Two-dimensional propagators and spatio-temporal correlations for flow in porous media: A comparative study

The two-dimensional displacement joint probability densityPΔ(X,Z) and the two-time probability density W₂(Z₁,Δ₁;Z₂,A₂) for water flowing through several porous systems have been measured by means of pulsed field-gradient nuclear magnetic resonance (PFG-NMR). The simultaneous particle displacementsX and Z perpendicular and parallel to the pressure gradient, respectively, at a given encoding time Δ are obtained from an experiment employing orthogonal magnetic field gradients. Time-correlated propagators which relate the displacement spectra at two consecutive times Δ_l, and Δ₂ with each other were derived by applying rephasing gradients in two steps. Flow through a random packing of glass beads and through natural sandstone is compared to flow through arrays of either oriented or unoriented fibers with different solid volume fractions. The dependence of the dispersion tensor D^* as a function of time is discussed and related to a characteristic length ξ_tT transverse to the flow direction. Within a certain range of Z values, displacements inX and Z are related by a power law <X²(Z)> ∝Z _γ. The spreading exponent γ is found to increase with growing orientational order in the porous system and is largest for fiber bundles being twisted with respect to the mean pressure gradient axis. The evolution of the correlation coefficient px²,z with time gives a measure for the typical correlation length of the system parallel to the flow axis, ξ_‖. Analyzing the shape ofW ₂(Z₁,Δ₁Z₂,Δ₂) allows one to investigate the loss of coherence in flow by an alternative approach. The decay of the two-time correlation coefficient,pZ ₁,Z₂, is sensitive to the change of the z-component of the particle velocity and probes a different lengthscale thanpx ₂z^.     

Infinite volume asymptotics inP(ø)2 field theory

We prove a number of asymptotic results in theP(φ)₂ theory in the limit when the space cut-offs are removed, in particular the behavior ofE _l andZ _t,l ast,l→∞. Such results are used to study the question of orthogonality of infinite volume Euclidean measuresμ _∞(λ) for varying interaction constants λ.     

Nonfactorization and the decaysD s +→φπ +,φρ + andφl + ν l

Using the experimentally measured values ofx=A ₂(0)/A ₁(0) andy=V(0)/A ₁(0) and the measured ratiosR _st=Γ(D _s ⁺ →φl ⁺ ν _l)/Γ(D _ins ⁺ →φπ ⁺) andR _h=Γ(D _s ⁺ →φρ ⁺)/Γ(D _s ⁺ →φπ ⁺), we present evidence for significant nonfactorization contribution in the decay amplitude forD _s ⁺ →φπ ⁺. We analyze the role of nonfactorization inD _s ⁺ →φρ ⁺ and conclude that present data onR _h are consistent with factorization inD _s ⁺ →φρ ⁺. A measurement of polarization inD _s ⁺ →φρ ⁺ would greatly assist our analysis.     

Multiquark clusters in nuclei. distributions ofu- andd-quarks

Effects related to the possible admixture of multiquark (mainly 12q) clusters (bags) in nuclei are discussed. In particular the differencies in theu- andd-quark distributions inN≠Znuclei are considered. The quark distribution function is assumed to consist of two components: the nucleon component and the bag one (mainly the 12q-bag). The yields ofπ-mesons and nucleons into the backward hemisphere are governed mainly by the contribution of the bag component. It comes from the available data on theπ ⁺/π ^? andn/p ratios that thed-quarks in the bag component of nuclei withN>Z are “more soft” than theu-quarks in contrast to the situation in the nucleon component. The manifestation of the latter effect in theA-dependence of the ratio of structure functionsR=F _2A(x)/F _2D(x) is also discussed.     

QCD and QED corrections to the longitudinal polarization asymmetry

The interplay between QED and QCD corrections to the longitudinal polarization asymmetry,A _LR, ine ⁺ e ^?, annihilation is studied. It is found that measurements with hadronic final states will be well suited for precision tests of the standard model. QCD corrections to the asymmetry are particularly small on top of theZ ⁰, with the leading terms induced by quark mass effects. The influence of initial state radiation inA _LR is essentially accounted for by a slight shift in beam energy. Initial/final state QED bremsstrahlung interference (QED boxes) is studied in detail and its influence onA _LR is found to be negligibly small, especially close to the top of theZ ⁰ peak. A comment on the importance of helicity nonconservation for polarized beams in the presence of photon emission is also included.     

Anisotropic longitudinal electron diffusion coefficient in wurtzite gallium nitride

The longitudinal electron diffusion coefficient (D _l ) of wurtzite (WZ) gallium nitride (GaN) is calculated by an ensemble Monte Carlo (EMC) method. By using the power spectral density associated with velocity fluctuation, the relationship between D _l and electric field strength, frequency, doping concentration and temperature is presented. The anisotropic D _l of GaN impacted by anisotropy of the electronic dispersion is also investigated. It has been found that the D _l in Γ–A direction (c-direction) is larger than that in Γ–M direction (basal plane) in most cases. For lower electric field, the D _l keeps constant at first, then decreases with increasing frequency. However, for higher electric field, the D _l firstly approaches a peak value, then decreases with increasing frequency. When the frequency is zero, the D _l decreases with the increasing electric field, and then increases until a peak value. Finally, it decreases with increasing electric field again. When the temperature increases, the D _l decreases in both directions for increasing scattering rate. A comparison between our calculated diffusion coefficient and the mobility under low electric field by Einstein equation is presented.     

Infrared crystal spectra of C2H4, C2D4, and as-C2H2D2 and the general harmonic force field of ethylene

Carbon-13 frequency shifts for C₂H₄, C₂D₄, and as-C₂H₂D₂ have been measured in isotopic solid solutions in crystalline films at 60 K. All but two of the shifts (for as-C₂H₂D₂) are compatible with recently determined ζ data for C₂H₄, with ¹³C frequency shifts for C₂H₄ and C₂D₄ in the gas phase and with conventional frequency data. Together, these data completely determine with precision all 18 parameters of the GHFF for ethylene, the previous ambiguity in choice between two sets of A_g species force constants being removed. The force field reproduces closely the observed centrifugal distortion constants for C₂H₄, a ζ constant observed for trans-C₂H₂D₂, and the inertia defects for C₂H₄, C₂D₄, and as-C₂H₂D₂. Vibration and rotation constants for all isotopically deuterated ethylenes are calculated.Possible explanations for the two anomalous crystal shifts in as-C₂H₂D₂ involve the effects of the crystal field, and failure of the use of Dennison's rule for making anharmonic corrections to the shifts. The former explanation is preferred as a result of thorough analysis of the anharmonicity constants for as-C₂H₂D₂ determined from many overtone and combination bands in the gas and crystal spectra.     

Action-angle maps and scattering theory for some finite-dimensional integrable systems

We construct an action-angle transformation for the Calogero-Moser systems with repulsive potentials, and for relativistic generalizations thereof. This map is shown to be closely related to the wave transformations for a large classl of Hamiltonians, and is shown to have remarkable duality properties. All dynamics inl lead to the same scattering transformation, which is obtained explicitly and exhibits a soliton structure. An auxiliary result concerns the spectral asymptotics of matrices of the formM exp(tD) ast→∞. It pertains to diagonal matricesD whose diagonal elements have pairwise different real parts and to matricesM for which certain principal minors are non-zero.     

Longitudinal purely spatial coherence of a light field

The effects of longitudinal purely spatial coherence of light and the results of observation of these effects in an interference experiment are considered under the condition that the length of temporal coherence l _c is considerably smaller than the length of longitudinal spatial coherence ρ_‖ of the field. It is shown that, for l _c ? ρ_‖, the longitudinal purely spatial coherence of the light field in fact governs the coherence of the wave train in the process of its propagation. The length and the time of coherent (“free”) path of the wave train are considered as new spatial and temporal scales of a partially coherent light field.     

D=1+2 phase diagram forZ N with a variational method

Trial ground state are constructed which forZ _N gauge theories inD=1+2 dimensions lead to phase diagrams which are in agreement both with theoretical expectations and Monte Carlo results. The nature of the phase transition is correctly predicted for eachN.     

Analysis of checkerboard pattern in ultrathin magnetic films

We discuss the magnetostatic energy of checkerboard domain structures in ultrathin magnetic films (of a few monolayer thickness) and in an atomic monolayer using simple magnetostatic considerations where the easy direction of magnetization is perpendicular to the film. The checkerboard domain size, D, the domain-wall width, ω, the ratio f of the uniaxial surface anisotropy, K_s, to the dipolar energy and the binding energy, (BE), have been calculated numerically with the variational parameter δ and the number of atomic layers, n_l, as parameters.     

Particle-hole excitations in the208Pb mass region

Spectra, magnetic dipole moments and spectroscopic factors of a number ofA=205–209 nuclei as well asM1 transitions in²⁰⁸Pb are investigated in terms of large-scale shell-model calculations which include 1p ?1h excitations and for some nuclei 2p ?2h excitations. The calculated spectra agree well with the data. The calculatedg-factors are in fair agreement with the data in most cases. The predicted strength forM1 transitions to low-lying states in²⁰⁸Pb is less than that obtained from previous calculations. Spectroscopic factors forl=0 proton pick-up from²⁰⁸Pb and²⁰⁶Pb agree very well with recent experimental data from (e, e′p) reactions.     

Structural analysis of three-spin systems of photosystem II by PELDOR

The pulsed electron electron double resonance (PELDOR) pulse sequence is applied to a three-spin system consisting of three radicals (Y _D ^· , Y _Z ^· and Q _A ^? ) generated in spinach PS II. The distance between Y_Z and Q_A has been determined to be 3.4 nm with the previously derived distances of the other radical pairs, 2.9 nm for Y _D ^· -Y _Z ^· and 3.9 nm for Y _D ^· -Q _A ^? . This distance has been derived from the Y _Z ^· -Q _A ^? radical pair trapped in Y_D-less mutants ofChlamydomonas reinhardtii. Furthermore the method was applied to the Y _D ^· -Q _A ^? -Chl _Z ⁺ system to find the unknown distance between Q_A and Chl_Z. The derived distance was 3.4 nm. A triangular configuration was found in the membrane system that gives the relative positions of the electron transfer components.     

s- and p-wave neutron spectroscopy: Part VI. Level density and neutron excess

Neutron total cross-section curves for Ca⁴⁰, Ca⁴⁴, Cr⁵⁰, Cr⁵², Cr⁵⁴, Fe⁵⁴ and natural Fe, Ti, and Cr have been measured in the kev region. Level spacings have been estimated for the predominant isotope in each of the samples measured, and are compared to similar data found for even N, odd Z targets. After correcting for differences in the angular momenta and excitation energies, it is found that on the average (between A = 35 and 60) $\text{d [}\text{ln}\text{D}{}_0\text{(6}\text{Mev}\text{)] = (?}\text{ln}\text{D}{}_0\text{?Z}\text{)dZ + (?}\text{ln}\text{D}{}_0\text{?N}\text{) dN ? 0.3 dZ ? 0.3 dN}$, and hence D₀(6 Mev) is proportional to exp ?0.3(N ? Z). D₀(6 Mev) is the spin and energy independent spacing parameter. Except for slight signs of a maximum at N = 28, D₀ (6 Mev) appears (between A = 35 and 60) to be strongly dependent only on the neutron excess, N ? Z, and not on N, Z, or A; uncertainties in the correction for excitation are such that it is likely that the absolute value of the exponent, 0.3 (N ? Z) is a lower limit. Isotopic and J^π assignments of many resonances in the natural fluorine and chromium cross-section curves are suggested.     

Phase coexistence in binary mixtures in thin films with symmetric walls: model calculations for two- and three-dimensional Ising lattices

Binary mixtures (A, B) that undergo phase separation in the bulk are considered in thin film geometry, assuming that one of the components is preferentially attracted to one of the walls. We discuss the average profile of the order parameter {volume fraction φ(z) of one of the components} in the z-direction (perpendicular to the surfaces), paying attention to the lateral inhomogeneity of the thin film when the average volume fraction corresponds to a state inside the coexistence curve. We consider the situation where due to (short range) surface forces a second-order wetting transition would occur in semi-infinite geometry: in the thin film geometry, this transition is rounded off and its only remnant is a smooth increase of the adsorbed mass in the surface-enriched layer in the transition region. Monte Carlo calculations for nearest neighbor Ising square and simple cubic lattices are used to derive typical concentration profiles. In the two-dimensional case, also the kinetics of domain formation after the quench from a disordered state is considered, and it is shown that the typical concentration oscillations perpendicular to the wall (“surface directed spinodal decomposition”) do not occur, due to strong lateral fluctuations of the local position of the interface between the enrichment layer at the surface and the neighboring depleted region. Finally, also phase-separated states in thin films with competing walls (where one surface prefers A and the other prefers B) are briefly treated, and experimental applications are discussed.     

Radio-frequency spectroscopy in the states3 D 3,2 of platinum

The magnetic dipole hyperfine interaction constantsA of the atomic ground state³ D ₃ and of the first excited state³ D ₃ in¹⁹⁵Pt have been measured by atomic beam magnetic resonance. The electronicg _J factors of these states were determined from the Zeeman splitting in¹⁹⁴Pt. Using intermediate coupling wave functions derived for the configurations (5d+6s)¹⁰ effective hyperfine radial integrals are evaluated.     

Study of isotope shifts,isotone shifts and nuclear compressibility from the analysis of muonic x-ray transitions

Muonic x-ray transitions in various spherical nuclei in the region 13?Z?83 have been analysed and the isotope and isotone shifts in charge radiusR are investigated. AssumingR=r ₀ A ^1/3, the isotopic and isotonic behaviour of the parameterr ₀ (=RA ^?1/3) is also studied. The variation ofr ₀ with mass numberA reveals the variation of average nucleon density, which in turn sheds light on the compressibility of nuclear matter. The isotope and isotone shifts inR exhibit the shell effects in the vicinity of magic neutron and proton numbers: 20, 28, 50, 82 and 126. The results indicate that neutron-proton interaction is maximum at the beginning of a major neutron shell and decreases gradually as the shell gets filled up. The behaviour of parameterr ₀ clearly suggests that low-Z nuclei are highly compressible while high-Z nuclei are more or less incompressible. The parameterr ₀ too is observed to exhibit profound shell effects.     

Study of the surface relaxation and single vacancy formation in very thin Cu (001) film by using MAEAM

The surface relaxation and the formation of a single vacancy in very thin Cu (001) film formed by 2 ～ 14 atomic layers have been studied by using MAEAM and MD simulation. For the surface relaxtion, the highest surface energy is in the l = 2 atomic layers. The multilayer relaxation mainly occurs between the first two atomic layers, and the maximum contractive displacement is obtained in the very thin Cu (001) film formed by l = 3 atomic layers. For the vacancy formed in l′ = 1 of the very thin Cu (001) film formed by l = 2 ～ 14 layers, the most difficult site in the film formed by l = 3 atomic layers.     

Effect of laser irradiation on the structure and properties of dielectric column clusters in the YBaCuO superconducting films

The effect of laser irradiation on the structure and properties of the YBa₂Cu₃O_{7 ? δ} epitaxial super-conducting films (T _c = 90–91 K) that are grown on the SrTiO₃ and LaAlO₃ substrates is studied. The films exhibit a system of pyramidal peaks that are incorporated in the single-crystal structure of the film whose system of the (00l) planes is parallel to the surface of the substrate. It is demonstrated that the peaks represent growth defects that result from the relaxation of the accumulating strain due to the mismatch of the crystallographic parameters of the growing layers of the film and substrate. The island structures that are formed owing to the relaxation of strains acquire the (11l) or (10l) orientation and penetrate through the film layers in the course of growth. It is demonstrated that the irradiation using relatively short laser pulses makes it possible to modify the structure of the dielectric clusters and allows the smoothing of the film surface at an insignificant (5–10%) decrease in the concentration of the superconducting phase. An increase in the energy density to a level of greater than 100 mJ/cm² when the number of pulses is greater than five causes an increase in the volume of dielectric phases and the worsening of parameters.