bluuebunny/crossref_metadata_2025 huggingface dataset:
Sample-rotation mechanism for an ultralow-temperature cryostat
Authors: Roach Pat R. , Hilleke R. O.
Published: July 2002

We have developed a mechanism for precisely rotating the nuclear demagnetization stage and sample attached to it through an angle of up to 60° while keeping the temperature below 100 mK.
High-temperature, alkali–rare-gas optical cell
Authors: Johnson D. E. , Eden J. G.
Published: July 2002

A new type of optical cell is described which is designed specifically for work with alkali– rare-gas mixtures. Comprised of commercially available components, the cell is capable of operating at 950 K and rare-gas pressures greater than an atmosphere.
Method to compensate laser fluctuation in photon correlation spectroscopy
Authors: Ohbayashi K. , Kohno T. , Fukino Y. , Terui G.
Published: July 2002

A method to compensate the laser power fluctuation in the photon correlation spectroscopy has been developed. In the method, as the key TTL IC element, rate multipliers are used to modulate the sequential digital photoelectron pulses by the parallel digital signal which is processed to be proportional to the inverse of the incident laser intensity. Details of the circuit design are given. To show the usefulness of the method, a case is illustrated in which the ac line noise is compensated in the observation of the Brownian motion of polystyrene latex spheres suspended in water. The bandwidth of the method is estimated to be about 180 kHz.
Measurement of the errors in two radial diffraction gratings by their mutual intercomparison
Authors: Barnes T. H.
Published: July 2002

Precision measurements of the mounting and ruling errors of two 32400 line radial gratings are described. The measurements were made by automatically intercomparing the gratings as they rotated, using ac moiré fringe techniques.
Two-dimensional laser-induced fluorescence-detection system for measurements of number density profiles of seed alkali atoms in MHD combustion gas plasmas
Authors: Watanabe Y. , Ikegami T. , Ueno T. , Masuda M. , Akazaki M.
Published: July 2002

A thermally assisted laser-induced fluorescence (LIF) detection system is developed to measure two-dimensional spatial profiles of number density of alkali atoms seeded in an open-cycle MHD generator, especially in the boundary layer on channel electrodes. The spatial resolution of this system is evaluated to be 1.3 mm. To assess the system, the LIF intensity from Na atoms used as a seed tracer is measured in a laminar air-acetylene flame. The detected spatial profiles of the intensity show good agreement with those of the number density of sodium atoms measured by the spectral line absorption method. The LIF intensity near the surface of a cooled metal piece placed in the acetylene flame is also measured with this system as a preliminary experiment for applying it to the boundary layer on MHD channel electrodes.
Lithium-free scintillation glasses for fast-neutron detection
Authors: Smith J. R. , Fisher R. K. , Leffler J. S.
Published: July 2002

In this article, we present observed characteristics of new lithium-free scintillation glasses which have been developed to make time-resolved measurements of the 14-MeV neutron flux from deuterium plasmas. These measurements will yield information on the burnup of tritons in today’s deuterium plasmas and are needed to better predict the confinement and slowdown of alpha particles in future D–T burning plasmas. The new glasses were formulated to have good detection efficiency for 14-MeV neutrons, and yet be insensitive to 2.5-MeV and lower-energy neutrons. The glass response to alpha, gamma, and neutron radiation is shown. The intrinsic neutron detection efficiency of the scintillation glass is seen to increase significantly as a function of neutron energy, providing the necessary discrimination against low-energy neutrons. We discuss the reactions which determine the glass neutron response and suggest that this response is dominated at higher neutron energies by gamma rays created by neutrons inelastically scattering from oxygen present in the glass. For high-energy neutron detection in the presence of excessive background gamma radiation, we discuss a new coincidence configuration of lithium-free scintillation glass with NE213 liquid scintillator.
Development of a high-sensitivity, computer-controlled titration calorimeter
Authors: Baisden P. A. , Grant P. M. , Kinard W. F.
Published: July 2002

A highly sensitive, adiabatic titration calorimeter controlled by a personal computer is described. Operation of the entire calorimetric titration is automated, including the thermoelectric offset of the heat of stirring, the electrical calibration of the heat capacity, the addition of titrant, and the measurement of the heat of reaction. The average uncertainty in heat measurements was ≊±0.003 J for titrant additions generating 0.025 to 1.0 J of heat change in a 50-ml sample. Calibration of the calorimeter using tris-(hydroxymethyl) aminomethane [TRIS] gave excellent agreement with previously published values.
Instrument/procedure which prepares a fresh surface of highly oriented pyrolytic graphite in a closed-cycle helium refrigerator
Authors: Graham Daniel J. , Victor Robert , Wise Carl
Published: July 2002

An instrument/procedure which prepares a fresh surface of highly oriented pyrolytic graphite in a closed-cycle helium refrigerator is described. The instrument and procedure assist in low-temperature studies of the laser-induced fluorescence of molecules adsorbed to graphite surfaces.
Method of reducing temperature gradients in contained gas flows and its application to the control of sample temperatures in a gas flow at 300 °C
Authors: Kemp R. C.
Published: July 2002

A simple method of reducing temperature gradients in contained gas flows is described. The method is used to reduce the temperature gradient within a contained gas flow at 300 °C by a factor of about 100 and applied to the control of the temperature of a sample in the cavity of an EPR spectrometer.
Stoichiometry and thickness variation of YBa2Cu3O7−x in off-axis pulsed laser deposition
Authors: Trajanovic Z. , Senapati L. , Sharma R. P. , Venkatesan T.
Published: July 2002

We studied the dependence of the thickness and stoichiometry of YBa2Cu3O7−x deposited in an off-axis pulsed laser deposition geometry on the background oxygen pressure and the distance from the target. We observe a biregional drop-off in thickness with increasing axial distance, with the border between the two regions at 3–4 cm away from the target. The thickness was proportional to the deposition pressure raised to the 2/3 power, at axial distances greater than 4 cm. Atomic force microscope studies of the two regions showed the density of micron sized particles to be 2–5×104/cm2 within the first region (closer to the target) with no such particles in the second region. The stoichiometric composition did not exhibit this biregional dependence. At an optimum oxygen pressure of 200 mTorr, we were able to obtain a stoichiometrically uniform region as large as 3×4 cm2.
The double-ring electrodynamic balance for microparticle characterization
Authors: Davis E. James , Buehler Mark F. , Ward Timothy L.
Published: July 2002

A simple form of the electrodynamic balance, suitable for a wide range of microparticle measurements, is described and analyzed. The ac electrode of the device consists of a pair of parallel rings, and the dc endcaps are either simple disks or they can be eliminated entirely by applying suitable dc bias voltages to the rings. The stability characteristics of the device are determined by extension of well-established stability theory, and experiments are compared with that theory. The device is particularly well-suited for detection of radioactive aerosols, for it has significant advantages over the bihyperboloidal device for radioactivity measurement. The detection of radioactivity levels of less than 20 pCi is feasible. Coupled with a Raman spectrometer the balance serves as a stable ‘‘platform’’ for the study of the chemistry of microparticles, and both qualitative and quantitative analysis of microdroplet chemistry are demonstrated for binary droplets of 1-octadecene and 1-bromoctadecane.
Monosize droplet stream generator
Authors: Stricker J. , Sofer D.
Published: July 2002

A simple low-cost, uniform-sized liquid droplet generator is described. The generator is based on the breakup phenomenon of a liquid jet flowing out of a capillary by imposing mechanical disturbances on it. The generator enables the injection of droplets into systems where injection is difficult, with minimum disturbance. It has been shown, theoretically and experimentally, that scattering of the droplets around the mean trajectory due to capillary vertical vibrations is negligible over a wide range of disturbance frequencies. The performance of the droplet generator is considerably deteriorated around the resonance frequencies of the capillary.
Ultrahigh-vacuum furnace for sintering studies of ultrafine ceramic particles
Authors: Bonevich John E. , Teng Mao-Hua , Johnson D. Lynn , Marks Laurence D.
Published: July 2002

An ultrahigh-vacuum (UHV) furnace has been designed and constructed for the purpose of investigating the sintering behavior of ultrafine ceramic particles. The UHV furnace has three main chambers for particle production, sintering, and collection with additional facilities for an UHV transfer system. The furnace system achieves a base pressure of 4 × 10−7 Pa through the use of turbomolecular and ion pumps. The ultrafine particles of aluminum oxide are produced by the arc discharge method resulting in the formation of highly faceted particles in the size range of 20–50 nm. The particles are then carried into the tube furnace by a flowing gas stream where they sinter at elevated temperatures. The sintered samples are collected onto a specimen cartridge which is then transported under vacuum conditions to an UHV high-resolution electron microscope for structural characterization. The unique feature of this UHV furnace system is that one is able to perform sintering studies in a clean environment thereby minimizing the influence of contaminating species on the sintering behavior.
Fluid density measurement using transducers based upon loudspeaker technology
Authors: Blake-Coleman B. C. , Fryer P.
Published: July 2002

By selecting particular types of currently available plastic coned miniature loudspeakers, and appropriately configuring each device with a suitable closed oscillatory circuit, it is possible to construct a liquid density transducer. Whereas current resonant densitometers operating in either the transverse, radial, torsional, or longitudinal resonance mode, are subject to relatively costly manufacturing and calibration procedures, the present development promises a very low-cost, easily calibrated, high-resolution [10−4] instrument with potentially very wide applications hitherto unavailable because of cost and size limitations. We show that this essentially simple apparatus embodies all the physical and operational requirements of established instruments.
Recent developments in SHADOW
Authors: Welnak C. , Anderson P. , Khan M. , Singh S. , Cerrina F.
Published: July 2002

SHADOW is the ray-tracing program of choice for the synchrotron radiation community. The program can raytrace essentially any x-ray optical system and predict image shapes and intensities with great accuracy. Several new extensions have been included. The optical database has been extended to the 10-eV region by inclusion of the new data from the Center for X-ray Optics, Lawrence Berkeley Lab. Two major physical models have been added to the code; the first being a surface roughness model to add to the error surface option. The second addition is to the crystal model. It now includes an asymmetric crystal, a model of a mosaic crystal, and a model for the Johannson case of a figured, bent crystal. Until now, SHADOW has operated under Digital Equipment Corporation’s (DEC) VMS operating system (VMS). The advent of powerful RISC workstations has prompted a porting to the UNIX environment, opening a multiplatform operability. So far, the code has been validated for Ultrix (DEC) and is undergoing beta testing for Sun operating system and IBM Corporation’s AIX operating system. Porting to a 386/486 platform is also considered. Finally, an optimization algorithm based on a combination of the Simplex and simulated annealing is being implemented.
Force feedback surface force apparatus: Principles of operation
Authors: Stewart A. M. , Parker J. L.
Published: July 2002

The principles of operation of a force feedback surface force apparatus are described. A magnetic force transducer and a bimorph displacement sensor are connected in a servo loop. The dynamic behavior of the system is analyzed and the effect of eddy currents on the frequency response of the magnetic field is discussed. The apparatus has several advantages over more traditional force measuring techniques. Cantilever instability associated with the measurement of attractive forces is reduced and the apparatus may be used for hydrodynamic measurements. A resonance technique for measuring the spring constant is also described.
Pre-preionization of a long optical pulse magnetic-spiker sustainer XeCl laser
Authors: Taylor R. S. , Leopold K. E.
Published: July 2002

A novel preionization technique which uses a surface corona discharge to produce preionization electrons for the controlled low jitter breakdown of a main corona-gap preionizer is described. The pre-preionization scheme has been used to reliably preionize a long optical pulse (450 ns full width at half-maximum) XeCl laser. The laser excitation circuit is a new version of the overshoot mode of magnetic-spiker sustainer excitation specifically designed to be simple, reliable, and capable of high repetition rate operation.
Optimization of a SQUID flux transformer coupled to ferromagnetic cores for registering the magnetic moment of a two-dimensional sample
Authors: Enichlmair H. , Thumfart D. , Krenn H. , Preis K.
Published: July 2002

A nonconductive ferromagnetic core is inserted into the pickup coil of a superconducting flux transformer which is matched to a 19 MHz rf-superconducting quantum interference device (SQUID). We demonstrate that the flux sensitivity of the SQUID is enhanced by a factor of 2–2.7 with respect to a comparable air core flux transformer for signals up to 80 kHz. The equivalent flux noise of 2×10−3 Φ0/√Hz is of the same magnitude as for a conventional transformer and associated with external fluctuations from vibrations and from the superconducting shields. We take as a source a very thin spin sheet like that which is formed by spin-polarized electrons excited in thin semiconducting epitaxial layers in a photomagnetization experiment. Under experimental conditions (changes of the irradiated area, absorption depth, beam deflections) one expects distinct distributions of spins in the sheet and corresponding variations of the flux depicted by the flux transformer. To detect the magnetic moment of a certain number (≳1010) of spins the proportionality between the detected flux Φ and the excited total magnetic moment m of the spins is checked. We compare various configurations of spin sheets of distinct size and locations beginning with an air core flux transformer. The flux threading the pickup loop is then more efficiently coupled by employing a ferromagnetic shell-shaped core with an axial hole (for the entrance of the light beam in photomagnetization studies). Thus flux line patterns are simulated for various sizes of cores, different permeabilities, and different air slits (where the sample is located). Due to additional degrees of freedom of design parameters a simultaneous increase of sensitivity is achieved together with a response Φ∝m. Simulations and measurements are compared. The ultimate resolution of the magnetic moment is Δm=10−13 A m2/√Hz.
Application of new synchrotron powder diffraction techniques to anomalous scattering from glasses
Authors: Beno M. A. , Knapp G. S. , Armand P. , Price D. L. , Saboungi M.-L.
Published: July 2002

We have applied two synchrotron powder diffraction techniques to the measurement of high quality anomalous scattering diffraction data for amorphous materials. One of these methods, which uses a curved perfect crystal analyzer to simultaneously diffract multiple powder lines into a position sensitive detector has been shown to possess high resolution, low background, and very high counting rates. This data measurement technique provides excellent energy resolution while minimizing systematic errors resulting from detector nonlinearity. Anomalous scattering data for a Cesium Germanate glass collected using this technique will be presented. The second powder diffraction technique uses a flat analyzer crystal to deflect multiple diffraction lines out of the equatorial plane. Calculations show that this method possesses sufficient energy resolution for anomalous scattering experiments when a perfect crystal analyzer is used and is experimentally much simpler. Future studies will make use of a rapid sample changer allowing the scattering from the sample and a standard material (a material not containing the anomalous scatterer) to be measured alternately at each angle, reducing systematic errors due to beam instability or sample misalignment.
TORE SUPRA fast reciprocating radio frequency probea)
Authors: Thomas C. E. , Harris J. H. , Haste G. R. , Kwon M. , Goulding R. H. , Hoffman D. J. , Saoutic B. , Becoulet A. , Fraboulet D. , Beaumont B. , Kuus H. , Ladurelle L. , Pascal J. Y.
Published: July 2002

A fast reciprocating ion cyclotron range of frequencies (ICRF) probe was installed and operated on TORE SUPRA during 1992/1993. The body of the probe was originally used on the ATF experiment at Oak Ridge National Laboratory. The probe was adapted for use on TORE SUPRA, and mounted on one of the two fast reciprocating probe mounts. The probe consists of two orthogonal single-turn wire loops, mounted so that one loop senses toroidal rf magnetic fields and the other senses poloidal rf magnetic fields. The probe began operation in June, 1993. The probe active area is approximately 5 cm long by 2 cm, and the reciprocating mount has a slow stroke (5 cm/s) of 30 cm and a fast stroke (1.5 m/s) of about 10 cm. The probe was operated at distances from the plasma edge ranging from 30 to −5 cm (i.e., inside the last closed flux surface). The probe design, electronics, calibration, data acquisition, and data processing are discussed. First data from the probe are presented as a function of ICRF power, distance from the plasma, loop orientation, and other plasma parameters. Initial data show parametric instabilities do not play an important role for ICRF in the TORE SUPRA edge and scrape-off-layer (SOL) plasmas. Additionally it is observed that the probe signal has little or no dependence on position in the SOL/plasma edge.
Ultrasonic deformation of crystals with frequencies near 100 kHz
Authors: Klimm D.
Published: July 2002

An experimental setup is presented which allows the performance of high amplitude (σ≤75 MPa) ultrasonic treatment of materials at frequencies near 100 kHz and at temperatures up to 750 K. Resonant vibrations of a quartz piezoelectric transducer permit the investigation of the effect of different levels of mechanical stress in one certain sample. During ultrasonic treatment, measurements of amplitude dependent internal friction can be performed.
A new high resolution digital spectrometer for radioastronomy applications
Authors: Montebugnoli S. , Bortolotti C. , Buttaccio S. , Cattani A. , D’Amico N. , Grueff G. , Maccaferri A. , Maccaferri G. , Orfei A. , Roma M. , Tuccari G. , Tugnoli M.
Published: July 2002

We describe a real-time, fast Fourier transform digital spectrometer, based on the new Sharp LH9124 chip. The system is fully programable, and in the present configuration it can measure the power spectrum of an incoming signal with a bandwidth of up to 20 MHz, a time resolution of 30 ms, a frequency resolution of up to 128 K channels, and a temporal duty cycle of 45% at 6 MHz bandwidth. An upgrade of the spectrometer is in progress, which will allow a duty cycle (efficiency) of 100% at 12 MHz bandwidth (single channel) or 6 MHz (dual channel). This new approach to the spectrum analysis will open new observational capabilities in radio astronomy and other fields.
A new cluster source for the generation of binary metal clusters
Authors: Heiz U. , Vayloyan A. , Schumacher E.
Published: July 2002

A new thermal, supersonic cluster source for the investigation of binary metal cluster formation at thermodynamically well-defined expansion conditions is described. The source consists of two separately heatable cartridges. A first cartridge can be heated up to 1220 K and the second high temperature cartridge reaches maximal temperatures of 1800 K. A temperature difference of 1000 K between the two cartridges can be maintained for at least 3 h. Clustering occurs upon supersonic expansion from a conical nozzle. This cluster source has two main applications: (a) the generation of mixed metal clusters and (b) the investigation of pure metal clusters at various expansion conditions. The performance and applications of this source are illustrated by presenting results of the heterocluster formation of mixed sodium/gold and sodium/silver heteroexpansions. In addition, the influence of the oven parameters on the internal temperatures of the generated clusters is illustrated with the example of Na2.
A novel and sensitive Faraday-type magnetometer for the field range from 0 to 12 T
Authors: Zhang D. , Probst Ch. , Andres K.
Published: July 2002

A Faraday-type magnetometer is described in which the magnetic force is measured capacitively by monitoring the displacement of a spring-suspended quartz sample holder. A double gradient coil is used in order to compensate the force on the empty sample holder, thus minimizing the background signal. The magnetometer can be used at any temperature down to 1.4 K and has an ultimate sensitivity for magnetic moments of 2×10−6emu (G cm3).
Comparative results for germanium and platinum thermometer calibration test data approximation
Authors: Bogdanova Nina B. , Terzijska Bonka M.
Published: July 2002

Three-interval approximations of T=f(R) and R=g(T) functions for germanium resistance thermometer (GRT) (1.4–5.7) K; (5.7–27.4) K; (27.4–100) K and platinum resistance thermometer (PRT) (14–31) K; (31–95) K; (95–325) K is carried out, using a weighted orthonormal polynomial expansion method (OPEM). A two-interval OPEM approximation of T(R)and R(T) functions for PRT (14–70)K; (70–325) K is also presented. Our OPEM approximation of the T(R) function for the GRT and PRT, compared with other descriptions, based on Chebyshev or ordinary polynomials with the same calibration test data is discussed also. The results, shown in tables and figures, demonstrate the reliability and the advantages of the proposed OPEM, in cryogenic thermometry.
A 10 kg transportable flexure-strip beam balance
Authors: Shoemaker Gary H. N. , Robel Robb , Lewis Charles , Ramonda Tom
Published: July 2002

The design and construction of a 10 kg transportable flexure-strip beam balance to be used in searches of composition-dependent forces and/or tests of the weak equivalence principle is discussed. The results of the instrument performance presented herein are based upon operation of the balance under simulated experimental conditions that require our balance maintains a high level of sensitivity (i.e., resolution associated with the standard deviation of our data sample) during a continuous measurement process which alternates between two different elevations, a unique application for a beam-balance measuring device. Our results indicate that this balance is the most sensitive transportable balance used in measurement in the 10 kg load capacity range, obtaining a measurement sensitivity of about 15–20 μGal. Also, we have established that our method of balance transport affects the sensitivity less than 15 μGal at the 95% confidence level. An increase in sensitivity of approximately 30 would be required to establish new upper limits on composition-dependent forces in the interaction range of most interest.
A two-dimensional flow sensor using integrated silicon spreading-resistance temperature detectors
Authors: Baiyong Liu , Lai P. T. , Xueren Zheng , Zhaohui Wu , Bin Li
Published: July 2002

A simple silicon two-dimensional (2D) flow sensor for the measurement of both flow direction and speed is described. By integrating two couples of silicon spreading-resistance temperature (SRT) sensors in two perpendicular directions on the surface of a silicon chip, this sensor can detect flow speed and flow direction φ in a full range of 360°. Experimental results confirm theoretical analysis that the output of the sensor increases with the square root of the flow velocity, and the outputs in the two perpendicular directions are proportional to sin φ and cos φ, respectively. The effects of sensor layout are also discussed. With complete oxide isolation for the SRT sensors, the flow sensor could achieve higher sensitivity by operating above the intrinsic temperature of silicon (∼150 °C), or could be used to detect fluid flow at a temperature as high as 300 °C.
The archiving system of the Virgo antenna for gravitational wave detection
Authors: Barone Fabrizio , Garufi Fabio , Milano Leopoldo , Mours Benoit
Published: July 2002

In this article we describe the hardware and software architecture of the prototypes of the archiving system of the very long base line interferometric Virgo antenna for gravitational wave detection. The characteristics which make this system very interesting and innovative are not only its performances but also the modularity of the architecture which makes it easier to both follow the progress of the technology without dramatic changes of the hardware and software architecture and to match the requirements according to the Virgo needs. This prototype has been tested in the data acquisition of the 3 m pendularly suspended and evacuated Michelson interferometer prototype which is operational in Naples and in the monitoring of physical environmental quantities, like electromagnetic noise, acoustic noise, etc., necessary for the correlation of the output of the interferometer with the environment.
Improved energy resolution for scintillator based gamma-ray detectors obtained using a CsI(Tl)/Si-PIN detector
Authors: Patt B. E. , Iwanczyk J. S.
Published: July 2002

This note reports improved energy resolution measured using a gamma-ray detector consisting of a 2 mm×2 mm×4 mm long CsI(Tl) scintillator coupled to a 2 mm×2 mm photodiode. Energy resolution of 7.5% full width at half-maximum (FWHM) was obtained for the 122 keV photopeak of Co-57. Energy resolution of 35% FWHM was obtained for the 5.9 keV photopeak of Fe-55.
Coded-aperture x- or γ-ray telescope with least-squares image reconstruction. III. Data acquisition and analysis enhancements
Authors: Kohman Truman P.
Published: July 2002

The previously described design of a cosmic x- or γ-ray telescope with least-squares image reconstruction has been enhanced to provide for mask-antimask operation. This cancels and eliminates uncertainties in the detector background. The simulations of its operation have been made more realistic by incorporating instrumental blurring of sources. A second-stage least-squares procedure determines the precise positions and total fluxes of point sources responsible for clusters of above-background pixels in the field resulting from the first-stage reconstruction. Another program converts source positions in the image plane to celestial coordinates and vice versa, the image being a gnomic projection of a region of the sky. A complete sky-to-sky simulation of the imaging of a source field is presented. It is demonstrated that the point-spread function of the overall imaging process is essentially perfect.
Rietveld analysis using a laboratory-based high pressure x-ray diffraction system and film-based detection
Authors: Hasegawa Masashi , Badding John V.
Published: July 2002

Rietveld structure refinement using a laboratory-based high pressure x-ray diffraction system described previously and film-based detection is reported. Although there is currently much emphasis on the use of synchrotron radiation and advanced detectors such as imaging plates and position-sensitive detectors for collection of high pressure diffraction data suitable for Rietveld analysis, the results presented here demonstrate that excellent refinements can be performed on data collected at low cost in the laboratory with film-based detection. The diffraction system exhibits an instrumental profile suitable for Rietveld analysis, exhibiting no asymmetry and narrow linewidths.
Simple, linear, and safe light control for laser diodes
Authors: Mariani Tullio , Frediani Carlo , Ascoli Cesare
Published: July 2002

A simple but useful technique for feedback stabilization and modulation of diode lasers is described. The interposition of an optoelectronic coupler between laser diode and feedback amplifier allowed safe circuitry together with good linearity and relatively high speed.
Soft x-ray fluorescence spectrometer using a multilayer interferential transmission plate
Authors: André J.-M.
Published: July 2002

We give the principle of a soft x-ray fluorescence spectrometer based on a multilayer interferential transmission plate. When using photographic films or charge coupled device arrays, the apparatus does not require mechanical displacement. We illustrate the method with the Kα emission line of silicon and aluminum samples.
Application of a new noncryogenic x-ray detector in portable instruments for archaeometric analyses
Authors: Fiorini C. , Longoni A.
Published: July 2002

A new noncryogenic x-ray detection module is proposed for portable instruments used in nondestructive analyses on artistic and archaeological samples. The detection module, based on a silicon drift detector (SDD) cooled by a Peltier element, offers a typical energy resolution better than 160 eV full width at half maximum at 6 keV and 135 eV at 2.3 keV, measured at −15 °C and 2 μs of shaping time. A first prototype of portable energy dispersive x-ray fluorescence spectrometer based on a SDD module and a miniaturized x-ray generator, has been developed. The results of several measurements carried out with the spectrometer in laboratory tests and on works of arts analyzed directly “on-the-field” are here presented.
Photoacoustic procedure for measuring thermal parameters of transparent solids
Authors: Melo W. L. Barros , Faria R. M.
Published: July 2002

An application of photoacoustic technique is developed for determining the thermal diffusivity coefficient and the thermal conductivity of transparent materials. The backing material which supports the sample is made optically opaque, i.e., it entirely absorbs the incident light, and the converted heat diffuses through the sample heating the gas in contact with its opposite surface. The method is illustrated by fitting voltage amplitude and phase signals versus the chopping frequency in the photoacoustic cell, according to a theoretical model of heat diffusion. Thermal parameters obtained for three polymers compare very well with results from the literature.
Net optical gain at 1.53 μm in Er-doped Al2O3 waveguides on silicon
Authors: van den Hoven G. N. , Koper R. J. I. M. , Polman A. , van Dam C. , van Uffelen J. W. M. , Smit M. K.
Published: July 2002

A 4 cm long Er-doped Al2O3 spiral waveguide amplifier was fabricated on a Si substrate, and integrated with wavelength division multiplexers within a total area of 15 mm2. When pumped with 9 mW 1.48 μm light from a laser diode, the amplifier shows 2.3 dB net optical gain at 1.53 μm. The gain threshold was 3 mW. The amplifier was doped with Er by ion implantation to a concentration of 2.7×1020 cm−3. The data agree well with calculations based on a model which includes the effects of cooperative upconversion and excited state absorption. For an optimized amplifier, net optical gain of 20 dB is predicted.
Lock-in technique for measuring friction on a nanometer scale
Authors: Colchero J. , Luna M. , Baró A. M.
Published: July 2002

A method for measuring friction forces on a nanometer scale is described. This method combines a lock-in technique with scanning force and friction microscopy. Essentially, a lock-in amplifier is used to determine the amplitude of the friction loop, which is measured at high frequency. To demonstrate the capability of this method, the dependence of the friction force with normal load is measured and a two dimensional image is presented.
Broadband detection capability of ZnTe electro-optic field detectors
Authors: Wu Q. , Litz M. , Zhang X.-C.
Published: July 2002

We present our measurements of the broadband detection capability of copropagating electro-optic ZnTe field detectors for the characterization of free-space pulsed electromagnetic radiation. To demonstrate ultrawide detection bandwidth, radiation from both gigahertz and terahertz bandwidth pulsed microwave sources has been characterized. The high frequency limitation of the sensor is the first TO phonon resonance (5.31 THz). The ultrashort temporal resolution is demonstrated by the detection of a 177 fs (full width at half-maximum) pulse generated via THz optical rectification in 〈111〉 GaAs.
Comparison of pulsed laser deposition and thermal deposition: Improved layer-by-layer growth of Fe/Cu(111)
Authors: Jenniches H. , Klaua M. , Höche H. , Kirschner J.
Published: July 2002

In the search for a correlation between the magnetism and the microstructure of ultrathin films, straightforward layer-by-layer growth is desirable. The thermal deposition of Fe onto Cu(111), however, does not result in this growth mode. In this letter, we compare the initial growth of Fe on Cu(111) prepared by pulsed laser deposition (PLD) with thermally deposited Fe/Cu(111) using scanning tunneling microscopy (STM). In PLD, from the beginning there is two-dimensional nucleation and growth, in contrast to the initial bilayer nucleation and growth found for thermal deposition. Therefore, it is shown by STM that PLD grown films exhibit greatly improved layer-by-layer growth. The different experimental results are interpreted in terms of the very high deposition rate during PLD.
Interdigital cantilevers for atomic force microscopy
Authors: Manalis S. R. , Minne S. C. , Atalar A. , Quate C. F.
Published: July 2002

We present a sensor for the atomic force microscope (AFM) where a silicon cantilever is micromachined into the shape of interdigitated fingers that form a diffraction grating. When detecting a force, alternating fingers are displaced while remaining fingers are held fixed. This creates a phase sensitive diffraction grating, allowing the cantilever displacement to be determined by measuring the intensity of diffracted modes. This cantilever can be used with a standard AFM without modification while achieving the sensitivity of the interferometer and maintaining the simplicity of the optical lever. Since optical interference occurs between alternating fingers that are fabricated on the cantilever, laser intensity rather than position can be measured by crudely positioning a photodiode. We estimate that the rms noise of this sensor in a 10 hz–1 kHz bandwidth is ∼0.02 Å and present images of graphite with atomic resolution.
Radiative carrier lifetime, momentum matrix element, and hole effective mass in GaN
Authors: Im J. S. , Moritz A. , Steuber F. , Härle V. , Scholz F. , Hangleiter A.
Published: July 2002

By using picosecond time-resolved photoluminescence we have measured the lifetime of excess charge carriers in GaN epitaxial layers grown on sapphire at temperatures up to 300 K. The decay time turns out to be dominated by trapping processes at low excitation levels. The radiative lifetime derived from our data is dominated by free excitons at temperatures below 150 K, but also clearly shows the gradual thermal dissociation of excitons at higher temperatures. From our data, we are able to determine the free exciton binding energy and the free carrier radiative recombination coefficient. By combining these data with optical absorption data, we find the interband momentum matrix element and an estimate for the hole effective mass, which is much larger than previously thought.
Temperature dependence of large positive magnetoresistance in hybrid ferromagnetic/semiconductor devices
Authors: Overend N. , Nogaret A. , Gallagher B. L. , Main P. C. , Henini M. , Marrows C. H. , Howson M. A. , Beaumont S. P.
Published: July 2002

We investigate a new type of magnetoresistance (MR) in which the resistivity of a near-surface two-dimensional electron gas is controlled by the magnetization of a submicron ferromagnetic grating defined on the surface of the device. We observe an increase in resistance of up to ∼1500% at a temperature of 4 K and ∼1% at 300 K. The magnitude and temperature dependence of the MR are well accounted for by a semiclassical theory. Optimization of device parameters is expected to increase considerably the magnitude of the room temperature MR.
Fresnel coefficients of a rough interface
Authors: Lérondel G. , Romestain R.
Published: July 2002

Second-order perturbation theory has been used to compute the optical transfer coefficients of a rough dielectric interface. The derivation proceeds through classical solution of Maxwell’s equations at normal incidence. Reflection and transmission coefficients were first obtained for an interface represented by a sine profile of wave vector G interacting with a planar wave polarized perpendicular to G. Second, the expressions have been generalized to a real rough interface, i.e., the sum of sine profiles, and arbitrary polarization. We discuss the validity of the linear approximation, comparing the reflection calculated by the more general Davies–Bennett formula to that calculated by our formula. It appears that, for most real multilayer systems, this approximation is valid.
Photoluminescence from Si nanocrystals dispersed in phosphosilicate glass thin films: Improvement of photoluminescence efficiency
Authors: Fujii Minoru , Mimura Atsushi , Hayashi Shinji , Yamamoto Keiichi
Published: July 2002

Photoluminescence (PL) from Si nanocrystals (nc-Si) dispersed in phosphosilicate glass thin films was studied. It was found that, at room temperature, the 1.4 eV PL due to the recombination of electron-hole pairs in nc-Si becomes intense as the P concentration increases. At low temperatures, an additional peak related to defects at interfaces between nc-Si and the matrix was observed at about 0.9 eV. In contrast to the 1.4 eV peak, the 0.9 eV peak became weaker with increasing P concentration and almost disappeared at a P concentration of 1.5 mol %. These results suggest that the number of interface defects decreases with increasing P concentration and that this decrease leads to an improvement of the band-edge PL of nc-Si.
Ductility of bulk nanocrystalline composites and metallic glasses at room temperature
Authors: Fan Cang , Inoue Akihisa
Published: July 2002

Mechanical properties of bulk Zr60Cu20Pd10Al10 nanocrystalline composite and Zr55Ni5Cu30Al10 metallic glass were measured by compression tests at room temperature. The Zr60Cu20Pd10Al10 as-quenched alloy obviously exhibits plastic strain while no distinct plastic deformation is recognized in the Zr55Ni5Cu30Al10 metallic glass. Moreover, the plastic strain increased by increasing the volume fraction of nanocrystals and achieved maximum value in the early stage of the nanocrystallization. High-resolution electron microscopy showed that, different from the microstructure of Zr55Ni5Cu30Al10 metallic glass, nanocrystals with main grain sizes of about 2 nm were embedded in the amorphous matrix of the bulk Zr60Cu20Pd10Al10 alloy which showed the maximum plastic strain.
Effect of rotation on stability of suspended sediments
Authors: Chakraborty B. B. , Khattar Dinesh , Khalili A.
Published: July 2002

In this paper we consider the steady sedimentation of a uniform distribution of particles in a uniformly rotating liquid, and examine its stability by solving the set of conservation equations for a two-phase flow. The sixth order algebraic equation in the frequency which results from the perturbation equations is solved numerically. The effects of the variation of the rotation rate, sediment concentration, and vertical wave numbers of small disturbances are discussed and presented graphically.
Simulated structure, dynamics, and vibrational spectra of liquid benzene
Authors: Chelli Riccardo , Cardini Gianni , Procacci Piero , Righini Roberto , Califano Salvatore , Albrecht Andreas
Published: July 2002

A classical molecular dynamics simulation of liquid benzene is performed, using a potential model which allows for full molecular flexibility. The short range intermolecular radial distribution function is on average reminiscent of the crystalline structure, although practically no preferential orientation can be found for the molecules in the first coordination shell. The average cage lifetime and its vibrational dynamics are obtained from appropriate time correlation functions. The intramolecular vibrations are investigated by calculating the vibrational density of states and the infrared and Raman spectra, achieving an excellent agreement with the experimental data. Finally, the dephasing of the ν1(A1g) ring breathing mode and of the ν6(E2g) in-plane bending mode is analyzed on the basis of the Kubo dephasing function. For ν1 mode the Kubo correlation time of 516 fs agrees with the experimental value, and is consistent with a relaxation mechanism involving the cage reorganization. In contrast, ν6 has a practically pure Lorentzian line shape, with a width of 7.16 cm−1 in perfect agreement with the experimental value of 7.2 cm−1.
Viscous dislocation drag in KBr crystals at temperatures of 77–300 K
Authors: Matsokin V. P. , Petchenko G. A.
Published: July 2002

The resonance dislocation absorption of ultrasound in KBr crystals in the frequency region 7.5–217.5 MHz is investigated in the temperature interval 77–300 K. The temperature dependences of the shear modulus G, Debye temperature Θ, dislocation damping coefficient B, and the mean effective length L of a dislocation segment are determined in this temperature interval. The experimentally obtained B(T) curve is compared with the Al’shits–Indenbom theory of dynamic dislocation drag.
Molecular simulation study of water–methanol mixtures in activated carbon pores
Authors: Shevade Abhijit V. , Jiang Shaoyi , Gubbins Keith E.
Published: July 2002

We report a theoretical study of the adsorption behavior of water–methanol mixtures in slit activated carbon micropores. The adsorption isotherms are obtained for a pore of width 2 nm at a temperature of 298 K from grand canonical ensemble Monte Carlo simulations. The water molecules are modeled using the four point transferable intermolecular potential functions (TIP4P) and methanol by the optimized potentials for liquid simulations (OPLS). Carboxyl (COOH) groups are used as active sites on a structured carbon surface. The effect of the relative contributions from dispersion and hydrogen bonding interactions of adsorbates, and of the chemical activation of adsorbents on adsorption behavior is investigated. The adsorption of the mixture components in activated carbon pores occurs by continuous filling, without the sharp capillary condensation observed in graphite pores. Water is preferentially adsorbed over methanol in activated carbon pores for a wide range of pressures, except at lower pressures. The hydrophilic nature of activated carbon pores results in the complexation of both water and methanol molecules with the active sites on the surfaces, leading to bulklike water behavior over the entire pore width. Solvation forces are also calculated as a function of pore size. The negative values found for the solvation force for all pore sizes reflect the hydrophilic interactions of the mixtures with the activated carbon surfaces.
Reactions of laser-ablated aluminum atoms with nitrogen during condensation at 10 K. Infrared spectra and density functional calculations for AlxNy molecular species
Authors: Andrews L. , Zhou M. , Chertihin G. V. , Bare W. D. , Hannachi Y.
Published: July 2002

Laser-ablated aluminum atoms react with dinitrogen on condensation at 10 K to form N3 radicals and the subject molecules, which are identified by nitrogen isotopic substitution, further reactions on annealing, and comparison with isotopic frequencies computed by density functional theory. The major AlN3 product is identified from three fundamentals and a statistically mixed nitrogen isotopic octet pattern. The aluminum-rich Al2N and Al3N species are major products produced on annealing to allow diffusion and further reaction of trapped species. This work provides the first experimental evidence for molecular AlxNy species that may be involved in ceramic film growth.
Basis set approach to the quantum dissipative dynamics: Application of the multiconfiguration time-dependent Hartree method to the spin-boson problem
Authors: Wang Haobin
Published: July 2002

The feasibility of using a basis set approach to the study of quantum dissipative dynamics is investigated for the spin-boson model, a system of two discrete states linearly coupled to a harmonic bath. The infinite Hamiltonian is discretized to a finite number of degrees of freedom. Traditional basis set approach, in a multiconfiguration time-dependent Hartree context, is used to solve the time-dependent Schrödinger equations by explicitly including all the degrees of freedom (“system”+“bath”). Quantities such as the reduced density matrix are then evaluated via a quadrature summation/Monte Carlo procedure over a certain number of time-dependent wave functions. Numerically exact results are obtained by systematically increasing the number of bath modes used to represent the condensed phase environment, as well as other variational parameters (number of basis functions, configurations, etc.). The potential of the current method is briefly discussed.
Josephson properties of transparent tunnel junctions
Authors: Shlapak Yu. V. , Kasatkin A. L. , Rudenko É. M.
Published: July 2002

With allowance for possible deviations of the current–phase relation from the usual sinusoidal dependence, a modified Ferrell–Prange equation is used to examine the steady-state electrodynamics of transparent Josephson junctions in an external magnetic field. It is shown that in this case the penetration of a weak magnetic field into a transparent Josephson junction is generally nonexponential, and the field Hc1 at which vortices arise in transparent junctions and the dependence of the critical current on the magnetic field in them are calculated.
Light-induced reversible optical absorption in single-crystal slabs of yttrium iron garnets
Authors: Doroshenko R. A. , Nadezhdin M. D.
Published: July 2002

An additional increase of the optical absorption is observed when light of intensity greater than 1 W/cm2 acts on single-crystal slabs of yttrium iron garnets. When a sample is subsequently subjected briefly to illumination by IR light of low intensity (∼10 mW/cm2) this effect is partially diminished or vanishes completely.
Steep nonlinearity of the the forward-biased current–voltage characteristic of a system with a double-barrier resonant-tunneling structure built into a Schottky barrier
Authors: Korol’ A. N. , Tretyak O. V. , Sheka D. I.
Published: July 2002

A contact between a metal and an n-type semiconductor with a double-barrier resonant-tunneling structure built into the space-charge region is investigated. Besides the well-known effect in which the current falls sharply, there is an additional possibilty: in this system there can also be a steep nonlinearity of the current–voltage (I–V) characteristic, specifically, an effect wherein the current increases precipitously. It is shown that the differential slope of the forward branch of the I–V characteristic can be considerably greater than e/kT — by more than an order of magnitude at optimum values of the parameters of the problem. The dependence of the I–V characteristic on the parameters of the structure is analyzed.