bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled thermohydromechanical analysis of Venice lagoon salt marshes
Authors: Cola Simonetta , Sanavia Lorenzo , Simonini Paolo , Schrefler Bernhard A.
Published: July 2008

A fully coupled thermohydromechanical (THM) finite element approach is used here to model the groundwater and saturation response of a typical salt marsh of the Venice lagoon (Italy) subjected to both tide fluctuation and flooding. The soil forming the marsh, whose relevant material parameters have been measured experimentally in the laboratory, is assumed to be an homogeneous multiphase porous medium, in a thermodynamic equilibrium state both in fully saturated and partially saturated conditions. More particularly, the study is aimed at analyzing separately the various couplings of several factors such as soil stiffness, water conductivity, capillary suction, and humidity exchange with atmosphere including also the occurrence of marsh flooding on the overall mechanical response of the marsh subjected to tidal oscillations of very narrow amplitude. From the analysis carried out so far, the numerical approach adopted here seems capable of describing most of the relevant features of marsh behavior, thus showing the importance of THM couplings to explain the groundwater pressure evolution induced by lagoon tide cycles. In addition, the model seems to provide some interesting explanations concerning the evolving instability of marsh scarps, which is one of the main causes of the rapid overall deterioration of the typical Venice lagoon landscape.
Relationships between ENSO and drought over the southeastern United States
Authors: Mo Kingtse C. , Schemm Jae E.
Published: July 2008

A long term precipitation (P) data set over the United States and the sea surface temperature (SST) data from 1915 to 2006 were used to examine the impact of El Nino Southern Oscillation (ENSO) on drought and persistent wet spells over the southeastern United States. The meteorological droughts and wet spells were identified based on the 6‐month standardized precipitation index (SPI 6) calculated from P averaged over the Southeast. These events indicate that a drought (or wet spell) over the Southeast is more likely to start during a cold (warm) ENSO winter or early spring. The influence of ENSO on P is seasonally dependent. The P composites for cold ENSO events show positive P anomalies over the Southeast in winter but negative anomalies in summer. For warm ENSO events, the situation reverses. Therefore, a persistent cold (warm) ENSO from winter to summer does not create favorable conditions for drought (wet spells) to persist over the Southeast. While cold ENSO events are more likely to initiate droughts, droughts are likely to persist if the cold (warm) ENSO winter is followed by an ENSO neutral summer.
Comparison of auroral electrojet indices in the Northern and Southern Hemispheres
Authors: Weygand James M. , Zesta Eftyhia
Published: July 2008

The auroral electrojet (AE) index is traditionally calculated from a set of about 10 to 13 ground magnetometer stations located around the typical northern auroral oval location. Similar coverage in the Southern Hemisphere does not exist, so the AE calculation has only been performed using Northern Hemisphere data. In the present paper, we use seven southern auroral region ground magnetometers as well as their conjugate Northern Hemisphere data to calculate conjugate AE indices during the Northern Hemisphere winter using the standard method. The correlation coefficient between the northern and southern AE indices for many of the intervals is above 0.7, but in one interval, it is close to 0. We compare our conjugate AE indices with the standard AE index and find a number of asymmetries because of station coverage gaps both in our conjugate indices and in interplanetary magnetic field (IMF) conditions. When the southern AE index is compared with the standard AE index, we find that for most intervals the correlation is less than 0.7, and in one interval, the correlation is about 0. The correlation between the conjugate northern AE index and the standard AE index is somewhat better, suggesting true interhemispheric asymmetries. The mean difference between the southern and northern AE indices is largest during southward IMF and for large values of IMF ∣By∣ (>5 nT). This is most likely due to the increased activity levels during southward IMF and the greater twisting of the magnetic field lines during strong IMF By. IMF Bx seems to have no effect on the interhemispheric differences of the AE index. The mean differences between the southern and conjugate northern H component are of the order of ∼35 nT, with the largest differences occurring in the midnight magnetic local time (MLT) sector. We suggest that these differences may be related to seasonal effects, ionospheric effects, and MLT effects.
Experimental observations of deformation caused by mineral dissolution in variable‐aperture fractures
Authors: Detwiler Russell L.
Published: July 2008

Problems such as CO2 sequestration, petroleum production and nuclear waste isolation involve the potential for rock‐water reactions. Mineral alteration resulting from reactive fluid flow can lead to significant changes to fracture transport properties. At depth, these processes are further influenced by stresses in the host rock. To quantitatively explore these coupled processes, we built a new experimental apparatus designed to directly measure changes in fracture aperture in analog fractures subjected to the combined influence of a reactive fluid and an applied normal stress. Light transmission techniques provided direct measurements of the changing fracture aperture at high spatial resolution during two experiments in identical fractures with an initial mean fracture aperture of 95 μm. The two experiments were carried out at values of the dimensionless Damkohler number (Da = reaction rate/advection rate) that differed by a factor of 2. The high‐Da experiment resulted in the formation of a large‐scale dissolution channel in the middle of the fracture and regions with little dissolution and slow closure of the fracture surfaces. By contrast, the low‐Da experiment exhibited relatively uniform dissolution across the width of the fracture, with locally enhanced dissolution in small aperture regions. This resulted in increased stresses in contacting asperities and eventual damage of the asperities accompanied by large (up to 50 μm), instantaneous displacements of the surfaces and corresponding reductions in fracture aperture. The results demonstrate the importance of the spatial variability of dissolution rates, which are controlled by both local reaction kinetics and hydrodynamics, in fractures deforming because of combined dissolution and mechanical stress.
Seismic and hydroacoustic tremor generated by colliding icebergs
Authors: MacAyeal D. R. , Okal E. A. , Aster R. C. , Bassis J. N.
Published: July 2008

Iceberg harmonic tremor (IHT) emanating from tabular icebergs in the Southern Ocean and along calving margins of the Antarctic Ice Sheet is a complex, evolving signal at frequencies above approximately 0.5 Hz. IHT has been observed as T phases on islands in the equatorial Pacific, as hydroacoustic signals in the Indian Ocean, and by local and regional Antarctic seismic networks. To identify the IHT source mechanism and to understand its relevance to iceberg calving, evolution, and breakup, we deployed seismometers on a giant (25 by 50 km) tabular iceberg called C16 in the Ross Sea, Antarctica, during a uniquely accessible period (austral summer, 2003–2004) when it was aground against the northern shore of Ross Island. During the deployment period, C16 was in sporadic contact with another giant tabular iceberg, B15A, that was moving under the influence of local ocean currents. This study reveals that the C16‐associated IHT was a manifestation of extended episodes of discrete, repeating stick‐slip icequakes (typically thousands of individual subevents per hour) produced when the cliff‐like edges of the tabular icebergs underwent glancing, strike‐slip collisions. The IHT signal that we observed is thus not a phenomenon associated with iceberg elastic or fluid resonance modes, but is instead the consequence of long sequences of very regularly spaced and similar pulses of seismic radiation from these constituent stick‐slip subevents. IHT represents a newly identified glaciogenic source of seismicity that can be used to improve our understanding of iceberg dynamics and possibly of ice shelf disintegration processes.
Eating Behavior and Obesity at Chinese Buffets
Authors: Wansink Brian , Payne Collin R.
Published: July 2008

Objective: The aim of this study was to investigate whether the eating behaviors of people at all‐you‐can‐eat Chinese buffets differs depending upon their body mass. The resulting findings could confirm or disconfirm previous laboratory research that has been criticized for being artificial.

Methods and Procedures: Trained observers recorded the height, weight, sex, age, and behavior of 213 patrons at Chinese all‐you‐can‐eat restaurants. Various seating, serving, and eating behaviors were then compared across BMI levels.

Results: Patrons with higher levels of BMI were more likely to be associated with using larger plates vs. smaller plates (OR 1.16, P < 0.01) and facing the buffet vs. side or back (OR 1.10, P < 0.001). Patrons with higher levels of BMI were less likely to be associated with using chopsticks vs. forks (OR 0.90,P < 0.05), browsing the buffet before eating vs. serving themselves immediately (OR 0.92, P < 0.001), and having a napkin on their lap vs. not having a napkin on their lap (OR 0.92, P < 0.01). Patrons with lower BMIs left more food on their plates (10.6% vs. 6.0%, P < 0.05) and chewed more per bite of food (14.8 vs. 11.9, P < 0.001).

Discussion: These observational findings of real‐world behavior provide support for laboratory studies that have otherwise been dismissed as artificial.
OGTT‐derived Measures of Insulin Sensitivity Are Confounded by Factors Other Than Insulin Sensitivity Itself
Authors: Hücking Katrin , Watanabe Richard M. , Stefanovski Darko , Bergman Richard N.
Published: July 2008

Insulin resistance is an important risk factor for diabetes and other diseases. It has been important to estimate insulin resistance in epidemiological and genetic studies involving significant number of individuals. Complex and invasive protocols are impractical. Therefore, insulin sensitivity indices based on the oral glucose‐tolerance test (OGTT) have been introduced. The aim of the present study was to assess the accuracy with which OGTT‐derived indices would reflect changes in insulin sensitivity in the face of changes in other factors, such as rate of glucose absorption and/or B‐cell function. A computer model was employed to predict excursions of plasma glucose and insulin after a 75‐g oral glucose load. The model was then used to predict changes in these excursions, which would be observed with altered insulin resistance, with alterations in β‐cell sensitivity to glucose and/or alterations in glucose absorption rates. Published indices of insulin sensitivity could then be calculated from the predicted curves, to ask whether changes in β‐cell function or glucose absorptions rates might be misinterpreted (using the indices) as changes in insulin sensitivity. The model accurately represented OGTT data for a normal glucose tolerant subject, closely matching published data. Imposed 50% reductions or increases in insulin sensitivity alone in the model were reflected in only small changes in OGTT‐derived insulin sensitivity values. More important, imposed alterations in β‐cell sensitivity and glucose absorption without simulated changes in insulin sensitivity did change insulin sensitivity indices. These results indicate that caution is required for the interpretation of differences in OGTT‐derived values of insulin sensitivity, because variation in factors other than insulin sensitivity per se appear to have the greatest effects on indices calculated from the OGTT alone.
A chorem-based approach for visually synthesizing complex phenomena
Authors: Del Fatto Vincenzo , Laurini Robert , Lopez Karla , Sebillo Monica , Vitiello Giuliana
Published: July 2008

When dealing with scenarios referring to complex issues, such as political, economic and demographic problems, the usage of visual metaphors represents a more effective approach in supporting users to locate facts and new patterns. In this paper, we describe a research project whose aim is to investigate a cartographic solution able to represent dynamics, movements and changes that underlie possible problems. The solution we propose is based on the chorem concept. It represents an immediate synthesis of data of interest, and provides expert users with both a global view of objects and phenomena, and an insight into a specific issue. Based on preliminary studies, we first provide a formal definition and classification of chorems in terms of structure and meaning, meant to homogenize chorem construction and usage. Then, a system to generate chorematic maps from available data sets is described and an XML-like language, named ChorML is specified, enabling system modules communication. In order to validate our approach, we exemplify the construction of a chorematic map, which depicts the most significant flows of migrating population in Italy in 2000. Such a synthesis may represent the starting point for further processing tasks aimed to derive spatial analysis data, as well as to support expert users in decision making.
Applicability of hybrid density functional theory methods to calculation of molecular hyperpolarizability
Authors: Suponitsky Kyrill Yu. , Tafur Sergio , Masunov Artëm E.
Published: July 2008

The donor/acceptor (D/A) substituted π-conjugated organic molecules possess extremely fast nonlinear optical (NLO) response time that is purely electronic in origin. This makes them promising candidates for optoelectronic applications. In the present study, we utilized four hybrid density functionals (B3LYP, B97-2, PBE0, BMK), Hartree–Fock, and second order Møller–Plesset correlation energy correction, truncated at second-order (MP2) methods with different basis sets to estimate molecular first hyperpolarizability (β) of D/A-substituted benzenes and stilbenes (D=OMe, OH, NMe2, NH2; A=NO2, CN). The results of density functional theory (DFT) calculations are compared to those of MP2 method and to the experimental data. We addressed the following questions: (1) the accurate techniques to compare calculated results to each other and to experiment, (2) the choice of the basis set, (3) the effect of molecular planarity, and (4) the choice of the method. Comparison of the absolute values of hyperpolarizabilities obtained computationally and experimentally is complicated by the ambiguities in conventions and reference values used by different experimental groups. A much more tangible way is to compare the ratios of β’s for two (or more) given molecules of interest that were calculated at the same level of theory and measured at the same laboratory using the same conventions and reference values. Coincidentally, it is the relative hyperpolarizabilities rather than absolute ones that are of importance in the rational molecular design of effective NLO materials. This design includes prediction of the most promising candidates from particular homologous series, which are to be synthesized and used for further investigation. In order to accomplish this goal, semiquantitative level of accuracy is usually sufficient. Augmentation of the basis set with polarization and diffuse functions changes β by 20%; however, further extension of the basis set does not have significant effect. Thus, we recommend 6-31+G* basis set. We also show that the use of planar geometry constraints for the molecules, which can somewhat deviate from planarity in the gas phase, leads to sufficient accuracy (with an error less than 10%) of predicted values. For all the molecules studied, MP2 values are in better agreement with experiment, while DFT hybrid methods overestimate β values. BMK functional gives the best agreement with experiment, with systematic overestimation close to the factor of 1.4. We propose to use the scaled BMK results for prediction of molecular hyperpolarizability at semiquantitative level of accuracy.
Streaming instabilities in multicomponent interstellar clouds
Authors: Shan S. Ali , Saleem H. , Sajid M.
Published: July 2008

Streaming instabilities in interstellar clouds have been investigated. It is pointed out that the motion of a lighter dust species relative to a plasma containing a heavier dust species can give rise to low frequency electrostatic fluctuations. The dust ion acoustic and dust acoustic waves can become unstable in such plasmas. The instability regions are influenced by the presence of background dust. Since interstellar clouds have relative motions in many cases and contain dust species, therefore the present results indicate the presence of an electrostatic dust ion acoustic wave and dust acoustic wave in such systems. The results have been applied to interstellar medium using particular data and comparisons have been made with previous works.
A general formulation of magnetohydrodynamic stability including flow and a resistive wall
Authors: Guazzotto L. , Freidberg J. P. , Betti R.
Published: July 2008

A general formulation is presented for determining the ideal magnetohydrodynamic stability of an axisymmetric toroidal magnetic configuration including the effects of an arbitrary equilibrium flow velocity and a resistive wall. The system is inherently non-self-adjoint with the eigenvalue appearing in both the equations and the boundary conditions. Even so, after substantial analysis we show that the stability problem can be recast in the form of a standard eigenvalue problem, ωA⋅z=B⋅z, which is highly desirable for numerical computation.
Compact two-stream generator of millimeter- and submillimeter-wave radiation
Authors: Carlsten Bruce E. , Bishofberger Kip A. , Faehl Rickey J.
Published: July 2008

A novel approach to producing short-wavelength radiation is proposed, where two offset electron beams of slightly different energies are merged within a dipole magnet and interact. With proper modulation of the two beams, the two-stream instability can be exploited to efficiently generate narrow-band millimeter-wave radiation. This type of source dispenses with the problematic structure required in other generation mechanisms and eliminates complex machining, delicate alignment, expensive parts, and catastrophic failures. Preliminary simulations have shown promise for a 100-GHz design, which is also scalable to 1THz. This concept requires only low-voltage, low-current electron beams and could lead to a device capable of generating up to 100W at 1THz, while remaining simple and compact.
Solution of the Cauchy problem for a time-dependent Schrödinger equation
Authors: Meiler Maria , Cordero–Soto Ricardo , Suslov Sergei K.
Published: July 2008

We construct an explicit solution of the Cauchy initial value problem for the n-dimensional Schrödinger equation with certain time-dependent Hamiltonian operator of a modified oscillator. The dynamical SU(1,1) symmetry of the harmonic oscillator wave functions, Bargmann’s functions for the discrete positive series of the irreducible representations of this group, the Fourier integral of a weighted product of the Meixner–Pollaczek polynomials, a Hankel-type integral transform, and the hyperspherical harmonics are utilized in order to derive the corresponding Green function. It is then generalized to a case of the forced modified oscillator. The propagators for two models of the relativistic oscillator are also found. An expansion formula of a plane wave in terms of the hyperspherical harmonics and solution of certain infinite system of ordinary differential equations are derived as by-products.
Influence of suprathermal background electrons on strong auroral double layers: Laminar and turbulent regimes
Authors: Newman D. L. , Andersson L. , Goldman M. V. , Ergun R. E. , Sen N.
Published: July 2008

A series of one-dimensional Vlasov simulations [Newman et al., Phys. Plasmas 15, 072902 (2008), this issue] show that a sufficiently dense and hot suprathermal electron population can stabilize strong laminar double layers over long periods while regulating their strength and velocity. When suprathermals are less dense or absent, the double layers tend to be sporadic and turbulent. A detailed comparison of the laminar and turbulent regimes reveals that the disruption of the laminar state can be triggered by kinetically modified Buneman instabilities on the low-potential side of the double layer, and by density perturbations that develop into nonlinear coherent shocklike structures on the high-potential side. These findings suggest that the suprathermal electrons may be responsible for suppressing both of these routes to disruption of the laminar state.
Microfluidic on chip viscometers
Authors: Chevalier J. , Ayela F.
Published: July 2008

We present the design and the process of fabrication of micromachined capillary on chip rheometers which have performed wall shear stress and shear rate measurements on silicon oil and ethanol-based nanofluids. The originality of these devices comes from the fact that local pressure drop measurements are performed inside the microchannels. Thus, the advantage over existing microviscometers is that they can be used with the fluid under test alone; no reference fluid nor posttreatment of the data are needed. Each on chip viscometer consists of anodically bonded silicon-Pyrex derivative microchannels equipped with local probes. The anodic bonding allows to reach relatively high pressure levels (up to ≈10bars) in the channels, and a broad range of shear stress and shear rate values is attainable. Dielectrophoretic and electrorheological effects can be highlighted by employing alternate microstripe electrodes patterned onto the inner side of the Pyrex wall.
The global solution of the (2+1)-dimensional long wave–short wave resonance interaction equation
Authors: Xin Jie , Guo Boling , Han Yongqian , Huang Daiwen
Published: July 2008

In this paper, we prove the existence and uniqueness of the global smooth solution to the (2+1)-dimensional long wave–short wave resonance interaction equation.
Anomalous transport of particles in plasma flow with strong inhomogeneous velocity shear
Authors: Mikhailenko V. S. , Mikhailenko V. V. , Stepanov K. N. , Azarenkov N. A.
Published: July 2008

The temporal evolution of the drift modes and resulting anomalous transport are considered under the conditions of strong inhomogeneous flow shear [flow shear parameter dv0(r)∕dr is greater or comparable to the drift frequency] on the ground of the nonmodal approach with application to boundary regions of tokamaks. The nonmodal linear analysis of the effect of flow shear nonuniformity on the temporal evolution of the drift modes, performed on the base of the Hasegava–Wakatani model, has shown, that terms reflecting velocity profile curvature decay more rapidly with time, as compared with those containing only velocity shearing rate. Therefore, the linear effect of the flow shear nonuniformity appears to be subdominant and the long-time evolution of the drift modes is determined by more slowly damped shear rate contained terms. The anomalous transport of particles in shear flow due to nonmodal drift perturbations exhibits a subdiffusive behavior with the diffusion coefficient reducing in time as t−3.
Moduli spaces of low dimensional real Lie algebras
Authors: Fialowski Alice , Penkava Michael
Published: July 2008

Moduli spaces of low dimensional complex Lie algebras have a unique stratification, determined by deformation theory, in which each stratum has the structure of a projective orbifold, in fact, it is given by an action of a finite group on complex projective space. For low dimensional real Lie algebras, the picture is similar, except that the strata are orbifolds given by the action of finite groups on spheres. We give a complete decomposition of the moduli spaces of real three and four dimensional Lie algebras and compare the structure of these moduli spaces to that of the corresponding complex Lie algebras.
Higher-order contribution to dust-ion acoustic dressed solitons in a warm dusty plasma
Authors: El-Bedwehy N. A.
Published: July 2008

Propagations of ion-acoustic dressed solitons in an unmagnetized dusty plasma consisting of a mixture of hot nonisothermal electrons, warm ions, and high negatively charged warm dust particles have been investigated. The reductive perturbation theory has been employed. At the lowest order of the perturbation theory a modified Korteweg–de Vries equation is obtained. At the next order of the perturbation theory, a linear inhomogeneous equation is obtained. Using the renormalization procedure introduced by Kodama and Taniuti, a stationary solution of the coupled equations has been obtained.
Numerical study on the motion of microscopic oil droplets in high intensity isotropic turbulence
Authors: Snyder Murray R. , Knio Omar M. , Katz Joseph , Le Maître Olivier P.
Published: July 2008

The rise of small oil droplets in water under isotropic turbulence conditions is analyzed computationally. The effort focuses on the puzzling behavior observed by Friedman and Katz [Phys. Fluids 14, 3059 (2002)], namely, that the rise velocity of droplets smaller than 800μm in diameter is enhanced by turbulence, whereas the rise of larger droplets is suppressed. Specifically, the study explores whether these effects can be captured or explained using a simplified one-way coupling model that combines direct numerical simulation of the turbulent flow field with Lagrangian tracking of the droplets using a dynamical equation that accounts for buoyancy, virtual mass, pressure, drag, lift, and history forces. The computational method used is adapted from the model of Snyder et al. [Phys. Fluids 19, 065108 (2007)], which showed excellent correlation between computational results and extensive experimental data for microbubbles in isotropic turbulence. The computed results indicate that, using the quasisteady, empirically determined drag and lift coefficients, one is unable to reproduce the experimentally observed droplet rise velocities. Numerical experiments on the effect of lift and history forces also indicate that, within a broad range of uncertainty, these forces do not account for the discrepancy between measured and computed trends. Guided by correlations obtained for the settling of heavy particles under high turbulence intensities, suppression of the drag and virtual mass coefficients for droplet diameters near ten times the Kolmogorov lengthscale was consequently postulated. Computed results indicate that, using this postulate, the simplified model is able to recover the observed enhancement of the mean rise of small droplets. These experiences underscore the difficulties in modeling the motion of small particles under high turbulence intensities, especially when the particle size is close to the turbulence microscale.
Soliton reflection in magnetized plasma: Effect of ion temperature and nonisothermal electrons
Authors: Malik Hitendra K.
Published: July 2008

Reflection of solitons in magnetized inhomogeneous plasma is studied theoretically under the effect of ion temperature and low temperature nonisothermal electrons. The effect of ion temperature is to enhance (reduce) the amplitude (width) of the incident and reflected solitons, and this effect is more prominent in the case of a large number of nonisothermal electrons. The solitons are downshifted after the reflection and the stronger reflection is achieved when the ions of lower temperature and nonisothermal electrons with larger concentration are present in the plasma. The solitons shift more after the reflection for higher ion and electron temperatures, large concentration of the electrons, but the shift becomes smaller in the presence of stronger magnetic field. Both the incident and reflected solitons evolve with higher amplitudes if the temperature of nonisothermal electrons is raised, but the solitons are reflected weakly under this situation. The effect of magnetic field is to reduce the amplitudes of both the solitons, and the reduction in the amplitude of reflected soliton is at a faster rate, due to which the soliton reflection gets weaker. The magnetic field affects soliton reflection more significantly when it is applied at a larger angle with the direction of wave propagation.
Modulational instabilities of electromagnetic electron cyclotron waves in a dense magnetized plasma
Authors: Rios L. A. , Shukla P. K.
Published: July 2008

Modulational instabilities of electromagnetic electron-cyclotron waves in a dense magnetized plasma are investigated. Dispersion relations for the modulational instabilities are derived and analyzed. The effects of quantum statistical pressure and quantum electron tunneling are discussed.
A tabletop femtosecond time-resolved soft x-ray transient absorption spectrometer
Authors: Loh Zhi-Heng , Khalil Munira , Correa Raoul E. , Leone Stephen R.
Published: July 2008

A laser-based, tabletop instrument is constructed to perform femtosecond soft x-ray transient absorption spectroscopy. Ultrashort soft x-ray pulses produced via high-order harmonic generation of the amplified output of a femtosecond Ti:sapphire laser system are used to probe atomic core-level transient absorptions in atoms and molecules. The results provide chemically specific, time-resolved dynamics with sub-50-fs time resolution. In this setup, high-order harmonics generated in a Ne-filled capillary waveguide are refocused by a gold-coated toroidal mirror into the sample gas cell, where the soft x-ray light intersects with an optical pump pulse. The transmitted high-order harmonics are spectrally dispersed with a homebuilt soft x-ray spectrometer, which consists of a gold-coated toroidal mirror, a uniform-line spaced plane grating, and a soft x-ray charge coupled device camera. The optical layout of the instrument, design of the soft x-ray spectrometer, and spatial and temporal characterizations of the high-order harmonics are described. Examples of static and time-resolved photoabsorption spectra collected on this apparatus are presented.
The modeling of degenerate neck pinch singularities in Ricci flow by Bryant solitons
Authors: Garfinkle David , Isenberg James
Published: July 2008

In earlier work, carrying out numerical simulations of the Ricci flows of families of rotationally symmetric geometries on S3, we have found strong support for the contention that (at least in the rotationally symmetric case) the Ricci flow for a “critical” initial geometry—one which is at the transition point between initial geometries (on S3) whose volume-normalized Ricci flows develop a singular neck pinch, and other initial geometries whose volume-normalized Ricci flows converge to a round sphere—evolves into a “degenerate neck pinch.” That is, we have seen in this earlier work that the Ricci flows for the critical geometries become locally cylindrical in a neighborhood of the initial pinching and have the maximum amount of curvature at one or both of the poles. Here, we explore the behavior of these flows at the poles and find strong support for the conjecture that the Bryant steady solitons accurately model this polar flow.
Long-time self-similar asymptotic of the macroscopic quantum models
Authors: Li Hai-Liang , Zhang Guo-Jing , Zhang Min , Hao Chengchun
Published: July 2008

The unipolar and bipolar macroscopic quantum models derived recently, for instance, in the area of charge transport are considered in spatial one-dimensional whole space in the present paper. These models consist of nonlinear fourth-order parabolic equation for unipolar case or coupled nonlinear fourth-order parabolic system for bipolar case. We show for the first time the self-similarity property of the macroscopic quantum models in large time. Namely, we show that there exists a unique global strong solution with strictly positive density to the initial value problem of the macroscopic quantum models which tends to a self-similar wave (which is not the exact solution of the models) in large time at an algebraic time-decay rate.
Direct-current cathodic vacuum arc system with magnetic-field mechanism for plasma stabilization
Authors: Zhang H.-S. , Komvopoulos K.
Published: July 2008

Filtered cathodic vacuum arc (FCVA) deposition is characterized by plasma beam directionality, plasma energy adjustment via substrate biasing, macroparticle filtering, and independent substrate temperature control. Between the two modes of FCVA deposition, namely, direct current (dc) and pulsed arc, the dc mode yields higher deposition rates than the pulsed mode. However, maintaining the dc arc discharge is challenging because of its inherent plasma instabilities. A system generating a special configuration of magnetic field that stabilizes the dc arc discharge during film deposition is presented. This magnetic field is also part of the out-of-plane magnetic filter used to focus the plasma beam and prevent macroparticle film contamination. The efficiency of the plasma-stabilizing magnetic-field mechanism is demonstrated by the deposition of amorphous carbon (a-C) films exhibiting significantly high hardness and tetrahedral carbon hybridization (sp3) contents higher than 70%. Such high-quality films cannot be produced by dc arc deposition without the plasma-stabilizing mechanism presented in this study.
A geometric description of tensor product decompositions in su(3)
Authors: Wesslén Maria S. M.
Published: July 2008

The direct sum decomposition of tensor products for su(3) has many applications in physics, and the problem has been studied extensively. This has resulted in many decomposition methods, each with its advantages and disadvantages. The description given here is geometric in nature and it describes both the constituents of the direct sum and their multiplicities. In addition to providing decompositions of specific tensor products, this approach is very well suited to studying tensor products as the parameters vary and helping draw general conclusions. After a description and proof of the method, several consequences are discussed and proved. In particular, questions regarding multiplicities are considered.
Surface magnetization measurement with a spin-polarized metastable He beam under high magnetic fields of 0–5T
Authors: Kurahashi Mitsunori , Entani Shiro , Yamauchi Yasushi
Published: July 2008

An apparatus for measuring the surface magnetization with a spin-polarized metastable helium atom (He*) beam under external magnetic fields of 0–5T was developed. The He* beam, spin polarized by a sextupole magnet, was directed to the sample placed in the bore of 5T superconducting magnet. A zero–field spin flipper was used for switching the polarity of beam polarization. A Stern–Gerlach analysis indicated the beam polarization of nearly 100% and the spin flipping efficiency of >90%. A surface magnetization curve was successfully measured from 0to5T for an Fe∕Cu(100) surface.
High throughput operando studies using Fourier transform infrared imaging and Raman spectroscopy
Authors: Li Guosheng , Hu Dehong , Xia Guanguang , White J. M. , Zhang Conrad
Published: July 2008

A prototype high throughput operando (HTO) reactor designed and built for catalyst screening and characterization combines Fourier transform infrared (FT-IR) imaging and Raman spectroscopy in operando conditions. Using a focal plane array detector (HgCdTe focal plane array, 128×128pixels, and 1610Hz frame rate) for the FT-IR imaging system, the catalyst activity and selectivity of all parallel reaction channels can be simultaneously followed. Each image data set possesses 16 384 IR spectra with a spectral range of 800–4000cm−1 and with an 8cm−1 resolution. Depending on the signal-to-noise ratio, 2–20s are needed to generate a full image of all reaction channels for a data set. Results on reactant conversion and product selectivity are obtained from FT-IR spectral analysis. Six novel Raman probes, one for each reaction channel, were specially designed and house built at Pacific Northwest National Laboratory, to simultaneously collect Raman spectra of the catalysts and possible reaction intermediates on the catalyst surface under operando conditions. As a model system, methanol partial oxidation reaction on silica-supported molybdenum oxide (MoO3∕SiO2) catalysts has been studied under different reaction conditions to demonstrate the performance of the HTO reactor.
Hot tail runaway electron generation in tokamak disruptions
Authors: Smith H. M. , Verwichte E.
Published: July 2008

Hot tail runaway electron generation is caused by incomplete thermalization of the electron velocity distribution during rapid plasma cooling. It is an important runaway electron mechanism in tokamak disruptions if the thermal quench phase is sufficiently fast. Analytical estimates of the density of produced runaway electrons are derived for cases of exponential-like temperature decay with a cooling rate lower than the collision frequency. Numerical simulations, aided by the analytical results, are used to compare the strength of the hot tail runaway generation with the Dreicer mechanism for different disruption parameters (cooling rate, post-thermal quench temperature, and electron density) assuming that no losses of runaway electrons occur. It is seen that the hot tail runaway production is going to be the dominant of these two primary runaway mechanisms in ITER [R. Aymar et al., Plasma Phys. Controlled Fusion 44, 519 (2002)].
Electron energy recuperation in gyrodevices
Authors: Savilov A. V. , Nusinovich G. S. , Sinitsyn O. V.
Published: July 2008

For many applications of gyrodevices, it is extremely important to increase their overall efficiency and reduce the power consumption. Therefore, at present, there are many gyrotrons operating with depressed collectors. These gyrotrons and their depressed collectors are typically designed with the use of available numerical codes. This paper is devoted to the analysis of the energy recuperation in gyrotrons, which is performed with the use of the Hamiltonian formalism. Such consideration gives some insight into the physics of gyrodevices and can be useful for estimating the benefits from utilizing depressed collectors. Both single-cavity gyromonotrons and multicavity gyrodevices in which the last cavity is excited by a prebunched beam are analyzed. Special attention is paid to a three-cavity, frequency-quadrupling gyrodevice.
Simple map in action-angle coordinates
Authors: Kerwin Olivia , Punjabi Alkesh , Ali Halima
Published: July 2008

A simple map [A. Punjabi, A. Verma, and A. Boozer, Phys. Rev. Lett. 69, 3322 (1992)] is the simplest map that has the topology of divertor tokamaks [A. Punjabi, H. Ali, T. Evans, and A. Boozer, Phys. Lett. A 364, 140 (2007)]. Here, action-angle coordinates, the safety factor, and the equilibrium generating function for the simple map are calculated analytically. The simple map in action-angle coordinates is derived from canonical transformations. This map cannot be integrated across the separatrix surface because of the singularity in the safety factor there. The stochastic broadening of the ideal separatrix surface in action-angle representation is calculated by adding a perturbation to the simple map equilibrium generating function. This perturbation represents the spatial noise and field errors typical of the DIII-D [J. L. Luxon and L. E. Davis, Fusion Technol. 8, 441 (1985)] tokamak. The stationary Fourier modes of the perturbation have poloidal and toroidal mode numbers (m,n,)={(3,1),(4,1),(6,2),(7,2),(8,2),(9,3),(10,3),(11,3)} with amplitude δ=0.8×10−5. Near the X-point, about 0.12% of toroidal magnetic flux inside the separatrix, and about 0.06% of the poloidal flux inside the separatrix is lost. When the distance from the O-point to the X-point is 1m, the width of stochastic layer near the X-point is about 1.4cm. The average value of the action on the last good surface is 0.19072 compared to the action value of 3∕5π on the separatrix. The average width of stochastic layer in action coordinate is 2.7×10−4, while the average area of the stochastic layer in action-angle phase space is 1.69017×10−3. On average, about 0.14% of action or toroidal flux inside the ideal separatrix is lost due to broadening. Roughly five times more toroidal flux is lost in the simple map than in DIII-D for the same perturbation [A. Punjabi, H. Ali, A. Boozer, and T. Evans, Bull. Amer. Phys. Soc. 52, 124 (2007)].
A 1MA, variable risetime pulse generator for high energy density plasma research
Authors: Greenly J. B. , Douglas J. D. , Hammer D. A. , Kusse B. R. , Glidden S. C. , Sanders H. D.
Published: July 2008

COBRA is a 0.5Ω pulse generator driving loads of order 10nH inductance to >1MA current. The design is based on independently timed, laser-triggered switching of four water pulse-forming lines whose outputs are added in parallel to drive the load current pulse. The detailed design and operation of the switching to give a wide variety of current pulse shapes and rise times from 95to230ns is described. The design and operation of a simple inductive load voltage monitor are described which allows good accounting of load impedance and energy dissipation. A method of eliminating gas bubbles on the underside of nearly horizontal insulator surfaces in water was required for reliable operation of COBRA; a novel and effective solution to this problem is described.
Offset reduction in Hall effect measurements using a nonswitching van der Pauw technique
Authors: Riss O. , Shaked E. , Karpovsky M. , Gerber A.
Published: July 2008

A nonswitching van der Pauw technique, which uses two electrically isolated alternating current sources operating at two different frequencies and two lock-in amplifiers, is suggested for Hall effect measurements. Parasitic offset voltage, typical for this type of measurements, is reduced by averaging two sets of data accumulated simultaneously. Application of the technique is particularly useful when the offset changes on a time scale comparable to the measurement cycle.
Label-free, all-electrical, in situ human epidermal growth receptor 2 detection
Authors: Capobianco Joseph A. , Shih Wan Y. , Yuan Qing-An , Adams Gregory P. , Shih Wei-Heng
Published: July 2008

Using 3-mercaptopropyltrimethoxysilane (MPS)-coated (PbMg1∕3Nb2∕3O3)0.63–(PbTiO3)0.37 (PMN-PT)/tin and lead zirconate titanate/glass piezoelectric microcantilever sensors (PEMSs) with single-chain variable fragment (scFv) immobilized on the MPS surface, we have demonstrated real-time, label-free detection of human epidermal growth factor receptor 2 (Her2) in a background of 1mg∕ml bovine serum albumin. Coupled with a scFv with a KD of 3.4×10−8M, the MPS-insulated PMN-PT/tin PEMS 560μm long and 720μm wide exhibited a Her2 concentration sensitivity of 5ng∕ml in a background of 1mg∕ml BSA.
Reflection-time-of-flight spectrometer for two-electron (e,2e) coincidence spectroscopy on surfaces
Authors: Kirschner J. , Kerhervé G. , Winkler C.
Published: July 2008

In this article, a novel time-of-flight spectrometer for two-electron-emission (e,2e∕γ,2e) correlation spectroscopy from surfaces at low electron energies is presented. The spectrometer consists of electron optics that collect emitted electrons over a solid angle of approximately 1sr and focus them onto a multichannel plate using a reflection technique. The flight time of an electron with kinetic energy of Ekin≃25eV is around 100ns. The corresponding time- and energy resolution are typically ≈1ns and ≈0.65eV, respectively. The first (e,2e) data obtained with the present setup from a LiF film are presented.
On the evolution of a reflection coefficient under the Korteweg–de Vries flow
Authors: Rybkin Alexei
Published: July 2008

We are concerned with the Korteweg–de Vries equation on the full line with real nondecaying initial profiles. We find the time evolution of a (relative) reflection coefficient. An inverse spectral formalism is also considered for certain mixed problems on the full line.
Solutions for multidimensional fractional anomalous diffusion equations
Authors: Lv Long-Jin , Xiao Jian-Bin , Ren Fu-Yao , Gao Lei
Published: July 2008

In this paper, we investigate the solutions of a generalized fractional diffusion equation that extends some known diffusion equations by taking a spatial time-dependent diffusion coefficient and N-dimensional case into account, which subjects to natural boundaries and the general initial condition. In our analysis, the presence of external force is also taken into account. We obtain explicit analytical expressions for the probability distribution and study the relation between our solutions and those obtained within the maximum entropy principle by using the Tsallis entropy.
Double layer created by electron cyclotron resonance heating in an inhomogeneously magnetized plasma with high-speed ion flow
Authors: Takahashi K. , Kaneko T. , Hatakeyama R.
Published: July 2008

A potential jump, i.e., an electric double layer (DL) is formed near an electron cyclotron resonance (ECR) point when an electron cyclotron wave is injected into an inhomogeneously magnetized plasma with high-speed ion flow. A charge separation is caused by an electron reflection due to −μ∇Bz force enhanced by ECR heating and ion inertia. It is clearly demonstrated in the experiment that the potential height of the DL is almost proportional to the field-aligned ion flow energy; the DL is found to be self-consistently formed for maintaining charge neutrality by reflecting a part of the flowing ions.
Influence of nanocrystal size on the transport properties of Si nanocrystals
Authors: Zhou Xin , Usami Kouichi , Rafiq M. A. , Tsuchiya Yoshishige , Mizuta Hiroshi , Oda Shunri
Published: July 2008

In this study, we have investigated the carrier transport mechanism across silicon nanocrystals with the Al/p-Si/Si nanocrystals/Al structure. Sizes of silicon nanocrystals were controlled at diameters of ∼6, ∼8, and ∼11 nm. It is shown that the conductivity σ of silicon nanocrystals, both as-grown and annealed, exhibits σ∝exp[−(T0/T)]1/2 behavior under low electrical fields and over a wide temperature range. The phenomenon of material constant T0 increasing with the decrease of nanocrystal size has been observed. Considering nanocrystal size effect, experimental results can be explained by the hopping-percolation model. The influence of nanocrystal size on transport properties has been discussed. Based on this model, changes in T0 after annealing treatment are attributed to an increase in effective decay length.
Vertical-type chiroptical spectrophotometer (I): Instrumentation and application to diffuse reflectance circular dichroism measurement
Authors: Harada Takunori , Hayakawa Hiroshi , Kuroda Reiko
Published: July 2008

We have designed and built a novel universal chiroptical spectrophotometer (UCS-2: J-800KCMF), which can carry out in situ chirality measurement of solid samples without any pretreatment, in the UV-vis region and with high relative efficiency. The instrument was designed to carry out transmittance and diffuse reflectance (DR) circular dichroism (CD) measurements simultaneously, thus housing two photomultipliers. It has a unique feature that light impinges on samples vertically so that loose powders can be measured by placing them on a flat sample holder in an integrating sphere. As is our first universal chiroptical spectrophotometer, UCS-1, two lock-in amplifiers are installed to remove artifact signals arising from macroscopic anisotropies which are unique to solid samples. High performance was achieved by theoretically analyzing and experimentally proven the effect of the photoelastic modulator position on the CD base line shifts, and by selecting high-quality optical and electric components. Measurement of microcrystallines of both enantiomers of ammonium camphorsulfonate by the DRCD mode gave reasonable results.