bluuebunny/crossref_metadata_2025 huggingface dataset:
A study on the background and clustering seismicity in the Taiwan region by using point process models
Authors: Zhuang Jiancang , Chang Chung‐Pai , Ogata Yosihiko , Chen Yuh‐Ing
Published: May 2005

This paper investigates the shallow seismicity occurring in the Taiwan region during the 20th century using a stochastic declustering method that has been developed on the basis of the theory of the epidemic‐type aftershock sequence model. It provides a probability based tool to objectively separate the space‐time occurrences of earthquakes into a background and a clustering component. On the basis of the background and clustering seismicity rates, we discuss the correlation between the distribution of the cluster ratio and the regional seismotectonic structures. Specifically, we find that the areas of the highest clustering ratio correspond to the major strike‐slip fault traces in and around Taiwan. Additionally, in the Taiwan inland region, during the period 1960–1990, the outputs for the stochastically declustered catalogue show a clear quiescence in background seismicity preceding the recovery of activation and the occurrences of the 1999 Chi‐Chi earthquake of ML7.3, while the other active regions show stationary background activity. This could be interpreted as an effect of the aseismic slip in the Chi‐Chi rupture fault, whereby the inland region around the Chi‐Chi source becomes a stress shadow.
Onto what planes should Coulomb stress perturbations be resolved?
Authors: Steacy Sandy , Nalbant Süleyman S. , McCloskey John , Nostro Concetta , Scotti Oona , Baumont David
Published: May 2005

Coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation. It is often assumed that aftershock fault planes are “optimally oriented”; in other words, the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations. This practice assumes that faults capable of sustaining aftershocks exist at all orientations, an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends. Here we systematically investigate the best planes onto which stress should be resolved for the Landers, Hector Mine, Loma Prieta, and Northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes (two‐ and three‐dimensional), main shock orientation, and regional structural trend. We find that the best model differs between different tectonic regions but that in all cases, models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions, although not all such models do so equally well. Our results suggest that when the regional stress field is poorly defined, or in structurally complex areas, the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary.
Time‐dependent earthquake probabilities
Authors: Gomberg J. , Belardinelli M. E. , Cocco M. , Reasenberg P.
Published: May 2005

We have attempted to provide a careful examination of a class of approaches for estimating the conditional probability of failure of a single large earthquake, particularly approaches that account for static stress perturbations to tectonic loading as in the approaches of Stein et al. (1997) and Hardebeck (2004). We have developed a general framework based on a simple, generalized rate change formulation and applied it to these two approaches to show how they relate to one another. We also have attempted to show the connection between models of seismicity rate changes applied to (1) populations of independent faults as in background and aftershock seismicity and (2) changes in estimates of the conditional probability of failure of a single fault. In the first application, the notion of failure rate corresponds to successive failures of different members of a population of faults. The latter application requires specification of some probability distribution (density function or PDF) that describes some population of potential recurrence times. This PDF may reflect our imperfect knowledge of when past earthquakes have occurred on a fault (epistemic uncertainty), the true natural variability in failure times, or some combination of both. We suggest two end‐member conceptual single‐fault models that may explain natural variability in recurrence times and suggest how they might be distinguished observationally. When viewed deterministically, these single‐fault patch models differ significantly in their physical attributes, and when faults are immature, they differ in their responses to stress perturbations. Estimates of conditional failure probabilities effectively integrate over a range of possible deterministic fault models, usually with ranges that correspond to mature faults. Thus conditional failure probability estimates usually should not differ significantly for these models.
A parametric scheme for the retrieval of two‐dimensional ocean wave spectra from synthetic aperture radar look cross spectra
Authors: Schulz‐Stellenfleth J. , Lehner S. , Hoja D.
Published: May 2005

A parametric inversion scheme for the retrieval of two‐dimensional (2‐D) ocean wave spectra from look cross spectra acquired by spaceborne synthetic aperture radar (SAR) is presented. The scheme uses SAR observations to adjust numerical wave model spectra. The Partition Rescaling and Shift Algorithm (PARSA) is based on a maximum a posteriori approach in which an optimal estimate of a 2‐D wave spectrum is calculated given a measured SAR look cross spectrum (SLCS) and additional prior knowledge. The method is based on explicit models for measurement errors as well as on uncertainties in the SAR imaging model and the model wave spectra used as prior information. Parameters of the SAR imaging model are estimated as part of the retrieval. Uncertainties in the prior wave spectrum are expressed in terms of transformation variables, which are defined for each wave system in the spectrum, describing rotations and rescaling of wave numbers and energy as well as changes of directional spreading. Technically, the PARSA wave spectra retrieval is based on the minimization of a cost function. A Levenberg‐Marquardt method is used to find a numerical solution. The scheme is tested using both simulated SLCS and ERS‐2 SAR data. It is demonstrated that the algorithm makes use of the phase information contained in SLCS, which is of particular importance for multimodal sea states. Statistics are presented for a global data set of 11,000 ERS‐2 SAR wave mode SLCS acquired in southern winter 1996.
Quantifying global marine isoprene fluxes using MODIS chlorophyll observations
Authors: Palmer Paul I. , Shaw Stephanie L.
Published: May 2005

We report global distributions of marine isoprene flux, whose source is estimated by combining an empirical relationship for isoprene production rate with MODIS satellite chlorophyll observations from 2001. We use a steady‐state water column model including losses to chemistry, bacteria, and air‐sea exchange. Physical mixing is a negligible sink. Flux estimates range from 107–109 molecules cm−2s−1, with considerable spatial and temporal variability, resulting in a global annual total of 0.1 Tg C/yr. Air‐sea exchange is the dominant isoprene sink in the surface oceans, with bacteria the second largest, but much less important, sink. The reported fluxes represent a small loss of OH in the remote marine boundary layer (MBL) compared to other oxidants. Application of our approach to other reactive compounds may improve a priori flux estimates for coupled atmosphere‐ocean biogeochemistry inverse model studies.
Modeling thermal history of subducting crust in Nankai Trough: Constraints from in situ sediment temperature and diagenetic reaction progress
Authors: Spinelli G. A. , Underwood M. B.
Published: May 2005

Values of borehole temperature and %‐smectite in illite/smectite mixed‐layer clay provide important information about the basal heat flux history of the Nankai Trough subduction zone. Numerical simulations of sediment accumulation, heat conduction, and illite/smectite diagenesis permit comparisons of various thermal‐history scenarios for ODP Site 1173. In our preferred models, basal heat flux during the first 10 Ma of sedimentation was near typical values for conductively cooling crust. During the last 5 Ma, basal heat flux was higher than expected. The anomalous heat flux was likely influenced by both off‐axis volcanism and hydrothermal circulation.
Skin lesions in children with tuberous sclerosis complex: their prevalence, natural course, and diagnostic significance
Authors: Józ°wiak Sergiusz , Schwartz Robert A.. , Janniger Camila Krysicka , Michałowicz Roman , Chmielik Jolanta
Published: May 2005

Background Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by widespread cutaneous and visceral hamartomas.

Methods The prevalence of cutaneous lesions in 106 children with TSC (47 boys and

59 girls) aged 1 month–18 years was evaluated from 1984 to 1995. Assessing the diagnostic usefulness of each National Tuberous Sclerosis Association skin criterion was an aim of this study.

Results Hypopigmented macules were the most frequent finding, seen in 103 of 106 children (97.2%). In 66 children they were evident at birth, and in 20 others their presentation was delayed until the first months of age. Facial angiofibromas were seen next most often (79 of 103, 74.5%), followed by a shagreen patch in 51 of 103 (48.1%),

“café‐au‐lait” macules in 30 of 103 (28.3%), molluscum fibrosum pendulum (24 of 103, 22.6%), a forehead fibrous plaque (20 of 103, 18.9%), periungual fibromas (16 of 103, 15.1%) and “confetti‐like” macules (3 of 103, 2.8%). The hypomelanotic macules were seen within the first 2 years of life in 95 children, as were cafe‐au‐lait spots in 24, facial angiofibromas in eight, shagreen patches in six, and forehead fibrous plaques in six, whereas molluscum pendulum and periungual fibromas were not evident. Seizures were seen in 102 of 106 children (98%), with 80 (75%) occurring during the first year of life.

Conclusions Hypomelanotic macules were the overwhelmingly most common early finding in TSC. Infants with seizures or other possible stigmata of TSC should be carefully evaluated for these hypomelanotic macules, as well as for other associated findings.
Cast composite Co–Fe∕Sm–Pr–Co–Fe–Cu–Ti permanent magnets
Authors: Gabay A. M. , Zhang Y. , Hadjipanayis G. C.
Published: May 2005

Permanent magnets with a microstructure consisting of a cellular 2:17∕1:5 matrix and Co(Fe) inclusions were obtained via a heat treatment of cast R–Co(Fe)–Cu–Ti alloys containing less than 10 at. % R (R=Sm, Pr). Inclusions of the magnetically soft Co(Fe) phase are too large to be coupled with the hard matrix by a magnetic exchange interaction. Nevertheless, a complete magnetostatic coupling between the soft and hard components is evident from the smooth demagnetization curves. The resulting cast composite magnets show excellent mechanical strength, but moderate values of the coercivity and energy products (up to 3.3 kOe and 5.1 MG Oe, respectively).
Core-loss analysis of an (Fe, Co, Ni)-based nanocrystalline soft magnetic alloy
Authors: Willard M. A. , Francavilla T. , Harris V. G.
Published: May 2005

Nanocrystalline soft magnetic materials possess higher magnetization and operation temperatures than amorphous alloys with similar compositions. For these reasons, they are good candidate materials for power electronics applications. As an indication of their performance, core losses have been measured for a nanocrystalline alloy with the composition Fe64.08Co10.68Ni10.68Zr8.49B4.86Cu1.2 synthesized by a melt-spinning process with subsequent isothermal anneal at 550°C for 1h. The experiments were conducted on toroidal samples using a Walker ac permeameter over a frequency range of 100Hz–500kHz, at induction amplitudes of 100 and 1100mT, at room temperature. A measured toroidal sample possessed a saturation magnetization of 1.529T and core loss of 17.5W∕kg at a frequency of 10kHz and magnetic flux density of 100mT. The Steinmetz analysis of the static hysteresis losses yielded a power-law coefficient of 1.475. A statistical model for excess eddy current losses showed good agreement with experimental results. Excess eddy current losses were found to be the dominant factor in losses above 10kHz for these alloys.
Synthesis of Fe–Pd and Fe–Pd∕Ta magnetic nanocomposites by severe plastic deformation
Authors: Saha S. , Kulovits A. , Soffa W. A. , Barnard J. A.
Published: May 2005

Severe plastic deformation (SPD) and cyclic codeformation were used to prepare bulk magnetic nanocomposite of ordered L10Fe-Pd phase and soft α-Fe following an atomic ordering and precipitation reaction. Enhanced coercivity and remanence have been achieved with this method. Layering of Ta foils with the Fe–34at.%Pd foils was explored in an effort to minimize nanocomposite grain size by confinement. Faster kinetics and improvement in the remanence resulted from Ta layering.
Magnetic properties of manganese ferrite films grown at atomic scale
Authors: Zuo Xu , Yang Aria , Yoon Soack-Dae , Christodoulides Joe A. , Harris Vincent G. , Vittoria Carmine
Published: May 2005

Manganese ferrite is a partial inverse spinel which, when prepared by conventional growth techniques, has ∼20% of the Mn2+ ions on the octahedral sublattice. Here we describe a layer–by–layer growth scheme at atomic scale by which the percentage of Mn2+ ions on the octahedral sublattice can be artificially controlled. Manganese ferrite films grown by this technique exhibits different degrees of cation inversion when grown on {100} and {111} MgO substrates. It was observed that saturation magnetization varied in a wide range of values depending on chemical composition and oxygen pressure. Although bulk manganese ferrite was low anisotropy magnetic material, uniaxial anisotropy was observed at room temperature in the films deposited on {100} MgO substrates, and its magnitude and direction sensitively depended on chemical composition and oxygen pressure during deposition.
First-order reversal curve analysis of homogeneous nucleation in the two-dimensional kinetic Ising model
Authors: Robb D. T. , Novotny M. A. , Rikvold P. A.
Published: May 2005

The first-order reversal curve (FORC) method is applied to the two-dimensional kinetic Ising model. For the system size and magnetic field chosen, the system reverses by the homogeneous nucleation and growth of many droplets. This makes the dynamics of reversal nearly deterministic, in contrast to the strongly disordered systems previously studied by the FORC method. Consequently, the FORC diagrams appear different from those obtained in previous studies. The Kolmogorov–Johnson–Mehl–Avrami (KJMA) theory of phase transformation by nucleation and growth is applied to the system. Reasonable agreement with the Monte Carlo simulations is found, and the FORC method suggests how the KJMA theory could be extended.
Magnetic shielding properties of sheet metal products taking into account hysteresis effects
Authors: Sergeant Peter , Dupré Luc , Vandenbossche Lode , De Wulf Marc
Published: May 2005

Analytical expressions are presented to find the shielding effectiveness and the losses of a shield consisting of ferromagnetic, isotropic, nonlinear, and hysteretic material, characterized by the Preisach distribution function in the Rayleigh region. The nonlinear shield is divided into a sufficient number of piecewise linear sublayers with a permeability that is constant (space independent) and complex (to model hysteresis). Simulations of an infinitely long cylindrical shield in transverse sinusoidal flux show that the shielding of perfectly linear material is better than the one of nonlinear metal sheets. More hysteresis and nonlinearity deteriorate the shielding factor, as eddy current losses decrease.
Calculation of exchange constants in spinel ferrites with magnetic S-state ions
Authors: Zuo Xu , He Yongxue , Yang Aria , Bernardo Barbiellini , Harris Vincent G. , Vittoria Carmine
Published: May 2005

The exchange constants in spinel ferrites with S-state ions, including magnesium ferrite, lithium ferrite, and manganese ferrite, were calculated using modified Becke’s three-parameter density functional, where the percentage of Hartree–Fock exchange in total exchange was introduced as a variable parameter (w) to match the experimental results of exchange constants by controlling the localization and delocalization of the electrons. Consistently, the scaling factor of the 3d orbitals of ferric ions was also introduced as a variable parameter (α). From the calculation, the values of parameters w and α matching the experimental results of JAB (nearest-neighbor exchange constant between tetrahedral and octahedral sublattices) were concentrative, while those matching the experimental results of JAA (nearest-neighbor exchange constant inside tetrahedral sublattice) and JBB (nearest-neighbor exchange constant inside octahedral sublattice) were dispersive. Observing that JAB is dominant in most practical ferrimagnetic spinel ferrites and the current accuracy of the measurements of JBB and JAA may be insufficient to support more accurate conclusion, it is suggested that there may be an empirical universal law of parameters w and α for spinel ferrites with S-state ions.
Secondary peaks on microwave permeability spectra of soft ferromagnetic thin films with in-plane anisotropy
Authors: Dubourg S. , Queste S. , Acher O.
Published: May 2005

Complex permeability spectra of CoNbZr thin films have been measured up to 4GHz by a single coil pertubation technique. In addition to the well-known ferromagnetic resonance, multiple resonant modes have been evidenced in the increasing branches of the spectra. The number of “secondary peaks” observed depends on the sample thickness. Their resonance frequencies follow a nonlinear dispersion law versus the ratio of the mode number over the sample thickness with a power factor close to 1.5.
Temperature dependence of coercivity and magnetic reversal in SmCox thin films
Authors: Andreescu R. , O’Shea M. J.
Published: May 2005

Sm–Co magnets are prepared by sputter deposition with composition SmCox, x=5–12.3. A dependence of magnetization, coercivity, and energy product on the thickness for SmCo5 is found. The thickest samples have the largest values of each of these properties. Increasing the Co content leads to a two-phase system with hard Sm–Co and soft Co phases that are strongly exchange coupled. Large energy products are obtained (up to 17MGOe at 400K and 19MGOe at 300K). The temperature dependence of the coercivity indicates that domain walls are pinned at narrow pin sites.
Magnetic properties of Er1−xDyxTiCo11
Authors: Banerjee Debjani , Suresh K. G. , Nigam A. K.
Published: May 2005

The structural and magnetic properties of Er1−xDyxTiCo11 compounds with 0⩽x⩽1 have been studied to find out their suitability as permanent magnet materials. Crystal structure was analyzed using the Rietveld refinement of the powder x-ray diffractograms. Thermomagnetic analysis showed that the spin reorientation transitions shift to lower temperatures with increase in Dy concentration, which has been attributed to the increase in the axial anisotropy of these compounds. The magnetic properties have been explained by taking into account the structural details.
Entropy and entropy production in magnetic systems with hysteresis
Authors: LoBue M. , Basso V. , Sasso C. P. , Bertotti G.
Published: May 2005

A thermodynamic model of hysteresis is presented based on an internal variable reinterpretation of the Preisach model. Explicit expressions are obtained for the entropy and the entropy production for arbitrary open field histories. The model is applied to the prediction of nonmonotonic heat exchange along the hysteresis loop measured for ferromagnets.
Optimization of multilayered nonlinear crystalline alloys for shielding
Authors: Sergeant Peter , Dupré Luc , Vandenbossche Lode , Melkebeek Jan
Published: May 2005

An optimization of a multilayered material is presented for the shielding of sinusoidal magnetic fields. The shield consists of alternating layers of aluminum and (nonlinear hysteretic) steel. The optimization variables are the total shield thickness and the fraction of steel. The optimization goals are to obtain the desired shielding factor, to minimize the shield thickness, and to minimize the eddy currents and hysteresis losses. In the objective function, analytical expressions are used for the shielding factor and the electromagnetic losses. Simulation results of a planar shield show that both the optimal shield thickness and the fraction of steel decrease with the frequency.
Magnetic properties, phase evolution, and coercivity mechanism of CoxZr98−xB2 (x=74−86) nanocomposites
Authors: Chen L. Y. , Chang H. W. , Chiu C. H. , Chang C. W. , Chang W. C.
Published: May 2005

Magnetic properties, phase evolution, and coercivity mechanism of melt-spun CoxZr98−xB2 (74⩽x⩽86) nanocomposites were studied systematically. From x-ray diffraction analysis, nearly single magnetic phase, Co23Zr6, is found in Co74Zr24B2 ribbon (x=74). With increasing Co content x, an additional phase, Co5Zr, is found for x=76; two phases, namely, fcc Co and Co5Zr, are found for x=78−84, but fcc Co is the only phase that can be detected in ribbon with x=86. The optimal magnetic properties of Br=5.13kG (σr=49emu∕g), Hci=4.1kOe, and (BH)max=5.1MGOe are obtained in Co80Zr18B2 ribbons quenched at Vs=45m∕s, which possesses Co5Zr and minor fcc-Co phases with nanoscale grain size (∼50 and ∼20nm, respectively). Strong exchange-coupling effect occurred between grains as evidenced by the Henkel plot, giving rise to the improvement of remanence and magnetic energy product. The coercivity of CoxZr98−xB2 nanocomposites is mainly governed by reverse domain nucleation mechanism.
Improvement of magnetic softness in nanocrystalline soft magnetic materials by rotating magnetic field annealing
Authors: Ito N. , Suzuki K.
Published: May 2005

The effects of magnetic field annealing on the soft magnetic properties of nanocrystalline Fe84Nb7B9 have been investigated with particular attention paid to the annealing induced uniaxial magnetic anisotropies (Ku). A Ku value of ∼90J∕m3 is estimated from the sample annealed under a transverse field of 600kA∕m. The soft magnetic properties of nanocrystalline Fe84Nb7B9 are improved dramatically by rotating magnetic field annealing and the coercivity is reduced by 65%. An enhanced averaging effect of the random magnetocrystalline anisotropy ⟨K1⟩ as well as the suppression of Ku is suggested for the mechanism of the observed magnetic softening.
Highly resistive Mn-Zn ferrite films prepared from aqueous solution for GHz conducted noise suppressors
Authors: Matsushita Nobuhiro , Abe Tatsunobu , Kondo Koichi , Yoshida Shigeyoshi , Abe Masanori
Published: May 2005

We have prepared Mn-Zn ferrite films (MnxZnyFezO4.00−δ: 0.23<x<0.30, 0.0<y<0.38, 2.39<z<2.64) that are highly permeable in GHz range. The film resistivity ρ increased as the amount of Fe content z decreased and very high surface resistance R>108Ω∕sq was attained for the film having z<2.6. The deposited Mn-Zn ferrite films had a large saturation magnetization Ms=380–460emu∕cm3 and relatively low coercivity Hc=11–29Oe. The Mn-Zn ferrite films contacted to a microstrip line (50Ω) exhibited very large transmission loss ΔPloss per thickness t, ΔPloss∕t, of about 10 times larger than that of commercialized composite sheet. They exhibited sufficiently low reflection coefficient S11<−10dB. These films were applicable as noise current suppressors deposited on an interlayer of multilayer printed circuit boards.
Modeling of sharp change in magnetic hysteresis behavior of electrical steel at small plastic deformation
Authors: Sablik M. J. , Rios S. , Landgraf F. J. G. , Yonamine T. , de Campos M. F.
Published: May 2005

In 2.2% Si electrical steel, the magnetic hysteresis behavior is sharply sheared by a rather small plastic deformation (0.5%). A modification to the Jiles–Atherton hysteresis model makes it possible to model magnetic effects of plastic deformation. In this paper, with this model, it is shown how a narrow hysteresis with an almost steplike hysteresis curve for an undeformed specimen is sharply sheared by plastic deformation. Computed coercivity and hysteresis loss show a sharp step to higher values at small strain due to an n=1∕2 power law dependence on residual strain. The step is seen experimentally.
Composite-anisotropy amorphous magnetic materials for high-frequency devices
Authors: Lee D. W. , Crawford A. M. , Wang S. X.
Published: May 2005

In-plane biaxial anisotropy in permeability, desired for integrated inductor cores, was achieved using a composite-anisotropy sandwiched structure. With Tb-doped CoTaZr alloy as the material for magnetic layers, the permeability of the composite film was close to 50% of that of blanket film along the easy axes of both top and bottom magnetic layers, and the ferromagnetic-resonance frequencies were about 2GHz. Simulations show that the integrated inductors with the composite film as their magnetic cores have inductances near a half of that for the ideal isotropic permeability case.
Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: Acetonitrile in water, methanol in water, and methanol in acetonitrile
Authors: Kobryn Alexander E. , Yamaguchi Tsuyoshi , Hirata Fumio
Published: May 2005

We present results of the theoretical study and numerical calculation of the dynamics of molecular liquids based on the combination of the memory equation formalism and the reference interaction site model (RISM). Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density (pressure) dependence of translational diffusion coefficients D and orientational relaxation times τ for acetonitrile in water, methanol in water, and methanol in acetonitrile—all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the extended simple point charge model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and τ observed in real and computer experiments. In particular, anomalous behavior, i.e, the increase in mobility with density, is observed for D and τ of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.
Phenomenology treatment of magnetohydrodynamic turbulence with nonequipartition and anisotropy
Authors: Zhou Ye , Matthaeus W. H.
Published: May 2005

Magnetohydrodynamics (MHD) turbulence theory, often employed satisfactorily in astrophysical applications, has often focused on parameter ranges that imply nearly equal values of kinetic and magnetic energies and length scales. However, MHD flow may have disparity magnetic Prandtl number, dissimilar kinetic and magnetic Reynolds number, different kinetic and magnetic outer length scales, and strong anisotropy. Here a phenomenology for such “nonequipartitioned” MHD flow is discussed. Two conditions are proposed for a MHD flow to transition to strong turbulent flow, which are extensions of (i) Taylor’s constant flux in an inertial range and (ii) Kolmogorov’s scale separation between the large and small scale boundaries of an inertial range. For this analysis, the detailed information on turbulence structure is not needed. These two conditions for MHD transition are expected to provide consistent predictions and should be applicable to anisotropic MHD flows, after the length scales are replaced by their corresponding perpendicular components. Second, it is stressed that the dynamics and anisotropy of MHD fluctuations are controlled by the relative strength between the straining effects between eddies of similar size and the sweeping action by the large eddies, or propagation effect of the large-scale magnetic fields, on the small scales, and analysis of this balance, in principle, also requires consideration of nonequipartition effects.
On the transition to drift turbulence in a magnetized plasma column
Authors: Burin M. J. , Tynan G. R. , Antar G. Y. , Crocker N. A. , Holland C.
Published: May 2005

Experimental results from a magnetized argon plasma column demonstrate a controlled transition to a turbulent state as the magnetic field (B) strength is increased. At lower B there is an onset of fluctuations in density and potential. These are shown to be due to drift waves that have been modified by flow shear. As B is increased the character of the fluctuations undergoes several changes. These changes include a general decrease of coherence, an increase in the phase lag (between density and potential), and a straightening of the observed dispersion relation. Concomitantly, the intensifying and broadening fluctuation spectra lead to significant cross-field radial particle transport. Other nonlinear dynamical activity is inferred during the transition, e.g., three-wave interactions, the formation of localized structures (that do not significantly contribute to the net particle transport), and energy transfer to the largest available scales.
Combining molecular dynamics with Lattice Boltzmann: A hybrid method for the simulation of (charged) colloidal systems
Authors: Chatterji Apratim , Horbach Jürgen
Published: May 2005

We present a hybrid method for the simulation of colloidal systems that combines molecular dynamics (MD) with the Lattice Boltzmann (LB) scheme. The LB method is used as a model for the solvent in order to take into account the hydrodynamic mass and momentum transport through the solvent. The colloidal particles are propagated via MD and they are coupled to the LB fluid by viscous forces. With respect to the LB fluid, the colloids are represented by uniformly distributed points on a sphere. Each such point [with a velocity V(r) at any off-lattice position r] is interacting with the neighboring eight LB nodes by a frictional force F=ξ0(V(r)−u(r)), with ξ0 being a friction coefficient and u(r) being the velocity of the fluid at the position r. Thermal fluctuations are introduced in the framework of fluctuating hydrodynamics. This coupling scheme has been proposed recently for polymer systems by Ahlrichs and Dünweg [J. Chem. Phys. 111, 8225 (1999)]. We investigate several properties of a single colloidal particle in a LB fluid, namely, the effective Stokes friction and long-time tails in the autocorrelation functions for the translational and rotational velocity. Moreover, a charged colloidal system is considered consisting of a macroion, counterions, and coions that are coupled to a LB fluid. We study the behavior of the ions in a constant electric field. In particular, an estimate of the effective charge of the macroion is yielded from the number of counterions that move with the macroion in the direction of the electric field.
Functional and basis set dependence of K-edge shake-up spectra of molecules
Authors: Brena Barbara , Carniato Stéphane , Luo Yi
Published: May 2005

A straightforward approach for computing the K-edge shake-up spectra of molecules based on equivalent core-hole linear response theory at both Hartree–Fock and density functional theory levels is proposed. Benchmark calculations have been performed to explore its sensitivity to different types of functionals and basis sets for the carbon 1s shake-up spectra of benzene and metal-free phthalocyanine (H2Pc). A very good agreement with previous theoretical and experimental works for the benzene molecule has been obtained for all the functionals and basis sets tested. Electron correlation is found to be essential for a good description of the H2Pc system, whose experimental C 1s shake-up spectrum is best reproduced by the hybrid density functional.
A new universal law for the Liesegang pattern formation
Authors: Izsák Ferenc , Lagzi István
Published: May 2005

Classical regularities describing the Liesegang phenomenon have been observed and extensively studied in laboratory experiments for a long time. These have been verified in the last two decades, both theoretically and using simulations. However, they are only applicable if the observed system is driven by reaction and diffusion. We suggest here a new universal law, which is also valid in the case of various transport dynamics (purely diffusive, purely advective, and diffusion-advection cases). We state that ptot∝Xc, where ptot yields the total amount of the precipitate and Xc is the center of gravity. Besides the theoretical derivation experimental and numerical evidence for the universal law is provided. In contrast to the classical regularities, the introduced quantities are continuous functions of time.
N
H
3
adsorption and decomposition on Ir(110): A combined temperature programmed desorption and high resolution fast x-ray photoelectron spectroscopy study
Authors: Weststrate C. J. , Bakker J. W. , Rienks E. D. L. , Lizzit S. , Petaccia L. , Baraldi A. , Vinod C. P. , Nieuwenhuys B. E.
Published: May 2005

The adsorption and decomposition of NH3 on Ir(110) has been studied in the temperature range from 80Kto700K. By using high-energy resolution x-ray photoelectron spectroscopy it is possible to distinguish chemically different surface species. At low temperature a NH3 multilayer, which desorbs at ∼110K, was observed. The second layer of NH3 molecules desorbs around 140K, in a separate desorption peak. Chemisorbed NH3 desorbs in steps from the surface and several desorption peaks are observed between 200 and 400K. A part of the NH3ad decomposes into NHad between 225 and 300K. NHad decomposes into Nad between 400K and 500K and the hydrogen released in this process immediately desorbs. N2 desorption takes place between 500 and 700K via Nad combination. The steady state decomposition reaction of NH3 starts at 500K. The maximum reaction rate is observed between 540K and 610K. A model is presented to explain the occurrence of a maximum in the reaction rate. Hydrogenation of Nad below 400K results in NHad. No NH2ad or NH3ad∕NH3 were observed. The hydrogenation of NHad only takes place above 400K. On the basis of the experimental findings an energy scheme is presented to account for the observations.
Lifting the Pt{100} surface reconstruction through oxygen adsorption: A density functional theory analysis
Authors: Deskins N. Aaron , Lauterbach Jochen , Thomson Kendall T.
Published: May 2005

The adsorption of atomic oxygen on unreconstructed Pt{100}-(1×1) and reconstructed Pt{100}-(5×1) was modeled using density-functional theory in an attempt to understand the relative stability of the unreconstructed phase as a function of oxygen coverage. Our calculations showed that at zero temperature the (5×1) is more stable than the unreconstructed (1×1) phase at zero oxygen coverage. However, oxygen absorption on the Pt{100}-(5×1) phase removed the reconstruction, reversing the phase stability. Using thermochemical analysis, we show desorption of oxygen corresponding to a temperature near 730 K, consistent with experimentally observed desorption peaks for oxygen covered (1×1) surfaces. These results have ramifications for understanding the full Pt{100}(1×1)→Pt{100}-hex-R0.7° surface phase transition.
Ultrafast dynamics of pyrrolidinium cation ionic liquids
Authors: Shirota Hideaki , Funston Alison M. , Wishart James F. , Castner Edward W.
Published: May 2005

We have investigated the ultrafast molecular dynamics of five pyrrolidinium cation room temperature ionic liquids using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The ionic liquids studied are N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P14+∕NTf2−), N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P1EOE+∕NTf2−), N-ethoxyethyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide P1EOE+∕NTf2−), N-ethoxyethyl-N-methylpyrrolidinium bromideP1EOE+, and N-ethoxyethyl-N-methylpyrrolidinium dicyanoamide P1EOE+∕DCA−). For comparing dynamics among the five ionic liquids, we categorize the ionic liquids into two groups. One group of liquids comprises the three pyrrolidinium cations P14+, P1EOM+, and P1EOE+ paired with the NTf2− anion. The other group of liquids consists of the P1EOE+ cation paired with each of the three anions NTf2−,Br−, and DCA−. The overdamped relaxation for time scales longer than 2 ps has been fit by a triexponential function for each of the five pyrrolidinium ionic liquids. The fast (∼2ps) and intermediate (∼20ps) relaxation time constants vary little among these five ionic liquids. However, the slow relaxation time constant correlates with the viscosity. Thus, the Kerr spectra in the range from 0 to 750cm−1 are quite similar for the group of three pyrrolidinium ionic liquids paired with the NTf2− anion. The intermolecular vibrational line shapes between 0 and 150cm−1 are fit to a multimode Brownian oscillator model; adequate fits required at least three modes to be included in the line shape.
Quantum defect theory of dipole and vibronic mixing in Rydberg states of CaF
Authors: Field R. W. , Gittins C. M. , Harris N. A. , Jungen Ch.
Published: May 2005

The Rydberg spectra of CaF combine the simplicity of a single electron outside a doubly closed-shell Ca2+F− ion core with the exceptional polarity of the ion core. A global multichannel quantum defect (MQDT) fit to 612 previously assigned levels, 507 from n≈12–18,N=0–14,v+=1, 97 from n≈9–10,N=0–14,v+=2, and 8 from n≈7,N=3–10,v+=3, produces the complete ℓ=0–3 quantum defect matrix μ (with the exception of one element) and 19 of 20 elements of the ∂μ∕∂R matrix, as well as the molecular constants of the CaF+XΣ+1 state [ωe+=694.58(14),ωexe+=2.559(40),Be+=0.37307(16)cm−1, and the v=0,N=0 to v+=0,N+=0 ionization energy, 46996.40(8)cm−1]. This experimentally determined μ(R) matrix is unusual in the completeness of its representation of the spectrum of both core-penetrating and nonpenetrating Rydberg series, including both local perturbations and vibrational autoionization rates, as well as all dynamical processes encoded in the spectrum that result from the scattering (at negative energy) of the Rydberg electron off the Ca2+F− ion core. The MQDT theory is presented in a form that clarifies the relationships of the reaction (K) and phase (P) matrices of MQDT to effective Hamiltonian models for local interactions between accidentally near degenerate levels. In particular, a Hund’s case (b) like representation of the Hamiltonian is described in which the rovibronic K matrix is diagonalized and the P matrix, which contains information about the v+,N+ eigenstates of the ion, becomes nondiagonal.
Morphological switching in synchrotron-radiation-excited Ge homoepitaxy: Transition from kinetic roughening to smoothing
Authors: Akazawa Housei
Published: May 2005

The surface morphology of Ge films during GeH4-source molecular beam epitaxy on a Ge(100) substrate is dramatically changed through irradiation with synchrotron radiation (hν>100eV). At temperatures below 300 °C, a two-dimensionally flat film continues to grow with the surface tightly passivated by a GeHx hydride layer. At temperatures above 350 °C, dangling bonds are partially terminated with hydrogen atoms while Ge adatoms are highly mobile, resulting in a nonuniform nucleation that creates the islands. Small islands merge into a few-hundred-nanometer-tall islands surrounded by the (113)-face sidewalls. This kinetic roughening continues until the nucleation on the (001) plane ceases due to the buildup of the GeHx layer. Once the surface free energy is minimized by the hydrogen termination, flattening of the islands proceeds to reduce the chemical potential of the system. The valleys between the islands are preferentially filled, and the film is eventually converted into a smooth epilayer with no memory of the initial roughening.
Raman spectra of carbon nanowalls grown by plasma-enhanced chemical vapor deposition
Authors: Kurita S. , Yoshimura A. , Kawamoto H. , Uchida T. , Kojima K. , Tachibana M. , Molina-Morales P. , Nakai H.
Published: May 2005

Raman spectra of carbon nanowalls (CNWs) grown using dc plasma-enhanced chemical vapor deposition were analyzed. The Raman spectra of CNWs exhibited G and D bands at ∼1580 and ∼1350cm−1, respectively. It is found that the bandwidth of the G band is relatively narrow, even when the peak intensity ratio of D band to G band is significantly high. This spectral feature of CNWs is distinguished from those of typical graphitelike carbons reported so far. From the comparison of these spectral features, it is shown that CNWs are composed of small crystallites with a high degree of graphitization.
Miniconference on astrophysical jets
Authors: Bellan P. M.
Published: May 2005

This miniconference brought together observers of astrophysical jets, analytic and numerical modelers of both astrophysical jets and spheromaks, and laboratory experimentalists. The purpose of the miniconference was to encourage interaction between these diverse groups and also expose the plasma physics community to the interesting plasma issues associated with astrophysical jets. The miniconference emphasized magnetically driven astrophysical jets and consisted of three half-day sessions. The order of presentation was approximately: observations and general properties, experiments, numerical models, and special topics.
The effect of potential fluctuations on the optical properties of InGaAs∕InAlAs superlattices
Authors: Poças L. C. , Lopes E. M. , Duarte J. L. , Dias I. F. L. , Lourenço S. A. , Laureto E. , Valadares M. , Guimarães P. S. S. , Cury L. A. , Harmand J. C.
Published: May 2005

Photoluminescence (PL) measurements as a function of temperature and excitation intensity were carried out in a sample containing two InGaAs∕InAlAs superlattices, grown on the same InP substrate, with quantum wells and barriers of different widths. The fluctuations in the confinement potential for excitons in both structures are investigated by following the blueshift of the PL peaks with increasing temperature as well as with rising excitation intensity, at low temperatures. A decrease in the full width at half maximum of the PL peaks with increasing excitation power was also observed. The change in the PL linewidth with excitation power is interpreted in terms of the variation of the relative contribution of the excitons localized at the excitonic band tail (due to the potential fluctuations) and of the nonlocalized excitons. Moreover, the activation energies of the nonradiative channels responsible for the thermal quenching of the photoluminescence peaks are deduced from an Arrhenius plot of the integrated PL intensity.
Calculation of ferromagnetic states in metastable bcc and hcp Ni by projector-augmented wave method
Authors: He X. , Kong L. T. , Liu B. X.
Published: May 2005

Based on a projector-augmented wave method, ab initio calculations reveal that hcp Ni is ferromagnetic with a magnetic moment of 0.59μB, which is slightly smaller than 0.60μB in the stable fcc Ni. For bcc Ni, it is found that a ferromagnetic is energetically favored when the lattice constant a>2.69Å, below which there may be a coexisting state of ferromagnetic and nonmagnetic behaviors. Interestingly, although bcc Ni has a smallest magnetic moment of 0.55μB, it has a largest average atomic volume among the three structures, differing sharply from the cases of Fe and Co.
Multiple-wavelength-transmission filters based on Si-SiO2 one-dimensional photonic crystals
Authors: Lee Hyun-Yong , Cho Sung-June , Nam Gi-Yeon , Lee Wook-Hyun , Baba Takeshi , Makino Hisao , Cho Meoung-Whan , Yao Takafumi
Published: May 2005

The Si/SiO2 one-dimensional photonic crystals of heterostructural multilayers with two periods, ΛA and ΛB, have great potential for multiple-wavelength-transmission filters. These structures were prepared by inserting N pairs of ΛB (as the defect region) in the middle of two sets of two pairs of ΛA, so that the structure becomes air→[(2∙ΛA)→(N∙ΛB)→(2∙ΛA)]→substrate. N means the number of ΛB pairs in the defect region. The complex refractive indices of Si and SiO2 are assumed to be 3.7+i0 and 1.5+i0 in the transfer matrix calculation. The number of transmission channels or defect branches m is given by 2N, that is, m=2N. For large N(>10), the photonic band gap exists in a normalized frequency range ω of 0.0846–0.3838, which corresponds to the wavelength range of 0.84–6.67 μm. The defect branches are placed on a branch band between two symmetric flat bands. For a filling factor η=0.406, a matching condition of optical length in two alternating layers, the branches at the center of the branch band are divided into a uniform frequency interval. In particular, we claim that the transmission-defect branches can be precisely tuned by controlling the incident angles without external applied bias.
Ambipolar operation of fullerene field-effect transistors by semiconductor/metal interface modification
Authors: Nishikawa Takao , Kobayashi Shin-Ichiro , Nakanowatari Tomoyuki , Mitani Tadaoki , Shimoda Tatsuya , Kubozono Yoshihiro , Yamamoto Gakushi , Ishii Hisao , Niwano Michio , Iwasa Yoshihiro
Published: May 2005

We report an ambipolar operation in field-effect transistors of C60 and metallofullerene Dy@C82 by modification of semiconductor/metal electrode interface with perfluoroalkylsilane (FAS) molecules. Kelvin probe experiments revealed that the work function of the gold surface modified with FAS molecules increased by 0.55eV as compared to the untreated gold. Hole injection into fullerenes is qualitatively understood in terms of this work-function change induced by the FAS molecules. The present results indicate that the charge injection from electrodes to organic semiconductors can be controlled simply by modification of semiconductor/metal interface without changing materials themselves.
Effects of nanosecond-duration laser prepulses on solid targets
Authors: Wharton K. B. , Kim J. M. , Stuart B. C.
Published: May 2005

A critical issue in high-intensity laser-solid interactions is the effect of the laser prepulse on the target, but the experimental details of these lower-intensity interactions are often difficult to measure due to the subsequent high-intensity pulse. We have performed target experiments using a 0.5-ns duration, 800-nm wavelength laser pulse, specifically designed to mimic the typical amplified spontaneous emission (ASE) prepulse from a high-power Ti:Sapphire laser. Using this “artificial” ASE prepulse, we find that the threshold for relevant changes to typical solid targets occurs at a fluence of ∼0.1J∕cm2, or ∼108W∕cm2, well below the plasma formation threshold. Notably, the results are not consistent with simple surface vaporization, and suggest that the ASE prepulse causes multiatom clusters to be ejected from the target surface. In a full high-intensity experiment, this ablated material would then strongly interact with the subsequent primary laser pulse.