High frequency wave propagation in the earth: theory and observation

The wave-theoretical analysis of acoustic and elastic waves refracted by a spherical boundary across which both velocity and density increase abruptly and thence either increase or decrease continuously with depth is formulated in terms of the general problem of waves generated at a steady point source and scattered by a radially heterogeneous spherical body. A displacement potential representation is used for the elastic problem that results in high frequency decoupling of P-SV motion in a spherically symmetric, radially heterogeneous medium. Through the application of an earth-flattening transformation on the radial solution and the Watson transform on the sum over eigenfunctions, the solution to the spherical problem for high frequencies is expressed as a Weyl integral for the corresponding half-space problem in which the effect of boundary curvature maps into an effective positive velocity gradient. The results of both analytical and numerical evaluation of this integral can be summarized as follows for body waves in the crust and upper mantle:

1) In the special case of a critical velocity gradient (a gradient equal and opposite to the effective curvature gradient), the critically refracted wave reduces to the classical head wave for flat, homogeneous layers.

2) For gradients more negative than critical, the amplitude of the critically refracted wave decays more rapidly with distance than the classical head wave.

3) For positive, null, and gradients less negative than critical, the amplitude of the critically refracted wave decays less rapidly with distance than the classical head wave, and at sufficiently large distances, the refracted wave can be adequately described in terms of ray-theoretical diving waves. At intermediate distances from the critical point, the spectral amplitude of the refracted wave is scalloped due to multiple diving wave interference.

These theoretical results applied to published amplitude data for P-waves refracted by the major crustal and upper mantle horizons (the Pg, P*, and Pn travel-time branches) suggest that the 'granitic' upper crust, the 'basaltic' lower crust, and the mantle lid all have negative or near-critical velocity gradients in the tectonically active western United States. On the other hand, the corresponding horizons in the stable eastern United States appear to have null or slightly positive velocity gradients. The distribution of negative and positive velocity gradients correlates closely with high heat flow in tectonic regions and normal heat flow in stable regions. The velocity gradients inferred from the amplitude data are generally consistent with those inferred from ultrasonic measurements of the effects of temperature and pressure on crustal and mantle rocks and probable geothermal gradients. A notable exception is the strong positive velocity gradient in the mantle lid beneath the eastern United States (2 x 10^-3 sec^-1), which appears to require a compositional gradient to counter the effect of even a small geothermal gradient.

New seismic-refraction data were recorded along a 800 km profile extending due south from the Canadian border across the Columbia Plateau into eastern Oregon. The source for the seismic waves was a series of 20 high-energy chemical explosions detonated by the Canadian government in Greenbush Lake, British Columbia. The first arrivals recorded along this profile are on the Pn travel-time branch. In northern Washington and central Oregon their travel time is described by T = Δ/8.0 + 7.7 sec, but in the Columbia Plateau the Pn arrivals are as much as 0.9 sec early with respect to this line. An interpretation of these Pn arrivals together with later crustal arrivals suggest that the crust under the Columbia Plateau is thinner by about 10 km and has a higher average P-wave velocity than the 35-km-thick, 62-km/sec crust under the granitic-metamorphic terrain of northern Washington. A tentative interpretation of later arrivals recorded beyond 500 km from the shots suggests that a thin 8.4-km/sec horizon may be present in the upper mantle beneath the Columbia Plateau and that this horizon may form the lid to a pronounced low-velocity zone extending to a depth of about 140 km.

Surface effects in simple molecular systems

This thesis examines two problems concerned with surface effects in simple molecular systems. The first is the problem associated with the interaction of a fluid with a solid boundary, and the second originates from the interaction of a liquid with its own vapor.

For a fluid in contact with a solid wall, two sets of integro-differential equations, involving the molecular distribution functions of the system, are derived. One of these is a particular form of the well-known Bogolyubov-Born-Green-Kirkwood-Yvon equations. For the second set, the derivation, in contrast with the formulation of the B.B.G.K.Y. hierarchy, is independent of the pair-potential assumption. The density of the fluid, expressed as a power series in the uniform fluid density, is obtained by solving these equations under the requirement that the wall be ideal.

The liquid-vapor interface is analyzed with the aid of equations that describe the density and pair-correlation function. These equations are simplified and then solved by employing the superposition and the low vapor density approximations. The solutions are substituted into formulas for the surface energy and surface tension, and numerical results are obtained for selected systems. Finally, the liquid-vapor system near the critical point is examined by means of the lowest order B.B.G.K.Y. equation.

Structure and residual stress in gamma-LiAlO2, layer fabricated by vapor transport equilibration on (0001)sapphire

gamma-LiAlO2 layers with a highly preferred (1 0 0) orientation were prepared by vapor transport equilibration (VTE) technique on (0 0 0 1) sapphire substrate. Microststructure of the gamma-LiAlO2 layers was studied by XRD and SEM. In the temperature range from 750 to 1100 degrees C, the residual stress in the gamma-LiAlO2 layers varied from tensile to compressive with the increase of VTE temperature, and the critical point of the change between tensile and compressive stress is around 975 degrees C. (c) 2005 Elsevier B.V. All rights reserved.

As joint ventures na indústria do petróleo: um olhar crítico sobre a intervenção do Estado na autonomia privada

A atividade empresarial requer dos agentes econômicos soluções práticas para a transposição dos riscos inerentes ao exercício da empresa. A engenhosidade dos homens de negócio tem visualizado nos denominados contratos associativos um importante mecanismo para o sucesso do empreendimento. Na indústria do petróleo, especificamente no setor do upstream, as parcerias empresariais mostram-se como importante meio para compartilhamento dos riscos geológico, financeiro e político inerentes a esta atividade. Neste sentido o trabalho desenvolvido busca efetuar uma análise das associações empresariais, especialmente aquelas consagradas na prática como joint ventures, especificando suas peculiaridades, para posteriormente analisar a situação destas dentro do novo marco regulatório que se firma para exploração de petróleo, gás natural e outros hidrocarbonetos na região denominada de pré-sal e outras áreas estratégicas. Nesse sentido, foram analisadas as mudanças instituídas pela Lei n. 12.351/2010, a qual instituiu o modelo de partilha de produção, no qual se observou uma mudança do Estado que deixa de ser mero regulador para atuar mais diretamente, de modo a influenciar a atuação empresarial, limitando a autonomia privada no referido setor.

O egresso de enfermagem no mundo do trabalho: dimensão subjetiva entre o processo de formação e a prática laboral

O objeto deste estudo é a percepção dos egressos da Faculdade de Enfermagem da Universidade do Estado do Rio de Janeiro (ENF/UERJ) sobre o mundo do trabalho e a influência da formação na prática laboral, cujos objetivos foram: I) descrever a percepção dos egressos da ENF/UERJ sobre o mundo do trabalho em saúde e enfermagem, considerando o processo de formação na graduação; II) identificar as facilidades e as dificuldades percebidas pelos egressos na prática profissional e suas repercussões para o processo saúde-doença, considerando a configuração do mundo do trabalho; III) analisar os distanciamentos e as aproximações apontados pelos egressos entre a formação na ENF/UERJ e a configuração do mundo do trabalho em saúde e enfermagem; e IV) discutir as situações nas quais os egressos atuam e que se apresentam como real ou potencialmente transformadoras da realidade laboral em que se encontram. Pesquisa de natureza qualitativa, descritiva e exploratória, desenvolvida na ENF/UERJ e aprovado pela Plataforma Brasil, sob o número 360.021. Os participantes foram 30 egressos da ENF/UERJ, formados entre o ano 2000 no primeiro semestre até o ano de 2010 no segundo semestre. A coleta de dados ocorreu de dezembro de 2013 até fevereiro de 2014 por meio da entrevista semiestruturada. A técnica utilizada para tratamento dos dados ocorreu por meio da Análise Temática de Conteúdo, que fez emergir quatro categorias empíricas: A dinamicidade e a complexidade do mundo do trabalho contemporâneo e a formação: a ótica do egresso de enfermagem; A dialética do mundo do trabalho: facilidades e adversidades enfrentadas no cotidiano laboral e sua influência no processo saúde-doença; A formação em enfermagem e a interface com o mundo do trabalho: dilemas e desafios a superar; e Significados, habilidades e competências construídas ao longo da formação e suas repercussões na prática laboral. Conclui-se, na perspectiva dos objetivos deste estudo, que os participantes apresentam um ponto de vista crítico e uma visão macro estrutural sobre o mundo do trabalho contemporâneo aproximada da discussão de sociólogos e estudiosos do trabalho. Por conseguinte, pode-se considerar que a formação na ENF/UERJ contribuiu para a construção desta visão crítica, reflexiva e politizada sobre a realidade do trabalho que os egressos vivenciam.

Abordagens para a classificação contábil de instrumentos financeiros híbridos e/ou compostos: um estudo de caso com uma companhia aberta brasileira

Instrumentos financeiros híbridos e/ou compostos têm sido tema constante em matéria de regulação contábil. A literatura positiva apresenta uma hipótese que ajuda a compreender o porquê de algumas firmas recorrerem a ditos instrumentos para captar recursos: nível de endividamento no limite de quebra de covenants contratuais. No Brasil, firmas com registro na CVM, que se utilizaram desses instrumentos, classificando-os no patrimônio líquido, tiveram suas ITRs e/ou DFs reapresentadas e/ou republicadas por determinação da CVM. O ponto crítico de toda a discussão reside na distinção entre um item de passivo e um item de patrimônio líquido. Esse tema está disciplinado na IAS 32 (PT CPC n. 39) e presente no Discussion Paper - A review of the conceptual framework for financial reporting, emitido pelo IASB em julho de 2013, que apresenta duas abordagens que podem ser utilizadas, visando a simplificar a distinção entre um item de passivo e de patrimônio líquido: a narrow equity approach - NEA e a strict obligation approach - SOA. A adoção de cada uma dessas abordagens terá um impacto diferente nos níveis de endividamento/alavancagem e no potencial de diluição de participação dos acionistas. Este trabalho tem como objetivo investigar abordagens para a classificação contábil das debêntures mandatoriamente conversíveis em ações, vis-à-vis a IAS 32 (PT CPC n. 39) e o Discussion Paper do IASB (NEA x SOA). A metodologia adotada é um estudo de caso de uma companhia aberta brasileira, que em 2010 emitiu debêntures mandatoriamente conversíveis e efetuou uma classificação desses instrumentos considerada inadequada pelo órgão regulador. Observa-se que a strict obligation approach é a abordagem que impacta menos no nível de endividamento, enquanto a narrow equity approach é a que apresenta maior alavancagem. As evidências sugerem os covenants contratuais como possíveis indutores de tal prática, fato que está em linha com o que a literatura da área documenta como fenômeno esperado. É bem verdade que no caso concreto, houve quebra contínua de covenants contratuais, corroborando a hipótese apresentada por SILVA (2008) de que o baixo custo de violação de covenants contribua para tal situação. Alternativamente, uma possível explicação para a escolha contábil da companhia reside na complexidade da IAS 32 (PT CPC 39) e desconhecimento de suas nuances.

A coordination-based approach to elasticity of floppy and stiff random networks

We study the role of connectivity on the linear and nonlinear elastic behavior of amorphous systems using a two-dimensional random network of harmonic springs as a model system. A natural characterization of these systems arises in terms of the network coordination relative to that of an isostatic network $\delta z$; a floppy network has $\delta z<0$, while a stiff network has $\delta z>0$. Under the influence of an externally applied load we observe that the response of both floppy and rigid network are controlled by the same critical point, corresponding to the onset of rigidity. We use numerical simulations to compute the exponents which characterize the shear modulus, the amplitude of non-affine displacements, and the network stiffening as a function of $\delta z$, derive these theoretically and make predictions for the mechanical response of glasses and fibrous networks.

Optical constants of cubic GaN/GaAs(001): Experiment and modeling

The optical constants epsilon(E)=epsilon(1)(E)+iepsilon(2)(E) of unintentionally doped cubic GaN grown on GaAs(001) have been measured at 300 K using spectral ellipsometry in the range of 1.5-5.0 eV. The epsilon(E) spectra display a structure, associated with the critical point at E-0 (direct gap) and some contribution mainly coming from the E-1 critical point. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden-Munoz model dielectric function [M. Munoz et al., J. Appl. Phys. 92, 5878 (2002)]. This model is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E-0, E-0 + Delta(0) and the E-1, E-1 + Delta(1), doublet. In addition to evaluating the energy of the E-0 critical point, the binding energy (R-1) of the two-dimensional exciton related to the E-1 critical point was estimated using the effective mass/k.p theory. The line, shape of the imaginary part of the cubic-GaN dielectric function shows excitonic effects at room temperature not withstanding that the exciton was not resolved. (C) 2003 American Institute of Physics.

CHARACTERIZATION OF PHOTOCONDUCTIVE SEMICONDUCTOR SWITCHES UNDER NONLINEAR MODE CONDITION

A photoconductive semiconductor switch (PCSS) would work in a nonlinear mode under high biased electrical field. The experimental results of nonlinear critical state have shown that both the biased voltage and the laser energy may have working thresholds to turn on the nonlinear modes. The relation between the biased voltage (aid the laser energy is inverse ratio, i.e., higher biased field need lower laser energy for nonlinear mode, and vise versa. At the nonlinear critical point, the output of PCSS is unstable, as both the linear and nonlinear pulse may occur. As the laser energy and biased field increase, the PCSS would work in the nonlinear mode steadily. (C) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 56-59 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOT 10.1002/mop.24001

High quality hydrogenated amorphous silicon films with significantly improved stability

High quality hydrogenated amorphous silicon (a-Si:H) films have been prepared by a simple "uninterrupted growth/annealing" plasma enhanced chemical vapor deposition (PECVD) technique, combined with a subtle boron-compensated doping. These a-Si:H films possess a high photosensitivity over 10(6), and exhibit no degradation in photoconductivity and a low light-induced defect density after prolonged illumination. The central idea is to control the growth conditions adjacent to the critical point of phase transition from amorphous to crystalline state, and yet to locate the Fermi level close to the midgap. Our results show that the improved stability and photosensitivity of a-Si:H films prepared by this method can be mainly attributed to the formation of a more robust network structure and reduction in the precursors density of light-induced metastable defects.

Higher Moments of Net Proton Multiplicity Distributions at RHIC

200 GeV corresponding to baryon chemical potentials (mu(B)) between 200 and 20 MeV. Our measurements of the products kappa sigma(2) and S sigma, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long-range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the root s(NN) dependence of kappa sigma(2). From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for mu(B) below 200 MeV.

Power law behavior of the isotope yield distributions in the multifragmentation regime of heavy ion reactions

Isotope yield distributions in the multifragmentation regime were studied with high-quality isotope identification, focusing on the intermediate mass fragments (IMFs) produced in semiviolent collisions. The yields were analyzed within the framework of a modified Fisher model. Using the ratio of the mass-dependent symmetry energy coefficient relative to the temperature, a(sym)/T, extracted in previous work and that of the pairing term, a(p)/T, extracted from this work, and assuming that both reflect secondary decay processes, the experimentally observed isotope yields were corrected for these effects. For a given I = N - Z value, the corrected yields of isotopes relative to the yield of C-12 show a power law distribution Y (N, Z)/Y(C-12) similar to A(-tau) in the mass range 1 <= A <= 30, and the distributions are almost identical for the different reactions studied. The observed power law distributions change systematically when I of the isotopes changes and the extracted tau value decreases from 3.9 to 1.0 as I increases from -1 to 3. These observations are well reproduced by a simple deexcitation model, with which the power law distribution of the primary isotopes is determined to be tau(prim) = 2.4 +/- 0.2, suggesting that the disassembling system at the time of the fragment formation is indeed at, or very near, the critical point.

Identified particle production, azimuthal anisotropy, and interferometry measurements in Au plus Au collisions at root s(NN)=9.2 GeV

We present the first measurements of identified hadron production, azimuthal anisotropy, and pion interferometry from Au + Au collisions below the nominal injection energy at the BNL Relativistic Heavy-Ion Collider (RHIC) facility. The data were collected using the large acceptance solenoidal tracker at RHIC (STAR) detector at root s(NN) = 9.2 GeV from a test run of the collider in the year 2008. Midrapidity results on multiplicity density dN/dy in rapidity y, average transverse momentum < p(T)>, particle ratios, elliptic flow, and Hanbury-Brown-Twiss (HBT) radii are consistent with the corresponding results at similar root s(NN) from fixed-target experiments. Directed flow measurements are presented for both midrapidity and forward-rapidity regions. Furthermore the collision centrality dependence of identified particle dN/dy, < p(T)>, and particle ratios are discussed. These results also demonstrate that the capabilities of the STAR detector, although optimized for root s(NN) = 200 GeV, are suitable for the proposed QCD critical-point search and exploration of the QCD phase diagram at RHIC.

A novel approach to isoscaling: The role of the order parameter m = N-f-Z(f)/A(f)

Isoscaling is derived within a recently proposed modified Fisher model where the free energy near the critical point is described by the Landau O(m(6)) theory. In this model m = N-f-Z(f)/A(f) is the order parameter, a consequence of (one of) the symmetries of the nuclear Hamiltonian. Within this framework we show that isoscaling depends mainly on this order parameter through the 'external (conjugate) field' H. The external field is just given by the difference in chemical potentials of the neutrons and protons of the two sources. To distinguish from previously employed isoscaling relationships, this approach is dubbed: m-scaling. We discuss the relationship between this framework and the standard isoscaling formalism and point out some substantial differences in interpretation of experimental results which might result. These should be investigated further both theoretically and experimentally. (C) 2010 Elsevier B.V. All rights reserved.

Pressure effects on the thermodynamics of trans-decahydronaphthalene/polystyrene polymer solutions: Application of the Sanchez-Lacombe lattice fluid theory

The cloud-point temperatures (T-cl's) of trans-decahydronaphthalene(TD)/polystyrene (PS, (M) over bar (w) = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1-16degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol.-% polymer). The system phase separates upon cooling and T-cl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of polymer solutions under different pressures were observed for different compositions, which demonstrated that pressure has a greater effect on the TD/PS solutions when far from the critical point as opposed to near the critical point. The Sanchez-Lacombe lattice fluid theory (SLLFT) was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified PS scaling parameters can describe the thermodynamics of the TD/PS system well. Moreover the SLLFT describes the experimental results well.