bluuebunny/crossref_metadata_2025 huggingface dataset:
Focusing properties of an axicon pair
Authors: Couture Marc , Piché Michel
Published: April 2011

The focusing properties of a so-called reflaxicon (a combination of a diverging and a converging axicon) are studied both theoretically and experimentally. Calculations of intensity distributions produced by this system are made by evaluating the Kirchhoff–Fresnel diffraction integral, first by means of an approximate technique, the stationary phase method, then by a more exact numerical method. The calculations are presented for various planes along the axis of the axicons. The effects of the presence of the supporting mount of the axicons and of some important misalignments of the system on the distributions is also investigated. Experimental results of actual intensity distributions produced by focusing a near-fundamental Gaussian beam by such a system are also presented and are seen to be in fair agreement with numerical calculations. Such calculations would be valuable in many applications for predicting important characteristics (e.g., peak intensity, length of the focal line, degree of asymmetry) of the intensity distributions formed by optical systems containing an axicon pair as the focusing component.
Electric-field-induced Q branch of the vibrational fundamental of CO
Authors: Dagg I. R. , Chanda A. , Gush H. P. , Ho W. C. , Ozier I.
Published: April 2011

The electric-field-induced Q branch of the vibrational fundamental has been observed for the first time in a polar diatomic molecule in a study of 12C16O near 2143.−1 Intensity measurements of the Q(0), Q(1), and Q(2) transitions with a diode laser spectrometer have shown that these normally forbidden lines become allowed through the mixing of rotational levels generated by the interaction of the dipole moment with the externally applied electric field. Measurements have been made both with a static field and with a square-wave-modulated field. The electric dipole moment of 12C16O in the first-excited vibrational state, not previously measured experimentally, has been found to equal −0.0830 (23) D. The transition moment for the vibrational fundamental has been determined to be 0.1077 (38) D, which is in agreement with previous, more precise determinations based on the intensity of the allowed P and R branches. The results obtained here are in excellent agreement with earlier calculations of the dipole moment function.
A problem of a viscoelastic magnetohydrodynamic fluctuating-boundary-layer flow past an infinite porous plate
Authors: Sherief Hany H. , Ezzat Magdy A.
Published: April 2011

In this work we study the motion of a two-dimensional incompressible flow of an electrically conducting viscoelastic fluid past an infinite porous flat plate subject to uniform suction in the presence of a transverse uniform magnetic field. The effects of the flow on the temperature of the plate are studied when the plate is thermally insulated, and when it is kept at a constant temperature that is higher than that of the free stream. A method proposed by Lighthill and Stuart is utilized in solving the problem. The effects of various parameters such as the magnetic number, the viscoelastic parameter, and the frequency of the free-stream oscillations on the flow are studied.
The vector-ladder operators for the rotation group O3
Authors: Hardy J. E.
Published: April 2011

The two vector-ladder operators, which step from any state [Formula: see text] in an irreducible multiplet in the space of product states of two commuting angular momenta, are defined and all their nonvanishing matrix elements are given, facilitating direct, straightforward calculation of the six nearby nonsibling states [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text].
Nuclear charge density radius parameter and the β decay between mirror nuclei
Authors: Ozhasoglu Cihat , Rustgi M. L.
Published: April 2011

A two-parameter Fermi-type charge-density distribution is used to determine the Coulomb energy of a nucleus of a given charge Z. The expression is used to determine the nuclear charge-density-radius parameter, r1, and the diffuseness parameter, a, from the maximum kinetic energies in the β+-decay experiments. The deduced parameters r1 and a are compatible with the values obtained from the analyses of electron-scattering experiments.
Simple quark mass matrices and mixing
Authors: Margolis B. , Punch S.
Published: April 2011

We present mass matrices identical in form for both the up and down quark families, with the following remarkable properties. Both up and down quark masses, at a scale of 1 GeV, are well-approximated by geometric progressions. The five known quark masses and the Kobayashi–Maskawa (KM) mixing matrix agree with experiment. The KM matrix is expressed in terms of only two parameters. We give the KM matrix in the Wolfenstein form.
Effective field theory for plasmas at all temperatures and densities
Authors: Braaten Eric
Published: April 2011

The solution of the plasmon problem and the subsequent development of an effective field-theory approach to ultrarelativistic plasmas are reviewed. The effective Lagrangians that summarize collective effects in ultrarelativistic quark–gluon and electron–photon plasmas are presented. A generalization that describes an electromagnetic plasma at all temperatures and densities is proposed.
Effective actions for Braaten–Pisarski resummation
Authors: Brandt F. T. , Frenkel J. , Taylor J. C. , Wong S. M. H.
Published: April 2011

We discuss aspects of the effective action that generates the "hard thermal loops" used in the resummation programme of Braaten and Pisarski.
Screening of static quantum-electrodynamic electric fields in hot quantum chromodynamics
Authors: Kapusta Joseph
Published: April 2011

The screening length for static quantum-electrodynamic electric fields in hot quantum chromodynamics (QCD) is computed using hadronic degrees of freedom at low temperature and quark-gluon degrees of freedom at high temperature. The high temperature result is equivalent to computing the photon self-energy to two-loop order in QCD plus summation of the leading infrared divergent diagrams at three-loop and higher order. Comparison is made with the screening length extracted from singlet and nonsinglet susceptibilities as measured in two-flavor lattice QCD.
Anomalous damping in Boltzmann plasma
Authors: Smilga A. V.
Published: April 2011

We discuss the damping of the charged collective excitations in an ordinary nonrelativistic Boltzmann plasma. This damping turns out to be anomalously large, much larger than the normal physical scale associated with collisions (τrel)−1 considered usually by plasma physicists. The estimate for this anomalous damping is different at different regions for parameters T, N, m, and e. We distinguish the hot [Formula: see text] vs. cold [Formula: see text] and also dense vs. rarefied plasmas. It turns out that all physical effects have generally little dependence on the anomalous damping scale. If, however, the plasma density N is low enough, some subtle physical effects survive.
Absorption and index of refraction for the modeling of InGaAsP/InP photonic devices
Authors: Reid B. , Maciejko R. , Champagne A.
Published: April 2011

Methods for modeling, over an extended practical wavelength range, the index of refraction and the absorption in lattice-matched InGaAsP/InP-based photonic devices are reviewed, completed, and clarified. Carrier-induced effects on the optical properties are given special attention. For the index of refraction, the method gives results within 1% of the experimental ones. On the other hand, the results for absorption are more difficult to compare owing to the lack of experimental data.
Polymer waveguides: characterization through prism–film coupler method
Authors: Trepanier François , Manivannan Gurusamy , Changkakoti Rupak , Lessard Roger A.
Published: April 2011

Cr(VI) and Fe(III) doped polyvinyl alcohol) and poly(acrylic acid) polymers have been used as real-time holographic recording media as well as materials to fabricate planar waveguides. Planar wave guides were made of these metal ion doped polymer thin films. Changes in the absorption spectra of these polymer films due to irradiation with an intense illumination of 468 nm light were observed. Modifications in optical properties of dichromated poly(vinyl alcohol) (DCPVA), dichromated poly(acrylic acid) (DCPAA), and ferric chloride doped polyvinyl alcohol) (FePVA) were experimentally determined by the prism–film coupler (PFC) method for the first time. Changes in the refractive index at 632.8 nm were monitored for different exposure energies. Modification of the modal properties was observed and the refractive index of these films was also determined from the angular position of the guided modes. Optical losses in both exposed and unexposed films of DCPVA, DCPAA, and FePVA were measured employing a coupling set-up with two prisms. Observed results suggest that these materials can find successful applications in promising areas like integrated optics and planar optical interconnects.
Optical phase conjugation in aqueous rhodamine 6G solutions and in rhodamine 6G embedded in polyvinyl alcohol films
Authors: O'neill Claire , Blanchet Valérie , Roberge Marguerite-Marie Denariez , Galarneau Pierre
Published: April 2011

Studies on optical phase conjugation by degenerate four-wave mixing in aqueous rhodamine 6G solutions and in rhodamine 6G embedded in polyvinyl alcohol thin films are presented. The experiments were performed at 532 nm using picosecond pulses. Strong nonlinearities were observed in both media for three different polarization configurations of the incoming beams. The time dependence of the signals was also studied and was similar in both media. The decay kinetics in each case reflects the competition between two different processes: a fast one related to the relaxation of the anisotropic absorption and a slower one associated with the decay of the stable S1 state.
Magnetic form factors for a trinucleon system using different meson exchange nucleon–nucleon interactions
Authors: Osman Ahmed , Zaky M. , Allam M. A.
Published: April 2011

The magnetic form factors for the 3He and 3H nuclei have been calculated for different values of momentum transfer. The three-nucleon ground-state wave function is expressed in momentum space and is obtained from the solution of the Faddeev equations with realistic two-body potentials. The potential used is taken from the meson theory to include different meson-exchange contributions satisfying the requirements of current conservation. The different meson-exchange currents and their contributions to the trinucleon magnetic form factors are calculated. The virtual Δ-excitation and the meson–nucleon vertices form factors are included in the 3He and 3H magnetic-form-factors calculations. The present results show the importance of the higher momentum transfer region as being a good source of information to the short-range processes in the nuclear medium. Our results for the 3He and 3H magnetic form factors are in good agreements with the experimental data. The inclusion of the ρ and ω meson exchanges improves the agreement between positions of the minima of the magnetic form factors predicted and the experimental data.
On the nature of wire grid modelling for numerical solutions of electromagnetic problems
Authors: Yang Xian Hua , Shafai Lotfollah , Sebak Abdel Razik
Published: April 2011

Wire grid modelling has been used successfully for solving radiation and scattering problems of complicated structures, but its mathematical basis remains unclear. In this paper, we prove mathematically that wire grid modelling is equivalent to the point-matching method with subdomain basis functions. Other questions arising from applications of wire grid modelling, such as the selection of wire radius based on the "same surface area rule" and difficulties in satisfying the boundary conditions are considered and explained based on this equivalence.
Boltzmann-equation analysis of electron swarm parameters in mercury vapour at high values of E/N
Authors: Liu Jianfen , Raju G. R. Govinda
Published: April 2011

The electron swarm parameters in mercury vapour are studied for high values of E/N from 300 to 1400 Td (1 Td = 10−17 V cm2) by a rigorous Boltzmann-equation analysis. Three kinds of electron swarm parameters defined according to the time of flight (TOF), the pulsed Townsend, (PT) and the steady state Townsend (SST), conditions are calculated. The results for TOF agree very well with those obtained in a Monte-Carlo simulation.
Magnetic anisotropy of Sm2Fe17−xGax hydrides
Authors: Dunlap R. A. , Wang Z.
Published: April 2011

The magnetic properties of single-phase 2:17 compounds of the composition Sm2Fe17−xGaxHy were investigated. The substitution of Ga for Fe in the Sm2Fe17 compound resulted in a substantial increase in the Curie temperature and, for alloys with x > 2, the formation of a uniaxial magnetic anisotropy at room temperature. The diffusion of hydrogen into those compounds that exhibit an easy axis anisotropy causes a transition back to a planar anisotropy. This indicates that the presence of interstitial hydrogen is detrimental to the hard magnetic properties of these materials.
Determination of the A1(TO) soft-mode damping rate in KTa0.93Nb0.07O3
Authors: Grenier P. , Houde D. , Jandl S. , Boatner L. A.
Published: April 2011

Raman-scattering and infrared reflectivity experiments were conducted using a KTa0.93Nb0.07O3 single crystal with a ferroelectric phase transition temperature of Tc ≈ 68 K. The values obtained for the damping rate of the A1(TO(transverse optical)) soft-mode appear to be half of those determined by impulsive stimulated Raman scattering. Since the latter experiment probes the soft-mode in the polariton regime, while the former probes outside of this region, the observed discrepancy points towards some additional interaction for the polariton soft-mode.
Contributions of density-dependent interactions in heavy-ion transfer reactions
Authors: Osman Ahmed , Farra A. A.
Published: April 2011

Heavy-ion reactions with particle transfer are studied using the distorted-wave Born-approximation formalism. Different forms of the distorting optical model potentials are introduced in the initial and final channels. The form factors of the reactions are presented explicitly using modified real Woods–Saxon potentials for the nucleus–nucleus bound-state interactions in the entrance and exit channels. The differential cross sections of heavy-ion transfer reations are calculated numerically using the double-folding model for distorting potentials with an effective density-dependent nucleon–nucleon interaction. The present analyses of the angular distributions introduce good descriptions of the experimental data. The observed backward oscillations are described successfully by the explicit inclusion of the density- and the parity-dependent terms in the distorting optical-model potential calculations. The values of the extracted spectroscopic factors and normalization coefficients obtained are reasonable.
Angular distribution of optical photons from β decay of oriented nuclei
Authors: Al-Harkan A. M.
Published: April 2011

Internal and external optical bremsstrahlung accompanying the β decay of polarized nuclei were investigated. The features of angular distribution of light photons were analyzed taking into account multiple electron scattering. Monte-Carlo simulation was used to study the fate of β electrons and to calculate the intensity and angular distribution of the optical photons. It is shown that in pure water, the contribution of secondary electrons in the production of photons reaches 30–40%. We suggest using the angular distribution of optical photons to study the polarization states of β isotopes imbedded in transparent media.
Low-frequency noise in RF-sputtered Pb-doped 2223 phase BiSrCaCuO thin films
Authors: Shih I. , Li A. L. , Lam W. W. , Qiu C. X. , Phong L. Ngo , Tremblay B.
Published: April 2011

Noise measurements were carried out on RF-sputtered Pb-doped 2223 phase BiSrCaCuO superconducting thin films. No definite relationship between noise and bias current was observed in the superconducting state, however, a square-current dependence of noise was found in the normal state. The magnitude of the noise in the BiSrCaCuO films at room temperature was one to five orders of magnitude larger than that in a normal metal. Near the tail of the resistance transition, noise peaks were observed that were 3–12 K below the maximum of the derivative resistance–temperature curve. Noise dependence on frequency shows an approximate 1/f relation in both normal and superconducting states. The origin of the noise in the normal state is believed to be due to thermal fluctuation or resistance fluctuation and the larger noise near zero TC is possibly caused by grain boundaries in the films.
Reflection properties of conducting rectangular elements printed on a dielectric slab
Authors: Shaker J. , Shafai L.
Published: April 2011

The spectral domain dyadic Green's function that involves infinite spectral integrals is developed for stratified media. The Poisson summation formula is then used to transform these infinite spectral integrals into infinite double summations to make them applicable to infinite arrays of conductors printed on a dielectric slab. A Galerkin method is used to discretize and solve the electric-field integral equations for the geometry of a two-dimensional array of conducting patches. The method of analysis is then used to study the reflection and transmission properties of rectangular patch elements, for both co-polar and cross-polar components of the field. The variation of the resonance frequency with the aspect ratio of the rectangle is also investigated.
WZW fusion rules for the classical Lie algebras
Authors: Cummins C. J. , King R. C.
Published: April 2011

Fusion rules for WZW models based on the Lie algebras su(n), sp(2n) and so(n) are considered. Previous work has shown how, in the cases of su(n) and sp(2n), fusion rules may be computed using Young diagram methods and applying fusion modification rules similar to the rank modification rules required for tensor products. In this note we extend these results to include the so(n) case.
Lie subgroups of the symmetry group of the equations describing a nonstationary and isentropic flow: Invariant and partially invariant solutions
Authors: Grundland A. M. , Lalague L.
Published: April 2011

We study the symmetries of the equations describing a nonstationary and isentropic flow for an ideal and compressible fluid in four-dimensional space-time. We prove that this system of equations is invariant under the Galilean-similitude group. In the special case of the adiabatic exponent γ = 5/3, corresponding to a diatomic gas, the symmetry group of this system is larger. It is invariant under the Galilean-projective group. A representatives list of subalgebras of Galilean similitude and Galilean-projective Lie algebras, obtained by the method of classification by conjugacy classes under the action of their respective Lie groups, is presented. The results are given in a normalized list and summarized in tables. Examples of invariant and nonreducible partially invariant solutions, obtained from this classification, is constructed. The final part of this work contains an analysis of this classification in connection with a further classification of the symmetry algebras for the Euler and magnetohydrodynamics equations.
Tensor products and fusion rules
Authors: Walton M. A.
Published: April 2011

Methods of decomposing tensor products of integrable representations of semisimple Lie algebras are described. They include a formula due to Zelobenko, the descendant of a conjecture made by Parthasarathy et al., and identities found by Feingold. The methods are adapted to the calculation of fusion rules in Wess–Zumino–Novikov–Witten models.
In situ 64Cu Doppler-broadening positron-annihilation methods for elevated temperature study of defect formation in metals
Authors: Lawther D. W. , Dunlap R. A.
Published: April 2011

A Doppler-broadening positron-annihilation-spectroscopy experiment that utilizes an in situ 64Cu source for the study of Cu and Cu-containing materials is described. This technique is particularly useful for the investigation of defect structure at elevated temperatures, and the present instrumentation provides reliable results up to about 1000 °C. The method described is applicable to Cu-containing samples with as little as about 0.1 at.% Cu. Results from measurements on a single crystal of elemental Cu are compared with literature results obtained using other positron-annihilation methods and electrical-resistivity studies.
Laser-rf double-resonance study of SiO+
Authors: Scholl T. J. , Cameron R. , Rosner S. D. , Holt R. A.
Published: April 2011

We used the laser-rf double resonance method to measure 15 fine structure intervals for rotational quantum numbers ranging from N = 5 to 79 of the ν = 0 level of the X2Σ+ state of SiO+. We present a molecular model, including perturbations from the A2Π state, which explains the observed strong variation of fine structure as a function of rotational quantum number. These data yield greatly improved predictions of the microwave spectrum of the ground state of SiO+. In particular we predicted the ground state rotational transition (N = 2, J = 5/2) → (N = 1, J = 3/2) to be 86 063(1) MHz, confirming that this transition is not the source of the radio line known as U86.2 at 86 243.45(40) MHz.
Note on a logarithmic integral for the plasma energy of the electron gas
Authors: Lee M. Howard
Published: April 2011

The correlation energy of the electron gas in the ground state for small values of rs has a major contribution from the plasma oscillations. The plasma energy is known to be reducible to a logarithmic integral. This integral has been evaluated by a contour integration method. An alternative solution, perhaps much simpler, is presented here that utilizes the dilogarithm.
Dissipation-assisted tunneling in asymmetric double-well potentials
Authors: Razavy M.
Published: April 2011

The motion of the center of a wave packet localized in one of the wells of an asymmetric double-well potential is studied. The asymmetric potential is obtained from a solvable symmetric potential using the Gel'fand–Levitan formalism, by keeping the energy eigenvalues unchanged, but changing the normalization of the ground-state wave function. While in a symmetric double well the wave packet tunnels back and forth between the two wells, for an asymmetric well, in general, tunneling does not take place. This is independent of the initial location of the wave packet, i.e., whether it is centered at the minimum of the shallower or of the deeper well. However, when such a system is coupled to a dissipative force, then the tunneling becomes possible. For instance it is shown that if, as a model of dissipative coupling, one chooses Gisin's nonlinear evolution equation, then the center of the wave packet ends up in the deeper well (decay of false vacuum). This result depends on the particular model of dissipation, for instance, an optical potential model yields a different result.
Inorganic solution chemistry at elevated pressures
Authors: Swaddle T. W.
Published: April 2011

Recent interest in pressure effects on inorganic systems in solution has been centred upon the use of volumes of activation ΔV‡ as criteria of reaction mechanism. Work in our laboratory has sought to determine whether ΔV‡ is indeed a useful parameter in this respect, i.e., whether it is substantially independent of pressure and reaction conditions and whether it can be quantitatively predicted for suitably "simple" reactions. For solvent exchange on metal ions (the simplest conceivable substitution process), a semi-empirical model predicts ΔV‡ for limiting dissociative (bond breaking) and associative (bond making) mechanisms in water, but experimental values lie between these extremes, vindicating the Langford–Gray "interchange" model in which associative and dissociative processes are viewed as being concerted. For adiabatic electron transfer reactions of the outer-sphere type (the simplest conceivable oxidation–reduction process) in water, an adaptation of Marcus theory accounts for the essentially pressure-independent ΔV‡ satisfactorily, and failures of such predictions can be ascribed to complications such as nonadiabaticity or the incursion of inner-sphere (ligand-bridged) reaction pathways. The theory is less successful in nonaqueous solvents. Experimental methods used for these and related studies include high pressure adaptations of nuclear magnetic resonance, UV–visible spectrophotometry, stopped-flow techniques, cyclic voltammetry, and sampling under pressure.
Dynamic fracture under impact and high-strain-rate loading
Authors: Worswick M. J. , Clarke J. A. , Pick R. J.
Published: April 2011

A constitutive model based on a pressure-dependent yield criterion is used to predict damage evolution and ductile fracture under dynamic loading conditions. The model predicts the influence of porosity on plastic flow in metals and the nucleation, growth, and coalescence of internal microvoids to cause ductile fracture. The constitutive equations have been implemented in the DYNA2D finite-element code and have been used to simulate three high-strain-rate experiments: (i) the symmetric Taylor cylinder impact, (ii) the plate impact, and (iii) the tensile split Hopkinson bar experiments. In each case, the model is shown to capture qualitatively the damage and fracture within the experiments modelled. Comparison with recent symmetric Taylor impact experiments on leaded brass suggests that the model over-predicts the rate of damage evolution under the high-strain rate, high-triaxiality conditions associated with impact.
Investigation of correlations between conditional moments in nuclear fragmentation at high energy
Authors: Liu Fu-Hu , Sun Han-Cheng
Published: April 2011

The conditional moments of the charge distributions of the projectile fragments in O and S fragmentation are obtained using the partition method. Thus, the logarithmic correlations between the conditional moments can be observed. The electromagnetic dissociations are similar to the correlation behaviour of nuclear reactions. This is illustrated by the correlation behaviour of the oxygen nuclei, which are in agreement with that of the sulphur nuclei. The calculated results correspond to the experimental data of 3.7 and 200 GeV N−1 O–Em and 200 GeV N−1 S–Em interactions.
Finite-size effects in metallic superlattice systems
Authors: Chen J. , Kobes R. , Wang J.
Published: April 2011

Clean metallic superlattice systems composed of alternating layers of superconducting and normal materials are considered, particularly aspects of the proximity effect as it affects the critical temperature. A simple model is used to address the question of when a finite–sized system theoretically approximates well a true infinite superlattice. The methods used in the analysis afford some tests of the approximation used that the pair amplitude of the Cooper pairs is constant over a superconducting region. We also use these methods to construct a model of a single superconducting layer which intends to incorporate a more realistic form of the pair amplitude than a simple constant.
Comments on the crystal structure of solid trichlorofluoromethane
Authors: Prado Pablo , Armstrong Robin L. , Powell Brian
Published: April 2011

A neutron powder-diffraction profile of solid trichlorofluoromethane was obtained at 85 K. Analysis of the profile reveals a structure consistent with that previously reported at 1.5 K. This unique packing for a crystal composed of CXY3 molecules provides the explanation for earlier magnetic-resonance results.
Slow dynamics of interfacial water
Authors: Chen S.-H. , Gallo P. , Bellissent-Funel M.-C.
Published: April 2011

The highlights of our recent high-resolution quasi-elastic incoherent neutron: scattering studies of the translational dynamics of water molecules contained in the micropores of Vycor glass and on the surface of a deuterated protein are summarized. The incoherent quasi-elastic spectra from the confined H2O are first analyzed by a confined diffusion model to obtain the elastic incoherent structure factor (EISF), the short-time self-diffusion constant (D), and the probability per unit time for a jump (1/τ0) as functions of the surface coverage and temperature. The effect of the confinement on the slowing down of the translational motion is discussed. An alternative interpretation of the slow dynamics based on a molecular mechanism of a cage effect and an approach to the kinetic glass transition is put forth.
Neutron inelastic-scattering experiments on semimetallic actinide compounds
Authors: Lander G. H. , Stirling W. G. , Cooper B. R.
Published: April 2011

This paper traces the development of the study of the dynamical properties of the semimetallic actinide compounds that have a NaCl crystal structure (monopnictides and monochalcogenides) from the first experiment with a triple-axis spectrometer at Chalk River National Laboratory in 1976. The important realization that the excitations could be overdamped even in an ordered magnetic material, such as UN, because of the interaction between the 5f and conduction electrons remains one of the unique aspects of the physics of these materials. Later experiments on UTe and the transuranium material PuSb are discussed, together with the theoretical concepts that have allowed these results to be understood in terms of the hybridization between the 5f and conduction electrons.
Rigorous density functional theory for inhomogeneous Bose-condensed fluids
Authors: Griffin A.
Published: April 2011

The density functional theory originally developed by Hohenberg, Kohn, and Sham provides a rigorous conceptual framework for dealing with inhomogeneous interacting Fermi systems. We extend this approach to deal with inhomogeneous interacting Bose-condensed systems, limiting this presentation to setting up the formalism to deal with ground-state (T = 0) properties. The key new feature is that one must deal with energy functionals of both the local density n(r) and the local complex macroscopic wave function Φ(r) associated with the Bose broken-symmetry (the local condensate density is [Formula: see text]. Implementing the Kohn–Sham scheme, we reduce the problem to a gas of weakly interacting Bosons moving in self-consistent diagonal and off-diagonal one-body potentials. Our formalism should provide the basis for studies of the surface properties of liquid 4He as well as the properties of Bose-condensed atomic gases trapped in external potentials.
Finite lifetimes for intermediate phonon lines in anharmonic perturbation theory
Authors: Cowley E. Roger
Published: April 2011

The spectral functions for a linear chain show strong singularities when calculated with the usual perturbation-theory expressions. Results from molecular-dynamics simulations show no such signularities. We modify the perturbation-theory calculation to include lifetimes, and hence widths, for the intermediate phonons in the cubic term. The widths and shifts of the intermediate lines are assumed, for simplicity, to be proportional to their frequencies, and are calculated self-consistently. The agreement with the molecular-dynamics results is substantially improved.
Angular and polarization effects in relativistic potential scattering of electrons in a powerful laser field
Authors: Panek P , Kamiñski J Z , Ehlotzky F
Published: April 2011

In view of recent advances in the development of powerful laser sources renewed interest has been devoted to the investigation of electron-scattering processes in very strong laser fields. Here, were consider the scattering of electrons by a potential in a strong electromagnetic plane wave. Since to a first order of approximation spin effects can be neglected, we describe the scattered electron by a laser-dressed Klein-Gordon particle. It is shown in a first-order Born approximation that at nearly relativistic scattering conditions, in which the space-dependence of the laser field cannot be ignored, characteristic angular and polarization effects can be encountered for specific scattering configurations that will not show up in the nonrelativistic case where the radiation field is treated in the dipole approximation. We also demonstrate that even for laser-field intensities at which nonrelativistic calculations should apply one can observe discrepancies between relativistic and nonrelativistic results.PACS Nos.: 34.50.Rk, 34.80.Qb, 32.80.Wr
A laboratory study on the thermomechanical behaviour of clayey soils
Authors: Burghignoli A , Desideri A , Miliziano S
Published: April 2011

This paper presents the findings of a laboratory investigation of the thermomechanical behaviour of clayey soils. The tests were performed on reconstituted and natural clayey soils using triaxial cells modified to control temperature. The range of temperatures that were investigated is from 20° to 60°C. The thermal behaviour of the clays and the influence of temperature on their mechanical behaviour were investigated separately. The analysis of the experimental results obtained in drained and undrained nonisothermal tests and during thermal consolidation made it possible to identify a link between the thermal and the time-dependent behaviour of the soil skeleton. Therefore, as for creep processes, the response of the soil to thermal loading is not unique but among other factors depends strongly on the overall and recent stress history experienced by the soil. In the range of temperatures investigated, the deformability and strength of the soil were found to be relatively independent of temperature. Stiffening of the soil results from thermal cycles.Key words: clay, temperature, creep, stress history, recent stress history.
Strain-rate-dependent stress-strain behavior of overconsolidated Hong Kong marine clay
Authors: Zhu Jun-Gao , Yin Jian-Hua
Published: April 2011

A total number of 24 consolidated undrained triaxial shear tests on reconsolidated saturated Hong Kong marine clay (HKMC) have been performed in both compression and extension shear states. The specimens were prepared in four different overconsolidation ratios (OCRs) and sheared at three different axial strain rates. The strain-rate dependency of undrained shear strength, pore-water pressure, stress path, and secant Young's modulus are investigated. The influence of OCR on the stressstrainstrength behavior of HKMC is also examined. The results of all tests are presented and interpreted. The interpreted results are compared with the results in the literature. For the HKMC with OCR varying from 1 to 8, the average value of the strain-rate parameter [Formula: see text] 0.15is 5.5% for compression tests and 8.4% for extension tests. Most interpreted results are conclusive and consistent with the published results, whereas some results are not conclusive. A new parameter for describing the strain-rate dependency of undrained shear strength of overconsolidated soil is introduced.Key words: strain-rate effects, clay, overconsolidated, triaxial, shear strength, pore-water pressure.
Engineering geology characterization of lacustrine overconsolidated clays in an alpine area of Italy
Authors: Meriggi R , Paronuzzi P , Simeoni L
Published: April 2011

This study reports the main geotechnical characteristics of the Steggio Clay unit, a lacustrine sequence located in a valley of the Veneto Piedmont area (northern Italy). Analyzing the variations of overconsolidation pressure with depth, and the compressibility characteristics of natural, swelled, and reconstituted samples, one can hypothesize about the existence and influence of swelling processes on the stress history of the deposit. The yield pressures, determined by oedometric tests for the various lithostratigraphic units, are compared with the preconsolidation pressures deduced from the geological analysis, and a reduction in apparent preconsolidation pressures is evident in the upper layers. Comparing the natural water content of each stratigraphic unit with that of the overconsolidated and normally consolidated states, it can be seen that the same layers are softened. These phenomena could have been caused by swelling induced by erosion of the overlying deposits, sliding of glacial masses, and unloading due to deglaciation. The results of undrained consolidated triaxial compression tests indicate that the variations between the parameters of mechanical resistance of some lithological units can be attributed to the different values of the void index, Ivo, corresponding to the lithostatic in situ stress.Key words: overconsolidated clays, stress history, swelling, intrinsic characteristics, post-depositional processes, glaciation.
A field trial of jet-grouting in marine clay
Authors: Poh Teoh Yaw , Wong Ing Hieng
Published: April 2011

The basement excavation of the Singapore Post Center involved extensive jet-grouting to improve the soft marine clay present within the excavation. The treated soil mass, with much improved strength and deformation characteristics, was intended to act as an internal strut below the bottom of the excavation level, reducing movements caused by the basement excavation. This paper presents the performance of a well-instrumented field jet-grouting trial during the construction of the building basement. Results of monitoring suggest that the jet-grouting trial caused the retaining diaphragm walls and the adjacent soils immediately behind and at some distance away from the walls to move away from the jet-grouted area. The maximum free field lateral soil movements in the excavation side of the jet-grouted mass were much larger than the corresponding lateral movements behind the wall. The results suggest that the diaphragm wall provided considerable restraint, thereby reducing the lateral movements of the soil behind the wall induced by the jet-grouting. Bending moments were induced in the diaphragm walls due to the jet-grouting work. The jet-grouting also caused some increase in the lateral earth pressure and the piezometric levels.Key words: jet-grouting, ground improvement, diaphragm wall, ground movements.
Fracturing in low-permeability soils for remediation of contaminated ground
Authors: Wong Ron CK , Alfaro Marolo C
Published: April 2011

This paper presents a field study on hydraulic fracturing for in situ remediation of contaminated ground. Sand-propped hydraulic fractures were placed from vertical and horizontal wells at a test facility. Field excavations were conducted to expose the fractures and inspect their distribution and geometry. Fractures that were mapped by field excavation were found to be near horizontal, implying that the soil formation is overconsolidated. It was also observed that the sand "proppant" was thicker at locations where the soil layers were relatively weak or contained weak fissures. Electrical resistivity tomography (ERT) was also conducted in an attempt to map the fractures. There was no indication that fractures were being mapped by this geophysical technique. Fracture mapping based on tiltmeter data analyses conformed closely with the actual fracture placement in the vertical well but did not properly predict the actual fracture placement in the horizontal well.Key words: hydraulic fracturing, field test, low-permeability soil, electrical resistivity tomography, tiltmeters, horizontal well, vertical well.
Complex permittivity measurement system for detecting soil contamination
Authors: Rowe R K , Shang J Q , Xie Y
Published: April 2011

The design, calibration, and operation of a laboratory-scale system to assess the viability of detecting contaminants in soil based on changes in its electromagnetic response are described. The complex permittivity measurement device, permeation apparatus, and dielectric responses of soil specimens measured before and after permeation with different CaCl2 solutions are discussed. It is shown that the change in the complex permittivity of the soil is best characterized in terms of the permittivity and loss factor at the frequency of 250 MHz, since they exhibit a significant response to changes in the pore-fluid chemistry. The laboratory system can be used routinely to create soil samples permeated with a known contaminant at known concentrations and then measure the complex permittivity of the contaminated soil samples directly after permeation. The system is such that other factors (e.g., density and water content) which could influence the complex permittivity can be carefully controlled, allowing the relationship between the type and level of contamination and dielectric behaviour of soils to be established.Key words: complex permittivity, nondestructive testing, soil contamination, detection of soil contamination, environmental technology.
Field evidence of resuspension in a mine tailings pond
Authors: Adu-Wusu Celestina , Yanful Ernest K , Mian Mohammed H
Published: April 2011

Flooding of tailings under shallow water covers is an effective method of decommissioning potentially acid generating mine tailings. The low diffusivity and solubility of oxygen in water are attractive features of this technology. However, wind-induced waves can resuspend flooded tailings and expose them to greater contact with dissolved oxygen, thereby increasing the potential for oxidation and acid generation. Field measurements of wind activity and waves under different water cover depths and associated resuspension for a mine tailings pond in Ontario are presented and discussed. The results show that wind speeds greater than 8 m/s above water covers that are shallower than 1 m create waves of height greater than 10 cm and bottom shear stresses greater than 0.2 Pa. Under these conditions the critical shear stress of the mine tailings was exceeded, resulting in erosion and subsequent resuspension.Key words: mine tailings, water cover, wind-induced waves, resuspension, wind speed, shear stress.
Back-calculation of consolidation parameters from field measurements at a reclamation site
Authors: Cao Lai Fa , Chang Ming-Fang , Teh Cee Ing , Na Yung Mook
Published: April 2011

A pilot test was carried out at a land reclamation project site to study the effect of vertical drains on the rate of consolidation of a marine clay deposit in Singapore. Theoretical and numerical analyses were conducted to interpret the field measurements of pore pressure and settlement, and consolidation parameters were back-calculated. The back-calculated preconsolidation pressure is similar to that obtained from the laboratory consolidation test on undisturbed samples, but the field-deduced compression index is generally larger than that measured in the laboratory. The coefficient of consolidation back-calculated from the settlement measurement is larger than that from the pore-pressure measurement. The coefficient of consolidation for horizontal flow obtained from the Rowe cell test, which is comparable to that back-calculated from the field settlement measurement, is recommended for the preliminary design of vertical drains without the need of considering the smear effect.Key words: clays, consolidation, ground improvement, numerical modelling and analysis, permeability, vertical drains.
Measurement and estimation of pore shrinkage and pore distribution in a clayey till during soil-water characteristic curve tests
Authors: Simms Paul H , Yanful Ernest K
Published: April 2011

The soil-water characteristic curve (SWCC) of fine-grained soils is usually determined experimentally. In many applications, such as design of mine waste covers and landfill liners, the unsaturated permeability function, k(h), is often derived theoretically from the measured SWCC. Implicit in these derivations is the transformation of the SWCC to a pore-size distribution (PSD), typically assumed to be constant and mono-modal. PSDs of a clayey till compacted at various water contents were measured after compaction, after flexible-wall permeability testing, and during and after SWCC tests. The measurements show that the PSD changes significantly during permeability and SWCC testing. A method is advanced for predicting the observed changes in PSD during SWCC testing. PSDs are determined for soil samples subjected to the highest and lowest suctions applied during the SWCC test. The measured PSDs are transformed to account for pore trapping; the transform assumes that flow occurs through two sets of randomly distributed pores in series. To model pore shrinkage, the pores are idealized as elastic cylinders. PSDs measured after different suction applications in the SWCC tests are compared with predictions of the shrinkage model. The method can also be used to predict the SWCC. Measured and predicted values are compared.Key words: landfill liners, mine waste covers, soil-water characteristic curve, pore-size distribution.
Numerical oscillation in seepage analysis of unsaturated soils
Authors: Karthikeyan Muthusamy , Tan Thiam-Soon , Phoon Kok-Kwang
Published: April 2011

The finite element method provides a popular means of analyzing groundwater flow in an unsaturated soil. In such problems, oscillatory results are often observed in the finite element solution. Such a phenomenon is observed, for example, when a typical finite element program such as Seep/w is used to model water infiltration into unsaturated soils. Numerical oscillations are often found near the wetting front where the hydraulic gradient is the steepest. These oscillations do not always reduce with decreasing or increasing time-step size alone; rather, an appropriate ratio between time-step size and element size is required. As the pore-water pressures predicted from a transient seepage analysis are used as input groundwater conditions for other types of analysis such as slope stability, contaminant transport, and capillary barrier, these oscillations may have important practical ramifications. Since seepage analysis is common in engineering practice, it is important that appropriate criteria are identified to minimize, if not to remove, the oscillations. In this paper, numerical examples are provided to demonstrate that a simple set of criteria, developed in heat diffusion problems with constant properties to control oscillation, is also applicable to one- and two-dimensional unsaturated seepage analyses, for a range of material nonlinearities that are frequently encountered in unsaturated soils.Key words: unsaturated soil, soil-water characteristic curve, seepage analysis, finite element method, numerical oscillation.
Evaluation of ground and building settlement near braced excavation sites by model testing
Authors: Seok Jeong Woo , Kim Oon Young , Chung Choong Ki , Kim Myoung Mo
Published: April 2011

Braced excavations inevitably result in deformation of the adjacent ground and settlement of adjacent buildings behind the wall. Building settlement is believed to exceed the amount of associated ground settlement because of the additional settlement under building weight. This is due to a decrease in stiffness of the foundation soil that is caused by lateral movement of the excavation face. To quantify the amount of building settlement, model testing was conducted to determine the magnitude of the additional settlement due to the structure and the effect of varying the building's depth in the ground and of its distance away from the excavation wall. The building's settlement, when at ground level, was found to be up to 500% more than that of ground with no structure on it. This is for the case when the building's centroid on the ground surface is located within Rankine's active zone. When the building was embedded in the ground the degree of additional settlement decreases very rapidly, becoming negligible if the building is embedded at more than one half of the excavation depth. Additional model testing was conducted to estimate the extent of the soil improvement zone required to protect structures adjacent to an excavation. From the model testing results, soil improvement should be performed to reduce building settlement when the building's centroid is located in the excavation influence zone. The zone for this soil improvement is determined by setting the distance away from the excavation wall to be equal to the depth of the excavation.Key words: braced excavations, model testing, ground settlement, additional settlement volume, angular distortion, soil improvement.