bluuebunny/crossref_metadata_2025 huggingface dataset:
Early reduction in prefrontal theta QEEG cordance value predicts response to venlafaxine treatment in patients with resistant depressive disorder
Authors: Bares Martin , Brunovsky Martin , Kopecek Miloslav , Novak Tomas , Stopkova Pavla , Kozeny Jiri , Sos Peter , Krajca Vladimir , Höschl Cyril
Published: May 2008

Introduction

Previous studies of patients with unipolar depression have shown that early decrease of prefrontal EEG cordance in theta band can predict clinical response to various antidepressants. We have now examined whether decrease of prefrontal quantitative EEG (QEEG) cordance value after 1 week of venlafaxine treatment predicts clinical response to venlafaxine in resistant patients.

Method

We analyzed 25 inpatients who finished 4-week venlafaxine treatment. EEG data were monitored at baseline and after 1 week of treatment. QEEG cordance was computed at three frontal electrodes in theta frequency band. Depressive symptoms and clinical status were assessed using Montgomery–Åsberg Depression Rating Scale (MADRS), Beck Depression Inventory-Short Form (BDI-S) and Clinical Global Impression (CGI).

Results

Eleven of 12 responders (reduction of MADRS ≥50%) and only 5 of 13 non-responders had decreased prefrontal QEEG cordance value after the first week of treatment (p = 0.01). The decrease of prefrontal cordance after week 1 in responders was significant (p = 0.03) and there was no significant change in non-responders. Positive and negative predictive values of cordance reduction for response were 0.7 and 0.9, respectively.

Conclusion

The reduction of prefrontal theta QEEG cordance value after first week of treatment might be helpful in the prediction of response to venlafaxine.
Preference‐based quality of life in patients with Alzheimer's disease
Authors: Karlawish Jason H. , Zbrozek Art , Kinosian Bruce , Gregory Annemarie , Ferguson Allison , Glick Henry A.
Published: May 2008

Background

This study was developed to evaluate the feasibility, reliability, and validity of use of patients' ratings of health preference measures as outcomes for cost‐effectiveness analyses in persons with very mild to moderate Alzheimer's disease (AD).

Methods

Patients and caregivers completed ratings of the EuroQol‐5D system (EQ‐5D) and the Health Utilities Index Mark 2 (HUI2) and instruments that assess cognition, mood, insight, AD‐specific and generic health‐related quality of life (QOL) and activities of daily living.

Results

Patients' HUI2 scores were reliable. EQ‐5D scores were somewhat less so. Patients rated their utility high, with overall EQ‐5D and HUI2 scores greater than 0.8. Neither the EQ‐5D nor the HUI2 scores had a relationship with severity of cognitive impairment. Both the EQ‐5D and the HUI2 had expected relationships with patient‐rated measures of QOL, function, mood, and specific subscales we hypothesized should be associated with patient preferences. Patient insight into functional and cognitive impairments had little association with their health preference scores.

Conclusions

AD patients' scores on the EQ‐5D and the HUI2 have many of the characteristics of valid preference measures. However, the proportions of persons who do not perceive any disability, the lack of association with the caregivers' ratings of activities of daily living, limited associations with insight, and no association with their Mini‐Mental State Exam scores suggest that patients' reports of disability might reflect legitimate self‐perceptions of mood and function that are associated with comorbidities rather than with AD.
Two dimensions of the Europeanization of election programs: The case of the Czech Republic
Authors: Havlík Vlastimil , Vykoupilová Hana
Published: May 2008

This article represents a contribution to the debate over the Europeanization of political parties, one of the hot topics in contemporary political science. It explores the extent of Europeanization in political parties represented in the lower chamber of the Parliament of the Czech Republic by means of an analysis of party election manifestoes. The extent of Europeanization in these documents is analyzed using a bi-dimensional conceptualization. The first we call the quantitative dimension, assesses the space taken by the topic of European integration in each manifesto. The second one we call the qualitative dimension. This, using the analysis of content, measures the degree to which the European integration issue is elaborated in the programs. Using this conceptualization, we analyze the election manifestoes of five Czech political parties in the period 1996–2006.
Applying VaR to REITs: A comparison of alternative methods
Authors: Lu Chiuling , Wu Sheng‐Ching , Ho Lan‐Chih
Published: May 2008

This study employs five methods to calculate the VaR of twelve REITs portfolios and evaluates the accuracy of these methods. Firstly, we find that the VaR varies among individual portfolios. The Hotel REITs has consistently the largest VaR. The low‐leveraging portfolio tends to have the largest VaR measured by the parametric methods, while the high leveraging portfolio has the largest VaR calculated by the non‐parametric methods. Secondly, each method performs differently at different confidence levels, and no method dominates the others. At the 95% confidence level, the EWMA method performs relatively well. The EQWMA and the two non‐parametric methods perform equivalently and slightly overestimate VaRs. The EQWMAT method ranks the bottom and significantly overestimates VaRs for all portfolios. At the 99% confidence level, the EQWMA method performs the best. The EQWMAT and the two non‐parametric methods perform equivalently and may overestimate VaR for all portfolios. The EWMA method turns out to be the worst and tends to underestimate the VaR. These findings may provide more insights for institutional real estate investors.
Constraints on the transient climate response from observed global temperature and ocean heat uptake
Authors: Knutti Reto , Tomassini Lorenzo
Published: May 2008

Projections of future transient global temperature increase in climate models for a known forcing depend on the strength of the atmospheric feedbacks and the rate of transient ocean heat uptake. A Bayesian framework and an intermediate complexity climate model are used to calculate a probability density function (PDF) of the transient climate response (TCR), constrained by observations of global surface warming and ocean heat uptake. The PDF constrained by observations is wider than the TCR range of current climate models, and has a slightly lower mean. Uncertainties in the observed ocean warming are shown to potentially affect the TCR. It is proposed, however, that even if models were found to overestimate ocean heat uptake, correcting that bias would lead to revisions in surface temperature projections over the twenty‐first century that are smaller than the uncertainties introduced by poorly quantified atmospheric feedbacks.
The decline in arctic sea‐ice thickness: Separating the spatial, annual, and interannual variability in a quarter century of submarine data
Authors: Rothrock D. A. , Percival D. B. , Wensnahan M.
Published: May 2008

Naval submarines have collected operational data of sea‐ice draft (93% of thickness) in the Arctic Ocean since 1958. Data from 34 U.S. cruises are publicly archived. They span the years 1975 to 2000, are equally distributed in spring and autumn, and cover roughly half the Arctic Ocean. The data set is strong: we use 2203 values of mean draft, each value averaged over a nominal length of 50 km. These values range from 0 to 6 m with a standard deviation of 0.99 m. Multiple regression is used to separate the interannual change, the annual cycle, and the spatial field. The solution gives a climatology for ice draft as a function of space and time. The residuals of the regression have a standard deviation of 0.46 m, slightly more than the observational error standard deviation of 0.38 m. The overall mean of the solution is 2.97 m. Annual mean ice draft declined from a peak of 3.42 m in 1980 to a minimum of 2.29 m in 2000, a decrease of 1.13 m (1.25 m in thickness). The steepest rate of decrease is −0.08 meters per year (m/a) in 1990. The rate slows to −0.007 m/a at the end of the record. The annual cycle has a maximum on 30 April and a peak‐to‐trough amplitude of 1.06 m (1.12 m in thickness). The spatial contour map of the temporal mean draft varies from a minimum draft of 2.2 m near Alaska to a maximum just over 4 m at the edge of the data release area 200 miles north of Ellesmere Island.
Near‐surface heating on Enceladus and the south polar thermal anomaly
Authors: Roberts J. H. , Nimmo F.
Published: May 2008

Strike‐slip motion is predicted to be a consequence of diurnal tidal stresses in most satellites of the outer solar system. Such motion can lead to near‐surface heating through friction or viscous dissipation. Here we discuss the effect of near‐surface shear heating on convection in the underlying ice shells of icy satellites. We present models of convection in spherical shells including tidal and shear heating, and show that localized near‐surface heating enhances convective upwelling beneath it. The near‐surface heating promotes regional melting of the ice shell, which likely results in subsidence of the surface topography. The long‐wavelength geoid resulting from the subsidence, plume buoyancy and dynamic topography may lead to small (≲4° per Ma) amounts of true polar wander, potentially contributing to the south polar location of the observed thermal anomaly. However compositional effects are likely required in addition to thermal effects to generate larger degrees of reorientation.
Small states, international pressures, and interlocking directorates: the cases of Switzerland and the Netherlands
Authors: Heemskerk Eelke M. , Schnyder Gerhard
Published: May 2008

Abstract Interlocking directorate networks among business enterprises have increasingly come under pressure due to internationalization and deregulation of markets. We show that in the small and internationalized economies of Switzerland and the Netherlands extensive changes have taken place. However, considerable differences in the form and the extent of these changes exist between the two countries. We argue that only by investigating which actors change their behavior we can understand and interpret the reasons for changes in the network structure. Combining a review of the Dutch and Swiss corporate governance landscape with a network analysis of board interlocks, we show that the changes in corporate networks are strongly affected by individual corporate strategies. The changing role of financial institutions in particular explains much of the variance between the two countries. Increasing influence of market pressures through dispersed ownership, on the contrary, does not explain changing patterns of interlocking directorates.
A new finance capitalism? Mutual funds and ownership re‐concentration in the United States
Authors: Davis Gerald F.
Published: May 2008

Abstract American households have vastly increased their participation in equity markets since the early 1980s, primarily through the purchase of shares in mutual funds. The resulting growth in assets managed by the mutual fund industry has been concentrated in a few fund complexes. Some of these – Fidelity in particular – have ended up holding very large ownership positions simultaneously in hundreds of US companies in the past few years, creating a latent network reminiscent of that operated by JP Morgan a century ago. Yet unlike the Morgan interests, mutual funds are relatively transient owners, rarely holding large ownership blocks for as long as 5 years. Moreover, funds are reticent to exercise their power, in part due to conflicts of interest. The result is that even the largest mutual funds are more likely to exit than to exercise voice, making the current version of American finance capitalism rather different from its predecessor.
Carbon nanoadditives to enhance latent energy storage of phase change materials
Authors: Shaikh Shadab , Lafdi Khalid , Hallinan Kevin
Published: May 2008

Latent energy storage capacity was analyzed for a system consisting of carbon nanoparticles doped phase change materials (PCMs). Three types of samples were prepared by doping shell wax with single wall carbon nanotubes (SWCNTs), multiwall CNTs, and carbon nanofibers. Differential scanning calorimetry was used to measure the latent heat of fusion. The measured values of latent heat for all the samples showed a good enhancement over the latent heat of pure wax. A maximum enhancement of approximately 13% was observed for the wax/SWCNT composite corresponding to 1% loading of SWCNT. The change in latent heat was modeled by using an approximation for the intermolecular attraction based on the Lennard-Jones potential. A theoretical model was formulated to estimate the overall latent energy of the samples with the variation in volume fraction of the nanoparticles. The predicted values of latent energy from the model showed good agreement with the experimental results. It was concluded that the higher molecular density of the SWCNT and its large surface area were the reasons behind the greater intermolecular attraction in the wax/SWCNT composite, which resulted in its enhanced latent energy. The novel approach used to predict the latent heat of fusion of the wax/nanoparticle composites has a particular significance for investigating the latent heat of PCM with different types of nanoparticle additives.
Quadrupole mass spectrometry and time-of-flight analysis of ions resulting from 532nm pulsed laser ablation of Ni, Al, and ZnO targets
Authors: Sage Rebecca S. , Cappel Ute B. , Ashfold Michael N. R. , Walker Nicholas R.
Published: May 2008

This work describes the design and validation of an instrument to measure the kinetic energies of ions ejected by the pulsed laser ablation (PLA) of a solid target. Mass spectra show that the PLA of Ni, Al, and ZnO targets, in vacuum, using the second harmonic of a Nd:YAG laser (532nm, pulse duration ∼10ns) generates abundant Xn+ ions (n⩽3 for Ni, ⩽2 for Al, ⩽3 and ⩽2 for Zn and O respectively from ZnO). Ions are selected by their mass∕charge (m∕z) ratio prior to the determination of their times of flight. PLA of Ni has been studied in most detail. The mean velocities of ablated Nin+ ions are shown to follow the trend v(Ni3+)>v(Ni2+)>v(Ni+). Data from Ni2+ and Ni3+ are fitted to shifted Maxwellian functions and agree well with a model which assumes both thermal and Coulombic contributions to ion velocities. The dependence of ion velocities on laser pulse energy (and fluence) is investigated, and the high energy data are shown to be consistent with an effective accelerating voltage of ∼90V within the plume. The distribution of velocities associated with Ni3+ indicates a population at cooler temperature than Ni2+.
Generation of fast neutrals in a laser-blow-off of LiF–C film: A formation mechanism
Authors: Singh R. K. , Kumar Ajai , Prahlad V. , Joshi H. C.
Published: May 2008

The temporal profiles of the spectral lines LiI and LiII emitted by a laser blow off of LiF–C film were analyzed. Fast neutrals having energies of ∼310eV were observed. It was found that these fast neutrals have kinetic energies similar to that of the ablated ions. Photon production rates at 670.8nm were estimated for the recombination and charge exchange processes. We attempted to qualitatively understand the role of electron-ion recombination (two and three body recombinations) and charge exchange processes in producing observed fast neutrals. Our analysis indicates that charge exchange is the dominant process in the production of fast neutrals.
Study of the first pulse of Ne-Xe-HCl dielectric barrier discharge for the excimer lamp
Authors: Belasri A. , Bendella S. , Baba-Hamed T.
Published: May 2008

A global one-dimensional model of a dielectric barrier discharge which includes the sheath region and the positive column was developed. The model was used to study the electrical properties under operating conditions of the vacuum ultraviolet excimer lamp and to understand the basic processes of plasma kinetics. A 0.5cm interelectrode gap distance is filled with a Ne-Xe-HCl mixture. Time variations of the charged particles and excited species in the positive column were described. Then the one-dimensional model was used in the cathode region to illustrate (i) the spatio-temporal behavior of electronic and ionic densities and the electric field, and (ii) the time variation of the voltage, the current, and secondary currents due to ion and photon (λ=172nm) impact on the cathode. It shows a good resolution inside the sheath at high pressure and it correctly predicts the waveform of the discharge behavior. The obtained results have been discussed and analyzed.
Thermal stability of graded exchange spring media under the influence of external fields
Authors: Suess D. , Fidler J. , Zimanyi G. , Schrefl T. , Visscher P.
Published: May 2008

The thermal stability of graded exchange spring media for perpendicular recording is investigated. It is found that the energy barrier linearly decreases with the external field strength. This leads to a high thermal stability in the low frequency recording limit, where large demagnetizing fields act on the media. The attempt frequency of graded media is about a factor of 5 larger than the attempt frequency of comparable single phase media.
Trace explosive detection using photothermal deflection spectroscopy
Authors: Krause Adam R. , Van Neste Charles , Senesac Larry , Thundat Thomas , Finot Eric
Published: May 2008

Satisfying the conditions of high sensitivity and high selectivity using portable sensors that are also reversible is a challenge. Miniature sensors such as microcantilevers offer high sensitivity but suffer from poor selectivity due to the lack of sufficiently selective receptors. Although many of the mass deployable spectroscopic techniques provide high selectivity, they do not have high sensitivity. Here, we show that this challenge can be overcome by combining photothermal spectroscopy on a bimaterial microcantilever with the mass induced change in the cantilever’s resonance frequency. Detection using adsorption-induced resonant frequency shift together with photothermal deflection spectroscopy shows extremely high selectivity with a subnanogram limit of detection for vapor phase adsorbed explosives, such as pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitramine (RDX), and trinitrotoluene (TNT).
Optical properties of nitrogen-doped SnO2 films: Effect of the electronegativity on refractive index and band gap
Authors: Pan S. S. , Zhang Y. X. , Teng X. M. , Li G. H. , Li L.
Published: May 2008

The optical properties of nitrogen-doped SnO2 films with different N2∕(N2+O2) gas ratios grown by reactive sputtering were studied by spectroscopy ellipsometry. The optical dielectric functions of the films were simulated by the Tauc-Lorentz model. It was found that the refractive index and extinction coefficient of nitrogen-doped SnO2 films increase and the band gap has a redshift with the increase of the N2 ratios. The general influences of the electronegativity and bond ionicity on the band gap, the refractive index in the spectral region below the fundamental absorption edge of nitrogen-doped SnO2, and other doped semiconductors are demonstrated.
The effects of plasma-processing conditions on the morphology of adherent human blood platelets
Authors: Murugesan R. , Hanley E. , Albrecht R. M. , Oliver J. A. , Heintz J. A. , Lauer J. L. , Shohet J. L.
Published: May 2008

Hematocompatibility and nonfouling properties of materials are crucial for the development of small-scale biomedical devices. This study examines the adhesion and morphology of purified human platelets on plasma-polymerized tetraglyme-coated glass substrates. The effect of varying the plasma-processing parameters on platelet responses was determined using scanning electron microscopy. Images of platelets on the coated surfaces show that a significant reduction in platelet adhesion and spreading can be achieved as the processing parameters are varied.
Dynamic densification behavior of nanoiron powders under shock compression
Authors: Dai C. D. , Eakins D. E. , Thadhani N. N.
Published: May 2008

The dynamic densification behavior of nanoiron powder (∼25nm particle size) prepressed to ∼35% and ∼45% of solid density was determined based on measurements of shock input stress and wave velocity by using piezoelectric stress gauges. The experimentally determined shock densification response is observed to be sensitive to the initial density (or porosity) of prepressed nanoiron powder compacts. Hugoniot measurements show an obvious densification-distension transition at ∼2GPa for the ∼35% dense and ∼6GPa for the ∼45% dense powder compacts. The densification and shock compression responses of the nanoiron powders are also calculated by using isobaric and isochoric models. Correlations of the model calculations with the measured data indicate that the shock Hugoniot of nanoiron powders cannot be correctly described by the currently available analytical models that are otherwise capable of predicting the Hugoniot of highly porous materials (prepressed compacts) of micron-sized powders.
Photonic crystal enhanced light-trapping in thin film solar cells
Authors: Zhou Dayu , Biswas Rana
Published: May 2008

We utilize photonic crystals to simulate enhanced light-trapping in a-Si:H thin film solar cells. A one dimensional photonic crystal or distributed Bragg reflector with alternating dielectric layers acts as low loss backreflector. A two dimensional photonic crystal between the absorber layer and the Bragg reflector diffracts light at oblique angles within the absorber. The photonic crystal geometry is optimized to obtain maximum absorption. The photonic crystal provides lossless diffraction of photons, increasing the photon path length within the absorber layer. The simulation predicts significantly enhanced photon harvesting between 600 and 775nm below the band edge, and an absorption increase by more than a factor of 10 near the band edge. The optical path length ratio can exceed the classical limit predicted for randomly roughened scattering surfaces at most wavelengths near the band edge. The optical modeling is performed with a rigorous scattering matrix approach where Maxwell’s equations are solved in Fourier space.
Self-consistent fluctuating hydrodynamics simulations of thermal transport in nanoparticle suspensions
Authors: He P. , Qiao R.
Published: May 2008

We report on the mesoscopic simulation of heat conduction in nanoparticle suspensions (nanofluids) by using the energy-conserving dissipative particle dynamics (DPD) method. Through coarse graining, our simulations probe the thermal and momentum transport in nanofluids at a length scale much greater than that in atomistic methods. We show that our simulations model the fluctuating hydrodynamics in nanofluids in a thermodynamically self-consistent manner, which is critical for resolving the current controversies on mechanisms of heat conduction in nanofluids. Simulation results indicate that the Brownian motion of nanoparticles plays a negligible role in determining the thermal conductivity of nanofluids at least within the framework of fluctuating hydrodynamics at mesoscales.
Exceptional points in linear gyrokinetics
Authors: Kammerer M. , Merz F. , Jenko F.
Published: May 2008

When performing linear gyrokinetic simulations, it is found that various types of microinstabilities, which are usually considered as strictly separated, can actually be transformed into each other via continuous variations of the plasma parameters. This behavior can be explained in terms of so-called exceptional points, which have their origin in the non-Hermiticity of the linear gyrokinetic operator and also occur in many other branches of physics. As a consequence, in large regions of parameter space, the designation of unstable modes should be done very carefully or even be avoided altogether.
Capillary threads and viscous droplets in square microchannels
Authors: Cubaud Thomas , Mason Thomas G.
Published: May 2008

We experimentally study the formation and evolution of threads containing more viscous liquids surrounded by less viscous, immiscible liquids through hydrodynamic focusing in square microchannels. Over a large range of viscosities and interfacial tensions, five characteristic regimes of flow behavior are identified: threading, jetting, dripping, tubing, and displacement. We locate the boundaries between these regimes on a flow map based on the capillary number of each fluid. In the jetting and the dripping regimes, the droplet size is measured and related to fluid properties, flow parameters, and geometry. The critical thread length before jetting droplets and the critical length of a viscous tail before breakup in dripping are also examined. This study classifies and defines regimes of thread instabilities that can be used to produce supra- and subchannel size viscous droplets in an elementary microfluidic geometry.
Bifurcations as dissociation mechanism in bichromatically driven diatomic molecules
Authors: Huang S. , Chandre C. , Uzer T.
Published: May 2008

We discuss the influence of periodic orbits on the dissociation of a model diatomic molecule driven by a strong bichromatic laser fields. Through the stability of periodic orbits, we analyze the dissociation probability when parameters, such as the two amplitudes and the phase lag between the laser fields, are varied. We find that qualitative features of dissociation can be reproduced by considering a small set of short periodic orbits. The good agreement with direct simulations demonstrates the importance of bifurcations of short periodic orbits in the dissociation dynamics of diatomic molecules.
Velocity correction and refractive index changes for [100] lithium fluoride optical windows under shock compression, recompression, and unloading
Authors: LaLone B. M. , Fat’yanov O. V. , Asay J. R. , Gupta Y. M.
Published: May 2008

Plate impact experiments were conducted to produce two and three step shock wave loadings in [100] ultrapure, lithium fluoride (LiF) crystals to examine the role of loading history on optical window response in laser interferometry measurements. Peak compressive stresses ranged between 5.0 and 17.5 GPa, and the window response was characterized by measuring the difference between the apparent and actual velocities of reflecting surfaces by using a velocity interferometer. In some experimental configurations, this velocity correction was obtained independently from the projectile velocity. Our results show that the velocity correction in [100] lithium fluoride windows can be described in all cases by a single linear relation, Δu=(0.2739±0.0016)u. Because this correction is independent of the loading history, it is applicable to arbitrary loading, which includes ramp-wave or shockless compression. By using the velocity correction and the measured particle and shock velocities, we have also determined the density dependence of the refractive index for [100] lithium fluoride at 532 nm to be n=(1.2769±0.0024)+(0.0443±0.000 82)ρ.
Invariants of the velocity-gradient, rate-of-strain, and rate-of-rotation tensors across the turbulent/nonturbulent interface in jets
Authors: da Silva Carlos B. , Pereira José C. F.
Published: May 2008

The invariants of the velocity gradient (R and Q), rate-of-strain (RS and QS), and rate-of-rotation (QW) tensors are analyzed across the turbulent/nonturbulent (T/NT) interface by using a direct numerical simulation (DNS) of a turbulent plane jet at Reλ≈120. The invariants allow a detailed characterization of the dynamics, geometry and topology of the flow during the entrainment. The invariants Q and QS are almost equal and negative outside the turbulent region close to the T/NT interface, which shows the existence of high values of strain product (hence viscous dissipation of kinetic energy) at that location. Right at the T/NT interface, the invariants QW and QS show that virtually all flow points there are characterized by irrotational dissipation, with no discernible sign of the coherent structures which are known to exist deep inside the turbulent region. Moreover, the invariants of the velocity gradient tensor (Q and R) show that the classical “teardrop” shape of their associated phase map is not yet formed at the T/NT interface. All the invariants rapidly change after the T/NT interface is crossed into the turbulent region. For instance, the enstrophy density, proportional to QW, is zero in the irrotational flow region and high and more or less constant inside the turbulent region, after it undergoes a sharp jump near the T/NT interface. Inside the turbulent region, at a distance of only 1.7η from the T/NT interface, where η is the Kolmogorov microscale, the invariants QW and QS suggest that large scale coherent vortices already exist in the flow. Furthermore, the joint probability density function of Q and R already displays its well known teardrop shape at that location. Moreover, the geometry of the straining (or deformation) of the fluid elements during the turbulent entrainment process is preferentially characterized by biaxial expansion with αS:βS:γS=2:1:−3, where αS, βS, and γS are the eigenvalues of the rate-of-strain tensor arranged in descending order. Based on an analysis of the invariants, many aspects of the flow topology inside the turbulent region at a distance of only 1.7η from the T/NT interface are already similar to those observed deep inside the turbulent region.
Temperature and doping dependence of phonon lifetimes and decay pathways in GaN
Authors: Beechem Thomas , Graham Samuel
Published: May 2008

The lifetimes of polar optical phonons are known to affect both the electrical and thermal performances of gallium nitride (GaN) based devices. Hence, understanding the dynamical behavior of these phonons in GaN is integral to the elucidation of carrier drift velocities, hot phonon effects, and temperature localization in these nitride semiconductors. To investigate this dynamic behavior, temperature dependent phonon lifetimes were acquired through utilization of the linewidth of the Raman response for GaN samples having various doping types and concentrations. The temperature dependent lifetimes of the four examined phonon modes were then correlated with the Klemens decay model modified to account for four-phonon processes to deduce the decomposition of the zone center phonons. A graphical method that maps this decomposition in the high symmetry directions of the Brillouin zone is also presented. From the variation in lifetime with free carrier concentration, dominant scattering mechanisms are subsequently found for each of four different phonon modes. It is observed that the phonon-carrier interaction directly determines the lifetimes of the polar optical A1 and E1(LO) modes, while the transverse modes into which these longitudinal phonons decay are independent of this interplay. These results indicate that temperature localization likely arises due to the continual emission and reabsorption between the LO phonon modes and the free carriers rather than the persistence of lattice/carrier interaction throughout the entirety of the energy cascade.
Dynamic fracture instability of tough bulk metallic glass
Authors: Meng J. X. , Ling Z. , Jiang M. Q. , Zhang H. S. , Dai L. H.
Published: May 2008

We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit.1) bulk metallic glass (BMGs) under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young’s modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs.
An evaluation of thermal stability of TiB2 metal gate on Hf silicate for p-channel metal oxide semiconductor application
Authors: Son S. Y. , Kumar P. , Cho H. , Min K. J. , Kang C. J. , Singh R. K.
Published: May 2008

An evaluation of TiB2 gate metal on Hf-silicate dielectric prepared by atomic layer deposition method has been reported. The extracted effective metal work function for TiB2 gate was about 5.08eV. The work function showed almost identical values and the sharp interface between metal and dielectric was confirmed after postdeposition annealing at 1000°C. The work function lowering (4.91eV) at 1100°C was caused by metal-dielectric intermixing and oxygen vacancy formation. TiB2 gate electrode was found to be suitable for use in p-channel metal oxide semiconductor device.
Analytical solutions for the electric field and dielectrophoretic force in a dielectrophoretic focusing electrode structure
Authors: Sun Tao , Green Nicolas G. , Morgan Hywel
Published: May 2008

The analysis of the movement of particles in a nonuniform field requires accurate knowledge of the electric field distribution. In this letter, the Schwarz–Christoffel mapping method is used to analytically solve the electric field distribution in a dielectrophoretic focusing electrode structure. The analytical result for the electric field distribution is validated by comparison with numerical simulations using the finite element method. The electric field solution is used to calculate the dielectrophoretic force on a particle in the system.
Standoff detection of trace amounts of solids by nonlinear Raman spectroscopy using shaped femtosecond pulses
Authors: Katz O. , Natan A. , Silberberg Y. , Rosenwaks S.
Published: May 2008

We demonstrate a single-beam, standoff (>10m) detection and identification of various materials including minute amounts of explosives under ambient light conditions. This is obtained by multiplex coherent anti-Stokes Raman scattering spectroscopy (CARS) using a single femtosecond phase-shaped laser pulse. We exploit the strong nonresonant background for amplification of the backscattered resonant CARS signals by employing a homodyne detection scheme. The simple and highly sensitive spectroscopic technique has a potential for hazardous materials standoff detection applications.
Crucial role of interdiffusion on magnetic properties of in situ formed MgO∕Fe3−δO4 heterostructured nanowires
Authors: Marcu Aurelian , Yanagida Takeshi , Nagashima Kazuki , Oka Keisuke , Tanaka Hidekazu , Kawai Tomoji
Published: May 2008

Although a heterointerface in oxides plays a crucial role on the properties, such heterointerface effects on oxide nanowires have not been well understood. Here, we demonstrate the crucial role of atomic interdiffusion on the magnetic properties of in situ formed MgO∕Fe3−δO4 heterostructured nanowires. The wide variation of nanowire heterointerfaces was found when varying the growth atmosphere. The occurrence of the interdiffusion and the large interface area of nanowires strongly affect the magnetism via forming mixed spinel structures at the heterointerface. Thus, it is crucial to precisely control the atomic interdiffusion at the heterointerface for the desired properties of heterostructured oxide nanowires.
Chemical nature of colossal dielectric constant of CaCu3Ti4O12 thin film by pulsed laser deposition
Authors: Deng Guochu , Xanthopoulos Nicolas , Muralt Paul
Published: May 2008

Epitaxial CaCu3Ti4O12 thin films grown by pulsed laser deposition were studied in the as-deposited and oxygen annealed state. The first one exhibited the usual transition from dielectric to colossal dielectric behavior upon increasing the temperature to above 100K. This transition disappeared after annealing at 900°C in air. The two states significantly differ in their x-ray photoelectron spectra. The state of colossal dielectric constant corresponds to a bulk material with considerable amounts of Cu+ and Ti3+, combined with Cu species enrichment at the surface. The annealed state exhibited a nearly stoichiometric composition with no Cu+ and Ti3+. The previously observed p-type conduction in the as-deposited state is thus related to oxygen vacancies compensated by the point defects of Cu+ and Ti3+.
Microwave-absorption properties of ZnO-coated iron nanocapsules
Authors: Liu X. G. , Geng D. Y. , Meng H. , Shang P. J. , Zhang Z. D.
Published: May 2008

The electromagnetic (EM) characteristics of ZnO-coated Fe nanocapsules synthesized by arc discharging were studied at 2–18GHz. A reflection loss (RL) exceeding −20dB was obtained in the frequency range of 6.1–15.7GHz for an absorber thickness of 1.5–5mm. An optimal RL of −57.1dB was found at 7.8GHz for an absorber thickness of 3.00mm. The excellent microwave-absorption properties are a consequence of a proper EM match in the nano-microstructure, a strong natural resonance, as well as multipolarization mechanisms. ZnO-coated Fe nanocapsules may be attractive candidates for EM-wave-absorption materials.
Growth evolution and decay properties of the abnormally switched domains in LiNbO3 crystals
Authors: Kan Yi , Bo Huifeng , Lu Xiaomei , Cai Wei , Liu Yunfei , Zhu Jinsong
Published: May 2008

Direct domain writing is carried out in single-crystalline stoichiometric LiNbO3 crystals using a scanning probe microscope. The abnormally switched domains with polarization antiparallel to the poling field are observed, and their growth and decay processes are systematically studied. The radius of these domains is proportional to the pulse magnitude while it remains constant as the pulse width varies. These abnormal domains quickly decay, the lifetime of which is linear with the poling pulse magnitude while it stretched exponentially increases with the increasing pulse width. The experimental results are carefully discussed in relation to the reported charge injection model.
Resolving cross sensitivity of fiber Bragg gratings with different polymeric coatings
Authors: Lu Ping , Men Liqiu , Chen Qiying
Published: May 2008

An approach to resolve the cross sensitivity of fiber Bragg gratings (FBGs) is proposed by the adoption of different polymers as the coating materials for gratings. From the different optical responses resulted from the gratings of different polymeric coatings, sensitivity to individual parameter can be exactly revealed. As an application of this approach, simultaneous discrimination of axial strain and temperature with two FBGs of different polymeric coatings is demonstrated with the axial strain and temperature sensitivities of 1.228pm∕με and 11.433pm∕°C for the acrylate-coated FBG, and 1.170pm∕με and 11.333pm∕°C for the polyimide-coated FBG, respectively.
Terahertz radiation from bacteriorhodopsin reveals correlated primary electron and proton transfer processes
Authors: Groma G. I. , Hebling J. , Kozma I. Z. , Váró G. , Hauer J. , Kuhl J. , Riedle E.
Published: May 2008

The kinetics of electrogenic events associated with the different steps of the light-induced proton pump of bacteriorhodopsin is well studied in a wide range of time scales by direct electric methods. However, the investigation of the fundamental primary charge translocation phenomena taking place in the functional energy conversion process of this protein, and in other biomolecular assemblies using light energy, has remained experimentally unfeasible because of the lack of proper detection technique operating in the 0.1- to 20-THz region. Here, we show that extending the concept of the familiar Hertzian dipole emission into the extreme spatial and temporal range of intramolecular polarization processes provides an alternative way to study ultrafast electrogenic events on naturally ordered biological systems. Applying a relatively simple experimental arrangement based on this idea, we were able to observe light-induced coherent terahertz radiation from bacteriorhodopsin with femtosecond time resolution. The detected terahertz signal was analyzed by numerical simulation in the framework of different models for the elementary polarization processes. It was found that the principal component of the terahertz emission can be well described by excited-state intramolecular electron transfer within the retinal chromophore. An additional slower process is attributed to the earliest phase of the proton pump, probably occurring by the redistribution of a H bond near the retinal. The correlated electron and proton translocation supports the concept, assigning a functional role to the light-induced sudden polarization in retinal proteins.
Regression supports two mechanisms of fork processing in phage T4
Authors: Long David T. , Kreuzer Kenneth N.
Published: May 2008

Replication forks routinely encounter damaged DNA and tightly bound proteins, leading to fork stalling and inactivation. To complete DNA synthesis, it is necessary to remove fork-blocking lesions and reactivate stalled fork structures, which can occur by multiple mechanisms. To study the mechanisms of stalled fork reactivation, we used a model fork intermediate, the origin fork, which is formed during replication from the bacteriophage T4 origin,
ori(34)
. The origin fork accumulates within the T4 chromosome in a site-specific manner without the need for replication inhibitors or DNA damage. We report here that the origin fork is processed
in vivo
to generate a regressed fork structure. Furthermore, origin fork regression supports two mechanisms of fork resolution that can potentially lead to fork reactivation. Fork regression generates both a site-specific double-stranded end (DSE) and a Holliday junction. Each of these DNA elements serves as a target for processing by the T4 ATPase/exonuclease complex [gene product (gp) 46/47] and Holliday junction-cleaving enzyme (EndoVII), respectively. In the absence of both gp46 and EndoVII, regressed origin forks are stabilized and persist throughout infection. In the presence of EndoVII, but not gp46, there is significantly less regressed origin fork accumulation apparently due to cleavage of the regressed fork Holliday junction. In the presence of gp46, but not EndoVII, regressed origin fork DSEs are processed by degradation of the DSE and a pathway that includes recombination proteins. Although both mechanisms can occur independently, they may normally function together as a single fork reactivation pathway.
The effect of a serotonin-induced dissociation between spiking and perisynaptic activity on BOLD functional MRI
Authors: Rauch Alexander , Rainer Gregor , Logothetis Nikos K.
Published: May 2008

The relationship of the blood oxygen-level-dependent (BOLD) signal to its underlying neuronal activity is still poorly understood. Combined physiology and functional MRI experiments suggested that local field potential (LFP) is a better predictor of the BOLD signal than multiunit activity (MUA). To further explore this relationship, we simultaneously recorded BOLD and electrophysiological activity while inducing a dissociation of MUA from LFP activity with injections of the neuromodulator BP554 into the primary visual cortex of anesthetized monkeys. BP554 is a 5-HT1A agonist acting primarily on the membrane of efferent neurons by potassium-induced hyperpolarization. Its infusion in visual cortex reliably reduced MUA without affecting either LFP or BOLD activity. This finding suggests that the efferents of a neuronal network pose relatively little metabolic burden compared with the overall presynaptic and postsynaptic processing of incoming afferents. We discuss implications of this finding for the interpretation of BOLD activity.
On the protection of “protected areas”
Authors: Joppa Lucas N. , Loarie Scott R. , Pimm Stuart L.
Published: May 2008

Tropical moist forests contain the majority of terrestrial species. Human actions destroy between 1 and 2 million km
2
of such forests per decade, with concomitant carbon release into the atmosphere. Within these forests, protected areas are the principle defense against forest loss and species extinctions. Four regions—the Amazon, Congo, South American Atlantic Coast, and West Africa—once constituted about half the world's tropical moist forest. We measure forest cover at progressively larger distances inside and outside of protected areas within these four regions, using datasets on protected areas and land-cover. We find important geographical differences. In the Amazon and Congo, protected areas are generally large and retain high levels of forest cover, as do their surroundings. These areas are protected
de facto
by being inaccessible and will likely remain protected if they continue to be so. Deciding whether they are also protected
de jure
—that is, whether effective laws also protect them—is statistically difficult, for there are few controls. In contrast, protected areas in the Atlantic Coast forest and West Africa show sharp boundaries in forest cover at their edges. This effective protection of forest cover is partially offset by their very small size: little area is deep inside protected area boundaries. Lands outside protected areas in the Atlantic Coast forest are unusually fragmented. Finally, we ask whether global databases on protected areas are biased toward highly protected areas and ignore “paper parks.” Analysis of a Brazilian database does not support this presumption.
Characteristics and Motives of College Students Who Engage in Nonmedical Use of Methylphenidate
Authors: DuPont Robert L. , Coleman John J. , Bucher Richard H. , Wilford Bonnie B.
Published: May 2008

Methylphenidate (MPH) has a long history of being an effective medication for attention deficit/hyperactivity disorder (ADHD). Recently, the nonmedical use of MPH has increased, particularly among college students. To investigate this, we surveyed 2,087 students regarding MPH misuse. Of 2,087 respondents, 110 (5.3%) used MPH nonmedically at least once. Most obtained MPH free from a friend, acquaintance, or family member. Misuse of Ritalin® occurred four times more frequently than Concerta.® Among Ritalin abusers, Intranasal use was reported more often than oral. Students reported using MPH nonmedically for recreational reasons as well as to improve academic performance.
Anhedonia and Amotivation in Psychiatric Outpatients with Fully Remitted Stimulant Use Disorder
Authors: Leventhal Adam M. , Kahler Christopher W. , Ray Lara A. , Stone Kristen , Young Diane , Chelminski Iwona , Zimmerman Mark
Published: May 2008

This study evaluated whether psychiatric outpatients with a past stimulant use disorder in full remission for ≥ 2 months (STIM+, n = 204) and those with no history of stimulant use disorder (STIM−, n = 2070) differed in the prevalence of current anhedonia and amotivation. Results showed that a significantly greater proportion of STIM+ participants reported anhedonia and amotivation than STIM− participants. The relation between stimulant use disorder history and anhedonia remained robust after controlling for other relevant clinical and demographic factors. These findings suggest that anhedonia may be a preexisting risk factor or protracted effect of stimulant misuse.
Correlates of Substance Use Among Homeless Youths in Eight Cities
Authors: Salomonsen‐Sautel Stacy , Van Leeuwen James M. , Gilroy Christine , Boyle Susan , Malberg Danielle , Hopfer Christian
Published: May 2008

Homeless youths (N = 684) in eight cities participated in this study to understand the rates and correlates of substance use. Rates of lifetime and recent substance use ranged from 66% to 90%. Variability in lifetime and recent substance use was partially explained by being white (ages 14–17); ever attempting suicide (ages 14–17); not being African American (lifetime substance use) or Hispanic (ages 18–24); being male (ages 18–24); identifying as lesbian, gay, or bisexual (ages 18–24); using substances with a parent; beginning substance use at a young age; and having a family history of a substance problem.