303 research outputs found
Topics on the geometry of D-brane charges and Ramond-Ramond fields
In this paper we discuss some topics on the geometry of type II superstring
backgrounds with D-branes, in particular on the geometrical meaning of the
D-brane charge, the Ramond-Ramond fields and the Wess-Zumino action. We see
that, depending on the behaviour of the D-brane on the four non-compact
space-time directions, we need different notions of homology and cohomology to
discuss the associated fields and charge: we give a mathematical definition of
such notions and show their physical applications. We then discuss the problem
of corretly defining Wess-Zumino action using the theory of p-gerbes. Finally,
we recall the so-called *-problem and make some brief remarks about it.Comment: 29 pages, no figure
Regression of murine lung tumors by the let-7 microRNA.
MicroRNAs (miRNAs) have recently emerged as an important new class of cellular regulators that control various cellular processes and are implicated in human diseases, including cancer. Here, we show that loss of let-7 function enhances lung tumor formation in vivo, strongly supporting the hypothesis that let-7 is a tumor suppressor. Moreover, we report that exogenous delivery of let-7 to established tumors in mouse models of non-small-cell lung cancer (NSCLC) significantly reduces the tumor burden. These results demonstrate the therapeutic potential of let-7 in NSCLC and point to miRNA replacement therapy as a promising approach in cancer treatment
Etiological diagnosis, prognostic significance and role of electrophysiological study in patients with Brugada ECG and syncope.
BACKGROUND: Syncope is considered a risk factor for life-threatening arrhythmias in Brugada patients. Distinguishing a benign syncope from one due to ventricular arrhythmias is often difficult, unless an ECG is recorded during the episode. Aim of the study was to analyze the characteristics of syncopal episodes in a large population of Brugada patients and evaluate the role of electrophysiological study (EPS) and the prognosis in the different subgroups. METHODS AND RESULTS: One hundred ninety-five Brugada patients with history of syncope were considered. Syncope were classified as neurally mediated (group 1, 61%) or unexplained (group 2, 39%) on the basis of personal and family history, clinical features, triggers, situations, associated signs, concomitant therapy. Most patients underwent EPS; they received ICD or implantable loop-recorder on the basis of the result of investigations and physician's judgment. At 62±45months of mean follow-up, group 1 showed a significantly lower incidence of arrhythmic events (2%) as compared to group 2 (9%, p<0.001). Group 2 patients with positive EPS showed the highest risk of arrhythmic events (27%). No ventricular events occurred in subjects with negative EPS. CONCLUSION: Etiological definition of syncope in Brugada patients is important, as it allows identifying two groups with different outcome. Patients with unexplained syncope and ventricular fibrillation induced at EPS have the highest risk of arrhythmic events. Patients presenting with neurally mediated syncope showed a prognosis similar to that of the asymptomatic and the role of EPS in this group is unproven
A Combined Ion Implantation/Nanosecond Laser Irradiation Approach towards Si Nanostructures Doping
The exploitation of Si nanostructures for electronic and optoelectronic devices depends on their electronic doping. We investigate a methodology for As doping of Si nanostructures taking advantages of ion beam implantation and nanosecond laser irradiation melting dynamics. We illustrate the behaviour of As when it is confined, by the implantation technique, in a SiO2/Si/SiO2multilayer and its spatial redistribution after annealing processes. As accumulation at the Si/SiO2interfaces was observed by Rutherford backscattering spectrometry in agreement with a model that assumes a traps distribution in the Si in the first 2-3 nm above the SiO2/Si interfaces. A concentration of 1014 traps/cm2has been evaluated. This result opens perspectives for As doping of Si nanoclusters embedded in SiO2since a Si nanocluster of radius 1 nm embedded in SiO2should trap 13 As atoms at the interface. In order to promote the As incorporation in the nanoclusters for an effective doping, an approach based on ion implantation and nanosecond laser irradiation was investigated. Si nanoclusters were produced in SiO2layer. After As ion implantation and nanosecond laser irradiation, spectroscopic ellipsometry measurements show nanoclusters optical properties consistent with their effective doping
Molybdenum sputtering film characterization for high gradient accelerating structures
Technological advancements are strongly required to fulfill the demands of
new accelerator devices with the highest accelerating gradients and operation
reliability for the future colliders. To this purpose an extensive R&D
regarding molybdenum coatings on copper is in progress. In this contribution we
describe chemical composition, deposition quality and resistivity properties of
different molybdenum coatings obtained via sputtering. The deposited films are
thick metallic disorder layers with different resistivity values above and
below the molibdenum dioxide reference value. Chemical and electrical
properties of these sputtered coatings have been characterized by Rutherford
backscattering, XANES and photoemission spectroscopy. We will also present a
three cells standing wave section coated by a molybdenum layer 500 nm
thick designed to improve the performance of X-Band accelerating systems.Comment: manuscript has been submitted and accepted by Chinese Physics C
(2012
Avaliação do excesso de casos de tuberculose atribuídos a infecção HIV/AIDS: ensaio preliminar
Optimizing Sewage Sludge Digestion in Wastewater Treatment Plants: a Case Study from the Largest WWTP in Italy
This study is part of a multi-objective, integrated approach to analyze various possibilities for increasing energy efficiency of the largest Italian wastewater treatment plant (WWTP) at Castiglione Torinese, NW Italy. The final goal of this study was evaluating the optimization interventions on the sludge treatment process in terms of mass, energy and greenhouse gas (GHG) emission balance. An optimization scenario of sludge digestion was simulated and compared the present operating situation. In the optimized scenario, a hybrid thermo-chemical pre-treatment of the waste activated sludge (WAS) entering the digestion process was considered. The biogas produced was upgraded to biomethane with a process working with selective membranes. Full scale simulation of the whole sewage sludge treatment line was performed with the screening model MCBioCH4, developed by the Authors. The results showed that the optimization interventions would provide two important positive impacts. Firstly, a reduction of the sludge volume entering into the digestion process. Secondly, biomethane production would be around 20% higher than the methane fraction contained in the biogas actually produced. The energy saving and the increased specific biomethane production would improve the overall GHG balance of the system
Emergency management of iatrogenic arterial injuries with a low-profile balloon-expandable stent-graft: Preliminary results
Classifying A-field and B-field configurations in the presence of D-branes
We "solve" the Freed-Witten anomaly equation, i.e., we find a geometrical
classification of the B-field and A-field configurations in the presence of
D-branes that are anomaly-free. The mathematical setting being provided by the
geometry of gerbes, we find that the allowed configurations are jointly
described by a coset of a certain hypercohomology group. We then describe in
detail various cases that arise according to such classification. As is
well-known, only under suitable hypotheses the A-field turns out to be a
connection on a canonical gauge bundle. However, even in these cases, there is
a residual freedom in the choice of the bundle, naturally arising from the
hypercohomological description. For a B-field which is flat on a D-brane,
fractional or irrational charges of subbranes naturally appear; for a suitable
gauge choice, they can be seen as arising from "gauge bundles with not integral
Chern class": we give a precise geometric interpretation of these objects.Comment: 28 pages, no figure
Atomic Force Microscopy Study of the Kinetic Roughening in Nanostructured Gold Films on SiO2
Dynamic scaling behavior has been observed during the room-temperature growth of sputtered Au films on SiO2using the atomic force microscopy technique. By the analyses of the dependence of the roughness, σ, of the surface roughness power,P(f), and of the correlation length,ξ, on the film thickness,h, the roughness exponent,α = 0.9 ± 0.1, the growth exponent,β = 0.3 ± 0.1, and the dynamic scaling exponent,z = 3.0 ± 0.1 were independently obtained. These values suggest that the sputtering deposition of Au on SiO2at room temperature belongs to a conservative growth process in which the Au grain boundary diffusion plays a dominant role
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