bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Asymmetries in Normophonic Speakers: Visual Judgments and Objective Findings
Authors: Bonilha Heather Shaw , Deliyski Dimitar D. , Gerlach Terri Treman
Published: October 2008

Purpose

To ascertain the amount of phase asymmetry of the vocal fold vibration in normophonic speakers via visualization techniques and compare findings for habitual and pressed phonations.

Method

Fifty-two normophonic speakers underwent stroboscopy and high-speed videoendoscopy (HSV). The HSV images were further processed into 4 visual displays: HSV playbacks, digital kymography (DKG) playbacks, mucosal wave kymography playbacks, and static kymographic images of the medial line from the DKG playback. Two types of phase asymmetries, left-right and anterior-posterior, were rated on a scale from 1 to 5. Objective measures of left-right phase asymmetry were obtained.

Results

The majority of normophonic speakers (81%) were noted to display anterior-posterior asymmetry; however, 66% of those were characterized as mild. Seventy-nine percent of participants were noted to display left-right asymmetry; however, 72% of those were mild. A moderate relationship between the objective measures and subjective ratings was found.

Conclusions

Most normophonic speakers exhibit mild left-right and anterior-posterior asymmetries for both habitual and pressed phonations. Asymmetries were noted more often during habitual than pressed phonations, and when visualized by HSV and kymography than stroboscopy. Differences between objective measures and visual judgments support the need to quantify vocal fold vibratory features.
A Buyer's Guide to Generic Pharmaceutical Acquisitions
Authors: Sayre Stephen D.
Published: October 2008

This paper provides the generic pharmaceutical executive with a legal roadmap for acquiring pharmaceutical assets. It describes the three main steps to product acquisition, which are as follows: (1) negotiation and execution of a detailed letter of intent; (2) performance of buyer's due diligence; and (3) negotiation and closing of the acquisition agreement. It also explains the relationship among these three steps and why each step is important to the buyer. In discussing each step of the acquisition process, this paper identifies the key considerations and issues for the buyer to help the buyer mitigate the risks inherent in the acquisition of generic pharmaceutical assets.
Rapid degradation of CdSe∕ZnS colloidal quantum dots exposed to gamma irradiation
Authors: Withers Nathan J. , Sankar Krishnaprasad , Akins Brian A. , Memon Tosifa A. , Gu Tingyi , Gu Jiangjiang , Smolyakov Gennady A. , Greenberg Melisa R. , Boyle Timothy J. , Osiński Marek
Published: October 2008

Effects of Cs137 gamma irradiation on photoluminescent properties of CdSe∕ZnS colloidal quantum dots are reported. Optical degradation is evaluated by tracking the dependence of photoluminescence intensity on irradiation dose. CdSe∕ZnS quantum dots show poor radiation hardness, and severely degrade after less than 20kR exposure to 662keV gamma photons.
A correlation electron cyclotron emission diagnostic and the importance of multifield fluctuation measurements for testing nonlinear gyrokinetic turbulence simulations
Authors: White A. E. , Schmitz L. , Peebles W. A. , Carter T. A. , Rhodes T. L. , Doyle E. J. , Gourdain P. A. , Hillesheim J. C. , Wang G. , Holland C. , Tynan G. R. , Austin M. E. , McKee G. R. , Shafer M. W. , Burrell K. H. , Candy J. , DeBoo J. C. , Prater R. , Staebler G. M. , Waltz R. E. , Makowski M. A.
Published: October 2008

A correlation electron cyclotron emission (CECE) diagnostic has been used to measure local, turbulent fluctuations of the electron temperature in the core of DIII-D plasmas. This paper describes the hardware and testing of the CECE diagnostic and highlights the importance of measurements of multifield fluctuation profiles for the testing and validation of nonlinear gyrokinetic codes. The process of testing and validating such codes is critical for extrapolation to next-step fusion devices. For the first time, the radial profiles of electron temperature and density fluctuations are compared to nonlinear gyrokinetic simulations. The CECE diagnostic at DIII-D uses correlation radiometry to measure the rms amplitude and spectrum of the electron temperature fluctuations. Gaussian optics are used to produce a poloidal spot size with wo∼1.75 cm in the plasma. The intermediate frequency filters and the natural linewidth of the EC emission determine the radial resolution of the CECE diagnostic, which can be less than 1 cm. Wavenumbers resolved by the CECE diagnostic are kθ≤1.8 cm−1 and kr≤4 cm−1, relevant for studies of long-wavelength turbulence associated with the trapped electron mode and the ion temperature gradient mode. In neutral beam heated L-mode plasmas, core electron temperature fluctuations in the region 0.5<r/a<0.9, increase with radius from ∼0.5% to ∼2%, similar to density fluctuations that are measured simultaneously with beam emission spectroscopy. After incorporating “synthetic diagnostics” to effectively filter the code output, the simulations reproduce the characteristics of the turbulence and transport at one radial location r/a=0.5, but not at a second location, r/a=0.75. These results illustrate that measurements of the profiles of multiple fluctuating fields can provide a significant constraint on the turbulence models employed by the code.
Detailed characteristics of drop-laden mixing layers: Large eddy simulation predictions compared to direct numerical simulation
Authors: Okong’o Nora , Leboissetier Anthony , Bellan Josette
Published: October 2008

Results are compared from direct numerical simulation (DNS) and large eddy simulation (LES) of a temporal mixing layer laden with evaporating drops to assess the ability of LES to reproduce detailed characteristics of DNS. The LES used computational drops, each of which represented eight physical drops, and a reduced flow field resolution using a grid spacing four times larger than that of the DNS. The LES also used models for the filtered source terms, which express the coupling of the drops with the flow, and for the unresolved subgrid-scale (SGS) fluxes of species mass, momentum, and enthalpy. The LESs were conducted using one of three different SGS-flux models: dynamic-coefficient gradient (GRD), dynamic-coefficient Smagorinsky (SMD), and constant-coefficient scale similarity (SSC). The comparison of the LES with the filtered-and-coarsened (FC) DNS considered detailed aspects of the flow that are of interest in ignition or full combustion. All LESs captured the largest-scale vortex, the global amount of vapor emanating from the drops, and the overall size distribution of the drops. All LESs tended to underpredict the global amount of irreversible entropy production (dissipation). The SMD model was found unable to capture either the global or local vorticity variation and had minimal small-scale activity in dynamic and thermodynamic variables compared to the FC-DNS. The SMD model was also deficient in predicting the spatial distribution of drops and of the dissipation. In contrast, the GRD and SSC models did mimic the small-scale activity of the FC-DNS and the spatial distribution of drops and of the dissipation. Therefore, the GRD and SSC models are recommended, while the SMD model seems inappropriate for combustion or other problems where the local activity must be predicted.
Azimuthal asymmetries of the large-scale circulation in turbulent Rayleigh–Bénard convection
Authors: Brown Eric , Ahlers Guenter
Published: October 2008

Previously we published a dynamical model [E. Brown and G. Ahlers, Phys. Fluids 20, 075101 (2008)] for the large-scale-circulation (LSC) dynamics of Rayleigh–Bénard convection in cylindrical containers. The model consists of a pair of stochastic ordinary differential equations, motivated by the Navier–Stokes equations, one each for the strength δ and the orientation θ0 of the LSC. Here we extend it to cases where the rotational invariance of the system is broken by one of several physically relevant perturbations. As an example of this symmetry breaking we present experimental measurements of the LSC dynamics for a container tilted relative to gravity. In that case the model predicts that the buoyancy of the thermal boundary layers encourages fluid to travel along the steepest slope, that it locks the LSC in this direction, and that it strengthens the flow, as seen in experiments. The increase in LSC strength is shown to be responsible for the observed suppression of cessations and azimuthal fluctuations. We predict and observe that for large enough tilt angles, the restoring force that aligns the flow with the slope is strong enough to cause oscillations of the LSC around this orientation. This planar oscillation mode is different from coherent torsional oscillations that have been observed previously. The model was applied also to containers with elliptical cross sections and predicts that the pressure due to the side wall forces the flow into a preferred orientation in the direction of the longest diameter. When the ellipticity is large enough, then oscillations around this orientation are predicted. The model shows that various azimuthal asymmetries will lock the LSC orientation. However, only those that act on the δ-equation (such as tilting relative to gravity) will enhance the LSC strength and suppress cessations and other azimuthal dynamics. Those that affect only the θ0 equation, such as an interaction with Earth’s Coriolis force, will align the flow but will not influence its strength and the frequency of cessations.
Modeling the sequence-dependent diffusion coefficients of short DNA molecules
Authors: Gonzalez O. , Li J.
Published: October 2008

A boundary element model for the computation of sequence-dependent hydrodynamic properties of short DNA molecules is introduced. The hydrated surface is modeled as a curved tube of uniform radius with ends capped by hemispheres, and the axis of the tube is a general space curve whose length and curvature are determined locally by the sequence using a rigid basepair model of double-helical DNA with parameters based on x-ray crystallography. Diffusion coefficients for families of random and periodic DNA sequences are computed and compared with theories for straight tubes and experimental data. Our results indicate that sequence-dependent curvature can have a measurable impact on both the translational and rotational diffusion coefficients, even for relatively short fragments of lengths less than about 150 basepairs, and that previous estimates of the hydrated radius of DNA are likely to be underestimates. Moreover, our results suggest a possible method for refining the rigid basepair model parameters for DNA in solution as well as the hydrated radius.
Patterns in surface driven flows
Authors: Osman Kahar Bin , McHugh John P. , Wei Timothy
Published: October 2008

Flow in a rectangular basin driven by a surface force is considered. The problem is motivated by flow in geophysical bodies of water driven by wind at the water surface. Results are obtained via numerical computations of the Navier–Stokes equations assuming constant density. The numerical integration is achieved with a splitting method, with Crank–Nicolson for the linear terms, and Adams–Bashforth for the nonlinear terms. Spatial derivatives are treated with finite differences. The forcing has a sinusoidal variation across the top with a sequence of length scales. The results show a symmetric steady stable flow for small Reynolds numbers. As the Reynolds number is increased, the system experiences either a subcritical or supercritical pitchfork bifurcation to an asymmetric steady stable flow, or a local Hopf bifurcation, depending on the aspect ratio of the container and the length scale of the forcing. The asymmetric flow is cellular for forcing length scales commensurate with the depth. For smaller forcing length scales, the asymmetric flow has a basin-filling character at the bottom portion of the basin.
Free energy landscapes of a highly structured β-hairpin peptide and its single mutant
Authors: Kim Eunae , Yang Changwon , Jang Soonmin , Pak Youngshang
Published: October 2008

We investigated the free energy landscapes of a highly structured β-hairpin peptide (MBH12) and a less structured peptide with a single mutation of Tyr6 to Asp6 (MBH10). For the free energy mapping, starting from an extended conformation, the replica exchange molecular dynamic simulations for two β-hairpins were performed using a modified version of an all-atom force field employing an implicit solvation (param99MOD5/GBSA). With the present simulation approach, we demonstrated that detailed stability changes associated with the sequence modification from MBH12 to MBH10 are quantitatively well predicted at the all-atom level.
Ionization and shielding of interface states in native p+-Si/SiO2 probed by electric field induced second harmonic generation
Authors: Scheidt T. , Rohwer E. G. , Neethling P. , von Bergmann H. M. , Stafast H.
Published: October 2008

Electric field induced second harmonic measurements applying femtosecond laser pulses (1.59 eV, 80±5 fs, 80 MHz) to substantially boron doped p+-Si/SiO2 interfaces reveal a temporal evolution of the second harmonic (SH) signal, which differs drastically from that of weakly doped samples. A significant initial SH signal is observed in native p+-Si/SiO2 interfaces for boron doping concentrations >7.5×1017 cm−3. This SH signal is attributed to a built-in interfacial electric field E0 generated by the doping induced accumulation of charges at the Si/SiO2 interface following the ionization of interface defect states. A sign reversal is observed in the azimuthal SH anisotropy pattern of the initial SH signal relative to that of the saturated SH signal in p+-Si/SiO2 indicating that the doping related and electron induced interfacial field components oppose each other. Furthermore, the intensity dependence of the initial SH signal in p+-Si/SiO2 is found to be nonquadratic and, in particular, shows a nonmonotonic behavior at incident intensities above ∼60 GW/cm2. These observations are attributed to ultrafast screening of E0 caused by linearly as well as nonlinearly photoexcited electron-hole pairs.
On the quantum and quasiclassical angular distributions of photofragments
Authors: Beswick J. Alberto , Zare Richard N.
Published: October 2008

Quantum and quasiclassical expressions for the angular distribution of photofragments from an initially polarized precursor molecule are compared under the conditions of a one-photon electric dipole transition to a repulsive state followed by prompt axial recoil into two separating fragments. The treatment is most readily applicable to diatomic molecules, but it is more general than that. It is shown that when the rotational and electronic angular momentum Ji and its projection along the body-fixed z axis Ωi are well defined in the initial state, the quantum and quasiclassical expressions are identical for any initial polarization of the molecule prior to photolysis and for all values of Ji and Ωi. For the particular case of an |JiΩiMi⟩ selected state this is in agreement with a previous result [T. Seideman, Chem. Phys. Lett. 253, 279 (1996)]. Moreover, the quasiclassical expression is still a good approximation even when the initial state is a coherent superposition of |Ji,Ωi,Mi⟩ levels for the same Ωi. This near identity still pertains even when Ωi is not well defined for a parallel transition (ΔΩ=0) but fails for a perpendicular transition (ΔΩ=±1) if the initial state is in a coherent superposition of Ωi states differing by ±2. These conclusions apply to preparation schemes employing optical excitation, static inhomogeneous and/or homogeneous electric and/or magnetic fields, as well as to molecules physisorbed on solids or clusters. We discuss the importance of these results in the interpretation of photofragment distributions when some other angular momenta are involved, such as electronic angular momentum, with and without nuclear spin, coupled to molecular rotation, asymmetric top rotational angular momentum, or internal vibrational angular momentum in polyatomics.
High-resolution imaging spectrometer for recording absolutely calibrated far ultraviolet spectra from laser-produced plasmas
Authors: Brown Charles M. , Seely John F. , Feldman Uri , Holland Glenn E. , Weaver James L. , Obenschain Steven P. , Kjornrattanawanich Benjawan , Fielding Drew
Published: October 2008

An imaging spectrometer was designed and fabricated for recording far ultraviolet spectra from laser-produced plasmas with wavelengths as short as 155 nm. The spectrometer implements a Cassegrain telescope and two gratings in a tandem Wadsworth optical configuration that provides diffraction limited resolution. Spectral images were recorded from plasmas produced by the irradiation of various target materials by intense KrF laser radiation with 248 nm wavelength. Two pairs of high-resolution gratings can be selected for the coverage of two wavebands, one grating pair with 1800 grooves/mm and covering approximately 155–175 nm and another grating pair with 1200 grooves/mm covering 230–260 nm. The latter waveband includes the 248 nm KrF laser wavelength, and the former waveband includes the wavelength of the two-plasmon decay instability at 23 the KrF laser wavelength (165 nm). The detection media consist of a complementary metal oxide semiconductor imager, photostimulable phosphor image plates, and a linear array of 1 mm2 square silicon photodiodes with 0.4 ns rise time. The telescope mirrors, spectrometer gratings, and 1 mm2 photodiode were calibrated using synchrotron radiation, and this enables the measurement of the absolute emission from the laser-produced plasmas with temporal, spatial, and spectral resolutions. The spectrometer is capable of measuring absolute spectral emissions at 165 nm wavelength as small as 5×10−7 J/nm from a plasma source area of 0.37 mm2 and with 0.4 ns time resolution.
Temperature dependence of conformation and self-assembly of Pt-TBPP on Ag(110)
Authors: Yokoyama Takashi , Tomita Yuuki
Published: October 2008

The conformation and self-assembly of tertiary butyl-phenyl substituted Pt-porphyrin (Pt-TBPP) on an Ag(110) surface have been studied as a function of deposition and annealing temperatures using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). While a stable two-dimensional arrangement is formed by room-temperature deposition, one-dimensional chains of Pt-TBPP along the [11¯0] direction are assembled by decreasing the deposition temperature, wherein the molecular orientation is orthogonal to that formed at room temperature. From a careful comparison of STM images and molecular orbital calculation results, the molecular conformations within these assembled structures were determined by the bending angles of the tertiary butyl-phenyl substituents, as well as the rotation angles, which result from conformational adaptation of the adsorbed Pt-TBPP to the substrate lattice. We also observed the structural transformation from one-dimensional chains formed at low temperature to the two-dimensional arrangement by thermal annealing at 280–310K.
Experimental study of oscillatory motion of particles and bubbles with applications to Coriolis flow meters
Authors: Weinstein J. A. , Kassoy D. R. , Bell M. J.
Published: October 2008

The present experimental study is designed to measure the motion of a spherical particle in a noninertial reference frame when the environment oscillates horizontally at a prescribed frequency and amplitude. Measurements are compared with theoretical equations of motion, for example, Basset [A Treatise on Hydrodynamics (Deighton Hall, London, 1888), Vol. 2], over wide ranges of density ratio (ρf/ρp), inverse Stokes number (δ), and amplitude ratio (Ap/Af), the three most critical nondimensional parameters. The experimental configuration consists of a bubble or solid sphere rising or falling in a bubble column while vibration occurs in the horizontal direction. Motion is measured with a high speed video camera and contemporary image and signal processing techniques are used to evaluate the data. The setup closely resembles multiphase flow in a Coriolis flow meter, a device which measures mass flow rate and density by oscillating two tubes at resonance. Accurate predictions of the motion of the sphere may lead to estimates of measurement errors due to entrained gas or solid particles. Excellent agreement for amplitude and phase shift is found between theory and experiment over the full range of testing, which is defined by small oscillatory Reynolds numbers (Re<2.5), finite Strouhal numbers (5<St<45), widely varying density ratios (0.1<ρf/ρp<700), inverse Stokes numbers (0.5<δ<3.5), and amplitude ratios (0.6<Ap/Af<1.7).
Stark-tunable electroluminescence from cavity polariton states
Authors: Todorov Y. , Jouy P. , Vasanelli A. , Sapienza L. , Colombelli R. , Gennser U. , Sirtori C.
Published: October 2008

Electric-field tunable electroluminescence from intersubband transitions in a quantum well has been demonstrated via the strong coupling of the electronic transitions with an optical cavity mode. The device consists of a quantum cascade structure embedded in a planar metal-dielectric microcavity where electrons can be resonantly injected at different energies, thanks to the polariton dispersion curve. The electroluminescence tuning shows a strong far field angular dependence in accordance with the conservation of the in-plane momentum. Our experiment illustrates that it is possible to connect quantum optics and electronic transport in semiconductor heterostructures.
Spectroscopic characterization of rovibrational temperatures in atmospheric pressure He∕CH4 plasmas
Authors: Moon Se Youn , Kim D. B. , Gweon B. , Choe W.
Published: October 2008

Atmospheric pressure of helium (He) and methane (CH4) mixture discharge characteristics are investigated using emission spectroscopic methods. Plasmas are produced in a radio frequency capacitively coupled device at atmospheric pressure in the ambient air. Without the CH4 gas introduced in the plasma, the emission spectrum exhibits typical helium discharge characteristics showing helium atomic lines with nitrogen molecular bands and oxygen atomic lines resulting from air impurities. Addition of a small amount (<1%) of CH4 to the supplied He results in the emission of CN (B2∑+-X2∑+: violet system) and CH (A2Δ-X2∏: 430nm system) molecular bands. Analyzing the CN and CH diatomic molecular emission spectra, the vibrational temperature (Tvib) and rotational temperature (Trot) are simultaneously obtained. As input power levels are raised from 20Wto200W, Tvib and Trot are increased from 4230Kto6310K and from 340K to500K, respectively. On the contrary, increasing the CH4 amount brings about the decrease of both temperatures because CH4 is harder to ionize than He. The emission intensities of CN and CH radicals, which are important in plasma processing, are also changed along with the temperature variation. From the results, the atmospheric pressure plasma shows strong nonequilibrium discharge properties, which may be effectively utilized for thermal damage free material treatments.
An infrared filter radiometer for atmospheric cluster-ion detection
Authors: Aplin K. L. , McPheat R. A.
Published: October 2008

Motivated by the detection of infrared absorption bands from atmospheric cluster ions in laboratory experiments, a narrowband filter radiometer has been constructed for ion detection in the atmosphere. It uses a filter centered at 9.15 μm wavelength with 5% bandwidth, protected by a diamond-like-carbon coated germanium auxiliary filter, and fitted to a standard pyrradiometer. A sensitivity of (29.3±0.1) μV/(W m−2) has been determined in a laboratory calibration using a blackbody source. Atmospheric experiments show that the filter radiometer, when used with a stable, low-noise amplifier, can respond to cluster-ion fluctuations. The filter radiometer’s sensitivity to atmospheric ion changes is (0.47±0.05) (mW m−2)/(ions cm−3).
Finite Larmor radius effects on nondiffusive tracer transport in a zonal flow
Authors: Gustafson K. , del-Castillo-Negrete D. , Dorland W.
Published: October 2008

Finite Larmor radius (FLR) effects on nondiffusive transport in a prototypical zonal flow with drift waves are studied in the context of a simplified chaotic transport model. The model consists of a superposition of drift waves from the linearized Hasegawa–Mima equation and a zonal shear flow perpendicular to the density gradient. High frequency FLR effects are incorporated by gyroaveraging the E×B velocity. Transport in the direction of the density gradient is negligible and we therefore focus on transport parallel to the zonal flows. A prescribed asymmetry produces strongly asymmetric non-Gaussian probability distribution functions (PDFs) of particle displacements, with Lévy flights in one direction only. For k⊥ρth=0, where k⊥ is the characteristic wavelength of the flow and ρth is the thermal Larmor radius, a transition is observed in the scaling of the second moment of particle displacements: σ2∼tγ. The transition separates ballistic motion (γ≈2) at intermediate times from superdiffusion (γ=1.6) at larger times. This change of scaling is accompanied by the transition of the PDF of particle displacements from algebraic decay to exponential decay. However, FLR effects seem to eliminate this transition. In all cases, the Lagrangian velocity autocorrelation function exhibits nondiffusive algebraic decay, C∼τ−κ, with κ=2−γ to a good approximation. The PDFs of trapping and flight events show clear evidence of algebraic scaling with decay exponents depending on the value of k⊥ρth. The shape and spatiotemporal self-similar anomalous scaling of the PDFs of particle displacements are reproduced accurately with a neutral (α=β), asymmetric, effective fractional diffusion model, where α and β are the orders of the spatial and temporal fractional derivatives, respectively.
Influence of substrate geometry on the distribution and stress on Ge nanocrystals in silicon oxide matrix
Authors: Zheng F. , Choi W. K. , Liew T. H.
Published: October 2008

Synthesis of germanium (Ge) nanocrystals embedded in silicon oxide matrix was carried out on cosputtered Ge plus silicon oxide films deposited on the surface of silicon (Si) wafer etched with V- or U-grooves. The V- or U-grooves were fabricated via the laser interference lithography technique. We found that the substrate geometry has a significant influence on the distribution of the Ge nanocrystals in the silicon oxide matrix. The variation in the distribution of the nanocrystals in the silicon oxide matrix may be due to defective oxide regions caused by sputter deposited silicon oxide film on the V- or U-grooves or may also be related to the different strain fields in the oxide layer.
Field emission of electrons from cylindrical metallic surfaces
Authors: Sodha Mahendra Singh , Dixit Amrit
Published: October 2008

In this communication the authors have derived an almost exact expression for the tunneling probability of an electron through the surface potential barrier on account of a negative charge on a cylindrical metallic dust particle and have used it to obtain the field emission current density from the surface of the particle. Based on these results, a parametric analysis of the phenomenon and comparison to the results of JWKB approximation (similar to Fowler–Nordheim theory) has been presented. These results are also applicable to a number of applications based on electric field emission from a thin metallic wire surrounded by a coaxial cylindrical surface at a high electric potential with respect to the wire. The investigation is of relevance to dusty plasmas in space and laboratory and carbon nanotubes.
A short-pulse Ka-band instrumentation radar for foliage attenuation measurements
Authors: Puranen Mikko , Eskelinen Pekka
Published: October 2008

A portable Ka-band instrumentation radar for foliage attenuation measurements has been designed. It uses direct dielectric resonator oscillator multiplier pulse modulation giving a half power pulse width of 17 ns. The dual conversion scalar receiver utilizes either a digital storage oscilloscope in envelope detection format or a special gated comparator arrangement providing 1 m resolution and associated led seven segment display for data analysis. The calibrated dynamic range is better than 37 dB with an equivalent noise floor of 0.005 dBsm at 25 m test range distance. First experiments indicate an effective beamwidth close to 1°. The total weight is below 5 kg and the unit can be mounted on a conventional photographic tripod. Power is supplied from a 12 V/6 A h sealed lead acid battery giving an operating time in excess of 10 h.
Determination of the intershell conductance in a multiwall carbon nanotube
Authors: Stetter A. , Vancea J. , Back C. H.
Published: October 2008

We have measured the current induced voltage drop along an individual multiwall carbon nanotube as a function of the distance to the current injecting electrode. The measurements have been performed at room temperature using scanning probe potentiometry combined with scanning electron microscopy. For a nanotube with an incomplete outer shell, a sharp potential jump was observed at the end of the outermost shell. The electric potential variation along the carbon nanotube has been used to determine the contact resistance between metal electrodes and the tube, the intrashell resistance, and the intershell conductance.
Enhanced electrical properties of atomic layer deposited La2O3 thin films with embedded ZrO2 nanocrystals
Authors: Jinesh K. B. , Klootwijk J. H. , Lamy Y. , Wolters R. , Tois E. , Tuominen M. , Roozeboom F. , Besling W. F. A.
Published: October 2008

The deposition of alternating (sub)monolayers of lanthanum oxide (La2O3) and zirconium oxide (ZrO2) by atomic layer deposition has been carried out to create uniform LayZr1−yOx mixed oxide films. However, spontaneous nucleation of ZrO2 nanocrystals occurs during deposition within an amorphous La2O3 matrix. Such ZrO2 embedded La2O3 films exhibit low leakage currents in combination with higher electric breakdown fields and higher dielectric permittivities than the pure lanthanum and zirconium oxide films. The possible scenarios that account for this enhanced electric performance of these nanocluster-embedded dielectric thin films are explained.
Asymmetric critical current of niobium microbridges with ferromagnetic stripe
Authors: Papon A. , Senapati K. , Barber Z. H.
Published: October 2008

A highly asymmetric current-voltage (IV) characteristic is reported in long Nb microbridges with a ferromagnetic cobalt overlayer. In the hysteretic regime, asymmetry as high as 100% was observed between forward and reverse critical currents. Such an asymmetry is a result of the competing magnetic fields produced at the edge of the bridge due to the bias current and the magnetic overlayer. While the temperature dependence of the critical current in the shallow branch of hysteretic IV curves (Ic−) followed a typical Ginzburg–Landau (GL) behavior, Ic+, the critical current of the other branch increased more sharply at low temperature. Local heating of the bridge due to the bias current was found to have no significant effect on the nature of critical current asymmetry.
Observations of gas-phase nanoparticles during InGaN metal-organic chemical vapor deposition
Authors: Creighton J. Randall , Coltrin Michael E. , Figiel Jeffrey J.
Published: October 2008

Using in situ laser light scattering, we have directly observed the formation of gas-phase nanoparticles during InN and InGaN metal-organic chemical vapor deposition. The angular dependence of the light scattering intensity suggests that the nanoparticles are metallic In or InGa alloys. From the angle-resolved scattering profile, we determined that the particle diameters were in the range 20–50nm, and particle densities were mostly in the 108–109cm−3 range. Results indicate that for growth temperatures near 800°C nearly 100% of the indium near the surface is converted into gas-phase nanoparticles and is no longer available for InGaN growth.
Ni diffusion and its influence on electrical properties of AlxGa1−xN∕GaN heterostructures
Authors: Huang S. , Shen B. , Lin F. , Ma N. , Xu F. J. , Miao Z. L. , Song J. , Lu L. , Liu F. , Wang Y. , Qin Z. X. , Yang Z. J. , Zhang G. Y.
Published: October 2008

The effect of thermal annealing of Ni∕AlxGa1−xN∕GaN structures on electric properties of AlxGa1−xN∕GaN heterostructures has been studied by means of temperature-dependent Hall measurements and deep level transient spectroscopy. It is found that the mobility of the two-dimensional electron gas (2DEG) decreases from 1530to986cm2∕Vs at room temperature (RT) after annealing the Al0.25Ga0.75N∕GaN heterostructure with a 10nm thick Ni cap layer at 600°C. The density of the 2DEG is also reduced by 2.0×1012cm−2 at RT after the annealing, and decreases with increasing temperature between 100 and 460K. It is determined that an acceptorlike deep level with an activation energy of 1.23eV and apparent capture cross section of 2.8×10−13cm2 is introduced into the heterostructures. We believe that the acceptorlike deep level is induced by Ni diffusion during the annealing, and it results in the significant degradation of the transport properties of the 2DEG in the heterostructures.
Diamondoids as low-κ dielectric materials
Authors: Clay W. A. , Sasagawa T. , Kelly M. , Dahl J. E. , Carlson R. M. K. , Melosh N. , Shen Z.-X.
Published: October 2008

The dielectric properties of several diamondoids are investigated in theory and experiment. The dielectric constant (κ) is experimentally evaluated from cavity microwave measurements, while the theoretical value is obtained from first principles calculations based on the density functional theory. The results show that the diamondoids have low dielectric constants in the range of 2.46–2.68, less than half of that of bulk diamond. Due to their high thermal stability and outstanding mechanical and insulating properties, diamondoids are excellent candidates for low-κ dielectric applications.
Gas-phase activation of methane by ligated transition-metal cations
Authors: Schröder Detlef , Schwarz Helmut
Published: October 2008

Motivated by the search for ways of a more efficient usage of the large, unexploited resources of methane, recent progress in the gas-phase activation of methane by ligated transition-metal ions is discussed. Mass spectrometric experiments demonstrate that the ligands can crucially influence both reactivity and selectivity of transition-metal cations in bond-activation processes, and the most reactive species derive from combinations of transition metals with the electronegative elements fluorine, oxygen, and chlorine. Furthermore, the collected knowledge about intramolecular kinetic isotope effects associated with the activation of C–H(D) bonds of methane can be used to distinguish the nature of the bond activation as a mere hydrogen-abstraction, a metal-assisted mechanism or more complex reactions such as formation of insertion intermediates or σ-bond metathesis.
A p38 MAPK-MEF2C pathway regulates B-cell proliferation
Authors: Khiem Dustin , Cyster Jason G. , Schwarz John J. , Black Brian L.
Published: October 2008

B lymphocytes are an integral part of the adaptive immune system. On antigen binding to the B-cell receptor (BCR), B cells rapidly proliferate and differentiate into antibody-secreting plasma cells. The p38 mitogen-activated protein kinase (MAPK) pathway functions downstream of the BCR to control cell proliferation, but the transcriptional effectors of this pathway in B cells have remained elusive. In the present study, we inactivated
Mef2c
exclusively in B cells by conditional gene targeting in mice. Loss of MEF2C function resulted in a reduced immune response to antigen, defective germinal center formation, and a severe defect in B-cell proliferation, and we show that MEF2C regulates proliferation in response to BCR stimulation via the p38 MAPK pathway. p38 directly phosphorylates MEF2C via three residues in the C-terminal transactivation domain, establishing MEF2C as a direct transcriptional effector of BCR signaling via p38 MAPK.
In vivo supramolecular templating enhances the activity of multivalent ligands: A potential therapeutic against the
Escherichia coli
O157 AB
5
toxins
Authors: Kitov Pavel I. , Mulvey George L. , Griener Thomas P. , Lipinski Tomasz , Solomon Dmitry , Paszkiewicz Eugenia , Jacobson Jared M. , Sadowska Joanna M. , Suzuki Missao , Yamamura Ken-ichi , Armstrong Glen D. , Bundle David R.
Published: October 2008

We demonstrate that interactions between multimeric receptors and multivalent ligands are dramatically enhanced by recruiting a complementary templating receptor such as an endogenous multimeric protein but only when individual ligands are attached to a polymer as preorganized, covalent, heterobifunctional pairs. This effect cannot be replicated by a multivalent ligand if the same recognition elements are independently arrayed on the scaffold. Application of this principle offers an approach to create high-avidity inhibitors for multimeric receptors. Judicious selection of the ligand that engages the templating protein allows appropriate effector function to be incorporated in the polymeric construct, thereby providing an opportunity for therapeutic applications. The power of this approach is exemplified by the design of exceptionally potent
Escherichia coli
Shiga toxin antagonists that protect transgenic mice that constitutively express a human pentraxin, serum amyloid P component.
Microglial activation and TNFα production mediate altered CNS excitability following peripheral inflammation
Authors: Riazi Kiarash , Galic Michael A. , Kuzmiski J. Brent , Ho Winnie , Sharkey Keith A. , Pittman Quentin J.
Published: October 2008

Peripheral inflammation leads to a number of centrally mediated physiological and behavioral changes. The underlying mechanisms and the signaling pathways involved in these phenomena are not yet well understood. We hypothesized that peripheral inflammation leads to increased neuronal excitability arising from a CNS immune response. We induced inflammation in the gut by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) to adult male rats. To examine the excitability of the brainin vivo, we administered pentylenetetrazole (PTZ; a GABAergic antagonist) intravenously to evoke clonic seizures. Rats treated with TNBS showed increased susceptibility to PTZ seizures that was strongly correlated with the severity and progression of intestinal inflammation.In vitrohippocampal slices from inflamed, TNBS-treated rats showed increased spontaneous interictal burst firing following application of 4-aminopyridine, indicating increased intrinsic excitability. The TNBS-treated rats exhibited a marked, reversible inflammatory response within the hippocampus, characterized by microglial activation and increases in tumor necrosis factor α (TNFα) levels. Central antagonism of TNFα using a monoclonal antibody or inhibition of microglial activation by i.c.v. injection of minocycline prevented the increase in seizure susceptibility. Moreover, i.c.v. infusion of TNFα in untreated rats for 4 days also increased seizure susceptibility and thus mimicked the changes in seizure threshold observed with intestinal inflammation. Our finding of a microglia-dependent TNFα-mediated increase in CNS excitability provides insight into potential mechanisms underlying the disparate neurological and behavioral changes associated with chronic inflammation.
Rapamycin differentially inhibits S6Ks and 4E-BP1 to mediate cell-type-specific repression of mRNA translation
Authors: Choo Andrew Y. , Yoon Sang-Oh , Kim Sang Gyun , Roux Philippe P. , Blenis John
Published: October 2008

The mammalian translational initiation machinery is a tightly controlled system that is composed of eukaryotic initiation factors, and which controls the recruitment of ribosomes to mediate cap-dependent translation. Accordingly, the mTORC1 complex functionally controls this cap-dependent translation machinery through the phosphorylation of its downstream substrates 4E-BPs and S6Ks. It is generally accepted that rapamycin, a specific inhibitor of mTORC1, is a potent translational repressor. Here we report the unexpected discovery that rapamycin's ability to regulate cap-dependent translation varies significantly among cell types. We show that this effect is mechanistically caused by rapamycin's differential effect on 4E-BP1 versus S6Ks. While rapamycin potently inhibits S6K activity throughout the duration of treatment, 4E-BP1 recovers in phosphorylation within 6 h despite initial inhibition (1–3 h). This reemerged 4E-BP1 phosphorylation is rapamycin-resistant but still requires mTOR, Raptor, and mTORC1's activity. Therefore, these results explain how cap-dependent translation can be maintained in the presence of rapamycin. In addition, we have also defined the condition by which rapamycin can control cap-dependent translation in various cell types. Finally, we show that mTOR catalytic inhibitors are effective inhibitors of the rapamycin-resistant phenotype.
Endothelial adhesion receptors are recruited to adherent leukocytes by inclusion in preformed tetraspanin nanoplatforms
Authors: Barreiro Olga , Zamai Moreno , Yáñez-Mó María , Tejera Emilio , López-Romero Pedro , Monk Peter N. , Gratton Enrico , Caiolfa Valeria R. , Sánchez-Madrid Francisco
Published: October 2008

VCAM-1 and ICAM-1, receptors for leukocyte integrins, are recruited to cell–cell contact sites on the apical membrane of activated endothelial cells. In this study, we show that this recruitment is independent of ligand engagement, actin cytoskeleton anchorage, and heterodimer formation. Instead, VCAM-1 and ICAM-1 are recruited by inclusion within specialized preformed tetraspanin-enriched microdomains, which act as endothelial adhesive platforms (EAPs). Using advanced analytical fluorescence techniques, we have characterized the diffusion properties at the single-molecule level, nanoscale organization, and specific intradomain molecular interactions of EAPs in living primary endothelial cells. This study provides compelling evidence for the existence of EAPs as physical entities at the plasma membrane, distinct from lipid rafts. Scanning electron microscopy of immunogold-labeled samples treated with a specific tetraspanin-blocking peptide identify nanoclustering of VCAM-1 and ICAM-1 within EAPs as a novel mechanism for supramolecular organization that regulates the leukocyte integrin–binding capacity of both endothelial receptors during extravasation.
Memo–RhoA–mDia1 signaling controls microtubules, the actin network, and adhesion site formation in migrating cells
Authors: Zaoui Kossay , Honoré Stéphane , Isnardon Daniel , Braguer Diane , Badache Ali
Published: October 2008

Actin assembly at the cell front drives membrane protrusion and initiates the cell migration cycle. Microtubules (MTs) extend within forward protrusions to sustain cell polarity and promote adhesion site turnover. Memo is an effector of the ErbB2 receptor tyrosine kinase involved in breast carcinoma cell migration. However, its mechanism of action remained unknown. We report in this study that Memo controls ErbB2-regulated MT dynamics by altering the transition frequency between MT growth and shortening phases. Moreover, although Memo-depleted cells can assemble the Rac1-dependent actin meshwork and form lamellipodia, they show defective localization of lamellipodial markers such as α-actinin-1 and a reduced number of short-lived adhesion sites underlying the advancing edge of migrating cells. Finally, we demonstrate that Memo is required for the localization of the RhoA guanosine triphosphatase and its effector mDia1 to the plasma membrane and that Memo–RhoA–mDia1 signaling coordinates the organization of the lamellipodial actin network, adhesion site formation, and MT outgrowth within the cell leading edge to sustain cell motility.
A novel genetic strategy reveals unexpected roles of the Swi–Snf–like chromatin-remodeling BAF complex in thymocyte development
Authors: Jani Anant , Wan Mimi , Zhang Jianmin , Cui Kairong , Wu Jie , Preston-Hurlburt Paula , Khatri Rohini , Zhao Keji , Chi Tian
Published: October 2008

We have developed a general strategy for creating littermates bearing either a tissue-specific point mutation or deletion in any target gene, and used the method to dissect the roles of Brg, the ATPase subunit of the chromatin-remodeling Brg-associated factor (BAF) complex, in early thymocyte development. We found that a point mutation that inactivates the Brg ATPase recapitulates multiple defects previously described for Brg deletion (Chi, T.H., M. Wan, P.P. Lee, K. Akashi, D. Metzger, P. Chambon, C.B. Wilson, and G.R. Crabtree. 2003. Immunity. 19:169–182). However, the point mutant helps reveal unexpected roles of Brg in CD25 repression and CD4 activation. Surprisingly, CD4 activation occurs independently of the Brg ATPase and is perhaps mediated by physical interactions between Brg and the CD4 locus. Our study thus suggests that the BAF complex harbors novel activities that can be necessary and even sufficient for stimulating transcription from an endogenous chromatin template in the absence of Brg-dependent remodeling of that template. We conclude that conditional point mutants, rarely used in mammalian genetics, can help uncover important gene functions undetectable or overlooked in deletion mutants.
Valproic acid inhibits Aβ production, neuritic plaque formation, and behavioral deficits in Alzheimer's disease mouse models
Authors: Qing Hong , He Guiqiong , Ly Philip T. T. , Fox Christopher J. , Staufenbiel Matthias , Cai Fang , Zhang Zhuohua , Wei Shengcai , Sun Xiulian , Chen Chia-Hsiung , Zhou Weihui , Wang Ke , Song Weihong
Published: October 2008

Neuritic plaques in the brains are one of the pathological hallmarks of Alzheimer's disease (AD). Amyloid β-protein (Aβ), the central component of neuritic plaques, is derived from β-amyloid precursor protein (APP) after β- and γ-secretase cleavage. The molecular mechanism underlying the pathogenesis of AD is not yet well defined, and there has been no effective treatment for AD. Valproic acid (VPA) is one of the most widely used anticonvulsant and mood-stabilizing agents for treating epilepsy and bipolar disorder. We found that VPA decreased Aβ production by inhibiting GSK-3β–mediated γ-secretase cleavage of APP both in vitro and in vivo. VPA treatment significantly reduced neuritic plaque formation and improved memory deficits in transgenic AD model mice. We also found that early application of VPA was important for alleviating memory deficits of AD model mice. Our study suggests that VPA may be beneficial in the prevention and treatment of AD.
Meridional surfaces and (1,1)-knots
Authors: Eudave-Muñoz Mario , Ramírez-Losada Enrique
Published: October 2008

We determine all

(
1
,
1
)

(1,1)

-knots which admit an essential meridional surface, namely, we give a construction which produces

(
1
,
1
)

(1,1)

-knots having essential meridional surfaces, and show that if a

(
1
,
1
)

(1,1)

-knot admits an essential meridional surface, then it comes from the given construction.
The pluricomplex Poisson kernel for strongly convex domains
Authors: Bracci Filippo , Patrizio Giorgio , Trapani Stefano
Published: October 2008

LetDDbe a bounded strongly convex domain in the complex space of dimensionnn. For a fixed pointp∈∂Dp\in \partial D, we consider the solution of a homogeneous complex Monge-Ampère equation with a simple pole atpp. We prove that such a solution enjoys many properties of the classical Poisson kernel in the unit disc and thus deserves to be called the pluricomplex Poisson kernel ofDDwith pole atpp. In particular we discuss extremality properties (such as a generalization of the classical Phragmen-Lindelof theorem), relations with the pluricomplex Green function ofDD, uniqueness in terms of the associated foliation and boundary behaviors. Finally, using such a kernel we obtain explicit reproducing formulas for plurisubharmonic functions.