bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for new bands in the 3ν1 and 4ν1 regions of propyne
Authors: Ganot Yuval , Rosenwaks Salman , Bar Ilana
Published: June 2005

Vibrationally mediated photodissociation and room-temperature photoacoustic (PA) spectroscopy have been used for obtaining action (monitoring the yield of H photofragments) and absorption spectra of the second (3ν1) and third (4ν1) C–H acetylenic stretches overtone regions in propyne. The band contours appearing in these regions seem mostly regular even though they are perturbed, as expressed by the origin shifts in different K components, splitting of the K structure, and splitting due to resonances between neighboring states. Symmetric rotor simulations of the band contours of the PA and action spectra allowed extraction of the molecular parameters and rough estimates for the homogeneous broadening arising from energy flow to the bath vibrational states. We particularly benefited from the reduced congestion in the jet-cooled action spectra and their simulations, which enabled observation of yet unknown features in the vicinity of the 3ν1 and 4ν1 states. Particularly, the emergence of the new state in the 3ν1 region was confirmed by the action spectra monitored at several differing jet temperatures, suggesting that it is a dark state in IR vibrational excitation that becomes brighter in UV excitation to the upper electronic state. The monitored and Gaussian-fitted Doppler profiles point to the release of H photofragments with low average translational energies, attributed to an indirect dissociation process occurring after internal conversion to the ground electronic state and isomerization to allene.
Ab initio study of small acetonitrile cluster anions
Authors: Takayanagi Toshiyuki
Published: June 2005

Ab initio electronic structure calculations have been performed for (CH3CN)2− and (CH3CN)3− cluster anions using a diffuse basis set. We found both the dipole-bound structures and internal structures, where in the former structure an excess electron is mainly distributed on the surface of the cluster while an excess electron is internally trapped in the latter configuration. The optimized structures found for cluster anions were compared to those for neutral clusters. Potential-energy surfaces were also plotted as a function of appropriate internal coordinates in order to understand the interconversions of the optimized structures of clusters. The relative stabilities of the optimized confirmers have been discussed on the basis of the characteristics of these potential surfaces, relative energies, and electron vertical detachment energies.
Generalized linear stability of noninertial coating flows over topographical features
Authors: Davis Jeffrey M. , Troian Sandra M.
Published: June 2005

The transient evolution of perturbations to steady lubrication flow over a topographically patterned surface is investigated via a nonmodal linear stability analysis of the non-normal disturbance operator. In contrast to the capillary ridges that form near moving contact lines, the stationary capillary ridges near trenches or elevations have only stable eigenvalues. Minimal transient amplification of perturbations occurs, regardless of the magnitude or steepness of the topographical features. The absence of transient amplification and the stability of the ridge are explained on physical grounds. By comparison to unstable ridge formation on smooth, flat, and homogeneous surfaces, the lack of closed, recirculating streamlines beneath the capillary ridge is linked to the linear stability.
High throughput system for DNA sequencing
Authors: El-Difrawy Sameh A. , Lam Roger , Aborn James H. , Novotny Mark , Gismondi Elizabeth A. , Matsudaira Paul , Mckenna Brian K. , O’Neil Thomas , Streechon Philip , Ehrlich Daniel J.
Published: June 2005

A 768-lane DNA sequencing system based on micromachined plates has been designed as a near-term successor to 96-lane capillary arrays. Electrophoretic separations are implemented in large-format (25cm by 50cm) microfabricated devices with the objective of proving realistic read length, parallelism, and the scaled sample requirements for long-read de novo sequencing. Two 384-lane plates are alternatively cycled between electrophoresis and regeneration via a robotic pipettor and switching optical system. The instrument minimizes the DNA sample requirement to “1∕32×” Sanger chemistry, equal to typical genome center operation, and a 16-fold improvement in scaling relative to previous microfabricated devices. The 40-cm-long channels permit an increase in read length (several hundred base pairs) relative to previous multichannel microfabricated devices. These advances directly address the cost and automation model for adaptation of the technology.
Self-sustained annihilation of magnetic islands in helical plasmas
Authors: Itoh Kimitaka , Itoh Sanae-I. , Yagi Masatoshi
Published: June 2005

The evolution of the magnetic island which is induced by the resonant deformation by external currents in helical systems (such as the large helical device (LHD) [A. Iiyoshi, Phys. Plasmas 2, 2349 (1995)]) is analyzed. The defect of the bootstrap current, caused by the magnetic island, has a parity which reduces the size of the magnetic island, if the bootstrap current enhances the vacuum rotational transform. The width of magnetic island can be suppressed to the level of ion banana width if the pressure gradient exceeds a threshold value. This island annihilation is self-sustained. That is, the annihilation continues, for fixed beta value, until the external drive for island generation exceeds a threshold. The effects of the reversal of the direction of the bootstrap current and of the sign of radial electric field are also investigated. The possibility of the neoclassical tearing mode in the LHD-like plasma is discussed.
Spectroscopic investigation of the solvation of organic molecules in superfluid helium droplets
Authors: Lehnig R. , Slenczka A.
Published: June 2005

The spectroscopy of molecules doped into superfluid helium nanodroplets provides valuable information on the process of solvation in superfluid helium. In continuation of an earlier report on emission spectra of various phthalocyanines showing a splitting of all molecular transitions in the range of about 5–12cm−1, the emission spectra of tetracene, pentacene, and perylene in superfluid helium droplets are presented. The new spectra and the results obtained for the phthalocyanines are explained by an empirical model which accounts for the existence of different metastable configurations of a nonsuperfluid solvation layer around the guest molecule.
Reaction of SO2 with Au∕CeO2(111): Importance of O vacancies in the activation of gold
Authors: Rodriguez J. A. , Pérez M. , Evans J. , Liu G. , Hrbek J.
Published: June 2005

Synchrotron-based high-resolution photoemission was used to study the adsorption and chemistry of SO2 on Au∕CeO2(111) and AuOx∕CeO2 surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO2(111) was 4–7kcal∕mol larger than on Au(111). However, there was negligible dissociation of SO2 on the Au∕CeO2(111) surfaces. The full decomposition of SO2 was observed only after introducing O vacancies in the ceria support. AuOx∕CeO2 surfaces were found to be much less chemically active than Au∕CeO2(111) or Au∕CeO2−x(111) surfaces. The active sites in {Au+AuOx}∕ceria catalysts should involve pure gold nanoparticles in contact with O vacancies.
Discontinuous switching in antiferroelectric ceramics monitored by acoustic emissions
Authors: Zhou Longjie , Lupascu Doru C. , Zimmermann Andre , Zhang Yong
Published: June 2005

Acoustic emission patterns were monitored during electric-field-induced antiferroelectric to ferroelectric phase transitions for fine- and coarse-grained antiferroelectric lead lanthanum zirconate stannate titanate ceramics [Pb0.97La0.02(Zr0.77Sn0.14Ti0.09)O3]. For the initial phase-transition cycle, acoustic emissions were detected just before and right after the major strain changes. During subsequent cycles, the strain response becomes jumplike and associated with additional acoustic emissions. Acoustic emissions before strain changes are assigned to domain nucleation and those at high fields to domain jumps, nucleation-annihilation processes, or microcracking. The intermediate ones are associated with defect charge rearrangement within the material. Backswitching generates acoustic emissions in the fine-grained material but only for certain drive conditions in the coarse-grained ceramic. Implications for domain nucleation processes, strain, and the role of defects in antiferroelectrics are discussed.
Gate inversion effect in Si1−xGex∕HfO2∕Si metal-oxide-semiconductor devices
Authors: Costa e Silva J. , de Oliveira E. L. , de Sousa J. S. , Freire J. A. K. , Freire V. N. , Farias G. A.
Published: June 2005

The electrical properties of polycrystalline Si1−xGex∕HfO2∕Si metal-oxide-semiconductor (MOS) devices are investigated theoretically by solving self-consistently the Poisson and Schrödinger equations. Our calculations demonstrate that the combination of HfO2 as dielectric film and polycrystalline gates causes charge inversion in both substrate and gate layer for ultrathin oxide layers. This effect is a consequence of the high dielectric constant of HfO2, and it is expected to occur for all high-κ-based polygated MOS devices. However, the relative doping concentration between polycrystalline gate and substrate can be used to decrease the effect of gate inversion.
Local correlation potentials from Brueckner coupled-cluster theory
Authors: Heßelmann A.
Published: June 2005

Local correlation potentials have been obtained from the nonlocal Brueckner coupled-cluster correlation potentials for the rare-gas atoms He, Ne, and Ar and the CO molecule. It is shown that the local correlation potential can mainly be expressed as a sum of two components: a “pure” correlation part and a relaxation contribution. While the total correlation potentials show an oscillating behavior near the nuclei, indicating the atomic shell structure, their components decrease rather monotonously, with a step structure in case of Ne and Ar. By looking at the determinantal overlap and one-electron properties it has been found that the orbitals obtained from these local potentials form a determinant which very well corresponds with the Brueckner determinant. Thus the previously found closeness between the Hartree–Fock determinant and the exchange-only Kohn–Sham determinant [Della Sala and Görling, J. Chem. Phys. 115, 5718 (2001)] is confirmed also for the correlated case.
Penetrative phototactic bioconvection
Authors: Ghorai S. , Hill N. A.
Published: June 2005

Using the generic model of Vincent and Hill [J. Fluid Mech. 327, 343 (1996)] for phototaxis in a suspension of swimming algae, we investigate two-dimensional phototactic bioconvection in a suspension confined between a rigid bottom boundary, and stress-free top and lateral boundaries. Phototaxis denotes swimming towards (positive) or away (negative) from light. The model of Vincent and Hill also incorporates the effect of shading where microorganisms close to the light source absorb and scatter light before it reaches those further away. The system is governed by the Navier–Stokes equations for an incompressible fluid coupled with a microorganism conservation equation. These equations are solved numerically using a conservative finite-difference scheme. Convection driven by phototactic microorganisms, which are slightly denser than water, has been investigated in a series of numerical experiments. The solutions show transition from steady state to periodic oscillations, and periodic oscillations to steady state to periodic oscillations again, as the governing parameters are varied. The mechanism driving the oscillatory solution just above the critical parameter values is explained.
Novel technique for high-precision Bragg-angle determination in crystal x-ray spectroscopy
Authors: Braun J. , Bruhns H. , Trinczek M. , López-Urrutia J. R. Crespo , Ullrich J.
Published: June 2005

A novel technique for a high-precision large acceptance determination of the Bragg angle in crystal x-ray spectroscopy is presented and demonstrated. The method exploits visible light beams as fiducials reflected on the x-ray crystal’s surface to ensure exact knowledge of the position on the crystal at which the x rays are reflected, replacing entrance slits, thus making flat crystals suitable for low x-ray fluxes. It can be shown that many error sources arising from uncertainties in the determination of geometrical properties are eliminated in this way. A flat crystal x-ray spectrometer based on this technique has been designed, built, and tested using the most precisely known wavelengths emitted by highly charged ions, namely H- and He-like argon. The result for the 1s2pP11→1s2S01 w-line of He-like argon exhibits a statistical uncertainty of 3.8ppm and an estimated systematic error of about 3ppm, thus becoming the most accurate measurement of the He-like resonance transition in highly charged ions. It is shown that achieving a systematic error of below 1ppm is feasible with this method. Therefore, our technique should allow reaching total accuracies approaching 1ppm on transitions of mid-Z highly charged ions, which would provide challenging tests for state-of-the-art theoretical predictions.
Low jitter metal vapor vacuum arc ion source for electron beam ion trap injections
Authors: Holland Glenn E. , Boyer Craig N. , Seely John F. , Tan J. N. , Pomeroy J. M. , Gillaspy J. D.
Published: June 2005

We describe a metal vapor vacuum arc (MeVVA) ion source containing eight different cathodes that are individually selectable via the control electronics which does not require moving components in vacuum. Inside the vacuum assembly, the arc plasma is produced by means of a 30μs pulse (26kV,125A) delivering 2.4mC of charge to the cathode sample material. The trigger jitter is minimized (<200ns) to improve the capture efficiency of the ions which are injected into an ion trap. During a single discharge, the over-damped pulse produces an ion flux of 8.4×109ions∕cm2, measured by an unbiased Faraday cup positioned 20cm from the extractor grid, at discharge rates up to 5Hz. The electronic triggering of the discharge is via a fiber optic interface. We present the design, fabrication details, and performance of this MeVVA, recently installed on the National Institute of Standards and Technology electron beam ion trap (EBIT).
The flow of a very concentrated slurry in a parallel-plate device: Influence of gravity
Authors: Lenoble Marie , Snabre Patrick , Pouligny Bernard
Published: June 2005

We investigate, both experimentally and theoretically, the flow and structure of a slurry when sheared between two horizontal plates. The slurry, otherwise called “wet granular material,” is made of non-Brownian particles immersed in a viscous fluid. The particles are heavier than the immersion fluid, in contrast to the so-called “suspensions,” corresponding to density-matched fluid and particles. Consequently, gravity influences the structure and flow profiles of the sheared material. Experiments are carried out in a plane Couette device with a model slurry composed of quasimonodispersed spherical polymethylmetacrylate particles in oil, at high average solid concentration (about 59%). Optical observation reveals a typical two-phase configuration, with a fluidized layer in contact with the upper plate and on top of an amorphous solid phase. We provide data on velocity profiles, wall slip, average shear stress, and average normal stress, versus the angular velocity of the upper plate. To interpret the data, we propose a model for the ideal case of infinite horizontal flat plates (plane Couette flow). The model, of mean-field type, is based on local constitutive equations for the tangential (τ) and normal (N) components of the stress tensor and on material expressions relating the material viscometric coefficients (the shear viscosity η and the normal stress viscosity ψ) with the local concentration (Φ) and the local shear rate. One-, two-, and three-phase configurations are predicted, with nonlinear flow and concentration profiles. We conclude that model equations correctly describe the experimental data, provided that appropriate forms are chosen for the divergences of η and ψ near the packing concentration (Φm), namely, a (Φm−Φ)−1 singularity.
Beta scaling of transport in microturbulence simulations
Authors: Candy J.
Published: June 2005

A systematic study of the beta (β) scaling and spatial structure of thermal and particle transport in gyrokinetic turbulence simulations is presented. Here, β is the ratio of the plasma kinetic pressure to the magnetic pressure. Results show that the nonlinear self-consistent temperature profiles exhibit a (statistically) time-stationary flattening in the vicinity of rational surfaces with a concomitant drop in the electrostatic components of the thermal diffusivity. Simultaneously, the increased magnetic fluctuation amplitude at these surfaces enhances the steady-state electromagnetic (flutter) component of the electron thermal diffusivity. The electromagnetic components of the ion transport coefficients remain close to zero, as expected on theoretical grounds. Only a weak dependence of ion energy transport on β is observed, consistent with recent tokamak experiments [C. C. Petty et al., Phys. Plasmas 11, 2514 (2004)].
Plasmon Bragg reflectors and nanocavities on flat metallic surfaces
Authors: Wang Bing , Wang Guo Ping
Published: June 2005

Metal heterostructures constructed surface plasmon polaritons (SPPs) Bragg reflectors and nanocavities on flat metallic surfaces are proposed and demonstrated numerically. A metal heterowaveguide structured by alternately stacking two kinds of metal gap waveguides (MGWs) shows periodically effective refraction index modulation to SPPs and produces SPP propagation on flat metallic surfaces a band gap in certain frequencies, known as plasmonic band gap, in which SPP propagation is forbidden. Changing the width of one MGW in the heterowaveguide, a SPP nanocavity with high quality factor can be created. Our results imply a broad possibility of constructed SPP-based Bragg reflectors, emitter, and filters, etc., on flat metallic surfaces for planar nanometeric photonic networks.
Measurement of thermal conductivity of individual multiwalled carbon nanotubes by the 3-ω method
Authors: Choi Tae Y. , Poulikakos Dimos , Tharian Joy , Sennhauser Urs
Published: June 2005

The thermal conductivity of individual multiwalled carbon nanotubes (outer diameter of ∼45nm) was obtained by employing the 3-ω method. To this end, the third-harmonic amplitude as a response to the applied alternate current at fundamental frequency (ω) is expressed in terms of thermal conductivity. A microfabricated device composed of a pair of metal electrodes 1μm apart is used to place a single nanotube across the designated metal electrodes by utilizing the principle of dielectrophoresis. The multiwalled carbon nanotube was modeled as a one-dimensional diffusive energy transporter and its thermal conductivity was measured to be 650–830W∕mK at room temperature.
Fourier transform of delta compressed data
Authors: Russev S. C. , Stefanov Y. S.
Published: June 2005

Delta compression is a well-known, simple and efficient method for compressing smooth data sequences by using differences between successive values, instead of the values themselves. This kind of data sequence results after digitalization of physical signals in many scientific, medical, industrial, and other applications. Many of them use discrete Fourier transform (DFT) as a part of the data treatment. In this work, the Fourier transform directly over delta-compressed data is investigated. It is shown that the Fourier coefficients of the original data can be calculated in a simple manner from the Fourier coefficients of the compressed data sequence without decompression. DFT on delta-compressed data using delta-compressed pre-computed basis functions (sine and cosine) values is also considered. It is shown that this greatly reduces required memory space and computational time. Possible applications of these results are discussed.
Optimization of phase contrast imaging using hard x rays
Authors: Zabler S. , Cloetens P. , Guigay J.-P. , Baruchel J. , Schlenker M.
Published: June 2005

X ray radiography and tomography are important tools in medicine as well as in life science and materials science. Not long ago an approach called in-line holography based on simple propagation became possible using partially coherent synchrotron beams like the ones available at the European Synchrotron Radiation Facility (ESRF). Theoretical and experimental work by Cloetens et al. [Appl. Phys. Lett 75, 2912 (1999)] have shown that quantitative retrieval of the optical phase, from a set of radiographs taken at different sample-to-detector distances, is feasible. Mathematically speaking we are dealing with a direct method based on linearization in order to solve an inverse nonlinear problem. The phase retrieval can be combined with classical tomography in order to obtain a three-dimensional representation of the object’s electron density (holotomography). In order to optimize the image contrast for the numerical phase retrieval process, we have carried out calculations resulting in an optimized choice of value and number of the sample-to-detector distances as well as of the photon energy. These results were then confirmed by experiments on the ESRF long beamline ID19.
Plasma-enhanced chemical vapor deposition method to coat micropipettes with diamond-like carbon
Authors: Kakuta Naoto , Watanabe Mayu , Yamada Yukio , Okuyama Naoki , Mabuchi Kunihiko
Published: June 2005

This article provides a simple method for coating glass micropipettes with diamond-like carbon (DLC) through plasma-enhanced chemical vapor deposition. The apparatus uses a cathode that is a thin-metal-coated micropipette itself and an anode that is a meshed cylinder with its cylinder axis along the micropipette length. To produce a uniform plasma and prevent a temperature increase at the tip due to ion collision concentration, we investigated the effect of the height and diameter of the meshed cylindrical anode on the plasma. Intermittent deposition is also effective for inhibiting the temperature rise and producing high quality DLC films. Measured Raman spectra and electric resistivity indicate that a DLC film suitable for use as an insulating film can be produced on the micropipette. This coating method should also be useful for other extremely small probes.
Observation of far-infrared emission from excited cytosine molecules
Authors: Shen Y. C. , Upadhya P. C. , Linfield E. H. , Davies A. G.
Published: June 2005

We report a time-resolved investigation of the resonant absorption of far-infrared radiation and the subsequent vibrational relaxation processes in a sample of polycrystalline cytosine at 4K, using terahertz time-domain spectroscopy. The subpicosecond time resolution achieved in our experiments corresponds to a near single-cycle of far-infrared radiation, and this enables us to observe the damped oscillations of the electric field produced by excited molecules as they decay. Furthermore, we show that the progressive absorption and subsequent emission of far-infrared radiation at the frequency of the corresponding vibrational mode can be followed directly as a function of time by means of time-partitioned Fourier transforms of the transmitted signal.
Surface oxide reduction and bilayer molecular assembly of a thiol-terminated organosilane on Cu
Authors: Ganesan P. G. , Kumar A. , Ramanath G.
Published: June 2005

We demonstrate the use of thiol-terminated organosilane to reduce the surface oxide and form a protective layer on Cu surfaces. The thiol termini of mercapto-propyl-trimethoxy-silane molecules reduce the copper oxide, and release disulfide- and sulfonate-terminated silanes. Unreacted mercaptosilanes and disulfides then assemble on the clean Cu surface forming a monolayer via chemisorption. The outward pointing methoxy groups react with other methoxysilane termini of sulfonated- and unreacted organosilanes, forming a molecular bilayer with Si–O–Si linkages between the two layers. These findings open up new possibilities for surface cleaning and passivating Cu interconnects with molecular nanolayers, and minimize surface-scattering-induced conductivity decrease in nanometer-thick Cu lines, without destructively etching the surface Cu oxide.
Ultraviolet direct printing of rare-earth-doped polymer waveguide amplifiers
Authors: Wong W. H. , Chan K. S. , Pun E. Y. B.
Published: June 2005

Polymer channel waveguide amplifier arrays were fabricated using ultraviolet direct printing methodology. The effects of different weight percentage (wt. %) combinations of rare-earth ions erbium (Er3+) and ytterbium (Yb3+) on the absorption spectrum, as well as the internal gain, were investigated. With an input signal power of ∼−18dBm, the highest internal gain obtained is ∼16.5dB at a wavelength of 1533nm for a 20mm long multimode channel waveguide codoped with ∼1wt.% of Er3+ and ∼10wt.% of Yb3+ derivatives. The UV direct printing methodology opens a simple platform for the fabrication of dense and compact polymer waveguide laser arrays.
ZnO nanopencils: Efficient field emitters
Authors: Wang R. C. , Liu C. P. , Huang J. L. , Chen S.-J. , Tseng Y.-K. , Kung S.-C.
Published: June 2005

ZnO nanopencils were synthesized on a silicon wafer without catalysts at a low temperature of 550 ° C through a simple two-step pressure controlled thermal evaporation. Penholders were well-hexagonal faceted and the diameter of pen tips on the nanopencils was in the range of 20–30 nm. High-resolution transmission electron microscopy shows that the nanopencils were single crystals growing along the [0001] direction and the pen tips subtend a small angle with multiple surface perturbations. Field-emission measurements on the nanopencils show a low turn-on field of 3.7V∕μm at a current density of 10μA∕cm2. The emission current density reached 1.3mA∕cm2 at an applied field of 4.6V∕μm. The emission at the low field is attributed to the sharp tip and surface perturbations on the nanopencils.
Influence of plasmons on terahertz conductivity measurements
Authors: Nienhuys Han-Kwang , Sundström Villy
Published: June 2005

Time-domain terahertz spectroscopy allows measuring the complex conductivity spectrum of materials at frequencies on the order of 1 THz. Typically, terahertz (THz) studies produce conductivity spectra that are different from those predicted by the classical Drude model, especially in nanostructured materials. We claim that plasmon resonances in particles that are small compared to the THz wavelength cause these deviations. This is supported by measurements on photoexcited silicon, in bulk as well as in micron-sized particles. In the latter, the behavior is vastly different and strongly dependent on charge carrier concentration.
Optimal design of a flexure hinge-based XYZ atomic force microscopy scanner for minimizing Abbe errors
Authors: Kim Dongmin , Kang Dongwoo , Shim Jongyeop , Song Incheon , Gweon Daegab
Published: June 2005

To establish of standard technique of nanolength measurement in a two-dimensional plane, a new (AFM) system has been designed. In this system, measurement uncertainty is dominantly affected by the Abbe error of the XYZ scanning stage. No linear stage is perfectly straight; in other words, every scanning stage is subject to tilting, pitch, and yaw motion. In this article, an AFM system with minimum offset of XYZ sensing is designed. And, the XYZ scanning stage is designed to minimize the rotation angle because Abbe errors occur through the multiply of offset and rotation angle. For XY stage, optimal design is performed to minimize the rotation angle by maximizing the stiffness ratio of motion direction to the parasitic motion direction of each stage. For the Z stage, the optimal design of maximizing the first-resonant frequency is performed. When the resonant frequency increases, the scan speed is improved, thereby reducing errors caused by sensor drift. This article describes the procedures of selecting parameters for the optimal design. The full range of the XYZ scanner is 100μm×100μm×10μm. Based on the solution of the optimization problem, the XYZ scanner is fabricated. And tilting, pitch, and yaw motion are measured by autocollimator to evaluate the performance of XY stage.
Critical size for exchange bias in ferromagnetic-antiferromagnetic particles
Authors: Dobrynin A. N. , Ievlev D. N. , Temst K. , Lievens P. , Margueritat J. , Gonzalo J. , Afonso C. N. , Zhou S. Q. , Vantomme A. , Piscopiello E. , Van Tendeloo G.
Published: June 2005

We present a study of the magnetic properties of oxidized Co nanoparticles with an average grain size of 3nm, embedded in an amorphous Al2O3 matrix. These nanoparticles can be considered as imperfect Co-core CoO-shell systems. Magnetization measurements after magnetic field cooling show a vertical shift of the hysteresis loop, while no exchange bias is observed. With a simple model, we show that there is a critical grain size for hybrid ferromagnetic-antiferromagnetic particles, below which exchange bias is absent for any ratio of ferromagnetic and antiferromagnetic constituents. The reason is that the interfacial exchange energy dominates over other energies in the system due to a large surface-to-volume ratio in the nanoparticles.
Rapid DNA hybridization based on ac field focusing of magnetically labeled target DNA
Authors: Ferreira H. A. , Feliciano N. , Graham D. L. , Clarke L. A. , Amaral M. D. , Freitas P. P.
Published: June 2005

Rapid DNA-DNA hybridization between surface-bound probe DNA and magnetically labeled complementary target DNA was achieved using current carrying line structures and oscillating external magnetic fields. Magnetic particles of 250 nm in diameter were focused and manipulated over on-chip U-shaped current lines using dc currents of 40 mA and oscillating magnetic fields of 1.4kA∕mrms with frequencies ranging from 0.1 to 20 Hz. The focusing process was both time and frequency dependent and, consequently, hybridization degree varied with focusing efficiency. Extensive label binding was observed in 5–25 min at 0.1–20 Hz. This technique has strong potential in commercial DNA chip development.
Chemical reaction at the interface between polycrystalline Si electrodes and HfO2∕Si gate dielectrics by annealing in ultrahigh vacuum
Authors: Takahashi H. , Toyoda S. , Okabayashi J. , Kumigashira H. , Oshima M. , Sugita Y. , Liu G. L. , Liu Z. , Usuda K.
Published: June 2005

We have investigated the chemical reaction at the interface between polycrystalline-Si (poly-Si) electrodes and HfO2∕Si gate dielectrics by photoemission spectroscopy and x-ray absorption spectroscopy depending on the annealing temperature in an ultrahigh vacuum. From Si2p and Hf4f high-resolution core-level photoemission spectra, we revealed that the Hf-silicide formation starts at as low temperature as 700°C and that the Hf-silicate layer is also formed at the interface between poly-Si electrodes and HfO2. Crystallization of the amorphous HfO2 layer even at 700°C was suggested from valence-band and OK-edge absorption spectra. By the annealing at 800°C, the HfO2 layer disappeared completely and the Hf-silicide clusters were formed on the Si substrate. Direct contact between poly-Si electrodes and HfO2 promotes the interfacial reaction compared to the case without poly-Si electrodes.
Aluminum nanocantilevers for high sensitivity mass sensors
Authors: Davis Zachary J. , Boisen Anja
Published: June 2005

We have fabricated Al nanocantilevers using a simple, one mask contact UV lithography technique with lateral and vertical dimensions under 500 and 100 nm, respectively. These devices are demonstrated as highly sensitive mass sensors by measuring their dynamic properties. Furthermore, it is shown that Al has a potential higher sensitivity than Si based dynamic sensors. Initial testing of these devices has been conducted using a scanning electron microscope setup were the devices were tested under high vacuum conditions. The Q factor was measured to be approximately 200 and the mass sensitivity was measured to 2ag∕Hz by depositing electron-beam-induced carbon at the end of the nanocantilever.
High-temperature self-circulating thermoacoustic heat exchanger
Authors: Backhaus S. , Swift G. W. , Reid R. S.
Published: June 2005

Thermoacoustic and Stirling engines and refrigerators use heat exchangers to transfer heat between the oscillating flow of their thermodynamic working fluids and external heat sources and sinks. An acoustically driven heat-exchange loop uses an engine’s own pressure oscillations to steadily circulate its own thermodynamic working fluid through a physically remote high-temperature heat source without using moving parts, allowing for a significant reduction in the cost and complexity of thermoacoustic and Stirling heat exchangers. The simplicity and flexibility of such heat-exchanger loops will allow thermoacoustic and Stirling machines to access diverse heat sources and sinks. Measurements of the temperatures at the interface between such a heat-exchange loop and the hot end of a thermoacoustic-Stirling engine are presented. When the steady flow is too small to flush out the mixing chamber in one acoustic cycle, the heat transfer to the regenerator is excellent, with important implications for practical use.
Dielectric relaxation of atomic-layer-deposited HfO2 thin films from 1kHzto5GHz
Authors: Lee Byungjoo , Moon Taeho , Kim Tae-Gon , Choi Duck-Kyun , Park Byungwoo
Published: June 2005

The dielectric relaxation of HfO2 thin films grown by atomic-layer deposition (ALD) was studied as a function of frequency from 1kHzto5GHz. The dielectric relaxation of the ALD HfO2 films followed a power-law dependence known as the Curie–von Schweidler relaxation law both in the kHz and GHz ranges, and the relaxation exponents were consistent with the measured dielectric losses. The behavior of the dielectric response for the HfO2 thin films may be attributed to defect sites in the HfO2 layer and∕or interface.
Direct experimental evidence of hybridization of Pb states with O2p states in ferroelectric perovskite oxides
Authors: Jan J. C. , Tsai H. M. , Pao C. W. , Chiou J. W. , Asokan K. , Kumar K. P. Krishna , Pong W. F. , Tang Y. H. , Tsai M.-H. , Kuo S. Y. , Hsieh W. F.
Published: June 2005

This work presents the OK- and TiL3,2-edge x-ray absorption near-edge structure (XANES) spectra of PbxSr1−xTiO3 (PxSTO) and BaxSr1−xTiO3 (BxSTO) compounds with various Pb and Ba concentrations. The result provides direct evidence that the Pb–O bonding strongly affects O2p–Ti3d hybridization in the TiO6 octahedron of PxSTO. In contrast, the Ba–O bonding does not substantially affect O2p–Ti3d hybridization in BxSTO. The TiL3-edge XANES spectra show the splitting of the eg band for PxSTO with x≳0.5, which provides an evidence of Pb-induced tetragonal distortion in the TiO6 octahedron. In contrast, eg band splitting is absent in BxSTO.
Active Q-switched distributed feedback erbium-doped fiber lasers
Authors: Pérez-Millán P. , Cruz J. L. , Andrés M. V.
Published: June 2005

This letter presents a distributed feedback fiber laser that operates in an actively controlled Q-switched regime. The laser is based on a Bragg grating made in an erbium-doped fiber. The grating has a defect induced by a magnetostrictive transducer that configures the distributed feedback laser structure. The phase shift generated by the defect can be dynamically modified by an electric current, permitting active Q-switching of the laser. The laser generates pulses of 75ns duration and the repetition rate can be continuously adjusted from 0to10kHz.
Electronic properties of N- and C-doped TiO2
Authors: Lee Jung-Yup , Park Jaewon , Cho Jun-Hyung
Published: June 2005

We present first-principles density-functional calculations for the electronic properties of nitrogen(N)-doped as well as carbon(C)-doped titanium dioxide (TiO2). We find that the bands originating from N (C) 2p states appear in the band gap of TiO2, but the mixing of N (C) with O2p states is too weak to produce a significant band-gap narrowing. Our results are consistent with several recent experimental data of N-doped TiO2, where the absorption of visible light is due to isolated N2p states above the valence-band maximum of TiO2 rather than due to a band-gap narrowing.
Magnetoelectric effect of Pb(Zr,Ti)O3 rod arrays in a (Tb,Dy)Fe2∕epoxy medium
Authors: Shi Z. , Nan C. W. , Zhang Jie , Cai N. , Li J.-F.
Published: June 2005

We report a kind of multiferroic and multifunctional composite with Pb(Zr,Ti)O3 rod arrays embedded in a ferromagnetic medium of (Tb,Dy)Fe2∕epoxy. The composite structure is similar to that of 1–3-type piezoelectric composites with Pb(Zr,Ti)O3 rod arrays embedded in an inert epoxy for already commercial applications as transducers. The large magnetoelectric effect, especially at high frequency at which the electromechanical resonance appears, is observed for such multiferroic composites due to coupling elastic interaction between Pb(Zr,Ti)O3 rods and the ferromagnetic medium, which suggests avenues for designing novel multiferroic materials for practical applications.
CD26, adenosine deaminase, and adenosine receptors mediate costimulatory signals in the immunological synapse
Authors: Pacheco R. , Martinez-Navio J. M. , Lejeune M. , Climent N. , Oliva H. , Gatell J. M. , Gallart T. , Mallol J. , Lluis C. , Franco R.
Published: June 2005

Adenosine deaminase (ADA), a protein whose deficit leads to severe combined immunodeficiency, binds to the cell surface by means of either CD26, A1adenosine receptors, or A2Badenosine receptors. The physiological role of these interactions is not well understood. Our results show that by a 3-fold reduction in the EC50for the antigen, ADA potentiated T cell proliferation in autologous cocultures with antigen-pulsed immature or mature dendritic cells. Costimulation was not due to the enzymatic activity but to the interaction of ADA–CD26 complexes in T cells with an ADA-anchoring protein in dendritic cells. From colocalization studies, it is deduced that ADA colocalizing with adenosine receptors on dendritic cells interact with CD26 expressed on lymphocytes. This costimulatory signal in the immunological synapse leads to a marked increase (3- to 34-fold) in the production of the T helper 1 and proimmflamatory cytokines IFN-γ, TNF-α, and IL-6.
Sampling motifs on phylogenetic trees
Authors: Li Xiaoman , Wong Wing H.
Published: June 2005

We present a method to find motifs by simultaneously using the overrepresentation property and the evolutionary conservation property of motifs. This method is applicable to divergent species where alignment is unreliable, which overcomes a major limitation of the current methods. The method has been applied to search regulatory motifs in four yeast species based on ChIP-chip data inSaccharomyces cerevisiaeand obtained 20% higher accuracy than the best current methods. We also discovered cis-regulatory elements that govern the tight regulation of ribosomal protein genes in two distantly related insects by using this method. These results demonstrate that our method will be useful for the extraction of regulatory signals in multiple genomes.
Graded bidirectional synaptic plasticity is composed of switch-like unitary events
Authors: O'Connor Daniel H. , Wittenberg Gayle M. , Wang Samuel S.-H.
Published: June 2005

Biological information storage events are often rapid transitions between discrete states. In neural systems, the initiation of bidirectional plasticity by all-or-none events may help confer robustness on memory storage. Here, we report that at CA3–CA1 hippocampal synapses, individual potentiation and depression plasticity events are discrete and heterogeneous in nature. Individual synapses began from extreme high and low strength states. Unitary plasticity events were all-or-none and drove synaptic strength between extremes in <1 min. Under naïve conditions, approximately three-fourths of synapses began in a low-strength state. The timing of these unitary events can account for the time course of macroscopic synaptic plasticity.
Efficient synthetic inhibitors of anthrax lethal factor
Authors: Forino Martino , Johnson Sherida , Wong Thiang Y. , Rozanov Dmitri V. , Savinov Alexei Y. , Li Wei , Fattorusso Roberto , Becattini Barbara , Orry Andrew J. , Jung Dawoon , Abagyan Ruben A. , Smith Jeffrey W. , Alibek Ken , Liddington Robert C. , Strongin Alex Y. , Pellecchia Maurizio
Published: June 2005

Inhalation anthrax is a deadly disease for which there is currently no effective treatment.
Bacillus anthracis
lethal factor (LF) metalloproteinase is an integral component of the tripartite anthrax lethal toxin that is essential for the onset and progression of anthrax. We report here on a fragment-based approach that allowed us to develop inhibitors of LF. The small-molecule inhibitors we have designed, synthesized, and tested are highly potent and selective against LF in both
in vitro
tests and cell-based assays. These inhibitors do not affect the prototype human metalloproteinases that are structurally similar to LF. Initial
in vivo
evaluation of postexposure efficacy of our inhibitors combined with antibiotic ciprofloxican against
B. anthracis
resulted in significant protection. Our data strongly indicate that the scaffold of inhibitors we have identified is the foundation for the development of novel, safe, and effective emergency therapy of postexposure inhalation anthrax.
Protein identification using sequential ion/ion reactions and tandem mass spectrometry
Authors: Coon Joshua J. , Ueberheide Beatrix , Syka John E. P. , Dryhurst Deanna D. , Ausio Juan , Shabanowitz Jeffrey , Hunt Donald F.
Published: June 2005

A method for rapid sequencing of intact proteins simultaneously from the N and C termini (1–2 s) with online chromatography is described and applied to the characterization of histone H3.1 posttranslational modifications and the identification of an additional member of the H2A gene family. Proteins are converted to gas-phase multiply charged positive ions by electrospray ionization and then allowed to react with fluoranthene radical anions. Electron transfer to the multiply charged protein promotes random dissociation of the N—Cα bonds of the protein backbone. Multiply charged fragment ions are then deprotonated in a second ion/ion reaction with the carboxylate anion of benzoic acid. The
m
/
z
values for the resulting singly and doubly charged ions are used to read a sequence of 15–40 aa at both the N and C termini of the protein. This information, with the measured mass of the intact protein, is used to search protein or nucleotide databases for possible matches, detect posttranslational modifications, and determine possible splice variants.
Isolation and functional expression of an animal geranyl diphosphate synthase and its role in bark beetle pheromone biosynthesis
Authors: Gilg Anna B. , Bearfield Jeremy C. , Tittiger Claus , Welch William H. , Blomquist Gary J.
Published: June 2005

Geranyl diphosphate synthase (GPPS) catalyzes the condensation of dimethylallyl diphosphate and isopentenyl diphosphate to form geranyl diphosphate. Geranyl diphosphate is the precursor of monoterpenes, a large family of natural occurring C
10
compounds predominately found in plants. Similar to plants but unique to animals, some bark beetle genera (Coleoptera: Scolytidae) produce monoterpenes that function in intraspecific chemical communication as aggregation and dispersion pheromones. The release of monoterpene aggregation pheromone mediates host colonization and mating. It has been debated whether these monoterpene pheromone components are derived
de novo
through the mevalonate pathway or result from simple modifications of dietary precursors. The data reported here provide conclusive evidence for
de novo
biosynthesis of monoterpene pheromone components from bark beetles. We describe GPPS in the midgut tissue of pheromone-producing male
Ips pini
.
GPPS
expression levels are regulated by juvenile hormone III, similar to other mevalonate pathway genes involved in pheromone biosynthesis. In addition, GPPS transcript is almost exclusively expressed in the anterior midgut of male
I. pini
, the site of aggregation pheromone biosynthesis. The recombinant enzyme was functionally expressed and produced geranyl diphosphate as its major product. The three-dimensional model structure of GPPS shows that the insect enzyme has the sequence structural motifs common to
E
-isoprenyl diphosphate synthases.
Roles of steroid receptor coactivator (SRC)-1 and transcriptional intermediary factor (TIF) 2 in androgen receptor activity in mice
Authors: Ye Xiangcang , Han Sang Jun , Tsai Sophia Y. , DeMayo Francesco J. , Xu Jianming , Tsai Ming-Jer , O'Malley Bert W.
Published: June 2005

Genetic disruption of the steroid receptor coactivator (SRC)-1 and transcriptional intermediary factor (TIF)2/SRC-2 in mouse resulted in distinctive mutant phenotypes. To quantify their roles in the function of androgen receptor (AR) transcriptional activityin vivo, we generated a unique transgenic AR-reporter mouse and analyzed the cell-specific contributions of SRC-1 and TIF2 to the activity of AR in mouse testis. Transgenic AR-luciferase and transgenic AR-lacZ mice harbor a recombinant mouse AR gene, ARGAL4DBD, which is functionally coupled with a upstream activation sequence-mediated reporter gene (AR activity indicator). After characterization of these mice in terms of AR function, we further derived bigenic mice by crossing AR activity indicator mice with theSRC-1-/-orTIF2+/-mutant mice. Analyses of the resultant bigenic mice byin vivoimaging and luciferase assays showed that testicular AR activity was decreased significantly in those with theTIF2+/-mutation but not in theSRC-1+/-background, suggesting that TIF2 serves as the preferential coactivator for AR in testis. Immunohistological analysis confirmed that AR and TIF2 coexist in mouse testicular Sertoli cell nuclei under normal conditions. Although SRC-1 concentrates in Sertoli cell nuclei in the absence of TIF2, nuclear SRC-1 is not able to rescue AR activity in the TIF2 mutant background. Interestingly, SRC-1 appears to negatively influence AR activity, thereby counterbalancing the TIF2-stimulated AR activity. Our results provide uniquein vivoinsights to the multidimensional cell-type-specific interactions between AR and coregulators.
Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record
Authors: Peterson Kevin J. , Butterfield Nicholas J.
Published: June 2005

Molecular clocks have the potential to shed light on the timing of early metazoan divergences, but differing algorithms and calibration points yield conspicuously discordant results. We argue here that competing molecular clock hypotheses should be testable in the fossil record, on the principle that fundamentally new grades of animal organization will have ecosystem-wide impacts. Using a set of seven nuclear-encoded protein sequences, we demonstrate the paraphyly of Porifera and calculate sponge/eumetazoan and cnidarian/bilaterian divergence times by using both distance [minimum evolution (ME)] and maximum likelihood (ML) molecular clocks; ME brackets the appearance of Eumetazoa between 634 and 604 Ma, whereas ML suggests it was between 867 and 748 Ma. Significantly, the ME, but not the ML, estimate is coincident with a major regime change in the Proterozoic acritarch record, including: (i) disappearance of low-diversity, evolutionarily static, pre-Ediacaran acanthomorphs; (ii) radiation of the high-diversity, short-lived Doushantuo-Pertatataka microbiota; and (iii) an order-of-magnitude increase in evolutionary turnover rate. We interpret this turnover as a consequence of the novel ecological challenges accompanying the evolution of the eumetazoan nervous system and gut. Thus, the more readily preserved microfossil record provides positive evidence for the absence of pre-Ediacaran eumetazoans and strongly supports the veracity, and therefore more general application, of the ME molecular clock.