bluuebunny/crossref_metadata_2025 huggingface dataset:
Size‐resolved fluxes of sub‐100‐nm particles over forests
Authors: Pryor S. C. , Barthelmie R. J. , Spaulding A. M , Larsen S. E. , Petroff A.
Published: September 2009

Dry deposition of atmospheric particles is critically dependent on particle size and plays a key role in dictating the mass and number distributions of atmospheric particles. However, modeling dry deposition is constrained by a lack of understanding of controlling dependencies and accurate size‐resolved observations. We present size‐resolved particle number fluxes for sub‐100‐nm particle diameters (Dp) over a deciduous forest derived using eddy covariance applied to data from a fast mobility particle sizer. The size‐resolved particle number fluxes in 18 diameters between 8 and 100 nm were collected during leaf‐on and are statistically robust. Particle deposition velocities normalized by friction velocity (vd+) are approximately four times smaller than comparable values for coniferous forests reported elsewhere. Comparison of the data with output from a new one‐dimensional mechanistic particle deposition model designed for broadleaf forest exhibits greater accord with the measurements than two previous analytical models, but modeled vd+ underestimate observed values by at least a factor of two for all Dp between 6 and 100 nm. When size‐resolved particle deposition velocities for Dp < 100 nm are normalized by friction velocity, the key controlling role of particle diffusivity is strongly manifest. On the basis of analyses of these new measurements and recently published size‐resolved particle number fluxes from a conifer forest, we present working parameterizations for size‐resolved particle deposition velocities over forests that could reasonably be applied in regional and global atmospheric chemistry transport models.
Aprosodia Secondary to Right Hemisphere Damage
Authors: Rodriguez Amy D.
Published: September 2009

Purpose: This article introduces two types of prosody in human communication; describes right hemisphere contributions to prosody; describes prosodic deficits associated with right hemisphere damage; and discusses prevalence, quality of life, spontaneous recovery, and treatment of aprosodia.

Method: Definitions of affective and linguistic prosody and aprosodia are provided. Results of lesion studies and neuroimaging studies are reviewed to inform the reader of the importance of the right hemisphere in prosody expression and comprehension, as well as to describe patterns of prosodic deficits in individuals with right hemisphere damage.

Results and Conclusions: There is a large body of evidence supporting the role of the right hemisphere in affective prosody comprehension and production. Specifically, frontal brain regions and the basal ganglia are associated with aprosodia, suggesting there may be an underlying motor impairment. Because aprosodia is enduring and can impact quality of life, it is important to gain a better understanding of this disorder so that clinicians can accurately diagnose prosodic deficits and provide informed treatment.
Acoustic Correlates of Prosodic Abnormality in Acquired Apraxia of Speech
Authors: Jacks Adam
Published: September 2009

Purpose: Prosodic abnormality is one of the primary characteristics used for the perceptual differentiation between acquired apraxia of speech (AOS) and phonemic paraphasias in the context of fluent aphasia. Acoustic measures of speech prosody are not frequently used in the clinical assessment of AOS, but would be useful as a method of quantifying prosodic abnormality. The purpose of this paper is to describe acoustic characteristics of prosodic abnormality in adult speakers with AOS.

Method: Previous investigations of acoustic measures of speech prosody in AOS were reviewed, focusing on studies of duration, fundamental frequency (F0), and speech intensity.

Results and Conclusions: Prosodic abnormality in adults with AOS is primarily characterized by articulatory prolongation. In some individuals, relational patterns among syllables are retained despite overall increased duration, while others produce syllables that are temporally isolated, giving the impression that speech is programmed one syllable at a time. Syllable segregation is also noted in F0 and intensity contours that lack continuity across syllables. Metrics are suggested for use in quantification of prosodic abnormality in AOS. The review of findings, particularly slowed speech rate, is interpreted in the context of theoretical models of speech including impaired or intact feedback mechanisms in speakers with AOS.
Dysprosody and the Foreign Accent Syndrome
Authors: Haley Katarina L.
Published: September 2009

Purpose: The sudden emergence of a foreign accent in an individual's native language has been described in the literature for over 60 years. In one of the most famous cases, the terms prosody and dysprosody first were introduced to the literature. The purpose of this paper is to summarize the prosodic changes seen in the foreign accent syndrome (FAS) and to review its etiology and clinical course.

Method: Case studies were reviewed, with an emphasis on information about clinical presentation and course and on speech changes affecting stress, rate, duration, and intonation.

Results and Conclusions: In the majority of published cases with FAS, there has been documented focal brain injury in the left cerebral hemisphere, and the foreign accent has emerged after a period of recovery from muteness, nonfluent aphasia, and/or motor speech disorder. In other cases, a psychogenic etiology has been established or suggested. Stress, rate, and duration changes are similar to those seen in nonfluent aphasia and apraxia of speech, whereas intonation changes are more specific to the foreign accent presentation. Information about recovery and psychosocial consequences of the accented speech is sparse and these areas are in need of further study. In particular, there is a need for detailed and clinically oriented case studies with longitudinal follow-up.
Prosodic Impairment Associated With Traumatic Brain Injury
Authors: Irwin Billy
Published: September 2009

Purpose: This article discusses impaired prosody production subsequent to traumatic brain injury (TBI). Prosody may affect naturalness and intelligibility of speech significantly, often for the long term, and TBI may result in a variety of impairments.

Method: Intonation, rate, and stress production are discussed in terms of the perceptual, physiological, and acoustic characteristics associated with TBI.

Results and Conclusions: All aspects of prosodic production are susceptible to the effects of damage resulting from TBI. There are commonly associated prosodic impairments; however, individual variations in specific aspects of prosody require detailed analysis.
Antenna effects and improved efficiency in multiple heterojunction photovoltaic cells based on pentacene, zinc phthalocyanine, and C60
Authors: Hong Z. R. , Lessmann R. , Maennig B. , Huang Q. , Harada K. , Riede M. , Leo K.
Published: September 2009

For organic solar cells, effective absorption over a wide wavelength range is important. A simple donor-acceptor pair is usually not sufficient to reach this goal. Thus, it would be desirable to utilize multiple photoactive materials in a single cell. In this work, two hole conducting materials, pentacene and zinc phthalocyanine (ZnPc), and electron conducting C60 are chosen to construct three-component heterojunctions aiming at improved effective photon harvesting in organic solar cells. It is found that in pentacene/ZnPc/C60 multiple heterojunctions, part of the excitons in pentacene reach the ZnPc/C60 interface, where efficient exciton separation occurs and contributes to the photocurrent (PC). Triplet excitons are confirmed to be the major origin of PC by transient PC response measurements, suggesting that triplet-to-triplet energy transfer from pentacene to ZnPc is responsible for the improved PC of pentacene/ZnPc/C60 multiheterojunctions. Furthermore, exothermic energy transfer from ZnPc to the lower lying triplet levels of pentacene is employed for extending the absorption range and enlarging the absorption intensity. To realize such a structure, an ultrathin ZnPc layer is embedded in the pentacene film in pentacene/C60 single heterojunctions, leading to an enhanced quantum efficiency in the long wavelength range compared to the reference cell. These findings pave a way to efficient photovoltaic cells with a wide photoresponse ranging from near UV through the visible to the near infrared.
Theory of high field carrier transport and impact ionization in wurtzite GaN. Part II: Application to avalanche photodetectors
Authors: Moresco Michele , Bertazzi Francesco , Bellotti Enrico
Published: September 2009

The coming to age of GaN-based ultraviolet avalanche photodiodes (APDs) has made them increasingly preferred over PIN photodetectors in several areas spanning from communication to defense systems, and from commercial to scientific applications. In this work, which is the second article of a two-part series, we study the physics and performance of GaN APDs using the full-band Monte Carlo (FBMC) model described in Part I. The proposed FBMC model is based on a realistic electronic structure obtained by pseudopotential calculations and a phonon dispersion relation determined by ab initio techniques. We determine the key performance figures such as the carrier multiplication gain and the breakdown voltage for several GaN APD structures that have been fabricated by a number of experimental groups. The calculated electron and hole multiplication gains as a function of the applied bias, as well as the breakdown voltage, are found to be in good agreement with the experimental data available. Based on the FBMC results we also propose an efficient recurrence equation model, which provides a first-order estimate of the multiplication gain without resorting to the full fledge microscopic approach.
Excitation of surface plasma waves by an electron beam in a magnetized dusty plasma
Authors: Prakash Ved , Sharma Suresh C.
Published: September 2009

An electron beam drives surface plasma waves to instability on a vacuum magnetized dusty plasma interface and in a magnetized dusty plasma cylinder via Cerenkov and fast cyclotron interaction. The dispersion relation of a surface plasma wave has been derived and it has been shown that the phase velocity of waves increases with increase in relative density δ(=ni0/ne0)), where ni0 is the ion plasma density and ne0 is the electron plasma density of negatively charged dust grains. The frequency and the growth rate of the unstable wave instability also increases with δ. The growth rate of the instability increases with beam density and scales as the one-third power of the beam density in Cerenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there is no dust in the plasma cylinder.
Effect of electric field on negative linear expansion of ferroelectric-semiconductor TlGaSe2
Authors: Seyidov MirHasan Yu. , Suleymanov Rauf A. , Yakar Emin , Abdullayev N. A. , Mammadov T. G.
Published: September 2009

The effect of electric field on the thermal expansion of the TlGaSe2 ferroelectric-semiconductor with a layer crystalline structure has been investigated. A strong transformation of negative linear expansion coefficient in the layer plane has been observed as a result of the applied electric field. It was concluded that internal electric fields created by local polarized states in the ferroelectric- semiconductor are responsible for a negative thermal expansion and its behavior under the electric field. Predominantly, the electrostriction effect is the driving mechanism of the lattice deformation of TlGaSe2 crystals at low temperatures.
Meso-origami: Folding multilayer graphene sheets
Authors: Cranford Steven , Sen Dipanjan , Buehler Markus J.
Published: September 2009

Graphene features unique electronic, thermal, and mechanical properties, and the flexibility and strong attraction between graphene layers promotes the formation of self-folded nanostructures. Here we study the self-folding of mono- and multilayer graphene sheets, utilizing a coarse-grained hierarchical multiscale model derived directly from atomistic simulation. Our model, developed by enforcing assertion of energy conservation, enables the simulation of graphene folding across a range of length scales from nanometers to micrometers. Through theoretical and simulation analysis we show that the critical self-folded length is πC/γ, where C and γ are the bending stiffness per unit length and the surface energy per unit length.
Hall effect mobility of epitaxial graphene grown on silicon carbide
Authors: Tedesco J. L. , VanMil B. L. , Myers-Ward R. L. , McCrate J. M. , Kitt S. A. , Campbell P. M. , Jernigan G. G. , Culbertson J. C. , Eddy C. R. , Gaskill D. K.
Published: September 2009

Epitaxial graphene (EG) films were grown in vacuo by silicon sublimation from the (0001) and (0001¯) faces of 4H-SiC and 6H-SiC. Hall effect mobilities and sheet carrier densities of the films were measured at 300 and 77 K and the data depended on the growth face. About 40% of the samples exhibited holes as the dominant carrier, independent of face. Generally, mobilities increased with decreasing carrier density, independent of carrier type and substrate polytype. The contributions of scattering mechanisms to the conductivities of the films are discussed. The results suggest that for near-intrinsic carrier densities at 300 K epitaxial graphene mobilities will be ∼150 000 cm2 V−1 s−1 on the (0001¯) face and ∼5800 cm2 V−1 s−1 on the (0001) face.
Localized surface plasmon enhanced photoluminescence from ZnO films: Extraction direction and emitting layer thickness
Authors: Cheng Peihong , Li Dongsheng , Li Xiaoqiang , Liu Tao , Yang Deren
Published: September 2009

The light emission from ZnO films is enhanced by localized surface plasmon (LSP) of Ag island films. The dependence of LSP coupled emission on light-extracting direction and the thickness of ZnO films is investigated. It is found that the photoluminescence (PL) enhancement factors for upward extraction are much smaller than those for downward extraction. This is ascribed to the low transmittance and nonradiative absorption loss of Ag films. The near-field effect of LSP results in the dependence of the PL enhancement of ZnO films on the film thickness. A maximum PL enhancement factor of more than 15 is obtained when the thickness of ZnO was about 40 nm.
Surface chemistry dependence of native oxidation formation on silicon nanocrystals
Authors: Liptak R. W. , Kortshagen U. , Campbell S. A.
Published: September 2009

The growth of silicon oxide on bare and SF6-etched silicon nanocrystals (Si-NCs), which were synthesized by an all gas phase approach, was investigated by examining the surface chemistry and optical properties of the NCs over time. Consistent with previous work in the low temperature oxidation of silicon, the oxidation follows the Cabrera–Mott mechanism, and the measured data are well fitted to the Elovich equation. The use of the SF6 plasma is found to reduce the surface Si–H bond density and dramatically increase the monolayer growth rate. This is believed to be due to the much larger volatility of Si–F bonds compared to Si–H bonds on the surface of the NC.
Dynamics of the exchange field supplied by MnIr layers studied by network analyzer ferromagnetic resonance
Authors: Bilzer C. , Devolder T. , Kim Joo-Von , Chappert C. , Ruehrig M. , Baer L.
Published: September 2009

We study the interlayer exchange phenomenon in MnIr/permalloy and MnIr/CoFeB thin films. Using network analyzer ferromagnetic resonance, we determine the interlayer exchange field acting on the ferromagnetic layer at each point of its hysteresis loop. These exchange fields indicate that the exchange bias value extracted from the back and forth coercivities does not describe correctly the magnitude and time evolution of the interlayer exchange field upon reversal of the ferromagnet magnetization. In particular for CoFeB layers, the interlayer exchange field can vary by 60% in a small applied field span at 300 K, which foreseen consequences for device reliability.
Friction of soft elastomeric wrinkled surfaces
Authors: Rand Charles J. , Crosby Alfred J.
Published: September 2009

We evaluate the sliding of a rigid spherical lens over a surface-wrinkled, elastomeric substrate. Sliding is conducted both parallel and perpendicular to the aligned surface wrinkles, and the sliding force is compared to the required sliding forces on nonwrinkled surfaces. We evaluate the effects of wrinkle dimensions and applied normal force on the sliding resistance. A simple Bowden–Tabor friction model can describe the dependence of the sliding force on normal load, with different coefficients of friction associated with the nonwrinkled and wrinkled surfaces both perpendicular and parallel. The aspect ratio of the wrinkles has a secondary effect on the sliding force. We associate the changes in friction to changes in the tangential stiffness and fracture angle caused by the surface wrinkles.
Reinvestigation of the magnetic behavior of O3–LiCoO2
Authors: Artemenko Alla , Ménétrier Michel , Pollet Michaël , Delmas Claude
Published: September 2009

Stoichiometric high temperature LiCoO2 obtained by long annealing in oxygen was characterized by electron spin resonance and magnetization measurements. Both methods allow identifying unambiguously not only the presence of traces of cobalt oxides in the material but also paramagnetic defects in lithium cobaltite itself. We report on the presence of surface Li+–O− centers in pure LiCoO2, which has not been observed before in this material, and on the presence of Co2+ related centers in argon- and subsequent oxygen-annealed samples.
Scattering effects of phonons in two polymorphic structures of gallium nitride
Authors: Kang Nam Lyong , Choi Sang Don
Published: September 2009

Effects of piezoelectric and longitudinal optical (LO) phonon scatterings on transport of electrons confined in quasi-two-dimensional square wells of wurtzite and zinc-blende structures are compared by using a theory of absorption power derived in the linear response scheme. We find for GaN that the absorption power for both wurtzite and zinc-blende structures is keenly affected by the screening in such a way that the power increases, but the half width decreases as the electron density increases, and the piezoelectric phonon scattering is affected by the screening more than the optical phonon scattering. We also find that the piezoelectric phonon scattering (LO phonon scattering) is dominant at high (low) density and low (high) temperature in the wurtzite structure, whereas the tendency is reverse for the zinc-blende structure.
Synthesis of GaAs nanowires with very small diameters and their optical properties with the radial quantum-confinement effect
Authors: Zhang Guoqiang , Tateno Kouta , Sanada Haruki , Tawara Takehiko , Gotoh Hideki , Nakano Hidetoshi
Published: September 2009

We report the synthesis and optical properties of GaAs nanowires with very small diameters. We grew the GaAs nanowires by using size-selective gold particles with nominal diameters of 5, 10, 20, 40, and 60 nm. The diameter-controlled nanowires enable us to observe blueshifts of the free exitononic emission peak from individual nanowires with decreasing gold-particle size due to the two-dimensional radial quantum-confinement effect. We also analyze the absorption and emission polarization anisotropies of these bare GaAs quantum nanowires.
Tuning the remanent polarization of epitaxial ferroelectric thin films with strain
Authors: Zhang J. X. , Schlom D. G. , Chen L. Q. , Eom C. B.
Published: September 2009

The effect of biaxial strain on the remanent polarization of epitaxial thin films of various ferroelectric materials is studied using phenomenological Landau–Devonshire theory. It is shown that the strain dependences of the remanent polarizations are strongly dependent on crystal symmetries and film orientations. For (001)p-oriented ferroelectric films with (distorted) rhombohedral symmetry, strain-induced polarization rotation leads to stronger strain dependences than in ferroelectric films with tetragonal or orthorhombic symmetries. For (111)p-oriented ferroelectric films with rhombohedral symmetry, however, the remanent polarization is less sensitive to the biaxial strain.
Enhancement of light energy extraction from elliptical microcavity using external magnetic field for switching applications
Authors: Khoo E. H. , Ahmed I. , Li E. P.
Published: September 2009

In this letter, the extraction efficiency of light energy from an elliptically shaped microcavity laser is enhanced with external magnetic field. The magnetic field causes electrons to accumulate on the minor arc edge of the elliptical microcavity due to Lorentz force. As a result, the field amplitude at the minor arc edge is higher, and this improves light energy tunneling mechanism from the edge. The extraction efficiency from the microcavity increases by more than 30% after the application of magnetic field. Alternating the direction of the magnetic field allows the elliptical microcavity to function as a switching device.
Transient drain current characteristics of ZnO nanowire field effect transistors
Authors: Maeng Jongsun , Park Woojin , Choe Minhyeok , Jo Gunho , Kahng Yung Ho , Lee Takhee
Published: September 2009

We investigated the characteristics of the time-dependent drain current of ZnO nanowire field effect transistors (FETs). The drain current of ZnO nanowire FETs in ambient air decreases from an initial current level in the microampere range and saturates to the 1–100 nA range in tens of seconds. This transient phenomenon is ascribed to electrically interactive adsorption of oxygen ions to the nanowire surface. Exposure to ambient air during positive gate biasing reduces the conduction channel width by extending the depletion region, resulting in a higher resistivity with conduction only through the narrower nanowire core.
Experimental measurement of negative index in an all-dielectric metamaterial
Authors: Lepetit T. , Akmansoy É. , Ganne J.-P.
Published: September 2009

We designed and fabricated an all-dielectric metamaterial which exhibits negative index of refraction. This metamaterial consists of one layer made up of two sets of high permittivity resonators. We experimentally showed that this metamaterial exhibits resonant effective permeability and permittivity issued from the first two modes of Mie resonances, respectively, and that matching both these parameters results in negative effective index.
Relaxation and emission of Bragg-mode and cavity-mode polaritons in a ZnO microcavity at room temperature
Authors: Faure S. , Brimont C. , Guillet T. , Bretagnon T. , Gil B. , Médard F. , Lagarde D. , Disseix P. , Leymarie J. , Zúñiga-Pérez J. , Leroux M. , Frayssinet E. , Moreno J. C. , Semond F. , Bouchoule S.
Published: September 2009

The strong coupling regime in a ZnO microcavity is investigated through room temperature photoluminescence and reflectivity experiments. The simultaneous strong coupling of excitons to the cavity mode and the first Bragg mode is demonstrated at room temperature. The polariton relaxation is followed as a function of the excitation density, showing a nonthermal polariton distribution. A relaxation bottleneck is evidenced in the Bragg-mode polariton branch. It is partly broken under strong excitation density, so that the emission from this branch dominates the one from cavity-mode polaritons.
Branched carbon treelike structures grown in direct current plasmas
Authors: Ding F. , Zhu X. D. , Zhan R. J. , Ni T. L. , Ke B. , Zhou H. Y. , Chen M. D. , Wen X. H.
Published: September 2009

The growth of centimeter-scale treelike carbon structures in a hydrocarbon direct current (dc) plasma without the help of catalyst particles is reported. Starting from the edge of the anode, the carbon trees have a tendency to grow toward the cathode along the direction of the electric field. It is found that the trees exhibit graphitelike characteristics, or have a diamond body with a graphitelike core depending on the formation conditions. A growth model is proposed for the unusual growths, where powders formed in the dc plasma play a crucial role.
Harmonics and intermodulation in subthreshold FitzHugh–Nagumo neuron
Authors: Si Wenjie , Wang Jiang , Tsang K. M. , Chan W. L.
Published: September 2009

Intermodulation and harmonics are important in frequency analysis of nonlinear systems. In neuron research, most investigations are taken in studying synchronization between the external stimuli and the output of neuron, but harmonics and intermodulation are often ignored. In this paper, harmonics and intermodulation of the subthreshold FitzHugh–Nagumo neuron are investigated and their magnitudes are used to predict frequency response of the neuron. Furthermore, through analyzing the magnitudes of harmonics, the intrinsic frequencies of the neuron could be identified.
Fully nonlinear features of the energetic beam-driven instability
Authors: Lesur M. , Idomura Y. , Garbet X.
Published: September 2009

The so-called Berk–Breizman model is applied to a cold bulk, weak warm beam, one-dimensional plasma, to investigate the kinetic instability arising from the resonance of a single electrostatic wave with an energetic particle beam. A Vlasov code is developed to solve the initial value problem for the full-f distribution, and the nonlinear evolution is categorized in the whole parameter space as damped, steady-state, periodic, chaotic, or chirping. The saturation level of steady-state solutions and the bifurcation between steady-state and periodic solutions near marginal stability match analytic predictions. The limit of a perturbative numerical approach when the resonant region extends into the bulk is shown. Frequency sweeping is observed, with time-evolution approaching theoretical results. A new method to extract the dissipation rate from frequency diagnostics is proposed. For small collision rates, instabilities are observed in the linearly barely stable region.
Electronic properties of graphene nanoribbons embedded in boron nitride sheets
Authors: Ding Yi , Wang Yanli , Ni Jun
Published: September 2009

Using first principles calculations, we investigate the stabilities and electronic properties of graphene nanoribbons which are embedded in boron nitride (BN) sheets. We find that carbon atoms doped in BN sheets have stable hexagonal configurations and can form one-dimensional nanoribbons under suitable chemical potential conditions. All the armchair graphene nanoribbons embedded in BN sheets are semiconductors. While for the zigzag ones, the wide nanoribbons become half-metals.
Highly asymmetric magnetic behavior in exchange biased systems induced by noncollinear field cooling
Authors: Jiménez E. , Camarero J. , Sort J. , Nogués J. , Hoffmann A. , Teran F. J. , Perna P. , García-Martín J. M. , Dieny B. , Miranda R.
Published: September 2009

A detailed study of the angular dependence of the magnetization reversal in polycrystalline ferromagnetic (FM)/antiferromagnetic Co/IrMn bilayers with noncollinear FM and unidirectional anisotropies shows a peculiar asymmetric magnetic behavior. The anisotropy configuration is set via a field cooling (FC) procedure with the magnetic field misaligned with respect to the easy magnetization direction of the FM layer. Different magnetization reversal modes are observed for either positive or negative angles with respect to the FC direction. The angular dependence of both coercivity and exchange bias also clearly displays the broken symmetry of the induced noncollinearity. Our findings are reproduced with a modified Stoner–Wohlfarth model including the induced anisotropy configuration. Our results highlight the importance of the relative angle between anisotropies in exchange bias systems, opening a new path for the tailoring of their magnetic properties.
Fixed-angle observation of surface plasmon coupled chemiluminescence from palladium thin films
Authors: Aslan Kadir , Weisenberg Micah , Hortle Elinor , Geddes Chris D.
Published: September 2009

In this letter, the fixed-angle observation of surface plasmon coupled chemiluminescence (SPCC) from palladium thin films is reported. Fresnel calculations predict that light 492–549 nm spectral range can efficiently induce surface plasmon modes in 15 nm palladium thin films. Free-space emission from blue, green, and chartreuse chemiluminescent solutions on palladium thin films was isotropic, while the SPCC emission was highly directional and predominantly p-polarized in accordance with the predictions of the Fresnel calculations. In addition, the decay rates of the SPCC and free-space emission were similar, which suggests that palladium thin films have no catalytic effect on chemiluminescence emission.
The performance volatility of carbon nanotube-based devices: Impact of ambient oxygen
Authors: Chen Gugang , Paronyan Tereza M. , Pigos Elena M. , Sumanasekera Gamini U. , Harutyunyan Avetik R.
Published: September 2009

Understanding the performance volatility of carbon nanotube-based devices will expedite their applications. We performed in situ electrical and Raman scattering studies on an individual semiconducting single-walled carbon nanotube in the field-effect transistor geometry under different ambient and temperatures. The Raman G+ mode frequency responds in synchronization with changes in the charge density induced by an external gate voltage. Ambient caused a blueshift in the G+ mode and a reversible transformation of the device performance from n-type in vacuum to p-type in air, owing to the charge transfer-induced phonon renormalization by oxygen.
Quantum pumping with adiabatically modulated barriers in graphene
Authors: Zhu Rui , Chen Huiming
Published: September 2009

We study the adiabatic quantum pumping characteristics in graphene modulated by two oscillating gate potentials out of phase. The angular and energy dependence of the pumped current (PC) is presented. The direction of the PC can be reversed when a high potential barrier demonstrates stronger transparency than a low one, which results from the Klein paradox. The underlying physics of the pumping process is illuminated.
Hartree–Fock solutions as a quasidiabatic basis for nonorthogonal configuration interaction
Authors: Thom Alex J. W. , Head-Gordon Martin
Published: September 2009

Using the method of self-consistent field metadynamics, we locate some of the low-energy solutions to the Hartree–Fock (HF) equations on LiF and O3. The located solutions qualitatively resemble the adiabatic electronic states in these systems. We formulate the method of nonorthogonal Configuration Interaction (CI) to interact these solutions with cubic scaling with system size and quadratic scaling with the number of solutions. The resultant solutions display the avoided crossings and, in O3, a conical intersection expected of the adiabatic states. In LiF the relevant solutions coalesce and disappear from Unrestricted HF space indicating a more general HF theory is required.
Properties of the exact universal functional in multicomponent density functional theory
Authors: Chakraborty Arindam , Pak Michael V. , Hammes-Schiffer Sharon
Published: September 2009

Multicomponent density functional theory has been developed to treat systems with more than one type of quantum particle, such as electrons and nuclei, in an external potential. The existence of the exact universal multicomponent density functional in terms of the one-particle densities for each type of quantum particle has been proven. In the present paper, a number of important mathematical properties of the exact universal multicomponent density functional are derived. The expression relating the electron-proton pair density to the one-particle densities leads to an inequality for the potential energy component of the electron-proton correlation functional under well-defined conditions. General inequalities for the kinetic energy correlation functionals and the total electron-proton correlation functional are also derived. The coordinate scaling analysis leads to mathematical inequalities describing the effect of scaled densities on the kinetic, potential, and total energy functionals. The adiabatic connection formula defines the exact electron-proton functional in terms of an adiabatic scaling parameter that smoothly connects the noninteracting system with the fully interacting system. The virial expression provides the relation between the exact kinetic and potential energy functionals for the ground state densities of multicomponent systems. These mathematical relationships provide insight into the fundamental properties of the exact universal multicomponent density functional and serve as a guide for the development of approximate electron-proton density functionals.
Spatiotemporal dynamics and transport reduction in helical magnetic configuration
Authors: Rajković Milan , Watanabe Tomo-Hiko , Škorić Miloš
Published: September 2009

Effects of multihelicity confinement magnetic fields on turbulent transport and zonal flows are investigated by means of spatiotemporal analysis of gyrokinetic Vlasov simulation results for the ion temperature gradient turbulence, where the standard and the inward-shifted configurations of the Large Helical Device are considered. The analysis of simulation results demonstrates that fluctuations of electrostatic potential for zonal flows exhibit spatiotemporal chaos in both configurations. However, the intensity of chaos found is considerably decreased in the inward-shifted configuration consistent with improved confinement. Enhanced zonal flow generation in the inward shifted case is accompanied by transport reduction which may be a direct consequence of chaos suppression.
The influence of Saffman lift force on nanoparticle concentration distribution near a wall
Authors: Zheng Xu , Silber-Li Zhanhua
Published: September 2009

The lift force on a spherical nanoparticle near a wall in micro/nanofluidics has not received sufficient attention so far. In this letter the concentration of ϕ200 nm particles is measured at 0.25–2.0 μm to a wall in a microchannel with pressure-driven de-ionized water flow (pressure gradient 0–2000 kPa/m). The measured data show the influence of the lift force on the nanoparticle concentration distribution. By introducing the Saffman lift force into the Nernst–Planck equation near a wall, we find that the lift force is dominant at the range of 2<z+<6 (z+=z/2r, r is the particle radius, z is the distance from the wall).
A high-Q hybrid acoustic mode in thin film ZnO solidly mounted resonators
Authors: Wathen Adam D. , Munir Farasat , Hunt William D.
Published: September 2009

An extremely high-Q hybrid acoustic mode was observed in laterally excited c-axis ZnO solidly mounted resonators. The acoustic velocity through the thickness is approximately 3500 m/s which is inconsistent with both the thickness shear and longitudinal modes (2800 and 6400 m/s, respectively). In nearly 300 devices tested, the mode exhibits an average Q of 1957 with the highest observed being 34 000. With small device sizes relative to excitation wavelength and resonant frequency invariant with electrode geometry, we attribute this resonance to purely acoustic effects and not electromagnetic radiative effects. These devices have great potential for high frequency filters and sensing applications.
Photocarrier recombination dynamics in highly excited SrTiO3 studied by transient absorption and photoluminescence spectroscopy
Authors: Yamada Yasuhiro , Yasuda Hideki , Tayagaki Takeshi , Kanemitsu Yoshihiko
Published: September 2009

We studied photocarrier recombination processes in highly excited SrTiO3 crystals using pump-probe transient absorption (TA) and photoluminescence (PL) spectroscopy at room temperature. TA signals of nondoped SrTiO3 crystals clearly appear in the visible and infrared spectral region under intense interband photoexcitation, and TA spectra show Drude-like photon-energy dependence. Both TA and PL decay curves are well explained by the same simple rate equation including three-body Auger recombination and single-carrier trapping.
Nucleation of wetting films on cylindrical and spherical substrates: A numerical study by the string method
Authors: Qiu Chunyin , Qian Tiezheng
Published: September 2009

Using the mean-field diffuse-interface model for liquid-vapor system and employing the numerical string method, we study the critical nuclei involved in the prewetting transitions on curved substrates. We first introduce three distinct kinds of critical nuclei, namely, the disklike, bandlike, and layerlike ones, which respectively correspond to three possible growth modes of wetting films. We show the disklike growth mode to be the only mode for infinite planar substrates. We then turn to cylindrical and spherical substrates, the two simplest but most important geometries in the real world. We focus on the critical nuclei of finite size, through which the wetting films may be formed with finite thermodynamic probabilities. It is shown that the disklike growth mode is always the most probable for wetting film nucleation and growth as long as a disklike critical nucleus exists. It is also shown that on a cylindrical substrate, the disklike critical nucleus can no longer exist if the substrate radius is smaller than some critical value, comparable to the radius of the disklike critical nucleus on planar substrate. We find that on a cylindrical substrate whose radius is below the critical value, the nucleation and growth of a wetting film can only occur through the bandlike critical nucleus. It is worth emphasizing that the results concerning the bandlike and layerlike growth modes can only be obtained from the diffuse-interface model, beyond the macroscopic description based on the line and surface tensions.
Agents of Exception: Border Security and the Marginalization of Muslims in India
Authors: Jones Reece
Published: September 2009

The narratives of fear and uncertainty from the discourse of the ‘global war on terror’ have been used by many governments to expand securitization processes. As more aggressive security tactics have been deployed, scholars have sought to understand the changing relationship between individual rights and the authority of sovereign states by drawing on Giorgio Agamben's insights into the state of exception. In this paper I argue that borderlands are a key site for investigating the connections between the state of exception and securitization processes because political borders are the symbolic markers of the limits of a sovereign's authority. I trace the securitization of the borderlands between India and Bangladesh and I describe the increasingly exceptional measures employed by Indian border security forces in order to prevent terrorist threats from entering India. At the intersection of the state of exception in the borderlands and the securitization narratives and practices of the global war on terror, Muslims in both India and Bangladesh are marginalized in the affairs of the state and targeted in state-sanctioned violence. I conclude that borderlands, as an explicitly spatial example of the state of exception, are a crucial site for locating and understanding the decision on the exception.
The Regularity of Non-Being: Space and Form in Alain Badiou's System
Authors: Madarasz Norman
Published: September 2009

The aim of this paper is to show that insofar as it is possible to isolate a theory of space in Badiou's ontology it is incomplete and fragmented along at least three possible motifs: ruptured space, flat space, and dense space. From the presence of these motifs, I argue that the radical contingency Badiou seeks to give his concept of event is, in fact, closer to randomness. Randomness is predicted upon regulative patterns, however minimal they might be. This leads me to argue that there is a latent nonvitalist morphogenetic idea to the emergence of subjectivity in Badiou, which I call ‘formationism’: that is, an event-specific form is concomitant to the subject's naming of an event. This leads me to test Badiou's choice-based theory of subject against three other perspectives in the work of Jocelyn Benoist, Gilles Châtelet, and Jean Petitot. Finally, I contrast the concept of event with the reading Barbara Cassin gives in kairos, which submits ontology to an exclusionist charge. The upshot of this critique holds as much for an empowered reading of rhetoric against formal logic as it does for securing the contribution made by sophists to ontology.
Precaution, Preemption: Arts and Technologies of the Actionable Future
Authors: de Goede Marieke , Randalls Samuel
Published: September 2009

Terrorism and climate change are frequently perceived as ‘total threats’ articulated and imagined through a wide array of arts and technologies. If the construction of these threats appears similar then so are the pleas for preemptive and precautionary action. In this paper we explore the ways in which terrorism and climate change are imagined, drawing on a conjoined history in which preemption and precaution are not easily separable. We then trace this through the knowledges, models, and ideas of risk that inform contemporary debates on these issues and suggest that these are caught between a desire for rationality and affective governance through catastrophic visions. Furthermore, we argue that these imaginations of an actionable future have political consequences that depoliticize and delegitimate debate and that potentially bring the unimaginable into being. Reconceiving precautionary politics is thus vital if we are to engage ethically with the world.
The implementation of routine outcome measures in a Tier 3 Psychological Therapies Service: The process of enhancing data quality and reflections of implementation challenges
Authors: Rao Amra S. , Hendry Gemma , Watson Robert
Published: September 2009

Background: The Newham Psychological Therapies Service (PTS) has been using the CORE System of evaluation to demonstrate effectiveness since 2004. More recently there has been the national and local drive to improve outcomes as outlined by a number of Department of Health policies and the Improving Access to Psychological Therapies (IAPT) initiative. Aims: This paper describes how, as a secondary care complex mental health service, we have engaged with the process of outcome measurement through complementing the usage of the CORE System with additional measures forming the service pilot minimum dataset. The process of implementation is outlined along with reflections on the challenges which the service faced in introducing outcome measurement. Findings: Engagement with outcome measurement by a service requires attention to be paid to the organisational and professional aspects and personal resonances for clinicians if it is to become established as a meaningful enterprise within secondary care services. Despite success at this task, challenges remain to the further development of this area of work.
Who drops‐out? Do measures of risk to self and to others predict unplanned endings in primary care counselling?
Authors: Saxon David , Ricketts Tom , Heywood Joanna
Published: September 2009

Aims: Unplanned endings, where clients unilaterally end therapy, are of concern for psychological therapy services generally as they raise questions about the appropriateness of the treatment and it's delivery for some clients. Limited available data indicates that those who drop‐out often have more severe symptoms at entry, and have poorer clinical outcomes. This raises further questions about risk to self and others for those clients who leave therapy prematurely and how these clients might be identified and kept engaged. Method: This paper uses a large dataset of CORE data collected routinely in a primary care counselling service between 2000 and 2003. Logistic regression was utilised to consider different measures of risk and other client characteristics recorded at assessment to predict drop‐out from the service. Results: These indicate that younger age, greater psychological distress at assessment, an addiction problem and greater risk to others, are associated with an unplanned ending. However, no reliable logistic regression model could be produced. This may be partly due to data quality issues or important characteristics not being available in the data. Implications for practice: The paper concludes that counsellors should actively seek to minimise unplanned endings, as amongst them may be represented the more distressed and risky clients referred to primary care counselling.
Suppression of Ca2+ syntillas increases spontaneous exocytosis in mouse adrenal chromaffin cells
Authors: Lefkowitz Jason J. , Fogarty Kevin E. , Lifshitz Lawrence M. , Bellve Karl D. , Tuft Richard A. , ZhuGe Ronghua , Walsh John V. , De Crescenzo Valerie
Published: September 2009

A central concept in the physiology of neurosecretion is that a rise in cytosolic [Ca2+] in the vicinity of plasmalemmal Ca2+ channels due to Ca2+ influx elicits exocytosis. Here, we examine the effect on spontaneous exocytosis of a rise in focal cytosolic [Ca2+] in the vicinity of ryanodine receptors (RYRs) due to release from internal stores in the form of Ca2+ syntillas. Ca2+ syntillas are focal cytosolic transients mediated by RYRs, which we first found in hypothalamic magnocellular neuronal terminals. (scintilla, Latin for spark; found in nerve terminals, normally synaptic structures.) We have also observed Ca2+ syntillas in mouse adrenal chromaffin cells. Here, we examine the effect of Ca2+ syntillas on exocytosis in chromaffin cells. In such a study on elicited exocytosis, there are two sources of Ca2+: one due to influx from the cell exterior through voltage-gated Ca2+ channels, and that due to release from intracellular stores. To eliminate complications arising from Ca2+ influx, we have examined spontaneous exocytosis where influx is not activated. We report here that decreasing syntillas leads to an increase in spontaneous exocytosis measured amperometrically. Two independent lines of experimentation each lead to this conclusion. In one case, release from stores was blocked by ryanodine; in another, stores were partially emptied using thapsigargin plus caffeine, after which syntillas were decreased. We conclude that Ca2+ syntillas act to inhibit spontaneous exocytosis, and we propose a simple model to account quantitatively for this action of syntillas.