bluuebunny/crossref_metadata_2025 huggingface dataset:
Representing the effects of subgrid variability of soil moisture on runoff generation in a land surface model
Authors: Clark Douglas B. , Gedney Nicola
Published: May 2008

Different representations of runoff generation processes were implemented in the MOSES land surface model which is used with mesoscale and global atmospheric models. The standard model was compared with versions in which runoff generation was described by parameterizations based on either the Probability Distributed Model (PDM) or modified forms of TOPMODEL, all of which used probability functions to describe the subgrid distribution of soil moisture. The model results were compared with observed streamflow in three catchments in southern France. After calibration, the PDM‐ and TOPMODEL‐based parameterizations performed substantially better than the standard model. The TOPMODEL approach gave the best results through allowing a more responsive subsurface flow that contributed to peak flows and also better captured the slower changes during recessions. This approach was sensitive to uncertainty in the value of the topographic index. The PDM‐based model only changed the calculation of surface runoff and retained the standard description of subsurface runoff, and this limited the possible improvement in performance. In principle the values of the new parameters can be determined from observations, but in practice calibration is likely to be required. However, for each new parameterization, a single set of parameter values was found that performed well in all catchments. The simulated soil moisture and surface heat fluxes during summer dry periods were affected by the choice of runoff parameterization.
Updated estimate of aerosol direct radiative forcing from satellite observations and comparison against the Hadley Centre climate model
Authors: Bellouin Nicolas , Jones Andy , Haywood Jim , Christopher Sundar A.
Published: May 2008

The fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC) includes a comparison of observation‐based and modeling‐based estimates of the aerosol direct radiative forcing. In this comparison, satellite‐based studies suggest a more negative aerosol direct radiative forcing than modeling studies. A previous satellite‐based study, part of the IPCC comparison, uses aerosol optical depths and accumulation‐mode fractions retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS) at collection 4. The latest version of MODIS products, named collection 5, improves aerosol retrievals. Using these products, the direct forcing in the shortwave spectrum defined with respect to present‐day natural aerosols is now estimated at −1.30 and −0.65 Wm−2 on a global clear‐sky and all‐sky average, respectively, for 2002. These values are still significantly more negative than the numbers reported by modeling studies. By accounting for differences between present‐day natural and preindustrial aerosol concentrations, sampling biases, and investigating the impact of differences in the zonal distribution of anthropogenic aerosols, good agreement is reached between the direct forcing derived from MODIS and the Hadley Centre climate model HadGEM2‐A over clear‐sky oceans. Results also suggest that satellite estimates of anthropogenic aerosol optical depth over land should be coupled with a robust validation strategy in order to refine the observation‐based estimate of aerosol direct radiative forcing. In addition, the complex problem of deriving the aerosol direct radiative forcing when aerosols are located above cloud still needs to be addressed.
Sensitivity of multiangle imaging to the optical and microphysical properties of biomass burning aerosols
Authors: Chen Wei‐Ting , Kahn Ralph A. , Nelson David , Yau Kevin , Seinfeld John H.
Published: May 2008

The treatment of biomass burning (BB) carbonaceous particles in the Multiangle Imaging SpectroRadiometer (MISR) Standard Aerosol Retrieval Algorithm is assessed, and algorithm refinements are suggested, based on a theoretical sensitivity analysis and comparisons with near‐coincident AERONET measurements at representative BB sites. Over the natural ranges of BB aerosol microphysical and optical properties observed in past field campaigns, patterns of retrieved Aerosol Optical Depth (AOD), particle size, and single scattering albedo (SSA) are evaluated. On the basis of the theoretical analysis, assuming total column AOD of 0.2, over a dark, uniform surface, MISR can distinguish two to three groups in each of size and SSA, except when the assumed atmospheric particles are significantly absorbing (mid‐visible SSA ∼0.84), or of medium sizes (mean radius ∼0.13μm); sensitivity to absorbing, medium‐large size particles increases considerably when the assumed column AOD is raised to 0.5. MISR Research Aerosol Retrievals confirm the theoretical results, based on coincident AERONET inversions under BB‐dominated conditions. When BB is externally mixed with dust in the atmosphere, dust optical model and surface reflection uncertainties, along with spatial variability, contribute to differences between the Research Retrievals and AERONET. These results suggest specific refinements to the MISR Standard Aerosol Algorithm complement of component particles and mixtures. They also highlight the importance for satellite aerosol retrievals of surface reflectance characterization, with accuracies that can be difficult to achieve with coupled surface‐aerosol algorithms in some higher AOD situations.
Effects of solution chemistry on straining of colloids in porous media under unfavorable conditions
Authors: Shen Chongyang , Huang Yuanfang , Li Baoguo , Jin Yan
Published: May 2008

This study examines effects of solution chemistry on straining of colloids in porous media under unfavorable conditions via theoretical analysis and laboratory column experiments. Geometric analysis was used to estimate the effects of solution chemistry on the critical straining ratio of colloid diameter (dp) to collector diameter (dc), above which straining occurs. Column experiments were conducted with various sizes of latex particles and glass beads at different solution ionic strengths. A two‐ or three‐step procedure was used to measure colloid rentention and release by monitoring effluent colloid concentrations, and the columns were dissected at the end of experiments to determine distribution profiles of retained colloids. Measured effluent breakthrough curves and spatial deposition profiles were modeled with the convection‐diffusion equation including terms of attachment and straining. The experimental results confirm our theoretical analysis that the critical straining ratio is significantly reduced at higher ionic strength due to additional straining induced by attachment, predominantly at the grain‐to‐grain contacts. Through systematic evaluation of contributions of physical and physiochemical factors to colloid straining, this study provides explanations for the inconsistent and wide range of dp/dc ratios reported in the literature as well as some of the reported limitations of filtration theory.
Viscous Relaxation and Early Planetary Evolution
Authors: Mohit P. Surdas
Published: May 2008

Through observation and modeling, a great deal has been learned about the viscosity structure of the Earth and its influence on such processes as plate tectonics, mantle convection, postglacial rebound, and continental uplift. In particular, it has been shown that where the crust is unusually thick and/or warm, the lower crust is able to flow to relax stresses produced by crustal thickness variations and crustal extension or shortening [e.g., McKenzie et al., 2000]. Viscous relaxation models have been applied to other planets since the 1960s, and the results show that some large impact basins may have formed in the presence of a warm, ductile lower crust [e.g., Solomon et al., 1982].
Small temblor rattles Missouri
Authors: Showstack Randy
Published: May 2008

A magnitude 2.7 earthquake shook part of central Missouri at about 6:25 A.M. local time on 5 May. The event, which caused no reported damage, follows an 18 April magnitude 5.2 earthquake whose epicenter was in Illinois near the border of Indiana. That earlier quake, classified as moderate by the U.S. Geological Survey (USGS), occurred in the Wabash Valley seismic zone and was the strongest earthquake in southern Illinois since 1968.
Ocean Monitoring Collaborations Between Europe and China: DRAGONESS Project Kickoff Meeting; Beijing, China, 11–12 October 2007
Authors: Johannessen Johnny A. , He Ming‐Xia , Hu Chuanmin
Published: May 2008

A coordinated, concerted action between Europe and China in ocean monitoring kicked off with its first meeting, held in Beijing.

The project, named DRAGONESS (DRAGON in support of harmonizing European and Chinese marine monitoring for Environment and Security System), is funded by the European Union's (EU) Framework Programme for 3 years. Researchers from the two continents will establish an inventory of Chinese and European capacities in marine monitoring for environment and security in the framework of challenges identified within international programs such as Global Ocean Observing System, Global Earth Observing System of Systems, and Global Monitoring for Environment and Security. In particular, the DRAGONESS aims to (1) assess existing Chinese and European information products and services arising from integrated use of remote‐sensing, in situ observations, models, and data assimilation methods; (2) identify monitoring gaps and barriers (e.g., restrictive data availability); and (3) stimulate exchange and initiation of a new European‐Chinese partnership in Earth observation science and technology in support of global environmental monitoring.
Some decline in contaminants affecting U.S. coastal waters
Authors: Showstack Randy
Published: May 2008

A new report indicates that environmental laws enacted in the 1970s are having a positive effect on reducing overall contaminant levels in U.S. coastal waters. However, there are continuing concerns with elevated levels of metals and organic contaminants found near urban and industrial areas of the coasts, according to the 12 May report issued by the U.S. National Oceanic and Atmospheric Administration (NOAA). “Pesticides such as DDT [dichlorodiphenyltrichloroethane] and industrial chemicals such as PCBs [polychlorinated biphenyls] show significant decreasing trends around the nation, but similar trends were not found for trace metals,” said Gunnar Lauenstein, manager of the NOAA Mussel Watch program, the nation's longest continuous national contaminant‐monitoring program in U.S. coastal waters.
Impact of Indian Ocean Dipole on intraseasonal zonal currents at 90°E on the equator as revealed by self‐organizing map
Authors: Iskandar Iskhaq , Tozuka Tomoki , Masumoto Yukio , Yamagata Toshio
Published: May 2008

A neural network pattern recognition approach called self‐organizing map (SOM) has been used to examine the impact of the Indian Ocean Dipole (IOD) on intraseasonal zonal currents in the eastern equatorial Indian Ocean. This study shows that during negative IOD events the intraseasonal zonal currents are mostly dominated by the first two modes. On the other hand, contributions from the higher modes to the intraseasonal zonal current significantly increase during positive IOD events. This is attributed to the change in the background stratification associated with the IOD events; the sharp pycnocline in the eastern basin during the positive IOD events causes the wind forcing to project more onto the higher modes.
Characteristic size and shape of the mirror mode structures in the solar wind at 0.72 AU
Authors: Zhang T. L. , Russell C. T. , Baumjohann W. , Jian L. K. , Balikhin M. A. , Cao J. B. , Wang C. , Blanco‐Cano X. , Glassmeier K.‐H. , Zambelli W. , Volwerk M. , Delva M. , Vörös Z.
Published: May 2008

We investigate the structure of mirror modes in the solar wind at 0.72 AU using Venus Express magnetic field measurements. The mirror mode structure is identified as the presence of magnetic depression or magnetic “holes” in the solar wind with little or no directional change across them. We determine the characteristic size and shape of these structures by examining their durations as a function of the orientation of the magnetic field to the solar wind flow. The mirror mode structure is best fitted with an ellipsoid of revolution, and the resultant shape of the mirror mode structure is a prolate spheroid, or in other words, a rotational ellipsoid. We introduce two parameters, namely the width across the field and the eccentricity to give a full description of the size and shape of the structures. We find that the mirror mode structures in the solar wind are two‐dimensional and are more elongated along the magnetic field direction.
The FOXP3+ subset of human CD4+CD8+ thymocytes is immature and subject to intrathymic selection
Authors: Tuovinen Heli , Pekkarinen Pirkka T , Rossi Laura H , Mattila Ilkka , Arstila T Petteri
Published: May 2008

FOXP3, believed to be the regulatory T (Treg)‐cell determining factor, is already expressed at the CD4+CD8+ thymocyte stage, but there is disagreement whether these cells are the precursors of mature CD4+CD8− Treg cells. Here, we provide a quantitative analysis of FOXP3 expression in the human thymus. We show that a subset of CD4+CD8+ cells already expressed as much FOXP3 as the FOXP3+ CD4+CD8− cells, and like mature Treg cells were CD127low. In contrast to earlier data, CD8+CD4− thymocytes expressed significantly lower levels of FOXP3 than either the CD4+CD8+ or CD4+CD8− subsets. The CD4+CD8+ double‐positive cells also expressed recombination‐activating gene‐2, suggesting that they were still immature. Although the FOXP3+ double‐positive cells are thus putatively the precursors of the mature CD4+CD8−FOXP3+ subset, their frequency did not predict the frequency of more mature Treg cells, and analysis of T‐cell antigen receptor repertoire showed clear differences between the two subsets. Although these data do not rule out an independent CD4+CD8+ Treg cell subset, they are consistent with a model of human Treg cell development in which the upregulation of FOXP3 is an early event, but the first FOXP3+ population is still immature and subject to further selection. The upregulation of FOXP3 may thus not be the final determining factor in the commitment of human thymocytes to the Treg cell lineage.
Is Parent–Child Interaction Therapy Effective in Reducing Stuttering?
Authors: Millard Sharon K. , Nicholas Alison , Cook Frances M.
Published: May 2008

Purpose

To investigate the efficacy of parent–child interaction therapy (PCIT) with young children who stutter.

Method

This is a longitudinal, multiple single-subject study. The participants were 6 children aged 3;3–4;10 [years;months] who had been stuttering for longer than 12 months. Therapy consisted of 6 sessions of clinic-based therapy and 6 weeks of home consolidation. Speech samples were videorecorded during free play with parents at home and analyzed to obtain stuttering data for each child before therapy, during therapy, and up to 12 months posttherapy.

Results

Stuttering frequency data obtained during therapy and posttherapy were compared with the frequency and variability of stuttering in the baseline phase. Four of the 6 children significantly reduced stuttering with both parents by the end of the therapy phase.

Conclusions

PCIT can reduce stuttering in preschool children with 6 sessions of clinic-based therapy and 6 weeks of parent-led, home-based therapy. The study highlights the individual response to therapy. Suggestions for future research directions are made.
Late Childhood Stuttering
Authors: Howell Peter , Davis Stephen , Williams Roberta
Published: May 2008

Purpose

A study was conducted that examined factors that lead children who stutter at around age 8 years to persist in the disorder when they reach age 12 years.

Method

Seventy-six children were verified to be stuttering at initial assessment. When they reached 12 years of age, they were classified as persistent or recovered. A range of measures was taken at the 2 age points, and measures were examined by recovery group.

Results

Although the tendency for more males than females to stutter was confirmed, the reasons for this tendency are not apparent for these speakers. Different patterns in speech were observed: Severity ratings of the recovered speakers dropped by age 12+. The severity ratings for the persistent speakers remained high at 12+, and dysfluency types tended to change from whole words to part words. Persistent and recovered speakers differed on temperamental performance at around age 8 years and performed differently on sensory and motor tasks at age 12+ years.

Conclusions

Stuttering in late childhood affects mainly males. The later a child attends clinic, the longer he or she will stutter. Speech patterns of children who persist diverge from those who recover or who are fluent. As speakers persist, there are temperamental, sensory, and motor changes.
Extending the Research Agenda on Diffusion: The Case of Public Program Interventions for the Adoption of E-business Systems in SMEs
Authors: Vega Arturo , Chiasson Mike , Brown David
Published: May 2008

Given the importance of contextual influences on the diffusion of innovations, the theories and methodologies that take context into account are increasingly relevant to research and practice. One such approach, the systems of innovation approach, considers context to be a cascading set of effects arising from various participants and innovations surrounding the production and diffusion of a focal innovation. Based on this approach, we focus on a public program involved in the diffusion of e-business systems to small and medium-sized enterprises (SMEs). E-business systems are complex innovations, and the contextual influences are particularly important here, because SMEs often lack the knowledge and resources to strategically adopt, modify, and use these innovations. Using the systems of innovation approach, we examined the contexts around public program interventions with an SME in order to explain their form and influence on e-business adoption processes. The empirical findings suggest that many public programs fail to effectively deliver interventions because program contexts restrict program personnel's ability to completely assess and respond to the range of adopter needs. While some aspects of the program contexts can be altered by the program directors, others are further removed and are currently beyond our collective control at this point-in-time. The implications for diffusion research and practice are discussed.
Cryogenic fluid dynamics of pressure swirl injectors at supercritical conditions
Authors: Zong Nan , Yang Vigor
Published: May 2008

A comprehensive numerical analysis has been conducted to explore the development of liquid-oxygen (LOX) flow in pressure swirl injectors operating at supercritical pressures. The model is based on full-conservation laws and accommodates real-fluid thermodynamics and transport phenomena over the entire range of fluid states of concern. Three different flow regimes with distinct characteristics, the developing, stationary, and accelerating regimes, are identified within the injector. Results are compared to predictions from classical hydrodynamics theories to acquire direct insight into the flow physics involved. In addition, various flow dynamics are investigated by means of the spectral and proper-orthogonal-decomposition techniques. The interactions between the hydrodynamic instabilities in the LOX film and acoustic oscillations in the gaseous core are clearly observed and studied. The influences of flow conditions (mass flowrate, swirl strength of the injected fluid, and ambient pressure) and injector geometry (injector length and tangential entry location) on the injector flow behavior are systematically characterized in terms of the LOX film thickness and spreading angle. The axial and azimuthal momentum exchange and loss mechanisms are also examined.
Spin-up flow of ferrofluids: Asymptotic theory and experimental measurements
Authors: Chaves Arlex , Zahn Markus , Rinaldi Carlos
Published: May 2008

We treat the flow of ferrofluid in a cylindrical container subjected to a uniform rotating magnetic field, commonly referred to as spin-up flow. A review of theoretical and experimental results published since the phenomenon was first observed in 1967 shows that the experimental data from surface observations of tracer particles are inadequate for the assessment of bulk flow theories. We present direct measurements of the bulk flow by using the ultrasound velocity profile method, and torque measurements for water and kerosene based ferrofluids, showing the fluid corotating with the field in a rigid-body-like fashion throughout most of the bulk region of the container, except near the air-fluid interface, where it was observed to counter-rotate. We obtain an extension of the spin diffusion theory of Zaitsev and Shliomis, using the regular perturbation method. The solution is rigorously valid for αK⪡3∕2, where αK is the Langevin parameter evaluated by using the applied field magnitude, and provides a means for obtaining successively higher contributions of the nonlinearity of the equilibrium magnetization response and the spin-magnetization coupling in the magnetization relaxation equation. Because of limitations in the sensitivity of our apparatus, experiments were carried out under conditions for which α∼1. Still, under such conditions the predictions of the analysis are in good qualitative agreement with the experimental observations. An estimate of the spin viscosity is obtained from comparison of flow measurements and theoretical results of the extrapolated wall velocity from the regular perturbation method. The estimated value lies in the range of 10−8–10−12kgms−1 and is several orders of magnitude higher than that obtained from dimensional analysis of a suspension of noninteracting particles in a Newtonian fluid.
Defining and identifying three-dimensional magnetic reconnection in resistive magnetohydrodynamic simulations of Earth’s magnetosphere
Authors: Dorelli John C. , Bhattacharjee A.
Published: May 2008

Magnetic reconnection is thought to be the primary mode by which the solar wind couples to the terrestrial magnetosphere, driving phenomena such as magnetic storms and aurorae. While the theory of two-dimensional reconnection is well developed and has been applied with great success to axisymmetric and toroidal systems such as laboratory plasma experiments and fusion devices, it is difficult to justify the application of two-dimensional theory to nontoroidal plasma systems such as Earth’s magnetosphere. Unfortunately, the theory of three-dimensional magnetic reconnection is much less well developed, and even defining magnetic reconnection has turned out to be controversial. In this paper, recent progress in the use of magnetohydrodynamics (MHD) to address the physics of three-dimensional reconnection in Earth’s magnetosphere is reviewed. The paper consists of two parts. In the first part, various definitions of three-dimensional reconnection are reviewed, with the goal of mapping these definitions to sets of physical phenomena that have been identified as “reconnection” in various contexts. In the second part of the paper, MHD simulation results for the magnetosphere are presented, and two qualitatively distinct types of reconnection phenomena are identified: (1) Steady separator reconnection under generic northward interplanetary magnetic field (IMF) conditions, involving plasma flow across magnetic separatrices, and (2) time-dependent reconnection under generic southward IMF conditions, involving a locally detectable change in the magnetic field topology. It is concluded that magnetic reconnection phenomena at Earth’s dayside magnetopause are adequately captured by two distinct definitions: The Vasyliunas definition [V. M. Vasyliunas, Rev. Geophys 13, 303 (1975)], which identifies magnetic reconnection with plasma flow across magnetic separatrices, and the Greene definition [J. Greene, Phys. Fluids B 5, 2355 (1993)], which identifies magnetic reconnection with a violation of magnetic flux conservation. Further generalizations of the definition of magnetic reconnection—e.g., the Schindler–Hesse [K. Schindler and M. Hesse, J. Geophys. Res. 93, 5547 (1988)] definition, which identifies reconnection with spatially localized violations of ideal MHD—are, while potentially useful in characterizing reconnection phenomena in the absence of magnetic nulls, separators, or separatrices, unnecessary in the magnetospheric context.
Quantum capture, adiabatic channel, and classical trajectory study of the high pressure rate constant of the reaction H+O2→HO2 between 0 and 5000K
Authors: Troe J. , Ushakov V. G.
Published: May 2008

Limiting high pressure rate constants for the recombination reaction H+O2→HO2 are modeled between 0 and 5000K on an ab initio potential. Quantum capture theory is employed for the temperature range from 0 to about 1K, while classical trajectory calculations are suitable for covering temperatures above about 200K. The intermediate temperature range is analyzed by adiabatic channel capture theory. The system is characterized by transition-state switching from outer transition states in the long-range-C6∕R6 potential to inner transition states in the range of a “shoulder” of the potential. The limiting high pressure rate constants from the trajectory calculations are sufficient for comparison with the experimental data which are available over the range from 300to900K. Specific rate constants k(E,J) for HO2 dissociation are also given and analyzed with respect to internal consistency with capture cross sections.
Arsenic dependence on the morphology of ultrathin GaAs layers on In0.53Ga0.47As∕InP(001)
Authors: Lee Jennifer Y. , Pearson Chris , Millunchick Joanna M.
Published: May 2008

Thin GaAs films grown on lattice-matched In0.53Ga0.47As∕InP(001) have been imaged by in vacuo scanning tunneling microscopy. We observe that the morphological evolution of these strained films depends on the deposition and diffusion of group III adatoms and the incorporation of As from the vapor, in addition to Asaro–Tiller–Grinfeld instabilities. We compare step edge densities to a model for the Ga adatom density and find that the absolute magnitude of the group V and group III fluxes has a strong effect on the number of adatoms on the surface and, thus, the morphology of the films.
Measurement of edge density profiles of Large Helical Device plasmas using an ultrashort-pulse reflectometer
Authors: Yokota Y. , Mase A. , Kogi Y. , Bruskin L. G. , Tokuzawa T. , Kawahata K.
Published: May 2008

We report here on the application of an ultrashort-pulse reflectometer (USPR) to Large Helical Device in National Institute for Fusion Science. An impulse with picosecond pulse width is used as a source in an USPR. Since the bandwidth of a source is inversely related to the pulse width, we can utilize the frequency range of microwave to millimeter-wave by using wide band transmission lines. The density profiles can be reconstructed by collecting time-of-flight signal of each frequency component of an impulse reflected from each cutoff layer. Remote control system using super science information network has been introduced to the present USPR system.
Creating large area molecular electronic junctions using atomic layer deposition
Authors: Preiner Michael J. , Melosh Nicholas A.
Published: May 2008

We demonstrate a technique for creating large area, electrically stable molecular junctions. We use atomic layer deposition to create nanometer thick passivating layers of aluminum oxide on top of self-assembled organic monolayers with hydrophilic terminal groups. This layer acts as a protective barrier and allows simple vapor deposition of the top electrode without short circuits or molecular damage. This method allows nonshorting molecular junctions of up to 9mm2 to be easily and reliably fabricated. The effect of passivation on molecular monolayers is studied with Auger and x-ray spectroscopy, while electronic transport measurements confirm molecular tunneling as the transport mechanism for these devices.
Generation of periodic ultrashort electron bunches and strongly asymmetric ion Coulomb explosion in nanometer foils interacting with ultra-intense laser pulse
Authors: Tian Youwei , Yu Wei , Lu Peixiang , Xu Han , Senecha Vinod , Lei Anle , Shen Baifei , Wang Xin
Published: May 2008

The interaction of a linearly polarized intense laser pulse with an ultrathin nanometer plasma layer is investigated to understand the physics of the ion acceleration. It is shown by the computer simulation that the plasma response to the laser pulse comprises two steps. First, due to the v×B effect, electrons in the plasma layer are extracted and periodic ultrashort relativistic electron bunches are generated every half of a laser period. Second, strongly asymmetric Coulomb explosion of ions in the foil occurs due to the strong electrostatic charge separation, once the foil is burnt through. Followed by the laser accelerated electron bunch, the ion expansion in the forward direction occurs along the laser beam that is much stronger as compared to the backward direction.
The momentum flux probability distribution function for ion-temperature-gradient turbulence
Authors: Anderson Johan , Kim Eun-jin
Published: May 2008

There has been overwhelming evidence that coherent structures play a critical role in determining the overall transport in a variety of systems. We compute the probability distribution function (PDF) tails of momentum flux and heat flux in ion-temperature-gradient turbulence, by taking into account the interaction among modons, which are assumed to be coherent structures responsible for bursty and intermittent events, contributing to the PDF tails. The tail of PDF of momentum flux R=⟨vxvy⟩ is shown to be exponential with the form exp{−ξR3∕2}, which is broader than a Gaussian, similar to what was found in the previous local studies. An analogous expression with the same functional dependence is found for the PDF tails of heat flux. Furthermore, we present a detailed numerical study of the dependence of the PDF tail on the temperature and density scale lengths and other physical parameters through the coefficient ξ.
Polymer-induced phase separation and crystallization in immunoglobulin G solutions
Authors: Li Jianguo , Rajagopalan Raj , Jiang Jianwen
Published: May 2008

We study the effects of the size of polymer additives and ionic strength on the phase behavior of a nonglobular protein—immunoglobulin G (IgG)—by using a simple four-site model to mimic the shape of IgG. The interaction potential between the protein molecules consists of a Derjaguin–Landau–Verwey–Overbeek-type colloidal potential and an Asakura–Oosawa depletion potential arising from the addition of polymer. Liquid-liquid equilibria and fluid-solid equilibria are calculated by using the Gibbs ensemble Monte Carlo technique and the Gibbs–Duhem integration (GDI) method, respectively. Absolute Helmholtz energy is also calculated to get an initial coexisting point as required by GDI. The results reveal a nonmonotonic dependence of the critical polymer concentration ρPEG* (i.e., the minimum polymer concentration needed to induce liquid-liquid phase separation) on the polymer-to-protein size ratio q (equivalently, the range of the polymer-induced depletion interaction potential). We have developed a simple equation for estimating the minimum amount of polymer needed to induce the liquid-liquid phase separation and show that ρPEG*∼[q∕(1+q)3]. The results also show that the liquid-liquid phase separation is metastable for low-molecular weight polymers (q=0.2) but stable at large molecular weights (q=1.0), thereby indicating that small sizes of polymer are required for protein crystallization. The simulation results provide practical guidelines for the selection of polymer size and ionic strength for protein phase separation and crystallization.
Dynamics of solid particles in a tangle of superfluid vortices at low temperatures
Authors: Kivotides D. , Sergeev Y. A. , Barenghi C. F.
Published: May 2008

We present results of numerical study of motion of micron-size, neutrally buoyant, solid particles in liquid helium at temperatures small enough that the normal fluid is negligible and turbulence manifests itself as a tangle of superfluid line vortices. Based on dynamically self-consistent model of interaction between a solid particle and the quantized vortex, we analyze first an influence of temperature on particle trapping on the vortex core. We find that the particle can be trapped only in the case where the particle experiences the damping force, such as the viscous drag force exerted by the normal fluid. However, at temperature below 0.7K, when the normal fluid is practically absent, the moving particle still experiences the damping force caused by the ballistic scattering of quasiparticles (phonons and rotons) off the particle surface. Using, together with our calculation of close interaction between the particle and the quantized vortex, available experimental data and theoretical results for this force, we show that trapping of micron-size, neutrally buoyant particles on quantized vortices becomes impossible at temperatures below 0.5K. At such temperatures, the particle motion in the vortex tangle can be studied based on the simpler, “one-way coupling” model ignoring the backreaction of the particle on the motion and evolution of quantized vortices. Based on such a model, we present results of numerical calculation of particle trajectories in the vortex tangle and show that, due to instability of trajectories and the mismatch of initial velocities of particles and the fluid, the motion of inertial particles does not reveal the motion of turbulent superfluid. We show that particle trajectories between vortex cores are ballistic. Interaction of particles with moving vortices leads to increase of the average particle velocity until it saturates at the value much larger than the fluid rms velocity. These results prevent the use of small tracer particles to study vortex tangles at low temperatures, but open to investigation a new and remarkably simple model of Lagrangian turbulence. We present the probability density function of the turbulent velocity and show that the particle velocity spectrum obeys a simple scaling law.
Phase integral approximation for coupled ordinary differential equations of the Schrödinger type
Authors: Skorupski Andrzej A.
Published: May 2008

Four generalizations of the phase integral approximation (PIA) to sets of ordinary differential equations of Schrödinger type [uj″(x)+∑k=1NRjk(x)uk(x)=0, j=1,2,…,N] are described. The recurrence relations for higher order corrections are given in a form valid to arbitrary order and for the matrix R(x)[≡{Rjk(x)}] either Hermitian or non-Hermitian. For Hermitian and negative definite R(x) matrices, a Wronskian conserving PIA theory is formulated, which generalizes Fulling’s current conserving theory pertinent to positive definite R(x) matrices. The idea of a modification of the PIA, which is well known for one equation [u″(x)+R(x)u(x)=0], is generalized to sets. A simplification of Wronskian or current conserving theories is proposed which in each order eliminates one integration from the formulas for higher order corrections. If the PIA is generated by a nondegenerate eigenvalue of the R(x) matrix, the eliminated integration is the only one present. In that case, the simplified theory becomes fully algorithmic and is generalized to non-Hermitian R(x) matrices. The general theory is illustrated by a few examples automatically generated by using the author’s program in MATHEMATICA published in e-print arXiv:0710.5406 [math-ph].
Study of the Xe–NH3 van der Waals complex: High-resolution microwave spectra and ab initio calculations
Authors: Wen Qing , Jäger Wolfgang
Published: May 2008

An ab initio potential energy surface of the Xe–NH3 van der Waals complex was constructed at the coupled cluster level of theory with single, double, and pertubatively included triple excitations. The small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-ζ basis set was used for the Xe atom and Dunning’s augmented correlation-consistent polarized valence triple-ζ basis set for the other atoms. The basis sets were supplemented with midbond functions. Rotational spectra of the Xe–NH3 van der Waals complex were recorded using a pulsed-nozzle Fourier transform microwave spectrometer. Rotational transitions within two internal rotor states, namely, the Σ00 and Π11lower states, were measured and assigned to the Xe–N14H3 and Xe–N15H3 isotopologues. For the deuterated isotopologues, only the Σ00 states were observed. Two inversion components were observed for each state except for the “s” component of the Σ00 state of the Xe–N14H3 and Xe–N15H3 isotopologues, which has a spin statistical weight of zero. Nuclear quadrupole hyperfine structures arising from the N14 (nuclear spin angular momentum quantum number I=1) and Xe131 (I=3∕2) nuclei were detected and analyzed. The observed spectra suggest that the Π11lower state has lower energy than the unobserved Σ11 state, in contrast to the case of Ar–NH3.
Free-electron maser based on a cavity with two- and one-dimensional distributed feedback
Authors: Konoplev I. V. , Cross A. W. , MacInnes P. , He W. , Phelps A. D. R. , Whyte C. G. , Ronald K. , Robertson C. W.
Published: May 2008

The study of a coaxial free-electron maser (FEM) based on two-dimensional (2D) and one-dimensional (1D) distributed feedback, driven by a 70mm diameter, annular electron beam is presented. A new cavity formed with 2D and 1D periodic lattices, positioned at the input and output of the interaction region, respectively, was used. It has been demonstrated that 2D distributed feedback in the input mirror allowed 8mm radiation emitted from different parts of the electron beam to be synchronized. The FEM operating in the 35.9–38.9GHz frequency region generated 65MW, 150ns duration millimeter wave pulses which contained ∼10J of energy in the pulse.
Thermal conductivity measurement and interface thermal resistance estimation using SiO2 thin film
Authors: Chien Heng-Chieh , Yao Da-Jeng , Huang Mei-Jiau , Chang Tien-Yao
Published: May 2008

In this paper, we describe an easy-to-use method to measure the thermal conductivity of thin films based on an electrical heating/sensing mechanism and a steady-state technique. The method used relative commonly used instruments, and without any signal processing circuit, is easy to be used in such thin-film thermal conductivity measurement. The SiO2 thin-film samples, prepared by thermal oxidation, plasma enhanced chemical vapor deposition (PECVD), and E-beam evaporator, were deposited on a silicon substrate. The apparent thermal conductivity, the intrinsic thermal conductivity of SiO2 films, and the total interface thermal resistance of the heater/SiO2/silicon system were evaluated. Our data showed agreement with those data obtained from previous literatures and from the 3ω method. Furthermore, by using a sandwiched structure, the interface thermal resistance of Cr/PECVD SiO2 and PECVD SiO2/silicon were also separately evaluated in this work. The data showed that the interface thermal resistance of Cr/PECVD SiO2 (metal/dielectric) is about one order of magnitude larger than that of PECVD SiO2/silicon (dielectric/dielectric).
Shadowing growth of three-dimensional nanostructures on finite size seeds
Authors: Ye D.-X. , Ellison C. L. , Lim B.-K. , Lu T.-M.
Published: May 2008

We reported the fabrication of silicon (Si) nanorods and springs on arrays of seeds with different diameters by using glancing angle deposition technique. Single nanorod is possible to grow on individual seeds if the size of the seeds is small enough. On large size seeds, however, multiple Si nanorods are observed in experiments. The effects of the size of seeds were studied by using Monte Carlo simulations based on a ballistic aggregation model. The simulation model also includes ballistic sticking, shadowing, and surface mobility. Both of the top-view and cross-sectional images of the nanostructures were generated in simulation and compared to the images of experimental samples taken by scanning electron microscopy. We also investigated the effect of surface diffusion on the formation of nanostructures. In our experiments, no separate rods formed when the surface mobility is sufficiently high, such as the deposition of cobalt on the large size seeds.
Excellent electrical properties of TiO2∕HfSiO∕SiO2 layered higher-k gate dielectrics with sub-1nm equivalent oxide thickness
Authors: Arimura Hiroaki , Kitano Naomu , Naitou Yuichi , Oku Yudai , Minami Takashi , Kosuda Motomu , Hosoi Takuji , Shimura Takayoshi , Watanabe Heiji
Published: May 2008

Equivalent oxide thickness (EOT) scaling, as well as improved interface properties, of metal/higher-k gate stacks for the sub-1nm region was achieved using a TiO2∕HfSiO∕SiO2 layered dielectric structure. Ti diffusion into the bottom oxides was found to form electrical defects, which lead to an increase of leakage current, fixed charge, interface trap density (Dit), and reliability degradation of the gate stacks. By controlling Ti diffusion and terminating Ti-induced defects using forming gas annealing, we successfully obtained a superior interface property (Dit=9.9×1010eV−1cm−2) and reduced gate leakage (Jg=7.2×10−2A∕cm2) at the 0.71-nm-EOT region.
Multidomain ultrasonic transducers
Authors: Ostrovskii Igor , Nadtochiy Andriy
Published: May 2008

A different class of high frequency ultrasonic transducers is theoretically considered and experimentally demonstrated. This transducer generates plane longitudinal waves using a two-dimensional structure of inversely poled ferroelectric domains. The crystalline ferroelectric wafer from which the transducer is fabricated is bounded along the plate thickness, and the ferroelectric multidomain system has its dimension along the plate length. Possible applications include medical imaging, nondestructive testing, and improved acoustic microscopy for use both in biological and physical sciences. Experimental measurements and theoretical calculations are in good agreement.
High-speed wavelength conversion in quantum dot and quantum well semiconductor optical amplifiers
Authors: Nielsen D. , Chuang S. L. , Kim N. J. , Lee D. , Pyun S. H. , Jeong W. G. , Chen C. Y. , Lay T. S.
Published: May 2008

We experimentally investigate wavelength conversion in quantum dot and quantum well optical amplifiers via four-wave mixing. Our results show superior conversion efficiency in a quantum dot device compared to a quantum well device with identical gain. Furthermore, a small-signal modulation bandwidth >25GHz was measured with greater than 100% efficiency. Cross talk between two simultaneously input beams was found to be 20dB below the signal power demonstrating the possibility for high-speed, multichannel performance. Cross-gain modulation measurements were performed as well and show a much smaller bandwidth of 1GHz indicating that four-wave mixing is superior for high-speed signals.
The characteristics and interfacial electronic structures of organic thin film transistor devices with ultrathin (HfO2)x(SiO2)1−x gate dielectrics
Authors: Cho S. W. , Jeong J. G. , Park S. H. , Cho M.-H. , Jeong K. , Whang C.-N. , Yi Y.
Published: May 2008

Pentacene-based thin film transistors with ultrathin (6nm) (HfO2)x(SiO2)1−x gate dielectric layers (x=0.25 and 0.75) were fabricated for low-voltage operation. The devices with ultrathin (HfO2)x(SiO2)1−x as the gate dielectric layer were operated at a gate voltage lower than −4.0eV. However, the threshold voltage and drain current have different values depending on the composition of the (HfO2)x(SiO2)1−x gate dielectric layer. The device with (HfO2)0.75(SiO2)0.25 gate dielectrics, having larger capacitance, shows a higher drain current than that with (HfO2)0.25(SiO2)0.75 gate dielectrics. On the other hand, the device with (HfO2)0.25(SiO2)0.75 gate dielectrics, which has a larger work function, shows a lower threshold voltage. The in situ ultraviolet photoelectron spectroscopy shows that this is caused by the difference in electronic structures and by changes in band alignment of the interface between the pentacene and dielectric layers.
Spontaneous oxidation of disordered fcc FePt nanoparticles
Authors: de la Presa P. , Rueda T. , Hernando A. , Ramallo-López J. M. , Giovanetti L. J. , Requejo F. G.
Published: May 2008

In this work we present new results on spontaneous oxidation of disordered fcc FePt nanoparticles. The “as-made” oleic acid and oleylamine coated FePt nanoparticles of average size 4 nm synthesized by a high-boiling coordinating solvent method were exposed to air over a period of days and characterized structurally and magnetically by means of different techniques such as XANES, XPS, EXAFS, and SQUID magnetometry. The “as-made” FePt nanoparticles stabilize in the disordered fcc structure and have a very low magnetic saturation (Ms=11 emu/g) and a huge coercive field (Hc=1800 Oe) compared to the low temperature bulk values of the disordered fcc FePt. We observed that the coercive field and the magnetic saturation change with the time the sample is exposed to air and these changes are associated with the oxidation or passivation of the nanoparticle surface that gives place to a core-shell structure. Indeed, the study on the electronic properties of the nanoparticles confirms the magnetic results and indicates that when the nanoparticles are exposed to air, changes in the oxidation state of both Fe and Pt occur, the oxidation state of Fe coming close to hematite. The formation of hematite tends to soften the “as-made” FePt nanoparticles as observed by the reduction of the coercive field to almost one third of the original value. Although the hematite softens the FePt nanoparticles, there is an exchange coupling at the interface of the core-shell characterized by the increase of the coercive field from 300 to 900 Oe when the sample is cooled in an applied field of 50 kOe.
Electron transport characteristics of the carbon nanotubes/Si heterodimensional heterostructure
Authors: Kuo Teng-Fang , Tzolov Marian B. , Straus Daniel A. , Xu Jimmy
Published: May 2008

The properties of nanosize heterojunctions are of increasing interest as the trend of scaling down the size of electronic devices continues. We present here the direct growth of carbon nanotubes on a silicon substrate to form a heterodimensional heterojunction. Current-voltage measurements reveal the characteristics of a Schottky diode. However, a close examination of the data suggests that the device is limited in the forward bias direction by space charge limited current. In the reverse direction, it is functionally altered by the heterodimensionality of the junction and its associated enhancement of field emission.
Effect of oxygenation on the structural and dielectric properties of Sr1−xCaxTiO3 with 0.20⩽x⩽0.40
Authors: Anwar Shahid , Lalla N. P.
Published: May 2008

Effects of oxygenation on the structural and dielectric properties of Sr1−xCaxTiO3 (0.20⩽x⩽0.40) ceramics, prepared through solid-state reaction, have been studied employing x-ray diffraction, transmission electron microscopy, and temperature dependent dielectric permittivity measurements. It has been found that oxygenation has drastic effects on the ceramics’ dielectric properties, but their crystal structure remains least affected. The effect of oxygenation on the sharpening of the first order antiferroelectric phase transition has been studied.