bluuebunny/crossref_metadata_2025 huggingface dataset:
QBO as potential amplifier of solar cycle influence
Authors: Mayr Hans G. , Mengel John G. , Wolff Charles L. , Porter Hayden S.
Published: March 2006

The solar cycle (SC) effect in the lower atmosphere has been linked observationally to the quasi‐biennial oscillation (QBO) of the zonal circulation. Salby and Callaghan (2000) in particular analyzed the QBO covering more than 40 years and found that it contains a large SC signature at 20 km. We discuss a 3D study in which we simulate the QBO under the influence of the SC. For a SC period of 10 years, the relative amplitude of radiative forcing is taken to vary with height: 0.2% (surface), 2% (50 km), 20% (100 km and above). This model produces in the lower stratosphere a relatively large modulation of the QBO, which appears to come from the SC and qualitatively agrees with the observations. The modulation of the QBO, with constant phase relative to the SC, is shown to persist at least for 50 years, and it is induced by a SC modulated annual oscillation that is hemispherically symmetric and confined to low latitudes (Mayr et al., 2005).
Bifurcated current sheets: Statistics from Cluster magnetometer measurements
Authors: Thompson S. M. , Kivelson M. G. , El‐Alaoui M. , Balogh A. , Réme H. , Kistler L. M.
Published: March 2006

We report on a statistical study of bifurcated current sheets in the near‐Earth plasma sheet and the association of such current sheets with a near‐Earth neutral line. Support for this interpretation is provided by a global MHD simulation generated for geomagnetic and solar wind conditions prevailing at the time when a bifurcated current sheet was previously identified in 2001 Cluster magnetometer data. A local bifurcation of the current sheet with spatial scales of 3–7 RE in Y and Z GSM was present in the MHD simulation at the −19 RE apogee distance of Cluster. Magnetic field line tracing revealed a clear connection to a local neutral line at ∼22 RE downtail. For our statistical study, criteria developed to characterize bifurcations were automatically applied to the magnetic field and particle observations of the four Cluster spacecraft for 1500 km and 5000 km separations. We found that bifurcations are detected ∼25% of the time Cluster is in the current sheet. Thickness estimates from our statistical results reveal structures 1–3 RE in scale size (north‐south), comparable with those present in our MHD simulation results. Our simulation and statistical results show that bifurcated current flows near the boundary of the plasma sheet. Local conditions at Cluster for our selected events are often consistent with the presence of a nearby neutral line. We propose that bifurcated current density profiles develop in association with small‐scale (few RE) neutral lines that do not stretch across the entire magnetotail. Therefore bifurcated current sheets may well be a signature of magnetotail dynamics rather than an equilibrium current sheet configuration.
Raman spectra from very concentrated aqueous NaOH and from wet and dry, solid, and anhydrous molten, LiOH, NaOH, and KOH
Authors: Walrafen George E. , Douglas Rudolph T. W.
Published: March 2006

High-temperature, high-pressure Raman spectra were obtained from aqueous NaOH solutions up to 2NaOH∕H2O, with XNaOH=0.667 at 480K. The spectra corresponding to the highest compositions, XNaOH⩾0.5, are dominated by H3O2−. An IR ξ-function dispersion curve for aqueous NaOH, at 473K and 1kbar, calculated from the data of Franck and Charuel indicates that the OH− ion forms H3O2− by preferential H bonding with nonhydrogen-bonded OH groups. Raman spectra from wet to anhydrous, solid LiOH, NaOH, and KOH yield sharp, symmetric OH− stretching peaks at 3664, 3633, and 3596cm−1, respectively, plus water-related, i.e., H3O2−, peaks near LiOH, 3562cm−1, NaOH, 3596cm−1, and, KOH, 3500cm−1. Absence of H3O2− peaks from the solid assures that the corresponding melt is anhydrous. Raman spectra from the anhydrous melts yield OH− stretching peak frequencies: LiOH, 3614±4cm−1, 873K; NaOH, 3610±2cm−1, 975K; and, KOH, 3607±2cm−1, 773K, but low-frequency asymmetry due to ion-pair interactions is present which is centered near 3550cm−1. The ion-pair-related asymmetry corresponds to the sole IR maximum near 3550cm−1 from anhydrous molten NaOH, at 623K. Bose-Einstein correction of published low-frequency Raman data from molten LiOH revealed an acoustic phonon, near 205cm−1, related to restricted translation of OH− versus Li+, and an optical phonon, at 625cm−1 and τ≈0.05ps, due to protonic precession and/or pendular motion. Strong H bonding between water and the O atom of OH− forms H3O2−, but the proton of OH− does not bond with H significantly. Large Raman bandwidths (aqueous solutions) are explained in terms of inhomogeneous broadening due to proton transfer in a double well. Vibrational assignments are presented for H3O2−.
Microwave ion source with permanent magnet for 100 keV ion implantation
Authors: Ming Jianchuan , Guo Qiqian , Wang Jinhui , Zhao Weijiang , Bai Yulan , Zhu Qiliang , Ding Jia
Published: March 2006

An electron cyclotron resonance ion source has been developed in RIAMB for 100 keV ion implantation. Its magnetic field was produced by NdFeB permanent magnet and its outline dimension is about 160 mm in diameter and 150 mm in height. It operates in pulse mode, at nitrogen discharge, 100 kV extraction voltages, and 60 kV acceleration voltages; more than 40 mA ion pulse current was extracted from seven emission apertures of 3.5 mm in diameter. Even ion beam over an area of about 250 mm in diameter has been obtained on the sample stage at a distance about 1000 mm from the emission aperture.
Status of the ion source DECRIS-SC
Authors: Efremov A. , Bekhterev V. , Bogomolov S. , Dmitriev S. , Lebedev A. , Leporis M. , Nikiforov A. , Paschenko S. , Yakovlev B. , Yazvitsky N. , Datskov V. , Drobin V. , Seleznev V. , Tsvineva G. , Shishov Yu. A.
Published: March 2006

A “liquid He-free” superconducting electron cyclotron resonance ion Source DECRIS-SC, to be used as an injector for the compact IC-100 cyclotron, has been designed and built in cooperation between the FLNR and LHE (JINR). The main feature is that a compact refrigerator of the Gifford-McMahon type is used to cool the solenoid coils. Due to a very small cooling power at 4.2K (about 1W) our efforts were aimed at optimizing the magnetic structure and minimizing external heating of the coils. The maximum magnetic-field strengths are 3 and 2T in the injection and extraction regions, respectively. When the source had been assembled and magnetic field measured, the ion source was immediately installed at the injection line of the cyclotron. During the first tests, which were run only a few days, some problems arose due to a relatively poor efficiency of the beam transport and analyzing line. From the moment of the first reliable beam production up to now the ion source has been operating continuously for the cyclotron tuning and then for the experiment. Some results of the one-year operation are reported.
Diagnostic system for plasma/surface energy transfer characterization
Authors: Thomann A.-L. , Semmar N. , Dussart R. , Mathias J. , Lang V.
Published: March 2006

The knowledge of the effective energy deposited onto a surface by the reactive particles (ions, electrons, metastables, photons, etc.) in plasma processes such as thin-film deposition, sputtering, etching, etc., is of high interest to understand the basic mechanisms of energy transfer. In this article, a diagnostic is developed to directly measure the global energy transferred to surfaces (reactor walls, substrates, material to be modified, etc.) immerged in low-pressure plasmas. The diagnostic is based on a commercial HFM7-Vattel® microsensor, confined in a temperature-controlled substrate holder. The manufacturer calibration specifications are only given for atmospheric pressure. They cannot be used in low-pressure plasma conditions (typically 0.1–20Pa). Thus, for this particular application, a calibration of the microsensor is required. It is performed at various pressures, between vacuum and the ambient, according to the NIST protocol and using a homemade blackbody (BB). It is shown that only curves obtained in vacuum or pressures below 0.1Pa are valuable for a true calibration of the sensor. The others are perturbed by the heating of the gas in the BB surroundings. Measurements carried out in a typical transformer coupled plasma reactor in argon gas are presented. Typically the values are of the order of tens or hundreds of mW∕cm2 in our experimental conditions. They are consistent with an estimation of the energy transferred by charged particles (ions and electrons) performed from Langmuir probe characterization of the plasma.
Infrared laser spectroscopy of the CH3–HCN radical complex stabilized in helium nanodroplets
Authors: Rudić S. , Merritt J. M. , Miller R. E.
Published: March 2006

The CH3–HCN and CD3–HCN radical complexes have been formed in helium nanodroplets by sequential pickup of a CH3 (CD3) radical and a HCN molecule and have been studied by high-resolution infrared laser spectroscopy. The complexes have a hydrogen-bonded structure with C3v symmetry, as inferred from the analysis of their rotationally resolved ν=1←0 H–CN vibrational bands. The A rotational constants of the complexes are found to change significantly upon vibrational excitation of the C–H stretch of HCN within the complex, ΔA=A′−A″=−0.04cm−1 (for CH3–HCN), whereas the B rotational constants are found to be 2.9 times smaller than that predicted by theory. The reduction in B can be attributed to the effects of helium solvation, whereas the large ΔA is found to be a sensitive probe of the vibrational averaging dynamics of such weakly bound systems. The complex has a permanent electric dipole moment of 3.1±0.2D, as measured by Stark spectroscopy. A vibration-vibration resonance is observed to couple the excited C–H stretching vibration of HCN within the complex to the lower-frequency C–H stretches of the methyl radical. Deuteration of the methyl radical was used to detune these levels from resonance, increasing the lifetime of the complex by a factor of 2. Ab initio calculations for the energies and molecular parameters of the stationary points on the CN+CH4→HCN+CH3 potential-energy surface are also presented.
Effect of the plasma electrode position and shape on the beam intensity of the highly charged ions from RIKEN 18GHz electron-cyclotron-resonance ion source
Authors: Higurashi Y. , Nakagawa T. , Kidera M. , Aihara T. , Kobayashi K. , Kase M. , Goto A. , Yano Y.
Published: March 2006

Beam intensities of highly charged Ar ions (Ar11+,12+) were measured as a function of plasma electrode position. We observed that the beam intensity of Ar11+,12+ increased when putting the electrode far from the electron-cyclotron-resonance zone. On the other hand, lower charged heavy ions (Ar8+,7+) dramatically decreased. We observed that the intense beam extraction strongly affects the plasma condition. It may be due to the ion pumping effect.
Microwave dielectric dispersion process in perovskite ferroelectric systems
Authors: de Los S. Guerra J. , Lente M. H. , Eiras J. A.
Published: March 2006

The microwave dielectric dispersion process was investigated in relaxor and normal ferroelectric compositions of Pb1−xLaxTiO3 ceramics. The results revealed the following remarkable features: (i) the mechanism responsible for the microwave dielectric dispersion process in perovskite ferroelectric systems may be associated to the vibration of the boundaries of polar regions, independently of their size and dynamical properties; (ii) the characteristic frequency, fR, is governed by the ratio between the force constant and the effective mass of such boundaries; (iii) the temperature dependence of fR above the temperature of the maximum of the dielectric permittivity directly reflects the ferroelectric-type phase transition.
Modeling of anomalous electron mobility in Hall thrusters
Authors: Koo Justin W. , Boyd Iain D.
Published: March 2006

Accurate modeling of the anomalous electron mobility is absolutely critical for successful simulation of Hall thrusters. In this work, existing computational models for the anomalous electron mobility are used to simulate the UM/AFRL P5 Hall thruster (a 5kW laboratory model) in a two-dimensional axisymmetric hybrid particle-in-cell Monte Carlo collision code. Comparison to experimental results indicates that, while these computational models can be tuned to reproduce the correct thrust or discharge current, it is very difficult to match all integrated performance parameters (thrust, power, discharge current, etc.) simultaneously. Furthermore, multiple configurations of these computational models can produce reasonable integrated performance parameters. A semiempirical electron mobility profile is constructed from a combination of internal experimental data and modeling assumptions. This semiempirical electron mobility profile is used in the code and results in more accurate simulation of both the integrated performance parameters and the mean potential profile of the thruster. Results indicate that the anomalous electron mobility, while absolutely necessary in the near-field region, provides a substantially smaller contribution to the total electron mobility in the high Hall current region near the thruster exit plane.
Negative current profile measurements in tokamaks using internal Rogowskii coil
Authors: Narayanan Ramesh , Sekar Iyengar A. N.
Published: March 2006

An internal Rogowskii coil (IRC) has been developed to measure current profiles within SINP tokamak discharges. The present article has highlighted measurements using the IRC in SINP tokamak discharges exhibiting extension in phase after the discharge decays to approximately half its peak value. The IRC current profile results have been compared to that obtained from an internal Langmuir-magnetic probe system and have been observed to measure current profile directly (without employing any reconstruction methods) as well as the localized fluctuations much better than the latter. Interesting observation of negative currents in such Ohmic discharges is reported for the first time. The presence of negative currents has been observed to help in improving the confinement of the discharges. These results are important especially in relation to recent observations of “current holes,” in large fusion devices (such as JET and JT-60U), enhancing confinement properties.
Novel multiple-switch Blumlein generator
Authors: Liu Z. , Yan K. , Winands G. J. J. , Van Heesch E. J. M. , Pemen A. J. M.
Published: March 2006

The Blumlein generator has been one of the most popular pulsed-power circuits. The pulse forming lines are charged simultaneously, and then discharged via a single switch, such as a spark gap. The generator can be used for single pulse or at a high repletion rate. However, for large pulsed power generation, one critical issue for such a single-switch based circuit topology is related to large switching currents. In this article, we propose a novel Blumlein circuit topology based on multiple switches. The pulsed forming lines are charged in parallel and then are synchronously commutated via multiple switches. No special synchronization trigger circuit is needed for the proposed circuit topology; this robust circuit topology is simple and very reliable. A prototype multiple-switch Blumlein generator with two spark-gap switches has been experimentally evaluated with both resistive and corona plasma loads. In terms of the switching currents, it is observed that the two switches can be synchronized within 2–3 ns. The energy conversion efficiencies are 82% and 76.8% for a matched resistive load and a plasma reactor, respectively.
Towards a photophysical model for 5-hydroxyflavone
Authors: del Valle Juan Carlos
Published: March 2006

The photophysics of the 5-hydroxyflavone (5HF) molecule has been revised. Conversely to what has been hitherto reported, the proton-transfer fluorescence of 5HF has been recorded under xenon lamp excitation in cyclohexane, hexane, ethanol, ethyl ether, 2-methyl-2-propanol, and dimethylsulfoxide at room temperature. The 5HF fluorescence spectra only exhibit one emission band centered at ca. 700nm. A small photoreaction quantum yield of 10−5–10−6 denotes the great photostability exemplified by 5HF in hydrocarbon solvent, ethanol, and dimethylsulfoxide. This great photostability is predominantly explained owing to an internal conversion process from the first excited singlet state 1(π,π*)1 (S1), which has a repulsive (proton-transfer) potential energy curve with respect to the stretching of the OH bond and only one energy minimum for the proton-transfer tautomer. The S1′-S0′ energy gap proves to be small because of important modifications found in the molecular geometry of 5HF upon photoexcitation. A computational strategy, based upon theoretical calculations at the B3LYP density functional theory (DFT) and time-dependent DFT levels, supports the experimental spectroscopic evidence. Also an abnormal singlet-triplet splitting for a π,π* configuration has been found in 5HF.
Formation of silicon germanium nitride layer with distributed charge storage elements
Authors: Tu Chun-Hao , Chang Ting-Chang , Liu Po-Tsun , Liu Hsin-Chou , Chen Wei-Ren , Tsai Chia-Chou , Chang Li-Ting , Chang Chun-Yen
Published: March 2006

The formation of silicon germanium nitride (SiGeN) with distributed charge storage elements is proposed in this work. A large memory window is observed due to the retainable dangling bonds inside the SiGeN gate stack layer. The nonvolatile memory device with the high-temperature oxidized SiGeN stack layer exhibits 2V threshold voltage shift under 7V write operation, which is sufficient for a memory device to define the signal “0” and “1.” Also, the manufacture technology using the sequent high-temperature oxidation of the a-Si layer acting as the blocking oxide is proposed to enhance the performance of nonvolatile memory devices.
Enhancement of optical properties in organic light emitting diodes using the Mg–Al alloy cathode and IrOx-coated indium tin oxide anode
Authors: Kim Soo Young , Lee Jong-Lam
Published: March 2006

We report the enhancement of quantum efficiency using the Mg–Al alloy cathode and IrOx-coated indium tin oxide (ITO) anode in organic light emitting diodes (OLEDs). The external quantum efficiency at the current density of 64mA∕cm2 increased from 0.04% to 1.89% as the Al cathode and ITO anode changed to the Mg–Al cathode and IrOx-coated ITO anode, respectively. Synchrotron radiation photoelectron spectroscopy results show that the work function of IrOx-coated ITO is higher by 0.5eV than that of the ITO and the work function of the Mg–Al alloy is lower by 0.2eV than that of Al. Thus, both the hole and electron injection energy barriers were simultaneously lowered, reducing the turn-on voltage and increasing the quantum efficiency of OLEDs.
High quality step-edge substrates for high-Tc superconducting devices
Authors: Wu C. H. , Chen M. J. , Chen J. C. , Chen K. L. , Yang H. C. , Hsu M. S. , Lai T. S. , Tsai Y. S. , Horng H. E. , Chen J. H. , Jeng J. T.
Published: March 2006

Despite the significant progress in fabrication methods of step edge, the lack of reproducibility still hinders their use in more complicated systems. To pursue the high reproducibility and quality of step edge for high-Tc superconducting devices, we have developed the technique to fabricate high quality step-edge substrates with arbitrary step angles. We used two steps to improve the step ramp quality substantially. The surface microscopy of step substrates shows high uniformity with respect to any step angle. There are no needles, waves, trenches, cascades, or other flaws on these surfaces. Serial Josephson junctions and superconducting quantum interference device arrays were fabricated onto step-edge substrates. The step-edge devices exhibit excellent results.
Monolithic, high surface area, three-dimensional GeO2 nanostructures
Authors: Kucheyev S. O. , Baumann T. F. , Wang Y. M. , van Buuren T. , Poco J. F. , Satcher J. H. , Hamza A. V.
Published: March 2006

We report a sol-gel synthesis of monolithic three-dimensional GeO2 nanostructures (aerogels). Transmission electron microscopy shows that these ultralow-density (∼99.2% porous) nanostructures are formed by a continuous network of elongated amorphous GeO2 nanoligaments, ∼15–20nm in diameter and ∼50–200nm in length. As a result, monoliths exhibit a high surface area of ∼60m2g−1. A comparison of soft x-ray absorption spectra at GeL3 and OK edges with theoretical densities of states reveals that the electronic structure of aerogels is similar to that of hexagonal GeO2, indicating a (distorted) tetrahedral environment of Ge atoms in the amorphous nanostructure.
Plasma formation in fused silica induced by loosely focused femtosecond laser pulse
Authors: Wu Alexander Q. , Chowdhury Ihtesham H. , Xu Xianfan
Published: March 2006

The focusing position inside fused silica irradiated by a loosely focused high power femtosecond laser pulse is studied both experimentally and numerically. The experimental measurement of plasma radiation shows that the laser pulse is focused behind the focal plane, which is also found in the numerical calculation and is attributed to a complex interplay between self-focusing due to the Kerr effect and defocusing because of the free electron plasma. Also, when more than one pulse is incident at the same spot in the sample, plasma radiation is observed at more than one spot along the laser propagation direction.
Clusters of bundled nanorods in nanocarpet effect
Authors: Zhao Y.-P. , Fan J.-G.
Published: March 2006

A simple model based on the balance between mechanical bending and capillary interaction is proposed to understand the bundling of nanorods in nanocarpet effect. The cluster energy minimization reveals that the cluster size is closely related to the nanorod aspect ratio, diameter, density, Young's modulus, as well as the surface tension of the liquid. The experimental result on the cluster size versus the nanorod height is consistent with the prediction of the model.
Observation of low-lying excitations of electrons in coupled quantum dots
Authors: García César Pascual , Kalliakos Sokratis , Pellegrini Vittorio , Pinczuk Aron , Dennis Brian S. , Pfeiffer Loren N. , West Ken W.
Published: March 2006

Tunneling excitations of electrons in dry-etched modulation-doped AlGaAs∕GaAs coupled quantum dots (QDs) are probed by resonant inelastic light scattering. A sequence of intra- and intershell excitations are found at energies determined by the interplay between the QD confinement energy ℏω0 and the tunneling gap ΔSAS, the splitting between the symmetric and antisymmetric delocalized single particle molecular states. The narrow linewidths displayed by electronic excitations in these nanostructures indicate promising venues for the spectroscopic investigation of entanglement of electron states in these artificial molecules.
Excellent electrical and reliability characteristics of 11Å oxynitride gate dielectrics by remote plasma nitridation treatment
Authors: Pan Tung-Ming
Published: March 2006

Ultrathin oxynitride gate dielectrics of similar thickness (∼1.1nm) fabricated by a rapid thermal NO-nitrided oxide (RTNO), a RTNO with remote plasma nitridation (RPN) treatment (RTNO-RPN), an in situ steam generated (ISSG) NO oxide, and an ISSG with RPN treatment (ISSG-RPN) are investigated. The results demonstrate that ISSG-RPN gate dielectrics exhibit superior interface properties, reduced leakage current, and improved reliability compared to other gate dielectrics. The ISSG-RPN oxynitride film is an attractive candidate as the advanced gate dielectrics in future generations of ultralarge scale integration complementary metal-oxide semiconductor technologies.
Current-voltage curves of a cylinder with a power-law E(J)
Authors: Chen D.-X. , Gu C.
Published: March 2006

The current-voltage V(I) curve of a cylinder of radius a with E=Ec(J∕Jc)∣J∕Jc∣n−1 is numerically calculated for a set of given values of a, Ec, Jc, and the I-sweeping rate R at n=5, 10, 20, and 40. After deriving a scaling law and defining a full penetration point for each calculated I-sweeping-up curve, the results are extended to those for any values of parameters and so can be conveniently used in the study of high-temperature superconductors.
Reproducible low contact resistance in rubrene single-crystal field-effect transistors with nickel electrodes
Authors: Hulea Iulian N. , Russo Saverio , Molinari Anna , Morpurgo Alberto F.
Published: March 2006

We have investigated the contact resistance of rubrene single-crystal field-effect transistors (FETs) with nickel electrodes by performing scaling experiments on devices with channel length ranging from 200 nm up to 300μm. We find that the contact resistance can be as low as 100Ωcm with narrowly spread fluctuations. For comparison, we have also performed scaling experiments on similar gold-contacted devices, and found that the reproducibility of FETs with nickel electrodes is largely superior. These results indicate that nickel is a very promising electrode material for the reproducible fabrication of low resistance contacts in organic FETs.
Characterization of domain walls in BaTiO3 using simultaneous atomic force and piezo response force microscopy
Authors: Franck Christian , Ravichandran Guruswami , Bhattacharya Kaushik
Published: March 2006

In this letter a method to simultaneously measure the physical and the polarization thickness of a 90° domain wall in a ferroelectric perovskite is presented. This method combines accurate atomic force microscopy and piezoresponse force microscopy scans of the same area with little drift and an analysis of the entire scanned area. It is found that the physical thickness is significantly narrower (about seven and a half times) than the polarization thickness in a 90° domain wall in BaTiO3. Evidence of the trapping of defects at such domain walls is also found.
Growth and luminescence of elongated In2O3 micro- and nanostructures in thermally treated InN
Authors: Magdas D. Alina , Cremades Ana , Piqueras Javier
Published: March 2006

Indium oxide elongated micro- and nanostructures have been grown by thermal treatment of InN powder. Chains of nanopyramids connected by nanowires, forming a necklace-like structure, as well as cubes and arrow-like structures consisting of a long rod with a micron size pyramid on the top, grow at temperatures in the range 600–700°C in a catalyst free process. The structures have been characterized by scanning electron microscopy and cathodoluminescence.
Optical coupling at a distance between detuned spherical cavities
Authors: Kanaev Andrey V. , Astratov Vasily N. , Cai Wei
Published: March 2006

Using numerical modeling, we observe surprisingly high coupling efficiencies (up to 0.1) between spatially separated spherical cavities with strongly detuned whispering gallery modes. We show that the coupling arises from resonance between a discrete energy eigenstate in the sphere containing the source of light and a continuum of “quasi”-whispering gallery modes with noncircular shape and reduced quality factors in the sphere receiving the electromagnetic energy. Such coupling effects may make possible broad spectral transmission effects in coupled resonator optical waveguides, previously thought to be excluded in a real system with significant size disorder.
Low-loss tunable capacitors fabricated directly on gold bottom electrodes
Authors: Lu Jiwei , Schmidt Steffen , Boesch Damien S. , Pervez Nadia , York Robert A. , Stemmer Susanne
Published: March 2006

At microwave frequencies, conductor losses due to the bottom electrode resistance severely limit the performance of metal-insulator-metal capacitors that employ tunable dielectric thin films. Here we demonstrate that a novel tunable dielectric, bismuth zinc niobate (BZN), can be integrated directly with low-resistivity Au bottom electrodes. The favorable crystallization kinetics allowed for a low thermal budget process compatible with Au electrodes. BZN thin films on Au bottom electrodes showed low dielectric loss tangents of ∼0.0005 and high dielectric tunabilities of ∼50%. The Au/BZN interface was abrupt and free of reaction phases. At high frequencies (>1MHz) the total Au/BZN capacitor device loss was reduced compared to capacitors with Pt bottom electrodes. The low device losses of Au/BZN capacitors revealed a device geometry-dependent loss mechanism that contributed significantly to the device loss at high frequencies.
Advantages of top-gate, high-k dielectric carbon nanotube field-effect transistors
Authors: Yang M. H. , Teo K. B. K. , Gangloff Laurent , Milne W. I. , Hasko D. G. , Robert Y. , Legagneux P.
Published: March 2006

The subthreshold slope, transconductance, threshold voltage, and hysteresis of a carbon nanotube field-effect transistor (CNT FET) were examined as its configuration was changed from bottom-gate exposed channel, bottom-gate covered channel to top-gate FET. An individual single wall CNT was grown by chemical vapor deposition and its gate configuration was changed while determining its transistor characteristics to ensure that the measurements were not a function of different chirality or diameter CNTs. The bottom-gate exposed CNT FET utilized 900nm SiO2 as the gate insulator. This CNT FET was then covered with TiO2 to form the bottom-gate covered channel CNT FET. Finally, the top-gate CNT FET was fabricated and the device utilized TiO2 (κ∼80, equivalent oxide thickness=0.25nm) as the gate insulator. Of the three configurations investigated, the top-gate device exhibited best subthreshold slope (67–70mV∕dec), highest transconductance (1.3μS), and negligible hysteresis in terms of threshold voltage shift.
Microfabricated photoplastic cantilever with integrated photoplastic/carbon based piezoresistive strain sensor
Authors: Gammelgaard L. , Rasmussen P. A. , Calleja M. , Vettiger P. , Boisen A.
Published: March 2006

We present an SU-8 micrometer sized cantilever strain sensor with an integrated piezoresistor made of a conductive composite of SU-8 polymer and carbon black particles. The composite has been developed using ultrasonic mixing. Cleanroom processing of the polymer composite has been investigated and it has been shown that it is possible to pattern the composite by standard UV photolithography. The composite material has been integrated into an SU-8 microcantilever and the polymer composite has been demonstrated to be piezoresistive with gauge factors around 15–20. Since SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, this polymer based strain sensor is more sensitive than a similar silicon based cantilever sensor.
Electrical properties of field-effect transistors based on C60 nanowhiskers
Authors: Ogawa Kenichi , Kato Tomohiro , Ikegami Asato , Tsuji Hajime , Aoki Nobuyuki , Ochiai Yuichi , Bird Jonathan P.
Published: March 2006

We fabricate field-effect transistors (FETs) based on C60 nanowhiskers (C60 NWs) and investigate their structural and electrical properties. Thermally annealed C60 NWs show x-ray powder-diffraction spectra that are consistent with a similar fcc structure to that of C60 bulk crystals, although with a slightly reduced lattice constant (a=13.9Å). The C60 NW-FETs exhibit n-channel, normally-on, properties (or FETs) and their carrier mobility is estimated to be 2×10−2cm2∕Vs under vacuum conditions at room temperature.
Spectral-domain optical coherence tomography: Removal of autocorrelation using an optical switch
Authors: Ai Jun , Wang Lihong V.
Published: March 2006

A novel spectral-domain optical coherence tomography (SD-OCT), in which the self-interferogram of the object wave and the standard SD-OCT interferogram are acquired asynchronously using an optical switch in the reference arm, is presented. After Fourier transformation, the autocorrelation of the object is removed simply by subtraction from the standard SD-OCT image. The measured sensitivity is 103.5dB at z=0.115mm, and it gradually reduces to 84.1dB at z=3.275mm. The axial resolution is 15μm in the air. In vivo images of human skin are presented to demonstrate the performance of autocorrelation removal.
The Avellino 3780-yr-B.P. catastrophe as a worst-case scenario for a future eruption at Vesuvius
Authors: Mastrolorenzo Giuseppe , Petrone Pierpaolo , Pappalardo Lucia , Sheridan Michael F.
Published: March 2006

A volcanic catastrophe even more devastating than the famous
anno Domini
79 Pompeii eruption occurred during the Old Bronze Age at Vesuvius. The 3780-yr-B.P. Avellino plinian eruption produced an early violent pumice fallout and a late pyroclastic surge sequence that covered the volcano surroundings as far as 25 km away, burying land and villages. Here we present the reconstruction of this prehistoric catastrophe and its impact on the Bronze Age culture in Campania, drawn from an interdisciplinary volcanological and archaeoanthropological study. Evidence shows that a sudden, en masse evacuation of thousands of people occurred at the beginning of the eruption, before the last destructive plinian column collapse. Most of the fugitives likely survived, but the desertification of the total habitat due to the huge eruption size caused a social–demographic collapse and the abandonment of the entire area for centuries. Because an event of this scale is capable of devastating a broad territory that includes the present metropolitan district of Naples, it should be considered as a reference for the worst eruptive scenario at Vesuvius.
Genome-wide identification of mRNAs associated with the translational regulator PUMILIO in
Drosophila melanogaster
Authors: Gerber André P. , Luschnig Stefan , Krasnow Mark A. , Brown Patrick O. , Herschlag Daniel
Published: March 2006

Genome-wide identification of RNAs associated with RNA-binding proteins is crucial for deciphering posttranscriptional regulatory systems. PUMILIO is a member of the evolutionary conserved Puf-family of RNA-binding proteins that repress gene expression posttranscriptionally. We generated transgenic flies expressing affinity-tagged PUMILIO under the control of an ovary-specific promoter, and we purified PUMILIO from whole adult flies and embryos and analyzed associated mRNAs by using DNA microarrays. Distinct sets comprising hundreds of mRNAs were associated with PUMILIO at the two developmental stages. Many of these mRNAs encode functionally related proteins, supporting a model for coordinated regulation of posttranscriptional modules by specific RNA-binding proteins. We identified a characteristic sequence motif in the 3′-untranslated regions of mRNAs associated with PUMILIO, and the sufficiency of this motif for interaction with PUMILIO was confirmed by RNA pull-down experiments with biotinylated synthetic RNAs. The RNA motif strikingly resembles the one previously identified for Puf3p, one of five
Saccharomyces cerevisiae
Puf proteins; however, proteins encoded by the associated mRNAs in yeast and
Drosophila
do not appear to be related. The results suggest extensive posttranscriptional regulation by PUMILIO and uncover evolutionary features of this conserved family of RNA-binding proteins.
The DNA repair genes XPB and XPD defend cells from retroviral infection
Authors: Yoder Kristine , Sarasin Alain , Kraemer Kenneth , McIlhatton Michael , Bushman Frederic , Fishel Richard
Published: March 2006

Reverse transcription of retroviral RNA genomes produce a double-stranded linear cDNA molecule. A host degradation system prevents a majority of the cDNA molecules from completing the obligatory genomic integration necessary for pathogenesis. We demonstrate that the human TFIIH complex proteins XPB (ERCC3) and XPD (ERCC2) play a principal role in the degradation of retroviral cDNA. DNA repair-deficient XPB and XPD mutant cell lines exhibited an increase in transduction efficiency by both HIV- and Moloney murine leukemia virus-based retroviral vectors. Replicating Moloney murine leukemia virus viral production was greater in XPB or XPD mutant cells but not XPA mutant cells. Quantitative PCR showed an increase in total cDNA molecules, integrated provirus, and 2LTR circles in XPB and XPD mutant cells. In the presence of a reverse transcription inhibitor, the HIV cDNA appeared more stable in mutant XPB or XPD cells. These studies implicate the nuclear DNA repair proteins XPB and XPD in a cellular defense against retroviral infection.
Structural basis for conformational plasticity of the Parkinson's disease-associated ubiquitin hydrolase UCH-L1
Authors: Das Chittaranjan , Hoang Quyen Q. , Kreinbring Cheryl A. , Luchansky Sarah J. , Meray Robin K. , Ray Soumya S. , Lansbury Peter T. , Ringe Dagmar , Petsko Gregory A.
Published: March 2006

The ubiquitin C-terminal hydrolase UCH-L1 (PGP9.5) comprises >1% of total brain protein but is almost absent from other
tissues [Wilkinson, K. D.,
et al.
(1989)
Science
246, 670–673]. Mutations in
the UCH-L1 gene have been reported to be linked to susceptibility to
and protection from Parkinson's disease [Leroy, E.,
et al.
(1998)
Nature
395,
451–452; Maraganore, D. M.,
et al.
(1999)
Neurology
53, 1858–1860]. Abnormal
overexpression of UCH-L1 has been shown to correlate with several
forms of cancer [Hibi, K.,
et al.
(1998)
Cancer Res.
58, 5690–5694]. Because
the amino acid sequence of UCH-L1 is similar to that of other
ubiquitin C-terminal hydrolases, including the ubiquitously expressed
UCH-L3, which appear to be unconnected to neurodegenerative disease,
the structure of UCH-L1 and the effects of disease associated
mutations on the structure and function are of considerable
importance. We have determined the three-dimensional structure of
human UCH-L1 at 2.4-Å resolution by x-ray crystallography. The
overall fold resembles that of other ubiquitin hydrolases, including
UCH-L3, but there are a number of significant differences. In
particular, the geometry of the catalytic residues in the active site
of UCH-L1 is distorted in such a way that the hydrolytic activity
would appear to be impossible without substrate induced conformational
rearrangements.
Mechanism of substrate specificity in
Bacillus subtilis
ResA, a thioredoxin-like protein involved in cytochrome
c
maturation
Authors: Colbert Christopher L. , Wu Qiong , Erbel Paul J. A. , Gardner Kevin H. , Deisenhofer Johann
Published: March 2006

The covalent attachment of heme cofactors to the apo-polypeptides via thioether bonds is unique to the maturation of
c
-type cytochromes. A number of thiol-disulfide oxidoreductases prepare the apocytochrome for heme insertion in system I and II cytochrome
c
maturation. Although most thiol-disulfide oxidoreductases are nonspecific, the less common, specific thiol-disulfide oxidoreductases may be key to directing the usage of electrons. Here we demonstrate that unlike other thiol-disulfide oxidoreductases, the protein responsible for reducing oxidized apocytochrome
c
in
Bacillus subtilis
, ResA, is specific for cytochrome
c
550 and utilizes alternate conformations to recognize redox partners. We report solution NMR evidence that ResA undergoes a redox-dependent conformational change between oxidation states, as well as data showing that ResA utilizes a surface cavity present only in the reduced state to recognize a peptide derived from cytochrome
c
550. Finally, we confirm that ResA is a specific thiol-disulfide oxidoreductase by comparing its reactivity to our mimetic peptide with its reactivity to oxidized glutathione, a nonspecific substrate. This study biochemically demonstrates the specificity of this thiol-disulfide oxidoreductase and enables us to outline a structural mechanism of regulating the usage of electrons in a thiol-disulfide oxidoreductase system.
Low-Dose Cadmium Exposure Reduces Human Prostate Cell Transformation in Culture and Up-Regulates Metallothionein and MT-1G mRNA
Authors: Gaddipati Jaya P. , Rajeshkumar N.V. , Grove Jason C. , Maharaj Susan V. M. , Centeno Jose A. , Maheshwari Radha K. , Jonas Wayne B.
Published: March 2006

Chronic low-level exposure to environmental toxins, including cadmium (Cd), is a growing problem in the industrialized world. One promising strategy for protection from these toxins is the use of low-dose exposure of environmental chemicals to induce cell tolerance and recovery, a phenomenon known as “protective hormesis”. Hormetic [low-dose stimulatory] effects occur in a variety of systems and with a number of chemicals. Cd is a potent carcinogen in rodents and has also been linked to human lung and prostate cancers. In the present study, we have evaluated the protective effects of low and ultra-low dose, long-term Cd exposure in the normal human prostate cells, RWPE-1. Cells were exposed to low and ultra-low doses (0, 0 (S−36), 10−6, 10−7, 10−18, 10−21, 10−32, or 10−36 M) of Cd for 20 weeks followed by treatment with 10−5 M Cd for another 8 weeks. Continuous exposure of RWPE-1 cells to 10−5 M Cd results in malignant transformation. However, cells pretreated with low and ultra-low doses of Cd had delayed transformation compared with controls. In addition, the number of transformed cell mounds was lower in pretreated cells indicating that low and ultra-low dose exposure had protective effects against high-dose Cd induced carcinogenesis. The expression of metallothionein (MT), the primary Cd detoxification protein, was induced by low-dose exposure to Cd and maintained during the 20 weeks. In addition, MT-1G mRNA was up-regulated 2- to 3-fold by low-dose and ultralow-dose Cd exposures and may be the mechanism of protective hormesis in this model. MT-1G mRNA might also serve as a biological indicator of very low-dose environmental Cd exposure.
Constraints on HIV-1 evolution and immunodominance revealed in monozygotic adult twins infected with the same virus
Authors: Draenert Rika , Allen Todd M. , Liu Yang , Wrin Terri , Chappey Colombe , Verrill Cori L. , Sirera Guillem , Eldridge Robert L. , Lahaie Matthew P. , Ruiz Lidia , Clotet Bonaventura , Petropoulos Christos J. , Walker Bruce D. , Martinez-Picado Javier
Published: March 2006

The predictability of virus–host interactions and disease progression in rapidly evolving human viral infections has been difficult to assess because of host and genetic viral diversity. Here we examined adaptive HIV-specific cellular and humoral immune responses and viral evolution in adult monozygotic twins simultaneously infected with the same virus. CD4 T cell counts and viral loads followed similar trajectories over three years of follow up. The initial CD8 T cell response targeted 17 epitopes, 15 of which were identical in each twin, including two immunodominant responses. By 36 months after infection, 14 of 15 initial responses were still detectable in both, whereas all new responses were subdominant and remained so. Of four responses that declined in both twins, three demonstrated mutations at the same residue. In addition, the evolving antibody responses cross-neutralized the other twin's virus, with similar changes in the pattern of evolution in the envelope gene. These results reveal considerable concordance of adaptive cellular and humoral immune responses and HIV evolution in the same genetic environment, suggesting constraints on mutational pathways to HIV immune escape.
TRPM7 Channel Is Regulated by Magnesium Nucleotides via its Kinase Domain
Authors: Demeuse Philippe , Penner Reinhold , Fleig Andrea
Published: March 2006

TRPM7 is a Ca2+- and Mg2+-permeable cation channel that also contains a protein kinase domain. While there is general consensus that the channel is inhibited by free intracellular Mg2+, the functional roles of intracellular levels of Mg·ATP and the kinase domain in regulating TRPM7 channel activity have been discussed controversially. To obtain insight into these issues, we have determined the effect of purine and pyrimidine magnesium nucleotides on TRPM7 currents and investigated the possible involvement of the channel's kinase domain in mediating them. We report here that physiological Mg·ATP concentrations can inhibit TRPM7 channels and strongly enhance the channel blocking efficacy of free Mg2+. Mg·ADP, but not AMP, had similar, albeit smaller effects, indicating a double protection against possible Mg2+ and Ca2+ overflow during variations of cell energy levels. Furthermore, nearly all Mg-nucleotides were able to inhibit TRPM7 activity to varying degrees with the following rank in potency: ATP > TTP > CTP ≥ GTP ≥ UTP > ITP ≈ free Mg2+ alone. These nucleotides also enhanced TRPM7 inhibition by free Mg2+, suggesting the presence of two interacting binding sites that jointly regulate TRPM7 channel activity. Finally, the nucleotide-mediated inhibition was lost in phosphotransferase-deficient single-point mutants of TRPM7, while the Mg2+-dependent regulation was retained with reduced efficacy. Interestingly, truncated mutant channels with a complete deletion of the kinase domain regained Mg·NTP sensitivity; however, this inhibition did not discriminate between nucleotide species, suggesting that the COOH-terminal truncation exposes the previously inaccessible Mg2+ binding site to Mg-nucleotide binding without imparting nucleotide specificity. We conclude that the nucleotide-dependent regulation of TRPM7 is mediated by the nucleotide binding site on the channel's endogenous kinase domain and interacts synergistically with a Mg2+ binding site extrinsic to that domain.
Functional Roles of Charged Amino Acid Residues on the Wall of the Cytoplasmic Pore of Kir2.1
Authors: Fujiwara Yuichiro , Kubo Yoshihiro
Published: March 2006

It is known that rectification of currents through the inward rectifier K+ channel (Kir) is mainly due to blockade of the outward current by cytoplasmic Mg2+ and polyamines. Analyses of the crystal structure of the cytoplasmic region of Kir2.1 have revealed the presence of both negatively (E224, D255, D259, and E299) and positively (R228 and R260) charged residues on the wall of the cytoplasmic pore of Kir2.1, but the detail is not known about the contribution of these charged residues, the positive charges in particular, to the inward rectification. We therefore analyzed the functional significance of these charged amino acids using single/double point mutants in order to better understand the structure-based mechanism underlying inward rectification of Kir2.1 currents. As a first step, we used two-electrode voltage clamp to examine inward rectification in systematically prepared mutants in which one or two negatively or positively charged amino acids were neutralized by substitution. We found that the intensity of the inward rectification tended to be determined by the net negative charge within the cytoplasmic pore. We then used inside-out excised patch clamp recording to analyze the effect of the mutations on blockade by intracellular blockers and on K+ permeation. We observed that a decrease in the net negative charge within the cytoplasmic pore reduced both the susceptibility of the channel to blockade by Mg2+ or spermine and the voltage dependence of the blockade. It also reduced K+ permeation; i.e., it decreased single channel conductance, increased open-channel noise, and strengthened the intrinsic inward rectification in the total absence of cytoplasmic blockers. Taken together, these data suggest that the negatively charged cytoplasmic pore of Kir electrostatically gathers cations such as Mg2+, spermine, and K+ so that the transmembrane pore is sufficiently filled with K+ ions, which enables strong voltage-dependent blockade with adequate outward K+ conductance.