National Institute Of Materials Physics - Romania

We determined the Berezinskii-Kosterlitz-Thouless transition temperature T-KT at the superconducting layer level and the mean-field critical temperature T-c0 in oxygen-deficient YBa2Cu3Oy films (y similar to 6.5, 6.55, and 6.65). We used the T dependence of the quasi-two-dimensional I-V exponent for T <= T-KT, and the analysis of the resistive transition in the framework of the Ginzburg-Landau two-dimensional Coulomb gas model for T>T-KT. Both procedures give essentially the same results, with T-c0 remaining in the domain of the electrical resistivity drop.

Exchange-coupled Nd2Fe14B/alpha-Fe nanocomposite magnets receives considerable research interest, because these are regarded as promising candidate materials for permanent magnets, with an adequate performance while keeping the content of relatively expensive Nd low. The advantage of these new magnetic materials are the lower rare earth content (and consequently, cheaper magnets with better corrosion resistance). The Nd2Fe14B/alpha-Fe nanocomposites were obtained by recrystallisation treatment from an amorphous phase prepared by melt-spinning. For Fe contents, between 83 and 85 at. %, we have obtained the hardening of the alpha-Fe phase by exchange interactions between the hard Nd2Fe14B phase and the soft alpha-Fe phase. The evolution of the structure and main magnetic characteristics after different annealing conditions was studied. For all isotropic permanent magnets obtained from the prepared nanocomposites was measured a remanence ratio higher than 0.5, which confirm the existence of the mentioned exchange interactions.

CMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider ( LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007. The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This volume demonstrates the physics capability of the CMS experiment. The prime goals of CMS are to explore physics at the TeV scale and to study the mechanism of electroweak symmetry breaking - through the discovery of the Higgs particle or otherwise. To carry out this task, CMS must be prepared to search for new particles, such as the Higgs boson or supersymmetric partners of the Standard Model particles, from the start- up of the LHC since new physics at the TeV scale may manifest itself with modest data samples of the order of a few fb(-1) or less. The analysis tools that have been developed are applied to study in great detail and with all the methodology of performing an analysis on CMS data specific benchmark processes upon which to gauge the performance of CMS. These processes cover several Higgs boson decay channels, the production and decay of new particles such as Z\' and supersymmetric particles, B-s production and processes in heavy ion collisions. The simulation of these benchmark processes includes subtle effects such as possible detector miscalibration and misalignment. Besides these benchmark processes, the physics reach of CMS is studied for a large number of signatures arising in the Standard Model and also in theories beyond the Standard Model for integrated luminosities ranging from 1 fb(-1) to 30 fb(-1). The Standard Model processes include QCD, B-physics, diffraction, detailed studies of the top quark properties, and electroweak physics topics such as the W and Z(0) boson properties. The production and decay of the Higgs particle is studied for many observable decays, and the precision with which the Higgs boson properties can be derived is determined. About ten different supersymmetry benchmark points are analysed using full simulation. The CMS discovery reach is evaluated in the SUSY parameter space covering a large variety of decay signatures. Furthermore, the discovery reach for a plethora of alternative models for new physics is explored, notably extra dimensions, new vector boson high mass states, little Higgs models, technicolour and others. Methods to discriminate between models have been investigated. This report is organized as follows. Chapter 1, the Introduction, describes the context of this document. Chapters 2-6 describe examples of full analyses, with photons, electrons, muons, jets, missing E-T, B-mesons and tau\'s, and for quarkonia in heavy ion collisions. Chapters 7-15 describe the physics reach for Standard Model processes, Higgs discovery and searches for new physics beyond the Standard Model.

Silicon detectors will be used in the next generation of experiments in high energy physics and bulk damage is the main limitation in their utilisation. Although silicon is the most studied semiconductor, and the studies of defects in silicon have a long history, until now it is not completely established what are all primary defects in silicon, and what are their properties. In this contribution we investigate the new perspective in understanding fundamental phenomena in silicon and implications for the damage of detector characteristics due to the existence of the new primary fourfold coordinated defect, with a lower value of the formation energy in respect to the "classically" known vacancies and interstitials. The effects of its existence at device level are investigated, and possible consequences for the detectors in the next generation of experiments are discussed.

The effect of ammonium polymolybdate (APM) on the corrosion of carbon steel in a solution of 1M HC1 was studied by weight loss, electrochemical measurement and Mossbauer Spectrometry. Inhibition efficiencies (P) were obtained from weight measurement and galvanostatic polarization. The inhibition efficiencies increased with concentration, but decreased with temperature. Free energies of activation (E-a for the inhibition processes were estimated from rate constant data obtained at different temperatures and different concentration of APM. Mossbauer spectrometry shows that a superficial compound is formed on the electrode surface as a result of corrosion.

Magnetic iron oxide nanoparticles have a great potential in various applications in biomedical research and technology. Iron oxide particles such as magnetite (Fe3O4) is by far the most commonly employed magnetic materials for biomedical applications. Bioceramic composites were obtained by combining the magnetite with two biocompatible components (hydroxyapatite and bioglass). Their thermal behaviour has been studied by thermal analysis (DTA and TG). The interaction of iron oxide with the bioceramic matrix has been investigated using IR spectroscopy.

Samples of (Bi,Pb)(2)Sr2Ca2Cu3O10 (Bi(Pb)-2223) phase have been fabricated from two different oxide precursors with the same stoichiometry, synthesized by solid state reaction in the air at 815 degrees C for 20 h. The first precursor was prepared by mixing Bi2O3, PbO, SrCO3, CaCO3 and CuO powders, while the second one through mixing Bi2O3 and PbO with Sr2Ca2Cu3Ox produced from SrCO3, CaCO3 and CuO powders. Pellets from the two precursors were prepared in the same conditions; heat treatment time was varied and intermediate grindings were applied. Although the maximum attained Bi(Pb)2223 phase amount was about 50% and above 90% in the samples from the two precursors, respectively, the samples from the first precursor have generally shown better superconducting properties such as the critical temperature from resistivity measurements and intragrain critical current J(cg) from magnetic susceptibility measurements. For our particular case the influence of the final heat treatment is relatively low and at the same time the precursor plays a major role in controlling growth processes and final superconducting properties. Lower room-temperature Seebeck coefficient of the thermoelectric power for the samples fabricated from the first precursor suggests that one mechanism through which this control is realized might be the modification of the oxygenation level in the samples produced from different precursors. It was also found that for the samples prepared from the two precursors, intermediate grinding after 110h or more of heat treatment enhances density, almost does not influence J(cg) (or slightly improves it), decreases T-c, and does not influence significantly the amount of Bi(Pb)-2223 phase.

The problem of the thickness dependence of the dielectric constant, as well as the extrinsic contributions to its value, is analyzed for the case of epitaxial Pb(Zr,Ti)O-3 (PZT) thin films. It is shown that the frequency dependence of the measured capacitance is best simulated by an equivalent circuit incorporating the trap-containing capacitance of a Schottky contact. The thickness dependence of the dielectric constant, calculated using the formula of a plane capacitor, appears to be an extrinsic effect due to the interface phenomena in the metal-ferroelectric-metal structure. The intrinsic dielectric constant of the PZT material seems to be thickness independent and of low value of about 30-40. This is closer to the values estimated from Raman measurements or from quantum theories of ferroelectricity. The thickness independence is also proven by piezoresponse force microscopy measurements. The presence of traps is evidenced by the presence of a photovoltaic effect at subgap wavelengths.

Field Assisted Sintering Technique (FAST) is currently used to consolidate ceramic, metal and composite powders. This method combines a pulsed electrical current with simultaneous application of an external pressure. In this article we report fabrication by FAST of high density MgB2 ceramic with addition of 5% SiC and 5% B4C. The influence of sintering conditions such as temperature and time on bulk density, morphology and superconducting properties of the samples was investigated. All samples had bulk density of more than 90% of the theoretical one and the same critical temperature T-c = 38.5 K from magnetisation measurements. These preliminary results suggest that FAST is a promising method for processing of MgB2 superconductor.

Fine-grain BaTi0.87Sn0.13O3 (BTS13) powder was synthesized from an oxalate precursor and used to prepare sintered ferroelectric BTS13 ceramics. The evolution of the morphology and structure of a BTS13 precipitate precursor as a function of temperature was analyzed. We compare the sintering behavior as well as the dielectric properties of the BTS13 ceramics obtained using uniaxial and cold isostatic pressing.