Subjects -> PHYSICS (Total: 898 journals)     - ELECTRICITY AND MAGNETISM (9 journals)    - MECHANICS (22 journals)    - NUCLEAR PHYSICS (52 journals)    - OPTICS (97 journals)    - PHYSICS (659 journals)    - SOUND (26 journals)    - THERMODYNAMICS (33 journals) PHYSICS (659 journals)                  1 2 3 4 | Last

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 Brazilian Journal of PhysicsJournal Prestige (SJR): 0.276 Citation Impact (citeScore): 1Number of Followers: 1      Hybrid journal (It can contain Open Access articles) ISSN (Print) 0103-9733 - ISSN (Online) 1678-4448 Published by Springer-Verlag  [2626 journals]
• Correction to: Effect of Gold Nanoparticles and Unwanted Residues on Raman
Spectra of Graphene Sheets
• Abstract: In the original article Chiara Valsecchi’s last name was spelled incorrectly. It is correct as reflected here.
PubDate: 2019-04-01

• A Study on the Synthesis of Superheavy Element Z = 125
• Abstract: We have studied the α-decay chains of superheavy nuclei Z = 125 in the range 265 ≤ A ≤ 336. The nuclei 303–315125 were found to have long half-lives and hence could be sufficient to detect them if synthesized in a laboratory. After identifying the possible isotopes, we have identified the most probable projectile-target combinations by studying the fusion cross section, evaporation residue cross section, compound nucleus formation probability (PCN), and survival probability (PSurv). The selected most probable projectile-target combinations to synthesize superheavy nuclei 303–315125 are Co+Cf, Ni+Bk, and Cu+Cm. We hope that our predictions may be guide for the future experiments in the synthesis of the new superheavy element Z = 125.
PubDate: 2019-04-01

• Evolution of Statistical Properties of Hybrid System Starting from Binary
Field States Constructed in Experiments
• Abstract: In quantum optics, researchers usually study evolution of states starting from traditional ones: coherent, squeezed, Fock, and their superpositions. In a recent work (Ferreira et al. Int. J. Mod. Phys. B, 1850222, 2018), we discussed an example of ex- periment involving “atom”-field interaction allowing us to construct a list of field states inside a high-Q microwave cavity. The procedure employed a dispersive Hamiltonian ensuring both sub-systems to remain with only two Fock state components for all times of their evolution. The aim was to use this sequence of states having pre-selected properties as initial states in other investigations. Here, we use an updated platform and a variety of states at our disposal in the mentioned list to study the evolution of a hybrid system under the action of the Jaynes-Cummings Hamiltonian. Interesting results are obtai- ned, e.g., when we examine how the “atomic” population inversion and field statistics evolve in time from initial field states with different degrees of super- and sub-Poissonian effects. The experimental feasibility of the proposal was also discussed.
PubDate: 2019-04-01

• History and National Initiatives of Carbon Nanotube and Graphene Research
in Brazil
• Abstract: In this article, we first introduce and discuss the fundamental science of carbon nanomaterials (especially nanotubes and graphene) and the different technological applications from using these materials. We then discuss the first works of Brazilians scientists, done in collaboration with scientists of other countries and, in particular, the role of Prof. M. S. Dresselhaus from MIT, US, in the development of the nanocarbon science in Brazil. We briefly discuss some experimental and theoretical works about nanotubes and graphene done in Brazil in the late 1990s and early 2000s, and the formation of the first Brazilian network on carbon nanotubes in 2005. We present the activities of the National Institute of Science and Technology (INCT) in Carbon Nanomaterials (CN) created in 2009. A scientometric analysis is used to describe the INCT-CN network formation. Finally, we present the Center of Technology in Nanomaterials (CTNano) installed at UFMG, where pilot plants were developed to produce graphene and nanotubes at large scales, and the work being done at the center in collaboration with companies aiming to solve specific technological problems and to create bridges between the academic and the industrial sectors.
PubDate: 2019-04-01

• Feedback Control on Einstein-Podolsky-Rosen Steering of Dissipative System
• Abstract: In this article, we investigate the behaviors of Einstein-Podolsky-Rosen (EPR) steering for two uniformly accelerated atoms coupled with electromagnetic vacuum fluctuation. We firstly analyze the solving process of master equation that describes the system evolution. Unlike the complicated behaviors of entanglement, EPR steering decays with decoherent time and presents sudden death, the critical points of which can be located. In addition, small acceleration and interatomic distance can decrease the degradation of EPR steering. Since the measure of EPR steering adopted in this paper is equivalent to that of Bell non-locality, the EPR steering dynamics discussed in the article is applied equally to Bell non-locality.
PubDate: 2019-04-01

• Topology of the Magnetic Field and Resistivity of a Compact Torus
Generated in a Mirrorless Theta Pinch
• Abstract: The mapping of the magnetic field and analysis of the plasma resistivity were used to study the change of magnetic field topology during the formation of a reversed field configuration. Using a theta pinch with straight coil, the formation of the torus was observed during the early time of the plasma radial implosion, in scale comparable to Alfvén’s time and shorter than the resistive diffusion. The non-intrusive excluded flux probe also indicated the formation of the torus even in the absence of mirror coils in the system. The plasma at the end region of the coil has distributed in the entire cross section of the tube, slightly peaked at the null field region. The anomalous plasma resistivity at the reconnection site was close to the prediction given by numerical calculation using numerical hybrid code with anomalous collision frequency either calculated using Chodura’s algorithm or evolution of microinstabilities, particularly the lower hybrid drift instability.
PubDate: 2019-04-01

• White Dwarf Spectra for Studies of Time Variation of the Fine Structure
Constant
• Abstract: We report a newly updated constraint on space-time variation in the fine structure constant, $$\alpha =\frac{e^2}{4\pi {\varepsilon}_0\mathit{\hslash c}}$$ , from an analysis of white dwarf spectra. We obtain ∆α/α = (0.007 ± 0.087) × 10−6 from a comparison of laboratory spectra of Fe V with those found in the spectra from the white dwarf G191-B2B. The obtained result in this study is used to suggest further improvement in observational technique which would lead to a tighter constraint on ∆α/α.
PubDate: 2019-04-01

• Face to Face Collisions of Ion Acoustic Multi-Solitons and Phase Shifts in
a Dense Plasma
• Abstract: This work investigates the interactions among ion acoustic (IA) single- and multi-soliton and their corresponding phase shifts in an unmagnetized plasma composed of degenerate electrons, positrons, and positive ions. Two-sided Korteweg-de Vries (KdV) equations are derived by employing the extended Poincaré-Lighthill-Kuo (PLK) method for the stretched coordinates. The single- and multi-soliton solutions of the KdV equations are constructed by using the Hirota’s method. The phase shifts are determined for two-, four-, six-, and eight-IA scattering solitons. The effect of positron concentration on electrostatic IA resonances due to the interactions among solitons and their corresponding phase shifts are investigated.
PubDate: 2019-04-01

• Emergent D -Instanton as a Source of Dark Energy
• Abstract: We revisit a non-perturbative formulation leading to a vacuum-created gravitational pair of $$(3\bar {3})$$ -brane by a Poincare dual higher form U(1) gauge theory on a D4-brane. In particular, the analysis has revealed a dynamical geometric torsion $$\mathcal {H}_{3}$$ for an onshell Neveu-Schwarz (NS) form on a fat 4-brane. We argue that a D-instanton can be a viable candidate to incorporate the quintessence correction hidden to an emergent (3 + 1)-dimensional brane universe. It is shown that a dynamical non-perturbative correction may be realized with an axionic scalar QFT on an emergent anti-3-brane within a gravitational pair. The theoretical tool provokes thought to believe for an extra instantaneous dimension transverse to our classical brane-universe in an emergent scenario. Interestingly a D-instanton correction, sourced by an axion on an anti-3-brane, may serve as a potential candidate to explain the accelerated rate of expansion of our 3-brane universe and may provide a clue to the origin of dark energy.
PubDate: 2019-04-01

• Combining Small-Angle X-ray Scattering and X-ray Powder Diffraction to
Investigate Size, Shape and Crystallinity of Silver, Gold and Alloyed
Silver-Gold Nanoparticles
• Abstract: The combination of simultaneous measurements of small and wide angle X-ray scattering (SAXS/WAXS–SWAXS) to investigate the overall size, shape, and crystallinity of silver nanoparticles and alloyed silver-gold nanoparticles in the size range of 8 to 80 nm is shown. The obtained results for overall size are in agreement with the particle size obtained by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). In addition to the overall size, SWAXS provided precise information about the crystallographic internal structure of the particles, providing a powerful multi-scale tool for structural characterization of the studied systems.
PubDate: 2019-04-01

• Transitioning Scenario of Bianchi-I Universe Within f ( R , T ) Formalism
• Abstract: In this paper, we report the existence of transitioning scenario of Bianchi type I universe in the context of f (R,T) gravity with special case f (R,T) = f1(R) + f2(R)f3(T) and its functional forms f1(R) = f2(R) = R and f3(T) = αT with α being constant. The exact solution of the Einstein’s field equations is derived by using the generalized hybrid expansion law that yields the model of transitioning universe from early deceleration phase to current acceleration phase. Under this specification, we obtain the singular as well as non singular solution of Bianchi type I model depending upon the particular choice of the value of problem parameters. We also notice that the validation of weak energy condition and dominant energy condition and violation of strong energy condition occurs for these values of problem parameters. The deceleration parameter is found to be negative at present (z = 0) in the derived model which is supported by recent observations.
PubDate: 2019-04-01

• Dielectric, Photophysical, Solvatochromic, and DFT Studies on Laser Dye
Coumarin 334
• Abstract: The absorption and fluorescence spectra of laser dye, 10-acetyl-2,3,6,7-tetrahydro-1H,5H,11H-pyrano[2,3-f]pyrido[3,2,1-ij]quinolin-11-one [C-334], are recorded. The ground-state dipole moments (μg) were determined from density functional theory (DFT) computations, Guggenheim’s, and solvatochromic methods. The excited-state dipole moments (μe) were determined from Lippert’s, Bakhshiev’s, Kawski-Chamma-Viallet’s, and McRae’s equations. The μe values are found to be higher than μg values and this suggest that the probe molecule is more polar in the excited state. The absorption maxima and emission maxima of C-334 undergo bathochromic shift as the polarity of the solvent increases and indicates that the transitions involved are π → π*. The change in dipole moment (Δμ) and the angle between μe and μg is calculated. The absorption and fluorescence emission of the probe C-334 were investigated theoretically with the help of Gaussian 09W for all the studied solvents by using time-dependent (TD)-DFT combined with conductor-like polarizable continuum model (CPCM) solvation model and were compared with the experimental results. Further, the ground- and excited-state dipole moments were also estimated for all the studied solvents by using CPCM solvation model and are compared with the experimental results. The HOMO-LUMO energy gaps computed using DFT and from absorption threshold wavelengths are found to be in order with each other. The chemical hardness (η) of the probe molecule is estimated and the results suggest the soft nature of the molecule. Further, the reactive centers like electrophilic site and nucleophilic site were identified with the help of molecular electrostatic potential (MESP) 3D plots using DFT computational analysis.
PubDate: 2019-04-01

• The Double-Slit Electron Diffraction Experiment with Aharonov-Bohm Phase
Effect Revisited and the Divergence in its Asymptotic Form
• Abstract: In this work, we consider the experiment of diffraction and interference of electrons through a double slit added to the Aharonov-Bohm phase effect. We applied the asymptotic Fresnel functions to one term of the interference process obtaining an expression for the intensity with divergence for certain values of the flow parameter. This led us to an expression incapable of recovering the asymmetry effects of the diffraction pattern arising from the AB phase, as might be expected, since purely quantum effects cannot be classically reproduced.
PubDate: 2019-04-01

• Trojan Quantum Walks
• Abstract: We investigate the transport properties and entanglement between spin and position of one-dimensional quantum walks starting from a qubit over position states following a delta-like (local state) and Gaussian (delocalized state) distributions. We find out that if the initial state is delocalized enough and a NOT gate reflects this state backwards, then the interference pattern extinguishes the position dispersion without preventing the propagation of the state. This effect allows the creation of a Trojan wave packet, a non-spreading and non-stationary double-peak quantum state.
PubDate: 2019-04-01

• A New Algorithm to Study the Critical Behavior of Topological Phase
Transitions
• Abstract: Topological phase transitions such as the Berezinskii-Kosterlitz-Thouless (BKT) transition are difficult to characterize due to the difficulty in defining an appropriate order parameter or to unravel its critical properties. In this paper, we discuss the application of a newly introduced numerical algorithm that was inspired by the Fisher zeros of the partition function and is based on the partial knowledge of the zeros of the energy probability distribution (EPD zeros). This iterative method has proven to be quite general, furnishing the transition temperature with great precision and a relatively low computational effort. Since it does not need the a priori knowledge of any order parameter it provides an unbiased estimative of the transition temperature being convenient to the study of this kind of phase transition. Therefore, we applied the EPD zeros approach to the 2D XY model, which is well known for showing a BKT transition, in order to demonstrate its effectivity in the study of the BKT transition. Our results are consistent with the real and imaginary parts of the pseudo-transition temperature, T(L), having a different asymptotic behavior, which suggests a way to characterize a BKT like transition.
PubDate: 2019-04-01

• Head-on Collision of Ion-Acoustic Shock and Solitary Waves in
Collisionless Plasma with Pair Ions and Electrons
• Abstract: Unmagnetized collisionless plasma system consisting of positive and negative ions and electrons is considered to study the head-on collision of ion-acoustic shock and solitary waves (IASWs) and its effects on the formation of shock (monotonic and oscillatory) waves and phase shift. The soliton solution is derived from the two-sided Korteweg-de Vries Burger (KdVB) equations. The KdVB equations are obtained using extend Poincaré-Lighthill-Kuo (ePLK) method. It is assumed that the negative ions are immobile and the electrons follow the Boltzmann energy distribution in the plasma. The effects of plasma parameters such as density ratios and kinematic viscosities on electrostatic shock profiles, phase shift, amplitudes, and formation of shock (monotonic and oscillatory) as well as on the soliton solution are investigated. It is found that the density ratio of negative to positive ions plays a vital role on the formation of shock waves and phase shift after collision.
PubDate: 2019-04-01

• Quantum Coherence Behaviors for a Uniformly Accelerated Atom Immersed in
Fluctuating Vacuum Electromagnetic Field with a Boundary
• Abstract: We investigate the dynamics of quantum coherence (QC) for a uniformly accelerated atom interacting with fluctuating electromagnetic field subject to a conductor boundary. We firstly derive the master equation that the atom evolution obeys. We find that without boundary, QC declines under the effect of Unruh thermal bath and vacuum fluctuation. However, with a boundary, the degradation, fluctuation, and preservation of QC are closely related to boundary effect, atomic polarization, and acceleration. Furthermore, in the presence of a boundary, QC can effectively be protected under the influence of the vacuum fluctuation and Unruh thermal effect when the atom is transversely polarizable and near this boundary, and the presence of boundary gives us more freedom of controlling the QC behaviors.
PubDate: 2019-04-01

• Statistical Mesoscopic Hydro-thermodynamics: the Description of Kinetics
and Hydrodynamics of Nonequilibrium Processes in Single Liquids
• Abstract: Hydrodynamics, a term apparently introduced by Daniel Bernoulli (1700–1783) to comprise hydrostatic and hydraulics, has a long history with several theoretical approaches. Here, after a descriptive introduction, we present so-called mesoscopic hydro-thermodynamics, which is also referred to as higher order generalized hydrodynamics, built within the framework of a mechanical-statistical formalism. It consists of a description of the material and heat motion of fluids in terms of the corresponding densities and their associated fluxes of all orders. In this way, movements are characterized in terms of intermediate to short wavelengths and intermediate to high frequencies. The fluxes have associated Maxwell-like times, which play an important role in determining the appropriate contraction of the description (of the enormous set of fluxes of all orders) necessary to address the characterization of the motion in each experimental setup. This study is an extension of a preliminary article: Physical Review E 91, 063011 (2015).
PubDate: 2019-04-01

• Structure of Baryons in a Semi-Relativistic Quark Model
• Abstract: The spectroscopy of light and strange baryons and elastic electromagnetic form factors of nucleon have been studied through a simple semi-relativistic quark model. For SU(6)-invariant part of spectrum, we treated the baryons as a spin-independent three-body bound system and presented the exact analytical solution of three-body Klein–Gordon equation. Considering the SU(6)-invariant interaction as a combination of scalar linear and vector Coulombic-like potentials, we obtained analytical formulas for energy levels and the hyperradial wave functions which have been employed in the calculations of the mass spectrum of baryons, electromagnetic elastic form factors, and charge radii of nucleon. The evaluated observables have been compared with experimental data, and it has been shown that the present model leads to a fairly good description of the observed resonances.
PubDate: 2019-03-20

• Statistical Aspects and Dynamical Entanglement for a Two-Level Atom Moving
on Along Cavity Length of x-Direction: Atomic Position Distribution
• Abstract: In this work, the problem of the quantum optical model is considered where an one-mode quantized radiation field interacts with a two-level atom (TLA). Also, the atomic position distribution is taken into account, i.e., the atom passing through the length of the optical cavity. We believe that the atomic position affects the matter-field interaction and can be realized in several multiple experiments, such as ultracold atoms and trapped ions. We take into consideration the atom is moving along the cavity field in the x-direction so that the time-position Schrödinger equation for the atom in the x-direction is obtained. We suppose that the field is initially prepared in a coherent state optical field and the atom is initially prepared in an excited state. Also, the atomic motion along the cavity length vanishes in the cavity wall. By using the Laplace transformation method, an exact analytical solution for the coupled partial differential Schrödinger equation for the wave function is calculated. Some non-classical statistical aspects such as the atomic inversion and the photon distributions are discussed in detail. The collapses-revivals, the Poissonian distributions of the photon by Mandel Q parameter, the degrees of the entanglement, and the fidelity have been investigated. The effect of the atomic position distribution in the x-direction on these phenomena is examined. We observed that the atomic position distribution along the cavity has an effective effect on the quantum statistical properties of these phenomena. Minutely, the influence of the atom location distribution on the amount of quantum entanglement has been obtained.
PubDate: 2019-03-12

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