bluuebunny/crossref_metadata_2025 huggingface dataset:
12 May 2008 M = 7.9 Wenchuan, China, earthquake calculated to increase failure stress and seismicity rate on three major fault systems
Authors: Toda Shinji , Lin Jian , Meghraoui Mustapha , Stein Ross S.
Published: September 2008

The Wenchuan earthquake on the Longmen Shan fault zone devastated cities of Sichuan, claiming at least 69,000 lives. We calculate that the earthquake also brought the Xianshuihe, Kunlun and Min Jiang faults 150–400 km from the mainshock rupture in the eastern Tibetan Plateau 0.2–0.5 bars closer to Coulomb failure. Because some portions of these stressed faults have not ruptured in more than a century, the earthquake could trigger or hasten additional M > 7 earthquakes, potentially subjecting regions from Kangding to Daofu and Maqin to Rangtag to strong shaking. We use the calculated stress changes and the observed background seismicity to forecast the rate and distribution of damaging shocks. The earthquake probability in the region is estimated to be 57–71% for M ≥ 6 shocks during the next decade, and 8–12% for M ≥ 7 shocks. These are up to twice the probabilities for the decade before the Wenchuan earthquake struck.
On the variability of ENSO at millennial timescales
Authors: Wang Geli , Tsonis Anastasios A.
Published: September 2008

We present an analysis of a proxy ENSO record spanning the last 11,000 years and we investigate its scaling properties. We find that the data exhibit positive long‐term correlations (persistence) which extend to timescales up to half a millennium. This will indicate that a given ENSO state (El Nino or La Nina) may dominate the tropical Pacific for centuries. This provides new information on ENSO dynamics and its worldwide effects and opens new questions as to the kinds of mechanisms are responsible for these long‐term correlations.
Evaluation of whistler mode chorus amplification during an injection event observed on CRRES
Authors: Li W. , Thorne R. M. , Meredith N. P. , Horne R. B. , Bortnik J. , Shprits Y. Y. , Ni B.
Published: September 2008

The excitation of nightside whistler mode chorus emissions in the low‐density region outside the plasmapause is investigated during an injection of plasma sheet electrons into the inner magnetosphere. CRRES data of the electron phase space density (PSD) over the LEPA energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution function of injected low‐energy electrons. The path‐integrated growth of chorus waves is then evaluated with the HOTRAY code by tracing unducted whistler mode chorus waves in a hot magnetized plasma. The results indicate that newly injected electrons are responsible for the intensification of lower‐band whistler mode chorus. However, slightly higher electron anisotropy than that obtained from the 5 min‐averaged electron PSD data is required to reproduce the observed wave intensity during an injection event. We suggest that the injected electron anisotropy is reduced due to pitch angle scattering by the enhanced chorus waves within the 5‐min interval over which the CRRES data are analyzed.
Meteor‐induced transient sporadic E as inferred from rapid‐run ionosonde observations at midlatitudes
Authors: Maruyama Takashi , Kato Hisao , Nakamura Maho
Published: September 2008

Observations were made with a rapid‐run ionosonde during a 1‐month period from the end of July to the end of August 2002 that included the Perseid meteor shower. Ionograms were obtained at 1‐minute intervals. All the echo traces below a virtual height of 200 km were hand‐scaled for detecting weak and broken traces as well as well‐determined sporadic E. Among the scaled E‐region traces, a distinct meteor echo persisting for 40 min was observed. This long‐duration meteor event was similar to that observed during the Leonid meteor shower in 2001. However the apparent height of the echo traces in the current event first decreased and then increased after equaling the height of a persistent sporadic E layer, while the apparent height of the long‐duration meteor echo trace observed in Leonids 2001 remained nearly constant. The descending rate of the meteor echo was approximately 22 m/s, which was considerably greater than that of the tidal ion layer trapped in a downward‐moving wind shear node. We ascribe the long‐duration meteor echo to a transient and horizontally drifting sporadic E patch generated from meteor trail plasma.
Comparison of small‐scale flux rope magnetic properties to large‐scale magnetic clouds: Evidence for reconnection across the HCS?
Authors: Cartwright M. L. , Moldwin M. B.
Published: September 2008

A newly developed semi‐automated routine to identify small‐scale symmetric force‐free flux ropes in the solar wind was used to search 11 years (1995–2005) of WIND magnetic field data. We identified 68 flux ropes whose durations range from 39 minutes up to 12.2 hours, with the distribution strongly peaked at an hour or less. These small‐scale flux ropes have strong core field signatures in total magnetic field coincident with bipolar field inflection consistent with a cylindrically symmetric flux rope model. They are predominately observed in the slow and moderate solar wind (<500 km s−1). They are observed to have a solar cycle occurrence variation with most small‐scale flux rope events found during solar minimum. This database of small‐scale flux ropes is compared to previously published small‐scale flux rope surveys and interplanetary coronal mass ejection (ICME)/magnetic cloud databases. The size distribution of flux ropes in the solar wind appears to be bimodal, with the majority of events having durations 4 hours or less where the magnetic cloud distribution peaks between 12 and 16 hours. The results suggest different source mechanisms for small and large‐scale flux ropes.
Differences between observed and a coupled simulation of North Atlantic sea surface currents and temperature
Authors: Molinari Robert L. , Garraffo Zulema , Snowden Derrick
Published: September 2008

North Atlantic sea surface temperature (SST) distributions derived from observations and a coupled model from NOAA's Geophysical Fluid Dynamics Laboratory, CM2.1, are compared to evaluate the model's ability to simulate recent (1900 to the present) oceanic surface characteristics. The North Atlantic focus will limit our analyses to spatial scales less than gyre, scales usually not addressed in previous model‐observation comparisons. Identifying model differences from observations at these scales will assist modelers in identifying problems to be considered and remedies to be applied. The properties compared are the mean annual SST, standard deviation, amplitude of the annual and semiannual harmonic, decadal meridional movements of the axis of the Gulf Stream, propagation of SST anomalies along the axis of the Gulf Stream, and 100‐year trends in SST records. Because of the dependence of SST on surface currents, observed flow from surface drifters and simulated flow from 15 m fields are also compared. The model simulates the large‐scale properties of all the variables compared. However, there are areas of differences in some variables that can be related to inadequacies in the simulated current fields. For example, the model Gulf Stream (GS) axis after separation from the western boundary is located some 100 km north of the observed axis, which contributes to an area of warmer simulated SSTs. The absence of a slope current in the same region that advects colder water from the Labrador Sea in the observations also contributes to this area of higher model SSTs. The model North Atlantic Current (NAC) is located to the east of the observed NAC contributing to a large area of SST discrepancy. The patterns of the amplitude of the annual harmonic are similar with maximum amplitude off the east coast of northern North America. The semiannual harmonic exhibits relatively large amplitudes (>1°C) north of about 55°N, a signal not found in the observations. In both the model and observations, a region of increased standard deviations encompasses the GS and NAC. The model simulates north‐south migrations of the GS core but at a longer period (20 years) than observed. The model does not simulate the SST anomalies that propagate along the observed GS and NAC. The model captures both the spatial and temporal characteristics of the Atlantic Multidecadal Oscillation. Both model and observations exhibit a dipole in trends, with positive trends in the subtropical Atlantic and negative trends in the subpolar gyre. The modeled region of negative trends is limited to the western subpolar Atlantic. The observed trends extend farther to the east.
Topographic effects on the solar semidiurnal surface tide simulated in a very fine resolution general circulation model
Authors: Hamilton Kevin , Ryan Steven C. , Ohfuchi Wataru
Published: September 2008

We present an examination of the solar tidal variation of surface pressure in integrations conducted with the Atmospheric GCM for the Earth Simulator (AFES) global general circulation model run at very fine resolution (roughly 10 km horizontal grid spacing and 96 numerical levels from the ground up to 0.1 hPa pressure). The basic features of the observed diurnal and semidiurnal surface pressure oscillations are reasonably well simulated by the model, although simulated amplitudes of the semidiurnal oscillation have an overall enhancement of about 25% over those observed, a deficiency which is reasonably attributed to the effects of the upper boundary condition in the model. The focus of our analysis is the local‐/regional‐scale modulation of the semidiurnal tidal oscillation in the tropics and subtropics associated with high and steep topography. The results show that the first‐order effect of high topography is a reduction in the semidiurnal pressure amplitude with surface elevation, a feature that is consistent with our understanding of the semidiurnal tide as a vertically propagating inertia‐gravity wave primarily excited in the ozone layer. We also find evidence in the model for systematically weak semidiurnal pressure amplitudes to the west of very high and steep topography, which is reasonably attributed to a shadowing effect of topography on the global‐scale westward propagating tide. Support for these effects is presented in our analysis of previously published station observations of the semidiurnal pressure oscillation. In addition, we present new determinations of the semidiurnal pressure oscillation based on barometric data from a special array of nine sensors established on the island of Hawaii, representing an unprecedented sampling of surface tides over a large range of elevations in a relatively small geographical region. The results of the AFES simulations agree quite well with these new detailed observations in Hawaii.
Cytoskeletal toxicity of pectenotoxins in hepatic cells
Authors: Espiña B , Louzao M C , Ares I R , Cagide E , Vieytes M R , Vega F V , Rubiolo J A , Miles C O , Suzuki T , Yasumoto T , Botana L M
Published: September 2008

Background and purpose.

Pectenotoxins are macrocyclic lactones found in dinoflagellates of the genusDinophysis, which induce severe liver damage in mice after i.p. injection. Here, we have looked for the mechanism(s) underlying this hepatotoxicity.

Experimental approach.

Effects of pectenotoxin (PTX)‐1, PTX‐2, PTX‐2 seco acid (PTX‐2SA) and PTX‐11 were measured in a hepatocyte cell line with cancer cell characteristics (Clone 9) and in primary cultures of rat hepatocytes. Cell morphology was assessed by confocal microscopy; F‐ and G‐actin were selectively stained and cell viability measured by Alamar Blue fluorescence.

Key results.

Clone 9 cells and primary hepatocytes showed a marked depolymerization of F‐actin with PTX‐1, PTX‐2 and PTX‐11 (1–1000 nM) associated with an increase in G‐actin level. However, morphology was only clearly altered in Clone 9 cells. PTX‐2SA had no effect on the actin cytoskeleton. Despite the potent F‐actin depolymerizing effect, PTX‐1, PTX‐2 or PTX‐11 did not decrease the viability of Clone 9 cells after 24‐h treatment. Only prolonged incubation (>48 h) with PTXs induced a fall in viability, and under these conditions, morphology of both Clone 9 and primary hepatocytes was drastically changed.

Conclusions and implications.

Although the actin cytoskeleton was clearly altered by PTX‐1, PTX‐2 and PTX‐11 in the hepatocyte cell line and primary hepatocytes, morphological assessments indicated a higher sensitivity of the cancer‐like cell line to these toxins. However, viability of both cell types was not altered.

British Journal of Pharmacology(2008)155, 934–944; doi:10.1038/bjp.2008.323; published online 8 September 2008
Viral vectors: from virology to transgene expression
Authors: Bouard D , Alazard‐Dany N , Cosset F‐L
Published: September 2008

In the late 1970s, it was predicted that gene therapy would be applied to humans within a decade. However, despite some success, gene therapy has still not become a routine practise in medicine. In this review, we will examine the problems, both experimental and clinical, associated with the use of viral material for transgenic insertion. We shall also discuss the development of viral vectors involving the most important vector types derived from retroviruses, adenoviruses, herpes simplex viruses and adeno‐associated viruses.

This article is part of a themed section on Vector Design and Drug Delivery. For a list of all articles in this section see the end of this paper, or visit: http://www3.interscience.wiley.com/journal/121548564/issueyear?year=2009
STRING and STITCH: known and predicted interactions between proteins and chemicals
Authors: Jensen Lars , Kuhn Michael , Stark Manuel , Chaffron Samuel , von Mering Christian , Bork Peer
Published: September 2008

Information on protein-protein and protein-chemical interactions is essential for understanding cellular functions. The STRING and STITCH web resources integrate interaction evidence derived from pathways, automatic literature mining, primary experimental data, and genomic context. The resulting interaction networks cover 1.5 million proteins from 373 organisms and 68,000 chemicals.
Stability of a pair of co-rotating vortices with axial flow
Authors: Roy Clément , Schaeffer Nathanaël , Le Dizès Stéphane , Thompson Mark
Published: September 2008

The three-dimensional linear temporal stability properties of a flow composed of two corotating q-vortices (also called Batchelor vortices) are predicted by numerical stability analysis. As for the corresponding counter-rotating case, when the axial flow parameter is increased, different instability modes are observed and identified as a combination of resonant Kelvin modes of azimuthal wavenumbers m and m+2 within each vortex. In particular, we show that the sinuous mode, which is the dominant instability mode without axial flow, is stabilized in the presence of a moderate axial flow. Different types of mode with a large amplitude in the critical layer are also identified. For small separation distances (above the merging threshold), unstable eigenmodes, corresponding to axial wavenumbers that cannot be easily identified with simple resonant interactions of Kelvin modes, are also observed. Their growth rate is a substantial fraction of the growth rates of low-order resonant modes. The effects of the Reynolds number and vortex separation distance on the growth rate parameter map are considered. Finally, we analyze the similarities and differences between the stability characteristics of co- and counter-rotating vortex pairs.
Photoconductive response correction for detectors of terahertz radiation
Authors: Castro-Camus E. , Fu L. , Lloyd-Hughes J. , Tan H. H. , Jagadish C. , Johnston M. B.
Published: September 2008

Photoconductive detectors are convenient devices for detecting pulsed terahertz radiation. We have optimized Fe+ ion-damaged InP materials for photoconductive detector signal to noise performance using dual-energy doses in the range from 2.5×1012 to 1.0×1016 cm−2. Ion implantation allowed the production of semiconducting materials with free-carrier lifetimes between 0.5 and 2.1 ps, which were measured by optical pump terahertz probe spectroscopy. The time resolved photoconductivity of the detector substrates was acquired as a function of time after excitation by 2 nJ pulses from a laser oscillator. These data, when combined with a deconvolution algorithm, provide an excellent spectral response correction to the raw photocurrent signal recorded by the photoconductive detectors.
Columnar mesophases of hexabenzocoronene derivatives. II. Charge carrier mobility
Authors: Kirkpatrick James , Marcon Valentina , Kremer Kurt , Nelson Jenny , Andrienko Denis
Published: September 2008

Combining atomistic molecular dynamic simulations, Marcus–Hush theory description of charge transport rates, and master equation description of charge dynamics, we correlate the temperature-driven change of the mesophase structure with the change of charge carrier mobilities in columnar phases of hexabenzocoronene derivatives. The time dependence of fluctuations in transfer integrals shows that static disorder is predominant in determining charge transport characteristics. Both site energies and transfer integrals are distributed because of disorder in the molecular arrangement. It is shown that the contributions to the site energies from polarization and electrostatic effects are of opposite sign for positive charges. We look at three mesophases of hexabenzocoronene: herringbone, discotic, and columnar disordered. All results are compared to time resolved microwave conductivity data and show excellent agreement with no fitting parameters.
Solvent smectic order parameters from solute nematic order parameters
Authors: Celebre Giorgio , Cinacchi Giorgio , De Luca Giuseppina
Published: September 2008

In liquid crystals, while the second and fourth rank orientational order parameters characterizing a nematic phase can be experimentally determined via several techniques, there is no straightforward experiment rendering the positional order parameters characterizing a smectic A phase. This work illustrates a novel method to estimate the positional order parameters of a smectogenic liquid crystal solvent from knowledge of the orientational order parameters of a number of solutes dissolved therein. The latter order parameters can be experimentally determined via liquid crystal NMR spectroscopy. These data can be then analyzed with a statistical-thermodynamic density functional theory, whose basic ingredient is a model for solute-solvent intermolecular interactions. Its parametrization and the subsequent fitting procedure eventually permit one to obtain the positional order parameters of the solvent besides the positional-orientational distribution function of the solutes. The method is applied to the smectogen 4,4′-di-n-heptyl-azoxybenzene, in which the solutes 1,4-dichlorobenzene and naphthalene have been dissolved. With the help of this exploratory practical example, pros and cons of the method are pointed out and further developments prospected.
An excited state ab initio and multidimensional Franck–Condon analysis of the A B12←X A11 band system of fluorobenzene
Authors: Pugliesi Igor , Tonge Nicola M. , Cockett Martin C. R.
Published: September 2008

This work combines high level ab initio calculations with multidimensional Franck–Condon calculations to refine and augment previous assignments of the lower wavenumber region of the A B12←X A11 band system of fluorobenzene. The strength of the assignment has been greatly assisted by the use of zero electron kinetic energy spectroscopy in a series of pump-probe experiments where the response of the molecule to selective excitation in specific modes prior to ionization has been studied. The net result of this analysis is the reassignment of 7 of the 12 previously assigned bands in the region below about 1000 cm−1 using a strategy that aims to trace the origins of excited state normal modes of fluorobenzene to the well-known Wilson modes of benzene by taking full account of the Duschinsky mixing that accompanies electronic excitation. Duschinsky normal mode analyses of the ground and first excited states of fluorobenzene as well as the electronic ground state of fluorobenzene cation have shown that the common use of the benzene Wilson notation to describe normal modes of this prototypical benzene derivative is highly questionable, particularly following electronic excitation and ionization.
Water uptake coefficients and deliquescence of NaCl nanoparticles at atmospheric relative humidities from molecular dynamics simulations
Authors: Bahadur Ranjit , Russell Lynn M.
Published: September 2008

Deliquescence properties of sodium chloride are size dependent for particles smaller than 100 nm. Molecular dynamics (MD) simulations are used to determine deliquescence relative humidity (DRH) for particles in this size range by modeling idealized particles in contact with humid air. Constant humidity conditions are simulated by inclusion of a liquid reservoir of NaCl solution in contact with the vapor phase, which acts as a source of water molecules as uptake by the nanoparticle proceeds. DRH is bounded between the minimum humidity at which sustained water accumulation is observed at the particle surface and the maximum humidity at which water accumulation is not observed. Complete formation of a liquid layer is not observed due to computational limitations. The DRH determined increases with decreasing particle diameter, rising to between 91% and 93% for a 2.2 nm particle and between 81% and 85% for an 11 nm particle, higher than the 75% expected for particles larger than 100 nm. The simulated size dependence of DRH agrees well with predictions from bulk thermodynamic models and appears to converge with measurements for sizes larger than 10 nm. Complete deliquescence of nanoparticles in the 2–11 nm size range requires between 1 and 100 μs, exceeding the available computational resources for this study. Water uptake coefficients are near 0.1 with a negligible contribution from diffusion effects. Planar uptake coefficients decrease from 0.41 to 0.09 with increasing fractional water coverage from 0.002 to 1, showing a linear dependence on the logarithm of the coverage fraction with a slope of −0.08±0.01 (representing the effect of solvation). Particle uptake coefficients increase from 0.13 at 11 nm to 0.65 at 2.2 nm, showing a linear dependence on the logarithm of the edge fraction (which is a function of diameter) with a slope of 0.74±0.04 (representing larger edge effects in smaller particles).
Nanofabricated adjustable multicontact devices on membranes
Authors: Waitz Reimar , Schecker Olivier , Scheer Elke
Published: September 2008

Adjustable atomic size contacts realized by break junctions have become a standard tool during the last decade. Although nanofabricated break junctions may in principle be incorporated onto complex electronic circuits, a fundamental drawback of the standard break junction technique is its limitation to a single adjustable junction per device. We have fabricated single break junctions as well as devices containing two break junctions on a silicon membrane. The junctions are adjusted by positioning a fine tip via piezocontrol on the rear side of the membrane. We describe the fabrication process of the membranes and the devices and present results obtained on circuits made of gold and platinum. We show that the junctions can be addressed independently by a suitable choice of the tip position. Single-atom contacts, vacuum tunneling contacts as well as larger contacts can be stabilized.
Attraction between negatively charged surfaces mediated by spherical counterions with quadrupolar charge distribution
Authors: Urbanija Jasna , Bohinc Klemen , Bellen Alfredo , Maset Stefano , Iglič Aleš , Kralj-Iglič Veronika , Sunil Kumar P. B.
Published: September 2008

We observed monoclonal antibody mediated coalescence of negatively charged giant unilamellar phospholipid vesicles upon close approach of the vesicles. This feature is described, using a mean field density functional theory and Monte Carlo simulations, as that of two interacting flat electrical double layers. Antibodies are considered as spherical counterions of finite dimensions with two equal effective charges spatially separated by a fixed distance l inside it. We calculate the equilibrium configuration of the system by minimizing the free energy. The results obtained by solving the integrodifferential equation and by performing the Monte Carlo simulation are in excellent agreement. For high enough charge densities of the interacting surfaces and large enough l, we obtain within a mean field approach an attractive interaction between like-charged surfaces originating from orientational ordering of quadrupolar counterions. As expected, the interaction between surfaces turns repulsive as the distance between charges is reduced.
Limit curve theorems in Lorentzian geometry
Authors: Minguzzi E.
Published: September 2008

The subject of limit curve theorems in Lorentzian geometry is reviewed. A general limit curve theorem is formulated, which includes the case of converging curves with endpoints and the case in which the limit points assigned since the beginning are one, two, or at most denumerable. Some applications are considered. It is proved that in chronological spacetimes, strong causality is either everywhere verified or everywhere violated on maximizing lightlike segments with open domain. As a consequence, if in a chronological spacetime two distinct lightlike lines intersect each other then strong causality holds at their points. Finally, it is proved that two distinct components of the chronology violating set have disjoint closures or there is a lightlike line passing through each point of the intersection of the corresponding boundaries.
Variable optical delays at 1.55 μm using fast light in an InAs/InP quantum dash based semiconductor optical amplifier
Authors: Martinez A. , Aubin G. , Lelarge F. , Brenot R. , Landreau J. , Ramdane A.
Published: September 2008

Room temperature optical variable delays are demonstrated using InAs/InP quantum dash semiconductor optical amplifiers (SOAs) at 1.55 μm. A microwave frequency modulated single optical beam allows to demonstrate fast light through the achievement of maximum optical delays of 136 ps at 250 MHz and ∼55 ps at 2 GHz by means of electrical control of the SOA bias current. The group index variation is attributed to enhanced nearly degenerate four wave mixing of this material system as well as population pulsation.
Quantum dots embedded into silicon nanowires effectively partition electron confinement
Authors: Avramov Pavel V. , Fedorov Dmitri G. , Sorokin Pavel B. , Chernozatonskii Leonid A. , Ovchinnikov Sergei G.
Published: September 2008

Motivated by the experimental discovery of branched silicon nanowires, we performed theoretical electronic structure calculations of icosahedral silicon quantum dots embedded into pentagonal silicon nanowires. Using the semiempirical method, we studied the quantum confinement effect in the fully optimized embedded structures. It was found that (a) the band gaps of the embedded structures are closely related to the linear sizes of the longest constituting part rather than to the total linear dimension and (b) the discovered atypical quantum confinement with a plateau and a maximum can be attributed to the substantial interactions of near Fermi level electronic states of the quantum dots and nanowire segments.
Effect of polarity on the growth of InN films by metalorganic chemical vapor deposition
Authors: Jain Abhishek , Weng Xiaojun , Raghavan Srinivasan , VanMil Brenda L. , Myers Thomas , Redwing Joan M.
Published: September 2008

The effect of surface polarity on InN growth on GaN by metalorganic chemical vapor deposition (MOCVD) was investigated. The polarity of the InN was found to follow that of the initial GaN template as determined by a comparison of experimental and simulated convergent beam electron diffraction patterns. Under identical MOCVD growth conditions, In-polar InN was observed to nucleate and grow on Ga-polar GaN as pyramidal-shaped islands with (101¯1) as the stable surface facet. In contrast, enhanced lateral growth and reduced surface roughness were observed for N-polar InN grown on N-polar GaN. InN films grown on (0001) sapphire substrates using a thin AlN buffer under identical conditions to those used for growth on the GaN templates also exhibited reduced surface roughnesses and were determined to be N polar. A qualitative model based on the difference in surface terminations and crystal structures is proposed to explain the observed differences in the structural properties and growth modes of the In-polar and N-polar InN films.
Role of initial surface roughness on ion induced surface morphology
Authors: Karmakar P. , Mollick S. A. , Ghose D. , Chakrabarti A.
Published: September 2008

We report here the influence of initial surface roughness on the development of ion induced Si surface morphology. Surfaces of different initial roughness have been generated chemically and bombarded by 16.7keV O2+ ions at an oblique angle. It is observed that surface roughness enhances the initial perturbation, which aids to form the ion induced regular nanostructures at an ion fluence typically one to two orders of magnitude less than that are required to produce the same structures on an initially flat surface. This observation also explores the role of initial surface perturbation on the initiation of curvature dependent sputtering.
History force on an asymmetrically rotating body in Poiseuille flow inducing particle migration across a slit pore
Authors: Bhattacharya Sukalyan
Published: September 2008

Experimental evidence shows that suspended particles preferentially migrate away from confining boundaries due to the effect of a shear flow. In this paper, we consider an asymmetric particle in Poiseuille flow and determine an inertial lift force which can contribute to the particle migration. Under the influence of Poiseuille flow in a slit pore, an arbitrary particle undergoes periodic rotation which is described by Jeffery’s orbit [G. Jeffery, Proc. R. Soc. London, Ser. A 102, 161 (1922)]. In the absence of rotational symmetry, a rotating particle produces an unsteady scattered field. The fluid inertia due to the unsteadiness causes an inertial force on the rotating body if the Reynolds number Re and the temporal variation in viscous force on the particle are nonzero. The resulting effect of this force on the particle migration can be significant especially for microfluidic systems, where gravitational contribution is negligible. In this paper, we consider two systems where the Reynolds number is assumed to be small but finite. In the first problem, we analyze the inertial force on a body asymmetrically rotating around its fixed center. In the second case, we focus on a freely suspended heavy particle which is considerably denser than the solvent so that the product of Re and the particle-solvent density ratio is greater than unity. For both systems, the Reynolds number and the temporal variation in viscous force are significant enough to produce a considerable inertial force on the particle. Our results indicate that the mean of this inertial component perpendicular to the boundaries is nonzero and acts in the direction away from the wall. The magnitude of this force is relatively larger near the wall and gradually decays as the particle-wall distance increases. Hence, we conclude that the discussed effect influences the preferential particle migration in conjunction with other factors.
Laser wavelength dependence of extreme ultraviolet light and particle emissions from laser-produced lithium plasmas
Authors: Nagano Akihisa , Mochizuki Takayasu , Miyamoto Shuji , Amano Sho
Published: September 2008

Maximum extreme ultraviolet (EUV) conversion efficiencies (CEs) of 2.3% and 1.8% were achieved in planar Li targets by using pulsed 2ω and 1ω Nd:YAG laser irradiation, respectively. In a forced recombination scheme, the total CE can be expected to be about 4%. The maximum kinetic energy of the lithium ion debris was found to be less than 1 keV, indicating that mirror damage caused by lithium ion debris is more easily mitigated by using a magnetic field than for tin ions. These results suggest that a Li target is a reasonable candidate for an EUV lithography source.
A study of H and D doped ZnO epitaxial films grown by pulsed laser deposition
Authors: Li Y. J. , Kaspar T. C. , Droubay T. C. , Joly A. G. , Nachimuthu P. , Zhu Z. , Shutthanandan V. , Chambers S. A.
Published: September 2008

We examine the crystal structure and electrical and optical properties of ZnO epitaxial films grown by pulsed laser deposition in a H2 or D2 ambient. n-type electrical conductivity is enhanced by three orders of magnitude as a result of growing in H2 (D2) compared to ZnO films grown in O2. Hall effect measurements reveal very small carrier activation energies and carrier concentrations in the mid-1018 cm−3 range. Optical absorption measurements show that the enhanced conductivity is not a result of ZnO reduction and interstitial Zn formation. Photoluminescence spectra suggest excitonic emission associated with exciton-hydrogen donor complex formation and show no evidence for midgap emission resulting from defects. We have modeled the transport properties of H (D) doped ZnO films using variable range hopping and surface layer conductivity models, but our data do not fit well with these models. Rather, it appears that growth in H2 (D2) promotes the formation of an exceedingly shallow donor state not seen in ZnO crystals annealed in H2 after growth. This new state may be associated with H (D) substitution at O sites in the lattice.
Potential energy surface for interactions between two hydrogen molecules
Authors: Patkowski Konrad , Cencek Wojciech , Jankowski Piotr , Szalewicz Krzysztof , Mehl James B. , Garberoglio Giovanni , Harvey Allan H.
Published: September 2008

Nonrelativistic clamped-nuclei energies of interaction between two ground-state hydrogen molecules with intramolecular distances fixed at their average value in the lowest rovibrational state have been computed. The calculations applied the supermolecular coupled-cluster method with single, double, and noniterative triple excitations [CCSD(T)] and very large orbital basis sets—up to augmented quintuple zeta size supplemented with bond functions. The same basis sets were used in symmetry-adapted perturbation theory calculations performed mainly for larger separations to provide an independent check of the supermolecular approach. The contributions beyond CCSD(T) were computed using the full configuration interaction method and basis sets up to augmented triple zeta plus midbond size. All the calculations were followed by extrapolations to complete basis set limits. For two representative points, calculations were also performed using basis sets with the cardinal number increased by one or two. For the same two points, we have also solved the Schrödinger equation directly using four-electron explicitly correlated Gaussian (ECG) functions. These additional calculations allowed us to estimate the uncertainty in the interaction energies used to fit the potential to be about 0.15 K or 0.3% at the minimum of the potential well. This accuracy is about an order of magnitude better than that achieved by earlier potentials for this system. For a near-minimum T-shaped configuration with the center-of-mass distance R=6.4 bohrs, the ECG calculations give the interaction energy of −56.91±0.06 K, whereas the orbital calculations in the basis set used for all the points give −56.96±0.16 K. The computed points were fitted by an analytic four-dimensional potential function. The uncertainties in the fit relative to the ab initio energies are almost always smaller than the estimated uncertainty in the latter energies. The global minimum of the fit is −57.12 K for the T-shaped configuration at R=6.34 bohrs. The fit was applied to compute the second virial coefficient using a path-integral Monte Carlo approach. The achieved agreement with experiment is substantially better than in any previous work.
Resistance switching and retention behaviors in polycrystalline La-doped SrTiO3 ceramics chip devices
Authors: Hirose Sakyo , Nakayama Akinori , Niimi Hideaki , Kageyama Keisuke , Takagi Hiroshi
Published: September 2008

Resistance switching and retention behaviors in polycrystalline La-doped SrTiO3 ceramics have been investigated. La-doped SrTiO3 ceramics exhibits resistance switching as large as that of thin-film devices and exhibits a long-term memory effect of over 5 h. By means of a complex impedance analysis, it was clarified that these resistance changes can be reasonably attributed to the change in the electrical potential barrier at the interfaces and the resistance of the grain boundary changes remarkably by the application of voltage pulses. From the resistance retention properties at various temperatures, it was found that the high-resistance state is very stable even at 125 °C, whereas the resistance in the low-resistance state increases with time and its relaxation speed becomes remarkably faster with increasing temperatures. These results imply that the migration of the point defects could change the distribution of the space charge near the interface, resulting in a change in the interface resistances.
Direct spectral evidence of single-axis rotation and ortho-hydrogen-assisted nuclear spin conversion of CH3F in solid para-hydrogen
Authors: Lee Yuan-Pern , Wu Yu-Jong , Hougen Jon T.
Published: September 2008

Observation of two weak absorption lines from the E (K=1) level and one intense feature from A (K=0) for degenerate modes ν4 and ν6 of CH3F provides direct spectral evidence that CH3F isolated in p-H2 rotates about only its symmetry axis, and not about the other two axes. An interaction between A and E vibrational levels caused by the partially hindered spinning rotation is proposed. Conversion of nuclear spin between A and E components of CH3F is rapid when p-H2 contains some o-H2, but becomes slow when the proportion of o-H2 is much decreased.
Selective transport of ballistic phonon modes by an acoustic nanocavity in a Ψ-shaped semiconductor nanowire
Authors: Huang Wei-Qing , Yi Dan-Qing , Huang Bai-Yun , Wang Ming-Pu , Huang Gui-Fang , Wang Ling-Ling
Published: September 2008

We study theoretically ballistic phonon transport in a Ψ-shaped semiconductor nanowire at low temperatures. When ballistic acoustic phonons propagate through the nanowire, the region connecting the left lead and the three right leads of the nanowire acts as a cavity. Acoustic waves interfere with each other in the nanocavity to form standing waves with particular wavelengths due to multiple reflection by the boundaries of the cavity. Owing to the presence of the split cavity, different phonon modes are found to transport selectively into different channels, and phonon heat can be dissipated through different channels by properly tuning the parameters of the structure. This structure may be a promising split device for the ballistic phonon modes and control the phonon heat transport in nanophononics.
Transformation from molecular to polymeric nitrogen at high pressures and temperatures: In situ x-ray diffraction study
Authors: Trojan I. A. , Eremets M. I. , Medvedev S. A. , Gavriliuk A. G. , Prakapenka V. B.
Published: September 2008

We studied the mechanism of the structural transformation of molecular nitrogen to atomic single-bonded nitrogen with a cubic gauche (cg-N) crystal structure using x-ray diffraction in situ at a pressure of ∼140 GPa and temperatures up to 2000 K in a diamond anvil cell. The anvils, with a toroidal shape, allowed us to drastically increase the volume of the sample, reduce the acquisition time of the diffraction pattern, and improve the quality of the Raman spectra. Molecular nitrogen transforms to the cg-N phase through an intermediate disordered state. The Raman spectra are in good agreement with recent theoretical calculations.
Finite representations of continuum environments
Authors: Zwolak Michael
Published: September 2008

Understanding dissipative and decohering processes is fundamental to the study of quantum systems. An accurate and generic method for investigating these processes is to simulate both the system and environment, which, however, is computationally very demanding. We develop a novel approach to constructing finite representations of the environment based on the influence of different frequency scales on the system’s dynamics. As an illustration, we analyze a solvable model of an optical mode decaying into a reservoir. The influence of the environment modes is constant for small frequencies, but drops off rapidly for large frequencies, allowing for a very sparse representation at high frequencies that gives a significant computational speedup in simulating the environment. This approach provides a general framework for simulating open quantum systems.
A 0.2–0.5THz single-band heterodyne receiver based on a photonic local oscillator and a superconductor-insulator-superconductor mixer
Authors: Kohjiro Satoshi , Kikuchi Kenichi , Maezawa Masaaki , Furuta Tomofumi , Wakatsuki Atsushi , Ito Hiroshi , Shimizu Naofumi , Nagatsuma Tadao , Kado Yuichi
Published: September 2008

We have demonstrated that a superconductor-insulator-superconductor (SIS) mixer pumped by a photonic local oscillator (LO) covers the whole frequency range of 0.2–0.5THz. In the bandwidth of 74% of the center frequency, this single-band receiver exhibits noise temperature of TRX⩽20hf∕kB, where h is Planck’s constant, f is the frequency, and kB is Boltzmann’s constant. Resultant TRX is almost equal to TRX of the identical SIS mixer pumped by three conventional frequency-multiplier-based LOs which share the 0.2–0.5THz band. This technique will contribute to simple, wide-band, and low-noise heterodyne receivers in the terahertz region.
Multistep relaxation in equilibrium polymer solutions: A minimal model of relaxation in “complex” fluids
Authors: Stukalin Evgeny B. , Douglas Jack F. , Freed Karl F.
Published: September 2008

We examine the rheological and dielectric properties of solutions of equilibrium self-assembling particles and molecules that form polydisperse chains whose average length depends on temperature and concentration (free association model). Relaxation of the self-assembling clusters proceeds by motions associated either with cluster rotations, with diffusive internal chain dynamics, or with interchain entanglement interactions. A hierarchy of models is used to emphasize different physical effects: Unentangled rodlike clusters, unentangled flexible polymers, and entangled chains. All models yield a multistep relaxation for low polymer scission rates (“persistent polymers”). The short time relaxation is nearly exponential and is dominated by the monomeric species and solvent, and the long time relaxation is approximately a stretched exponential, exp[−(t/τ)β], a behavior that arises from an averaging over the equilibrium chain length distribution and the internal relaxation modes of the assembled structures. Relaxation functions indicate a bifurcation of the relaxation function into fast and slow contributions upon passing through the polymerization transition. The apparent activation energy for the long time relaxation becomes temperature dependent, while the fast monomeric relaxation process remains Arrhenius. The effective exponent β(T), describing the long time relaxation process, varies monotonically from near unity above the polymerization temperature to a low temperature limit, β≃13, when the self-assembly process is complete. The variation in the relaxation function with temperature is represented as a function of molecular parameters, such as the average chain length, friction coefficient, solvent viscosity, and the reaction rates for particle association and dissociation.
Silver diffusion bonding and layer transfer of lithium niobate to silicon
Authors: Diest Kenneth , Archer Melissa J. , Dionne Jennifer A. , Park Young-Bae , Czubakowski Matthew J. , Atwater Harry A.
Published: September 2008

A diffusion bonding method has been developed that enables layer transfer of single crystal lithium niobate thin films to silicon substrates. A silver film was deposited onto both the silicon and lithium niobate surfaces prior to bonding, and upon heating, a diffusion bond was formed. Transmission electron microscopy confirms the interface evolution via diffusion bonding which combines interfacial diffusion, power law creep, and growth of (111) silver grains to replace the as-bonded interface by a single polycrystalline silver film. The transferred film composition was the same as bulk lithium niobate.
Polarizability evolution on natural and artificial low dimensional binary semiconductor systems: A case study of stoichiometric aluminum phosphide semiconductor clusters
Authors: Karamanis Panaghiotis , Xenides Demetrios , Leszczynski Jerzy
Published: September 2008

The dependences of the static dipole polarizabilities per atom (PPAs) on the bonding and shape of selected stoichiometric aluminum phosphide clusters (ground states and higher lying species) of small and medium sizes have been comprehensively studied at Hartree–Fock and the second order Møller–Plesset perturbation levels of theory. It is shown that the nonmonotonic size variations in the mean PPAs of AlP species which maintain closed cagelike structures, frequently observed in clusters, are directly related to covalent homoatomic bonds inside each cluster's framework. Accordingly, the PPAs of clusters which are characterized by one or more bonds between the Al and P atoms are larger than the PPAs of clusters with the uniform alternating Al–P bond matrix. This is caused by the electron transfer increase from the electropositive Al to the electronegative P atom with the cluster growth. This transfer is larger for the clusters characterized by alternating Al–P bonding. The later effect explains the decrease in the PPA of AlP species which maintain closed cage-like structures, with the cluster growth. However, this picture drastically changes for artificial metastable prolate species built up by the ground states of smaller clusters. It is demonstrated that for prolate binary AlP clusters of medium size, the shape dominates against any other structural or bonding factor, forcing the PPA to increase with the cluster size. Nonetheless, as the cluster size grows, it is predicted that the PPAs of the studied prolate clusters will saturate eventually with the cluster size. Also, it is verified that the theoretical predicted polarizabilities of AlP semiconductor clusters are larger than the bulk polarizability in accord with other theoretical predictions for similar systems. Lastly, it is pointed out that major bonding or structural changes should take place in order the convergence with the bulk polarizability to be accomplished since it is revealed that the size increase is a necessary but not a sufficient factor for the cluster to bulk transition.
Electrophoresis system for high temperature mobility measurements of nanosize particles
Authors: Rodriguez-Santiago Victor , Fedkin Mark V. , Lvov Serguei N.
Published: September 2008

The electrophoretic mobility, which reflects the zeta potential of a solid material, is an important experimental quantity providing information about the electrical double layer at the solid/liquid interface. A new high temperature electrophoresis cell was developed suitable for electrophoretic mobility measurements of dispersed nanosize particles up to 150 °C and 40 bars. Amorphous silica (SiO2) particle size standards were used to test the particle size detection limit of the new instrument at 25, 100, and 150 °C and several pH values. The microscopic detection of the particles was enabled by dark-field illumination, which allowed extending the previously available capabilities and provided higher accuracy of the electrophoretic mobility data. The electrophoretic mobility measurements for SiO2 at temperatures above 100 °C were reported for the first time and indicated a gradual increase in particle electrophoretic response with increasing temperature. The obtained data indicated negatively charged SiO2 surface throughout the pH and temperature ranges studied.