bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative timing of substorm processes as derived from multifluid/multiscale simulations: Internally driven substorms
Authors: Winglee R. M. , Harnett E. , Kidder A.
Published: September 2009

The role of tail reconnection in initiating substorm onset remains highly controversial. Multifluid/multiscale simulations are used to examine this problem with the unique capability of being able to resolve ion skin depth and ion cyclotron processes within a very thin tail current sheet within a global magnetosphere. It is shown that, consistent with the near‐Earth neutral line model, a thin current sheet forms during the growth phase with the eventual formation of an X line and the ejection of a plasmoid. However, these processes do not produce substorm onset but are precursors to onset. The modeling indicates that in the wake of the plasmoid, a Y line forms within which there is the intermittent generation of flux ropes that can propagate either earthward or tailward with equal probability. The intensity and size of the flux ropes are seen to increase in time up to substorm onset. Depending on the size of the earthward moving flux rope, pseudobreakup or substorm onset occurs when the energy within the earthward moving flux rope is dissipated against the inner edge of the plasma sheet. This interaction leads to rapid (1 min) dipolarization, magnetospheric injection of energetic particles, and intensification of the nightside auroral currents that expand in local time and to higher latitudes. These processes are consistent with the current disruption model where onset occurs as a direct consequence of processes occurring at the inner edge of the plasma sheet. Ionospheric outflows and their energization with the thin current sheet play important roles in the buildup of energy in the plasma sheet that eventually produces substorm onset and drives breakup.
An updated Antarctic melt record through 2009 and its linkages to high‐latitude and tropical climate variability
Authors: Tedesco Marco , Monaghan Andrew J.
Published: September 2009

A 30‐year minimum Antarctic snowmelt record occurred during austral summer 2008–2009 according to spaceborne microwave observations for 1980–2009. Strong positive phases of both the El‐Niño Southern Oscillation (ENSO) and the Southern Hemisphere Annular Mode (SAM) were recorded during the months leading up to and including the 2008–2009 melt season. The 30‐year record confirms that significant negative correlations exist at regional and continental scales between austral summer melting and both the ENSO and SAM indices for October–January. In particular, the strongest negative melting anomalies (such as those in 2008 and 2009) are related to amplified large‐scale atmospheric forcing when both the SAM and ENSO are in positive phases. Our results suggest that enhanced snowmelt is likely to occur if recent positive summer SAM trends subside in conjunction with the projected recovery of stratospheric ozone levels, with subsequent impacts on ice sheet mass balance and sea level trends.
Dispersion inversion of electromagnetic pulse propagation within freezing and thawing soil waveguides
Authors: van der Kruk J. , Steelman C. M. , Endres A. L. , Vereecken H.
Published: September 2009

Freeze and thaw processes are important components in characterizing glacial, periglacial and frozen ground environments, and hence the response of cryospheric regions to climate change. High‐frequency ground‐penetrating radar is particularly well suited for monitoring the freezing and thawing processes within the shallow subsurface (i.e., < 1 m depth) due to its non‐invasive nature and its sensitivity to the liquid water component in soil. The freezing of moist soil and thawing of frozen soil induce leaky and low‐velocity waveguides, respectively. Within these waveguide layers, the internally reflected radar energy produces interfering multiples that appear as a package of dispersed waves. Here, we present a new method for characterizing very shallow freeze and thaw processes, in which the waveguide properties are obtained by inverting the observed dispersion curves. This new method can non‐invasively monitor freezing and thawing processes in a wide range of glacial, periglacial and frozen ground studies.
Observational relationship of climatologic beta drift with large‐scale environmental flows
Authors: Zhao Haikun , Wu Liguang , Zhou Weican
Published: September 2009

While many numerical studies suggested that large‐scale environmental flows significantly affect beta drift, this influence was not verified observationally and included in assessing changes of tropical cyclone (TC) tracks under the background of global warming. This study investigates the influence of large‐scale environmental flow on climatologic beta drift in the northern West Pacific using the best track dataset from Joint Typhoon Warming Center (JTWC) and the NCEP monthly reanalysis over the period from 1965 to 2007. Consistent with most previous numerical studies, the meridional shear of zonal wind, vertical shear of zonal wind and meridional gradient of relative vorticity, which are mainly associated with the zonal environmental wind, play an important role in affecting beta drift. For the meridional shear of zonal flows, the northward beta drift in an anticyclonic shear is faster than that in a cyclonic shear. A poleward (equatorward) gradient of relative vorticity leads to faster (slower) westward beta drift than in a resting environment. TCs tend to move to the left of the vector of vertical wind shear.
Divergence in seasonal hydrology across northern Eurasia: Emerging trends and water cycle linkages
Authors: Rawlins M. A. , Ye H. , Yang D. , Shiklomanov A. , McDonald K. C.
Published: September 2009

Discharge from large Eurasia rivers increased during the 20th century, yet much remains unknown regarding details of this increasing freshwater flux. Here, for the three largest Eurasian basins (the Ob, Yenisei, and Lena) we examine the nature of annual and seasonal discharge trends by investigating the flow changes along with those for precipitation, snow depth, and snow water equivalent. On the basis of a multiperiod trend analysis and examination of station data, we propose two characteristic regimes to explain the long‐term discharge increase from these large Eurasian rivers. Over the early decades from approximately 1936 to 1965, annual precipitation correlates well with annual discharge, and positive discharge trends are concurrent with summer/fall discharge increases. The latter decades were marked by a divergence between winter/spring flows, which increased, amid summer/fall discharge declines. A comparison of cold season precipitation (CSP) and spring discharge trends across subbasins of the Ob, Yenisei, and Lena shows limited agreement with one precipitation data set but good agreement (R2 > 0.90) when a second is used. While natural variability in the Arctic system tends to mask these emerging trends, spatial and temporal changes can generally be characterized by increased solid precipitation, primarily to the north, along with a drier hydrography during the warm season.
SEAES‐GEO: A spacecraft environmental anomalies expert system for geosynchronous orbit
Authors: O'Brien T. P.
Published: September 2009

Indications of the space environment hazard at any point in space and time along geosynchronous orbit (GEO) can be obtained using the set of rules described in this paper. These rules are implemented using real‐time Geostationary Operational Environmental Satellite particle sensor data and the magnetic index Kp. These rules should be useful for both real‐time and posthoc analysis of GEO spacecraft anomalies. The hazards covered are surface charging, internal charging, single‐event effects due to solar particle events, and total dose (solar arrays). The system provides a “hazard quotient,” the ratio of the instantaneous to mission‐averaged likelihood of an anomaly due to each hazard, based on environmental measurements. With the exception of total dose, the hazard quotients are derived from lists of on‐orbit anomalies or their proxies, and it is assumed that the probability of future anomalies will share the same functional dependence on the environment exhibited by the anomalies in the lists. Hazard quotients are potentially more valuable to satellite operators than are raw measurements, as hazard quotients directly convey the statistical relationship between the radiation environment and the likelihood of an anomaly.
Imaging of Hypoxic–Ischemic Penumbra with 18F-fluoromisonidazole PET/CT and Measurement of Related Cerebral Metabolism in Aneurysmal Subarachnoid Hemorrhage
Authors: Sarrafzadeh Asita S , Nagel Alexandra , Czabanka Marcus , Denecke Timm , Vajkoczy Peter , Plotkin Michail
Published: September 2009

This study aimed to characterize hypoxic, but salvageable, tissue imaged by 18F-fluoromisonidazole (18F-FMISO), combining with perfusion-computed tomography (PCT) for regional cerebral blood flow (rCBF) measurement and metabolism by microdialysis (MD) in aneurysmal subarachnoidal hemorrhage (SAH) patients. 18F-FMISO positron-emission tomography (PET)/CT was performed within the period of possible vasospasm (day 6.8±3 after SAH) in seven SAH patients. In parallel, rCBF was determined within the MD region of interest (MD-ROI) ( n=5). The MD catheter was inserted into the brain parenchyma with highest risk for ischemia; extracellular levels of glutamate and energy metabolites were registered at time of PET and hourly for 10 days. Twelve-month outcome was evaluated. In asymptomatic patients ( n=3) no hypoxia was detected and glutamate levels were low (<10 mmol/L), whereas symptomatic patients had higher glutamate concentrations ( P<0.001). Increased 18F-FMISO uptake within the MD-ROI ( n=3) was related to higher glutamate levels, while rCBF was above the ischemic range. Hypoxia (increased 18F-FMISO uptake) was present in symptomatic patients and associated with relevant metabolic derangement of extracellular glutamate levels, whereas energy metabolism and rCBF were preserved. This technique has the potential to improve our understanding of the role of cellular hypoxia in aneurysmal SAH.
Enhancement of ferromagnetism in Zn0.95Co0.05O films by lithium codoping
Authors: Li Jian-jun , Hao Wei-chang , Xu Huai-zhe , Wang Tian-min , Shi Ji
Published: September 2009

Zn 0.95 − x Co 0.05 Li x O  (x=0–0.12) thin films were synthesized by sol-gel method. Magnetic investigation showed that the ferromagnetism of the Zn0.95−xCo0.05LixO films increased with Li doping within the solubility limit of 9% but dropped sharply when x>9% owing to the presence of the second-phase LiCoO2. X-ray diffraction, UV-visible absorption spectrum (UV-vis), Raman spectrum (Raman), and electrical resistivity investigation indicated that the Li-doping process in Zn0.95Co0.05O was of three stages. The structure and magnetic properties of Zn0.95−xCo0.05LixO films had different change trends in different stages. It was found that not only LiZn′ related defects but also Li+ interstitials played important roles in enhancing the magnetic interaction between Co2+ ions, which was supported by the bound magnetic polaron model.
The integration of real and virtual magnetic resonance imaging experiments in a single instrument
Authors: Sharp Jonathan C. , Yin Donghui , Bernhardt Richard H. , Deng Qunli , Procca Andrew E. , Tyson Randy L. , Lo Kan , Tomanek Boguslaw
Published: September 2009

We present the design of an integrated system for performing both real and virtual (simulated) magnetic resonance imaging (MRI) experiments. We emphasize the approaches used to maximize the level of integration and also the benefits that tight real-virtual integration brings for a scientific instrument. The system has been implemented for both low field (0.2 T) and high field (9.4 T) imaging systems. The simulations can run for any MRI experiment and we demonstrate the operation of the system for T1, T2, T2∗, and diffusion contrasts.
Molecular dynamics simulations of the solid phase epitaxy of Si: Growth mechanism and orientation effects
Authors: Lampin E. , Krzeminski C.
Published: September 2009

The solid phase epitaxy of an amorphous layer on crystalline silicon is studied by means of molecular dynamics. Three stacks of 5120, 4928, and 5184 atoms respectively oriented along the [100], [110], and [111] directions are annealed with the Tersoff interatomic potential. The regrowth proceeds via the motion of a planar interface for [100], the formation of facets for [110], and the crystallization within (111) bilayers for the third case. In the absence of crystallization defects, the velocities of regrowth are similar for [100] and [110] and two to five times lower for [111]. Moreover, defects were obtained in 8% of the cases along [100], 19% of the cases along [110], and 52% of the cases along [111] with a systematic formation of one or more twins in the last case. The results are confronted with a schematic model of the solid phase epitaxy.
Solvent mediated interactions between model colloids and interfaces: A microscopic approach
Authors: Hopkins Paul , Archer Andrew J. , Evans Robert
Published: September 2009

We determine the solvent mediated contribution to the effective potentials for model colloidal or nanoparticles dispersed in a binary solvent that exhibits fluid-fluid phase separation. The interactions between the solvent particles are taken to be purely repulsive point Yukawa pair potentials. Using a simple density functional theory we calculate the density profiles of both solvent species in the presence of the “colloids,” which are treated as external potentials, and determine the solvent mediated (SM) potentials. Specifically, we calculate SM potentials between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface, and (iii) a colloid and a planar wall with an adsorbed wetting film. We consider three different types of colloidal particles: Colloid A that prefers the bulk solvent phase rich in species 2, colloid C that prefers the solvent phase rich in species 1, and “neutral” colloid B that has no strong preference for either phase, i.e., the free energies to insert the colloid into either of the coexisting bulk phases are almost equal. When a colloid that has a preference for one of the two solvent phases is inserted into the disfavored phase at state points close to coexistence a thick adsorbed “wetting” film of the preferred phase may form around the colloids. The presence of the adsorbed film has a profound influence on the form of the SM potentials. In case (i) reducing the separation between the two colloids of type A leads to a bridging transition whereby the two adsorbed films connect abruptly and form a single fluid bridge. The SM potential is strongly attractive in the bridged configuration. A similar phenomenon occurs in case (iii) whereby the thick adsorbed film on colloid A and that at the planar wall, which prefers the same phase as colloid A, connect as the separation between the colloid and the wall is reduced. In both cases the bridging transition is accompanied, in this mean-field treatment, by a discontinuity of the SM force. On the other hand, for the same wall, and a colloid of type C, the SM potential is strongly repulsive at small separations. For case (ii), inserting a single colloidal particle near the planar fluid-fluid interface of the solvent, the density profiles of the solvent show that the interface distortion depends strongly on the nature of the colloid-solvent interactions. When the interface disconnects from the colloid there is, once again, a discontinuity in the SM force.
Scanning Kelvin-probe study of the hydrogen-terminated diamond surface in ultrahigh vacuum
Authors: Pakes C. I. , Hoxley D. , Rabeau J. R. , Edmonds M. T. , Kalish R. , Prawer S.
Published: September 2009

Atomic-force and Kelvin-probe microscopies were employed in ultrahigh vacuum to image the surface topography and contact potential of the hydrogen-terminated and unterminated surfaces of diamond. A variation of about 25 meV in the contact potential was measured on a length scale of 20 nm and ascribed to differently orientated surface domains resulting from hydrogen-plasma processing of the sample. Shifts in the work function arising from sample heating in vacuum and the adsorption of C60 were measured. The Fermi level was found to be 0.7 and 1.1 eV below the valence band maximum for C60 coverages of 1 and 4 monolayer, respectively.
Ultrafast dynamics of femtosecond laser-induced nanostructure formation on metals
Authors: Hwang Taek Yong , Vorobyev A. Y. , Guo Chunlei
Published: September 2009

We perform a comparison study on femtosecond laser-induced nanostructures on three noble metals, Cu, Ag, and Au. Under identical experimental conditions, the three metals each gain a different amount of surface area increase resulting from nanostructuring. We show that the different surface area increase from nanostructuring directly relates to the competition of two ultrafast processes, electron-phonon coupling and hot electron diffusion, following femtosecond laser heating of metals.
Single-molecule pulling and the folding of donor-acceptor oligorotaxanes: Phenomenology and interpretation
Authors: Franco Ignacio , Schatz George C. , Ratner Mark A.
Published: September 2009

The thermodynamic driving force in the folding of a class of oligorotaxanes is elucidated by means of molecular dynamics simulations of equilibrium isometric single-molecule force spectroscopy by atomic force microscopy experiments. The oligorotaxanes consist of cyclobis(paraquat-p-phenylene) rings threaded onto an oligomer of 1,5-dioxynaphthalenes linked by polyethers. The simulations are performed in a high dielectric medium using MM3 as the force field. The resulting force versus extension isotherms show a mechanically unstable region in which the molecule unfolds and, for selected extensions, blinks in the force measurements between a high-force and a low-force regime. From the force versus extension data the molecular potential of mean force is reconstructed using the weighted histogram analysis method and decomposed into energetic and entropic contributions. The simulations indicate that the folding of the oligorotaxanes is energetically favored but entropically penalized, with the energetic contributions overcoming the entropy penalty and effectively driving the folding. In addition, an analogy between the single-molecule folding/unfolding events driven by the atomic force microscope (AFM) tip and the thermodynamic theory of first-order phase transitions is discussed. General conditions (on the molecule and the AFM cantilever) for the emergence of mechanical instabilities and blinks in the force measurements in equilibrium isometric pulling experiments are also presented. In particular, it is shown that the mechanical stability properties observed during the extension are intimately related to the fluctuations in the force measurements.
Isotope effects in the vibrational lifetime of hydrogen on germanium(100): Theory and experiment
Authors: Sakong Sung , Kratzer Peter , Han Xu , Balgar Thorsten , Hasselbrink Eckart
Published: September 2009

Combining first-principles calculations and sum frequency generation spectroscopy, we elucidate the microscopic details in the relaxation of the stretching vibration of hydrogen adsorbed on Ge(100). The dominant decay channels involve energy transfer from the stretching to the hydrogen bending modes, with the remaining energy difference being transferred to or from substrate phonons. The coupling between stretching and bending modes is treated from first principles using the calculated multidimensional adiabatic potential energy surface, while the coupling to phonons is treated in perturbation theory. For a surface solely saturated with light hydrogen, we calculate a vibrational lifetime of 1.56 ns at 400 K, in good agreement with experiment, and find a similar temperature dependence of the lifetime in both experiment and theory. The calculations show that the stretching energy dissipates to a vibrational state involving four bending quanta of hydrogen, concurrently absorbing a thermally excited surface phonon related to the Ge dimer rocking mode. For a Ge surface saturated with a mixture of H and D, our experiments find that the relaxation rate of the H stretching vibration is markedly increased when compared to a surface saturated with H only. Experimentally, a single decay is observed although H and D atoms will statistically pair on the surface dimers. The vibrational lifetime of the Ge–H stretching mode is up to six times shorter in the presence of adsorbed D atoms. The calculated relaxation rates are consistent with the experimentally observed trend. The theoretical analysis shows that the breaking of symmetry within the Ge surface dimer due to coadsorption of D opens up further relaxation channels that involve absorption or emission of a substrate phonon at various energies. Moreover, the calculations predict an even shorter vibrational lifetime of the Ge–D stretch mode due to efficient coupling to the Ge dimer rocking mode.
Transport properties of water at functionalized molecular interfaces
Authors: Feng Jun , Wong Ka-Yiu , Dyer Kippi , Pettitt B. Montgomery
Published: September 2009

Understanding transport properties of solvent such as diffusion and viscosity at interfaces with biomacromolecules and hard materials is of fundamental importance to both biology and biotechnology. Our study utilizes equilibrium molecular dynamics simulations to calculate solvent transport properties at a model peptide and microarray surface. Both diffusion and selected components of viscosity are considered. Solvent diffusion is found to be affected near the peptide and surface. The stress-stress correlation function of solvent near the hard surface exhibits long time memory. Both diffusion and viscosity are shown to be closely correlated with the density distribution function of water along the microarray surface.
Nanoscale optical tomography using volume-scanning near-field microscopy
Authors: Sun Jin , Schotland John C. , Hillenbrand Rainer , Carney P. Scott
Published: September 2009

The relationship between sample structure and data in volume-scanning backscattering mode near-field optical microscopy is investigated. It is shown that the three-dimensional structure of a dielectric sample is encoded in the phase and amplitude of the scattered field and that an approximate reconstruction of the sample structure may be obtained.
Laser-induced self-assembly of iron oxide nanostructures with controllable dimensionality
Authors: Henley Simon J. , Mollah Shafikuddin , Giusca Christina E. , Silva S. Ravi P.
Published: September 2009

The nanosecond pulsed laser ablation of fine iron powder submerged under different liquid media (water, methanol, ethanol, and isopropanol) is used to rapidly produce a variety of iron oxide nanostructures from nanoparticles to nanowires and nanosheets. The dimensionality of the nanostructures is shown to be a consequence of two controllable mechanisms. The rapid oxidation, collisional quenching, and coalescence of the ablation products are suggested as the dominant mechanisms for the formation of zero-dimensional nanostructures such as hematite (α-Fe2O3) nanoparticles in water, or iron oxyhydroxide nanoparticles under alcohols. By employing different laser wavelengths (248 and 532 nm) it is demonstrated that the growth of extended iron oxyhydroxide nanostructures (one-dimensional nanowires and two-dimensional nanosheets) under methanol is possible and is a consequence of a second self-assembly mechanism driven by interaction between the UV laser pulses and the ablation products.
A comparative study on field, temperature, and strain dependences of the critical current for doped and undoped MgB2 wires based on the percolation model
Authors: Oh Sangjun , Kim J. H. , Cho Kyuhwan , Lee Chulhee , Kim Chan-Joong , Dou S. X. , Rindfleisch M. , Tomsic M. , Ahn Jung-Ho
Published: September 2009

Field, temperature, and strain dependences of the critical current for a SiC doped multifilamentary in situ MgB2 wire have been studied. Measurement results were compared with that of the undoped wire, and the origin of the difference in the critical current is discussed. The critical current can be calculated with the percolation model considering the effect of anisotropy. The temperature dependence of the fitting parameters, the upper critical field along the ab-plane, and c-axis is compared with the dirty-limit two-gap theory. To assess the validity of the fitting parameters, resistive transition has been measured especially to extract the upper critical field directly. It is shown that even the resistive broadening can be well explained by a simple parallel path model using the fitting parameters obtained from the critical current analysis.
Fabrication of polydimethylsiloxane composites with nickel nanoparticle and nanowire fillers and study of their mechanical and magnetic properties
Authors: Denver Heather , Heiman Timothy , Martin Elizabeth , Gupta Amit , Borca-Tasciuc Diana-Andra
Published: September 2009

This work presents the fabrication and characterization of mechanical and magnetic properties of polydimethylsiloxane (PDMS) nanocomposites with nickel nanoparticles and nanowires as fillers. To enhance filler dispersion and polymer-filler interface bonding, allyltrimethoxysilane was used for nanofiller coating. Sample preparation was carried out by speed mixing and curing at 100 °C. Nanowire-PDMS composites were exposed to magnetic field prior to full curing in order to facilitate nanowire alignment. Composites with concentrations of 5, 10, and 15 vol % of nanoparticles and 5 vol % of nanowires were prepared and tested. An increase in elastic modulus of ∼30% was observed for composites with 5 vol % nanoparticle concentration. A much higher increase in elastic modulus, of ∼80%, was observed for nanowire-based composites of same concentration. The measured elastic modulus agrees well with predictions that assume strong interface bonding between the polymer and the filler. Magnetic anisotropy and higher remanent magnetization and coercivity are observed for the nanowire composite. These multifunctional materials could have a wide range of applications, from active structural components to sensing elements in macro- and particularly microsystem applications.
History force on coated microbubbles propelled by ultrasound
Authors: Garbin Valeria , Dollet Benjamin , Overvelde Marlies , Cojoc Dan , Di Fabrizio Enzo , van Wijngaarden Leen , Prosperetti Andrea , de Jong Nico , Lohse Detlef , Versluis Michel
Published: September 2009

In this paper the unsteady translation of coated microbubbles propelled by acoustic radiation force is studied experimentally. A system of two pulsating microbubbles of the type used as contrast agent in ultrasound medical imaging is considered, which attract each other as a result of the secondary Bjerknes force. Optical tweezers are used to isolate the bubble pair from neighboring boundaries so that it can be regarded as if in an unbounded fluid and the hydrodynamic forces acting on the system can be identified unambiguously. The radial and translational dynamics, excited by a 2.25 MHz ultrasound wave, is recorded with an ultrahigh speed camera at 15×106 frames/s. The time-resolved measurements reveal a quasisteady component of the translational velocity, at an average translational Reynolds number ⟨Ret⟩≈0.5, and an oscillatory component at the same frequency as the radial pulsations, as predicted by existing models. Since the coating enforces a no-slip boundary condition, an increased viscous dissipation is expected due to the oscillatory component, similar to the case of an oscillating rigid sphere that was first described by Stokes [“On the effect of the internal friction of fluids on the motion of pendulums,” Trans. Cambridge Philos. Soc. 9, 8 (1851)]. A history force term is therefore included in the force balance, in the form originally proposed by Basset and extended to the case of time-dependent radius by Takemura and Magnaudet [“The history force on a rapidly shrinking bubble rising at finite Reynolds number,” Phys. Fluids 16, 3247 (2004)]. The instantaneous values of the hydrodynamic forces extracted from the experimental data confirm that the history force accounts for the largest part of the viscous force. The trajectories of the bubbles predicted by numerically solving the equations of motion are in very good agreement with the experiment.
Exploring the magnetoroton excitations in quantum wires: Inverse dielectric functions
Authors: Kushwaha Manvir S.
Published: September 2009

A theoretical investigation has been made of the magnetoplasmon excitations in a quantum wire characterized by a confining harmonic potential and subjected to a perpendicular magnetic field. We study the (nonlocal, dynamic) inverse dielectric function to examine the charge-density excitations within a two-subband model in the framework of Bohm–Pines’ random-phase approximation. A particular stress is put on the (intersubband) magnetoroton excitation, which changes the sign of its group velocity twice before merging with the respective single-particle continuum. It has already been suggested that the electronic device based on such magnetoroton excitations can act as an active laser medium [see, e.g., M. S. Kushwaha, Phys. Rev. B 78, 153306 (2008)]. Scrutinizing the real and imaginary parts of the inverse dielectric function provides us with important information on the longitudinal and transverse (Hall) resistances of the system.
Lithographic positioning of fluorescent molecules on high-Q photonic crystal cavities
Authors: Rivoire Kelley , Kinkhabwala Anika , Hatami Fariba , Masselink W. Ted , Avlasevich Yuri , Müllen Klaus , Moerner W. E. , Vučković Jelena
Published: September 2009

Photoluminescent molecules are coupled to high quality photonic crystal nanocavities. The cavities are fabricated in a gallium phosphide membrane and show resonances from 735 to 860 nm with quality factors up to 12 000. The molecules, which are dispersed in a thin polymer film deposited on top of the cavities, can be selectively positioned onto the location of the cavity by using a lithographic technique, which is easily scalable to arrays of cavities.
Application of secondary electron potential contrast on junction leakage isolation
Authors: Liu Po-Tsun , Lee Jeng-Han , Huan Y. S. , Su David
Published: September 2009

Secondary electron potential contrast (SEPC) technology with an in situ dynamic trigger was studied to inspect P+/N-well junction leakage arising from P-well misalignment in a static random access memory cell. Combining SEPC with scanning electron microscopy observations allows direct identification of the junction shift. Furthermore, an in situ negative bias applied to the P-well can create a wider depletion region and eliminate the leakage path in P+/N-well contacts, allowing the P+/N well to operate normally. This proposed in situ dynamic trigger method is a promising and effective approach to investigating device physics under a dynamic scope.
Penetrable-square-well fluids: Analytical study and Monte Carlo simulations
Authors: Fantoni Riccardo , Giacometti Achille , Malijevský Alexandr , Santos Andrés
Published: September 2009

We study structural and thermophysical properties of a one-dimensional classical fluid made of penetrable spheres interacting via an attractive square-well potential. Penetrability of the spheres is enforced by reducing from infinite to finite the repulsive energy barrier in the pair potentials As a consequence, an exact analytical solution is lacking even in one dimension. Building upon previous exact analytical work in the low-density limit [A. Santos, R. Fantoni, and A. Giacometti, Phys. Rev. E 77, 051206 (2008)], we propose an approximate theory valid at any density and in the low-penetrable regime. By comparison with specialized Monte Carlo simulations and integral equation theories, we assess the regime of validity of the theory. We investigate the degree of inconsistency among the various routes to thermodynamics and explore the possibility of a fluid-fluid transition. Finally we locate the dependence of the Fisher–Widom line on the degree of penetrability. Our results constitute the first systematic study of penetrable spheres with attractions as a prototype model for soft systems.
Combinatorial design of protein sequences with applications to lattice and real proteins
Authors: Bhattacherjee Arnab , Biswas Parbati
Published: September 2009

Understanding the evolution of protein structures from specific sequences may be achieved by predicting the desired folded structure from a given sequence and by predicting compatible sequences from a known structure using principles of protein folding and design. Protein design requires the synthesis of a broad range of sequences consistent with a preassigned target conformation. However, the number of possible protein sequences for a given target structure exponentially increases with the number of residues making the explicit tabulation of all sequences intractable experimentally and computationally. For sequence libraries of arbitrary size, the results of a self-consistent mean field theory is applied to a three-dimensional cubic lattice model of proteins and real homologous protein sequences to estimate the number and probabilistic composition of sequences consistent with a generalized foldability criterion. Theoretically calculated site-specific monomer probabilities and the monomer pair probabilities at each position in a sequence are compared to those obtained from exact enumeration for cubic lattice proteins. For real proteins the theoretically predicted sequence variability are compared to that obtained from a set of homologous protein sequences. The theory results match extremely well with both the cubic lattice protein and real protein results. The theory also evaluates the mutability of specific residues and identifies the beneficial mutations. The theory may be used to quantify particular design strategies and explore site-directed mutagenesis strategies in crafting de novo proteins in context of in vitro protein evolution.
Impact of device configuration on the temperature instability of Al–Zn–Sn–O thin film transistors
Authors: Jeong Jae Kyeong , Yang Shinhyuk , Cho Doo-Hee , Park Sang-Hee Ko , Hwang Chi-Sun , Cho Kyoung Ik
Published: September 2009

We compared the effect of the temperature on the device stability of Al–Zn–Sn–O (AZTO) thin film transistors (TFTs) with top gate and bottom gate architectures. While the bottom gate device without any passivation layer on the AZTO channel layer showed a large threshold voltage (Vth) shift of 1.6 V after heating it from 298 to 398 K, the naturally passivated top gate device exhibited a smaller Vth shift of 0.6 V. This different behavior is discussed based on the concept of the thermal activation energy of the subthreshold drain current. It is proposed that the suitable passivation and lower interfacial trap density for the top gate TFT are responsible for its superior temperature stability compared to the bottom gate device.
Structure of YSi2 nanowires from scanning tunneling spectroscopy and first principles
Authors: Iancu V. , Kent P. R. C. , Zeng C. G. , Weitering H. H.
Published: September 2009

Exceptionally long and uniform YSi2 nanowires are formed via self-assembly on Si(001). The in-plane width of the thinnest wires is known to be quantized in odd multiples of the silicon lattice constant. Here, we identify a class of nanowires that violates the “odd multiple” rule. The structure of the thinnest wire in this category is determined by comparing scanning tunneling spectroscopy measurements with the calculated surface density of states of candidate models by means of the Pendry R-factor analysis. The relative stability of the odd and even wire systems is analyzed via first-principles calculations.
The Quantity and Quality of Jobs: Changes in UK Regions, 1997–2007
Authors: Jones Paul S , Green Anne E
Published: September 2009

In debates about employment creation there is increasing concern about the quality as well as the quantity of jobs. The authors examine the regional distribution of workplace employment in the UK using the ‘quality of jobs’ framework. Findings reveal evidence of marked regional differences in average ‘job quality’, with the gap between regions growing over the decade from 1997, and the focus of high-quality job creation biased towards already advantaged regions. There is evidence of increased job polarisation across most UK regions. The analyses suggest an important role of the public sector in providing high-quality jobs, particularly outside London and the South East.
Cosmic-Ray Exposure Ages of Large Presolar SiC Grains
Authors: Gyngard Frank , Amari Sachiko , Zinner Ernst , Ott Ulrich
Published: September 2009

Among presolar SiC grains found in the Murchison carbonaceous meteorites (average size less than 0.5 μm) are very large grains, ranging in size up to 50 μm. We interpret 6Li excesses measured in eight of these grains as being the result of spallation reactions by Galactic cosmic rays during the time the grains spent in the interstellar medium before their incorporation into the meteorite. Derived interstellar exposure ages range from 40 My to 1 Gy, the highest values being consistent with theoretical expectations of interstellar grain lifetimes. Although six grains have almost identical C and Si isotopic compositions, their exposure ages are very different. This observation, combined with low trace element contents, and unusual grain sizes, raises fundamental questions about their stellar sources.
New High-Precision Measurement of the Reaction Rate of the 18O(p, α)15N Reaction via THM
Authors: La Cognata M. , Spitaleri C. , Mukhamedzhanov A. M. , Irgaziev B. , Tribble R. E. , Banu A. , Cherubini S. , Coc A. , Crucillà V. , Goldberg V. Z. , Gulino M. , Kiss G. G. , Lamia L. , Chengbo L. , Mrazek J. , Pizzone R. G. , Puglia S. M. R. , Rapisarda G. G. , Romano S. , Sergi M. L. , Tabacaru G. , Trache L. , Trzaska W. , Tumino A.
Published: September 2009

The 18O(p, α)15N reaction rate has been extracted by means of the Trojan-Horse method. For the first time the contribution of the 20-keV peak has been directly evaluated, giving a value about 35% larger than previously estimated. The present approach has allowed to improve the accuracy of a factor 8.5, as it is based on the measured strength instead of educated guesses or spectroscopic measurements. The contribution of the 90-keV resonance has been determined as well, which turned out to be of negligible importance to astrophysics.
Neutron Capture Cross Sections for the Weak s Process
Authors: Heil M. , Juseviciute A. , Käppeler F. , Gallino R. , Pignatari M. , Uberseder E.
Published: September 2009

In past decades a lot of progress has been made towards understanding the main s-process component that takes place in thermally pulsing Asymptotic Giant Branch (AGB) stars. During this process about half of the heavy elements, mainly between 90 ≤ A ≤ 209 are synthesized. Improvements were made in stellar modeling as well as in measuring relevant nuclear data for a better description of the main s process. The weak s process, which contributes to the production of lighter nuclei in the mass range 56 ≤ A ≤ 90 operates in massive stars (M ≥ 8 M⊙) and is much less understood. A better characterization of the weak s component would help disentangle the various contributions to element production in this region. For this purpose, a series of measurements of neutron-capture cross sections have been performed on medium-mass nuclei at the 3.7-MV Van de Graaff accelerator at FZK using the activation method. Also, neutron captures on abundant light elements with A < 56 play an important role for s-process nucleosynthesis, since they act as neutron poisons and affect the stellar neutron balance. New results are presented for the (n, γ) cross sections of 41K and 45Sc, and revisions are reported for a number of cross sections based on improved spectroscopic information.
Tuning the Re/Os Clock: Stellar-Neutron Cross Sections
Authors: Mengoni A. , Mosconi M. , Fujii K. , Käppeler F. ,   The n_TOF Collaboration
Published: September 2009

The neutron-capture cross sections of 186,187Os have been recently measured at the CERN neutron time-of-flight facility n_TOF for an improved evaluation of the Re/Os cosmo-chronometer. This experimental information was complemented by nuclear model calculations for obtaining the proper astrophysical reaction rates at s-process temperatures. The calculated results and their implications for the determination of the time-duration of nucleosynthesis during galactic chemical evolution is discussed.
Generalized antifungal activity and 454-screening ofPseudonocardiaandAmycolatopsisbacteria in nests of fungus-growing ants
Authors: Sen Ruchira , Ishak Heather D. , Estrada Dora , Dowd Scot E. , Hong Eunki , Mueller Ulrich G.
Published: September 2009

In many host-microbe mutualisms, hosts use beneficial metabolites supplied by microbial symbionts. Fungus-growing (attine) ants are thought to form such a mutualism withPseudonocardiabacteria to derive antibiotics that specifically suppress the coevolving pathogenEscovopsis, which infects the ants' fungal gardens and reduces growth. Here we test 4 key assumptions of thisPseudonocardia-Escovopsiscoevolution model. Culture-dependent and culture-independent (tag-encoded 454-pyrosequencing) surveys reveal that severalPseudonocardiaspecies and occasionallyAmycolatopsis(a close relative ofPseudonocardia) co-occur on workers from a single nest, contradicting the assumption of a single pseudonocardiaceous strain per nest.Pseudonocardiacan occur on males, suggesting thatPseudonocardiacould also be horizontally transmitted during mating.PseudonocardiaandAmycolatopsissecretions kill or strongly suppress ant-cultivated fungi, contradicting the previous finding of a growth-enhancing effect ofPseudonocardiaon the cultivars. Attine ants therefore may harm their own cultivar if they apply pseudonocardiaceous secretions to actively growing gardens.PseudonocardiaandAmycolatopsisisolates also show nonspecific antifungal activities against saprotrophic, endophytic, entomopathogenic, and garden-pathogenic fungi, contrary to the original report of specific antibiosis againstEscovopsisalone. We conclude that attine-associated pseudonocardiaceous bacteria do not exhibit derived antibiotic properties to specifically suppressEscovopsis. We evaluate hypotheses on nonadaptive and adaptive functions of attine integumental bacteria, and develop an alternate conceptual framework to replace the prevailingPseudonocardia-Escovopsiscoevolution model. If association withPseudonocardiais adaptive to attine ants, alternate roles of such microbes could include the protection of ants or sanitation of the nest.
Distinct immune responses to transgene products from rAAV1 and rAAV8 vectors
Authors: Lu Yuanqing , Song Sihong
Published: September 2009

Recently developed serotypes of recombinant adeno-associated virus (rAAV) vectors have significantly enhanced the use of rAAV vectors for gene therapy. However, host immune responses to the transgene products from different serotypes remain uncharacterized. In the present study, we evaluated the differential immune responses to the transgene products from rAAV1 and rAAV8 vectors. In non-obese diabetic (NOD) mice, which have a hypersensitive immunity, rAAV serotype 1 vector (rAAV1-hAAT) induced high levels of both humoral and cellular responses, while rAAV8-hAAT did not. In vitro studies showed that rAAV1, but not rAAV8 vector transduced dendritic cells (DCs) efficiently. In vivo studies indicated that vector transduction of DCs was essential for the immune responses; while the presence of a transgene product (or foreign gene product produced by host cells) was not immunogenic. Intriguingly, preimmunization with rAAV8-hAAT vector or with serum of hAAT transgenic NOD mouse induced immune tolerance to rAAV1-hAAT injection. These results demonstrate the immunogenic differences of rAAV1 and rAAV8 and imply tremendous potential for these vectors in different applications, where an immune response to transgene is to be either elicited or avoided.
TOWARDS THE UNIVERSAL CARE COURSE MODEL
Authors: Haas Barbara , Hartel Margit
Published: September 2009

The principle aim is to analyse care policies and mothers' employment patterns in Austria in comparison with The Netherlands and Sweden. While Sweden fosters a Universal Breadwinner Model, Austrian policies set incentives for mothers to organize private care for their children for a relatively long period of time, similar to the Caregiver Parity model. The Netherlands, approaching the Universal Caregiver model, support part-time integration into the labour market, combined with private part-time caring facilities for the children. The cross-national comparative approach has been adopted throughout the description of care policies and the data analysis, using the European Social Survey. Drawing on the strong cross-national differences in policies and employment patterns, we outline the main principles of a Universal Care Course (UCC). The model addresses questions about how to achieve the ideal of a smooth transition between work and care in a gender-sensitive way.
The sensory nature of knowledge: Sensory priming effects in semantic categorization
Authors: Brunel Lionel , Lesourd Mathieu , Labeye Elodie , Versace Rémy
Published: September 2009

The aim of the present study was to show the perceptual nature of conceptual knowledge by using a priming paradigm that excluded an interpretation exclusively in terms of amodal representation. This paradigm was divided into two phases. The first phase consisted in learning a systematic association between a geometrical shape and a white noise. The second phase consisted of a short-term priming paradigm in which a primed shape (either associated or not with a sound in the first phase) preceded a picture of an object, which the participants had to categorize as representing a large or a small object. The objects were chosen in such a way that their principal function either was associated with the production of noise (“noisy” target) or was not typically associated the production of noise (“silent” target). The stimulus onset asynchrony (SOA) between the prime and the target was 100 ms or 500 ms. The results revealed an interference effect with a 100-ms SOA and a facilitatory effect with a 500-ms SOA for the noisy targets only. We interpreted the interference effect obtained at the 100-ms SOA as the result of an overlap between the components reactivated by the sound prime and those activated by the processing of the noisy target. At an SOA of 500 ms, there was no temporal overlap. The observed facilitatory effect was explained by the preactivation of auditory areas by the sound prime, thus facilitating the categorization of the noisy targets only.
Memory reloaded: Memory load effects in the attentional blink
Authors: Visser Troy A. W.
Published: September 2009

When two targets are presented in rapid succession, identification of the first is nearly perfect, while identification of the second is impaired when it follows the first by less than about 700 ms. According to bottleneck models, this attentional blink (AB) occurs because the second target is unable to gain access to capacity-limited working memory processes already occupied by the first target. Evidence for this hypothesis, however, has been mixed, with recent reports suggesting that increasing working memory load does not affect the AB. The present paper explores possible reasons for failures to find a link between memory load and the AB and shows that a reliable effect of load can be obtained when the item directly after T1 (Target 1) is omitted. This finding provides initial evidence that working memory load can influence the AB and additional evidence for a link between T1 processing time and the AB predicted by bottleneck models.