Brazilian Journal of Physics via MedWorm.com

Optical and electrical diagnostics of microdischarges at moderate to high pressure in argon

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

Microdischarges at moderate to high pressure in argon were investigated. A hole opening diameter of 500 µm direct current (dc) microhollow cathode discharges (MHCD) were characterized by electrical measurements and optical emission spectroscopy (OES) for pressures ranging between 90 and 800 Torr and current from 5 to 20 mA. Current-voltage characteristic curves were obtained as a function of the pressure for this hole diameter. MHCD enables stable dc discharges for molybdenum electrodes material at constant Ar + 2%H2 flow of 0.03 l/min. Optical emission spectroscopy and analysis of the spectral line broadening of plasma line emissions were performed in order to measure gas discharge parameters. Electron number densities were obtained from Hβ Balmer line ( ~ 10(14) cm-3). For the above me...

Effect of thermo-mechanical parameters on microstructure and mechanical properties of microalloyed steels

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

In this work the effects of controlled rolling parameters and adding of Niobium have been studied. In this order two steel grades with and without Niobium are planed and after steelmaking and continuous casting, rolling process are done. Then, laboratory investigations such as microstructure, mechanical properties and grain size analysis were performed Tensile and Charpy impact tests specimens were machined out of the central part of the rolled billets. The microstructure of the specimens was examined for each experimental condition using optical microscopy. The results indicate that increasing the reheating temperature above the dissolution temperature of Nb (C, N) improved the impact energy values. By increasing the cooling rate from 0.5 to 1.5 ºC/s both tensile strength and impact toug...

Experimental study of low-pressure nitrogen dielectric barrier discharge

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

The electrical and spectral characteristics of a dielectric barrier discharge (DBD) are experimentally investigated in a sealed off coaxial cylinder filled with nitrogen at a pressure of 10 mbar. The discharge is a transient diffused glow at low frequency alternating voltage (60 Hz) and changes to a filamentary mode at high frequency alternating voltage (35 kHz). In case of pulsed voltage, the discharge is always transient diffused glow at any frequency. The intensity of a second positive system (SPS) of the nitrogen molecule has been also measured to characterize the discharge excitation. The effective vibrational temperature is estimated from the SPS vibrational band, Δv = -2. It is concluded that the intensity of the SPS of the nitrogen and the effective vibrational temperature depends...

Vortex dynamics equation in type-II superconductors in a temperature gradient

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

In this work we determined a vortex dynamics equation in a temperature gradient in the frame of the time dependent Ginzburg-Landau equation. In this sense, we derived a local solvability condition, which governs the vortex dynamics. Also, we calculated the explicit form for the force coefficients, which are the keys for the understanding of the balance equation due to vortex interactions with the environment. (Source: Brazilian Journal of Physics)

Radiatively induced non linearity in the Walecka model

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

We evaluate the effective potential for the conventional linear Walecka non perturbatively up to one loop. This quantity is then renormalized with a prescription which allows finite vacuum contributions to the three as well as four 1PI Green's functions to survive. These terms, which are absent in the standard relativistic Hartree approximation, have a logarithmic energy scale dependence that can be tuned so as to mimic the effects of ø³ and ø4 type of terms present in the non linear Walecka model improving quantities such as the compressibility modulus and the effective nucleon mass, at saturation, by considering energy scales which are very close to the nucleon mass at vanishing density. (Source: Brazilian Journal of Physics)

Study of the structure of free radicals in gamma: irradiated amino acid derivatives

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

Electron paramagnetic resonance spectroscopy has been used for the study of the free radicals produced in the powders of L-arginine monohydrochloride, ala-ala and DL-β-leucine gamma-irradiated at room temperature. The structures of the radicals formed in compounds were determined as NH2(NH)NHCHCH2CH2CH(NH2)COOH, CH3CHCOOH and (CH3)2C CH(NH2)CH2COOH respectively. The paramagnetic species were found to be stable at room temperature more than three months. It was determined that unpaired electron interacted with nearby protons and 14N nucleus in these radicals. The g values of the radicals and the hyperfine structure constants of the free electron were also measured. These results were compared with the earlier studies in amino acid and derivatives radicals and discussed. (Source: Brazilian ...

Ion-polymer interaction analysis: an inversion of NMR spin echo experimental data

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

A methodology for ion-polymer interaction estimation is discussed in the present work. This method is based on the inversion of experimental spin echo NMR data using Hopfield neural network to retrieve transverse relaxation time distributions. The adopted model systems consist of aqueous solutions of poly (ethylene oxide), molar mass 1500, 4000 and 35000 γ mol-1 and sodium nitroprusside (NP) at different concentrations. Dipolar interaction is investigated in this work through the reduction in the transverse relaxation time and increase in the area under the distribution curves of the PEO protons which presented a linear correlation with the NP concentration. Neural network results were compared with the Simplex optimization procedure and experimental NMR values. The proposed methodology i...

Efficiency dynamics on two coupled small-world networks

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

We investigate the effect of clusters in complex networks on efficiency dynamics by studying a simple efficiency model in two coupled small-world networks. It is shown that the critical network randomness corresponding to transition from a stagnant phase to a growing one decreases to zero as the connection strength of clusters increases. It is also shown for fixed randomness that the state of clusters transits from a stagnant phase to a growing one as the connection strength of clusters increases. This work can be useful for understanding the critical transition appearing in many dynamic processes on the cluster networks. (Source: Brazilian Journal of Physics)

Neutron production evaluation from a ADS target utilizing the MCNPX 2.6.0 code

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

Accelerators Driven Systems (ADS) are an innovative type of nuclear system, which is useful for long-lived fission product transmutation and fuel regeneration. The ADS consist of a coupling of a sub-critical nuclear core reactor and a proton beam produced by particle accelerator. These particles are injected into a target for the neutrons production by spallation reactions. This target is of utmost importance for an ADS, representing the coupling of the accelerator and the sub-critical core. The determination of optimal materials for these targets is fundamental for the design of an ADS. The main characteristic of an ideal target is the high production of neutrons per incident proton. In this work are shown results for the neutron production of various types of targets using the MCNPX 2.6....

Pulsar binary systems in a nonsymmetric theory of gravitation II. Dipole radiation

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

This paper deals with the emission of gravitational radiation in the context of a previously studied metric nonsymmetric theory of gravitation. The part coming from the symmetric part of the metric coincides with the mass quadrupole moment result of general relativity. The one associated to the antisymmetric part of the metric involves the dipole moment of the fermionic charge of the system. The results are applied to binary star systems and the decrease of the period of the elliptical motion is calculated. (Source: Brazilian Journal of Physics)

Analysis of electron direct tunneling current through very-thin gate oxides in MOS capacitors with the parallel-perpendicular kinetic energy components and anisotropic masses

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

An electron direct tunneling current model of n+- poly - Si/SiO2/p - Si(100) metal-oxide-semiconductor (MOS) capacitors has been developed by considering a parallel-perpendicular kinetic energy coupling, which is represented by the gate electron phase velocity, and anisotropic masses under a parabolic E-k dispersion relationship. The electron effective mass in the oxide and the electron phase velocity in the n+ poly-Si gate are the only two fitting parameters to compare calculated tunneling currents to measured ones. It was obtained that the calculated tunneling currents fit well to the measured ones. The electron effective mass in the oxide layer tends to increase with decreasing the oxide thickness. In addition, the gate electron velocity is a constant of 1x10(5)m/s. Moreover, the theore...

Observational consequences of a dark interaction model

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

We study a model with decay of dark energy and creation of the dark matter particles. We integrate the field equations and find the transition redshift where the evolution process of the universe change the accelerated expansion, and discuss the luminosity distance, acoustic oscillations and the statefinder parameters. (Source: Brazilian Journal of Physics)

Theoretical-experimental analyses of simple geometry saturated conductivities for a Newtonian fluid

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

The conductivity (K) of porous media represents an important physical parameter in several areas of knowledge. In saturated flow, the saturated conductivity (K0) is the most important parameter of porous system and it is related to the fluid and porous media properties. In order to evaluate the potential of a new tool for measuring K0, such as the computational simulation with Boltzmann models for fluid flows, two experiments were carried out using two simplified media: 1) a cylindrical cavity and 2) a cavity having a parallelepiped shape. Both have simple geometries that allow analytical K0 solutions in order to compare with the experimental and simulated results. Glycerin was used as infiltrate fluid due to its high viscosity that permits laminar flows and the use of Darcy's law to evalu...

First-principles study of carbon chemisorption on γ-Fe(111) surface

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

In order to study the interaction between γ-Fe and carbon, the geometry structures, surface relaxations, adsorption energies and electronic structures for carbon chemisorption at four different adsorption sites on γ-Fe(111) surface at a monolayer coverage of 1 were studied using density functional theory. The electronic structures were compared with the chemisorption of carbon on nickel (111) at the fcc hollow site. Based on the computational adsorption energies, the relative stabilities were described as follows: hcp hollow ≈ fcc hollow > top-on site, whereas the atomic carbon can not occupy the bridge sites stably. The partial density of states indicated the strong C(2p)-Fe(3d, 4s+p) and the wide C(2s+p)-Fe(3d) ionic bonds, which largely confined the electrons of the surface iron. Ac...

2d Gravity with torsion, oriented matroids and 2+2 dimensions

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

We find a link between oriented matroid theory and 2d gravity with torsion. Our considerations may be useful in the context of noncommutative phase space in a target spacetime of signature (2+2) and in a possible theory of gravity ramification. (Source: Brazilian Journal of Physics)

Conformal field theory with two kinds of bosonic fields and two linear dilatons

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

We consider a two-dimensional conformal field theory which contains two kinds of the bosonic degrees of freedom. Two linear dilaton fields enable us to study a more general case. Various properties of the model such as OPEs, central charge, conformal properties of the fields and associated algebras will be studied. (Source: Brazilian Journal of Physics)

Aspects of nonmetricity in gravity theories

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

In this work, we show that a class of metric-affine gravities can be reduced to a Riemann-Cartan one. The reduction is based on the cancelation of the nonmetricity against the symmetric components of the spin connection. A heuristic proof, in the Einstein-Cartan formalism, is performed in the special case of diagonal unitary tangent metric tensor. The result is that the nonmetric degrees of freedom decouple from the geometry. Thus, from the point of view of isometries on the tangent manifold, the equivalence might be viewed as an isometry transition from the affine group to the Lorentz group, A(d,R) → SO(d). Furthermore, in this transition, depending on the form of the starting action, the nonmetricity degrees might present a dynamical matter field character, with no geometric interpreta...

The cold dark matter model with cosmological constant and the flatness constraint

Brazilian Journal of Physics — Sat, 08 Jan 2011 01:15:10 +0100

The Hubble parameter, a function of the cosmological redshift, is derived from the Friedmann-Robertson-Walker equation. The three physical parameters H0, Ω0m and ΩΛ are determined fitting the Hubble parameter to the data from measurements of redshift and luminosity distances of type-Ia supernovae. The best fit is not consistent with the flatness constraint (k = 0). On the other hand, the flatness constraint is imposed on the Hubble parameter and the physical parameters used are the published values of the standard model of cosmology. The result is shown to be inconsistent with the data from type-Ia supernovae. (Source: Brazilian Journal of Physics)

Theoretical studies of the EPR parameters for Ni2+ and Co+ in MgO

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

The electron paramagnetic resonance (EPR) parameters (g factors and the hyperfine structure constants) for Ni2+ and Co+ in MgO are theoretically studied from the perturbation formulas of these parameters for a 3d8 ion in octahedral crystal-fields. In the computations, the ligand orbital and spin-orbit coupling contributions are taken into account using the cluster approach. The calculated EPR parameters are in good agreement with the experimental data. The larger g factor and the smaller magnitude of the hyperfine structure constant for Ni2+ as compared with those for Co+ can be attributed to the higher spin-orbit coupling coefficient and the lower dipolar hyperfine structure parameter of the former, respectively. (Source: Brazilian Journal of Physics)

Pentacene based thin film transistors with high-k dielectric Nd2O3 as a gate insulator

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

We have investigated the pentacene based Organic Thin Film Transistors (OTFTs) with High-k Dielectric Nd2O3. Use of high dielectric constant (high-k) gate insulator Nd2O3 reduces the threshold voltage and sub threshold swing of the OTFTs. The calculated threshold voltage -2.2V and sub-threshold swing 1V/decade, current ON-OFF ratio is 1.7 × 10(4) and mobility is 0.13cm²/V.s. Pentacene film is deposited on Nd2O3 surface using two step deposition method. Deposited pentacene film is found poly crystalline in nature. (Source: Brazilian Journal of Physics)

Dielectric and piezoelectric properties of Ba(ZrxTi1-x)O3 lead-free ceramics

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

Lead-free ceramics Ba(Zr xTi1-x)O3 (x = 0.02-0.2) were prepared using a solid-state reaction technique. The structural and electrical properties were systemically investigated. Crystalline structures and microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. All the samples possess pure perovskite structure. A small amount of Zr content has great effect on the microstructure of Ba(Zr xTi1-x)O3 ceramics. The homogeneous microstructure with grain size about 30µm is obtained for the sample at x = 0.05. The phase transitions merge together in one peak for the samples at x = 0.10 and the highest dielectric constant 15900 is obtained for the sample at x = 0.15. The Ba(Zr xTi1-x)O3 ceramics at x=0.05 exhibit excellent piezoelectric properti...

Blue thermoluminescence emission of annealed lithium rich aluminosilicates

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

The blue thermoluminescence (TL) emission of different thermally annealed (i) β-eucryptite (LiAlSiO4), (ii) virgilite-petalite (LiAlSi5O12) and (iii) virgilite-petalite-bikitaite (LiAlSi10O22) mixed crystals have been studied. The observed changes in the TL glow curves could be linked to simultaneous processes taking place in the lithium aluminosilicate lattice structure (phase transitions, consecutive breaking linking of bonds, alkali self-diffusion, redox reactions, etc). The stability of the TL signal after four months of storage performed at RT under red light, shows big differences between annealed (12 hours at 1200ºC) and non-annealed samples. The fading process in non-annealed samples can be fitted to a first-order decay mathematical expression; however preheated samples could not...

Theoretical studies of the local structure and the EPR parameters for substitutional Mo5+ in TiO2

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

The electron paramagnetic resonance(EPR) parameters g-factors g i(i = x,y,z) and the hyperfine structure constants Ai for the substitutional Mo5+ in rutile are theoretically studied from the perturbation formulas of these parameters for a d¹ ion in a rhombically compressed octahedron. On the basis of the studies, The oxygen octahedron around Mo5+ is found to transform from the original elongation on the host Ti4+ site to compression in the impurity center due to the Jahn-Teller effect. The calculated EPR parameters based on the above local structure in this work are in good agreement with the experimental data. (Source: Brazilian Journal of Physics)

Influence of process parameters on the growth of pure-phase anatase and rutile TiO2 thin films deposited by low temperature reactive magnetron sputtering

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

In this work is investigated the optimal conditions for deposition of pure- phase anatase and rutile thin films prepared at low temperatures (less than 150ºC) by reactive dc magnetron sputtering onto well- cleaned p- type Si substrates. For this, the variation of deposition plasma parameters as substrate- to- target distance, total gas pressure, oxygen concentration, and substrate bias were studied and correlated with the characteristics of the deposited films. The XRD analysis indicates the formation of pure rutile phase when the substrate is biased at voltages between - 200 and - 300 V. Pure anatase phase is only attained when the total pressure is higher than 0.7 Pa. Moreover, it's noticeable a strong dependence of surface roughness with parameters studied. (Source: Brazilian Journal o...

Effect of electron inertial delay on Debye sheath formation

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

Present contribution deals with the role of weak but finite electron inertia on the sheath formation condition. As reported earlier this becomes effective when the ions' drift velocity exceeds the phase velocity of the acoustic wave fluctuations. Such situation has natural existence near the sheath edge. Keeping this in mind we have revisited the problem of usual Bohm sheath condition. Analytical and numerical analysis have been performed to re- derive the local condition for plasma sheath formation. It is found that the weak but finite electron inertia reduces the threshold value of ion Mach number that may be, at least in principle, of qualitative value to define the sheath edge boundary. Consideration of finite but weak equilibrium electron flow at the defined sheath edge shrinks the wi...

Study of the parameters affecting ion beam emerging from cold conical cathode ion source

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

The aim of this work is study of the parameters affecting ion beam emerging from cold conical cathode ion source. The input discharge and output ion beam characteristics have been measured at different pressures using nitrogen and argon gases. The optimum distance between the ion exit aperture of the cathode and the movable copper ion collector plate has been determined using nitrogen and argon gases. The ion collector plate has been placed at different distances from the ion exit aperture of the cathode equal to 2, 3, 4, 4.5, 5, 5.5 and 6 cm respectively. It is found that the optimum distance between the ion exit aperture of the cathode and the ion collector plate equals 5 cm for high output ion beam current. At this optimum distance, the efficiency of the ion source reaches 28.3% and 21....

Measurement of the plasma boundary shift and approximation of the magnetic surfaces on the IR-T1 Tokamak

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

In this research we measured the plasma boundary shift using array of magnetic pick- up coils on the IR- T1 tokamak. Also we approximated the magnetic surfaces by an equilibrium calculation. Firstly, four magnetic probes were designed, constructed, and installed on outer surface of the IR- T1 tokamak chamber and then plasma boundary displacement measured from them. On the other hand, magnetic surfaces approximated by equilibrium calculation of the Grad- Shafranov equation based on expansion of free functions as quadratic in flux function. (Source: Brazilian Journal of Physics)

Is it possible to accommodate massive photons in the framework of a gauge-invariant electrodynamics?

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

The construction of an alternative electromagnetic theory that preserves Lorentz and gauge symmetries, is considered. We start off by building up Maxwell electrodynamics in (3+1)D from the assumption that the associated Lagrangian is a gauge- invariant functional that depends on the electron and photon fields and their first derivatives only. In this scenario, as well- known, it is not possible to set up a Lorentz invariant gauge theory containing a massive photon. We show nevertheless that there exist two radically different electrodynamics, namely, the Chern- Simons and the Podolsky formulations, in which this problem can be overcome. The former is only valid in odd space- time dimensions, while the latter requires the presence of higher- order derivatives of the gauge field in the Lagra...

Energy momentum complex

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

We show that the definition of the energy- momentum complex given by Møller using Weitzenböck space- time in the calculations of gravitational energy gives results which are different from those obtained from other definitions given in the framework of general relativity. (Source: Brazilian Journal of Physics)

Final state interactions effects on kinetic energy sum spectra in nonmesonic weak decay

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

We analyze the effect of final state interactions (FSI) on coincidence spectra in nonmesonic hypernuclear weak decay, ΛN → nN, as a function of the kinetic energy sum, EnN = En+ E N, both for np and nn events. Adopting a formalism recently developed, the effects of FSI originated from the interaction between the outgoing nucleons and those in the residual core are included analytically in a very simple way within the eikonal approximation through the modification of the emerging particles momenta. Numerical results are shown for 5ΛHe and 12ΛC hypernucleus. We found that coincidence spectra are only slightly modified and the disagreement between theory and experimental data still persists, mainly for nn events in 5ΛHe where enough statistics exists. We conclude that admixtures of exci...

Identification of free radicals induced by gamma irradiation in amino acid derivatives

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

Powders of N- acetyl- L- leucine and N- methyl- L- glutamic acid were gamma irradiated and the free radicals formed were investigated at room temperature by electron paramagnetic resonance technique. The free radicals formed in compounds were attributed to the (CH3)2CCH2CH(NHCOCH3)COOH and HOOCCH2CH2C (NHCH3)COOH radicals respectively. Both radicals are very stable and we could observe them for five months without almost intensity diminution at room temperature. The g values of the radicals and the hyperfine structure constants of the free electron with nearby protons and 14N nucleus were determined. The results were found to be in good agreement with the existing literature data. (Source: Brazilian Journal of Physics)

Tuning luminescence of 3d transition- metal doped quantum particles: Ni+2: CdS and Fe+3: CdS

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

The room- temperature photoluminescence of Cd1- xMxS (M=Ni, Fe) nanoparticles were investigated. Compared with the photoluminescence of CdS which peaks at 475 nm, the photoemission of CdS:Fe nanoparticles was peaking at 537 nm because of Fe acting as luminescent centers. On the other hand, the green emission (503 nm) of CdS:Ni attributed to the ¹T2g(D)→ ³A2g(F) raditive transition. With the increase of the Ni+2 concentration, photoluminescence intensity is increased while by Fe replacement with Cd ions, PL intensity is decreased. Relative to bulk crystals, due to the quantum confinement effect the band gap of CdS clusters is significantly blue- shifted with decreasing cluster size. CdS nanoclusters present a mixed hexagonal/cubic structure and with increasing doping concentration the p...

Genetic transcriptional regulatory model driven by the time-correlated noises

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

Steady state properties of a kinetic model of Smolen- Baxter- Byrne [P. Smolen, D. A. Baxter, J. H. Byrne, Amer. J. Physiol. Cell. Physiol. 274, 531 (1998)] are investigated in presence of two time- correlated noises. The steady state probability distribution can be obtained by solving the Fokker- Planck equation. It is found that both the correlated- time between the white noise and the colored noise and that between the colored noises can convert the bistability to monostability while the former activates the transcription and the latter suppresses it. (Source: Brazilian Journal of Physics)

Polarized Raman spectra of L-arginine hydrochloride monohydrated single crystal

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

in nine different scattering geometries of the two irreducible representations of factor group C2 were studied at room temperature. The experimental wavenumber values are compared with those obtained from ab-initio calculation and the assignment of the Raman bands to the respective molecular vibrations is also given. Finally, a discussion related to a previously reported phase transition undergone by L-arginine hydrochloride monohydrated single crystal at low temperature is furnished. (Source: Brazilian Journal of Physics)

Torsional vibration of carbon nanotubes under initial compression stress

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

This study examines torsional vibration of Single-walled carbon nanotubes (SWCNTs) subjected to initial compression stresses. The nanotube structures are treated within the multilayer thin shell approximation with the elastic properties taken to be those of the graphene sheet. Simplified Flügge shell equations of motion are proposed as the governing equations of vibration for the carbon nanotubes. A new equation of motion and phase velocity of torsional waves propagating in carbon nanotubes (CNTs) subjected to initial compression stresses have been derived. The study reveals that the initial stresses present in the tube has a notable effect on the propagation of torsional waves. The results has been discussed and shown graphically. This investigation is very significant for potential appl...

Effective cosmology a la Brans-Dicke with a non-minimally coupling massive inflaton field interacting with minimally coupling massless field

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

We discuss an effective cosmology a la Brans-Dicke with two interacting scalar fields: a non-minimally coupling massive inflaton Higgs-like scalar field Φ interacting with a minimally coupling massless scalar field χ. Several features are observed and discussed in some details. (Source: Brazilian Journal of Physics)

Hot electron transport properties in characteristics of wurtzite GaN MESFETs using a five-valley model

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

Ensemble Monte Carlo simulations have been carried out to investigate the effects of upper valleys on the characteristics of wurtzite GaN MESFETs. Electronic states within the conduction band valleys at the Γ1, U, M, Γ3 and K are represented by non-parabolic ellipsoidal valleys centred on important symmetry points of the Brillouin zone. The following scattering mechanisims, i.e, impurity, polar optical phonon, acoustic phonon, alloy and piezoelectric are inculded in the calculation. Ionized imurity scattering has been treated beyound the Born approximation using the phase-shift analysis. The simulation results show that on the drain side of the gate region, hot electrons attained enough energy to be scattered into the upper satellite conduction valleys. Approximately %20 of the electrons...

Bianchi type I tilted cosmological model for barotropic perfect fluid distribution with heat conduction in general relativity

Brazilian Journal of Physics — Fri, 24 Sep 2010 20:26:57 +0100

Bianchi Type I tilted cosmological model for barotropic perfect fluid distribution with heat conduction is investigated.To get the deterministic solution, we have assumed barotropic condition p = γ ∈ ,0 < γ < 1, p being isotropic pressure, ∈ the matter density and a supplementary condition between metric potentials A, B, C as A = (BC)n where n is the constant. To get the model in terms of cosmic time, we have also discussed some special cases. The physical aspects of the model are also discussed. (Source: Brazilian Journal of Physics)

Effect of particle size on nonlinear refractive index of Au nanoparticle in PVA solution

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Basic quantum mechanics for three Dirac equations in a curved spacetime

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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 Hamiltonia...

The quantization of galilean duffin-kemmer-petiau field

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Multiloop calculations with implicit regularization in massless theories

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Nonlinear thermotropic and thermo-optical behaviour of planar oriented textures in nematic liquid crystals at phase transitions

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Comparative vibrational spectra of pilosine and epiisopilosine crystals

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Kinematic self-similar solutions of locally rotationally symmetric spacetimes

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Structural studies of liquid alkaline-earth metals: A molecular dynamics approach

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Effect of Mo interlayer on magnetic properties of exchange coupled Sm-Co/Fe bilayers

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Conductivity fluctuations of polycrystalline Ag-doped YBa2Cu3O7-δ superconductor

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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 obser...

Vacuum energies and multipole interactions

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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]. (Source: Brazilian Journal of Physics)

Dynamic radiation force of acoustic waves on absorbing spheres

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Contribution of adiabatic phases to noncyclic evolution

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

On the calculation of inner products of Schur functions

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Adiabatic index of hot and cold compact objects

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

On the modelling of rotational effects in the lower convective region of the sun

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source...

10-dimensional cosmology with Gauss-Bonnet gravity in generalized scalar-tensor theories from superstring theories

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Domain wall, stiff matter and ultra-relativistic particles from a generalized double-component dark energy model

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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) ∈ . Many interesting features are revealed in particular the manifestation of domain wall, cosmic string, stiff matter, dust and radiation/ultra-relativistic particles. (Source: Brazilian Journal of Physics)

Power and efficiency performances of a micro thermal Brownian heat engine with and without external forces

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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 ...

Controlling nonholonomic Chaplygin systems

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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. (Source: Brazilian Journal of Physics)

Construction and experimental study of a 2.5kJ, simply configured, mather type plasma focus device

Brazilian Journal of Physics — Fri, 02 Jul 2010 07:38:00 +0100

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). (Source: Brazilian Journal of Physics)

Retrieval of GammaCell 220 irradiator isodose curves with MCNP simulations and experimental measurements

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

Gamma irradiator facilities can be used in a wide range of applications such as biological and chemical researches, sterilization of medical devices and products. Dose mapping must be performed in these equipments in order to establish plant operational parameters, as dose uniformity, source utilization efficiency and maximum and minimum dose positions. The isodoses curves are measured using dosimeters or computer simulations. This work evaluates the absorbed dose in the CDTN/CNEN GammaCell Irradiation Facility, using the Monte Carlo N-Particles (MCNP) code. (Source: Brazilian Journal of Physics)

Autoionization of He atoms induced by partially stripped ion impact

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

A study of the autoionization process induced by partially stripped ion impact is performed. The Barrachina-Macek model is extended to the case in which the projectile-emitted electron interaction is represented by means of a non-Coulombic central potential at all times. Electron spectra in momentum space are predicted and compared to the Barrachina-Macek model and a recent model in which an asymptotically correct wave function was employed to treat this problem. The presence of rainbow scattering interference in the binary ring profile of the outgoing autoionized electrons for positive ion impact is discussed based on the different models. (Source: Brazilian Journal of Physics)

Design and characterization of an RF plasma cleaner

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The design and characterization of an innovative device for plasma cleaning, based upon a non-conventional radio-frequency discharge, is described. The RF fields are produced by an antenna placed inside the metallic vacuum chamber. Theoretical models are described to calculate both the electro-magnetic field structure and the spatial impurity distribution, due to erosion of the antenna. The electron energy distribution function is determined with a standard RF-filtered electrostatic probe; it is found that the plasma is well described by a Druyvesteyn energy distribution function. (Source: Brazilian Journal of Physics)

Collective coordinate analysis for double sine-Gordon model

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

Collective coordinate analysis for adding a space dependent potential to the double sine-Gordon model is presented. Interaction of solitons with a delta function potential barrier and also delta function potential well is investigated. Most of the features of interaction are derived analytically. We will find that the behaviour of a solitonic solution is like a point particle which moves under the influence of a complicated effective potential. The effective potential is a function of the field initial conditions and also parameters of added external potential. (Source: Brazilian Journal of Physics)

Time evolution of Wigner functions governed by bipartite Hamiltonian system with kinetic coupling

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

For the bipartite Hamiltonian system with kinetic coupling, we derive time evolution equation of Wigner functions by virtue of the bipartite entangled state representation and entangled Wigner operator, which just indicates that choosing a good representation indeed provides great convenience for us to deal with the dynamics problem. (Source: Brazilian Journal of Physics)

Generation of M2>0 anti-ghosts from M2>0 superbradyons at gravito-electroweak unification scale

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

We show that superbradyons defined as superluminal particles with positive-square mass may be created in the de-Sitter region under specific conformal coupling constraints and later propagates to the Minkowskian spacetime as anti-tachyons or anti-ghosts (normal particles). It was also proved that an increasing gravitational constant with distance enriches the study where some interesting features are discussed in some details. (Source: Brazilian Journal of Physics)

The role of nonequilibrium thermo-mechanical statistics in modern technologies and industrial processes: an overview

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The nowadays notable development of all the modern technology, fundamental for the progress and well being of world society, imposes a great deal of stress in the realm of basic Physics, more precisely on Thermo-Statistics. We do face situations in electronics and optoelectronics involving physical-chemical systems far-removed-from equilibrium, where ultrafast (in pico- and femto-second scale) and non-linear processes are present. Further, we need to be aware of the rapid unfolding of nano-technologies and use of low-dimensional systems (e.g., nanometric quantum wells and quantum dots in semiconductor heterostructures). All together this demands having an access to a Statistical Mechanics being efficient to deal with such requirements. It is worth noticing that the renowned Ryogo Kubo once...

Flux and dose rate evaluation of iter system using MCNP5

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The International Thermonuclear Experimental Reactor (ITER) will perform Deuterium-Tritium (DT) plasma experiments and the neutrons production rate at 14.1 MeV will achieve the level of 10(13) n.cm-2.s-1. In this work, the neutron flux and the dose rate during ITER operation has been calculated using the one-dimensional model of the Monte Carlo code MCNP5 and the FENDL/MC-2.1 nuclear data library. The neutron flux and dose rate associated during normal ITER operation were determined along the radial machine direction. Calculations for two different types of concrete compositions were performed to investigate the impact of the bioshield filling materials on the dose rate estimation. The results show that the dose rate level near to the outer wall of the tokamak hall is close to the allowabl...

First-principles study of structural, electronic and elastic properties of Nb4AlC3

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

Using First-principles calculations, we have studied the structural, electronic and elastic properties of Nb4AlC3, a new compound belonging to the MAX phases. Geometrical optimization of the unit cell is in good agreement with the experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions are higher along the c-axis than along the a-axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The band structure shows that this compound is electrical conductor. The analysis of the site and momentum projected densities shows that bonding is due to Nb d-C p and Nb d-Al p hybridizations. The Nb d-C p bond is lower in energy and stiffer than Nb d-Al p bond. The elastic constants are calculated using...

Thermal and epithermal neutron fluence rates in the irradiation facilities of the TRIGA IPR-R1 nuclear reactor

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The TRIGA IPR-R1 nuclear reactor at the Centro de Desenvolvimento da Tecnologia Nuclear CDTN/CNEN, Belo Horizonte, Brazil, has three irradiation facilities: a rotary specimen rack outside the reactor core with 40 irradiation channels which provide large scale isotope irradiation; the central tube placed at the center of the reactor core which permits sample irradiation with maximum neutron flux, as well as neutron beam extraction; a pneumatic transfer tube which makes possible the analysis of short half-life radioisotopes. The aim of this work is to evaluate the thermal and epithermal neutron fluence rates in the three irradiation facilities of the IPR-R1. Al-0.1%Au reference materials were irradiated bare and Cd-covered, at 100 kW thermal power, and gamma spectrometry was applied with an ...

UV dominant optical emission newly detected from radioisotopes and XRF sources

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The current paper reports first and definite experimental evidence for γ-, X-, or β radiation causing UV dominant optical radiation from (1) radiochemicals such as 131I; (2) XRF sources such as Rb XRF source present as salts; and (3) metal sources such as 57Co, and Cu XRF sources. Due to low quantum yield a need arose to develop two techniques with narrow band optical filters, and sheet polarizers that helped in the successful detection of optical radiation. The metal 57Co spectrum observed at room temperature hinted that it could be optical emission from excited 57Co atoms by a previously unknown phenomenon. In order to explain UV emission, it was predicted that some eV energies higher than that of UV, termed temporarily as Bharat radiation are generated within the excited atom, while �...

CGS based solar cells with In2S3 buffer layer deposited by CBD and coevaporation

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

In this paper we investigated In2S3 as substitute for CdS, which is conventionally used as buffer layer in chalcopyrite based solar cells. In2S3 thin films were deposited by CBD and co-evaporation methods and these were employed as buffer layer in CuGaSe2 based solar cells. Previous to the device fabrication, comparative study was carried out on In2S3 thin films properties deposited from chemical bath containing thioacetamide, Indium Chloride, and sodium citrate, and In2S3 thin films prepared by co-evaporation from its constituents elements. The influence of synthesis conditions on the growth rate, optical, structural and morphological properties of the as-grown In2S3 thin films have been carried out with Spectrophotometry, X-ray diffraction and AFM microscopy techniques. Suitable conditio...

Study of ion beam sputtering using a glow discharge ion source

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

In this work, sputtering yield in a glow discharge ion source system has been determined using the operating parameters of the ion source. The sputtering yield is found to be varied between 0.4 to 1 atoms removed per incident ion for nitrogen while for argon between 0.2 to 1.3 atoms removed per incident ion. The feature of this ion source is high output ion beam current and small size. Operation of the ion source is quite simple since a stable discharge can be obtained within a large range of main parameters such as, discharge voltage, discharge current and gas pressure. Also, beam profile for argon ion beam produced from the glow discharge ion source at Id = 2,3 mA (discharge current) using argon gas with different gas pressures has been investigated. (Source: Brazilian Journal of Physics...

Effect of warm ionized plasma medium on radiation properties of four elements microstrip antenna array printed on ferrite substrate

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

This paper describes theoretically the radiation properties of four element microstrip antenna array printed upon a typical ferrite substrate Ni1.062Co0.o2Fe1.948O4 in the presence of normal dc magnetic bias field. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to nonradiating surface waves. In the absence of an external magnetic field, the EM - mode and P-mode can be decoupled into two independent modes, the electoacoustic mode is longitudinal while the electromagnetic mode is transverse. Far zone electromagnetic mode and plasma mode radiation fields are derived using vector wave function technique and pattern multiplication approaches. The results are obtained in both plasma medium and fre...

Comparison of some theoretical models for fittings of the temperature dependence of the fundamental energy gap in GaAs

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

In this work we report on a comparison of some theoretical models usually used to fit the dependence on temperature of the fundamental energy gap of semiconductor materials. We used in our investigations the theoretical models of Viña, Pässler-p and Pässler-ρ to fit several sets of experimental data, available in the literature for the energy gap of GaAs in the temperature range from 12 to 974 K. Performing several fittings for different values of the upper limit of the analyzed temperature range (Tmax), we were able to follow in a systematic way the evolution of the fitting parameters up to the limit of high temperatures and make a comparison between the zero-point values obtained from the different models by extrapolating the linear dependence of the gaps at high T to T = 0 K and tha...

Variational calculation of low-energy positron life time in Xe atoms

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The least-squares variational method (LSVM) is used for determining trial wavefunctions representing low-energy positron-xenon elastic scattering, which are used to determine the positron lifetime. The trial function is taken to depend on several adjustable parameters, and is improved iteratively by increasing the number of terms. The bound state wavefunctions are obtained using Hartree-Fock-Slater method. The 2γ-rays annihilation rates of the positron in xenon atoms below Positronuim (Ps) formation threshold are calculated. Polarization potential Vpl (r) is applied to enhance annihilation rates and lifetime. The present results of annihilation parameters are consistent with semiempirical, theoretical and experimental results. (Source: Brazilian Journal of Physics)

Energy in an expanding universe in the teleparallel geometry

Brazilian Journal of Physics — Mon, 03 May 2010 15:34:45 +0100

The main purpose of this paper is to explicitly verify the consistency of the energy-momentum and angular momentum tensor of the gravitational field established in the Hamiltonian structure of the Teleparallel Equivalent of General Relativity (TEGR). In order to reach these objectives, we obtained the total energy and angular momentum (matter plus gravitational field) of the closed universe of the Friedmann-Lemaître-Robertson-Walker (FLRW). The result is compared with those obtained from the pseudotensors of Einstein and Landau-Lifshitz. We also applied the field equations (TEGR) in an expanding FLRW universe. Considering the stress energy-momentum tensor for a perfect fluid, we found a teleparallel equivalent of Friedmann equations of General Relativity (GR). (Source: Brazilian Journal o...

Phenomenological Model for the metal-insulator transition in two dimensions

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

The resistivity measured in two-dimensional MOSFET geometry is modeled by considering that the resistivity is a function of the temperature and the areal density of charges (electrons or holes). The logistics differential equation is proposed for the behaviour of the resistivity as a function of temperature, so that the two phases are obtained in a natural manner. At low temperatures, the Drude model behaviour is assumed for the resistivity as a function of density. Two characteristics then follow in a natural manner: The existance of a characteristic temperature for resistivity as a function of temperature, and the symmetry relationship. If the magnetic field is incorporated into the Drude model, reasonable results are obtained for the qualitative behaviour of resistivity for weak fields....

Heisenberg spin textures on a cylinder with topological defects

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

The present work aims to study equilibrium configurations of spins on a cylinder with topological defects such as screw dislocation and deficit angle. By making use of elliptic-f expansion method, which in turn utilizes the Jacobi elliptic functions, we obtain exact solutions of the nonlinear sigma model in this geometry. We have significant changes in the qualitative behavior of the solutions due to the presence of the parameter k of screw dislocation. In particular, the behavior of soliton-like solutions, characteristic of a cylinder without dislocation, was not found in the model here proposed. (Source: Brazilian Journal of Physics)

Aspects of nonrelativistic quantum gravity

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

A nonrelativistic approach to quantum gravity is studied. At least for weak gravitational fields it should be a valid approximation. Such an approach can be used to point out problems and prospects inherent in a more exact theory of quantum gravity, yet to be discovered. Nonrelativistic quantum gravity, e.g., shows promise for prohibiting black holes altogether (which would eliminate singularities and also solve the black hole information paradox), gives gravitational radiation even in the spherically symmetric case, and supports non-locality (quantum entanglement). Its predictions should also be testable at length scales well above the "Planck scale", by high-precision experiments feasible with existing technology. (Source: Brazilian Journal of Physics)

Non-universal interspecific allometric scaling of metabolism

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

We extend a previously theory for the interspecific allometric scaling developed in a d+1-dimensional space of metabolic states. The time, which is characteristic of all biological processes, is included as an extra dimension to d biological lengths. The different metabolic rates, such as basal (BMR) and maximum (MMR), are described by supposing that the biological lengths and time are related by different transport processes of energy and mass. We consider that the metabolic rates of animals are controlled by three main transport processes: convection, diffusion and anomalous diffusion. Different transport mechanisms are related to different metabolic states, with its own values for allometric exponents. In d = 3, we obtain that the exponent b of BMR is b = 0.71, and that the aerobic sust...

Graphene to graphite: electronic changes within DFT calculations

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

Calculations based on the first-principles pseudopotential plane-wave method and density-functional theory are performed to investigate the electronic properties of graphene, bilayer graphene, multilayer graphene, and graphite. From an analysis of the electronic band structure close to the Fermi level, we have quantified the gradual change in the Fermi surface topology from the point-like structure for graphene to a warped triangular shape for graphite. We have also discussed the gradual change in the electron and hole effective masses and velocities as the system evolves from graphene to graphite. (Source: Brazilian Journal of Physics)

Phenomenological analysis of elastic scattering reactions using different models

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

McIntyre and Frahn-Venter three-parameter models are used to analyze the experimental data of three elastic scattering reactions α+ 58Ni, α+ 116Sn and α+ 197Au at the same incident energy of 240MeV. The different α-scattering cases have the same number of minima and maxima in their oscillatory structures of angular distribution. The increase in the mass of target nucleus leads to a smaller nuclear deflection minimum and causes the corresponding angular distribution to become smoother and with steeper slope. The Coulomb damping of Fraunhofer oscillations has an effect accompanied with the increase of mass of target nucleus. The presence of semi-classical phenomena such as Fresnel and Fraunhofer diffraction patterns etc., has been found by analyzing the experimental data of elastic scatt...

Experimental evidence of an optical shutter in cholesteric phase of a double hydrogen bonded liquid crystal

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

A novel series of double hydrogen bonded liquid crystals have been isolated. Hydrogen bond was formed between non mesogen chiral ingredient levo tartaric acid (LTA) and mesogenic undecyloxy benzoic acids (11BA) Thermal and electrical properties exhibited by levo tartaric acid and undecyloxy benzoic acid (LTA+11BA) were discussed. Interesting feature of the present investigation was observation of an optical shuttering action in LTA+11BA hydrogen bonded complex on application of a stipulated applied dc bias voltage. By enhancement of the dc bias voltage the mesogen behaves like an optical shutter, thus this hydrogen bonded complex mesogen acts as an effective light modulator. It was noticed that this action of shuttering was reversible, in the sense that when applied bias voltage was remove...

Effect of an columnar defect on vortex configuration in a superconducting mesoscopic sample

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

In this work we investigate the vortex dynamics in a square mesoscopic superconducting cylinder in the presence of an applied magnetic field parallel to its axis. The rectangular cross-section of the sample is L² and an engineered columnar defect of area d² at the center is taken into account; L = 12ξ(0) for all simulations while d varies discretely from 1ξ(0) to 10ξ(0). We study the magnetization and the vortex configuration, increasing the magnetic field from zero to the normal state field. We found that for d > 7ξ(0) no vortices in the superconductor area are possible. Also, if the size of the defect is reduced, the nucleation fields decrease. (Source: Brazilian Journal of Physics)

Analysis of fluctuation conductivity of polycrystalline Er1-xPrxBa2Cu3O7-δsuperconductors

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

In this work we report on conductivity fluctuation measurements in polycrystalline samples of the Er1-xPr xBa2Cu3O7-δ superconductor (x = 0.00, 0.05 and 0.10). Samples were prepared by a standard solid-state reaction technique. The results were analyzed in terms of the temperature derivative of the resistivity and of the logarithmic temperature derivative of the conductivity that allowed the identification of power-law divergences of the conductivity. The results show that the transition proceeds in two stages: pairing and coherence transition. Also, our results, from the critical exponent analysis, show a two-peak splitting at pairing transition, indicating possibly a phase separation. On approaching the zero resistance state, our results show a power-law behavior that corresponds to a p...

Pairing gap energy correction in Shell model for the neutron-rich tin isotopes

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

The region in the vicinity of 132Sn, gathering numerous isotopes of important masses, shows lots of interests for explaining the most interesting phenomena. It offers among others the possibility to extract the N-N empirical interactions so as to test theoretical shell model description of nuclear structure in this region. The researches on the neutron-rich tin isotopes present the anomalies in a systematic variation on various spectroscopic data such as the first 2+ excited state and reduced probabilities B(E2;2+? 0+). In order to improve the OXBASH interactions which are based on the shell model calculations, we have modified some neutron-neutron and proton-proton tow body matrix elements of CW5082 interaction of 132Sn region by adding to them the pairing gap energy. The calculations tur...

Low-energy parabosonic membrane: new critical dimensions and deformed noncommutativity

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

We study a classical perturbative membrane based on the string-limit model and we discuss the consistency of the theory where the closure of the classical constraints algebra is verified. We paraquantize the model (extended string) both in the covariant and the transverse approaches. From the generalized Poincaré algebra, the so-called Poincaré (para) algebra, we show that the space-time critical dimensions D are related to the order of the paraquantization Q by the relation D = 3+24/Q. The symplectic structure is generalized for the paraquantum case and applied to the parabosonic membrane coupled to a constant 3-form field. This leads to a deformed noncommutative relations at the ends of the membrane (extended string) describing a geometry which might be called a q-noncommutativity. (So...

Instantonic methods for quantum tunneling in finite size

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

The instantonic approach for a Φ4 model potential is reexamined in the asymptotic limit. The path integral of the system is derived in semiclassical approximation expanding the action around the classical background. It is shown that the singularity in the path integral, arising from the zero mode in the quantum fluctuation spectrum, can be tackled only assuming a finite (although large) system size. On the other hand the standard instantonic method assumes the (anti)kink as classical background. But the (anti)kink is the solution of the Euler-Lagrange equation for the infinite size system. This formal contradiction can be consistently overcome by the finite size instantonic theory based on the Jacobi elliptic functions formalism. In terms of the latter I derive in detail the classical ba...

Effects of Ag addition on some physical properties of granular YBa2Cu3O7-δ superconductor

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

The effects of Ag addition on some physical properties of YBa2Cu3O7-δ superconductor has been studied. The samples were produced by different routes and characterized by scanning electron microscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction and nanoindentation. The superconducting properties were studied by dc magnetization and electrical resistivity measurements. The X-ray patterns revealed that all samples were polycrystalline and corresponded to the orthorhombic YBa2Cu3O7-δ phase. However, for some samples, silver appears to be present within the grains. The superconducting properties were not significantly influenced by Ag addition. Hardness and elastic modulus were also obtained by instrumented indentation. Ag addition was found to be effective in...

A lumped parameter model of free expanding plasma focus

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

In this paper, a model of Plasma Focus without surrounding cathode containing the radial expansion of the current sheath is presented. This configuration has been increasingly used in recent miniature devices. The model, based on the snowplow approximation, was applied to calculate the voltage along the pinch in a small 300 J device, showing good agreement with the experiments. The results can be useful in the design of x-rays applications of Plasma-Focus devices. (Source: Brazilian Journal of Physics)

Thickness dependence of the properties of indium tin oxide (ITO) FILMS prepared by activated reactive evaporation

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

Tin doped indium oxide thin films were prepared on glass substrates kept at room temperature, by activated reactive evaporation (ARE). Structural, electrical and optical properties were studied for films having different thickness. The resulting films are polycrystalline and show 90 % transmission in the visible region. Hall effect measurements at room temperature for a film with a nominal thickness of 350 nm shows a relatively high carrier concentration 6.3 × 10(20) cm-3, mobility 16 cm² V-1s-1, with a low resistivity 1.01×10-3W cm. (Source: Brazilian Journal of Physics)

LRS Bianchi type -V cosmology with heat flow in scalar: tensor theory

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

In this paper we present a spatially homogeneous locally rotationally symmetric (LRS) Bianchi type -V perfect fluid model with heat conduction in scalar tensor theory proposed by Saez and Ballester. The field equations are solved with and without heat conduction by using a law of variation for the mean Hubble parameter, which is related to the average scale factor of metric and yields a constant value for the deceleration parameter. The law of variation for the mean Hubble parameter generates two types of cosmologies one is of power -law form and second the exponential form. Using these two forms singular and non -singular solutions are obtained with and without heat conduction. We observe that a constant value of the deceleration parameter is reasonable a description of the different phas...

6 MV wedge photon beam profiles with the fricke xylenol gel dosimeter

Brazilian Journal of Physics — Fri, 26 Feb 2010 16:37:26 +0100

Wedged beam are often used in clinical radiotherapy to compensate missing tissues and dose gradients. In this work, the Fricke Xylenol Gel (FXG) dosimeter was used for 6 MV photons radiation wedge field profiles measurements, allowing to infer the wedge filter physical attenuation coefficient. This dosimeter is a chemical system of a Fe3+-Xylenol complex concentration, that when measured spectrophotometrically, the absorbance is directly proportional to the absorbed dose. From theses results one can infer that the FXG can be used also as an alternative dosimetric system for measurements of wedge filters. (Source: Brazilian Journal of Physics)

Interference of robust tori on the resonance overlap

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

We study a dynamical system which describes the overlap of resonances in a global integrable context and we present a new topological scenario for the reconnection of three resonance island chains in the presence of two robust tori. These tori induce this new scenario and they play the role of transport barriers which are relevant for plasma confinement in Tokamaks. (Source: Brazilian Journal of Physics)

Inter hydrogen bonded complexes of hexadecylaniline and alkoxy benzoic acids: a study of crystallization kinetics

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

A systematic crystallization kinetic study of two smectogens of homologous series of the inter molecular hydrogen bonded between undecyl, dodecyl benzoic acids and hexadecylaniline complexes viz., 16A+11BA and 16A+12BA respectively has been carried out by thermal microscopy, differential scanning calorimetry (DSC) and dielectric studies. FTIR studies indicate the formation of hydrogen bond in these complexes. The crystallization kinetics was studied by two techniques viz., the traditional thermal analysis (DSC) and electrical studies in which capacitance and dielectric loss variation with temperature were recorded and analyzed. The DSC thermograms were run from crystallization temperature to the isotropic melt for different time intervals. The liquid crystalline behaviour together with the...

A simple way to avoid metastable configurations in the density-matrix renormalization-group algorithms

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

We use the spin-1 Heisenberg chain with periodic boundary conditions to ilustrate that the systems get stuck in metastable configurations only when the density-matrix renormalization-group algorithm start with small number of states m. We also show that the convergence of the energies have a huge improvement if we start the algorithm with a large number of states m. (Source: Brazilian Journal of Physics)

MOND virial theorem applied to a galaxy cluster

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

Large values for the mass-to-light ratio (Ò) in self-gravitating systems is one of the most important evidences of dark matter. We propose a expression for the mass-to-light ratio in spherical systems using MOND. Results for the COMA cluster reveal that a modification of the gravity, as proposed by MOND, can reduce significantly this value. (Source: Brazilian Journal of Physics)

The spin dynamics of molecular magnets beyond Kubo's linear response theory

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

The description of quantum dynamics of nanomagnets is a central issue in most applications proposed for those systems. In this paper, we put forward a modified perturbation approach to study the spin dynamics of a molecular magnet in the presence of time-dependent magnetic fields.The non-perturbed Hamiltonian H0, which defines the interaction picture, may be time-dependent proviso it can be diagonalized at all times by the same basis of states. We probe the method using a simple model Hamiltonian, that contains the important anisotropy terms relevant for Fe8 molecular clusters, and solve as an example the case with the smallest non trivial spin value (S=1). Our modified perturbation approach converges rapidly to the exact solution, goes beyond the Kubo linear response theory, and is well d...

EPR study of gamma induced radicals in amino and iminodiacetic acid derivatives

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

In this study, electron paramagnetic resonance spectroscopy was used to investigate free radicals formed in gamma irradiated L-glutamine hydrochloride, iminodiacetic acid hydrochloride and N-(2-hyroxyethyl) iminodiacetic acid powders. The free radicals produced in L-glutamine hydrochloride powders were attributed to the CH2CHCOOH radical; and those in iminodiacetic acid hydrochloride and N-(2-hyroxyethyl) iminodiacetic acid powders to the HNCHCH2(COOH)2 and HOCH2CH2NCHCH2(COOH)2, respectively. The g-values of the radicals and the hyperfine structure constants of the free electron with the environmental protons and 14N nucleus were determined. The samples were not displayed before they were not irradiated. The free radicals were found stable at room temperature for more than six months. Som...

Implications of a decay law for the cosmological constant in higher dimensional cosmology and cosmological wormholes

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

Higher dimensional cosmological implications ofa decay law for the cosmological constant term are analyzed. Three independent cosmological models are explored mainly: 1) - In the first model, the effective cosmological constant was chosen to decay with times like Λeffective = Ca-2 + D(b/a i)² where aiis an arbitrary scale factor characterizing the isotropic epoch which proceeds the graceful exit period. Further, the extra-dimensional scale factor decays classically like b(t) ≈ a x (t),xisareal negative number. 2) - In the second model, we adopt in addition to Λeffective = Ca-2 + D(b/a i)² the phenomenological law b(t) = a(t) exp(-Qt) as we expect that at the origin of time, there is no distinction between the visible and extra dimensions; Qis a real number. 3) -In the third model, we...

GUP and higher dimensional Reissner-Nordström black hole radiation

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

Based on the generalized uncertainty principle (GUP), in which the quantum gravitational effects are taken in to account, the corrected Beckenstein-Hawking entropy of the higher dimensional Reissner-Nordström black hole, up to the square order of Planck length, is calculated. Using the corrected entropy, the black hole radiation probability is calculated in the tunneling formalism, which is corrected up to the same order of the Planck length and shows a more probable quantum tunneling. (Source: Brazilian Journal of Physics)

Angiogenic properties of natural rubber latex biomembranes and the serum fraction of Hevea brasiliensis

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

The angiogenic properties of natural rubber were evaluated in this work. We have used the chick chorioallantoic membrane assay (CAM) as a model to investigate the influence of the heating on biological activity in rubber membranes and in non rubber fraction as well. Results showed that natural rubber membranes can induce vascularization. It was observed that angiogenesis activity was maximum when membranes were heated in temperatures between 65ºC and 85ºC, considering a range from 55ºC to 105ºC. The same behavior was observed for non rubber fraction and it indicates that this serum fraction may be responsible for angiogenesis. When infrared spectroscopy was performed in the cast films of non rubber fraction samples, as a function of heating, no structural changes was observed. The resu...

Gupta-Bleuler quantization for massive and massless free vector fields

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

It is shown that the usual quantum field theory leads to an ultraviolet divergence in the vacuum energies and an infrared divergence in the two-point functions of the massive and massless vector fields. Using a new method of quantization it is shown that the vacuum energies converge, and the normal ordering procedure is not necessary. Also the propagators are calculated, which are automatically renormalied. (Source: Brazilian Journal of Physics)

Characteristics of austenitic stainless steel nitrided in a hybrid glow discharge plasma

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

A nitriding process based on two distinct nitrogen glow discharge modes, with sample temperatures ranging from 380 0C to 480 0C, was employed to treat the surface of austenitic stainless steel (SS 304). The temperature is controlled exclusively by switching the operation conditions of the discharges. First mode of operation is the conventional one, named cathodic, which runs at higher pressure values (1 mbar) in comparison to the second mode, named anodic, which runs at the pressure range of 10-3 - 10-2 mbar. Cathodic mode is used to quickly heat the sample holder, by the high ion flux. On the other hand, in the anodic mode, due to the lower operation pressure, higher effective ion acceleration takes place, which allows deeper ion implantation into the sample surface. This hybrid process w...

A 3-D four-wing attractor and its analysis

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

In this paper, several three dimensional (3-D) four-wing smooth quadratic autonomous chaotic systems are analyzed. It is shown that these systems have a number of similar features. A new 3-D continuous autonomous system is proposed based on these features. The new system can generate a four-wing chaotic attractor with less terms in the system equations. Several basic properties of the new system is analyzed by means of Lyapunov exponents, bifurcation diagrams and Poincare maps. Phase diagrams show that the equilibria are related to the existence of multiple wings. (Source: Brazilian Journal of Physics)

Annealing time effect on the properties of CuInSe2 grown by electrodeposition using two electrodes system

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

In this paper, we report the effect of annealing time on the properties of copper indium diselenide CuInSe2 films. The CuInSe2 thin films have been grown at room temperature by electrochemical deposition technique using two electrodes system. The as deposited films were annealed under argon atmosphere at 300 ºC during 15, 30, 45 and 60 min. The structural and morphological properties of the resulting films were characterized respectively by means of x-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical band gap was estimated from transmittance measurements. We have found, that after annealing, all films present CuInSe2 in its chalcopyrite structure and with preferred orientation along <112> direction. The film annealed during 45 min exhibits better crystallinity a...

Sequential and double sequential fission observed in heavy ion interaction Of (11.67 MeV/u)197Au projectile with 197Au target

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

The heavy ion interaction of 11.67 MeV/u 197Au + 197Au has been investigated using mica as a passive detector. By employing Solid State Nuclear Track Detection Technique the data of elastic scattering as well as inelastic reaction channel was collected. The off-line data analysis of multi-pronged events was performed by measuring the three-dimensional geometrical coordinates of correlated tracks on event-by-event basis. Multi-pronged events observed in this reaction were due to sequential and double sequential fission. Using a computer code PRONGY based on the procedure of internal calibration, it was possible to derive quantities like mass transfer, total kinetic energy loss and scattering angles. (Source: Brazilian Journal of Physics)

Coherent vorticity extraction in 3D homogeneous isotropic turbulence: influence of the Reynolds number and geometrical statistics

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

The coherent vorticity extraction method (CVE) is based on the nonlinear filtering of the vorticity field projected onto an orthonormal wavelet basis made of compactly supported functions. CVE decomposes each turbulent flow realization into two orthogonal components: a coherent and an incoherent random flow. They both contribute to all scales in the inertial range, but exhibit different statistical behavior. We apply CVE to 256³ subcubes extracted from 3D homogeneous isotropic turbulent flows at different Taylor microscale Reynolds numbers (R»= 140,240 and 680), computed by a direct numerical simulation (DNS) at different resolutions (N = 256³,512³ and 2048³), respectively. We compare the total, coherent and incoherent vorticity fields obtained by using CVE and show that few wavelets ...

Correlation energy in a triplet state of a two-electron spherical quantum dot

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

Correlation energies in the (1s-1p) triplet state of a two-electron spherical QD with square-well potential confinement are estimated for dots of different radii. The results are presented taking GaAs dot as an example. Our results show that the correlation energies are i) negative in a triplet state in contrast to the singlet state, ii)approaches zero as the dot size approaches infinity, and iii) the "fictitious crossing" of the singlet and triplet state energies at a particular dot size is explained on the basis of Hund's rules. (Source: Brazilian Journal of Physics)

Interatomic coulombic decay: a short review

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

The transition process of the interatomic Coulombic decay (ICD), is an electronic radiationless transition process, driving molecular complexes or clusters to a doubly ionized final state. This process differs from the Auger effect, because it takes place from a neutral monomer after the absorption of a released amount energy of the neighboring monomer in the weakly bound molecule. This process has been theoretically studied and the most recent experimental evidence was observed with neon dimer. This work presents a description of the process and a detailed revision of the derivation for the distribution kinetic energy equation to the emitted electrons by ICD decay, with a small variation in the wave packet form of the transition for the final states , with non-Hermitian time-dependent the...

Study on dual-concentric-core dispersion compensation photonic crystal fiber

Brazilian Journal of Physics — Fri, 23 Oct 2009 15:25:04 +0100

The dual-concentric-core photonic crystal fiber composed of pure silica and air is proposed in this paper. Around 1.55 ¼m, it exhibits a negative chromatic dispersion as high as -5850 ps/km/nm. Based on multipole method, a systemic and in-depth simulation is realized to investigate the mode characteristics. The explanations to propagation states of the fundamental mode and the second mode are given elaborately. Finally, the variation of structural parameters is investigated to evaluate the tolerance of the fabrication. As a result, the designed fiber can be fabricated easily. (Source: Brazilian Journal of Physics)

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