bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of the Adiabatic Elastic Moduli of Single-Crystal Alpha Uranium
Authors: McSkimin H. J. , Fisher E. S.
Published: April 2005

The ultrasonic-wave velocities in small alpha-uranium single crystals have been measured at various temperatures using the phase-comparison technique. Details in the experimental procedure, direct computation of the stiffness moduli, and cross-checking by indirect methods are given. The temperature dependence of the moduli are reported for the range −195° to +300°C for c11, c22, and c33 and −195° to +35°C for the remaining 6 principal moduli. The results show a very marked abnormal temperature dependence of the elasticity in the [100] direction; c11 decreases with temperature below −17.2°C and the linear compressibility in [100] increases from +35° to −195°C. The bulk modulus passes through a maximum at −100°C. These abnormalities indicate a strong temperature dependence of the electron interactions involved in the second nearest-neighbor bond.
Generation of Phonons in High-Power Ferromagnetic Resonance Experiments
Authors: Schlömann Ernst
Published: April 2005

The magnetoelastic energy of ferromagnets leads to a coupling between spin waves and elastic vibrations. Because of this coupling the normal modes are not purely magnetic or purely elastic but contain admixtures of both kinds of excitation, the mixing being strongest when the unperturbed waves have the same frequency and wavelength. It is shown theoretically that under suitable conditions (of frequency, dc field, and sample shape) coupled magnetoelastic waves with wavelengths of the order of 1 μ or less can be generated in high-power ferromagnetic resonance experiments. The magnetoelastic interaction increases the threshold precession angle of the uniform mode, the fractional increase being proportional to the group velocity times the relaxation time for spin waves divided by the same quantity for transverse phonons.
Crystallographic Aspects of Extra Reflections in X-Ray Spectrochemical Analysis
Authors: Spielberg N. , Ladell J.
Published: April 2005

In x-ray spectrochemical analysis, a given crystal monochromator can give rise to higher-order reflections of the incident wavelength, which may be ascribed to the planes (nh nk nl), which are parallel to the principal planes (hkl). In addition to these, however, there may occur reflections due to other sets of planes which are slightly tilted with respect to (hkl). These reflections may lead to undesirable spectral interferences. The identification of these undesirable reflections and their dependence upon choice of various angular divergence parameters, on wavelength, and on the selection and orientation of the monochromators are discussed in terms of an instrumental figure of reflection and a detecting volume in reciprocal space. Topaz and quartz are used as specific examples of the problem.
Formation of Thin Polymer Films by Electron Bombardment
Authors: Christy Robert W.
Published: April 2005

Thin insulating films, less than 100 A thick to a few thousand angstroms, were produced by bombarding a substrate with electrons in the presence of silicone oil vapor. The rate of deposition of the solid film was found to depend on the substrate temperature, electron beam current density, and oil vapor pressure. A theoretical expression for the rate is given which agrees satisfactorily with the experimental data. The films which were produced had excellent electrical insulating properties.
Fourier Analysis of X-Ray Scattering from Polyatomic Liquids
Authors: Pierce W. C.
Published: April 2005

It is shown that the Fourier integral analysis of x-ray scattering for liquids with polyatomic molecules containing like atoms may be simplified if the x-ray diffraction curve is corrected by subtraction of the gas scattering of the single molecules before the analysis is made. The method is tested by an analysis of Katzoff's data for benzene. The distribution function obtained indicates that a given molecule is surrounded by six neighbors in the plane of the benzene ring, with a mean separation of centers of about 6.7A. The neighbors of a given molecule are oriented with respect to the molecule. The parallel planes of flat molecules are separated by a distance of 3.7A. The structure is very similar to the crystal structure of hexamethyl benzene.
Calculation of the Rate of Elementary Association Reactions
Authors: Wigner E.
Published: April 2005

An upper limit for the rate of association reactions is found by determining the probability of a decrease of the relative energy of two atoms below zero energy, under the influence of a third body. The relation of this approximate calculation to the rigorous solution of the problem is discussed in Section 2. The results are applied to the recombination of J atoms, measured by Rabinowitch and Wood. Numerically, the agreement is quite good; however, the calculated values are somewhat too low, which cannot be explained by an inaccuracy of the method. Reasons for the discrepancy other than the possible nonadiabatic character of the reaction are discussed.
Rotatory Dispersion and Absorption Spectra of Carboxylic Acids and Hydrocarbons Containing a Phenyl or Cyclohexyl Group
Authors: Rothen Alexandre , Levene P. A.
Published: April 2005

The configurational relationships of aliphatic and aromatic disubstituted carboxylic acids having been established, it was possible to study the vicinal effect of the phenyl group on the carboxyl group. It was found that the effect of the phenyl group is not different from that of a normal hexyl or a cyclohexyl group. This phenomenon is due, perhaps, to the fact that the absorption bands of the phenyl group nearest to the visible region are not optically active.
n
-alkanes on MgO(100). I. Coverage-dependent desorption kinetics of n-butane
Authors: Tait Steven L. , Dohnálek Zdenek , Campbell Charles T. , Kay Bruce D.
Published: April 2005

High-quality temperature-programmed desorption (TPD) measurements of n-butane from MgO(100) have been made for a large number of initial butane coverages (0–3.70 ML, ML–monolayers) and a wide range of heating ramp rates (0.3–10K∕s). We present a TPD analysis technique which allows the coverage-dependent desorption energy to be accurately determined by mathematical inversion of a TPD spectrum, assuming only that the preexponential factor (prefactor) is coverage independent. A variational method is used to determine the prefactor that minimizes the difference between a set of simulated TPD spectra and corresponding experimental data. The best fit for butane desorption from MgO is obtained with a prefactor of 1015.7±1.6s−1. The desorption energy is 34.9±3.4kJ∕mol at 0.5-ML coverage, and varies with coverage approximately as Ed(θ)=34.5+0.566θ+8.37exp(−θ∕0.101). Simulations based on these results can accurately reproduce TPD experiments for submonolayer initial coverages over a wide range of heating ramp rates (0.3–10K∕s). Advantages and limitations of this method are discussed.
n
-alkanes on MgO(100). II. Chain length dependence of kinetic desorption parameters for small n-alkanes
Authors: Tait Steven L. , Dohnálek Zdenek , Campbell Charles T. , Kay Bruce D.
Published: April 2005

Coverage-dependent desorption-kinetics parameters are obtained from high-quality temperature-programmed desorption data for seven small n-alkane molecules on MgO(100). The molecules, CNH2N+2 (N=1–4,6,8,10), were each studied for a set of 29 initial coverages at a heating ramp rate of 0.6K∕s as well as at a set of nine ramp rates in the range of 0.3–10.0K∕s. The inversion analysis method with its least-squares preexponential factor (prefactor) optimization discussed in the accompanying article is applied to these data. This method allows for accurate determination of prefactors and coverage-dependent desorption energies. The prefactor for desorption increases dramatically with chain length from 1013.1to1019.1s−1 over the range of N=1–10. We show that this increase can be physically justified by considering the increase in rotational entropy available to the molecules in the gaslike transition state for desorption. The desorption energy increases with chain length as Ed(N)=6.5+7.1N, which implies an incremental increase of 7.1±0.2kJ∕mol per CH2.
Molecular diffusion in liquid crystals and chiral discrimination. I. Theory
Authors: Frezzato Diego , Moro Giorgio J. , Zannoni Claudio
Published: April 2005

The possibility of using cholesteric phases for discriminating enantiomers of a chiral solute on the basis of their different transport properties, motivates the investigation of the translational diffusion by taking fully into account the roto-translational coupling. In this article a detailed theoretical analysis is presented for the transport properties evaluated according to the asymptotic limit of the mean-squared displacement. A general relation is derived for the transport coefficients, having as main ingredients the mean-field potential due to the mesophase, and the diffusion tensor with its purely translational and rotational components, and with the blocks describing the roto-translational coupling. The application of the theory to nematic phases shows that the roto-translational coupling generates a dynamical contribution reducing the transport coefficients evaluated by taking into account only the translational diffusion components in the center of diffusion. The theory is also specialized to a cholesteric phase with a given helical pitch for the director arrangement, in a form which is suitable for calculations of model systems of chiral solutes to be presented in a forthcoming paper.
Molecular dynamics of confined glucose solutions
Authors: Lelong Gérald , Price David L. , Douy André , Kline Steve , Brady John W. , Saboungi Marie-Louise
Published: April 2005

Silica gels containing solutions of glucose in heavy water at different concentrations have been prepared by a sol-gel method. Dynamical studies with quasielastic neutron scattering, compared with previous results on bulk solutions, show that the dynamics of the glucose molecules are not appreciably affected by the confinement, even though the gels behave macroscopically as solid materials. Small-angle neutron-scattering spectra on the same systems, fitted with a fractal model, yield a correlation length that decreases from 20to2.5nm with increasing glucose concentration, suggesting a clustering of glucose molecules in concentrated solutions that is consistent with the dynamical measurements. These two sets of results imply that 20nm is an upper limit for the scale at which the dynamics of glucose molecules in solution are affected by confinement.
The inelastic hard dimer gas: A nonspherical model for granular matter
Authors: Costantini Giulio , Marini Bettolo Marconi Umberto , Kalibaeva Galina , Ciccotti Giovanni
Published: April 2005

We study a two-dimensional gas of inelastic smooth hard dimers. Since the collisions between dimers are dissipative, being characterized by a coefficient of restitution α<1, and no external driving force is present, the energy of the system decreases in time and no stationary state is achieved. However, the resulting nonequilibrium state of the system displays several interesting properties in close analogy with systems of inelastic hard spheres, whose relaxational dynamics has been thoroughly explored. We generalize to inelastic systems a recently method introduced [G. Ciccotti and G. Kalibaeva, J. Stat. Phys. 115, 701 (2004)] to study the dynamics of rigid elastic bodies made up of different spheres held together by rigid bonds. Each dimer consists of two hard disks of diameter d, whose centers are separated by a fixed distance a. By describing the rigid bonds by means of holonomic constraints and deriving the appropriate collision rules between dimers, we reduce the dynamics to a set of equations which can be solved by means of event-driven simulation. After deriving the algorithm we study the decay of the total kinetic energy, and of the ratio between the rotational and the translational kinetic energy of inelastic dimers. We show numerically that the celebrated Haff’s homogeneous cooling law t−2, describing how the kinetic energy of an inelastic hard-sphere system with a constant coefficient of restitution decreases in time, holds even in the case of these nonspherical particles. We fully characterize this homogeneous decay process in terms of appropriate decay constants and confirm numerically the scaling behavior of the velocity distributions.
Structural and optical characterization of WO3 thin films for gas sensor applications
Authors: György E. , Socol G. , Mihailescu I. N. , Ducu C. , Ciuca S.
Published: April 2005

The structure, chemical composition, and optical properties of tungsten trioxide thin films grown by pulsed laser deposition were investigated. An ultraviolet KrF* excimer laser (λ=248nm, τFWHM≅20ns, ν=2Hz) was used for irradiation of tungsten trioxide targets in oxygen atmosphere. Our research focused on the effect of the ambient gas pressure and substrate temperature on the chemical composition, crystalline status, and optical properties of the obtained thin films. To this end, the films were studied by x-ray diffractometry Raman spectroscopy, and energy dispersive x-ray spectroscopy. Optical transmittance measurements were performed with a double beam spectrometer within the 400–1200nm range. The films deposited at oxygen pressure values higher than 10Pa and substrate temperatures above 300°C consist of crystalline tungsten trioxide. Their average transmittance in the visible-infrared spectral region reaches about 85% appropriate for the envisaged applications.
The upper critical field of filamentary Nb3Sn conductors
Authors: Godeke A. , Jewell M. C. , Fischer C. M. , Squitieri A. A. , Lee P. J. , Larbalestier D. C.
Published: April 2005

We have examined the upper critical field of a large and representative set of present multifilamentary Nb3Sn wires and one bulk sample over a temperature range from 1.4 K up to the zero-field critical temperature. Since all present wires use a solid-state diffusion reaction to form the A15 layers, inhomogeneities with respect to Sn content are inevitable, in contrast to some previously studied homogeneous samples. Our study emphasizes the effects that these inevitable inhomogeneities have on the field-temperature phase boundary. The property inhomogeneities are extracted from field-dependent resistive transitions which we find broaden with increasing inhomogeneity. The upper 90%–99% of the transitions clearly separates alloyed and binary wires but a pure, Cu-free binary bulk sample also exhibits a zero-temperature critical field that is comparable to the ternary wires. The highest μ0Hc2 detected in the ternary wires are remarkably constant: The highest zero-temperature upper critical fields and zero-field critical temperatures fall within 29.5±0.3 and 17.8±0.3K, respectively, independent of the wire layout. The complete field-temperature phase boundary can be described very well with the relatively simple Maki–DeGennes model using a two-parameter fit, independent of composition, strain state, sample layout, or applied critical state criterion.
Domain structure and evolution in (PbMg1∕3Nb2∕3O3)0.75(PbTiO3)0.25 single crystal studied by temperature-dependent piezoresponse force microscopy
Authors: Zhao X. , Dai J. Y. , Wang J. , Chan H. L. W. , Choy C. L. , Wan X. M. , Luo H. S.
Published: April 2005

Ferroelectric domain structure and evolution in (110)-cut relaxor ferroelectric (PbMg1∕3Nb2∕3O3)0.75(PbTiO3)0.25 (PMN-25PT) single crystal have been studied by means of temperature-dependent piezoresponse force microscopy. It revealed that, during heating, the as-grown PMN-25PT single crystal exhibits a transition from a ferroelectric microdomain structure to a paraelectric phase; while after being cooled back to room temperature the microdomain structure is rebuilt. Domains with size of tens of nanometers were also observed embedded in the microdomains. By contrast, the poled sample exhibits transitions from macro- to microdomain structures at 90 °C and from microdomain structure to paraelectric phase at 115 °C. These direct observations are consistent with temperature-dependent relative permittivity measurements. In situ polarization switching of the domains was also demonstrated.
Frequency band-gap measurement of two-dimensional air/silicon phononic crystals using layered slanted finger interdigital transducers
Authors: Wu Tsung-Tsong , Wu Liang-Chen , Huang Zi-Gui
Published: April 2005

In this paper, we investigate the frequency band-gap features of micromachined air/silicon phononic band structures using layered slanted finger interdigital transducers (SFIT). In order to achieve the applications of phononic crystals on the microelectromechanical system related components, the frequency band-gap widths of surface waves are studied both theoretically and experimentally in micrometer scale phononic crystals. For further integration with the complementary metal-oxide semiconductor processing techniques, silicon is chosen as the base material of the two-dimensional phononic crystals in this study. To cover the frequency band-gap width of the phononic crystal, the wideband SFIT- and the SFIT∕ZnO∕Si-layered structures in the measurement are analyzed and discussed. For layered structures, the dispersive relation is calculated by the effective permittivity approach, and the frequency response of the layered SFIT is then simulated by the coupling-of-modes model. The frequency band-gap width and the frequency range of two-dimensional air/silicon phononic crystals in micrometer scale are measured, and the result agrees well with the theoretical evaluation.
Optical characterizations of heavily doped p-type AlxGa1−xAs and GaAs epitaxial films at terahertz frequencies
Authors: Hu Z. G. , Rinzan M. B. M. , Matsik S. G. , Perera A. G. U. , Von Winckel G. , Stintz A. , Krishna S.
Published: April 2005

The optical properties of p-type AlxGa1−xAs (x=0, 0.01, and 0.16) epitaxial films with different beryllium and carbon doping concentrations (1018–1019cm−3) were investigated by far-infrared reflectance spectroscopy in the 1.5–15-THz frequency range. The dielectric response functions of the film samples were expressed using the classical Lorentz–Drude model. Optical properties were obtained using a three-phase model (air∕film∕substrate) which agrees with the experimental reflectance spectral data. The effects of doping concentrations on the optical constants were studied in detail. The results indicate that the refractive index increases with the doping concentration in the low-frequency region (⩽5THz) where the free-carrier absorption plays an important role in the optical response. However, the extinction coefficient increases with the doping concentration in the entire frequency region. This indicates that the absorption coefficient increases with the doping concentration. The calculated plasma frequencies agree with the values obtained from the measured doping concentrations. The free-carrier scattering time is ∼1.39×10−14s. The longitudinal-optical phonon plasmon coupled modes of the AlxGa1−xAs films are presented. The upper coupled mode increases with the doping concentration and shows a transition from phononlike to plasmonlike behavior. A sublinear relationship between the absorption coefficient and the doping concentration for p-type AlxGa1−xAs epitaxial films was obtained at a frequency of 3.75THz (80μm). These results can be used to design and improve the performance of terahertz detectors.
Electron emission suppression characteristics of molybdenum grids coated with Pt films by ion-beam-assisted deposition
Authors: Jiang Jun , Jiang Bingyao , Ren Congxin , Zhang Fumin , Feng Tao , Wang Xi , Liu Xianghuai , Zou Shichang
Published: April 2005

Pt was deposited onto molybdenum grids by the ion-beam-assisted deposition method. The electron emission characteristics of molybdenum grids, with and without Pt, contaminated by active electron emission substances (Ba, BaO) of the cathode were measured using analogous diode method. The x-ray diffraction, energy dispersive x-ray, and x-ray photoelectron spectroscopy analyses were preformed on the surface of the molybdenum grids coated with Pt. The electron emission current from the molybdenum grid coated with a Pt film is smaller than that without the Pt film, and the mechanism for electron emission suppression of the molybdenum grid coated with the Pt film was discussed.
Laser ablation of human tooth
Authors: Franklin Sushmita R. , Chauhan P. , Mitra A. , Thareja R. K.
Published: April 2005

We report the measurements of ablation threshold of human tooth in air using photo-thermal deflection technique. A third harmonic (355nm) of Nd:YAG (yttrium aluminum garnet) laser was used for irradiation and a low power helium neon laser as a probe beam. The experimental observations of ablation threshold in conjunction with theoretical model based on heat conduction equations for simulating the interaction of a laser radiation with a calcified tissue are used to estimate the absorption coefficient of human tooth.
Continuous spin representations from group contraction
Authors: Khan Abu M. , Ramond Pierre
Published: April 2005

We consider how the continuous spin representation (CSR) of the Poincaré group in four dimensions can be generated by dimensional reduction. The analysis uses the front-form little group in five dimensions, which must yield the Euclidean group E(2), the little group of the CSR. We consider two cases, one is the single spin massless representation of the Poincaré group in five dimensions, the other is the infinite component Majorana equation, which describes an infinite tower of massive states in five dimensions. In the first case, the double singular limit j, R→∞, with j∕R fixed, where R is the Kaluza–Klein radius of the fifth dimension, and j is the spin of the particle in five dimensions, yields the CSR in four dimensions. It amounts to the Inönü–Wigner contraction, with the inverse Kaluza–Klein radius as contraction parameter. In the second case, the CSR appears only by taking a triple singular limit, where an internal coordinate of the Majorana theory goes to infinity, while leaving its ratio to the Kaluza–Klein radius fixed.
Quantitative analysis of electric force microscopy: The role of sample geometry
Authors: Tevaarwerk Emma , Keppel D. G. , Rugheimer P. , Lagally M. G. , Eriksson M. A.
Published: April 2005

Quantitative electric force microscopy (EFM) is usually restricted to flat samples, because vertical sample topography traditionally makes quantitative interpretation of EFM data difficult. Many important samples, including self-assembled nanostructures, possess interesting nanoscale electrical properties in addition to complex topography. Here we present techniques for analysis of EFM images of such samples, using voltage modulated EFM augmented by three-dimensional simulations. We demonstrate the effectiveness of these techniques in analyzing EFM images of self-assembled SiGe nanostructures on insulator, report measured dielectric properties, and discuss the limitations sample topography places on quantitative measurement.
Enhancement or suppression of instability in a two-layered liquid film flow
Authors: Jiang W. Y. , Lin S. P.
Published: April 2005

A two-layer liquid film with a free surface falling under gravity along a stationary vertical plate is inherently unstable. It is demonstrated that the onset of instability in this inherently unstable film flow can be suppressed in certain parameter regions by imparting oscillations of appropriate amplitudes and frequencies to the plate. The regions of possible instability suppression or windows of stability are shown to depend on the particular stratifications of viscosity and density as well as the layer thickness ratio. It is shown that outside of these windows of stability, there are regions in which the instability can be enhanced. In these regions, the increased interfacial and free surface areas resulting from the enhanced instability may be exploited to promote heat and mass transfer.
Electron density and temperature determination using the concept of particle confinement time uniqueness
Authors: Daltrini A. M. , Machida M.
Published: April 2005

The use of atomic hydrogen line emission to determine the particle confinement time τp of a tokamak plasma is a well-known diagnostic technique. Using such a method, for any one of the emission lines, be it from Lyman, Balmer, or Paschen series, the same (i.e., unique) value of τp must be obtained. Furthermore, this measurement is directly related to the local values of the electron temperature and density. We have developed a method based on the Hα, Hβ, and Hγ hydrogen line emissions and on the concept of τp uniqueness for a tokamak plasma, to determine the local electron density and temperature. The technique has been applied to plasma discharges generated in the NOVA-UNICAMP tokamak. The results show good agreement with measurements from multichannel Thomson scattering and Langmuir probe. A procedure to simulate the Hα emissivity radial profile using the obtained results is also discussed.
Velocity slice imaging for dissociative electron attachment
Authors: Nandi Dhananjay , Prabhudesai Vaibhav S. , Krishnakumar E. , Chatterjee A.
Published: April 2005

A velocity slice imaging method is developed for measuring the angular distribution of fragment negative ions arising from dissociative electron attachment (DEA) to molecules. A low energy pulsed electron gun, a pulsed field ion extraction, and a two-dimensional position sensitive detector consisting of microchannel plates and a wedge-and-strip anode are used for this purpose. Detection and storage of each ion separately for its position and flight time allows analysis of the data offline for any given time slice, without resorting to pulsing the detector bias. The performance of the system is evaluated by measuring the angular distribution of O− from O2 and comparing it with existing data obtained using conventional technique. The capability of this technique in obtaining forward and backward angular distribution data is shown to have helped in resolving one of the existing problems in the electron scattering on O2.
Microfabricated temperature standard based on Johnson noise measurement for the calibration of micro- and nano-thermometers
Authors: Dobson P. S. , Mills G. , Weaver J. M. R.
Published: April 2005

An instrument for the definition of absolute temperature on the scale of one micron based on the measurement of Johnson noise in a small metallic resistor has been constructed. The instrument uses conventional monolithic amplifiers and signal processing circuitry and a custom sensor fabricated by bulk micromachining and electron-beam lithography. The instrument is simple to use and accurate to better than 1 K over the range 300–600 K following a single point calibration to ambient temperature. The incorporation of an integrated thermocouple as a transfer standard allows the use of the instrument to define temperatures with a 1 K accuracy and a random error of better than 50 mK in a 1 kHz bandwidth, and permits its operation in electrically noisy environments. Extension to the measurement of temperature on a scale much smaller than 1μm is theoretically straightforward. The instrument has been used to calibrate a nano-thermometer (resistance thermometer atomic force microscopy probe) with applications in the temperature measurement of semiconductor devices. Finally the calibration of the system is confirmed by a calorimetric scan on a 100 pL sample of benzophenone.
A strategy for the assembly of three-dimensional mesoscopic structures using a ferrofluid
Authors: Ganguly Ranjan , Gaind Amit P. , Puri Ishwar K.
Published: April 2005

A novel technique for the self-assembly of three-dimensional mesoscopic structures in a forced fluid flow by employing a magnetic field is described. There are advantages of using magnetic fields for this purpose: unlike many other forces, a magnetic force is effective even from a distance, permitting “action at a distance,” it is also localized, and competition between the magnetic force and fluid shear enables unique self-assembled ferrofluid structures. Herein, a simulation provides insight into the possibility of using magnetic field to assemble colloidal nanoparticles into aggregates. Subsequently, a demonstration experiment is conducted to characterize the development and decay of such aggregates. The analysis provides a basis for developing effective self-assembly techniques for various engineering applications.
Calibration methods of a 2GHz evanescent microwave magnetic probe for noncontact and nondestructive metal characterization for corrosion, defects, conductivity, and thickness nonuniformities
Authors: Wang Run , Li Frank , Tabib-Azar Massood
Published: April 2005

A near-field magnetic-dipole probe suitable for noncontact and nondestructive imaging of metals is described and the effects of resonator coupling strength, operation frequency, and the probe wire tip geometry on the conductivity resolution of the probe are experimentally determined. Using a simplified circuit model of the resonator, we were able to interpret the system’s output and predict the magnitude of reflected wave and relate it to the properties of the samples under investigation. Thus, the probe was calibrated to perform quantitative conductivity measurements with the ability to detect metal nonuniformities with 1% accuracy and 5×10−3σ and 2×10−2σ conductivity resolutions at 2GHz operation frequency for both the critical and over-coupling probes, respectively. We also discussed the calibration results of probes with different coupling strengths over a 0.91Ω∕square resistive sample. The calibration results of a critical-coupled resonator probe were also compared with a microstrip transmission line probe. It was observed that the resonator probe has 100 times higher conductivity resolution than that of the transmission line probe. Furthermore, we characterized and compared the calibration results of probes with tip wires of different diameters. Images obtained by an evanescent microwave probe are presented.
Active damping of the scanner for high-speed atomic force microscopy
Authors: Kodera Noriyuki , Yamashita Hayato , Ando Toshio
Published: April 2005

The scanner that moves the sample stage in three dimensions is a crucial device that limits the imaging rate of atomic force microscopy. This limitation derives mainly from the resonant vibrations of the scanner in the z direction (the most frequent scanning direction). Resonance originates in the scanner’s mechanical structure as well as in the z piezoactuator itself. We previously demonstrated that the resonance originating in the structure can be minimized by a counterbalancing method. Here we report that the latter resonance from the actuator can be eliminated by an active damping method, with the result the bandwidth of the z scanner nearly reaches the first resonant frequency (150kHz) of the z piezoactuator.
Pump–probe Faraday rotation magnetometer using two diode lasers
Authors: Charnock Forrest T. , Lopusnik R. , Silva T. J.
Published: April 2005

A time-resolved Faraday rotation magnetometer using externally triggered pulsed diode lasers is described. This device permits measurement of the dynamic properties of polarized electronic spins in semiconductors. A nonequilibrium spin polarization is created in the conduction band electrons of n-type GaAs using a circularly polarized laser pulse generated by a pulsed laser diode. A subsequent linearly polarized pulse from a second laser diode probes the time evolved electronic polarization via the Faraday effect. Since two different laser diodes are used for the pump and probe process, the dynamics of optically pumped spins can be directly observed at arbitrarily long pump–probe delays with a temporal resolution of 75ps and a spatial resolution of 25μm. The signal-to-noise of the laser diodes is sufficient to achieve a sensitivity on the order of 3000 spins.
Alkali-vapor cell with metal coated windows for efficient application of an electric field
Authors: Sarkisyan D. , Sarkisyan A. S. , Guéna J. , Lintz M. , Bouchiat M.-A.
Published: April 2005

We describe the implementation of a cylindrical T-shaped alkali-vapor cell for laser spectroscopy in the presence of a longitudinal electric field. The two windows are used as two electrodes of the high-voltage assembly, which is made possible by a metallic coating which entirely covers the inner and outer sides of the windows except for a central area to let the laser beams in and out of the cell. This allows very efficient application of the electric field, up to 2kV∕cm in a rather dense superheated vapor, even when significant photoemission takes place at the windows during pulsed laser irradiation. The body of the cell is made of sapphire or alumina ceramic to prevent large currents resulting from surface conduction observed in cesiated glass cells. The technique used to attach the monocrystalline sapphire windows to the cell body causes minimal stress birefringence in the windows. In addition, reflection losses at the windows can be made very small. The vapor cell operates with no buffer gas and has no magnetic part. The use of this kind of cell has resulted in an improvement of the signal-to-noise ratio in the measurement of parity violation in cesium vapor underway at ENS, Paris. The technique can be applied to other situations where a brazed assembly would give rise to unacceptably large birefringence in the windows.
Scanning probe microscopes go video rate and beyond
Authors: Rost M. J. , Crama L. , Schakel P. , van Tol E. , van Velzen-Williams G. B. E. M. , Overgauw C. F. , ter Horst H. , Dekker H. , Okhuijsen B. , Seynen M. , Vijftigschild A. , Han P. , Katan A. J. , Schoots K. , Schumm R. , van Loo W. , Oosterkamp T. H. , Frenken J. W. M.
Published: April 2005

In this article we introduce a, video-rate, control system that can be used with any type of scanning probe microscope, and that allows frame rates up to 200images∕s. These electronics are capable of measuring in a fast, completely analog mode as well as in the more conventional digital mode. The latter allows measurements at low speeds and options, such as, e.g., atom manipulation, current–voltage spectroscopy, or force–distance curves. For scanning tunneling microscope (STM) application we implemented a hybrid mode between the well-known constant-height and constant-current modes. This hybrid mode not only increases the maximum speed at which the surface can be imaged, but also improves the resolution at lower speeds. Acceptable image quality at high speeds could only be obtained by pushing the performance of each individual part of the electronics to its limit: we developed a preamplifier with a bandwidth of 600kHz, a feedback electronics with a bandwidth of 1MHz, a home-built bus structure for the fast data transfer, fast analog to digital converters, and low-noise drivers. Future improvements and extensions to the control electronics can be realized easily and quickly, because of its open architecture with its modular plug-in units. In the second part of this article we show our high-speed results. The ultrahigh vacuum application of these control electronics on our (UHV)-STM enabled imaging speeds up to 0.3mm∕s, while still obtaining atomic step resolution. At high frame rates, the images suffered from noticeable distortions, which we have been able to analyze by virtue of the unique access to the error (dZ) signal. The distortions have all been associated with mechanical resonances in the scan head of the UHV-STM. In order to reduce such resonance effects, we have designed and built a scan head with high resonance frequencies (⩾64kHz), especially for the purpose of testing the fast electronics. Using this scanner we have reached video-rate imaging speeds up to 200frames∕s (5ms∕image), while still obtaining atomically resolved structures.
Setups for simultaneous measurement of isotherms and adsorption heats
Authors: Moreno Juan Carlos , Giraldo Liliana
Published: April 2005

A unit for the simultaneous measurement of isotherms and heats of adsorption was designed and built, and some of the results obtained are presented here. For this purpose, a Calvet heat-conducting microcalorimeter was developed and connected to a gas volumetric unit built to record adsorption isotherms. The microcalorimeter was electrically calibrated to establish its sensitivity and reproducibility, obtaining K=15.12±0.32WV−1. Additionally, the equipment was tested using the heat of neutralization for the tris-(hydroxmethyl)-aminomethane-HCL system, obtaining ΔH=−30.92±0.03kJmol−1. The unit was assembled to obtain adsorption isotherms and the corresponding heats of adsorption, from which Gibbs free energy was deduced.
Simultaneous static and dynamic light scattering approach to the characterization of the different fibrin gel structures occurring by changing chloride concentration
Authors: Papi Massimiliano , Arcovito Giuseppe , De Spirito Marco , Amiconi Gino , Bellelli Andrea , Boumis Giovanna
Published: April 2005

The structure of fibrin fibers has been investigated by simultaneous elastic and dynamic light scattering measurements. This approach allows the recovery of reliable structural parameters of the fibrin fibers while checking for the reliability of the necessarily ab initio assumptions on some nonexperimentally accessible parameters. The number of protofibrils per fiber section, N, related to the fiber diameter, and the gel mass fractal dimension Dm are obtained. Since the fiber size is largely controlled by ions in the gelling solution, a detailed characterization of the fiber structure formed by changing Cl− concentration is given. While N values decrease from 6000 to 1.5 protofibrils per fiber section, going from 0 to 300 mM in CCl−,Dm increases from 1 to 1.8. This means that the overall gel structure is affected by Cl−, being the fiber size decreased and branch points per unit volume increased.
Stabilization of a chaotic laser and quenching
Authors: Lee Dae-Sic , Ryu Jung-Wan , Park Young-Jai , Kye Won-Ho , Kurdoglyan Michael S. , Kim Chil-Min
Published: April 2005

We experimentally stabilize a chaotic output of a diode-laser-pumped Nd:yttrium–aluminum–garnet laser by using oscillation quenching. When the chaotic laser is mutually coupled with a Rössler oscillator that is implemented by an electronic circuit, both chaotic systems are stabilized to steady states. We experimentally study the route to the steady states as the coupling strength increases, and numerically confirm the route by coupling Lorenz and Rössler oscillators mutually.
Single molecule spectrum of rhodamine 6G on highly oriented pyrolytic graphite
Authors: Uehara Y. , Ushioda S.
Published: April 2005

We have measured the scanning tunneling microscope (STM) light emission spectrum of a single molecule of rhodamine 6G (R6G) adsorbed on highly oriented pyrolytic graphite (HOPG). Since the HOPG substrate radiates no STM light, we have succeeded in observing the spectrum radiated by R6G alone. The spectrum agrees well with the photoluminescence spectrum of R6G on HOPG with the exception of two structures that may arise from a triplet state whose transition is forbidden in photoluminescence. Based on this agreement, we have determined the STM light emission mechanism of adsorbed R6G.
Evolution of ferromagnetic circular dichroism coincident with magnetization and anomalous Hall effect in Co-doped rutile TiO2
Authors: Toyosaki H. , Fukumura T. , Yamada Y. , Kawasaki M.
Published: April 2005

Magnetic circular dichroism (MCD) of rutile Ti1−xCoxO2−δ is systematically examined with various x and δ to reveal a phase diagram for the appearance of ferromagnetism at higher carrier concentration and Co content. The phase diagram exactly matches with that determined from anomalous Hall effect (AHE). The magnetic field dependence of MCD also shows good coincidence with those of the magnetization and AHE. The coincidence of these independent measurements strongly suggests single and intrinsic ferromagnetic origin.
In vitro assembly and GTP hydrolysis by bacterial tubulins BtubA and BtubB
Authors: Sontag Christopher A. , Staley James T. , Erickson Harold P.
Published: April 2005

Arecent study identified genuine tubulin proteins, BtubA and BtubB, in the bacterial genus Prosthecobacter. We have expressed BtubA and BtubB in Escherichia coli and studied their in vitro assembly. BtubB by itself formed rings with an outer diameter of 35–36 nm in the presence of GTP or GDP. Mixtures of BtubB and BtubA formed long protofilament bundles, 4–7 protofilaments wide (20–30 protofilaments in the three-dimensional bundle). Regardless of the starting stoichiometry, the polymers always contained equal concentrations of BtubA and BtubB, suggesting that BtubA and B alternate along the protofilament. BtubA showed negligible GTP hydrolysis, whereas BtubB hydrolyzed 0.40 mol GTP per min per mol BtubB. This GTPase activity increased to 1.37 per min when mixed 1:1 with BtubA. A critical concentration of 0.4–1.0 μM was indicated by light scattering experiments and extrapolation of GTPase versus concentration, thus suggesting a cooperative assembly mechanism.
LL5β
Authors: Kishi Masashi , Kummer Terrance T. , Eglen Stephen J. , Sanes Joshua R.
Published: April 2005

In both neurons and muscle fibers, specific mRNAs are concentrated beneath and locally translated at synaptic sites. At the skeletal neuromuscular junction, all synaptic RNAs identified to date encode synaptic components. Using microarrays, we compared RNAs in synapse-rich and -free regions of muscles, thereby identifying transcripts that are enriched near synapses and that encode soluble membrane and nuclear proteins. One gene product, LL5β, binds to both phosphoinositides and a cytoskeletal protein, filamin, one form of which is concentrated at synaptic sites. LL5β is itself associated with the cytoplasmic face of the postsynaptic membrane; its highest levels border regions of highest acetylcholine receptor (AChR) density, which suggests a role in “corraling” AChRs. Consistent with this idea, perturbing LL5β expression in myotubes inhibits AChR aggregation. Thus, a strategy designed to identify novel synaptic components led to identification of a protein required for assembly of the postsynaptic apparatus.
Multiple angiopoietin recombinant proteins activate the Tie1 receptor tyrosine kinase and promote its interaction with Tie2
Authors: Saharinen Pipsa , Kerkelä Katja , Ekman Niklas , Marron Marie , Brindle Nicholas , Lee Gyun Min , Augustin Hellmut , Koh Gou Young , Alitalo Kari
Published: April 2005

The Tie1 receptor tyrosine kinase was isolated over a decade ago, but so far no ligand has been found to activate this receptor. Here, we have examined the potential of angiopoietins, ligands for the related Tie2 receptor, to mediate Tie1 activation. We show that a soluble Ang1 chimeric protein, COMP-Ang1, stimulates Tie1 phosphorylation in endothelial cells with similar kinetics and angiopoietin dose dependence when compared with Tie2. The phosphorylation of overexpressed Tie1 was weakly induced by COMP-Ang1 also in transfected cells that do not express Tie2. When cotransfected, Tie2 formed heteromeric complexes with Tie1, enhanced Tie1 activation, and induced phosphorylation of a kinase-inactive Tie1 in a ligand-dependent manner. Tie1 phosphorylation was also induced by native Ang1 and Ang4, although less efficiently than with COMP-Ang1. In conclusion, we show that Tie1 phosphorylation is induced by multiple angiopoietin proteins and that the activation is amplified via Tie2. These results should be important in dissecting the signal transduction pathways and biological functions of Tie1.
Disulfide bridge formation between SecY and a translocating polypeptide localizes the translocation pore to the center of SecY
Authors: Cannon Kurt S. , Or Eran , Clemons William M. , Shibata Yoko , Rapoport Tom A.
Published: April 2005

During their biosynthesis, many proteins pass through the membrane via a hydrophilic channel formed by the heterotrimeric Sec61/SecY complex. Whether this channel forms at the interface of multiple copies of Sec61/SecY or is intrinsic to a monomeric complex, as suggested by the recently solved X-ray structure of the Methanococcus jannaschii SecY complex, is a matter of contention. By introducing a single cysteine at various positions in Escherichia coli SecY and testing its ability to form a disulfide bond with a single cysteine in a translocating chain, we provide evidence that translocating polypeptides pass through the center of the SecY complex. The strongest cross-links were observed with residues that would form a constriction in an hourglass-shaped pore. This suggests that the channel makes only limited contact with a translocating polypeptide, thus minimizing the energy required for translocation.
Cell–cell Interaction Underlies Formation of Fluid in the Male Reproductive Tract of the Rat
Authors: Cheung King-ho , Leung George P.H. , Leung Matthew C.T. , Shum Winnie W.C. , Zhou Wen-liang , Wong Patrick Y.D.
Published: April 2005

The epithelia lining the epididymides of many species consists of several cell types. We have provided evidence that the basal cells are essential to the integrated functions of the epithelium. Basal cells, but not principal cells, and other cells in the epididymis express TRPC3 and COX-1. We have isolated basal cells from intact rat epididymis using antibody-coated Dynabeads and subjected them to whole-cell patch-clamp measurement of nonselective cation channel activity, a feature of TRPC3 protein, and Fluo-3 fluorescence measurement of intracellular Ca2+ concentration. The results show that a nonselective cation current blockable by La3+ (0.1 mM), Gd3+ (0.1 mM), or SKF96365 (20 μM) could be activated by lysylbradykinin (200 nM). In cells loaded with Fluo-3, addition of lysylbradykinin (100 nM) caused a sustained increase of intracellular Ca2+. This effect was blocked by Gd3+ (0.1 mM) or SKF96365 (20 μM) and was not observed in Fluo-3–loaded principal cells. Stimulation of basal cell/principal cell cocultures with lysylbradykinin (200 nM) evoked in principal cells a current with CFTR-Cl− channel characteristics. Isolated principal cells in the absence of basal cells did not respond to lysylbradykinin but responded to PGE2 (100 nM) with activation of a CFTR-like current. Basal cells, but not principal cells, released prostaglandin E2 when stimulated with lysylbradykinin (100 nM). The release was blocked by SKF96365 (20 μM) and BAPTA-AM (0.05 or 0.1 mM). Confluent cell monolayers harvested from a mixture of disaggregated principal cells and basal cells responded to lysylbradykinin (100 nM) and PGE2 (500 nM) with an increase in electrogenic anion secretion. The former response was dependent on prostaglandin synthesis as piroxicam blocked the response. However, cell cultures obtained from principal cells alone responded to PGE2 but not to bradykinin. These results support the notion that basal cells regulate principal cells through a Ca2+ and COX signaling pathway.
Consistent Rationalizability
Authors: Bossert Walter , Sprumont Yves , Suzumura Kotaro
Published: April 2005

Consistency of a binary relation requires any preference cycle to involve indifference only. It has been shown that consistency is necessary and sufficient for the existence of an ordering extension of a binary relation. It is therefore of interest to examine the rationalizability of choice functions by means of consistent relations. We describe the logical relationships between the different notions of rationalizability obtained if reflexivity or completeness are added to consistency. All but one such notion are characterized for general domains, and all are characterized for domains that contain all two‐element subsets of the universal set.