Showing papers in "Brazilian Journal of Physics in 2010"
TL;DR: In this paper, the structural, electronic and elastic properties of Nb4AlC3, a new compound belonging to the MAX phases, were studied using First-principles calculations.
Abstract: 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 the static finite strain technique. We derived the bulk and shear moduli, Young's modulus and Poisson's ratio for ideal polycrystalline Nb4AlC3 aggregate. We estimated the Debye temperature of Nb4AlC3 from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Nb4AlC3 compound, and it still awaits experimental confirmation.
69 citations
TL;DR: In this article, the basic quantum mechanics for a fully general set of Dirac matrices in a curved spacetime was studied by extending Pauli's method, and it was shown that the axioms of quantum mechanics impose a unique form for the Hilbert space scalar product.
Abstract: 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 $\gamma ^\mu $ satisfies a specific PDE. This equation is always satisfied for DFW with its restricted choice for the $\gamma ^\mu $ matrices. It similarly restricts the choice of the $\gamma ^\mu $ matrices for TRD. However, this restriction can be achieved. The frame dependence of a general Hamiltonian operator is studied. We show that in any given reference frame with minor restrictions on the spacetime metric, the axioms of quantum mechanics impose a unique form for the Hilbert space scalar product. Finally, the condition for the general Dirac Hamiltonian operator to be Hermitian is derived in a general curved spacetime. For DFW, the validity of this hermiticity condition depends on the choice of the $\gamma ^\mu $ matrices.
47 citations
TL;DR: In this article, the nonlinear refractive index of Au nanoparticles suspended in PVA solution was measured using a single beam Z-scan technique using a green CW laser beam operated at 532 nm as excitation source.
Abstract: 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.
42 citations
TL;DR: In this article, the structural and electrical properties of Ba(ZrxTi1-x)O3 (x = 0.02-0.2) were analyzed by X-ray diffraction and scanning electron microscopy at room temperature.
Abstract: Lead-free ceramics Ba(ZrxTi1-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(ZrxTi1-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(ZrxTi1-x)O3 ceramics at x=0.05 exhibit excellent piezoelectric properties of high d33 = 208 pC/N, kp = 31.5% and Qm = 500.
36 citations
TL;DR: In this paper, a non-equilibrium statistical ensemble formalism (NESEF) is proposed to deal with the problem of describing and objectivity in the context of thermodynamics.
Abstract: 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 stated that "statistical mechanics has been considered a theoretical endeavor. However, statistical mechanics exists for the sake of the real world, not for fictions. Further progress can only be hoped by close cooperation with experiment". Moreover, one needs to face the study of soft matter and fluids with complex structures (usually of the average self-affine fractal-like type). This is relevant for technological improvement in industries like, for example, that of polymers, petroleum, cosmetics, food, electronics and photonics (conducting polymers and glasses), in medical engineering, etc. It is then required to introduce a thermo-hydrodynamics going well beyond the classical (Onsagerian) one. Moreover, in the both type of situations above mentioned there often appear difficulties of description and objectivity (existence of so-called "hidden constraints"), which impair the proper application of the conventional ensemble approach used in the general, logically and physically sound, and well established Boltzmann-Gibbs statistics. A tentative to partially overcome such difficulties consists in resorting to non-conventional approaches. Here we briefly describe the construction of a Non-Equilibrium Statistical Ensemble Formalism (NESEF) that can deal, within a certain degree of success, with the situations above described. Several particular instances involving experimental observations and measurements in the area of semiconductor physics and in physics of fluids, which were analyzed in the context of the theory, are summarized. They comprise the cases of ultrafast optical spectroscopy; optical and transport processes in low-dimensional complex semiconductors; nonlinear transport in doped highly-polar semiconductors (of use in "blue diodes") under moderate to high electric fields; nonlinear higher-order thermo-hydrodynamics in fluids under driven flow, in normal solutions and in complex situations as in solutions of polymers, micelles, DNA, and in microbatteries.
30 citations
TL;DR: In this paper, the room temperature photoluminescence of Cd1- xMxS (M=Ni, Fe) nanoparticles was investigated and it was shown that the photo-emission of the CdS:Fe nanoparticles peaking at 537 nm because of Fe acting as luminescent centers.
Abstract: 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 peaks position of doped CdS shifts to higher angle.
28 citations
TL;DR: In this paper, the pentacene-based organic thin film transistors (OTFTs) with high-k dielectric Nd2O3 were investigated and a two-step deposition method was used.
Abstract: 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 × 104 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.
23 citations
TL;DR: In this article, the authors examined torsional vibration of single-walled carbon nanotubes (SWCNTs) subjected to initial compression stresses and revealed that the initial stresses present in the tube has a notable effect on the propagation of torsion waves.
Abstract: 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 Flugge 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 application and design of nanoelectronics and nanodevices.
22 citations
TL;DR: 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 1013 n.cm-2.s.h-1.s 1.
Abstract: 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 1013 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 allowable limit dose. Taking into account the use of large boron concentration in the biological shield concrete (2.9% weight fraction), it was obtained a dose rate reduction by one order of magnitude. The dose rate is dominated by the secondary gamma ray. The magnitude of the dose rate on the outside hall of bioshield during normal ITER operation can not be considered low in accordance with the result found in the simulation performed in this work, i.e., 1 µSv.h-1.
19 citations
TL;DR: In this paper, 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 were investigated.
Abstract: 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.
17 citations
TL;DR: In this paper, In2S3 thin films were deposited by CBD and co-evaporation methods and these were employed as buffer layer in CuGaSe2-based solar cells.
Abstract: 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 conditions were found for reproducible and good quality In2S3 thin films synthesis. By depositing In2S3 thin films as buffer layers in CuGaSe2 configuration, a maximum solar cell efficiency of 6% was achieved, whilst the reference solar cell with CdS/CuGaSe2 on similar absorber exhibited 7% efficiency.
TL;DR: In this paper, the power and efficiency performance of a thermal Brownian heat engine with and without external forces and contact with alternating hot and cold reservoirs along the space coordinate were investigated by numerical calculations.
Abstract: 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, ie barrier height of the potential, asymmetry of the potential and temperature ratio of the heat reservoirs on the power output, the efficiency and the current performances of the Brownian heat engine are investigated in detail by numerical analysis When there is no external force, the power output versus efficiency characteristic curves are closed loop-shaped ones, which are similar to those of real conventional irreversible heat engines; whereas when the external force is considered, the power output versus efficiency characteristic curves of the heat engine changed into open loop-shaped ones Furthermore, the limited regions of the external force and barrier height of the potential are explored by analyzing the current property of the model It is shown that by reasonable choice of the parameters, the Brownian heat engine can be controlled to operate in the optimal regimes
TL;DR: In this article, a quantum-field-theoretical description of the interaction between stationary and localized external sources linearly coupled to bosonic fields is presented, where external sources that simulate not only point charges but also higher-multipole distributions along D-dimensional branes.
Abstract: 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].
TL;DR: In this paper, 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.
Abstract: 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.
TL;DR: In this paper, the optical transmission, absorption coefficient and optical birefringence of 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.
Abstract: 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.
TL;DR: In this article, the role of weak but finite electron inertia on the sheath formation condition was investigated and it was found that the weak but fixed electron inertia reduces the threshold value of ion Mach number that may be, at least in principle, of qualitative value to define the boundary boundary.
Abstract: 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 width of non- neutral space charge layer over which major potential drop and charge imbalance occurs. Detailed numerical analysis and results of quantitative and qualitative importance are included in the text.
TL;DR: In this paper, the authors evaluated the thermal and epithermal neutron fluence rates in the three irradiation facilities of the TRIGA IPR-R1 nuclear reactor at the Centro de Desenvolvimento da Tecnologia Nuclear CDTN/CNEN, Belo Horizonte, Brazil.
Abstract: 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 HPGe detector. For the rotary specimen rack, the values obtained for thermal and epithermal neutron fluence rates are (8.2 ± 0.2) × 1011n.cm-2.s-1 and (3.5 ± 0.1) × 1010n.cm-2.s-1, respectively. For the pneumatic transfer tube and the central tube, epithermal neutron fluence rate values are respectively (3.3 ± 0.2) ×109n.cm-2.s-1 and (2.6 ± 0.1) x 1011n.cm-2.s-1. For these facilities, thermal neutron fluence rate values are (2.5 ± 0.2) × 1011n.cm-2.s-1 and (2.8 ± 0.1) × 1012n.cm-2.s-1, respectively. Knowledge of these parameters will be fundamental in the planning of sample irradiation for analysis or radioisotope production in a more accurate way.
TL;DR: In this article, the authors verified 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 the closed universe of the Friedmann-Lemaitre-Robertson-Walker (FLRW).
Abstract: 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-Lemaitre-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).
TL;DR: In this paper, a 2.5kJ plasma focus device (SBUPF1) was constructed on the basis of a simple configuration, which has been tested between 18-25kV and wide range of pressure for various gases including Argon, Neon and Deuterium.
Abstract: 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).
TL;DR: In this paper, the construction of an alternative electromagnetic theory that preserves Lorentz and gauge symmetries, is considered, and it is shown that there exist two radically different electrodynamics, namely, the Chern- Simons and the Podolsky formulations, in which this problem can be overcome.
Abstract: 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 Lagrangian. This theory, usually known as Podolsky electrodynamics, is simultaneously gauge and Lorentz invariant; in addition, it contains a massive photon. Therefore, a massive photon, unlike the popular belief, can be adequately accommodated within the context of a gauge- invariant electrodynamics.
TL;DR: In this article, the authors measured the plasma boundary shift using array of magnetic pick-up coils on the IR-T1 tokamak and also approximated the magnetic surfaces by an equilibrium calculation.
Abstract: 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.
TL;DR: In this paper, an effective cosmology a la Brans-Dicke with two interacting scalar fields is discussed, where a non-minimally coupling massive inflaton Higgs-like scalar field Φ interacting with a minimally coupling massless scalAR field χ.
Abstract: 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.
TL;DR: This work evaluates the absorbed dose in the CDTN/CNEN GammaCell Irradiation Facility, using the Monte Carlo N-Particles (MCNP) code, and the isodoses curves are measured using dosimeters or computer simulations.
Abstract: 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.
TL;DR: In this paper, it was shown that a class of metric-affine gravities can be reduced to a Riemann-Cartan one based on the cancelation of the non-metricity against the symmetric components of the spin connection.
Abstract: 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 interpretation in the Riemann-Cartan geometry.
TL;DR: Polarized Raman spectra of L-arginine hydrochloride monohydrated single crystal in nine different scattering geometries of the two irreducible representations of factor group C2 were studied at room temperature as discussed by the authors.
Abstract: Polarized Raman spectra of L-arginine hydrochloride monohydrated single crystal 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.
TL;DR: In this article, collective coordinate analysis for adding a space dependent potential to the double sine-Gordon model is presented, and the interaction of solitons with a delta function potential barrier and also delta function function potential well is investigated.
Abstract: 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.
TL;DR: In this paper, a modified Friedmann-Robertson-Walker cosmology is discussed in which the equation of state behaves like p = 3ηam ρn -ρ,(η,m,n) ∈.
Abstract: This letter discusses a modified Friedmann-Robertson-Walker cosmology in which the equation of state behaves like p = 3ηam 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.
TL;DR: In this article, the results for the neutrons production of various types of targets using the MCNPX 2.6.0 code are shown and a comparative study of transport models to describe the spallation reactions available in this code is performed.
Abstract: 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 2.6.0 code. Furthermore, it is performed a comparative study of transport models to describe the spallation reactions available in this code.
TL;DR: In this paper, the authors find a link between oriented matroid theory and 2D gravity with torsion, which 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.
Abstract: 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.
TL;DR: In this paper, the authors reported the first and definite experimental evidence for γ-, X-, or β radiation causing UV dominant optical radiation from radiochemicals such as 131I, XRF sources such as Rb XRF source present as salts, and metal sources, such as 57Co, and Cu XRF Source.
Abstract: 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 γ-, X-, or β radiation passes through core-Coulomb field. In turn, the Bharat energy internally produced within the excited atom causes UV dominant high-energy spectrum by valence excitation. As excited atoms become free from surrounding unexcited atoms by valence excitation, room temperature atomic spectra of solid radioisotopes and XRF sources became a possibility. It implies existence of temporary atomic state of solids. The experimental evidence that γ-, X-, and β radiations causing UV dominant optical emission from within excited atoms of radioisotopes suggests the possibility for solar γ-, X-, and β radiations causing EUV by the atomic phenomenon described here.