Coupling Constant Increases Research Articles

Structural aspects of barium borosilicate glasses containing thorium and uranium oxides

Barium borosilicate glasses incorporated with 15.86 wt% ThO 2 and containing different amounts of uranium oxide were prepared by conventional melt quench method. Based on 29Si and 11B magic angle spinning nuclear magnetic resonance (MAS NMR) studies, it has been confirmed that uranium oxide incorporation is associated with distortion of borosilicate network as revealed by the increase in the relative concentration of Q 2 structural units of silicon as well as the increase in the quadrupolar coupling constant ( C q) of BO 3 structural units. The increased number of non-bridging oxygen atoms brought about by the increase in Q 2 structural units of silicon facilitates the incorporation of both uranium and thorium ions in the sites created by non-bridging oxygen atoms (network modifying positions) in the glass. Uranium oxide incorporation above 7.5 wt% resulted in the phase separation of ThO 2 as revealed by the X-ray diffraction studies. The present study focuses on the structural changes with the borosilicate network of barium borosilicate glasses brought about by the introduction of thorium and uranium ions.

Experimental observation of partial amplitude death in coupled chaotic oscillators

The dynamics of coupled Lorenz circuits is investigated experimentally. The partial amplitude death reported in Phys. Rev. E 72, 057201 (2005) is verified by physical experiments with electronic circuits. With the increase of coupling constant, the coupled circuits undergo the transition from the breakdown of both the reflection symmetry and the translational symmetry to the partial amplitude death. Its stability is also confirmed by analysing the effects of noise.

Phase Separation of a Fast Rotating Boson-Fermion Mixture in the Lowest-Landau-Level Regime

By minimizing the coupled mean-field energy functionals, we investigate the ground-state properties of a rotating atomic boson-fermion mixture in a two-dimensional parabolic trap. At high angular frequencies in the mean-field lowest-Landau-level regime, quantized vortices enter the bosonic condensate, and a finite number of degenerate fermions form the maximum-density-droplet state. As the boson-fermion coupling constant increases, the maximum density droplet develops into a lower-density state associated with the phase separation, revealing characteristics of a Landau-level structure.

FERROMAGNETISM IN Co-DOPED TiO2 ANATASE DUE TO THE COBALT CLUSTERING

We have performed first-principles electronic structural calculations to investigate the nature and origin of ferromagnetism in Ti 1-x Co x O 2 with cobalt concentrations x being 0.0625 and 0.125 in the interesting experimental range. In x being 0.125, when all possible arrangements of two Co atoms within a large supercell are considered, the clustering of Co atoms at nearst-neighbour Ti sites is energetically preferred. Also the interplay between clustering and exchange interactions in Co -doped anatase TiO 2 is discussed. It is predicted that the exchange coupling constant increases up to a value corresponding to lower Co concentrations by decreasing the distance between Co atoms.

Specific Heat and Electrical Resistivity of an Icosahedral-Structure Zr[sub 70]Pd[sub 30] Alloy and of Its Amorphous and Crystalline Analogs

Binary icosahedral and crystalline phases of the Zr70Pd30 alloy were obtained in crystallization from the amorphous state during heat treatment. The specific heat and electrical resistivity of the icosahedral, amorphous, and crystalline phases were measured and compared. An increase in the electronic density of states on the Fermi surface, lattice softening, and an increase in the electron-phonon coupling constant were observed to occur with decreasing structural order. Despite the high valence electron density in the icosahedral phase, where the electronic densities of states are twice those in the crystal, the electrical resistivity of the icosahedral phase is ∼50 times as high. Superconductivity was observed for the first time in the icosahedral phase of a binary system of transition metal atoms, Zr70Pd30.

Parallel-Stranded Guanine Quadruplex Interactions with a Copper Cationic Porphyrin

G-quadruplexes are formed by association of DNA strands containing multiple contiguous guanines. The capability of drugs to induce formation of or stabilize G-quadruplexes is an active area of investigation. We report the interactions of CuTMpyP4, the Cu(2+) derivative of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine, with the parallel-stranded G-quadruplexes formed by d(T(4)G(4)T(4)) (1) and d(T(4)G(8)T(4)) (3). Absorption titrations of CuTMpyP4 with (1)(4) or (3)(4) cause both bathochromicity and hypochromicity of the porphyrin Soret band, with larger changes observed for the longer oligonucleotide. An approximate binding constant for (1)(4) and CuTMpyP4 according to the Scatchard model is 5.6 x 10(6) M(-)(1) in terms of quadruplexes and according to the McGhee-von Hippel model is 1.3 x 10(6) M(-)(1) in terms of potential binding sites. An approximate binding constant for (3)(4) and CuTMpyP4 according to the Scatchard model is 5.2 x 10(7) M(-)(1) in terms of quadruplexes and in terms of the McGhee-von Hippel model is 2.4 x 10(6) M(-)(1) in terms of potential binding sites. The site size for CuTMpyP4 and (1)(4) is four using the McGhee-von Hippel model. We find a 2:1 binding stoichiometry for CuTMpyP4 and (1)(4) and a 3:1 binding stoichiometry for CuTMpyP4 and (3)(4) using the method of continuous variation analysis. Induced emission spectra of CuTMpyP4 with (1)(4) or (3)(4) indicate a mode of binding in which the ligand is protected from the solvent. Electron paramagnetic resonance spectra of CuTMpyP4 with added oligonucleotide show an increase in the Cu-N superhyperfine coupling constant as the length of the oligonucleotide increases. On the basis of these data, we propose that for both (1)(4) and (3)(4), CuTMpyP4 molecules externally stack at each end of the run of guanines, similar to other planar G-quadruplex ligands. For (3)(4), our data are consistent with intercalation of a CuTMpyP4 molecule into the G-quadruplex.

Localized rotating-modes in capacitively coupled intrinsic Josephson junctions: Systematic study of branching structure and collective dynamical instability

A variety of the $I--V$ characteristics observed in a stack of intrinsic Josephson junctions is systematically explained in terms of the dynamics of the localized rotating mode in the discrete nonlinear systems. We clarify the effect of the capacitive coupling constant on the $I--V$ characteristics, using the capacitively coupled Josephson junction model. The branch structure in the $I--V$ characteristics changes from an assembly of equidistance branches to a single hysteresis-loop-like structure as the capacitive coupling constant increases. This behavior is in accordance with experiments. We predict that dynamical transitions between collective rotating states take place in the resistive state of a stack of intrinsic Josephson junctions in the strong capacitive coupling regime. These transitions create step-like structure in the $I--V$ characteristics, which is observed in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4\ensuremath{-}\ensuremath{\delta}}$.

Effect of memory on relaxation in a scalar field theory

We derive a kinetic equation with a non-Markovian collision term that includes a memory effect from Kadanoff-Baym equations in ${\ensuremath{\varphi}}^{4}$ theory within the three-loop level for the two-particle irreducible effective action. The memory effect is incorporated into the kinetic equation by a generalized Kadanoff-Baym ansatz. Based on the kinetic equations with and without the memory effect, we investigate the influence of this effect on the decay of a single particle excitation with zero momentum in 3+1 dimensions and the spatially homogeneous case. The numerical results show that, while the time evolution of the zero mode is completely unaffected by the memory effect due to a separation of scales in the weak coupling regime, this effect leads first to faster relaxation than the case without it and then to slower relaxation as the coupling constant increases.

Coupling constants in fractal and cantorian physics

Abstract Links between inverse coupling constants of various interactions (gravitational α G ≈10 38 , weak α W ≈10 5 –10 8 , electromagnetic α EM ≈137 and strong α S ≈0.1–10 ) in the three-dimensional Euclidean space are discussed. The analysis is based on the fact that such interactions between particles are generally realised both, by photons (electromagnetic radiation) and by particles. Ideal limit cases arise for α →∞ (the interaction is mediated just by photons) and for α =0 (completely mediated by particles). Dependences of inverse coupling constants, fractal dimensions and masses of final particles on masses of constituents (quarks and leptons) are shown for each case. It turns out that for some cases the coupling constant increase (interaction within quarks) and for other cases decrease (interaction between quarks). The inverse coupling constants mentioned previously represent special cases of the ascertained dependences. The possible structure of higher mass quarks with the help of up and down quarks (up quarks and leptons respectively) is also discussed.

A spectroscopic investigation of the interaction between nitrogen monoxide and copper sites of the fungal laccase from Rigidoporus lignosus.

The interaction of NO, with the copper centres of the laccase secreted by Rigidoporus lignosus was studied under both aerobic or anaerobic conditions. The reduction of the T1 site was always observed, as detected by the disappearance of the characteristic optical band at 604 nm (T3 presents probably the same behaviour because of the decreasing of the band at 330 nm) and the absence of its characteristic EPR signal, while T2 undergoes an initial partial and transitory reduction, its EPR signal intensity totally restoring after 24 h interaction. Different magnetic parameters of the T2 site have been detected, evidencing an increase of the hyperfine coupling constant. Furthermore, the number of superhyperfine lines on the fourth line of T2 copper was also found to increase from seven in the native to nine in the NO-treated laccase, this fact implying the coordination of a nitrogenous species to the T2 site. It was also shown that nitrite can be a source of NO, thus, paralleling the behaviour of NO-donor molecules or NO gas, but after longer interaction times. The nitrogenous species coordinated to T2 site is probably NO2-, which arises indirectly by NO oxidation. In order to understand the mechanistic pathway of this interaction, some experiments were also carried out in the presence of azide to study the interaction of NO with this laccase having its trinuclear cluster blocked by the presence of an exogenous ligand as N3-. After the addition of NO-donor molecules to the azide-treated laccase, a new EPR signal appeared at low temperatures, which is ascribable to the partially reduced T3 site, while the T1 and T2 sites were found to be totally reduced. The mechanistic pathway of the NO interaction seems to proceed through the reduction of T1 and T3 copper sites, followed by the coordination of nitrogenous species to T2.

Magnetotransport properties of alkali metal doped La–Ca–Mn–O system under pulsed magnetic field: Decrease of small polaron coupling constant and melting of polarons in the high temperature phase

Pulsed magnetic field (0–4.4 T) was used to study the magnetic field dependent resistivity (12–350 K) and thermoelectric power (0–1.5 T) of Na and K-doped La0.7Ca0.7−yAyMnO3 (0.0⩽y⩽0.3, A=Na, K) system showing semiconducting to metallic transitions around temperature Tp. Na/K-doping increases both conductivity and Tp. In La1−xCaxMnO3, an increase of Tp and conductivity with an increase of Ca (for x⩽0.33) are small and the small polaron coupling constant (γ) and hence the electron-lattice (phonon) interaction is strong. But in the Na/K doped system, γ is small and for y⩾0.05, Motts’ condition of strong el–ph interaction breaks down in the high temperature (T>Tp) phase. Increase of conductivity in the Na/K doped system is caused by the decrease of γ, binding energy (Wp), hopping energy (WH), and effective mass (mp) of the polarons leading to the melting (we call it) of polarons in the T>Tp phase. This melting results in an increase of exchange coupling constant between spins. Field dependent thermoelectric power (TEP) of the samples (measured between 80–300 K) also supports the small polaron hopping conduction. The resistivity data are well fitted with the variable range hopping model for a limited range of temperature (Tp<T<θD/2, θD being the Debye temperature) while thermally activated small polaron hopping model is found valid for T>θD/2. With the application of a magnetic field, the density of states at the Fermi level increases. The TEP data indicate the importance of electron-magnon contribution in the low temperature (T<Tp) ferromagnetic metallic phase. Estimated polaron bandwidth (J) satisfies Holstein’s condition of the adiabatic “small polaron” hopping conduction mechanism for the region T>Tp.

Minkowski solution of Dyson-Schwinger equations in momentum subtraction scheme

Using the Green function integral representation the Dyson-Schwinger equations are solved directly in Minkowski space. Essential ideas of the spectral techniques are discussed and applied on two renormalizable models: the Yukawa theory with massive pseudoscalar meson and conventional spinor QED. Within the momentum subtraction procedure, the appropriate renormalization is performed analytically which leads to the usual dispersion formulation. The electron propagator obtained in this frame is compared with the solution of Euclidean Dyson-Schwinger equation and with the perturbation theory results as well. The proposed method has the advantage of obtaining solutions in both the space- and {\bf{time}}-like regimes of momenta. In addition,when the coupling constant increases we find some un-expected discrepancy between the Euclidean and integral representation solutions. Especially, when the solutions of the original momentum DSE's exhibit the signal for confinement then the spectral approach gives no solution for Lehmann function of confined particle.

Bose-Einstein condensates with attractive interactions on a ring

Considering an effectively attractive quasi-one-dimensional Bose-Einstein condensate of atoms confined in a toroidal trap, we find that the system undergoes a phase transition from a uniform to a localized state, as the magnitude of the coupling constant increases. Both the mean-field approximation, as well as a diagonalization scheme are used to attack the problem.

Phase diagram and correlation function of a spin-Peierls system in the ground state: Effects of the quantum lattice fluctuations

Using a one-dimensional antiferromagnetic Heisenberg chain model with spin-phonon interaction, the effects of quantum lattice fluctuations on the phase diagram and correlation functions in the ground state of the spin-Peierls system are investigated by developing an analytical approach based on the unitary transformation method. To study the nonadiabatic case, the Green's function method is used to implement the perturbation treatment. We show that when the spin-phonon coupling constant decreases or phonon frequency increases, the lattice dimerization and the spin dimerization gap decrease gradually. At some finite critical value, the Peierls dimerization is destroyed by the quantum lattice fluctuations and the system becomes gapless. The inverse-square-root singularity of the density of states at the gap edge in the adiabatic case disappears because of the nonadiabatic effect, which is consistent with the measurement of the optical absorption spectrum in quasi-one-dimensional spin-Peierls systems. The dimerization gap is much more reduced by the quantum lattice fluctuations than the spin dimer order parameter is. This could result in a true spin dimerization gap that is smaller than the activation energy of the optical absorption spectrum.

Effects of Intermolecular Interactions on 33S Magnetic Shielding in Gaseous SF6

Density-dependent 33S magnetic shielding has been measured for the first time. For pure gaseous SF6 and its binary mixtures with Xe, CO2 and NH3 at 298 K, an increase in density linearly decreases the 33S shielding constant of SF6. This permits one to separate quantitatively the shielding contributions due to intermolecular interactions and the shielding parameter of an isolated SF6 molecule. Spin−spin coupling in SF6 (1JSF) has also been measured but only for gaseous samples of high densities. It was observed that the 1JSF coupling constant increases for more dense samples and that the increase is even more pronounced in liquid solutions. All of the new results can be used for an improved verification of ab initio calculations of sulfur shielding and spin−spin coupling in the SF6 molecule because the new 33S NMR measurements reveal the magnitudes of appropriate intermolecular effects.

Energy spectrum of the Hamiltonian of the Jaynes-Cummings model without rotating-wave approximation

The energy spectrum of the Hamiltonian of the Jaynes-Cummings model without a rotating-wave approximation is studied. The trajectories of eigenvalues as functions of the dimensionless coupling constant are constructed. It is shown that the spectrum approaches the equidistant spectrum, i.e., the oscillator spectrum, as the coupling constant increases. As a result, each energy level becomes doubly degenerate.

Micromagnetic simulation for antiferromagnetically coupled recording media

Hysteresis properties of the antiferromagnetic-coupled recording film media are studied via micromagnetic simulation. The theoretical model is discussed in detail. The effect of the antiferromagnetic coupling constant J on the hysteresis loop and recording performance is reported. Kink is observed in the hysteresis loop due to the reversal of lower layer magnetization. The kink occurs in the positive field region when |J|>2K/sub u/2t/sub 2/ (under zero temperature environment). The coercivity increased with the increase of the antiferromagnetic coupling constant. Antiferromagnetically coupled media with kink in positive field region show a smaller transition length and noise. The track edge-noise increased and broadened for AFC media with kink in the negative field region.

The polaron state of a crystal

The quantum mechanics of an electron-nuclear system with strong electron-phonon coupling is considered. First, a two-site model is treated in the adiabatic approximation. As the coupling constant increases, electron transfer undergoes qualitative changes; more specifically, a potential barrier forms in the adiabatic potential, the electron transfer becomes associated with the tunneling of nuclei through the barrier, and the level splitting in the system falls off exponentially. The properties of a similar crystal model are discussed. It is shown that electron transfer in a crystal in the case of strong coupling is likewise associated with the tunneling of nuclei through barriers in the deformation space. Strong coupling modifies the electron-electron interaction terms. The Hamiltonian (exchange) terms, which are not associated with electron transfer, are only weakly modified. At the same time, the terms involving transfer (the band terms) undergo exponential reduction and vanish in the limit as M → ∞ (M is the ion mass) and the carriers become small polarons. This reduction provides a basis for the natural mechanism of enhancement of the isotope effect.

Relativistic modification of the Gamow factor

In processes involving Coulomb-type initial- and final-state interactions, the Gamow factor has been traditionally used to take into account these additional interactions. The Gamow factor needs to be modified when the magnitude of the effective coupling constant increases or when the velocity increases. For the production of a pair of particles under their mutual Coulomb-type interaction, we obtain the modification of the Gamow factor in terms of the overlap of the Feynman amplitude with the relativistic wave function of the two particles. As a first example, we study the modification of the Gamow factor for the production of two bosons. The modification is substantial when the coupling constant is large.

Trapping of laser-vaporized alkali metal atoms in rare-gas matrices

Abstract Alkali metal atoms prepared by laser ablation of solid Li and Na are trapped in Ar, Kr, and Xe matrices and studied by electron paramagnetic resonance spectroscopy (EPR) at 15 K. Evidence for tight trapping sites, not observed for atoms generated by conventional Knudsen oven techniques, is presented. The novel tight trapping sites are characterized by a large increase in the isotropic hyperfine coupling constant and a simultaneous decrease in the isotropic g -value. Based on the EPR data, it is suggested that the observed tight trapping corresponds to single substitution of lattice atoms in Ar, Kr, and Xe matrices.