bluuebunny/crossref_metadata_2025 huggingface dataset:
Flood hazard in Europe in an ensemble of regional climate scenarios
Authors: Dankers Rutger , Feyen Luc
Published: August 2009

We analyze changes in flood hazard in Europe by examining extreme discharge levels as simulated by the hydrological model LISFLOOD when driven by a multimodel ensemble of climate simulations. The ensemble consists of simulations from two regional climate models (RCMs), both run with boundary conditions from two global models, and for two scenarios of greenhouse gas emissions. In northeastern Europe, a general decrease in extreme river discharge is observed in the scenario period, suggesting a reduction in the hazard of extreme snowmelt floods. Elsewhere, we find a consistent tendency toward a higher flood hazard in the majority of the model experiments in several major European rivers. These changes can partly be attributed to large, decadal‐scale variability in the simulated climate and can be expected to occur naturally when comparing two 30‐year time periods, even without a change in greenhouse gas forcing. We furthermore find evidence for a considerable influence of especially the global model that is used to drive the RCMs. At the scale of individual river basins, using a different combination of climate models or assuming a different emissions scenario sometimes results in a very different or even opposite climate change signal in flood hazard. We therefore believe that a multimodel approach as adopted in the present paper provides the best way to address the various uncertainties in impact studies of hydrometeorological extremes. Probabilistic scenarios that consist of multiple realizations of the current and future climate state are indispensable to better identify the climate signal amidst large variability.
Characterization of Mars' seasonal caps using neutron spectroscopy
Authors: Prettyman Thomas H. , Feldman William C. , Titus Timothy N.
Published: August 2009

Mars' seasonal caps are characterized during Mars years 26 and 27 (April 2002 to January 2006) using data acquired by the 2001 Mars Odyssey Neutron Spectrometer. Time‐dependent maps of the column abundance of seasonal CO2 surface ice poleward of 60° latitude in both hemispheres are determined from spatially deconvolved, epithermal neutron counting data. Sources of systematic error are analyzed, including spatial blurring by the spectrometer's broad footprint and the seasonal variations in the abundance of noncondensable gas at high southern latitudes, which are found to be consistent with results reported by Sprague et al. (2004, 2007). Corrections for spatial blurring are found to be important during the recession, when the column abundance of seasonal CO2 ice has the largest latitude gradient. The measured distribution and inventory of seasonal CO2 ice is compared to simulations by a general circulation model (GCM) calibrated using Viking lander pressure data, cap edge functions determined by thermal emission spectroscopy, and other nuclear spectroscopy data sets. On the basis of the amount of CO2 cycled through the caps during years 26 and 27, the gross polar energy balance has not changed significantly since Viking. The distribution of seasonal CO2 ice is longitudinally asymmetric: in the north, deposition rates of CO2 ice are elevated in Acidalia, which is exposed to katabatic winds from Chasma Borealis; in the south, CO2 deposition is highest near the residual cap. During southern recession, CO2 ice is present longer than calculated by the GCM, which has implications for the local polar energy balance.
Compositional, morphological, and hysteresis characterization of magnetic airborne particulate matter in Rome, Italy
Authors: Sagnotti Leonardo , Taddeucci Jacopo , Winkler Aldo , Cavallo Andrea
Published: August 2009

The magnetic properties of tree leaves may be used to delineate the abundance and dispersal of anthropogenic airborne particulate matter (PM) in urban environments. In the city of Rome, Italy, circulating vehicles are the main source of magnetic PM, already characterized as prevalently low‐coercivity, magnetite‐like particles. To further constrain the nature and origin of such magnetic particles, we carried out coupled field emission scanning electron microscopy and a variety of rock magnetic analyses on PM specimens from Quercus ilex leaves and from potential PM sources in circulating motor vehicles in Rome. Fe‐rich particles are mostly 0.1–5 μm in size, with irregular shapes and moss‐like surface. Particles from disk brakes and diesel and gasoline exhaust pipes show distinct compositional and magnetic hysteresis signatures, suggesting that the magnetic PM collected on tree leaves consists of a mixture of particle populations deriving mostly from the abrasion of disk brakes and, to a lesser extent, from fuel combustion residuals emitted by diesel and gasoline exhausts. The contribution of fine superparamagnetic particles to the overall magnetic assemblage has been evaluated with specific rock magnetic analyses. The combined magnetic and microtextural‐compositional analyses provide an effective and original tool to characterize urban PM air pollution.
Trend evaluation in records with long‐term memory: Application to global warming
Authors: Lennartz S. , Bunde A.
Published: August 2009

Previous statistical detection methods indicate that, on a global scale, the observed warming cannot be attributed solely to natural fluctuations. Here we estimate the probability W(Δ) that an observed trend Δ occurs naturally, and determine the anthropogenic part AQ(Δ) of the temperature increase within a given confidence interval Q. To obtain these quantities, we do not use climate simulations, but assume as statistical null hypothesis that monthly temperature records are long‐term correlated with a Hurst exponent α > 0.5 (including also nonstationary records with α values above 1). We show that for confidence intervals with Q above 80% analytical expressions for W(Δ) and AQ(Δ) can be derived, which request as input solely the Hurst exponent, as well as the temperature increase Δ obtained from the linear regression line and the standard deviation σt around it. We apply this approach to global and local temperature data and discuss the different results.
Why climate sensitivity may not be so unpredictable
Authors: Hannart A. , Dufresne J.‐L. , Naveau P.
Published: August 2009

Different explanations have been proposed as to why the range of climate sensitivity predicted by GCMs has not lessened substantially in the last decades, and subsequently if it can be reduced. One such study (Why is climate sensitivity so unpredictable?) addressed these questions using rather simple theoretical considerations and reached the conclusion that reducing uncertainties on climate feedbacks and underlying climate processes will not yield a large reduction in the envelope of climate sensitivity. In this letter, we revisit the premises of this conclusion. We show that it results from a mathematical artifact caused by a peculiar definition of uncertainty used by these authors. Applying standard concepts and definitions of descriptive statistics to the exact same framework of analysis as Roe and Baker, we show that within this simple framework, reducing inter‐model spread on feedbacks does in fact induce a reduction of uncertainty on climate sensitivity, almost proportionally. Therefore, following Roe and Baker assumptions, climate sensitivity is actually not so unpredictable.
Seasonal predictability of the Atlantic Warm Pool in the NCEP CFS
Authors: Misra Vasubandhu , Chan Steven
Published: August 2009

The July–August–September (JAS) seasonal predictability of the Atlantic Warm Pool (AWP) is examined in the extensive set of seasonal hindcasts of the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS). We conduct both deterministic and probabilistic skill analyses of the NCEP CFS Seasonal Hindcasts (SHs). This study reveals that the SHs have a reasonable climatology of the AWP. The presence of robust decadal variability in sea surface temperature (SST) observations, while absent in the SHs, does seem to indicate its influence on the seasonal errors of the AWP in the NCEP CFS. However, after filtering out the observed SST for variability greater than 8 years, there is no systematic relation of AWP seasonal errors in the NCEP CFS with lead time. The signal to noise ratio of the area of the AWP in the SHs decreases with lead time, largely due to increases in the ensemble spread (noise). It is sobering to note that there is barely any probabilistic skill in the NCEP CFS SHs for the prediction of the anomalous AWP events (occurring either in the upper or lower terciles) at nearly all lead times. However if we examine the SHs from 1981–1996, when the observed SST in the AWP region is in one uniform phase of the prevalent decadal variation, then the SHs display useful skill in the prediction of anomalously large AWP events at all lead times. Furthermore, these truncated SHs also show significant probabilistic skill in the prediction of small (lower tercile) and normal (middle tercile) AWP events up to a lead time of 1 month.
An investigation of the northern hemisphere midlatitude nighttime plasma density enhancements and their relations to the midlatitude nighttime trough during summer
Authors: Horvath Ildiko , Lovell Brian C.
Published: August 2009

This study has utilized regional surface maps and field‐aligned latitudinal profiles derived from multiinstrument DMSP‐F15 data. It investigates northern midlatitude plasma enhancements in the nighttime topside ionosphere during summer and their relation to the midlatitude heavy ion stagnation trough. The tracked midlatitude summer enhancements showed significant longitudinal variations. Their best development occurred in the 50°N–60°N/110°E–170°E (geographic) region. Proven by Coupled Thermosphere‐Ionosphere Plasmasphere wind velocity simulations, equatorward winds were strongest there. This region is the northern hemisphere equivalent of the Weddell Sea Anomaly's (WSA) locality. There, northern summer plasma enhancements resembled the nighttime WSA, a southern summer equinoctial phenomenon, and thus were named as WSA‐like feature. Their plasma density increased mainly owing to the mechanical or direct effects of the equatorward winds. However, as results show, the WSA‐like feature was an ordinary northern midlatitude nighttime enhancement occurring in summer. This was further confirmed by the WSA‐like feature's relation to the trough and by the trough's movement. Over the northern hemisphere, the summer trough appeared at (62.461 ± 2.93)°N (geomagnetic), poleward of the WSA‐like feature and other midlatitude plasma enhancements, and moved equatorward with a rate of (0.097 ± 0.04)°N/nT when magnetic activity increased. As our previous WSA investigation indicates, the southern summer trough develops at lower latitudes, at (47.1564 ± 2.16)°S, equatorward of the nighttime WSA and moves poleward with a rate of (0.0497 ± 0.003)°S/nT with increasing magnetic activity under the combined influence of the nighttime WSA and South Atlantic Magnetic Anomaly.
High static stability in the mixing layer above the extratropical tropopause
Authors: Kunz A. , Konopka P. , Müller R. , Pan L. L. , Schiller C. , Rohrer F.
Published: August 2009

The relationship between the static stability N2 and the mixing in the tropopause inversion layer (TIL) is investigated using in situ aircraft observations during SPURT (trace gas transport in the tropopause region). With a new simple measure of mixing degree based on O3‐CO tracer correlations, high N2 related to an enhanced mixing in the extratropical mixing layer is found. This relation becomes even more pronounced if fresh mixing events are excluded, indicating that mixing within the TIL occurs on a larger than synoptic timescale. A temporal variance analysis of N2 suggests that processes responsible for the composition of the TIL take place on seasonal timescales. Using radiative transfer calculations, we simulate the influence of a change in O3 and H2O vertical gradients on the temperature gradient and thus on the static stability above the tropopause, which are contrasted in an idealized nonmixed atmosphere and in a reference mixed atmosphere. The results show that N2 increases with enhanced mixing degree near the tropopause. At the same time, the temperature above the tropopause decreases together with the development of an inversion and the TIL. In the idealized case of nonmixed profiles the TIL vanishes. Furthermore, the results suggest that H2O plays a major role in maintaining the temperature inversion and the TIL structure compared to O3. The results substantiate the link between the extratropical mixing layer and the TIL.
Direct Magnitude Estimation of Articulation Rate in Boys With Fragile X Syndrome
Authors: Zajac David J. , Harris Adrianne A. , Roberts Joanne E. , Martin Gary E.
Published: August 2009

Purpose

To compare the perceived articulation rate of boys with fragile X syndrome (FXS) with that of chronologically age-matched (CA) boys and to determine segmental and/or prosodic factors that account for perceived rate.

Method

Ten listeners used direct magnitude estimation procedures to judge the articulation rates of 7 boys with FXS only, 5 boys with FXS and a diagnosis of autism spectrum disorder (ASD), and 12 CA boys during sentence repetition. Sentences had similar articulation rates in syllables per second as determined acoustically. Four segmental/prosodic factors were used to predict perceived rate: (a) percentage consonants correct, (b) overall fundamental frequency (F0) level, (c) sentence-final F0drop, and (d) acoustically determined articulation rate with the final word of the sentence excluded.

Results

Boys with FXS and ASD were judged to talk faster than CA controls. Multiple linear regression indicated that articulation rate with the final word of the sentence excluded and sentence-final F0drop accounted for 91% of the variance for perceived rate.

Conclusions

Descriptions of speakers with FXS as having fast and/or fluctuating articulation rates may be influenced by autism status. Also, atypical sentence-final prosody may be related to perceived rate in boys with FXS and ASD.
On the thermodynamic expansion of the nucleation free-energy barrier
Authors: Barrett Jonathan C.
Published: August 2009

Mean field density functional theory is used to calculate the nucleation free-energy barrier height, W∗, in vapor-liquid nucleation as a function of the excess chemical potential Δμ. Calculations are performed for a range of temperatures and for both Lennard-Jones and Yukawa interactions, scaled to give the same bulk properties. The leading terms in the expansion of W∗ in powers of Δμ depend on the planar surface tension and the planar limit of the Tolman length, which are obtained from density functional calculations for planar interfaces. The first correction term to the large cluster (classical) limit is proportional to (Δμ)−1 and is shown to be significant. For the Lennard-Jones interaction, W∗ also includes a term proportional to ln(Δμ). Once the leading terms are subtracted from W∗, the residual is almost independent of Δμ. For the Yukawa fluid, values for this residual are compared to values found using a new formula for the rigidity constants and satisfactory agreement is found.
Carrier lifetime and spin relaxation time study for electrical spin injection into GaAs
Authors: Oh Eunsoon , Lee T. K. , Park J. H. , Choi J. H. , Park Y. J. , Shin K. H. , Kim K. Y.
Published: August 2009

We fabricated spin light emitting diodes using oxide tunneling barriers between ferromagnetic materials (Ni0.8Fe0.2/Co0.9Fe0.1) and semiconductors (GaAs) and investigated the temperature-dependent carrier lifetime and spin relaxation time of the active GaAs layer. We observed the circular polarization of the free exciton from the electroluminescence spectra due to the spin injection from the ferromagnetic material, whereas the circular polarization of the conduction band to acceptor transition was negligible. From the temperature-dependent carrier lifetime and spin relaxation time of the active GaAs layer, we found that the spin injection efficiency was larger than 25% between 20 and 180 K, where the magnetic field dependence of the spin lifetime was ignored.
A gigahertz-range spin-wave filter composed of width-modulated nanostrip magnonic-crystal waveguides
Authors: Kim Sang-Koog , Lee Ki-Suk , Han Dong-Soo
Published: August 2009

We found a robust magnonic-crystal waveguide structure for use as an efficient gigahertz-range spin-wave filter that passes only spin waves of chosen narrow band frequencies and filters out the other frequencies. The structure consists of the serial combinations of various width modulations with different periodicities and motifs in planar-patterned thin-film nanostrips composed of a single soft magnetic material. The observed magnonic band gaps result from both the translation symmetry of the one-dimensional width modulation and the higher-quantized width-mode spin waves excited from scattering at the periodic edge-steps of the width modulation. This work brings us one step closer to practical implementations of spin waves in information transmission and processing devices.
The origin of p-type conduction in (P, N) codoped ZnO
Authors: Tian Ren-Yu , Zhao Yu-Jun
Published: August 2009

P monodoped and (P, N) codoped ZnO are investigated by the first-principles calculations. It is found that the substitutional P defect at O site (PO) and interstitial P (Pi) contribute little to the p-type conductivity of ZnO samples under equilibrium condition. Zinc vacancies (VZn) and PZn-2VZn complex are demonstrated to be shallow acceptors with ionization energies around 100 meV, but they are easily compensated by PZn defect. Fortunately, PZn–4NO complexes may have lower formation energy than that of PZn under Zn-rich condition by proper choices of P and N sources. In addition, the neutral PZn–3NO passive defects may form an impurity band right above the valence-band maximum of ZnO as in earlier reported (Ga,N) or (Zr,N) doped ZnO. This significantly reduces the acceptor level of PZn–4NO complexes and helps improving the p-type conductivity in ZnO. It is suggested that a better (P, N) codoped p-type ZnO could be obtained under oxygen-poor condition.
Two-parameter complex Hadamard matrices for N=6
Authors: Karlsson Bengt R.
Published: August 2009

A new, two-parameter, nonaffine family of complex Hadamard matrices of order 6 is reported. It interpolates between the two Fourier families and contains as one-parameter subfamilies the Diţǎ family, a symmetric family, and an almost (up to equivalence) self-adjoint family.
Boundary effects on the mass and coupling constant in the compactified Ginzburg–Landau model: The boundary dependent critical temperature
Authors: Malbouisson A. P. C. , Malbouisson J. M. C. , Pereira R. C.
Published: August 2009

We consider the Euclidean D-dimensional N-component λ|φ|4 (λ>0) model with d (d≤D) compactified dimensions. Introducing temperature by means of the Ginzburg–Landau prescription in the mass term of the Hamiltonian, this model can be interpreted as describing a second-order phase transition for a system in a region of the D-dimensional space, limited by d pairs of parallel planes, orthogonal to the coordinates axis x1,x2,…,xd. The planes in each pair are separated by distances L1,L2,…,Ld. Making the appropriate boundary corrections to the coupling constant, we obtain in the large-N limit the transition temperature as a function of the size of the system, Tc({Li}), i=1,2,…,d. For D=3 we particularize this formula, taking L1=L2=⋯=Ld=L for the physically interesting cases d=1 (a film), d=2 (an infinitely long wire having a square cross section), and d=3 (a cubic grain).
Electron transport in surface oxidized Si nanocrystal ensembles with thin film transistor structure
Authors: Zhou Xin , Uchida Ken , Mizuta Hiroshi , Oda Shunri
Published: August 2009

Electron transport in the surface oxidized Si nanocrystals ensembles is described based on electrical measurements of thin film transistor structures as functions of temperature and voltage. Contact resistance has been greatly reduced by using a heavily doped silicon-on-insulator layer as electrodes, compared with devices based on Al/SiNCs/Al structures. Traps with the activation energy of 147 and 103 meV have been found when SiNC channels are applied with high gate voltage. The mechanism that these two traps successively dominate the Poole–Frenkel type conduction in low and high drain-source voltage region is discussed based on an assumption that the density of these two traps is different. Trapped carriers’ effects on the electric field distribution are believed to be responsible for the difference of the G-Vds1/2 slopes in the different drain-sources regions, which is in accord with the experimental results of the hydrogen annealing treatment. The carrier mobility is also discussed based on the measurement of gate voltage dependence of the drain-source current.
Geometry of universal magnification invariants
Authors: Werner M. C.
Published: August 2009

Recent work in gravitational lensing and catastrophe theory has shown that the sum of the signed magnifications of images near folds, cusps, and also higher catastrophes is zero. Here, it is discussed how Lefschetz fixed point theory can be used to interpret this result geometrically for a subfamily of these catastrophes, namely, the generic case of folds, cusps, elliptic and hyperbolic umbilics, swallowtails, and the elliptic and hyperbolic umbilics in gravitational lensing.
On the self-consistent implementation of general occupied-orbital dependent exchange-correlation functionals with application to the B05 functional
Authors: Arbuznikov Alexei V. , Kaupp Martin
Published: August 2009

Occupied-orbital dependent (OOD) exchange-correlation functionals hold a particularly prominent place in current developments of density functional theory. Their self-consistent implementation is complicated by the fact that their orbital-dependent parts are not explicit but only implicit functionals of electron density, and the exchange-correlation potential may not be obtained straightforwardly by taking the functional derivative with respect to the density. A two-step procedure is required, in which initially the functional derivatives with respect to the orbitals (FDOs) are obtained, which may then be transformed into local and multiplicative potentials by techniques of the optimized-effective potential. In view of the rather large variety of OOD functionals under current study, we report here general, systematic, and transparent expressions of the FDOs of a generalized OOD functional and additionally a matrix-element version in a basis set of atomic orbitals. Explicit FDOs are for the first time derived and numerically tested for one of the currently most complex examples of an OOD functional, Becke’s real-space model of nondynamical correlation (B05 functional) [J. Chem. Phys. 122, 064101 (2005)].
Influence of the interface on the electronic channel switching of a Fe–Ag thin film on a Si substrate
Authors: Alonso J. , Fdez-Gubieda M. L. , Sarmiento G. , Barandiarán J. M. , Svalov A. , Orue I. , Chaboy J. , Barquín L. Fernández , Meneghini C. , Neisius T. , Kawamura N.
Published: August 2009

Fe x Ag 100 − x granular thin films, being 20<x<70, were prepared by pulsed laser deposition. The thermal evolution of the electric resistance shows a dramatic drop in the range of 200<T<300 K, completely reversible with temperature and associated to a current switching between the granular thin film and its Si substrate. High resolution transmission electron microscopy measurements have revealed an amorphous interface between the thin film and the substrate, and x-ray absorption spectroscopy studies have demonstrated an electronic localization associated to the Fe atoms in this interface, which is intrinsically responsible for the current switching.
Error-reduced channeled spectroscopic ellipsometer with palm-size sensing head
Authors: Okabe Hiroshi , Hayakawa Masayuki , Matoba Junichi , Naito Hitoshi , Oka Kazuhiko
Published: August 2009

This paper describes a newly developed prototype system of the channeled spectroscopic ellipsometer (CSE). The new system has a feature that the major systematic and random error sources of the previous CSEs are effectively reduced or compensated for. In addition, the prototype preserves the advantageous features of the CSE in that it has a palm-size sensing head and that its acquisition time is as fast as 20 ms. Its performance is experimentally examined by use of 12 films whose thicknesses are ranging approximately from 3 to 4000 nm. The film thicknesses measured by the new CSE show good agreements with the ones by the rotating-compensator spectroscopic ellipsometer. The stability of the film-thickness measurement of the new CSE against the temperature change from 5 to 45 °C is less than 0.11 nm. The CSE can open up new applications of the spectroscopic ellipsometers in which the compactness, the simplicity, and the rapid response are important.
Ultralow noise field-effect transistor from multilayer graphene
Authors: Pal Atindra Nath , Ghosh Arindam
Published: August 2009

We present low-frequency electrical resistance fluctuations, or noise, in graphene-based field-effect devices with varying number of layers. In single-layer devices, the noise magnitude decreases with increasing carrier density, which behaved oppositely in the devices with two or larger number of layers accompanied by a suppression in noise magnitude by more than two orders in the latter case. This behavior can be explained from the influence of external electric field on graphene band structure, and provides a simple transport-based route to isolate single-layer graphene devices from those with multiple layers.
P
-
N
junction with donor and acceptor encapsulated single-walled carbon nanotubes
Authors: Kato Toshiaki , Hatakeyama Rikizo , Shishido Jun , Oohara Wataru , Tohji Kazuyuki
Published: August 2009

Ultimate one-dimensional heterojunctions of electron donor and acceptor materials have been realized within the inner hollow space of a single-walled carbon nanotube (SWNT). The heterojunction structures of Cs/I and Cs/C60 inside SWNTs (Cs/I@SWNTs, Cs/C60@SWNTs) yield the air-stable rectifying performance. Clear tunneling currents through the p-n junction barrier could be also detected only for Cs/I@SWNTs, which is explained by the difference of depletion layer structures. Based on a potential calculation, symmetrical and asymmetrical depletion layers were found to be formed in Cs/I@SWNTs and Cs/C60@SWNTs, respectively. Low temperature measurements also supply evidence of asymmetric depletion layer formation in Cs/C60@SWNTs.
Rolling stones: The motion of a sphere down an inclined plane coated with a thin liquid film
Authors: Bico J. , Ashmore-Chakrabarty J. , McKinley G. H. , Stone H. A.
Published: August 2009

A spherical bead deposited on a smooth tilted dry plane wall rolls down the slope under the uniform acceleration of gravity. We describe an analogous experiment conducted using a plane wall that is coated with a thin layer (of order 50–100 μm) of a viscous liquid. The steady motion of the sphere under gravity involves a combination of rotation and sliding. We examine the dependence of the experimentally observed steady translational and rotational speeds on the physical parameters in the system. In particular, the interplay between viscous forces and interfacial forces leads to nontrivial exponents for the scaling of the speeds with the characteristics of the sphere and the viscous liquid. The overhang situation, in which the sphere rolls down the underside of an inclined lubricated plane, is also examined. In this case, the steady motion is still observed for a certain range of angles and bead sizes; that is, the sphere does not always detach from the surface. The adhesive force arises dynamically from the motion of the sphere and can exceed classical quasistatic capillary forces. Such a force should also play a role in other problems of lubrication mechanics such as humid granular flows.
The correlation between electron density and anchoring strength in the inorganic vertical alignment layer
Authors: Hwang Byoung Har , Yoo Young Bum , Oh Jin Young , Chae Soo Sang , Baik Hong Koo , Lee Se Jong , Song Kie Moon
Published: August 2009

The relationship between the liquid crystal (LC) alignment and the density of the silicon oxide alignment layer was studied by theoretical and experimental approaches. The thin films were deposited by various methods and conditions, and then their densities were analyzed by x-ray reflectivity measurement. The alignment of LC was highly dependent on their densities, which we found to be closely related to the number of interacting dipoles. Ultimately, a-SiOx thin film with lower density gives rise to the uniform vertical alignment of liquid crystal.
A torsional parametric oscillator based on carbon nanotubes
Authors: Jeong Byeong-Woo , Sinnott Susan B.
Published: August 2009

Parametric oscillations are observed in torsional electromechanical oscillators based on carbon nanotubes via molecular dynamics simulations. The stretch of nanotube torsion springs due to the vertical translational-electrostatic force acting on the paddle makes possible the parametric oscillations. The electrostatic force can provide control over nanotube stretching that allows it to parametrically modulate the torsional spring constant at twice the resonance frequency. This reveals potential building blocks for a variety of applications of the devices.
Investigation on the role of nitrogen in crystallization of Sb-rich phase change materials
Authors: Choi Jihoon , Lee Hyun Seok , Lee Taek Sung , Lee Suyoun , Kim Won Mok , Kim Donghwan , Cheong Byung-ki
Published: August 2009

To better understand the role of nitrogen (N) during crystallization of Sb-rich phase change materials, a study was conducted using Sb and Sb70Te30 as host materials of N. Crystallization of the as-sputtered Sb–N films of varying N content was examined to reveal that Sb–N bonds are formed in the as-sputtered states, enhancing amorphous phase stability increasingly with N content. Crystallization appeared to proceed with irreversible dissociation of these bonds to form N2 molecules that may then exist stably during the subsequent memory operations. N2 molecules are considered to play as growth-retarding agents as demonstrated with memory operations of N-doped Sb70Te30.
Effect of the atmospheric pressure nonequilibrium plasmas on the conformational changes of plasmid DNA
Authors: Yan Xu , Zou Fei , Lu Xin Pei , He Guangyuan , Shi Meng Jun , Xiong Qing , Gao Xuan , Xiong Zilan , Li Yin , Ma Feng Yun , Yu Men , Wang Chang Dong , Wang Yuesheng , Yang Guangxiao
Published: August 2009

The cold atmospheric pressure plasma, which has been widely used for biomedical applications, may potentially affect the conformation of DNA. In this letter, an atmospheric pressure plasma plume is used to investigate its effects on the conformational changes of DNA of plasmid pAHC25. It is found that the plasma plume could cause plasmid DNA topology alteration, resulting in the percentage of the supercoiled plasmid DNA form decreased while that of the open circular and linearized form of plasmid DNA increased as detected by agrose gel electrophoresis. On the other hand, further investigation by using polymerase chain reaction method shows that the atmospheric pressure plasma jet treatments under proper conditions does not affect the genes of the plasmid DNA, which may have potential application in increasing the transformation frequency by genetic engineering.
Turbulence-induced secondary motion in a buoyancy-driven flow in a circular pipe
Authors: Hallez Yannick , Magnaudet Jacques
Published: August 2009

We analyze the results of a direct numerical simulation of the turbulent buoyancy-driven flow that sets in after two miscible fluids of slightly different densities have been initially superimposed in an unstable configuration in an inclined circular pipe closed at both ends. In the central region located midway between the end walls, where the flow is fully developed, the resulting mean flow is found to exhibit nonzero secondary velocity components in the tube cross section. We present a detailed analysis of the generation mechanism of this secondary flow which turns out to be due to the combined effect of the lateral wall and the shear-induced anisotropy between the transverse components of the turbulent velocity fluctuations.
Multiferroic properties of layer-structured Bi5Fe0.5Co0.5Ti3O15 ceramics
Authors: Mao Xiangyu , Wang Wei , Chen Xiaobing , Lu Yalin
Published: August 2009

Layer-structured, single phase Bi5Fe0.5Co0.5Ti3O15 ceramics was synthesized following a multicalcination procedure. Magnetic moment increases more than three times by substituting half Fe sites by Co ions. The material exhibits an Aurivillius phase with a four-layer unit cell structure, and presents a remarkable coexistence of ferroelectricity and ferromagnetism above room temperature. The measured 2Pr and 2Mr are 13 μC/cm2 and 7.8 memu/g, respectively. The material’s magnetic behavior below 275 °C is relaxationlike and its magnetic Curie temperature is ∼345 °C.
Double walled carbon nanotubes as ultrafast optical switches
Authors: Kamaraju N. , Kumar Sunil , Kim Y. A. , Hayashi T. , Muramatsu H. , Endo M. , Sood A. K.
Published: August 2009

Pristine and molybdenum filled double walled carbon nanotubes (DWNTs) suspended in D2O show excellent ultrafast optical switching properties investigated through femtosecond Z-scan and degenerate pump-probe method using 50 fs pulses with central photon energy of 1.57 eV. For pristine-DWNT, the two photon absorption coefficient, β and nonlinear refraction coefficient, n2 are 4.9×10−8 cm/W, and 9.5×10−11 cm2/W, respectively, which yield one photon figure of merit, W=133 and two photon figure of merit, T=0.4. The degenerate pump-probe measurements show strong photoinduced bleaching with biexponential decay with time constants ∼150 and 600 fs.
Conductance through a single impurity in the metallic zigzag carbon nanotube
Authors: Chang Po-Yao , Lin Hsiu-Hau
Published: August 2009

We investigate the conductance through a single impurity in the metallic zigzag carbon nanotube and find that it sensitively depends on the impurity strength and the bias voltage. The interplay between the current-carrying scattering states and the evanescent modes lead to rich phenomena including resonant backward scattering, perfect tunneling, and charge accumulations. In addition to the Friedel sum rule, we also find an exact relation between the conductance and the scattering phase. Finally, relevance of our findings to the realistic transport in carbon nanotubes is discussed.
DNA vaccination in rhesus macaques induces potent immune responses and decreases acute and chronic viremia after SIVmac251 challenge
Authors: Rosati Margherita , Bergamaschi Cristina , Valentin Antonio , Kulkarni Viraj , Jalah Rashmi , Alicea Candido , Patel Vainav , von Gegerfelt Agneta S. , Montefiori David C. , Venzon David J. , Khan Amir S. , Draghia-Akli Ruxandra , Van Rompay Koen K. A. , Felber Barbara K. , Pavlakis George N.
Published: August 2009

Optimized plasmid DNAs encoding the majority of SIVmac239 proteins and delivered by electroporation (EP) elicited strong immune responses in rhesus macaques. Vaccination decreased viremia in both the acute and chronic phases of infection after challenge with pathogenic SIVmac251. Two groups of macaques were vaccinated with DNA plasmids producing different antigen forms, “native” and “modified,” inducing distinct immune responses. Both groups showed significantly lower viremia during the acute phase of infection, whereas the group immunized with the native antigens showed better protection during the chronic phase (1.7 log decrease in virus load,
P
= 0.009). Both groups developed strong cellular and humoral responses against the DNA vaccine antigens, which included Gag, Pol, Env, Nef, and Tat. Vaccination induced both central memory and effector memory T cells that were maintained at the day of challenge, suggesting the potential for rapid mobilization upon virus challenge. The group receiving the native antigens developed higher and more durable anti-Env antibodies, including neutralizing antibodies at the day of challenge. These results demonstrate that DNA vaccination in the absence of any heterologous boost can provide protection from high viremia comparable to any other vaccine modalities tested in this macaque model.
Divergent investment strategies of
Acacia
myrmecophytes and the coexistence of mutualists and exploiters
Authors: Heil Martin , González-Teuber Marcia , Clement Lars W. , Kautz Stefanie , Verhaagh Manfred , Bueno Juan Carlos Silva
Published: August 2009

Ant-plant interactions represent a diversity of strategies, from exploitative to mutualistic, and how these strategies evolve is poorly understood. Here, we link physiological, ecological, and phylogenetic approaches to study the evolution and coexistence of strategies in the
Acacia–Pseudomyrmex
system. Host plant species represented 2 different strategies. High-reward hosts produced significantly more extrafloral nectar (EFN), food bodies, and nesting space than low-reward hosts, even when being inhabited by the same species of ant mutualist. High-reward hosts were more effectively defended against herbivores and exploited to a lower extent by nondefending ants than low-reward hosts. At the phenotypic level, secretion of EFN and ant activity were positively correlated and a mutualistic ant species induced nectar secretion, whereas a nondefending exploiter did not. All of these mechanisms contribute to the stable association of high-reward hosts with defending ant species. However, exploiter ants are less dependent on the host-derived rewards and can colonize considerable proportions of the low-reward hosts. Mapping these strategies onto phylogenetic trees demonstrated that the low-reward hosts represent the derived clade within a monophyletic group of obligate ant plants and that the observed exploiter ant species evolved their strategy without having a mutualistic ancestor. We conclude that both types of host strategies coexist because of variable net outcomes of different investment–payoff regimes and that the effects of exploiters on the outcome of mutualisms can, thus, increase the diversity within the taxa involved.
The spectral side of Arthur's trace formula
Authors: Finis Tobias , Lapid Erez M. , Müller Werner
Published: August 2009

The trace formula is one of the most important tools in the theory of automorphic forms. It was invented in the 1950's by Selberg, who mostly studied the case of hyperbolic surfaces, and was later on developed extensively by Arthur in the generality of an adelic quotient of a reductive group over a number field. Here we provide an explicit expression for the spectral side, improving Arthur's fine spectral expansion. As a result, we obtain its absolute convergence for a wide class of test functions.
The Snf1-related kinase, Hunk, is essential for mammary tumor metastasis
Authors: Wertheim Gerald B. W. , Yang Thomas W. , Pan Tien-chi , Ramne Anna , Liu Zhandong , Gardner Heather P. , Dugan Katherine D. , Kristel Petra , Kreike Bas , van de Vijver Marc J. , Cardiff Robert D. , Reynolds Carol , Chodosh Lewis A.
Published: August 2009

We previously identified a SNF1/AMPK-related protein kinase, Hunk, from a mammary tumor arising in an MMTV-neu transgenic mouse. The function of this kinase is unknown. Using targeted deletion in mice, we now demonstrate that Hunk is required for the metastasis of c-myc-induced mammary tumors, but is dispensable for normal development. Reconstitution experiments revealed that Hunk is sufficient to restore the metastatic potential of Hunk-deficient tumor cells, as well as defects in migration and invasion, and does so in a manner that requires its kinase activity. Consistent with a role for this kinase in the progression of human cancers, the human homologue of Hunk is overexpressed in aggressive subsets of carcinomas of the ovary, colon, and breast. In addition, a murine gene expression signature that distinguishes Hunk-wild type from Hunk-deficient mammary tumors predicts clinical outcome in women with breast cancer in a manner consistent with the pro-metastatic function of Hunk in mice. These findings identify a direct role for Hunk kinase activity in metastasis and establish an in vivo function for this kinase.
Computation of conformational transitions in proteins by virtual atom molecular mechanics as validated in application to adenylate kinase
Authors: Korkut Anil , Hendrickson Wayne A.
Published: August 2009

Many proteins function through conformational transitions between structurally disparate states, and there is a need to explore transition pathways between experimentally accessible states by computation. The sizes of systems of interest and the scale of conformational changes are often beyond the scope of full atomic models, but appropriate coarse-grained approaches can capture significant features. We have designed a comprehensive knowledge-based potential function based on a Cα representation for proteins that we call the virtual atom molecular mechanics (VAMM) force field. Here, we describe an algorithm for using the VAMM potential to describe conformational transitions, and we validate this algorithm in application to a transition between open and closed states of adenylate kinase (ADK). The VAMM algorithm computes normal modes for each state and iteratively moves each structure toward the other through a series of intermediates. The move from each side at each step is taken along that normal mode showing greatest engagement with the other state. The process continues to convergence of terminal intermediates to within a defined limit—here, a root-mean-square deviation of 1 Å. Validations show that the VAMM algorithm is highly effective, and the transition pathways examined for ADK are compatible with other structural and biophysical information. We expect that the VAMM algorithm can address many biological systems.
Water dynamics at neutral and ionic interfaces
Authors: Fenn Emily E. , Wong Daryl B. , Fayer M. D.
Published: August 2009

The orientational dynamics of water at a neutral surfactant reverse micelle interface are measured with ultrafast infrared spectroscopy of the hydroxyl stretch, and the results are compared to orientational relaxation of water interacting with an ionic interface. The comparison provides insights into the influence of a neutral vs. ionic interface on hydrogen bond dynamics. Measurements are made and analyzed for large nonionic surfactant Igepal CO-520reverse micelles (water nanopool with a 9-nm diameter). The results are compared with those from a previous study of reverse micelles of the same size formed with the ionic surfactant Aerosol-OT (AOT). The results demonstrate that the orientational relaxation times for interfacial water molecules in the two types of reverse micelles are very similar (13 ps for Igepal and 18 ps for AOT) and are significantly slower than that of bulk water (2.6 ps). The comparison of water orientational relaxation at neutral and ionic interfaces shows that the presence of an interface plays the dominant role in determining the hydrogen bond dynamics, whereas the chemical nature of the interface plays a secondary role.
Double-strand DNA breaks recruit the centromeric histone CENP-A
Authors: Zeitlin Samantha G. , Baker Norman M. , Chapados Brian R. , Soutoglou Evi , Wang Jean Y. J. , Berns Michael W. , Cleveland Don W.
Published: August 2009

The histone H3 variant CENP-A is required for epigenetic specification of centromere identity through a loading mechanism independent of DNA sequence. Using multiphoton absorption and DNA cleavage at unique sites by I-
Sce
I endonuclease, we demonstrate that CENP-A is rapidly recruited to double-strand breaks in DNA, along with three components (CENP-N, CENP-T, and CENP-U) associated with CENP-A at centromeres. The centromere-targeting domain of CENP-A is both necessary and sufficient for recruitment to double-strand breaks. CENP-A accumulation at DNA breaks is enhanced by active non-homologous end-joining but does not require DNA-PKcs or Ligase IV, and is independent of H2AX. Thus, induction of a double-strand break is sufficient to recruit CENP-A in human and mouse cells. Finally, since cell survival after radiation-induced DNA damage correlates with CENP-A expression level, we propose that CENP-A may have a function in DNA repair.
Invisible experiences: Understanding the choices and needs of university students with dependent children
Authors: Marandet Elodie , Wainwright Emma
Published: August 2009

This paper analyses the results of a research project on the experiences and learning needs of students with dependent children in a 1960s university. The findings are based on semi‐structured interviews with university services and academic staff, as well as a questionnaire survey among students with dependent children and follow‐up in‐depth interviews with a sample of 18 of these students. The paper shows that, for those surveyed, future employment opportunities and being a role model for their children were the main motivations for entering higher education and that their choice of university was highly spatially restricted by their caring responsibilities. It also discusses the main issues students faced once at university, including time and timing, finance, childcare, confidence, sense of belonging and skills. The paper highlights how gender and other biographical characteristics influence parents' experiences and includes suggestions for lessening the barriers they face while at university.
Cultural distance, mindfulness and passive xenophobia: Using Integrated Threat Theory to explore home higher education students’ perspectives on ‘internationalisation at home’
Authors: Harrison Neil , Peacock Nicola
Published: August 2009

This paper addresses the question of interaction between home and international students using qualitative data from 100 home students at two ‘teaching intensive’ universities in the southwest of England. Stephan and Stephan's Integrated Threat Theory is used to analyse the data, finding evidence for all four types of threat that they predict when outgroups interact. It is found that home students perceive threats to their academic success and group identity from the presence of international students on the campus and in the classroom. These are linked to anxieties around ‘mindful’ forms of interaction and a taboo around the discussion of difference, leading to a ‘passive xenophobia’ for the majority. The paper concludes that Integrated Threat Theory is a useful tool in critiquing the ‘internationalisation at home’ agenda, making suggestions for policies and practices that may alleviate perceived threats, thereby improving the quality and outcomes of intercultural interaction.