Use of lithium niobate detector for measuring X-ray intensity in mammographic range

A detector system that can measure X-ray intensity in the mammographic range of 22 to 36 kVp (equivalent photon energies ofthe beam between 11 and 15 keV) is presented. It consists of a lithium mobate detector and a high-sensitivity current-to-voltage converter.

Síntese e caracterização de poliacrilamidas modificadas para utilização na indústria do petróleo

Modified polyacrylamides with ≅ 0.2 mol % of N,N-dihexylacrylamide and hydrolysis degree from 0 to 25 % were synthesized by micellar copolymerization. The hydrophobic monomer was obtained by the reaction between acryloyl chloride and N,Ndihexylamine and characterized by infrared (IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The polymer molecular structures were determined through 1H and 13C NMR spectroscopy and the polymers were studied in dilute and semi-dilute regimes by viscometry, rheometry, static light scattering and photon correlation spectroscopy, at the temperature range from 25 to 55 ºC. The data obtained by viscometry showed that the intrinsic viscosity from the hydrolyzed polymers is larger than the precursor polymers at the same ionic strength. The comparison between the charged polymers showed that the polymer with higher hydrolysis degree has a more compact structure in formation water (AFS). The increase of temperature led to an enhanced reduced viscosity to the polymers in Milli-Q water (AMQ), although, in brine, only the unhydrolyzed polymer had an increase in the reduced viscosity with the temperature, and the hydrolyzed derivatives had a decrease in the reduced viscosity. The static light scattering (SLS) analyses in salt solutions evidenced a decrease of weight-average molecular weight (⎯Mw) with the increase of the hydrolysis degree, due to the reduction of the thermodynamic interactions between polymer and solvent, which was evidenced by the decrease of the second virial coefficient (A2). The polymers showed more than one relaxation mode in solution, when analyzed by photon correlation spectroscopy, and these modes were attributed to isolated coils and aggregates of several sizes. The aggregation behavior depended strongly on the ionic strength, and also on the temperature, although in a lower extension. The polymers showed large aggregates in all studied conditions, however, their solutions did not displayed a good increase in water viscosity to be used in enhanced oil recovery (EOR) processes

Relação entre achados em neuroimagem, habilidades auditivas e metafonológicas em escolares com dislexia do desenvolvimento

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Termodinâmica de um gás de fótons no contexto de eletrodinâmicas não-lineares

The objective of this dissertation is the development of a general formalism to analyze the thermodynamical properties of a photon gas under the context of nonlinear electrodynamics (NLED). To this end it is obtained, through the systematic analysis of Maxwell s electromagnetism (EM) properties, the general dependence of the Lagrangian that describes this kind of theories. From this Lagrangian and in the background of classical field theory, we derive the general dispersion relation that photons must obey in terms of a background field and the NLED properties. It is important to note that, in order to achieve this result, an aproximation has been made in order to allow the separation of the total electromagnetic field into a strong background electromagnetic field and a perturbation. Once the dispersion relation is in hand, the usual Bose-Einstein statistical procedure is followed through which the thermodynamical properties, energy density and pressure relations are obtained. An important result of this work is the fact that equation of state remains identical to the one obtained under EM. Then, two examples are made where the thermodynamic properties are explicitly derived in the context of two NLED, Born-Infelds and a quadratic approximation. The choice of the first one is due to the vast appearance in literature and, the second one, because it is a first order approximation of a large class of NLED. Ultimately, both are chosen because of their simplicity. Finally, the results are compared to EM and interpreted, suggesting possible tests to verify the internal consistency of NLED and motivating further developement into the formalism s quantum case

Espectros fractais em sistemas nanoestruturados e cristais fotônicos

The study of the elementary excitations such as photons, phonons, plasmons, polaritons, polarons, excitons and magnons, in crystalline solids and nanostructures systems are nowdays important active field for research works in solid state physics as well as in statistical physics. With this aim in mind, this work has two distinct parts. In the first one, we investigate the propagation of excitons polaritons in nanostructured periodic and quasiperiodic multilayers, from the description of the behavior for bulk and surface modes in their individual constituents. Through analytical, as well as computational numerical calculation, we obtain the spectra for both surface and bulk exciton-polaritons modes in the superstructures. Besides, we investigate also how the quasiperiodicity modifies the band structure related to the periodic case, stressing their amazing self-similar behavior leaving to their fractal/multifractal aspects. Afterwards, we present our results related to the so-called photonic crystals, the eletromagnetic analogue of the electronic crystalline structure. We consider periodic and quasiperiodic structures, in which one of their component presents a negative refractive index. This unusual optic characteristic is obtained when the electric permissivity and the magnetic permeability µ are both negatives for the same range of angular frequency ω of the incident wave. The given curves show how the transmission of the photon waves is modified, with a striking self-similar profile. Moreover, we analyze the modification of the usual Planck´s thermal spectrum when we use a quasiperiodic fotonic superlattice as a filter.

Nuclear incoherent photoproduction of pi(0) and eta from 4 to 12 GeV

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of blood viscosity to cerebral blood flow in older humans compared to young subjects

Objective: Since blood viscosity (BV) is one of the most important factors determining blood flow, this study aimed to investigate the possible correlation between increased blood viscosity and reduction of regional cerebral blood flow (rCBF) in healthy ageing.Methods: Male subjects were distributed in two groups: "young", aged 20-30 (27 volunteers), or "elderly", aged 60-70 (50 volunteers). Whole blood viscosity was obtained with a Wells-Brookfield Cone/Plate Viscometer. Cerebral blood flow was analysed by means of single photon emission computed tomography (SPECT).Results: The mean BV values were 3.28 +/- 0.43 mPa in the group of young volunteers and 4.33 +/- 0.73 mPa in the group of elderly volunteers (t = -6.9, p < 0.0001). The elderly had a lower blood flow than the young in the following regions: bilateral parietal; temporal-parietal and temporal of the left hemisphere. Pearson's correlation between BV and rCBF showed a good inverse correlation when the BV was above 3.95 +/- 0.83 mPa.Conclusions: Our results point to a close relationship between the two parameters analysed, BV and rCBF. The impairment in rCBF observed in the elderly volunteers might be due to an increase in BV, among other factors.Significance: These findings suggest interesting possibilities for the treatment/prevention of brain ageing. (C) 2011 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

Neuroimaging in dementias

Purpose of reviewTo critically review data on the use of neuroimaging tools in the clinical diagnostic investigation of dementias.Recent findingsFor many years, the use of neuroimaging tools in the evaluation of dementias has been restricted to excluding neurosurgical lesions that may account for the cognitive decline. However, modern neuroimaging extends beyond this traditional role of excluding other conditions and has a key role in the clinical investigation of Alzheimer's disease and of other degenerative cortical dementias. MRI, PET with fluorodeoxyglucose, and single-photon emission computed tomography are topographic markers of neural damage and enable the identification of specific lesional patterns that characterize Alzheimer's disease and other cortical dementias. More recently, PET amyloid markers have enabled the in-vivo assessment of amyloid load, a key feature in the physiopathology of Alzheimer's disease.SummaryThe combined use of neuroimaging examinations with clinical, neuropsychological, and cerebrospinal fluid markers can improve the specificity of the diagnosis of Alzheimer's disease, even at early stages of the disease. In the following years, progress in research will provide standardized and validated imaging markers of Alzheimer's disease and other dementias, which may increase their application in clinical settings.

Efficiency of extrinsic and intrinsic charge-carrier photogeneration processes obtained from the steady-state photocurrent action spectra of poly(p-phenylene vinylene) derivatives

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Anomalous quartic gauge boson couplings at hadron colliders

We analyze the potential of the Fermilab Tevatron and CERN Large Hadron Collider (LHC) to study anomalous quartic vector-boson interactions gamma gamma ZZ and gammaW(+)W(-). Working in the framework of SU(2)(L) circle times U(1)(Y) chiral Lagrangians, we study the production of photon pairs accompanied by l(+) l(-), l(+/-) v, and jet pairs to impose bounds on these new couplings, taking into account the unitarity constraints. We compare our findings with the indirect limits coming from precision electroweak measurements as well as with presently available direct searches at CERN LEPII. We show that the Tevatron run II can provide limits on these quartic limits which are of the same order of magnitude as the existing bounds from LEPII searches. LHC will be able to tighten considerably the direct constraints on these possible new interactions, leading to more stringent limits than the presently available indirect ones.

Color evaporation description of inelastic photoproduction of J/psi at DESY HERA

The H1 Collaboration recently reported a new analysis of data on the inelastic photoproduction of J/psi mesons at DESY's HERA ep collider. We show that these new experimental results are well described by the color evaporation model for quarkonium production. Moreover, these new data require the introduction of resolved photon contributions in order to accommodate the results in the kinematic region where the fractional energy carried by the J/psi is small, demonstrating that colored perturbative c (c) over bar states contribute to the production of a color singlet.

Semiclassical approach to black hole absorption of electromagnetic radiation emitted by a rotating charge

We consider an electric charge, minimally coupled to the Maxwell field, rotating around a Schwarzschild black hole. We investigate how much of the radiation emitted from the swirling charge is absorbed by the black hole and show that most of the photons escape to infinity. For this purpose we use the Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman gauge developed in the context of quantum field theory in Schwarzschild spacetime. We obtain that the two photon polarizations contribute quite differently to the emitted power. In addition, we discuss the accurateness of the results obtained in a full general relativistic approach in comparison with the ones obtained when the electric charge is assumed to be orbiting a massive object due to a Newtonian force.

On high Q(2) behavior of the pion form factor for transitions gamma*gamma -> pi(0) and gamma*gamma* -> pi(0) within the nonlocal quark-pion model

The behavior of the transition pion form factor for processes gamma (*)gamma --> pi(0) and gamma (*)gamma (*) --> pi(0) at large values of space-like photon momenta is estimated within the nonlocal covariant quark-pion model. It is shown that, in general, the coefficient of the leading asymptotic term depends dynamically on the ratio of the constituent quark mass and the average virtuality of quarks in the vacuum and kinematically on the ratio of photon virtualities. The kinematic dependence of the transition form factor allows us to obtain the relation between the pion light-cone distribution amplitude and the quark-pion vertex function. The dynamic dependence indicates that the transition form factor gamma (*)gamma -->, pi(0) at high momentum transfers is very sensitive to the nonlocality size of nonperturbative fluctuations in the QCD vacuum. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Gravitational rainbow of massive particles

Photon propagation is non-dispersive within the context of semiclassical general relativity. What about the remaining massless particles? It can be shown that at the tree level the scattering of massless particles of spin 0, 1/2, 1 or whatever by a static gravitational field generated by a localized source such as the Sun, treated as an external field, is non-dispersive as well. It is amazing, however, that massive particles, regardless of whether they have integral or half-integral spin, experience an energy-dependent gravitational deflection. Therefore, semiclassical general relativity and gravitational rainbows of massive particles can coexist without conflict. We address this issue in this essay.

Gravitational rainbow

It is shown that, unlike Einstein's gravity, quadratic gravity produces dispersive photon propagation. The energy-dependent contribution to the deflection of photons passing by the Sun is computed and subsequently the angle at which the visible spectrum would be spread over is plotted as a function of the R-mu nu(2)-sector mass.