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Brazilian Journal of Physics, Volume: 40, Número: 2, Publicado: 2010
  • Construction and experimental study of a 2.5kJ, simply configured, mather type plasma focus device

    Shirani, B.; Abbasi, F.

    Resumo em Inglês:

    In this work, a 2.5kJ plasma focus device (named as SBUPF1) has been constructed on the basis of a simple configuration. The most important characteristics of this configuration is relative simplicity and using less components in its structure compared with common configurations. SBUPF1 has been tested between 18-25kV and wide range of pressure for various gases including Argon, Neon and Deuterium. The system shows consistent and reproducible plasma focusing action as well as fusion neutron production (when deuterium is used as working gas).
  • Controlling nonholonomic Chaplygin systems

    Antunes, Antonio Carlos Baptista; Sigaud, Cássio; Moraes, Pedro Claudio Guaranho de

    Resumo em Inglês:

    In this paper we deal with the problem of controlling some Chaplygin systems in the framework of the vakonomic approach for nonholonomic systems. Equations of motion for these systems are obtained which contain a free parameter that permits to control the system. It is show that given a prescribed path it is possible to determine the parameter of control which inserted in the equations of motion compel the trajectory of the system to follow the input function.
  • Power and efficiency performances of a micro thermal Brownian heat engine with and without external forces

    Ding, Zemin; Chen, Lingen; Sun, Fengrui

    Resumo em Inglês:

    Power and efficiency performances of a thermal Brownian heat engine, which consists of Brownian particles moving in a periodic sawtooth potential with and without external forces and contacting with alternating hot and cold reservoirs along the space coordinate, are studied in this paper. The performance characteristics are obtained by numerical calculations. It is shown that due to the heat flow via the change of kinetic energy of the particles, the Brownian heat engine is always irreversible and the efficiency can never approach the Carnot efficiency. The influences of the operation parameters, i.e. barrier height of the potential, asymmetry of the potential and temperature ratio of the heat reservoirs on the power output, the efficiency and the current performances of the Brownian heat engine are investigated in detail by numerical analysis. When there is no external force, the power output versus efficiency characteristic curves are closed loop-shaped ones, which are similar to those of real conventional irreversible heat engines; whereas when the external force is considered, the power output versus efficiency characteristic curves of the heat engine changed into open loop-shaped ones. Furthermore, the limited regions of the external force and barrier height of the potential are explored by analyzing the current property of the model. It is shown that by reasonable choice of the parameters, the Brownian heat engine can be controlled to operate in the optimal regimes.
  • Domain wall, stiff matter and ultra-relativistic particles from a generalized double-component dark energy model

    Rami, El-Nabulsi Ahmad

    Resumo em Inglês:

    This letter discusses a modified Friedmann-Robertson-Walker cosmology in which the equation of state behaves like p = 3ηa m ρn -ρ,(η,m,n) ∈ <img src="/img/revistas/bjp/v40n2/a04img01.gif" align="absmiddle">. Many interesting features are revealed in particular the manifestation of domain wall, cosmic string, stiff matter, dust and radiation/ultra-relativistic particles.
  • 10-dimensional cosmology with Gauss-Bonnet gravity in generalized scalar-tensor theories from superstring theories

    Rami, El-Nabulsi Ahmad

    Resumo em Inglês:

    Superstring theories are promising candidates for unifying gravity with all matter interactions. In this work, we discussed a particular 10-dimensional cosmology based on Gauss-Bonnet invariant term coupled to a generalized scalar-tensor theory as resulting from superstring theories. Some interesting features concerning the late-time dynamics are explored and described in some details.
  • On the modelling of rotational effects in the lower convective region of the sun

    Cavus, H.; Karafistan, A.I.

    Resumo em Inglês:

    The purpose of this work is to study effects of differential rotation in the lower convective region of the Sun. Similar to MHD case; the governing equations are separated in variables, allowing numerical integration in this layer. This algorithm facilitates solutions of more complicated systems, with less computing time. Two different known rotation profiles are used in order to fit the model. The fitting procedure is accomplished by making use of sphericity and density shape parameters related to the rotation profiles. It is also shown that the most important feature of rotation is to break the spherical symmetric distribution of density in this layer. As in the MHD effects found before, differential rotation changes considerably the density of the reference model for both cases.
  • Adiabatic index of hot and cold compact objects

    Casali, R. H.; Menezes, D. P.

    Resumo em Inglês:

    In the present work we calculate the adiabatic index of neutron stars formed by hadronic or quarkionic matter, under two possible conditions, with and without trapped neutrinos, and for two values of the entropy per baryon S = 0,2 kB/ baryon. We use the nonlinear Walecka model to describe hadronic stars, and the MIT bag model to describe quark stars. Particle fractions for each case are obtained and the appearance of particles are compared with drops in the adiabatic index, whenever possible.
  • On the calculation of inner products of Schur functions

    Alcarás, J.A. Castilho; Kota, V.K.B.

    Resumo em Inglês:

    Two methods for calculating inner products of Schur functions in terms of outer products and plethysms are given and they are easy to implement on a machine. One of these is derived from a recent analysis of the SO(8) proton-neutron pairing model of atomic nuclei. The two methods allow for generation of inner products for the Schur functions of degree up to 20 and even beyond.
  • Contribution of adiabatic phases to noncyclic evolution

    Thomaz, M.T.; Aguiar Pinto, A.C.; Moutinho, M.

    Resumo em Inglês:

    We show that the difference of adiabatic phases, that are basis-dependent, in noncyclic evolution of non-degenerate quantum systems have to be taken into account to give the correct interference result in the calculation of physical quantities in states that are a superposition of instantaneous eigenstates of energy. To verify the contribution of those adiabatic phases in the interference phenomena, we consider the spin-1/2 model coupled to a precessing external magnetic field. In the model, the adiabatic phase increases in time up to reach the difference of the Berry's phases of the model when the external magnetic field completes a period.
  • Dynamic radiation force of acoustic waves on absorbing spheres

    Silva, Glauber T.

    Resumo em Inglês:

    We present a theoretical study on how dynamic radiation force of acoustic waves actuates on absorbing spheres. We consider the radiation force is generated by the difference-frequency component of a bichromatic plane wave in a lossless fluid. We analyze the spectrum of the dynamic radiation force for polymethymethacrylate (lucite) and polyethylene spheres. Results reveal that absorption cause the appearance of resonances in the spectrum of the force. The information associated to the resonances might be useful in radiation force techniques for nondestructive material evaluation and biological tissue characterization.
  • Vacuum energies and multipole interactions

    Barone, F.A.; Flores-Hidalgo, G.

    Resumo em Inglês:

    In this paper, we present a quantum-field-theoretical description of the interaction between stationary and localized external sources linearly coupled to bosonic fields (specifically, we study models with a scalar and the Maxwell field). We consider external sources that simulate not only point charges but also higher-multipole distributions along D-dimensional branes. Our results complement the ones previously obtained in reference [1].
  • Conductivity fluctuations of polycrystalline Ag-doped YBa2Cu3O7-δ superconductor

    Azambuja, Paula de; Rodrigues Júnior, Pedro; Jurelo, Alcione Roberto; Costa, Rosângela Menegotto

    Resumo em Inglês:

    Systematic conductivity measurements near T C in granular Ag-doped YBa2Cu3O7-δ superconductors are presented. Silver doped YBa2Cu3O7-δ samples were produced by different routes and characterized by X-ray diffraction, dc magnetization and electrical resistivity. The results were analyzed in terms of the temperature derivative of the resistivity and of the logarithmic temperature derivative of the conductivity, that allowed identifying power-law divergences in the conductivity. The results show that the resistive transition proceeds in two stages. In the normal phase, Gaussian and critical fluctuation conductivity regimes were identified. Close to the zero-resistance temperature, a coherence transition related to the connective nature of the granular samples was evidenced. It was not observed significant differences in critical and Gaussian fluctuations between pure and Ag-doped YBa2Cu3O7-δ polycrystalline samples.
  • Effect of Mo interlayer on magnetic properties of exchange coupled Sm-Co/Fe bilayers

    Shahzad, Furrukh; Siddiqi, Saadat Anwar; Yan, Shi-Shen; Jing, Xu; Hong-liang, Bai; Min-jian, Tang; Peng-fei, Xing; Shu-min, He; Tong-shuai, Xu

    Resumo em Inglês:

    Sm-Co/Fe, hard/soft magnetic bilayers have been fabricated on 70 nm Cr buffered Si (100) substrate by dc and rf magnetron sputtering and annealed at 525O C for 30min. Very thin Mo layers (0-0.7 nm) were introduced between Sm-Co and Fe layers. The samples were analyzed by X-Ray Diffraction (XRD) and Alternating Gradient Magnetometer (AGM). All of the samples showed strong exchange coupling between hard and soft magnetic phases. Magnetization, coercivity and energy product (BH)max suggest a sinusoidal behavior. The energy product was found increased to 45% for 0.3 nm Mo interlayer as compared to sample without Mo layer.
  • Structural studies of liquid alkaline-earth metals: A molecular dynamics approach

    Baria, J. K.; Janib, A. R.

    Resumo em Inglês:

    In the present research article we have studied various properties like binding energy, the pair distribution function g(r), the structure factor S(q), specific heat at constant volume, and coordination number of alkaline-earth metals (Be, Mg, Ca, Sr, and Ba) near melting point temperature using molecular dynamics (MD) simulation technique with a pseudopotential proposed by us. Good agreement with the experiment is achieved for the binding energy, pair distribution function, and structure factor and these results compare favorably with the results obtained by other such calculations, showing the transferability of the pseudopotential used from solid to liquid environment in the case of alkaline-earth metals.
  • Kinematic self-similar solutions of locally rotationally symmetric spacetimes

    Sharif, M.; Amir, M. Jamil

    Resumo em Inglês:

    This paper contains locally rotationally symmetric kinematic self-similar perfect fluid and dust solutions. We consider three families of metrics which admit kinematic self-similar vectors of the first, second, zeroth and infinite kinds, not only for the tilted fluid case but also for the parallel and orthogonal cases. It is found that the orthogonal case gives contradiction both in perfect fluid and dust cases for all the three metrics while the tilted case reduces to the parallel case in both perfect fluid and dust cases for the second metric. The remaining cases give self-similar solutions of different kinds. We obtain a total of seventeen independent solutions out of which two are vacuum. The third metric yields contradiction in all the cases.
  • Comparative vibrational spectra of pilosine and epiisopilosine crystals

    Bento, R.R.F.; Silva, L.E. da; Faria, J.L.B.; Freire, P.T.C.; de Oliveira, M.C.F.; Romero, N.R.; Teixeira, A.M.R.; Pontes, F.M.

    Resumo em Inglês:

    This paper describes the study of two alkaloids extracted from Pilocarpus Microphyllus (Rutaceae): pilosine and epiisopilosine. These substances have potential application in the treatment of several diseases. In this work FT-Raman and the FT-IR spectra of pilosine and epiisopilosine were investigated at 300 K. Vibrational wavenumber and wave vector have been predicted using density functional theory (B3LYP) calculations with the 6-31 G(d,p) basis set. A comparison with experiment, allowed us to assign most of the normal modes of the crystals.
  • Nonlinear thermotropic and thermo-optical behaviour of planar oriented textures in nematic liquid crystals at phase transitions

    Avci, Nejmettin; Nesrullajev, Arif; Oktik, Şener

    Resumo em Inglês:

    Thermotropic, thermo-morphologic and thermo-optical properties of the planar oriented nematic liquid crystals have been investigated for large temperature interval and especially for the direct nematic - isotropic liquid and the reverse isotropic liquid - nematic phase transition regions. Temperature dependences of the optical transmission, absorption coefficient and optical birefringence for both heating and cooling processes were obtained. Nonlinear thermotropic and thermo-optical behaviour and temperature hysteresis for the optical transmission, absorption coefficient and optical birefringence at the phase transitions has been found.
  • Multiloop calculations with implicit regularization in massless theories

    Dias, E. W.; Scarpelli, A. P. Baêta; Brito, L. C. T.; Fargnoli, H. G.

    Resumo em Inglês:

    We establish a systematic way to calculate multiloop amplitudes of infrared safe massless models with Implicit Regularization (IR), with a direct cancelation of the fictitious mass introduced by the procedure. The ultraviolet content of such amplitudes have a simple structure and its separation permits the identification of all the potential symmetry violating terms, the surface terms. Moreover, we develop a technique for the calculation of an important kind of finite multiloop integral which seems particularly convenient to use Feynman parametrization. Finally, we discuss the Implicit Regularization of infrared divergent amplitudes, showing with an example how it can be dealt with an analogous procedure in the coordinate space.
  • The quantization of galilean duffin-kemmer-petiau field

    Abreu, L.M.; Ferreira, F.J.S.; Santos, E.S.

    Resumo em Inglês:

    We study the quantization of the Galilean covariant Duffin-Kemmer-Petiau (DKP) field in a five-dimensional manifold. The quantization is performed both in the canonical and in the path-integral scenario. It is considered a representation of the Duffin-Kemmer-Petiau matrices which provides the scalar sector of the model, generating the manifestly Galilei-covariant version of the quantized Schrödinger field in a consistent way. Besides, an analysis of the Green's function is done, as well as the basis of the interacting DKP field.
  • Basic quantum mechanics for three Dirac equations in a curved spacetime

    Arminjon, Mayeul; Reifler, Frank

    Resumo em Inglês:

    We study the basic quantum mechanics for a fully general set of Dirac matrices in a curved spacetime by extending Pauli's method. We further extend this study to three versions of the Dirac equation: the standard (Dirac-Fock-Weyl or DFW) equation, and two alternative versions, both of which are based on the recently proposed linear tensor representations of the Dirac field (TRD). We begin with the current conservation: we show that the latter applies to any solution of the Dirac equation, iff the field of Dirac matrices γµ satisfies a specific PDE. This equation is always satisfied for DFW with its restricted choice for the γµ matrices. It similarly restricts the choice of the γµ matrices for TRD. However, this restriction can be achieved. The frame dependence of a general Hamiltonian operator is studied. We show that in any given reference frame with minor restrictions on the spacetime metric, the axioms of quantum mechanics impose a unique form for the Hilbert space scalar product. Finally, the condition for the general Dirac Hamiltonian operator to be Hermitian is derived in a general curved spacetime. For DFW, the validity of this hermiticity condition depends on the choice of the γµ matrices.
  • Effect of particle size on nonlinear refractive index of Au nanoparticle in PVA solution

    Shahriari, Esmaeil; Yunus, W.Mahmood Mat; Saion, Elias

    Resumo em Inglês:

    Nonlinear refractive index of Au nanoparticle suspended in PVA solution was measured using a single beam Z-scan technique. Measurements were carried out using a green CW laser beam operated at 532 nm as excitation source. Five nanoparticle samples with different particle sizes were prepa red by γ radiation method. The Au nano-fluid shows a good third order nonlinear response for particle sizes ranging from 7.0 nm to 18.7 nm. The sign of the nonlinear refractive index was found to be negative and the magnitude was in the order of 10-8 cm²/W. The results show that the nonlinear effect tends to be increased linearly with the increasing of particle sizes thus could be a good candidate for nonlinear optical devices.
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