by monitoring the Doppler broadening of the annihilation radiation as a function of the positron implanting energy. The S-parameter against positron energy data was successfully fitted by a three-layer model (Al/interface/GaSb). The annealing out of the open volume defects in the polycrystalline Al layer was revealed by the decrease in the S-parameter and the increase in the effective diffusion length of the Al layer. For the as-deposited samples, a∼5 nm interfacial region with S-parameter larger than those of the Al overlayer and the bulk was identified. After the 400^ºC annealing, this interfacial region extends to over 40 nm and its S-parameter dramatically drops. This is possibly due to the new phase formation at the interface. Annealing behaviors of SB and L+,B of the GaSb bulk showed the annealing out of positron traps (possibly the VGa-related defect) at 250ºC. However, a further annealing at 400ºC induces the formation of positron traps, which are possibly of another kind of VGa-related defect and the positron shallow trap GaSb antisite.published_or_final_versionProceedings of the 35th Polish Seminar on Positron Annihilation (PSPA), Turawa, Poland, 20-24 September 2004. In Acta Physica Polonica Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics, 2005, v. 107 n. 5, p. 874-87

Photodynamic inactivation of Klebsiella pneumoniae biofilms and planktonic cells by 5-aminolevulinic acid and 5-aminolevulinic acid methyl ester

The treatment of Klebsiella pneumoniae, particularly extended-spectrum β-lactamase (ESBL)-producing K. pneumoniae, is currently a great challenge. Photodynamic antimicrobial chemotherapy is a promising approach for killing antibiotic-resistant bacteria. The aim of this study was to evaluate the capacity of 5-aminolevulinic acid (5-ALA) and its derivative 5-ALA methyl ester (MAL) in the presence of white light to cause photodynamic inactivation (PDI) of K. pneumoniae planktonic and biofilm cells. In the presence of white light, 5-ALA and MAL inactivated planktonic cells in a concentration-dependent manner. Biofilms were also sensitive to 5-ALA and MAL-mediated PDI. The mechanisms by which 5-ALA and MAL caused PDI of ESBL-producing K. pneumonia were also investigated. Exposure of K. pneumonia to light in the presence of either 5-ALA or MAL induced cleavage of genomic DNA and the rapid release of intracellular biopolymers. Intensely denatured cytoplasmic contents and aggregated ribosomes were also detected by transmission electron microscopy. Scanning electron microscopy showed that PDI of biofilms caused aggregated bacteria to detach and that the bacterial cell envelope was damaged. This study provides insights into 5-ALA and MAL-mediated PDI of ESBL-producing K. pneumoniae

Influence of the initial chemical conditions on the rational design of silica particles

The influence of the water content in the initial composition on the size of silica particles produced using the Stöber process is well known. We have shown that there are three morphological regimes defined by compositional boundaries. At low water levels (below stoichiometric ratio of water:tetraethoxysilane), very high surface area and aggregated structures are formed; at high water content (>40 wt%) similar structures are also seen. Between these two boundary conditions, discrete particles are formed whose size are dictated by the water content. Within the compositional regime that enables the classical Stöber silica, the structural evolution shows a more rapid attainment of final particle size than the rate of formation of silica supporting the monomer addition hypothesis. The clearer understanding of the role of the initial composition on the output of this synthesis method will be of considerable use for the establishment of reliable reproducible silica production for future industrial adoption

Weight management: a comparison of existing dietary approaches in a work-site setting

<b>OBJECTIVES:</b> (1) To compare the effectiveness a 2512 kJ (600 kcal) daily energy deficit diet (ED) with a 6279 kJ (1500 kcal) generalized low-calorie diet (GLC) over a 24 week period (12 weeks weight loss plus 12 weeks weight maintenance). (2) To determine if the inclusion of lean red meat at least five times per week as part of a slimming diet is compatible with weight loss in comparison with a diet that excludes lean red meat. DESIGN: Randomized controlled trial. <b>SETTING:</b> Large petrochemical work-site. <b>PARTICIPANTS:</b> One-hundred and twenty-two men aged between 18 and 55 y. <b>MAIN OUTCOME MEASURES:</b> Weight loss and maintenance of weight loss. <b>INTERVENTION:</b> Eligible volunteers were randomized to one of the four diet=meat combinations (ED meat, ED no meat, GLC meat, GLC no meat). One-third of subjects in each diet/meat combination were randomized to an initial control period prior to receiving dietary advice. All subjects attended for review every 2 weeks during the weight loss period. For the 12 week structured weight maintenance phase, individualized energy prescriptions were re-calculated for the ED group as 1.4 (activity factor)x basal metabolic rate. Healthy eating advice was reviewed with subjects in the GLC group. All subjects were contacted by electronic mail at 2 week intervals and anthropometric and dietary information requested. <b>RESULTS:</b> No difference was evident between diet groups in mean weight loss at 12 weeks (4.3 (s.d. 3.4) kg ED group vs 5.0 (s.d. 3.5) kg GLC group, P=0.34). Mean weight loss was closer to the intended weight loss in the 2512 kJ (600 kcal) ED group. The dropout rate was also lower than the GLC group. The inclusion of lean red meat in the diet on at least five occasions per week did not impair weight loss. Mean weight gain following 12 weeks weight maintenance was þ1.1 (s.d. 1.8) kg, P<0.0001. No differences were found between groups. <b>CONCLUSIONS:</b> This study has shown that the individualized 2512 kJ (600 kcal) ED approach was no more effective in terms of weight loss than the 6279 kJ (1500 kcal) GLC approach. However the ED approach might be considered preferable as compliance was better with this less demanding prescription. In terms of weight loss the elimination of red meat from the diet is unnecessary. The weight maintenance intervention was designed as a low-input approach, however weight regain was significant and weight maintenance strategies require further development

Superconducting, Insulating, and Anomalous Metallic Regimes in a Gated Two-Dimensional Semiconductor-Superconductor Array

The superconductor-insulator transition in two dimensions has been widely investigated as a paradigmatic quantum phase transition. The topic remains controversial, however, because many experiments exhibit a metallic regime with saturating low-temperature resistance, at odds with conventional theory. Here, we explore this transition in a novel, highly controllable system, a semiconductor heterostructure with epitaxial Al, patterned to form a regular array of superconducting islands connected by a gateable quantum well. Spanning nine orders of magnitude in resistance, the system exhibits regimes of superconducting, metallic, and insulating behavior, along with signatures of flux commensurability and vortex penetration. An in-plane magnetic field eliminates the metallic regime, restoring the direct superconductor-insulator transition, and improves scaling, while strongly altering the scaling exponent

Hitting sbottom in natural SUSY

We compare the experimental prospects of direct stop and sbottom pair production searches at the LHC. Such searches for stops are of great interest as they directly probe for states that are motivated by the SUSY solution to the hierarchy problem of the Higgs mass parameter - leading to a "Natural" SUSY spectrum. Noting that sbottom searches are less experimentally challenging and scale up in reach directly with the improvement on b-tagging algorithms, we discuss the interplay of small TeV scale custodial symmetry violation with sbottom direct pair production searches as a path to obtaining strong sub-TeV constraints on stops in a natural SUSY scenario. We argue that if a weak scale natural SUSY spectrum does not exist within the reach of LHC, then hopes for such a spectrum for large regions of parameter space should sbottom out. Conversely, the same arguments make clear that a discovery of such a spectrum is likely to proceed in a sbottom up manner.Comment: 18 pages, 8 figures,v2 refs added, JHEP versio

Composite Higgs Search at the LHC

The Higgs boson production cross-sections and decay rates depend, within the Standard Model (SM), on a single unknown parameter, the Higgs mass. In composite Higgs models where the Higgs boson emerges as a pseudo-Goldstone boson from a strongly-interacting sector, additional parameters control the Higgs properties which then deviate from the SM ones. These deviations modify the LEP and Tevatron exclusion bounds and significantly affect the searches for the Higgs boson at the LHC. In some cases, all the Higgs couplings are reduced, which results in deterioration of the Higgs searches but the deviations of the Higgs couplings can also allow for an enhancement of the gluon-fusion production channel, leading to higher statistical significances. The search in the H to gamma gamma channel can also be substantially improved due to an enhancement of the branching fraction for the decay of the Higgs boson into a pair of photons.Comment: 32 pages, 16 figure

Collapse of superconductivity in a hybrid tin-graphene Josephson junction array

When a Josephson junction array is built with hybrid superconductor/metal/superconductor junctions, a quantum phase transition from a superconducting to a two-dimensional (2D) metallic ground state is predicted to happen upon increasing the junction normal state resistance. Owing to its surface-exposed 2D electron gas and its gate-tunable charge carrier density, graphene coupled to superconductors is the ideal platform to study the above-mentioned transition between ground states. Here we show that decorating graphene with a sparse and regular array of superconducting nanodisks enables to continuously gate-tune the quantum superconductor-to-metal transition of the Josephson junction array into a zero-temperature metallic state. The suppression of proximity-induced superconductivity is a direct consequence of the emergence of quantum fluctuations of the superconducting phase of the disks. Under perpendicular magnetic field, the competition between quantum fluctuations and disorder is responsible for the resilience at the lowest temperatures of a superconducting glassy state that persists above the upper critical field. Our results provide the entire phase diagram of the disorder and magnetic field-tuned transition and unveil the fundamental impact of quantum phase fluctuations in 2D superconducting systems.Comment: 25 pages, 6 figure

First observation of psi(2S)-->K_S K_L

The decay psi(2S)-->K_S K_L is observed for the first time using psi(2S) data collected with the Beijing Spectrometer (BESII) at the Beijing Electron Positron Collider (BEPC); the branching ratio is determined to be B(psi(2S)-->K_S K_L) = (5.24\pm 0.47 \pm 0.48)\times 10^{-5}. Compared with J/psi-->K_S K_L, the psi(2S) branching ratio is enhanced relative to the prediction of the perturbative QCD ``12%'' rule. The result, together with the branching ratios of psi(2S) decays to other pseudoscalar meson pairs (\pi^+\pi^- and K^+K^-), is used to investigate the relative phase between the three-gluon and the one-photon annihilation amplitudes of psi(2S) decays.Comment: 5 pages, 4 figures, 2 tables, submitted to Phys. Rev. Let