8,187 research outputs found
High quality MgB2 thin films in-situ grown by dc magnetron sputtering
Thin films of the recently discovered magnesium diboride (MgB2) intermetalic
superconducting compound have been grown using a magnetron sputtering
deposition technique followed by in-situ annealing at 830 C. High quality films
were obtained on both sapphire and MgO substrates. The best films showed
maximum Tc = 35 K (onset), a transition width of 0.5 K, a residual resistivity
ratio up to 1.6, a low temperature critical current density Jc > 1 MA/cm2 and
anisotropic critical field with gamma = 2.5 close to the values obtained for
single crystals. The preparation technique can be easily scaled to produce
large area in-situ films.Comment: 7 pages, 4 figure
Role of interband scattering in neutron irradiated MgB thin films by Scanning Tunneling Spectroscopy measurements
A series of MgB thin films systematically disordered by neutron
irradiation have been studied by Scanning Tunneling Spectroscopy. The c-axis
orientation of the films allowed a reliable determination of local density of
state of the band. With increasing disorder, the conductance peak moves
towards higher voltages and becomes lower and broader, indicating a monotonic
increase of the gap and of the broadening parameter. These results are
discussed in the frame of two-band superconductivity.Comment: The text will be submitted in Latex format, and the corresponding pdf
file should take 6 pages. There are 5 figures (eps files submitted) and 1
tabl
The VELO High Voltage System Control Software
This note describes the VELO high voltage control software. The implementation of its structure as a PVSS Finite State Machine is emphasized. The main error conditions that may occur during operation is also discussed. The VELO HV software conforms to the specification of the VELO
Ensemble-averaged Rabi oscillations in a ferromagnetic CoFeB film
Rabi oscillations describe the process whereby electromagnetic radiation interacts coherently with spin states in a non-equilibrium interaction. To date, Rabi oscillations have not been studied in one of the most common spin ensembles in nature: spins in ferromagnets. Here, using a combination of femtosecond laser pulses and microwave excitations, we report the classical analogue of Rabi oscillations in ensemble-averaged spins of a ferromagnet. The microwave stimuli are shown to extend the coherence-time resulting in resonant spin amplification. The results we present in a dense magnetic system are qualitatively similar to those reported previously in semiconductors which have five orders of magnitude fewer spins and which require resonant optical excitations to spin-polarize the ensemble. Our study is a step towards connecting concepts used in quantum processing with spin-transport effects in ferromagnets. For example, coherent control may become possible without the complications of driving an electromagnetic field but rather by using spin-polarized currents
Condicionantes jurÃdicos y polÃtico-normativos en la organización y gestión del espacio neuquino
El municipio es por definición la entidad jurÃdico-administrativa y polÃtica asentada en un espacio territorial determinado, con capacidad y autonomÃa para atender las necesidades básicas de la comunidad que habita en dicho territorio, con un gobierno propio, democrático y representativo y con una sociedad local que cuenta con derechos y capacidades para tomar decisiones o de influir sobre ellas, y de controlar directa o indirectamente las decisiones que tomen los entes gubernamentales locales. En otras palabras es el ente más vinculado a las demandas, necesidades e intereses de la población, al mismo tiempo que es el órgano de representación y participación ciudadana. Pero debido al fuerte centralismo del poder provincial el municipio neuquino, es una de las instancias más debilitadas.Fil: Capua, Olga C. Universidad Nacional del Comahue. Facultad de Humanidades. Departamento de GeografÃa; Argentina
A new generation photodetector for astroparticle physics: the VSiPMT
The VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an innovative design we
proposed for a revolutionary photon detector. The main idea is to replace the
classical dynode chain of a PMT with a SiPM (G-APD), the latter acting as an
electron detector and amplifier. The aim is to match the large sensitive area
of a photocathode with the performance of the SiPM technology. The VSiPMT has
many attractive features. In particular, a low power consumption and an
excellent photon counting capability. To prove the feasibility of the idea we
first tested the performance of a special non-windowed SiPM by Hamamatsu (MPPC)
as electron detector and current amplifier. Thanks to this result Hamamatsu
realized two VSiPMT industrial prototypes. In this work, we present the results
of a full characterization of the VSiPMT prototype
The Transmissibility of Highly Pathogenic Avian Influenza in Commercial Poultry in Industrialised Countries
BACKGROUND: With the increased occurrence of outbreaks of H5N1 worldwide there is concern that the virus could enter commercial poultry farms with severe economic consequences. METHODOLOGY/PRINCIPAL FINDINGS: We analyse data from four recent outbreaks of highly pathogenic avian influenza (HPAI) in commercial poultry to estimate the farm-to-farm reproductive number for HPAI. The reproductive number is a key measure of the transmissibility of HPAI at the farm level because it can be used to evaluate the effectiveness of the control measures. In these outbreaks the mean farm-to-farm reproductive number prior to controls ranged from 1.1 to 2.4, with the maximum farm-based reproductive number in the range 2.2 to 3.2. Enhanced bio-security, movement restrictions and prompt isolation of the infected farms in all four outbreaks substantially reduced the reproductive number, but it remained close to the threshold value 1 necessary to ensure the disease will be eradicated. CONCLUSIONS/SIGNIFICANCE: Our results show that depending on the particular situation in which an outbreak of avian influenza occurs, current controls might not be enough to eradicate the disease, and therefore a close monitoring of the outbreak is required. The method we used for estimating the reproductive number is straightforward to implement and can be used in real-time. It therefore can be a useful tool to inform policy decisions
Scanning Tunneling Spectroscopy study of paramagnetic superconducting β’’-ET4[(H3O)Fe(C2O4)3]•C6H5Br crystals
Scanning tunnelling spectroscopy (STS) and microscopy (STM) were performed on the paramagnetic molecular superconductor beta''-ET4[(H3O)Fe(C2O4)(3)]C6H5Br. Under ambient pressure, this compound is located near the boundary separating superconducting and insulating phases of the phase diagram. In spite of a strongly reduced critical temperature T-c (T-c = 4.0 K at the onset, zero resistance at T-c = 0.5 K), the low temperature STS spectra taken in the superconducting regions show strong similarities with the higher T-c ET kappa-derivatives series. We exploited different models for the density of states (DOS), with conventional and unconventional order parameters to take into account the role played by possible magnetic and non-magnetic disorder in the superconducting order parameter. The values of the superconducting order parameter obtained by the fitting procedure are close to the ones obtained on more metallic and higher T-c organic crystals and far above the BCS values, suggesting an intrinsic role of disorder in the superconductivity of organic superconductors and a further confirmation of the non-conventional superconductivity in such compounds
Peptide-chelating agent conjugate for selective targeting of somatostatin receptor type1: Synthesis and characterization
Previously reported results suggest that the analogue of the somatostatin des-AA 1,2,5[D-Trp 8,IAmp 9]-somatostatin (CH-275) peptide bearing chelating agents able to coordinate radioactive metals could be used for scintigraphic imaging of tumor lesions overexpressing sstr1. An efficient synthetic procedure for the preparation of the somatostatin analogue CH-275 and its conjugate DTPAGlu-Gly-CH-275, bearing the chelating agent DTPAGlu (DTPAGlu = N,N-bis[2-[bis(carboxy-ethyl)amino]ethyl]-L-glutamic acid) on the N-terminus, by solid-phase peptide synthesis and 9-flourenymethyoxycarbonyl (Fmoc) chemistry, is here reported. Rapid and efficient labeling of DTPAGlu-Gly-CH-275 was achieved by addition of IIIIn(III) to the compound. Typical yields were greater than 97% as determined by reversed phase high performance liquid chromatography (HPLC) at specific activities in the range 4-9 GBq/μmol (100-250 Ci/mmol). A preliminary biological assay of the binding ability of IIIIn-DTPAGlu-Gly-CH-275 indicates, however, that the labeled compound does not display any specific interaction with somatostatin sstrl receptors in the tested cell lines. To confirm this unexpected negative result, competition binding experiments were carried out, in which fixed tracer amounts of the 125!-labeled somatostatin-14 were incubated with the receptor-expressing cells in the presence of DTPAGlu-Gly-CH-275 or CH-275 at concentrations ranging from 10 -10 to 10 -3 M. While CH-275 shows a IC 50 of 80 nM similar to that already found in displacement experiments on CHO-Kl sstrl-transfected cells, DTPAGlu-Gly-CH-275 displays instead very low or negligible affinity towards this receptor. The NMR solution characterization indicates that the presence of DTPAGlu does not influence the conformational and chemical features of the peptide moiety, thus suggesting that the loss in binding activity should be due to steric hindrance of either the chelating agent DTPAGlu or its indium comple
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