bluuebunny/crossref_metadata_2025 huggingface dataset:
THE CJT CALCULATION IN STUDYING NUCLEAR MATTER BEYOND MEAN FIELD APPROXIMATION
Authors: SHU SONG , LI JIA-RONG
Published: July 2008

We have introduced the Cornwall–Jackiw–Tomboulis (CJT) resummation scheme in studying nuclear matter. Based on the CJT formalism and using Walecka model, we have derived a set of coupled Dyson equations of nucleons and mesons. Neglecting the medium effects of the mesons, the usual mean field theory (MFT) results can be obtained. The beyond MFT calculations have been performed by thermodynamic consistently determining the meson effective masses and solving the coupled gap equations for nucleons and mesons together. The numerical results for the nucleon and meson effective masses at finite temperature and chemical potential in nuclear matter are discussed.
CANONICAL, LIE-ALGEBRAIC AND QUADRATIC TWIST DEFORMATIONS OF GALILEI GROUP
Authors: DASZKIEWICZ MARCIN
Published: July 2008

New Galilei quantum groups dual to the Hopf algebras proposed in Ref. 1 are obtained by the nonrelativistic contraction procedures. The corresponding Lie-algebraic and quadratic quantum spacetimes are identified with the translation sectors of considered algebras.
GENERAL RELATIVISTIC VELOCITY: THE ALTERNATIVE TO DARK MATTER
Authors: COOPERSTOCK F. I. , TIEU S.
Published: July 2008

We consider the gravitational collapse of a spherically symmetric ball of dust in the general relativistic weak gravity regime. The velocity of the matter as viewed by external observers is compared to the velocity gauged by local observers. While the comparison in the case of very strong gravity is seen to follow the pattern familiar to the studies of test particles falling towards a concentrated mass, the case of weak gravity is very different. The velocity of the dust that is witnessed by external observers is derived for the critically open case and is seen to differ markedly from the expectations based upon Newtonian gravity theory. Viewed as an idealized model for a cluster of galaxies, we find that with the general relativistic velocity expression, the higher-than-expected constituent velocities observed can be readily correlated with the solely baryonic measure of the mass, obviating the need to introduce extraneous dark matter. It would be particularly valuable if a laboratory or space-based realization of a spherical collapse could be implemented to compare the velocity expression as a new test of general relativity.
TESTING THE UNITARITY OF THE CKM MATRIX WITH A SPACE-BASED NEUTRON DECAY EXPERIMENT
Authors: NIETO MICHAEL MARTIN , FELDMAN WILLIAM C. , LAWRENCE DAVID J.
Published: July 2008

If the Standard Model is correct, and fundamental fermions exist only in the three generations, then the CKM matrix should be unitary. However, there remains a question over a deviation from unitarity from the value of the neutron lifetime. We discuss a simple space-based experiment that, at an orbit height of 500 km above Earth, would measure the kinetic-energy, solid-angle, flux spectrum of gravitationally bound neutrons (kinetic energy K< 0.606 eV at this altitude). The difference between the energy spectrum of neutrons that come up from the Earth's atmosphere and that of the undecayed neutrons that return back down to the Earth would yield a measurement of the neutron lifetime. This measurement would be free of the systematics of laboratory experiments. A package of mass < 25 kg could provide a 10-3 precision in two years.
HAWKING RADIATION OF BLACK p-BRANES FROM GRAVITATIONAL ANOMALY
Authors: MA ZHENG ZE
Published: July 2008

We investigate the Hawking radiation of black p-branes of superstring theories using the method of anomaly cancellation, specially, we use the method of S. Iso, H. Umetsu and F. Wilczek, Phys. Rev. Lett.96, 151302 (2006) and Phys. Rev. D74, 044017 (2006). The metrics of black p-branes are spherically symmetric, but not the Schwarzschild-type. In order to simplify the calculation, we first make a coordinate transformation to transform the metric to the Schwarzschild-type. Then we calculate its energy–momentum flux from the method of anomaly cancellation of the above-mentioned references. The obtained energy–momentum flux is equal to a blackbody radiation, the thermodynamic temperature of the radiation is equal to its Hawking temperature. And we find that the results are not changed for the original non-Schwarzschild-type spherically symmetric metric.
TOP OFF THE UNPARTICLE
Authors: CHOUDHURY DEBAJYOTI , GHOSH DILIP KUMAR
Published: July 2008

The existence of an exactly scale invariant sector possessing a nontrivial infrared fixed point at a higher energy scale and its possible communication with the Standard Model particles through a heavy messenger sector has been shown to lead to curious unparticle effects. We demonstrate that top physics at the Tevatron can already constrain such theories. We also consider possible improvements at the LHC and delineate some striking signatures.
DIRAC SEA AND HOLE THEORY FOR BOSONS I: A NEW FORMULATION OF QUANTUM FIELD THEORIES
Authors: HABARA YOSHINOBU , NAGATANI YUKINORI , NIELSEN HOLGER B. , NINOMIYA MASAO
Published: July 2008

Bosonic formulation of the negative energy sea, so-called Dirac sea, is proposed by constructing a hole theory for bosons as a new formulation of the second quantization of bosonic fields. The original idea of Dirac sea for fermions, where the vacuum state is considered as a state completely filled by fermions of negative energy and holes in the sea are identified as antiparticles, is extended to boson case in a consistent manner. The bosonic vacuum consists of a sea filled by negative energy bosonic states, while physical probabilities become always positive definite. We introduce a method of the double harmonic oscillator to formulate the hole theory of bosons. Our formulation is also applicable to supersymmetric field theory. The sea for supersymmetric theories has an explicit supersymmetry. We suggest applications of our formulations to the anomaly theories and the string theories.
FIELD THEORY ON κ-MINKOWSKI SPACE REVISITED: NOETHER CHARGES AND BREAKING OF LORENTZ SYMMETRY
Authors: FREIDEL LAURENT , KOWALSKI-GLIKMAN JERZY , NOWAK SEBASTIAN
Published: July 2008

This paper is devoted to detailed investigations of free scalar field theory on κ-Minkowski space. After reviewing necessary mathematical tools, we discuss in detail the Lagrangian and solutions of field equations. We analyze the space–time symmetries of the model and construct the conserved charges associated with translational and Lorentz symmetries. We show that the version of the theory usually studied breaks Lorentz invariance in a subtle way: there is an additional trans-Planckian mode present, and an associated conserved charge (the number of such modes) is not a Lorentz scalar.
SYMPLECTIC DEFORMATIONS, NONCOMMUTATIVE SCALAR FIELDS AND FRACTIONAL QUANTUM HALL EFFECT
Authors: DAOUD M. , HAMAMA A.
Published: July 2008

We clearly show that the symplectic structures deformations lead, upon quantization, to quantum theories of noncommutative fields. Two variants of deformations are considered. The quantization is performed and the modes expansions of the quantum fields are derived. The Hamiltonians are given and the degeneracies lifting induced by the deformation is also discussed. As an illustration, we consider the noncommutative chiral boson fields in the context of fractional quantum Hall effect. A generalized fractional filling factor is derived and shown to reproduce the Jain Hall states. We also show that the coupling of left and right edge excitations of a quantum Hall sample, gives rise a noncommutative chiral boson theory. The coupling or the noncommutativity induces a shift of the chiral components velocities. A nonlinear dispersion relation is obtained, corroborating some recent analytical and numerical analysis.
GENERAL SPHERICAL SYMMETRY SOLUTION TO EINSTEIN EQUATIONS AND NEWTONIAN GRAVITY MODIFICATION AT SMALL LENGTH SCALE
Authors: DUAN YI-SHI , TIAN MIAO
Published: July 2008

In this paper, we first we present a general spherical symmetry solution, independent of any coordinate condition, to the Einstein equations. By using this solution, we obtain different cases in different coordinate conditions, such as Schwarzschild solution, Fock solution, which have different forms of f(r). Then, we obtain a modified formula with respect to f(r) of the Newtonian gravity. This formula may describe the gravity at small length scale.
UNIVERSAL NEAR-HORIZON CONFORMAL STRUCTURE AND BLACK HOLE ENTROPY
Authors: CHAKRABARTI SAYAN K. , GUPTA KUMAR S. , SEN SIDDHARTHA
Published: July 2008

It is shown that a massless scalar probe reveals a universal near-horizon conformal structure for a wide class of black holes, including the BTZ. The central charge of the corresponding Virasoro algebra contains information about the black hole. With a suitable quantization condition on the central charge, the CFT associated with the black hole in our approach is consistent with the recent observation of Witten, where the dual theory for the BTZ in the AdS/CFT framework has been identified with the construction of Frenkel, Lepowsky and Meurman. This CFT admits the Fischer–Griess monster group as its symmetry. The logarithm of the dimension of a specific representation of the monster group has been identified by Witten as the entropy of the BTZ black hole. Our algebraic approach shows that a wide class of black holes share the same near-horizon conformal structure as that for the BTZ. With a suitable quantization condition, the CFT's for all these black holes in our formalism can be identified with the FLM model, although not through the AdS/CFT correspondence. The corresponding entropy for the BTZ provides a lower bound for the entropy of this entire class of black holes.
THE QUANTUM THEORY OF SCALAR FIELDS ON THE DE SITTER EXPANDING UNIVERSE
Authors: COTĂESCU ION I. , CRUCEAN COSMIN , POP ADRIAN
Published: July 2008

New quantum modes of the free scalar field are derived in a special time-evolution picture that may be introduced in moving charts of de Sitter backgrounds. The wave functions of these new modes are solutions of the Klein–Gordon equation and energy eigenfunctions, defining the energy basis. This completes the scalar quantum mechanics where the momentum basis is well known for long time. In this enlarged framework the quantization of the scalar field can be done in canonical way obtaining the principal conserved one-particle operators and the Green functions.
ANISOTROPIC BIANCHI-V COSMOLOGICAL MODELS IN SAEZ–BALLESTER THEORY OF GRAVITATION
Authors: SINGH C. P. , ZEYAUDDIN MOHD. , RAM SHRI
Published: July 2008

A general approach for investigating Bianchi-V cosmological models is introduced in a scalar-tensor theory of gravitation proposed by Saez and Ballester in which the law of variation for Hubble's parameter is taken into account. This variation for Hubble's parameter that yields a constant value of deceleration parameter is then utilized to solve the field equations governing anisotropic Bianchi-V space–time filled with perfect fluid. Two types of exact solutions that correspond to singular and nonsingular models are presented. Finally, we arrive to the conclusion that the universe decelerates for positive value of deceleration parameter whereas it accelerates for negative one. The behaviors of observationally important parameters are discussed in detail. Exact expressions for look-back time, luminosity distance and event horizon versus redshift are derived and their significance are discussed in detail. It has been observed that the solutions are compatible with the results of recent observations.
Θ-TWISTED GRAVITY
Authors: KOBAKHIDZE ARCHIL
Published: July 2008

We describe a theory of gravitation on canonical noncommutative space–times. The construction is based on θ-twisted general coordinate transformations and local Lorentz invariance.
ON SYNCHRONIZABILITY OF DYNAMICAL LOCAL-WORLD NETWORKS
Authors: SUN SHIWEN , LIU ZHONGXIN , CHEN ZENGQIANG , YUAN ZHUZHI
Published: July 2008

Synchronization phenomena in dynamical systems with local-world topologies are investigated. The effect of local-world size M on the synchronizability is studied. A larger M makes networks more synchronizable. Then the ability of dynamical networks to resist random errors and attacks is analyzed and compared with those of scale-free and exponential networks. Two attacking strategies are adopted, and a better quantity is used to measure the changes in synchronizability after node removal.
COLLAPSES AND REVIVALS IN TWO-LEVEL ATOMS IN A SUPERPOSED STATE INTERACTING WITH A SINGLE MODE SUPERPOSED COHERENT RADIATION
Authors: PRAKASH HARI , KUMAR RAKESH
Published: July 2008

Collapses and revivals phenomenon in system of a single two-level atom and two two-level atoms existing in some superposed states and interacting with a single mode superposed coherent radiation is studied. For superposed Dicke states |1/2, ±1/2> of a single two-level atom interacting with even or odd coherent state, only odd revivals occur. For two two-level atoms, it is found that the collapse and revival times for even and odd coherent states are equal to one half of the corresponding times for coherent state. For this system, Rabi oscillations occur with a main mean frequency and also some second harmonics are present, in general. However, if the two atoms are in the superradiant state, only the second harmonics with large amplitude are obtained. The appearance of weak double frequency revivals for superposed atomic and coherent states was studied and a condition for their disappearance is found.
RAPIDLY ROTATING BOSE–EINSTEIN CONDENSATES IN AN APPLIED ELECTRIC FIELD
Authors: LU LI-HUA , LI YOU-QUAN
Published: July 2008

The rapidly rotating Bose–Einstein condensate in the presence of an external electric field is studied. The vortex lattice formed in the condensate will shift after the electric field is applied. The electric field changes the particle density distribution and makes the system more stable. A method to detect this shift is also suggested.
PHOTOELECTRICAL PROPERTIES OF TlInS2-LAYERED SINGLE CRYSTALS
Authors: BADR A. M. , ASHRAF I. M. , SANAA M. F.
Published: July 2008

TlInS 2-layered single crystals were prepared by using a special technique for crystal growth, and the obtained crystals were analyzed by X-ray diffraction. The reflectance and transmittance spectra were measured for the mentioned layered crystals and analyzed over the incident photon energy range 1.96–2.46 eV and in the temperature range 77–300 K. In this work and with the aid of these spectra, the temperature dependence of optical transports and parameters were investigated. In line with the transmittance and reflectance analyses, the refractive index as a function of wavelength was determined in the low-energy region of the studied incident photon energy range. As results of the refractive index–wavelength variations, the oscillator and dispersion energies of the refractive index for the TlInS 2-layered single crystals were determined in the temperature range under investigation. Thereafter, static refractive index and static dielectric constant were also investigated.
AN APPROACH TO DEFORMATION THEORY BASED ON THERMODYNAMIC PRINCIPLES
Authors: KOENEMANN FALK H.
Published: July 2008

The Cauchy stress theory has been shown to be profoundly at variance with the principles of the theory of potentials. Thus, a new physical approach to deformation theory is presented, which is based on the balance of externally applied forces and material forces. The equation of state is generalized to apply to solids, and transformed into vector form. By taking the derivatives of an external potential and the material internal energy with respect to the coordinates, two vector fields are defined for the forces exerted by surrounding the system, subject to the boundary conditions, and vice versa, subject to the material properties. These vector fields are then merged into a third one that represents the properties of the loaded state. Through the work function, the force field is then directly transformed into the displacement field. The approach permits fully satisfactory prediction of all geometric and energetic properties of elastic and plastic simple shear. It predicts the existence of a bifurcation at the transition from reversible to irreversible behavior whose properties permit correct prediction of cracks in solids. It also offers a mechanism for the generation of sheath folds in plastic shear zones and for turbulence in viscous flow. Finally, an example is given on how to apply the new approach to deformation of a discrete sample as a function of loading configuration and sample shape.
MONTE CARLO MODELING OF HOT ELECTRON TRANSPORT IN BULK AlAs, AlGaAs AND GaAs AT ROOM TEMPERATURE
Authors: ARABSHAHI H. , KHALVATI M. R. , ROKN-ABADI M. REZAEE
Published: July 2008

The results of an ensemble Monte Carlo simulation of electron drift velocity response on the application field in bulk AlAs , AlGaAs and GaAs are presented. All dominant scattering mechanisms in the structure considered have been taken into account. For all materials, it is found that electron velocity overshoot only occurs when the electric field is increased to a value above a certain critical field, unique to each material. This critical field is strongly dependent on the material parameters. Transient velocity overshoot has also been simulated, with the sudden application of fields up to 1600 kVm-1, appropriate to the gate-drain fields expected within an operational field effect transistor. The electron drift velocity relaxes to the saturation value of ~105 ms-1 within 4 ps, for all crystal structures. The steady state and transient velocity overshoot characteristics are in fair agreement with other recent calculations.
SUPERCONDUCTING STATE OF AN EXCITONIC INSULATOR
Authors: BATYEV E. G.
Published: July 2008

A new state of an excitonic insulator, namely, the state with the non-dissipative electric current, is considered. It is assumed that at higher temperatures, in the metallic state, the current is induced externally, e.g. by placing the sample in a closed circuit, and electrons and holes are moving in the opposite directions carrying finite current. As temperature is decreased, transition to an ordered state due to formation of electron–hole pairs can occur, similar to the ordinary insulating state of excitonic insulator. We study the properties of such an ordered state at zero temperature and find that the spectrum of its elementary excitations has a gap, so that the state with the current is a superconductor. It is argued that this conclusion is valid in the limit of strong overlap of electron–hole pairs.
FLUCTUATION CONDUCTIVITY IN MELT-TEXTURED YBa2Cu3O7-δ
Authors: RODRIGUES PEDRO , JURELO ALCIONE ROBERTO , DE AZAMBUJA PAULA , DIAS FABIO TEIXEIRA , COSTA ROSÂNGELA MENEGOTTO
Published: July 2008

Systematic measurements of the in-plane and out-of-plane fluctuations magnetoconductivity in a melt-textured sample of YBa 2 Cu 3 O 7-δ are presented. The experiments were performed in fields ranging from 0.02 T to 5 T applied perpendicular to CuO 2 atomic (ab) planes. The measurements of the in-plane fluctuations were performed in zero applied field. The method of analysis is based on the determination of the quantity [Formula: see text], where Δσ = σ - σR is the fluctuation conductivity. In the normal phase, contributions from Gaussian regimes are clearly evidenced. These regimes are unstable regarding the application of magnetic fields perpendicular to the ab plane. Below TC, in approaching the zero resistance state, our results show a power-law behavior, that is indicative of a phase transition from paracoherent to a coherent state of the granular array.
INVESTIGATIONS ON THE LOCAL STRUCTURE AND THE EPR PARAMETERS FORCu2+-DOPEDGaN
Authors: WEI LI-HUA , WU SHAO-YI , ZHANG ZHI-HONG , WANG HUI , WANG XUE-FENG
Published: July 2008

The local structure and the EPR parameters (g factors and the hyperfine structure constants) for Cu2+in GaN are theoretically studied from the perturbation formulas of these parameters for a 3d9ion in trigonally distorted tetrahedra. In these formulas, the ligand orbital and spin-orbit coupling contributions are taken into account from the cluster approach, in view of the strong covalency effect of the system. Based on the studies, the impurity Cu2+is found not to occupy exactly the host Ga3+site but to suffer a slight displacement (≈ 0.004 Å ) towards the ligand triangle along C3axis due to charge and size mismatching substitution. The theoretical EPR parameters show good agreement with the experimental data. The validity of the impurity displacement is also discussed.
A MODELING METHODOLOGY FOR CONFLICT CONTROL IN MULTI-AGENT SYSTEMS
Authors: LIAN JIEXIN , SHATZ SOL M.
Published: July 2008

Multi-agent systems (MASs) have become an important topic in distributed systems research. These distributed multi-agent systems call for special software modeling methods that explicitly support key system properties such as resource constraints and control of conflicts. Although there have been some system modeling techniques to support MASs design and automatic analysis, most state-of-the-art techniques have not distinguished potential conflicts from real conflicts during the design stage. To solve this problem, we define a new concept, called "potential arcs," which is integrated into colored Petri net modeling to support the modeling of MASs. We present a modeling methodology based on the potential arc concept and illustrate the methodology with a case study, including some associated model analysis.
NULL-FIELD INTEGRAL EQUATION APPROACH FOR EIGENPROBLEMS WITH CIRCULAR BOUNDARIES
Authors: CHEN J. T. , CHEN C. T. , CHEN I. L.
Published: July 2008

In this paper, the eigenproblems with circular boundaries of multiply-connected domain are studied by using the null-field integral equations in conjunction with degenerate kernels and Fourier series to avoid calculating the Cauchy and Hadamard principal values. An adaptive observer system of polar coordinate is considered to fully employ the property of degenerate kernels. For the hypersingular equation, vector decomposition for the radial and tangential gradients is carefully considered in the polar coordinate system. Direct-searching scheme is employed to detect the eigenvalues by using the singular value decomposition (SVD) technique. Both the singular and hypersingular equations result in spurious eigenvalues which are the associated interior Dirichlet and Neumann problems of interior domain of inner circles, respectively. It is analytically verified that the spurious eigenvalue depends on the radius of any inner circle and numerical experiments support this point. Several examples are demonstrated to see the validity of the present formulation. More number of degrees of freedom of BEM is required to obtain the same accuracy of the present approach.
SIMULATION OF THE TRANSFER FUNCTION FOR A HEAD-AND-TORSO MODEL OVER THE ENTIRE AUDIBLE FREQUENCY RANGE
Authors: HUTTUNEN TOMI , SEPPÄLÄ EIRA T. , KIRKEBY OLE , KÄRKKÄINEN ASTA , KÄRKKÄINEN LEO
Published: July 2008

In this study, a method for simulating the transfer function of a head-and-torso model over the entire audible frequency range is introduced. The simulation method uses the ultra-weak variational formulation (UWVF) which is a finite element type method tailored for wave problems. In particular, the UWVF uses plane wave basis functions which better approximate the oscillatory field than a polynomial basis used in the standard finite element methods (FEM). This leads to reduction in the computational complexity at the high frequencies which, accompanied with parallel computing, extends the feasible frequency range of the UWVF method. The accuracy of the new simulation tool is investigated using a simple spherical geometry after which the method used for preliminary HRTF simulations in the geometry of a widely used head-and-torso mannequin.
NUMERICAL ANALYSIS OF LARGE-SCALE SOUND FIELDS USING ITERATIVE METHODS PART I: APPLICATION OF KRYLOV SUBSPACE METHODS TO BOUNDARY ELEMENT ANALYSIS
Authors: YASUDA Y. , SAKAMOTO S. , KOSAKA Y. , SAKUMA T. , OKAMOTO N. , OSHIMA T.
Published: July 2008

The convergence behavior of the Krylov subspace iterative solvers towards the systems with the 3D acoustical BEM is investigated through numerical experiments. The fast multipole BEM, which is an efficient BEM based on the fast multipole method, is used for solving problems with up to about 100,000 DOF. It is verified that the convergence behavior of solvers is much affected by the formulation of the BEM (singular, hypersingular, and Burton-Miller formulation), the complexity of the shape of the problem, and the sound absorption property of the boundaries. In BiCG-like solvers, GPBiCG and BiCGStab2 have more stable convergence than others, and these solvers are useful when solving interior problems in basic singular formulation. When solving exterior problems with greatly complex shape in Burton-Miller formulation, all solvers hardly converge without preconditioning, whereas the convergence behavior is much improved with ILU-type preconditioning. In these cases GMRes is the fastest, whereas CGS is one of the good choices, when taken into account the difficulty of determining the timing of restart for GMRes. As for calculation for rigid thin objects in hypersingular formulation, much more rapid convergence is observed than ordinary interior/exterior problems, especially using BiCG-like solvers.
NUMERICAL SOLUTION OF ONE-DIMENSIONAL WAVE EQUATION WITH STOCHASTIC PARAMETERS USING GENERALIZED POLYNOMIAL CHAOS EXPANSION
Authors: SEPAHVAND K. , MARBURG S. , HARDTKE H.-J.
Published: July 2008

This paper presents a numerical algorithm which is using generalized polynomial chaos combined with the finite difference method for the solution of the one-dimensional wave equation with stochastic physical parameters. The stochastic parameters are represented by the Hermite polynomial chaos. A spectral–finite difference model for the numerical solution is introduced using generalized polynomial chaos expansion. The general conditions for convergence and stability of numerical algorithms are derived. Finally, the method is applied to a vibrating string. Results are compared with those of a Monte Carlo simulation.
NUMERICAL METHODS FOR WAVE SCATTERING PHENOMENA BY MEANS OF DIFFERENT BOUNDARY INTEGRAL FORMULATIONS
Authors: NOLTE BODO , SCHÄFER INGO , EHRLICH JAN , OCHMANN MARTIN , BURGSCHWEIGER RALF , MARBURG STEFFEN
Published: July 2008

Different numerical approaches for the physical phenomena of scattering waves from an obstacle are presented. They are based on different integral formulations. Fluid structure interaction effects are numerically treatable as well. We use the Boundary Element Method (BEM) in different approaches because the inherently satisfied Sommerfeld radiation condition makes sure that no reflecting waves from boundaries at infinity occur. One of the biggest disadvantages of numerical methods like BEM is the fact that they have difficulties with handling the high frequency range. For the high frequency range approximations like the Kirchhoff–Helmholtz integral equation have to be used. With varying assumptions of the reflecting behavior of the structure different approaches for the higher frequency range are obtained, where the explicit solving of a system of equations is not necessary. Another high frequency approach is the plane wave approximation which is compared with the Kirchhoff approach of the first kind.

Additionally a modified Kirchhoff approach is introduced. Because the incident pressure on the scatterer's surface is known the integral is evaluated analytically on triangular patches. The discretization is no longer frequency dependent and the size of the patches only depends on the curvature of the structure. Large planar parts can be discretized with one element only. This leads to a substantial advantage in terms of calculation time over the traditional Kirchhoff approach. Like the traditional approach this procedure is valid under the assumption of high frequency or far field conditions.
GENERALIZED EIGENPROBLEM FOR ACOUSTIC WAVE PROPAGATION IN PERIODICALLY LAYERED ANISOTROPIC MEDIA
Authors: TAN ENG LEONG
Published: July 2008

A stable matrix method is presented for studying acoustic wave propagation in thick periodically layered anisotropic media at high frequencies. The method enables Floquet waves to be determined reliably based on the solutions to a generalized eigenproblem involving scattering matrix. The method thus overcomes the numerical difficulty in the standard eigenproblem involving cell transfer matrix, which occurs when the unit cell is thick or the frequency is high. With its numerical stability and reliability, the method is useful for analysis of periodic media with wide range of thickness at high frequencies.
ACOUSTIC PERFORMANCE OF NONREFLECTING BOUNDARY CONDITIONS FOR A RANGE OF INCIDENT ANGLES
Authors: MESBAH M. , MEYERS J. , BAELMANS M.
Published: July 2008

A detailed study on the accuracy and reflection behavior of nonreflection boundary conditions is presented. To this end, a selection of five distinct nonreflecting boundary conditions is evaluated and the mechanisms which dominate the reflection properties of boundary conditions are identified based on a rigorous quantification of reflection levels. It is shown that the reflection behavior is significantly affected by the incident angle. The relation between the boundary condition effectiveness and the incident angle is investigated and the reflection rates as a function of the incident angle are quantified. Furthermore, the obtained results are used to predict the reflections from boundary conditions in general applications. It is shown that these predictions are reliable for different test cases.
HYBRID ALGORITHM OF THE DEPTH SOLVER FOR WAVENUMBER INTEGRATION TECHNIQUE IN AN OCEAN WAVEGUIDE WITH A POROUS BOTTOM
Authors: LEE KEUNHWA , SEONG WOOJAE
Published: July 2008

A new hybrid algorithm of the depth solver for the wavenumber integration technique is derived. The global matrix method is adopted as the depth solver in the ocean, where there are sources and receivers present, and the reflectivity scheme is used for calculating the wave field of the porous ocean bottom. In order to hybridize both depth solvers, a novel technique has been developed where a virtual fluid layer with zero thickness is inserted between the ocean and the porous ocean bottom. This technique makes the hybrid algorithm simple to implement and compatible with any other depth solvers for the ocean bottom. Numerical simulation shows the proposed algorithm to work well.
UNDERWATER ACOUSTIC SENSING OF SEA SURFACE WAVES
Authors: MCDANIEL SUZANNE T.
Published: July 2008

Rough surface scattering theory is applied to the problem of estimating gravity-capillary wavenumber spectra from measurements of sea surface backscatter at high acoustic frequencies. Ensemble averaged scattering cross sections predicted by small-slope expansions are evaluated to examine the inversion of acoustic data assuming Bragg scatter. The ratio of the full fourth-order small-slope and Bragg predictions is found to exhibit a minimum value of ~ 2dB at moderate angles of incidence. At such angles, the corrections to perturbation theory depend weakly on acoustic frequency and environmental conditions. This latter finding indicates that only a modest effort is required to monitor sea surface conditions to estimate the correction. Corrections to Bragg predictions increase rapidly with increasing incidence angle and at high angles, the fourth-order contributions of the small-slope and extended small-slope expansions differ. This finding casts some doubt on the applicability of small-slope approximations to predict scattering at high-incidence angles.
FUNCTIONALIZATION EFFECT ON THE ELECTRONIC PROPERTIES OF SINGLE WALLED CARBON NANOTUBES
Authors: LIM SAN HUA , LIN JIANYI , LIU LEI , PAN HUI , PAN HUA LONG , JI WEI , FENG YUAN PENG , SHEN ZEXIANG
Published: July 2008

OH-functionalized single-walled carbon nanotubes (SWNTs), i.e. SWNT–OH, were prepared through the ball-milling of purified SWNTs with KOH. The composition of the pristine SWNTs bulk sample was characterized by resonance Raman scattering. The OH-functionalization-induced shrinking of the energy gap, the charge transfer from C to –OH, the depletion of top valence band density, the modification of energy band structure and the significant reduction in the work function of SWNTs were experimentally studied by variable temperature FTIR, Raman scattering, ultra-violet photoelectron spectroscopy, X-ray photoelectron energy loss spectroscopy etc. Ab initio calculation was also performed to assist the discussion.
CORRELATION BETWEEN CRITICAL COERCIVE FIELD AND RESIDUAL STRESS IN ANTIFERROELECTRIC PZT 95/05 FILMS
Authors: CORKOVIC S. , ZHANG Q.
Published: July 2008

Two types of antiferroelectric Pb ( Zr 0.95 Ti 0.05) O 3 (PZT 95/05) films having a single layer thickness of either 50 nm/layer or 200 nm/layer were fabricated and their antiferroelectric properties studied. The films were derived via chemical solution deposition (CSD). A difference in the critical coercive field between films with similar total thickness but different single layer thickness was found. Films having 200 nm thick single layers required lower electric field to switch from antiferroelectric to ferroelectric phase. The residual stress, determined for both types of films, showed much lower values for films made with 200 nm thick single layers. The other type of film (50 nm/layer) showed a thickness-dependent residual stress, coercive field and dielectric constant. At low thickness (< 0.5 μ m ) residual stress up to 600 MPa was determined, which decreased to around 180 MPa upon further thickness increase. A similar trend was found for the dielectric constant with initially high values decreasing with increasing thickness. It was concluded that there is a correlation between the residual stress and critical coercive field.
THE INSERTION EFFECT OF Bi-EXCESS LAYERS ON STOICHIOMETRIC BiFeO3 THIN FILMS PREPARED BY CHEMICAL SOLUTION DEPOSITION
Authors: NAKAMURA YOSHITAKA , NAKASHIMA SEIJI , RICINSCHI DAN , OKUYAMA MASANORI
Published: July 2008

The insertion effect of Bi -excess layers on stoichiometric BiFeO 3 thin films prepared by chemical solution deposition is investigated. A stoichiometric BiFeO 3 thin film with both the Bi -excess top and bottom surface layers shows improved crystallinity with the remanent polarization of 65 μC/cm2 at 80 K, which is larger than for BiFeO 3 film prepared by the same process using stoichiometric solution. These results are attributed to the reduction of the imperfect crystal at the interface between the BiFeO 3 film and electrode. By inserting Bi-excess layers, the saturated magnetization of all the films becomes smaller than that of the film using stoichiometric solution. Bi -excess surface layers at the top and bottom interfaces are an effective way to obtain good ferroelectric properties.
BISMUTH NIOBATE-BASED GLASS-CERAMICS FOR DIELECTRICALLY LOADED MICROWAVE ANTENNAS
Authors: MIRSANEH MEHDI , ZALINSKA BEATA , LEISTEN OLIVER P. , REANEY IAN M.
Published: July 2008

A castable, low melting temperature glass-ceramic system (30% Bi2O3, 30% Nb2O5, 30% B2O3and 10% SiO2, in mol%) suitable for microwave applications is fabricated and characterized. Depending on heat treatment temperature, the glass ceramic exhibits permittivity, 15 ≤ εr≤ 41, temperature coefficient of resonant frequency of -160 ≤ τf≤ +100 MK-1and microwave quality factor of 300 GHz ≤ Qf ≤ 15000 GHz . The highest Qf occurs at 960°C heat treatment with εr= 15, τf= -80 MK-1and Qf = 15000 GHz . Applications are envisaged such as castable dielectrically-loaded antenna pucks, removing the need for complex ceramic processing.
THE BEHAVIOR OF GALLIUM CONFINED IN CARBON NANOTUBES DURING HEATING AND COOLING
Authors: LIU ZONGWEN , ZHENG RONGKUN , RATINAC KYLE R. , RINGER SIMON P.
Published: July 2008

The thermal expansion of gallium ( Ga ) encapsulated in carbon nanotubes has been studied. It is demonstrated that the volumetric expansion and contraction of the Ga confined in the carbon nanotubes display a linear relationship with temperature. While the level of the tip of the Ga column changes linearly with temperature, it returns to its previous position, without any hysteresis, when reheated or cooled to the original temperature, provided the Ga has not frozen and electron-beam irradiation is minimized. It is shown that electron beam irradiation can cause shrinkage in carbon-nanotube diameter, and that a high-intensity electron beam can also induce the formation of new carbon shells inside the carbon nanotubes. Upon freezing, the solid Ga has two unique orientation relationships with the carbon nanotubes.
THERMAL CHARACTERIZATION OF MULTI-WALL CARBON NANOTUBE BUNDLES BASED ON PULSED LASER-ASSISTED THERMAL RELAXATION
Authors: GUO JIAQI , WANG XINWEI , GEOHEGAN DAVID B. , ERES GYULA
Published: July 2008

A novel transient technique is developed to measure the thermal diffusivity of one-dimensional microscale wires. In this technique, a pulsed nanosecond laser is used to quickly heat the wire. After laser heating, the wire temperature decays slowly. Such temperature decay is sensed and used to determine the thermal diffusivity of the wire. A 25.4 μm thin Pt wire is characterized to verify this technique. The thermal diffusivity of multi-wall carbon nanotube bundles is measured. Based on the measurement result and the inside structure, the thermal diffusivity of individual carbon nanotubes is estimated.
STUDY OF LOW-k DIELECTRIC ORGANIC POLYMER THIN FILMS DEPOSITED BY A PECVD METHOD
Authors: CHO S.-J. , BAE I.-S. , BOO J.-H.
Published: July 2008

Plasma polymerized methylcyclohexane thin films were deposited on silicon substrates at room temperature and different RF powers using a plasma-enhanced chemical vapor deposition (PECVD) method. The as-grown thin films were annealed in a vacuum. Methylcyclohexane monomer was utilized as an organic precursor, and hydrogen and argon were used as the bubbled and carrier gases, respectively. The as-grown plasma-polymer organic thin films were analyzed by FT-IR and SEM and in terms of their hardness and modulus and their capacitance values. Annealed polymer thin films were also analyzed. The dielectric constant of the thin films increased as the plasma power was increased. The minimum dielectric constant was 1.82.
Application of molar element ratio analysis of lag talus composite samples to the exploration for iron oxide–copper–gold mineralization: Mantoverde area, northern Chile
Authors: Benavides Jorge , Kyser T. Kurtis , Clark Alan H. , Stanley Clifford , Oates Christopher
Published: July 2008

A molar element ratio analysis based on whole-rock, multi-element geochemical data for regional lag talus composite samples is evaluated as an exploratory method for iron oxide–copper–gold mineralization (IOCG) in hyperarid settings. This study is focused in the now hyperarid Mantoverde area, III Región of northern Chile (latitude 26°01′ to 26°53′S), and comprises the Andean Coastal Cordillera and Central Valley. The area contains numerous structurally controlled iron oxide-Cu-(Au) prospects and deposits hosted by calc-alkaline volcanic and plutonic rocks of Jurassic–Cretaceous age. Comparison with data for outcrop samples indicates that lag talus composite samples reflect the composition of bedrock in terms of major and selected trace elements. As with outcrop samples, zirconium is the most conserved element in the talus samples, and is therefore used as common denominator in different molar ratios.

A molar element ratio analysis using geochemical data from talus composite samples indicates that rocks associated with mineralization have been K-enriched and Na-depleted. Consequently, gradients in the K/Al and Na/Al molar ratios are useful targeting parameters. Similarly, a lithogeochemical alteration index, recently defined by the authors, quantifies the degree of hydrothermal alteration of host rocks and can be used to both target potential anomalous sectors (strongly altered rocks) and delimit barren areas. It is evident that lag talus composite samples constitute a reliable and effective sampling medium in regional exploration programmes for IOCG deposits in hyperarid settings.
Use of trans-Gaussian kriging for national soil geochemical mapping in Ireland
Authors: Zhang Chaosheng , Fay Deirdre , McGrath David , Grennan Eamonn , Carton Owen T.
Published: July 2008

Geochemical mapping requires a good understanding of geochemical variables and proper use of mathematical and mapping techniques. In this study, GIS mapping for the geochemical variables in Irish soils was achieved using trans-Gaussian kriging following investigation of probability features, outlier identification, optimal power transformation by the Box–Cox method and spatial structure modelling. Relatively high nugget effect values for the variogram models were observed for most variables. The assumption of spatial autocorrelation was seriously breached by two variables, available P and available K, and spatial interpolation was not performed for these. Two or even three nested theoretical models were needed to model variogram structures for most variables reflecting their variation at different spatial scales. The spatial distribution patterns for most elements illustrated the influences of underlying bedrock and soil type, while some of the heavy metals (e.g. Pb, Zn and Cu) were also affected by mining activities and urban sprawl. The available nutrients (P, K and Mg) appeared to be most affected by agricultural activities.
From geochemical prospecting to international geochemical mapping: a historical overview
Authors: Garrett R.G. , Reimann C. , Smith D.B. , Xie X.
Published: July 2008

This paper provides a history of the development of regional geochemical mapping. Modern geochemistry was born in the Soviet Union in the 1930s, and the basic methodologies for regional mapping had been developed by the late 1960s, with important extensions being made in the 1980s. The paper records the development of regional geochemical surveys, or mapping, in the context of spatial scale and transition from a mineral exploration and resource assessment tool to an environmental mapping exercise supporting multi-disciplinary research. Attention is drawn to the role of the International Geological Correlation Program's Projects 259 and 360, and the continuing role of the International Union of Geological Sciences, in providing an international focus and dimension to global geochemical mapping. The paper closes with a section on some of the current research issues, opportunities and challenges for regional geochemical mapping.
Environmental geochemical maps of Italy from the FOREGS database
Authors: De Vivo Benedetto , Lima Annamaria , Bove Maria A. , Albanese Stefano , Cicchella Domenico , Sabatini Giuseppe , Di Lella Luigi A. , Protano Giuseppe , Riccobono Francesco , Frizzo Pietro , Raccagni Lorenzo
Published: July 2008

The
Geochemical Atlas of Italy
addresses the need for geochemical mapping of the country, based on FOREGS procedures. Data from samples of Italian topsoil, subsoil, stream water, stream sediment and floodplain sediment have been extracted from the FOREGS database and supplemented with data from eight new sample sites. In total 360 geochemical maps have been produced and spatial correlations have been found between the underlying geology and element abundances in the sampled media. The aim of the
Geochemical Atlas of Italy
is to document background/baseline chemical element variation at the national scale. It is found to be a suitable tool to support government decision-makers to assess trigger and action limits at the local scale, when considered in the light of the complex spatial variability of Italian geology. Maps presented here demonstrate that low density geochemical mapping is a viable tool to obtain an impression of natural element variation at the country scale and to identify areas where more detailed sampling is advisable.
Indications of deposits of gold and platinum group elements from a regional geochemical stream sediment survey in NW Tanzania
Authors: Salminen Reijo , Kashabano Jonathan , Myumbilwa Yokbeth , Nyanda Petro Faustin , Partanen Matti
Published: July 2008

A regional-scale geochemical survey was carried out in Mpanda, Kahama and Biharamulo target areas of northwestern Tanzania. Minerogenic stream sediments were collected from a grid based on small catchment basins. The average sample density was 1 sample per 10 km
2
and each sample represents a drainage basin of between 3 and 10 km
2
in size. The <0.18-mm fraction was analysed for Au, Pd and Te. Major element total concentrations and aqua regia extractable concentrations of more than 30 elements were also determined. The results indicate earlier unknown Au-bearing greenstones in the Kahama region, and unknown rocks hosting anomalous concentrations of Au and Pt group elements in the Kahama and Biharamulo areas. In the Mpanda area, the Mpanda Mineral Field was detected, including the presence of Au and Cu ores.
Geochemical mapping of major and trace elements in soils from the Altiplano Potosino, Mexico: a multi-scale comparison
Authors: Chiprés J.A. , Salinas J.C. , Castro-Larragoitia J. , Monroy M.G.
Published: July 2008

A geochemical survey of the Altiplano Potosino, Mexico, was conducted at three different scales (i.e. sample density). A study representing a national-scale geochemical mapping programme sampled 16 sites at a density of 1 site per 1600 km
2
within a 160 × 160 km cell. A second study representing regional-scale mapping sampled 100 sites at a density of 1 site per 16 km
2
within a 40 × 40 km cell selected from within the larger cell. A third study representing local-scale mapping sampled 100 sites at a density of 1 site per km
2
in a selected 10 × 10 km cell within the regional-scale 40 × 40 km cell. A comparison of four environmentally important elements (Ag, As, Cd and Hg) showed the widest range of concentrations at the local scale. This was attributed to the presence of soils developed on mineralized bedrock. The smallest range was observed for the low-density national-scale survey sampling. The extent of mineralized areas was very small with respect to this scale. Mercury showed a relatively large range of concentrations at the regional scale because the selected 40 × 40 km cell contained mercury-bearing mineral deposits. Geochemical mapping projects conducted at different scales generally complement each other. Very low sample density studies at a continental or national scale will outline the broad variations in the geochemistry of the sample medium caused by such factors as changes in rock type (soil parent material) or large-scale differences in climate. Studies at local scales are more likely to identify effects of human activity as well as natural processes affecting small areas of the Earth's surface. Based on data generated from such surveys, exploratory and spatial data analysis can be used to propose a range of values representing background concentrations of potentially toxic elements in soil.