The self-diffusion constant for large heavy particles

We construct a closed-form expression for the self-diffusion constant, D, for a hard-sphere particle whose mass and radius are large compared to the corresponding bath-particle quantities. The expression yields the Stokes-Einstein law at high bath-particle densities and the Boltzmann form for low densities. In addition, the first density correction to D is obtained and the higher-order density corrections are shown to diverge. The second density correction diverges as ?log(k₀R), where k₀ is a cutoff wavevector and R is the radius of the particle.     

Entropy correction to stationary black hole via fermions tunneling beyond semiclassical approximation

Recently, fermions tunneling beyond semiclassical approximation from an uncharged static black hole was investigated by Majhi, which was based on the work of Banerjee and Majhi, it was found that the black hole entropy correction can be produced as the quantum effect of a particle is taken into account. In this paper, we further extend this idea to the stationary Kerr black hole to discuss its entropy correction. To get the corrections correctly, the proportionality parameters of quantum corrections of action I _i to the semiclassical action I ₀ in this case are regarded as the inverse of the product of Planck Length and Planck Mass. The result shows that entropy corrections to the stationary black hole also include the logarithmic term and inverse area term in Bekenstein–Hawking entropy beyond semiclassical approximation.     

Predicting macroscopic thermal expansion of metastable liquid metals with only one thousand atoms

Results of thermal expansion prediction from atomic scale for metastable liquid metals are reported herein. Three pure liquid metals Ni, Fe, and Cu together with ternary Ni₆₀Fe₂₀Cu₂₀ alloy are used as models. The pair distribution functions were employed to monitor the atomic structure. This indicates that the simulated systems are ordered in atomic short range and disordered in long range. The thermal expansion coefficient was computed as functions of temperature and atom cutoff radius, which tends to maintain a constant when the cutoff radius increases to approximately 15 Å. In such a case, slightly more than 1000 atoms are required for liquid Ni, Cu, Fe and Ni₆₀Fe₂₀Cu₂₀ alloy, that is, the macroscopic thermal expansion can be predicted from the volume change of such a tiny cell. Furthermore, the expansion behaviors of the three types of atoms in liquid Ni₆₀Fe₂₀Cu₂₀ alloy are revealed by the calculated partial expansion coefficient. This provides a fundamental method to predict the macroscopic thermal expansion from the atomic scale for liquid alloys, especially in the undercooled regime.     

Finite temperature QCD corrections to lepton-pair formation in a quark-gluon plasma

We discuss theO(α _S ) corrections to lepton-pair production in a quark-gluon plasma in equilibrium, assuming the quarks are massless at zero temperature. The corrections are found to be very small in the domain of interest for ultrarelativistic heavy ions collisions. Interesting effects, however, appear at the annihilation threshold of the thermalized quarks where the correction factor has a (1/α _S ) behavior.     

Gate-controlled electron–electron interactions in an In0.53Ga0.47As/InP quantum well structure

We study the parabolic negative magnetoresistivity in a gated In_0.53Ga_0.47As/InP quantum well structure where the scattering potential is predominantly long range. This magnetoresistivity is caused by the electron–electron interactions and is fitted to estimate the interaction corrections to the Drude conductivity. These corrections are smaller than the prediction of a recent theory [I.V. Gornyi, A.D. Mirlin, Phys. Rev. Lett. 90 (2003) 076801], and can be quantitatively described by Altshuler’s theory.     

Emergence of electromagnetically induced absorption in a perturbation solution of optical Bloch equations

We study phenomenon of electromagnetically induced absorption (EIA) in the Hanle configuration by applying a perturbative method to solve linear system of optical Bloch equations (OBEs) for the case of closed F _g = 1 → F _e = 2 transition. The method is applied assuming stationary case and a weak laser fields (Ω ≪ Γ, i.e., Rabi frequency small compared to spontaneous emission rate). This way, we calculate (both numerically and analytically) higher order corrections to density matrix. Odd corrections give contributions to optical coherences, while even corrections contribute to populations and Zeeman coherences. The method gives insight into mechanism of transfer of coherences and transfer of populations between Zeeman sublevels. We have found that the ground-state coherences (2nd correction to coherences) are crucial for the 4th correction to the change of populations which brings EIA type behavior of the Hanle spectrum. Using exact analytical expressions we further discuss further the role of decoherence of the ground-state sublevels when forming EIA.     

Entropic Corrections to Coulomb’s Law

Two well-known quantum corrections to the area law have been introduced in the literatures, namely, logarithmic and power-law corrections. Logarithmic corrections, arises from loop quantum gravity due to thermal equilibrium fluctuations and quantum fluctuations, while, power-law correction appears in dealing with the entanglement of quantum fields in and out the horizon. Inspired by Verlinde’s argument on the entropic force, and assuming the quantum corrected relation for the entropy, we propose the entropic origin for the Coulomb’s law in this note. Also we investigate the Uehling potential as a radiative correction to Coulomb potential in 1-loop order and show that for some value of distance the entropic corrections of the Coulomb’s law is compatible with the vacuum-polarization correction in QED. So, we derive modified Coulomb’s law as well as the entropy corrected Poisson’s equation which governing the evolution of the scalar potential ϕ. Our study further supports the unification of gravity and electromagnetic interactions based on the holographic principle.     

Nonlocal quark model beyond mean field

The nonlocal chiral quark model is extended beyond mean field using a strict 1/N _c expansion scheme. The nonlocal interaction has the advantage that all diagrams are finite and leads to unique evaluation of the 1/N _c corrections. Parameters of the nonlocal model are refitted making use of the physical values of the pion mass and the weak pion decay constant. The size of the 1/N _c correction to the quark condensate is carefully studied in nonlocal and local Nambu-Jona-Lasinio models. It is found that even the sign of the corrections can be different.     

Thermodynamic translational invariance in concurrent multiscale simulations of liquids

AdResS multi scale simulations of liquid systems allow for a free exchange of particles between regions, where their interactions are described by different models. The desired “model coexistence” is somewhat reminiscent of phase-coexistence. But while the latter describes heterogeneous systems with position-independent interactions, AdResS is meant to generate homogeneous systems with position-dependent interactions. Here we formulate the bulk equilibrium conditions for model coexistence, discuss the connection between the Hamiltonian H-AdResS scheme and widely used free energy methods based on the Kirkwood coupling parameter method of thermodynamic integration, and point out the relation between thermodynamic corrections in AdResS simulations and tail corrections for truncated long-range potentials. In particular, we use the analogy to derive expressions for the form of the correction profiles in narrow transition zones, which cannot be fully described by the local coupling parameter approximation. Finally, we illustrate how to treat transient mergers of small, diffusing all atom zones attached to reference particles in dynamic AdResS simulations without additional calibrations beyond the initial parameterization of the correction profile for individual all atom zones.     

The effect of Fermi momentum cutoff on the binding energy of closed shell nuclei in the LOCV framework

The ground state binding energies of the light symmetric closed-shell nuclei, i.e., ⁴He, ¹²C, ¹⁶O and ⁴⁰Ca and the heavy asymmetric ones, i.e., ⁴⁸Ca, ⁹⁰Zr and ¹²⁰Sn are calculated in the harmonic oscillator (HOS) basis, by imposing the relative Fermi momentum cutoff of two point-like interacting nucleons on the density dependent average effective interactions (DDAEI). The DDAEI are generated through the lowest order constrained variational (LOCV) method calculations for the asymmetric nuclear matter with the operator and the channel dependent type bare nucleon-nucleon potentials, such as the Argonne $Av_{18}^{j_{\max } = 2}$ and the Reid soft core, Reid68, interactions. In the framework of harmonic oscillator shell model, the cutoff is imposed by defining the maximum value of the relative quantum numbers (RQN_max) in two ways: (1) The RQN_max of the last shell and (2) the RQN_max of each shell, in the ground state of the nucleus. It is shown that present results on the binding energies and the root means square radius are closer to the corresponding experimental data than, our previous works with the same DDAEI potentials, but without the cutoff constraint. However, for the light symmetric nuclei, the second scheme gives less binding energy and larger root mean square radius compare to the first one. While the situation is reversed for the heavier nuclei.     

The quark compound bag model: Defining the admixture of six-quark bag in the deuteron

The probability of the six-quark bag part of the deuteron is defined within recently formulated quark compound bag (QCB) model. An upper limit of about 1 % for the admixture of the confined bag in the deuteron is found for the QCB potential supplied by the long range Paris interaction. The six-quark bag corrections to the static multipole moments of the deuteron are estimated to be ?1 % forμ _d and ?6% forQ _d .     

Laser-induced gas-surface interactions

Chemical reactions in homogeneous systems activated by laser radiation have been extensively investigated for more than a decade. The applications of lasers to promote gas-surface interactions have just been realized in recent years. The purpose of this paper is to examine the fundamental processes involved in laser-induced gas-surface chemical interactions. Specifically, the photon-enhanced adsorption, adsorbate-adsorbate and adsorbate-solid reactions, product formation and desorption processes are discussed in detail. The dynamic processes involved in photoexcitation of the electronic and vibrational states, the energy transfer and relaxation in competition with chemical interactions are considered. These include both single and multiple photon adsorption, and fundamental and overtone transitions in the excitation process, and inter- and intra-molecular energy transfer, and coupling with phonons, electron-hole pairs and surface plasmons in the energy relaxation process. Many current experimental and theoretical studies on the subject are reviewed and discussed with the goal of clarifying the relative importance of the surface interaction steps and relating the resulting concepts to the experimentally observed phenomena. Among the many gas-solid systems that have been investigated, there has been more extensive use of CO adsorbed on metals, and SF₆ and XeF₂ interactions with silicon as examples to illustrate the many facets of the electronically and vibrationally activated surface processes. Results on IR laser stimulated desorption of C₅H₅N and C₅D₅N molecules from various solid surfaces are also presented. It is clearly shown that rapid intermolecular energy exchange and molecule to surface energy transfer can have important effects on photodesorption cross sections and isotope selectivities. It is concluded that utilization of lasers in gas-surface studies not only can provide fundamental insight into the mechanism and dynamics involved in heterogeneous interactions, but also offer the possibility for technical innovation for practical applications.     

On the corrections of the wave function in weakly bound quarkonium

A non-relativistic quark-antiquark system with perturbative gluonic interactions (quarkonium) is considered, which allows a systematic expansion in the strong coupling constant α_s. In a non-abelian gauge theory, non-trivial corrections of the wave function already occur to O(α_s). We emphasize the existence of a renormalization, which is “natural” for such a system leaving only little freedom in the choice of the renormalization point Λ. The general corrections to O(α_s) including coulombic binding are presented. An explicit application to the lowest-order gluonic corrections of the leptonic decay of quarkonium is made. In this process the new term is sometimes much larger than the gluonic correction at the photon vertex and it varies greatly between different coulombic (S-wave) bound states.     

Radiative corrections to positronium decay

In this work a method for calculating radiative corrections to positronium decay is presented that is direct, and allows for a systematic extension applicable to the calculation of corrections beyond the first [o(α)] correction. An expression for the decay amplitude in terms of the Bethe-Salpeter wavefunction is employed. The Bethe-Salpeter wavefunction is evaluated perturbatively in a scheme having a lowest-order bound state equation that is exactly soluble. The decay amplitude is evaluated in Coulomb gauge, without the introduction of a photon mass. One-loop renormalization in Coulomb gauge is shown to be consistent. Using this method the known analytic result for the o(α) correction to the parapositronium decay rate is obtained. The same method is applied to orthopositronium, and the existing theoretical discrepancy in the value of the o(α) correction to the decay rate is resolved. This o(α) correction is obtained with an error which corresponds to an uncertainty in the total rate much smaller than α²Γ_LO (where Γ_LO is the lowest-order rate). Also, the o(α) correction to the differential decay rate is computed for the first time.     

On a quasi-elastic mechanism of the reaction d(p, 2p)n

The problem on validity of quasi-elastic mechanism of the reaction d(p, 2p)n in the range of low energies (20–50 MeV) is studied. While estimating the effect of multiple scattering it is shown that the condition of quasi-elasticity holds sufficiently well in all the considered cases under the assumption on peripheral collision of counted particles (the cutoff method). The dependence of the cutoff radius R₀ on the energy of incident particles E₀ is discussed.     

Properties of high-Tc superconducting circular waveguides with Meissner boundary

The propagation properties of the TE-modes in a high-temperature superconducting circular waveguide using the Mei\ner boundary conditions on the wall are presented for the first time. The results show that now the normalized cutoff parameterk _c R, (whereR is the radius of the superconducting circular waveguide andk _c the cutoff wavenumber,) is dependent on the radius unlike conventional metallic circular waveguide whose normalized cutoff parameterk _c R is a constant for a given mode and the filled dielectrics. Instead of TE₁₁-mode now TE₀₁ mode becomes the dominant mode and the normal component of magnetic field for the dominant mode is not equal to zero on the wall. Other unique results of high-T _c superconducting circular waveguides are illustrated, too.supported by Deutscher Akademischer Austauschdienst (DAAD)     

Universal Finite Size Corrections and the Central Charge in Non-solvable Ising Models

We investigate a non-solvable two-dimensional ferromagnetic Ising model with nearest neighbor plus weak finite range interactions of strength λ. We rigorously establish one of the predictions of Conformal Field Theory (CFT), namely the fact that at the critical temperature the finite size corrections to the free energy are universal, in the sense that they are exactly independent of the interaction. The corresponding central charge, defined in terms of the coefficient of the first subleading term to the free energy, as proposed by Affleck and Blote-Cardy-Nightingale, is constant and equal to 1/2 for all ${0\leq \lambda \leq \lambda_0}$ and λ ₀ a small but finite convergence radius. This is one of the very few cases where the predictions of CFT can be rigorously verified starting from a microscopic non solvable statistical model. The proof uses a combination of rigorous renormalization group methods with a novel partition function inequality, valid for ferromagnetic interactions.     

On the importance of long range summation of oscillatory interactions in Monte Carlo modeling

Kinetic and standard Monte Carlo (kMC and sMC) simulation of the system, where a pair-interaction energy is an oscillatory function of interatomic distance, requires a very careful selection of a cutoff radius r_cut of the pair-interactions. As an example, the homoepitaxy of Cu on Cu(1 1 1) is investigated. The surface-state mediated interaction between the Cu adatoms has a very long range and oscillates between attraction and repulsion as a function of the adatom-adatom distance. The simulations reveal that, at 15 K and 0.03 monolayer coverage, the Cu adatoms self-assemble into a dilute nanostructure with a weak local hexagonal order, where the average separation between adatoms equals 11.7 Å. The nanostructure consists of islands and chains of adatoms. The simulated structure of adlayer surprisingly strongly depends on the cutoff radius applied to the Monte Carlo model. The tendency to the dilute island formation strengthens and weakens with the same periodicity vs. r_cut as the pair-interaction energy vs. interatomic distance. The submonolayer morphology stabilizes when r_cut becomes longer than 50 Å.     

Core polarization and Coulomb displacement energies

A systematic study of the core polarization correction to Coulomb displacement energies is carried out. A zero range density independent and density dependent force is used to calculate this correction in the A = 16, A = 40, and A = 208 regions. It is found that the core polarization correction does not increase the Coulomb displacement energies and, therefore, cannot resolve the existing discrepancy between theory and experiment. Moreover, when the mean square radius of the excess neutron distribution is decreased the core polarization correction to the Coulomb energy becomes attractive and cancels the gain resulting from the direct Coulomb term. Hence, it is concluded that the discrepancy cannot be resolved even when the excess neutron distribution has an anomalously small radius. It is also pointed out that when the core polarization term is added the discrepancy is almost equal in mirror nuclei with a single hole in the N = Z core and those with a single particle outside the same core. Evidently, additional charge asymmetric corrections are required to resolve the discrepancies in Coulomb displacement energies.     

On the kinetics of oxygen adsorption on a Pt(111) surface

The kinetics of O₂ adsorption on a clean Pt(111) surface were investigated in the temperature range 214–400°C. The oxygen coverage was measured by CO titration as well as Auger electron spectroscopy both of which show the same dependence on O₂ exposure. The initial sticking coefficient on clean Pt(111) is 0.08–0.10 and decreases exponentially with increasing oxygen coverage. For θ > 0.23 a (2 × 2)-O LEED pattern was observed. The highest oxygen coverage obtained was approximately 0.45. A theoretical model was proposed which correlates the coverage dependence of the sticking coefficient with adsorbate interactions in the chemisorbed state. These interactions cause a coverage dependent activation energy of adsorption assuming the existence of a precursor state. Experiments dealing with the effect of carbon contamination on the sticking coefficient showed that the initial sticking coefficient decreases with increasing carbon coverage.