bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of the function of presynaptic α7 and non‐α7 nicotinic receptors by the tryptophan metabolites, 5‐hydroxyindole and kynurenate in mouse brain
Authors: Grilli M , Raiteri L , Patti L , Parodi M , Robino F , Raiteri M , Marchi M
Published: October 2006

Background and purpose:

Two metabolites of tryptophan, 5‐hydroxyindole and kynurenic acid (kynurenate) affect the function of α7 nicotinic acetylcholine receptors (nAChRs), as measured by electrophysiological and Ca2+ fluorescence techniques. To better understand the modulations by 5‐hydroxyindole and kynurenate of the function of nAChR subtypes, we compared the effects of 5‐hydroxyindole and kynurenate on the release of various transmitters evoked by nAChR activation.

Experimental approach:

The function of α7nAChRs located on glutamatergic terminals was investigated by monitoring the release of [3H]D‐aspartate or of endogenous glutamate from neocortical synaptosomes. We also comparatively considered non‐α7 release‐enhancing nAChRs localized on hippocampal noradrenergic or cholinergic terminals, as well as on striatal dopaminergic terminals.

Key results:

Epibatidine or nicotine, inactive on their own on basal release, enhanced [3H]D‐ aspartate and glutamate efflux in presence of 5‐hydroxyindole. The release evoked by nicotine plus 5‐hydroxyindole was abolished by methyllycaconitine or α‐bungarotoxin. Presynaptic nAChRs mediating the release of [3H]noradrenaline ([3H]NA), [3H]dopamine ([3H]DA), or [3H]ACh were inhibited by 5‐OHi. The α7nAChR‐mediated release of [3H]D‐aspartate was reduced by kynurenate at concentrations unable to affect the non‐α7 receptor‐mediated release of tritiated NA, DA or ACh.

Conclusions and Implications:

(i) 5‐hydroxyindole permits selective activation of α7nAChRs mediating glutamate release; (ii) kynurenate down‐regulates the permissive role of 5‐hydroxyindole on α7nAChR activation; (iii) the non‐α7nAChRs mediating release of NA, DA or ACh can be inhibited by 5‐hydroxyindole, but not by kynurenate. These findings suggest up the possibility of developing novel drugs able to modulate selectively the cholinergic‐glutamatergic transmission.

British Journal of Pharmacology (2006) 149, 724–732. doi:10.1038/sj.bjp.0706914
Tamoxifen dilates porcine coronary arteries: roles for nitric oxide and ouabain‐sensitive mechanisms
Authors: Leung H S , Yung L M , Leung F P , Yao X , Chen Z Y , Ko W H , Laher I , Huang Y
Published: October 2006

Background and purpose:

Experiments were designed to determine the mechanism of the relaxation induced by tamoxifen in porcine coronary arteries at the tissue, cellular and molecular levels.

Experimental approach:

Porcine left circumflex coronary arteries were isolated and isometric tension was measured. [Ca2+]i in native endothelial cells of intact arteries was determined by a calcium fluorescence imaging technique and eNOS ser1177 phosphorylation was assayed by Western blotting.

Key results:

Tamoxifen induced an endothelium‐dependent relaxation that was antagonized by ICI 182,780 and abolished by NG‐nitro‐L‐arginine methyl ester (L‐NAME) or 1H‐[1,2,4]oxadizolo[4,3‐a]quinoxalin‐1‐one (ODQ). L‐Arginine reversed the effect of L‐NAME while indomethacin was without effect. Tamoxifen‐induced relaxation was attenuated by charybdotoxin (CTX) plus apamin, ouabain or by incubation in a K+‐free solution. Moreover, tamoxifen triggered extracellular Ca2+‐dependent increases in endothelial [Ca2+]i and this effect was abolished by ICI 182,780. Endothelium‐independent relaxation to sodium nitroprusside was also inhibited by ouabain or in a K+‐free solution. Furthermore, tamoxifen increased endothelial nitric oxide synthase (eNOS) phosphorylation at Ser‐1177 and ICI 182,780 prevented this effect.

Conclusions and Implications:

The present results suggest that tamoxifen mainly induces endothelium‐dependent relaxation and that endothelial nitric oxide (NO) is the primary mediator of this effect. NO‐dependent responses may result from elevated [Ca2+]i in endothelial cells; an effect abolished by ICI 182,780. NO activates Na+/K+‐ATPase in vascular smooth muscle, leading to relaxation. These results suggest that tamoxifen is able to modulate eNOS phosphorylation directly.

British Journal of Pharmacology (2006) 149, 703–711. doi:10.1038/sj.bjp.0706921
Rovibrationally selected and resolved state-to-state photoionization of ethylene using the infrared-vacuum ultraviolet pulsed field ionization-photoelectron method
Authors: Xing Xi , Bahng Mi-Kyung , Wang Peng , Lau Kai-Chung , Baek Sun Jong , Ng C. Y.
Published: October 2006

By preparing ethylene [C2H4(X̃Ag1)] in selected rotational levels of the ν11(b1u), ν2+ν12(b1u), or ν9(b2u) vibrational state with infrared (IR) laser photoexcitation prior to vacuum ultraviolet (VUV) laser photoionization, we have recorded rotationally resolved pulsed field ionization-photoelectron (PFI-PE) spectra for C2H4+(X̃B3u2) in the energy region of 0–3000cm−1 above the ionization energy (IE) of C2H4(X̃Ag1). Here, ν2(ag), ν9(b2u), ν11(b1u), and ν12(b1u) represent the C–C stretching, CH2 stretching, CH2 stretching, and CH2 bending modes of C2H4(X̃Ag1), respectively. The fully rovibrationally resolved spectra have allowed unambiguous symmetry assignments of the observed vibrational bands, which in turn have provided valuable information on the photoionization dynamics of C2H4. The IR-VUV photoionization of C2H4(X̃Ag1) via the ν11(b1u) or ν2+ν12(b1u) vibrational states is found to predominantly produce vibrational states of C2H4+(X̃B3u2) with b1u symmetry, which cannot be observed in single-photon VUV-PFI-PE measurements of C2H4(X̃Ag1). The analysis of the observed IR-VUV-PFI-PE bands has provided the IE(C2H4)=84790.2(2)cm−1 and accurate vibrational frequencies for the ν4+(au)[84.1(2)cm−1], ν12+(b1u)[1411.7(2)cm−1], ν4++ν12+(b1g)[1482.5(2)cm−1], ν2+(ag)[1488.3(2)cm−1], ν2++ν4+(au)[1559.2(2)cm−1], 2ν4++ν12+(b1u)[1848.5(2)cm−1], 4ν4++ν12+(b1u)[2558.8(2)cm−1], ν2++ν12+(b1u)[2872.7(2)cm−1], and ν11+(b1u)[2978.7(2)cm−1] vibrational states of C2H4+(X̃B3u2), where ν4+ is the ion torsional state. The IE(C2H4) and the ν4+(au), ν2+(ag), and ν2++ν4+(au) frequencies are in excellent accord with those obtained in previous single-photon VUV-PFI-PE measurements. The other ion vibrational frequencies represent new experimental determinations. We have also performed high-level ab initio anharmonic vibrational frequency calculations for C2H4(X̃Ag1) and C2H4+(X̃B3u2) at the CCSD(T)/aug-cc-pVQZ level for guidance in the assignment of the IR-VUV-PFI-PE spectra. All theoretical vibrational frequencies for the neutral and ion, except the ion torsional frequency, are found to agree with experimental vibrational frequencies to better than 1%.
A crossed molecular beam study on the dynamics of F atom reaction with SiH4
Authors: Shen Guanlin , Yang Xueming , Shu Jinian , Yang Chung-Hsin , Lee Yuan T.
Published: October 2006

In this report, the dynamics of the F+SiH4 reaction has been studied using the universal crossed molecular beam method. Angular resolved time-of-flight spectra have been measured for all reaction products in a single set of experiments. Two different reaction channels have been observed: HF+SiH3 and SiH3F+H. Product angular distributions as well as energy distributions were determined for these two product channels. Experimental results show that the HF product is forward scattered relative to the F atom beam direction, while the SiH3F product is backward scattered relative the F atom beam direction, suggesting that two reaction channels proceed with distinctive reaction dynamics. The relative branching ratios of the two channels have also been estimated.
Metallic nanocluster formation in neutral gas-confined laser produced plasma afterglow
Authors: Kim Yong W. , Lee Hedok , Belony Paul
Published: October 2006

Dense atom vapors are created as remnants of a three-dimensional (3D) laser-produced plasma (LPP) plume driven from a solid aluminum target by a gigawatt-class Nd:glass laser pulse. Formation of nanoclusters as the terminal state of aluminum vapors has been investigated. By plasma structure diagnosis, we have fully characterized the LPP plume in 3D as a function of time and from its evolution modeled its cooling to the critical point in more than 110 000 vapor cells. Clustering of atoms is calculated by numerical simulation of interparticle collisions. When the cluster size histogram is rescaled relative to the maximum population and the maximal radius, the rescaled histograms all collapse into a single functional form regardless of the time or the initial atom vapor density. The cluster size distribution for the entire plasma plume is obtained by summing over all plasma cells. Independently, the clusters are captured onto electron microscope grids and size analyzed by means of transmission electron microscopy. The computed result is in excellent agreement with the measured histograms of clusters by size.
On the migration of tidal free bars
Authors: Garotta Valeria , Bolla Pittaluga Michele , Seminara Giovanni
Published: October 2006

We derive and employ a depth-averaged model for the formation of free bars in infinitely long tidal channels in order to investigate the mechanism whereby tidal bars may experience a net migration over a tidal cycle. The flux of the suspended sediment is modeled by means of an analytical relationship derived by Bolla Pittaluga and Seminara [M. Bolla Pittaluga and G. Seminara, Water Resour. Res. 39, 5 (2003)] for slowly varying flows. The model is validated by performing a linear stability analysis of flow and bed topography in a rectangular channel with an erodible bed, subject to the propagation of a symmetric tidal wave of small amplitude. The results of the present depth averaged model show a fairly satisfactory agreement with previous results based on a three-dimensional model [G. Seminara and M. Tubino, J. Fluid Mech. 440, 49 (2001)]. We then investigate the role of overtides, showing that a flood or ebb asymmetry of the basic flow gives rise to a net migration of bars. The mechanism is due to the nonlinearity of the dependence of sediment flux on bottom stress. This phenomenon is somewhat similar to processes occurring in various fields of fluid mechanics, such as steady streaming in an oscillatory boundary layer [N. Riley, Annu. Rev. Fluid Mech. 33, 43 (2001)] or acoustic streaming. The present investigation also bears some relevance to the problem of nonlinear development of tidal bars, as it suggests that a depth averaged approach may be adequate to its treatment, while definitely requiring a computational effort much smaller than treatments based on 3D formulations.
Performance of the solid state neutral particle analyzer array on the national spherical torus experiment
Authors: Liu D. , Heidbrink W. W. , Darrow D. S. , Roquemore A. L. , Medley S. S. , Shinohara K.
Published: October 2006

The solid state neutral particle analyzer (SSNPA) array on the national spherical torus experiment (NSTX) consists of four chords with tangency radii of 60, 90, 100, and 120cm that view across the three coinjection neutral beam lines. Each chord utilizes a silicon photodiode that is coupled to fast digitizers to measure the energy distribution of charge exchange fast neutral particles (30–100keV). By the end of the NSTX 2005 experimental campaign, the electromagnetic noise in the SSNPA was reduced by half and reasonable signals were obtained with good electromagnetic shielding, fast digitization of raw signals, software-based pulse height analysis, and pulse shape discrimination. Energy resolution of ∼10keV and time resolution of 2ms have been achieved. Temporal evolutions of energetic neutral flux obtained with the SSNPA are in good agreement with those obtained with the E‖B-type neutral particle analyzer. With these improvements, the SSNPA can be used to study magnetohydrodynamic instabilities and fast ion redistribution. Example data from plasma discharges are presented along with the noise reduction techniques and postshot pulse height analysis methods.
Field emission from carbon nanotube emitters fabricated by the metal intermediation layer
Authors: Jeong Taewon , Heo Jungna , Lee Jeonghee , Park Sanghyun , Jin Yongwan , Kim J. M. , Oh Taesik , Park Chongwyun , Yoo Ji-Beom , Gong Byoungyun , Lee Naesung , Yu SeGi
Published: October 2006

Multiwalled carbon nanotube (MWNT) emitters fabricated by the metal intermediation process were studied. This was intended to allow strong adhesion and high electrical contact between the cathode electrode and MWNT emitters. The process was performed by hot-pressed bonding of a metal layer to a MWNT film surface, where the metal layer was deposited on a main substrate. Through this process, MWNTs have open and sharp ends, and the metal layer and the MWNTs have strong electrical contact. Together with unchanged crystallinity of MWNTs as before the process, these effects improve the field emission properties, resulting in 64% reduction of turn on field and two to three orders of magnitude increase of current density.
Enhancement of second harmonic generation signal in thermally poled glass ceramic with NaNbO3 nanocrystals
Authors: Malakho Artem , Fargin Evelyne , Lahaye Michel , Lazoryak Bogdan , Morozov Vladimir , Van Tendeloo Gustaaf , Rodriguez Vincent , Adamietz Frederic
Published: October 2006

Glass ceramic composites were prepared by bulk crystallization of NaNbO3 in sodium niobium borate glasses. A homogeneous bulk crystallization of the NaNbO3 phase takes place during heat treatments that produces visible-near infrared transparent materials with ∼30nm NaNbO3 nanocrystallites. Upon thermal poling, a strong Na+ depleted nonlinear optical thin layer is observed at the anode side that should induce a large internal static electric field. In addition, the χ(2) response of the poled glass ceramic composites increases from 0.2 up to 1.9pm∕V with the rate of crystallization. Two mechanisms may be considered: a pure structural χ(2) process connected with the occurrence of a spontaneous ferroelectric polarization or an increase of the χ(3) response of the nanocrystallites that enhances the electric field induced second harmonic generation process.
Experimental verification of the applicability of the homogenization approximation to rough one-dimensional photonic crystals using a holographically fabricated reflection grating
Authors: Maskaly Karlene Rosera , Hsiao Vincent K. S. , Cartwright Alexander N. , Prasad Paras N. , Lloyd P. F. , Bunning Timothy J. , Craig Carter W.
Published: October 2006

The theoretical reflectance spectrum of a one-dimensional photonic crystal with large amounts of interfacial roughness has been calculated using a previously proposed method, and compared to the actual experimental reflectivity of the structure. The photonic crystal was fabricated using a simple and fast method involving the holographic exposure of a liquid crystal/photosensitive prepolymer syrup via the self-interference patterns from two laser beams. The calculated reflectance spectrum for this structure matched the experimental one extremely well, giving very similar reflectivity peak positions and intensities. Slight discrepancies between the two reflectance spectra are attributed to either small variations in the microstructure of the reflection grating beyond that which is captured in the transmission electron micrograph, or the dispersion of the polymer which was not taken into account. These results serve as experimental verification of the theory for rough photonic crystals reported previously.
Elasticity theory of pseudomorphic heterostructures grown on substrates of arbitrary thickness
Authors: Povolotskyi Michael , Di Carlo Aldo
Published: October 2006

A theoretical model for lattice mismatched pseudomorphically grown heterostructure, which is based on continuum elasticity theory is described. Two distinct types of coherently grown structures are considered, namely, those grown on a thick substrate and these grown on a freestanding one. Special cases of structures that are homogeneous or periodic in some directions are considered. The theory can be applied for an arbitrary crystallographic direction of the heterostructure growth. The model has been applied to AlN∕GaN nanocolumn and GaAs∕InAs heterostructure. Calculation of strain induced shape deformation is shown.
Evolution of a localized vortex in plane nonparallel viscous flows with constant velocity shear. I. Hyperbolic flow
Authors: Shukhman I. G.
Published: October 2006

The framework of the linear theory is employed to study the evolution of an initial compact vortical disturbance in unbounded plane nonparallel viscous incompressible flows with constant velocity gradients. Two types of such flows are known to be possible: hyperbolical and elliptical (as well as an intermediate case of the well-studied parallel Couette flow). The results presented here are obtained for a hyperbolical flow. (Results concerning the elliptical flow are to be issued in a separate publication.) This paper is a development of earlier work by R. R. Lagnado, N. Phan-Thien, and L. G. Leal [Phys. Fluids 27, 1094 (1984)] studying the stability of a hyperbolical flow relative to the simplest perturbations in the form of plane waves with a time-dependent wave vector. The dynamics of vortex intensity is investigated as well as the evolution of its geometrical form and orientation. The results are discussed in the context of the problem of hairpin vortex formation.
High open-circuit voltage values on fine-grained thin-film polysilicon solar cells
Authors: Carnel L. , Gordon I. , Van Gestel D. , Beaucarne G. , Poortmans J. , Stesmans A.
Published: October 2006

Grain boundaries are known to be the main limiting factor for a high performance of polysilicon solar cells. Defects at these grain boundaries serve as recombination centers for minority and majority carriers. Grain boundaries are also known to be paths for enhanced hydrogen diffusion, which results in passivation of part of the defects. In this paper, we show that grain boundaries are also paths for an enhanced phosphorus diffusion that limits the effect of hydrogen passivation. Phosphorus spikes along the grain boundaries enhance the junction area and determine the collection and the recombination volumes. Avoiding this preferential diffusion of phosphorus atoms during emitter formation, we obtained open-circuit voltages (Voc) up to 536mV on polysilicon material with a grain size of only 0.2μm. These high Voc values can only be accounted for by theory if a much smaller grain boundary recombination velocity is assumed than what was previously accepted for p-n junctions on fine-grained polysilicon solar cells.
Analysis on dielectric response of polar nanoregions in paraelectric phase of relaxor ferroelectrics
Authors: Wei Xiaoyong , Yao Xi
Published: October 2006

Ferroelectric phase shifter is preferred to be used in paraelectric phase due to the demand of low loss. Dielectric response of polar nanoregions was analyzed in the present study, including their characteristics and contributions both to dielectric polarization and tunability. The corresponding dielectric constant of paraelectric phase consists of two parts, intrinsic one and extrinsic one. The former one, which depends on volume fraction of paraelectric phase, was mainly contributed by ionic displacement. The latter one, proportional to the volume specific surface of nanoregions, was mainly contributed by the boundary vibration of polar nanoregions. The possible mechanism of tunability in paraelectric phase consists of intrinsic tunability of polarization of ionic displacement and extrinsic tunability of boundary vibration of polar nanoregions.
Electromagnetic continuous-wave generation using switch lines
Authors: Narahara Koichi
Published: October 2006

Characterization of wave propagation on a switch line, which means a transmission line periodically loaded with electronic switches, is discussed for the generation of electrical continuous waves. We consider the case of a step pulse, which crosses the threshold voltage of loaded shunt switches, inputted to a switch line. Due to the effects of the electrode loss and the switch conductance, the forward pulse on a switch line is gradually attenuated, and finally dissappears. At this point, a stable exponential wave develops and then travels backward to the input port. At the input port, the pulse is reflected to travel forward again. This process continues permanently to give a method of generating electrical continuous waves. By designing the values of electrode loss, switch conductance, and the characteristic impedance of a switch line, the oscillation frequency covers a very wide range.
Diamagnetism, transport, magnetothermoelectric power, and magnetothermal conductivity in electron-doped CaMn1−xVxO3 manganites
Authors: Ang R. , Sun Y. P. , Ma Y. Q. , Zhao B. C. , Zhu X. B. , Song W. H.
Published: October 2006

The effects of V doping on field-cooled magnetization MFC(T), zero-field-cooled magnetization MZFC(T), resistivity ρ, thermoelectric power S, and thermal conductivity κ in manganites CaMn1−xVxO3 (0.02⩽x⩽0.08) have been investigated systematically. As the V doping level exceeds 0.02, an anomalous “diamagnetism” has been observed. It is suggested that the force generated by the orbit rotation of eg electron in Mn3+O6 octahedron makes the spin tilt, as a result, the vector sum of individual spins may be along or opposite to the direction of the applied magnetic field, and macroscopically, the average magnetization exhibits positive or negative values. In addition, the transport mechanism in the high and low temperature ranges is dominated by the small polaron conduction and the variable-range-hopping conduction, respectively, according to the fitting analysis of the temperature dependence of Seebeck coefficient S(T) and resistivity ρ(T). Both S and κ peaks appearing at low temperature is gradually suppressed by V doping. Additionally, obvious magnetothermoelectric power and magnetothermal conductivity are observed in the temperature region which an anomalous diamagnetism appears. The results are discussed based on spin-orbital coupling and spin-phonon coupling induced due to V doping, respectively. Moreover, the large thermoelectric figure of merit Z=S2∕ρκ for the slightly V-doped sample suggests that the V-doped manganite may be a good candidate for thermoelectric materials.
Microwave response of a nearly ferroelectric superconductor
Authors: Wu Chien-Jang
Published: October 2006

Microwave response of a nearly ferroelectric superconductor is theoretically investigated based on the electrodynamics of nearly ferroelectric superconductors. Microwave response is studied via the calculations of the microwave surface impedances for three model structures in which dielectriclike superconductors are considered. Firstly, the calculated intrinsic surface impedance for a bulk material occupying the half space decreases with increasing frequency. Secondly, the calculated intrinsic surface resistance for a superconductor film of a finite thickness shows some anomalous resonance peaks. The distribution of these sharp peaks is strongly dependent on the film thickness. Discussion of these comblike peaks is also given. Finally, we calculate the effective microwave surface impedance of a superconductor/dielectric layered system. The substrate resonance behavior in the surface resistance will be illustrated and discussed.
The influence of Co addition on the magnetocaloric effect of Nanoperm-type amorphous alloys
Authors: Franco V. , Blázquez J. S. , Conde A.
Published: October 2006

The effect of Co addition on the magnetocaloric effect of amorphous alloys with Nanoperm-type composition has been studied for temperatures above room temperature. Co addition produces an increase in the maximum magnetic entropy change and a shift of its associated temperature to higher temperatures. The maximum refrigerant capacity (RC) value obtained in this study is 82Jkg−1 for a maximum applied field H=15kOe. This value is ∼30% larger than that of a Mo-containing Finemet-type alloy measured under the same experimental conditions. However, the RC of the alloys, when calculated from temperatures corresponding to the half-maximum entropy change value, deteriorates with the presence of Co in the alloy. The field dependence of the magnetic entropy change has also been analyzed, showing a power dependence for all the magnetic regimes of the samples. This field dependence at the Curie temperature deviates from mean field predictions.
Field dependence of high-frequency magnetic noise in tunneling magnetoresistive heads
Authors: Han G. C. , Zheng Y. K. , Liu Z. Y. , Liu B. , Mao S. N.
Published: October 2006

Thermal magnetization fluctuations in tunneling magnetoresistive heads with track width of ∼100nm have been studied through high-frequency magnetic noise measurement as a function of both transverse and longitudinal fields. The study suggests that in the dynamic region of the heads, the related power spectral density is determined by the magnetization fluctuations of the free layer. At high fields which drive the sensor to the magnetization saturation, an “abnormal” resonance with substantially high amplitude in comparison with that of the free layer is observed when the magnetization of the free layer is nearly antiparallel to that of the reference layer. This abnormal resonance is excluded from the spin torque effect. The detailed analysis suggests that this resonance is due to the magnetization fluctuations in the reference/pinned layers.
Performance improvement of top-emitting organic light-emitting diodes by an organic capping layer: An experimental study
Authors: Huang Qiang , Walzer Karsten , Pfeiffer Martin , Leo Karl , Hofmann Michael , Stübinger Thomas
Published: October 2006

The optical outcoupling of top-emitting organic light-emitting diodes (OLEDs) can be improved by a thin dielectric capping layer on top of the transparent cathode. We investigate the emission properties of a set of top-emitting OLEDs with the same device structure, but different organic capping layer thicknesses to understand the capping layer effect. We demonstrate that the distribution pattern of the emitted light from top-emitting OLEDs depends strongly on the capping layer thickness, showing not only a maximum current efficiency enhancement by a factor of 1.38 (up to 78cd∕A in forward direction at 1000cd∕m2), but also a quantum efficiency improvement by 35%. This leads to a device efficiency of up to 17.8% and 69lm∕W at a brightness of 1000cd∕m2. We show that this efficiency enhancement is not due to the redistribution of emitted light, but mainly due to the improvement of outcoupling efficiency by changing the optical structure of the devices with the organic capping layer. The maximum outcoupling efficiency is achieved at a capping layer thickness where the top contact stack (cathode+capping layer) shows low absorption and high reflection.
A phasor-particle model for coupling between an automatching network and electrical plasma in radio frequency capacitive discharged system
Authors: Kwok Dixon T. K.
Published: October 2006

A phasor-particle model for coupling between an automatching network and electrical plasma is developed. The external circuit consists of an automatching box and an ideal voltage source is described by phasor equations. The plasma is modeled by hybrid particle-in-cell ions and Boltzmann distribution of electrons. The chamber consisted of the radio frequency powered electrode and the grounded chamber wall is a good capacitor. The accumulated surface charges and the potential of the powered electrode are modified by the plasma in the proposed model. The amplitude and phase of the voltage/current of the external matching network are numerically simulated. The negative direct current bias voltage in an asymmetrical system is generated.
Hysteresis in acoustic properties of ferroelectric relaxor Pb[(Zn1∕3Nb2∕3)0.955Ti0.045]O3 single crystals studied by Brillouin and dielectric spectroscopies
Authors: Ko Jae-Hyeon , Kim Do Han , Kojima Seiji , Chen Wenzhi , Ye Zuo-Guang
Published: October 2006

Acoustic and dielectric properties of Pb[(Zn1∕3Nb2∕3)1−xTix]O3 (PZN-xPT) single crystals with x=0.045 have been studied by the high-resolution micro-Brillouin scattering and dielectric spectroscopy in a wide temperature range. The softening of the Brillouin shift and the increase of dielectric relaxation time upon cooling indicated the formation of polar nanoregions (PNRs) and the slowing down of their dynamics. In contrast to the acoustic properties of typical model relaxors such as lead magnesioniobate, the change in the Brillouin shift near its minimum became sharper on heating compared to the change on cooling, pointing to the clear existence of hysteresis in the dynamics of the diffuse phase transition in PZN-4.5%PT. Since the number of PNRs will increase upon cooling, it may be expected that the kinetics of the phase transition would become slower, the lower the transition temperature resulting in the more sluggish, broad feature of the Brillouin shift observed during cooling. This result may indicate that the number and size of polar nanoregions, which are dependent on temperature, play an important role in the development of the mesoscopic ferroelectric order in PZN-4.5%PT.
Enhanced polarization and reduced leakage current in BiFeO3 thin films fabricated by chemical solution deposition
Authors: Singh S. K. , Ishiwara H. , Maruyama K.
Published: October 2006

Bi Fe O 3 (BFO) thin films were fabricated by chemical solution deposition on Pt∕Ti∕SiO2∕Si(100) and Pt/sapphire(0001) structures. In order to reduce leakage current density in BFO films, the stoichiometric BFO chemical solution of 0.1–0.2mol∕l concentration was used to deposit approximately 10–20-nm-thick films at one step in the spin-coating method. The optimized conditions for preannealing were determined to be at 350°C for 10min in air, and those for annealing were at 550°C for 5min in nitrogen atmosphere. It was found from x-ray diffraction analysis that the obtained films on both Si and sapphire substrates were mostly composed of polycrystalline BFO grains with a perovskite structure. It was also confirmed from x-ray photoelectron spectroscopy that the origin of low leakage current was due to the presence of Fe3+ valance state. In the P-E (polarization versus electric field) measurements for BFO films on both Si and sapphire substrates we observed nonsaturate and saturated hysteresis loops at room temperature and 80K, respectively. At 80K, the remanent polarization and coercive field in the film on sapphire were approximately 100μC∕cm2 and 0.4MV∕cm at 2MV∕cm electric applied field, respectively, and the polarization was about 10% smaller in the film on Si. Improved ferroelectric properties of BFO films on sapphire substrates are considered to be due to the improved BFO/Pt interface.
Ion beam synthesis of cubic-SiC layer on Si(111) substrate
Authors: Maltez R. L. , de Oliveira R. M. , dos Reis R. M. S. , Boudinov H.
Published: October 2006

We have investigated SiC layers produced by ion beam synthesis on Si(111) substrates using different procedures. Bare Si(111) and SiO2∕Si(111) structures were implanted with carbon at 40keV up to a fluence of 4×1017cm−2 at a temperature of 600°C. Postimplantation annealing was carried out at 1250°C for 2h in pure O2 or Ar (with 1% of O2). A SiC layer was synthesized for all the procedures involving annealing under Ar. However, for the samples annealed under pure O2 flux, only that employing implantation into the bare Si(111) resulted in SiC synthesis. Rutherford backscattering spectrometry shows that, after annealing, the stoichiometric composition is obtained. Transmission electron microscopy measurements demonstrate the synthesis of cubic-SiC layers that are completely epitaxial to the Si(111) substrate. However, there is a high density of nanometric twins, stacking faults, and also narrow amorphous inclusions of laminar shape between the crystalline regions. The procedure based on high temperature implantation through a SiO2 cap, etching the cap off, 1250°C postimplantation annealing under Ar ambient (with 1% of O2), and final etching has shown advantages from the point of view of surface flatness and increased layer thickness, keeping the same layer epitaxy and accurate composition.
Zero-crossing Shapiro step generated in an asymmetric and nonhysteretic rf-current-driven two-junction superconducting quantum interference device
Authors: Mizugaki Yoshinao , Katoh Kazuyuki
Published: October 2006

A zero-crossing Shapiro step (ZCSS) in an asymmetric and nonhysteretic two-junction superconducting quantum interference device (SQUID) driven by one sinusoidal rf signal is presented. The operation is based on imbalanced evolution of the junction phases owing to the tilted interference diagrams. Dependence of ZCSS generation upon the frequency and amplitude of a rf signal was numerically obtained. A test circuit was designed and fabricated using a Nb∕AlOx∕Nb junction technology. When we irradiated a rf signal of 10GHz, a ZCSS at the voltage position of the first order was observed. The polarity of the step voltage was switched by a dc control flux to the SQUID loop. The experimental bias-current versus voltage and control-current versus voltage curves were quantitatively reproduced by numerical simulation.
Ultraviolet photodissociation of the van der Waals dimer (CH3I)2 revisited. II. Pathways giving rise to neutral molecular iodine
Authors: Vidma Konstantin V. , Baklanov Alexey V. , Zhang Yongwei , Parker David H.
Published: October 2006

The formation of neutral I2 by the photodissociation of the methyl iodide dimer, (CH3I)2, excited within the A band at 249.5nm is evaluated using velocity map imaging. In previous work [J. Chem. Phys. 122, 204301 (2005)], we showed that the formation of I2+ from photodissociation of the methyl iodide dimer takes place via ionic channels (through the formation of (CH3I)2+). It is thus not possible to detect neutral I2 by monitoring I2+. Neutral I2 is detected in this study by monitoring I atoms arising from the photodissociation of I2. Iodine atoms from I2 photodissociation have a characteristic kinetic energy and angular anisotropy, which is registered using velocity map imaging. We use a two-color probe scheme involving the photodissociation of nascent I2 at 499nm, which gives rise to I atoms that are ionized by (2+1) resonance enhanced multiphoton ionization at 304.67nm. Our estimate of the yield of nascent I2 is based on the comparison with the signal from I2 at a known concentration. Using molecular beams with a small fraction of CH3I (1% in the expanded mixture) where smaller clusters should prevail, the production of I2 was found to be negligible. An upper estimate for the quantum yield of I2 from (CH3I)2 dimers was found to be less than 0.4%. Experiments with a higher fraction of CH3I (4% in the expanded mixture), which favor the formation of larger clusters, revealed an observable formation of I2, with an estimated translational temperature of about 820K. We suggest that this observed I2 signal arises from the photodissociation of several CH3I molecules in the larger cluster by the same UV pulse, followed by recombination of two nascent iodine atoms is responsible for neutral I2 production.
Experimental study and global model of inductively coupled CF4∕O2 discharges
Authors: Kimura Takashi , Noto Masahisa
Published: October 2006

Experiments with a Langmuir probe and optical emission spectroscopy combined with actinometry were carried out in inductive CF4∕O2 discharges at three pressures of 8, 15, and 25mTorr. The measured electron energy probability functions are approximately Maxwellian at any oxygen content. The measured electron density decreases with increasing the oxygen in the oxygen content below 20%, beyond which it remains nearly constant. On the other hand, the measured electron temperature is not sensitive to the content. The atomic fluorine density estimated by actinometry increases markedly as oxygen is mixed to CF4 discharges, and then reaches the maximum around the oxygen content of 20%–30%, beyond which it decreases with increasing oxygen content. The atomic oxygen density increases with the increase in the oxygen content except for the oxygen content higher than 90%. A global model for electronegative plasma is used in order to investigate the plasma chemistry in CF4∕O2 discharges assuming the Maxwellian electron energy distribution. The model results are compared with the experimental results, obtaining reasonably good agreement.
Simple detection of light polarization by using crossed polarization gratings
Authors: Sasaki Tomoyuki , Hatayama Akira , Emoto Akira , Ono Hiroshi , Kawatsuki Nobuhiro
Published: October 2006

A simple procedure to detect light polarization by use of crossed polarization gratings in photo-cross-linkable liquid crystals is presented. Crossed polarization gratings consisting of four anisotropic gratings with different grating vectors were designed according to the theoretical expectation obtained on the basis of the Jones calculus, and fabricated by means of multiple holographic recording. The polarization state of the incident beam was estimated by measuring the intensity of the diffracted beams, and by analyzing them on the basis of Jones calculus. The presented result, which requires no mechanical driver to rotate the polarizing prisms, provides a high-speed detection system for light polarization.
Impact response by a foamlike forest of coiled carbon nanotubes
Authors: Daraio Chiara , Nesterenko Vitali F. , Jin Sungho , Wang Wei , Rao Apparao M.
Published: October 2006

We studied the dynamic response of a foamlike forest of coiled carbon nanotubes under high strain rate deformation using a simple drop-ball test. The method is based on measuring the dynamic force between the ball and the foam on the substrate during the stages of penetration and restitution. The analysis of the forest’s morphology after impact has shown no trace of plastic deformation and a full recovery of the foamlike layer of coiled carbon nanotubes under various impact velocities. The contact force exhibits a strongly nonlinear dependence on displacement and appears fundamentally different from the response of a forest of straight carbon nanotubes, and from the Hertzian type of plane-sphere interaction. “Brittle” fracture of the foamlike layer is observed after repeated high velocity impacts. Such layers of coiled nanotubes may be used as a strongly nonlinear spring in discrete systems for monitoring their dynamic behavior and as a nanostructure for localized microimpact protection.
Measurements and computations of mass flow and momentum flux through short tubes in rarefied gases
Authors: Lilly T. C. , Gimelshein S. F. , Ketsdever A. D. , Markelov G. N.
Published: October 2006

Gas flows through orifices and short tubes have been extensively studied from the 1960s through the 1980s for both fundamental and practical reasons. These flows are a basic and often important element of various modern gas driven instruments. Recent advances in micro- and nanoscale technologies have paved the way for a generation of miniaturized devices in various application areas, from clinical analyses to biochemical detection to aerospace propulsion. The latter is the main area of interest of this study, where rarefied gas flow into a vacuum through short tubes with thickness-to-diameter ratios varying from 0.015 to 1.2 is investigated both experimentally and numerically with kinetic and continuum approaches. Helium and nitrogen gases are used in the range of Reynolds numbers from 0.02 to 770 (based on the tube diameter), corresponding to Knudsen numbers from 40 down to about 0.001. Propulsion properties of relatively thin and thick tubes are examined. Good agreement between experimental and numerical results is observed for mass flow rate and momentum flux, the latter being corrected for the experimental facility background pressure. For thick-to-thin tube ratios of mass flow and momentum flux versus pressure, a minimum is observed at a Knudsen number of about 0.5. A short tube propulsion efficiency is shown to be much higher than that of a thin orifice. The effect of surface specularity on a thicker tube specific impulse was found to be relatively small.
Enhanced electrical characteristics of Au nanoparticles embedded in high-k HfO2 matrix
Authors: Yang Jung Yup , Kim Ju Hyung , Choi Won Joon , Do Young Ho , Kim Chae Ok , Hong Jin Pyo
Published: October 2006

We present experimental results for laser-induced Au nanoparticle (NP) embedded in a HfO2 high-k dielectric matrix. Cross-sectional transmission electron microscopy images showed that the Au NPs of 8nm in diameter were clearly embedded in HfO2 matrix. Capacitance-voltage measurements of Pt∕HfO2∕AuNPs∕HfO2 on p-type Si substrate reliably exhibited metal-oxide-semiconductor behavior with a large flatband shift of 4.7V. In addition, the charge retention time at room temperature was found to exceed 105h. This longer time was attributed to the higher electron barrier height via high work function of the Au NP.
Polymeric conducting anode for small organic transporting molecules in dark injection experiments
Authors: Tse S. C. , Tsang S. W. , So S. K.
Published: October 2006

Poly(3,4-ethylenedioxythiophene) doped with polystrenesulphonic acid (PEDOT:PSS) is used as a hole-injecting anode for small organic hole transporters in current-voltage (JV) and dark injection space-charge-limited current (DI-SCLC) experiments. The hole transporters under investigation are phenylamine-based 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (MTDATA), N,N′-diphenyl-N,N′-bis(1-naphthyl) (1,1′-biphenyl)-4,4′diamine (NPB), and N,N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′diamine (TPD). Clear DI-SCLC transient peaks were observed over a wide range of electric fields in all cases. For MTDATA and NPB, hole mobilities evaluated by DI experiments are in excellent agreement with mobilties deduced from independent time-of-flight technique. It can be concluded that, for the purpose of JV and DI experiments, PEDOT:PSS forms an Ohmic contact with MTDATA and a quasi-Ohmic contact with NPB despite the relatively low-lying highest occupied molecular orbital of the latter. In the case of TPD, hole injection from PEDOT:PSS deviates substantially from Ohmic injection, leading to a lower than expected DI-extracted hole mobility. The performances of other hole-injecting anodes for DI experiments were also examined.
Spatio-temporal growth of disturbances in a boundary layer and energy based receptivity analysis
Authors: Sengupta T. K. , Rao A. Kameswara , Venkatasubbaiah K.
Published: October 2006

In fluid dynamical systems, it is not known a priori whether disturbances grow either in space or in time or as spatio-temporal structures. However, for boundary layers, it is customary to treat it as a spatial problem and some limited comparison between prediction and laboratory experiments exist. In the present work, the receptivity problem of a zero pressure gradient boundary layer excited by a localized harmonic source is investigated under the general spatio-temporal framework, using the Bromwich contour integral method. While this approach has been shown to be equivalent to the spatial study, for unstable systems excited by a single frequency source [T. K. Sengupta, M. Ballav, and S. Nijhawan, Phys. Fluids 6, 1213 (1994)], here we additionally show, how the boundary layer behaves when it is excited (i) at a single frequency that corresponds to a stable condition (given by spatial normal-mode analysis) and (ii) by wideband frequencies, that shows the possibility of flow transition due to a spatio-temporally growing forerunner or wave front. An energy based receptivity analysis tool is also developed as an alternative to traditional instability theory. Using this, we reinterpret the concept of critical layer that was originally postulated to explain the mathematical singularity of inviscid disturbance field in traditional instability theory of normal modes.
The effect of the in-plane demagnetizing field on films with weak perpendicular magnetic anisotropy
Authors: de Abril Oscar , Sánchez María del Carmen , Aroca Claudio
Published: October 2006

The effect of reduced lateral dimension on the magnetic behavior of long microstrips with weak perpendicular magnetic anisotropy has been studied. The hysteresis loops of the surface and the whole volume of microstrips and large films have been recorded by magneto-optic Kerr effect magnetometry and vibrating sample magnetometry. Also, the magnetic structure of the microstrips and its evolution under an applied field have been studied by magnetic force microscopy and the Bitter technique. It has been observed that the transversal dimension of the microstrips gives rise mainly to an in-plane demagnetizing field which affects their hysteresis loops and magnetic structure in a different manner. A great increase in the surface coercivity in the transversal direction of the microstrips is the main unexpected effect that has been observed. On the other hand, the magnetic structure in remanence and its evolution with increasing thickness have not revealed a significant dependence on the direction of the last saturating field. It has also been observed that the reduced size of the microstrips in their transversal direction does not prevent the occurrence of the property known as rotatable anisotropy, typical of films with stripe domain structure, although it makes this property very anisotropic. Finally, a two-dimensional qualitative model of closed flux stripe domain structure has been used for correlating the enlargement of the surface coercivity of the microstrips with the evolution of their magnetic structure.
Synthesis and local structure of doped nanocrystalline zinc oxides
Authors: Brehm Joachim U. , Winterer Markus , Hahn Horst
Published: October 2006

Nanocrystalline zinc oxides are produced by chemical vapor synthesis and characterized by x-ray diffraction, high resolution transmission electron microscopy, nitrogen sorption, and extended x-ray absorption fine structure. Dopant elements (aluminum, gallium, and indium) influence the particle size of the powders as well as lattice parameters and local structure. The different effects of the three dopant elements are characterized.
Mean value and fluctuations in a model of diffusion in porous media
Authors: Ourrad O. , Erochenkova G. , Lima R. , Vittot M.
Published: October 2006

We consider a stochastic model for the diffusion in a porous media. For a case where the average satisfies an anomalous diffusion equation, we investigate the behavior of the realizations around the mean value. The most relevant result of our work is that, although the concentration corresponding to each realization diffuses normally for large times, it experiences large deviations from the mean value during intermediate times. As a consequence, the experimental measurements will always depart from the average value of the realizations (with respect to the stochastic process) for unpredictable times.
Comparative study of HfNx and Hf–Ge–N copper diffusion barriers on Ge
Authors: Rawal S. , Lambers E. , Norton D. P. , Anderson T. J. , McElwee-White L.
Published: October 2006

The diffusion barrier properties of HfNx and Hf–Ge–N thin films for Cu metallization on Ge are examined. The diffusion barrier films were deposited by reactive sputtering on p-Ge (001) single crystal substrates with varying thicknesses. Cu thin films were then deposited in situ on the diffusion barrier. The multilayer film structure was subsequently annealed in an Ar atmosphere. X-ray diffraction was used to determine the film crystallinity and identify intermetallic phases due to reactions involving the film and substrate. The HfNx and Hf–Ge–N diffusion barrier films remained amorphous for annealing temperatures up to 700°C. At thickness of 50nm, the HfNx films showed superior diffusion barrier properties as compared to Hf–Ge–N based on the appearance of secondary phases due to reactions and changes in the Cu morphology. These results suggest that HfNx is an effective barrier material for Cu integration on Ge.