bluuebunny/crossref_metadata_2025 huggingface dataset:
An ultrasonic atomizing device using coupled-mode vibration
Authors: Toda Kohji , Akimura Yoshikazu
Published: July 2002

A small, compact ultrasonic atomizing device is composed of a rectangular piezoelectric ceramic bar and a metal plate with minute holes. The resonance arising from the coupling between two vibration modes in the ceramic bar is used for the effective device operation. The best atomizing occurs when one of the coupled-mode resonant frequencies of the atomizing device is equal to that of the device without the metal vibrating plate. For an efficient power usage a self-oscillation type circuit, composed of the atomizing device as a resonant element and a power amplification transistor, is utilized.
A fast-firing shrinkage rate controlled dilatometer using an infrared image furnace
Authors: Hackenberger W. S. , Speyer R. F.
Published: July 2002

A novel dilatometer design is described for performing rate controlled sintering experiments on powder compacts. Previous rate controlled sintering systems, which control the shrinkage of a sintering compact, possessed only limited shrinkage rate control and shrinkage profile complexity due to the high thermal mass of conventional furnaces and dilatometers. The instrument described in this work features an infrared imaging furnace and a low thermal mass dilatometer assembly which together provide a very rapid temperature response. The system is capable of heating and cooling ceramic samples at up to 500 °C/min. Shrinkage control is accomplished using a modified, computer interfaced proportional-integral-derivative algorithm, and tests on glass–alumina composite samples demonstrated excellent shrinkage control with differences routinely less than 0.2% between the set point and actual shrinkage.
Diamond anvil cell high-pressure Mössbauer measurements on 155Gd, an isotope with a high Eγ
Authors: Mulder F. M. , Thiel R. C.
Published: July 2002

High-pressure 155Gd Mössbauer measurements in the range 0–20 GPa have been performed in a diamond anvil cell (DAC) at low temperatures. Due to the high Mössbauer transition energy of 86.54 keV, problems with pressure calibration, shielding, and gasketting arise, which are not present in DAC measurements on lower-energy Mössbauer isotopes. A strong point source has been produced using hot neutrons. Consequences for measuring times are discussed, together with a description of the optical system used for the pressure calibration.
A method to reduce sensor bridge dependence on loading and excitation voltage
Authors: Abatti P. J. , Schneider B.
Published: July 2002

A method to reduce the sensor bridge circuits readout dependence on loading, introduced by the meter and/or amplifier, and on eventual variations on excitation voltage is described. Experimental results on simulated strain gages and thermistors bridges, where both power and signal have been coupled directly using transformers (relatively low load impedances), are also reported.
A chamber for the in-situ IR measurement of C60 thin films while doping with alkali metals
Authors: Koller Daniel , Martin Michael C. , Stephens P. W. , Mihaly L.
Published: July 2002

A sample chamber has been designed to simultaneously measure the DC resistivity and IR transmission of C60 thin films while the films are doped with alkali metals in-situ. The chamber construction allows a choice of windows to cover the entire IR and visible range, while x-ray diffraction studies are also possible to determine the sample stoichiometry.
Novel discharge circuit for a multijoule TEA CO2 laser
Authors: Bhadani P. K. , Harrison R. G.
Published: July 2002

A novel discharge circuit that reduces significantly the amount of energy conducted by the switch in a TEA CO2 laser is reported. We demonstrate this circuit on a working multijoule TEA CO2 laser in which the switch is shown to conduct typically only 5% of the total input pulse energy. The laser has worked reliably in gas mixtures that place stringent demands on the discharge and circuit. It has produced an output of 7 J at an efficiency of 9.6% using a CO2:N2:He (1:1:4) gas mixture at atmospheric pressure and further using a helium-free gas mixture (CO2:N2:H2 at 400 mbar) it has produced a maximum efficiency of 14.6% for an output of 7.8 J. The great simplicity and high efficiency of the new discharge circuit allow it to be incorporated in the existing laser designs with minimal modifications.
Conversion of the Finnigan-MAT TSQ-70 thermospray ionization interface to an electrospray ionization interface
Authors: Jackett Sharon , Moini Mehdi
Published: July 2002

The conversion of a thermospray ionization (TSI) feature of a Finnigan-MAT TSQ-70 mass spectrometer to electrospray ionization (ESI) and its performance are described. The existing source, pumping capacity, flanges, and temperature controller of the TSQ-70 TS feature were used with a few modifications. Conversion of the commercial TS option to a simple and economically viable ES option has made the analysis of large biomolecules possible without expensive upgrades. To preserve the simplicity of the conversion, desolvation is effected by a heated-capillary tube (HCT). The HCT and its housing are inserted inside the TSQ-70 TS flange like a solid probe. Mass spectrometric results of low and high molecular weight biomolecules, the mass accuracy, sensitivity, and charge states of the observed ions are comparable to published results by other laboratories. Adequate spectral quality was obtained at short scan times, a required characteristic for interfacing ESI with separation methods such as capillary zone electrophoresis.
The Howard Hughes Medical Institute cassette for storage phosphor plates
Authors: Staudenmann J.-L. , Zotterman W. L. , Cook D. W. , Ogata C. M. , Hendrickson W. A.
Published: July 2002

New cassettes for 201 mm×252 mm (8″×10″) and 201 mm×400 mm (8″×15.75″) storage phosphor plates have been developed at the Synchrotron Resource of the Howard Hughes Medical Institute. The purpose for this work was mainly twofold. Firstly, to diminish the number of manual operations when putting the storage phosphor plate into the cassette or when extracting it from the cassette. Secondly, to render such a cassette much lighter than the former metal cassette previously in use. These two goals were achieved by making new cassettes that are operated as one piece instead of two or three independent parts as with the former systems. The cassettes have been extensively tested and found to be very useful.
Production of high-density sheet plasma by an rf magnetron device with high-frequency operation
Authors: Murata Kenji , Okuno Yoshihiro , Fujita Hiroharu
Published: July 2002

Production of a sheet plasma with a high electron density is successfully realized in an rf magnetron device with a rectangular hollow cathode by operating at a high driving frequency. The electron density ne of the sheet plasma increased up to about 2×1011 cm−3 with the relation of ne∝f2 for f≤20 MHz at a fixed driving voltage, and tended to saturate for f≳20 MHz. This saturation frequency is found to exceed the value in a conventional rf discharge by about four times. A hollow electrode with a size larger than the optimum value decreased the electron density slightly and produced electrons with two temperatures. The frequency dependencies of the rf oscillating potentials at the electrode and in the plasma were also studied to explain the results.
Anharmonic modulation for noise reduction in magnetic resonance force microscopy
Authors: Bruland K. J. , Krzystek J. , Garbini J. L. , Sidles J. A.
Published: July 2002

This article presents a new modulation technique for noise reduction in magnetic resonance force microscopy. Applied fields are modulated at frequencies that are not rational fractions of the cantilever resonant frequency, thus avoiding overtones that contribute to the noise level. An on-resonance signal is obtained because the nonlinear sample magnetization acts as a frequency mixer of the two modulation frequencies, producing a net force modulation at the cantilever resonant frequency. These techniques are experimentally demonstrated using electron spin resonance in a <15 ng sample of diphenylpicrylhydrazil.
Damped-structure cavity for a high-brilliant vacuum ultraviolet and soft x-ray storage ring
Authors: Koseki T. , Izawa M. , Kamiya Y.
Published: July 2002

This paper describes a new 500 MHz cavity which has a simple damped structure for the 2.0 GeV high-brilliant synchrotron radiation source. The damping of higher-order modes (HOMs) is achieved by large hole beam ducts, a part of which is made of microwave absorber. We have adopted as the microwave absorber a sintered SiC named CERASIC-B manufactured by Toshiba Ceramics Co. Ltd. The latest design of the cavity with CERASIC-B beam ducts is presented in this paper. We have fabricated a prototype model of the cavity. The results of the low power measurement are also reported here. It was confirmed that by using the CERASIC-B beam ducts the Q values of HOMs were strongly damped.
Conceptual design of quasiperiodic undulator
Authors: Sasaki Shigemi , Kobayashi Hideki , Takao Masaru , Miyahara Yoshikazu , Hashimoto Shinya
Published: July 2002

A new type of undulator which suppresses the rational harmonics is considered. This undulator consists of quasiperiodic arrays of magnet blocks and generates irrational harmonics which can be eliminated by the conventional crystal monochromators. The radiation power emitted from this undulator and the width of each radiation peak are comparable with that of the conventional periodic undulator of the same periods.
Superbrilliant x-ray undulator for the Tristan Super Light Facility
Authors: Yamamoto Shigeru , Shioya Tatsuro , Kitamura Hideo , Tsuchiya Kimichika
Published: July 2002

We have developed a construction method for very long undulators which are potentially capable of having various magnetic specifications and fit long straight sections in third- or fourth-generation light sources. A prototype device was built by constructing three rigid and precise standardized-unit undulators and connecting them to form a 5.4-mm-long undulator. This prototype will also be used as a superbrilliant light source for a feasibility study, which is planned in 1995, using the Tristan Main Ring.
X-ray instrumentation for a focused wiggler beamline at the EMBL Outstation Hamburg
Authors: van Silfhout R. G. , Hermes C.
Published: July 2002

A flexible setup consisting of two independent water-cooled X-ray monochromators providing radiation for two separate beamlines (A and B) has been installed on the multipole wiggler BW7 at the DORIS III storage ring. The first optical element of both lines is a Rh-coated SiC mirror that reduces the heat load on subsequent energy defining elements. Line B, which will be predominantly used for protein crystallography, is optimized for flux and employs a triangular monochromator and segmented glass mirror for horizontal and vertical focusing, respectively; it can be operated in a wavelength range from 0.5 to 1.8 Å. Line A features a high-energy resolution fixed exit, nondispersive double monochromator, optimized for accurate and fast energy scans. It will mainly be used for anomalous scattering, EXAFS, and small-angle scattering. The use of encoders, intelligent stepper/dc-motor controllers, and position sensitive beam monitors allow a comfortable and fast alignment of all axes. Both experimental hutches are equipped with large motorized optical tables, offering a versatile and convenient mounting surface for experiments.
Numerical simulation of flux density spectra for tapered undulators
Authors: Bandyopadhyay Pathikrit , Boyanov Boyan I. , Mitrovic Vesna , Bunker Grant B.
Published: July 2002

Calculations of the angular distribution of brightness from tapered undulators were performed as a function of energy. Modulations in the on-axis brightness spectra versus energy are correlated with modulations in the angular pattern of emitted photons. When the angular acceptance of the monochromator crystals is included, the alterations in the angular pattern arising from tapering may result in larger transmitted flux modulations than are apparent from on-axis brilliance or brightness of the spectra alone.
Phase-space measurement of stored electron beam at the Cornell Electron Storage Ring using a combination of slit array and CCD detector
Authors: Cai Z. , Lai B. , Yun W. , Gluskin E. , Dejus R. , Ilinski P.
Published: July 2002

A new technique for fast phase-space measurement has been developed and tested during a recent APS/CHESS undulator run. A measurement time of a few seconds was obtained by using a slit array and a high-resolution position sensitive detector system. The detector system consists of a CdWO4 scintillation crystal, an optical imaging system, and a CCD detector. The short measurement time increases the measurement accuracy by reducing the effects from the instabilities of the electron beam in storage ring. The vertical emittance at the Cornell Electron Storage Ring in single-bunch and low-current mode was measured, and reasonable agreement with the expected values for both source size and source divergence were obtained (σy=75 μm and σy′=12 μrad). The effects of the finite size of the first slit on the measurement results are discussed, and a comprehensive data analysis procedure is described.
Ultrahigh-vacuum-compatible position and shape monitor for high brilliance synchrotron radiation beams
Authors: Fajardo P. , Ferrer S.
Published: July 2002

A beam position monitor for small x-ray beams in an ultrahigh-vacuum environment is presented along with the results for a prototype. The instrument, initially conceived to monitor monochromatic beams, has shown to be useful for white radiation too. The integrated profiles of the spatial distribution of the beam are measured by scanning two perpendicular thin metallic wires across the detection area. The prototype has been tested with undulator beams at the European Synchrotron Radiation Facility and the measured resolution is better than 5 μm when full power beams are monitored. Beryllium and tungsten wires of 50 and 100 μm diam have been used for white and monochromatic beams, respectively, and typical peak current values are 500 nA and 400 pA for unfocused beams. The minimum scan time is 1 s and therefore this instrument is not suitable for fast position corrections. On the other hand it is inherently free of electronic drift and it is well suited to monitor the beam during long unattended experiments.
The Naval Research Laboratory’s new hard x-ray beamline at the National Synchrotron Light Source
Authors: Kirkland J. P. , Elam W. T.
Published: July 2002

The Naval Research Laboratory is currently rebuilding its hard x-ray beamline at the National Synchrotron Light Source (NSLS, X-23B) to increase the flux and energy range. The optical and mechanical design of the new configuration is described and its performance predicted. The new design contains a fixed-exit pair of mirrors for harmonic rejection and source collimation and a fixed-exit two-crystal monochromator with sagittally focusing second crystal. In addition, the horizontal acceptance of the line will be increased from 6 to 18 mrad. The line is expected to focus radiation to a spot 0.5 mm vertical by 1.0 mm horizontal in the energy range 2 to 30 keV. At 8.5 keV a throughput of 5.7×1012 photons/s/200 mA is expected with an E/ΔE of 5×103 with Si (111) crystals, a factor of 10 to 30 over present beamline throughput. The increased flux is due to improved mirror surfaces, decreased optical aberrations from conical sagittal focusing, and the increased horizontal acceptance.
Design of an x-ray beamline on a bending magnet at the ESRF for magnetic and high resolution diffraction
Authors: Paul D. F. , Cooper M. J. , Stirling W. G.
Published: July 2002

In this paper, the options for the optical design for the UK-CRG beamline that is to be built at the ESRF are described here. This paper discusses how the options were narrowed to just two configurations and results are presented from ray-tracing simulations that were used to provide comparative flux outputs in order to assist in making the final choice. In conclusion, a discussion is presented of how a novel mirror concept, derived for one of the configurations, might have wider application.
Virtual instrumentation of a resonant spectrophone
Authors: Lei G. , Di Bartolo B.
Published: July 2002

The acoustic modes of a gaseous system in a cylindrical resonant cavity were excited with a tunable CO2 laser. The experimental setup is completely controlled by a personal computer and virtualized as an application-oriented system by employing a so-called virtual instrumentation software through a GPIB interface. A detailed description of the hardware arrangement, software virtualization, and the measured resonant profile of the spectrophone is presented.
An absolute cryogenic calibration source for a 2.5 GHz radiometer
Authors: Gervasi M. , Bonelli G. , Sironi G. , Cavaliere F. , Passerini A. , Casani S.
Published: July 2002

We describe a liquid helium-cooled absolute reference load for the calibration of a 2.5 GHz radiometer. This calibration system provides an absolute reference near the liquid helium boiling point. The accuracy of the reference source is better than 100 mK. We use this cold load to perform absolute temperature measurements of the cosmic microwave background radiation.
A modified scheme of Johann spectrograph
Authors: Kopecký M.
Published: July 2002

The article presents a novel vertical-dispersion variant of the Johann spectrograph. Very good focusing properties, extremely high spectral resolution, and one-dimensional spatial resolution of this instrument open new possibilities in x-ray spectroscopy, especially in x-ray diagnostics of high-temperature plasmas. Basic characteristics of the spectrograph scheme are analyzed in detail by using ray tracing procedure.
Investigations on calibration sources for soft-x-ray plasma spectroscopy and impurity monitors
Authors: Schumacher U. , Asmussen K. , Fussmann G. , Liebsch T. , Neu R.
Published: July 2002

For absolute soft-x-ray line intensity measurements to deduce elemental concentrations and parameters of magnetically confined plasmas large-area x-ray sources are developed and investigated. These calibration sources use K, L, and M transitions in different elements and cover a wide photon energy (and wavelength) range. From the measured absolute line intensities of these sources the quantum efficiency values of numerous elements for K-, L-, and M-line emission per incident electron are deduced. They represent the basis of simple soft-x-ray monitors for impurities in fusion plasmas.
Accurate refractive index measurements of doped and undoped InP by a grating coupling technique
Authors: Martin Patrick , Skouri El Mostafa , Chusseau Laurent , Alibert Claude , Bissessur Hans
Published: July 2002

Accurate measurements of InP refractive indices in the 1300–1600 nm wavelength range are reported. They are obtained using the grating coupling technique within an asymmetrical slab waveguide where an intrinsic InP guiding layer was grown on a doped InP substrate (N=2×1018 cm−3). Modal indices are obtained with an absolute precision of a few 10−4 from either guided or reflected waves. Bulk refractive indices of intrinsic and N-doped InP are then deduced from the allowed modes propagating in the layered structure. With sample temperature maintained to within 0.01 K, InP bulk indices are obtained with a typical accuracy of 5×10−4. Furthermore, a (2.02±0.02) 10−4 K−1 refractive index temperature coefficient has been measured for bulk InP at room temperature.
Measurement of heat capacity by fitting the whole temperature response of a heat-pulse calorimeter
Authors: Hwang Jih Shang , Lin Kai Jan , Tien Cheng
Published: July 2002

A new method that fits the whole temperature response of a heat-pulse calorimeter for heat capacity is developed. Analyzing the thermal response of a heat-pulse calorimeter on a model that was used by the relaxation method, the authors derived some useful relations and further utilized the numeric method of the general linear least squares to determine the heat capacity of a sample. Absolute accuracy of the proposed method was verified by determining the heat capacity of a 0.249 76 g copper sample (purity 99.999%) on a self-designed and fully automated calorimetric system from 4.5 to 80 K. Comparing the result with the literature, the deviation in average was 1.2% from 4.5 to 20 K and 2.0% from 20 to 80 K. It is found that the proposed method is capable of measuring heat capacity regardless if the sample is adiabatically or nonadiabatically isolated. The size of the specimen is not critical for the application of the method and the temperature range of measurement can be expanded. It also deals with the τ2 effect. Details of the employed calorimetric system are described. Stability, inherent limitations, and further improvement of the system are also discussed.
Differential wavelength meter for laser tuning
Authors: Howard Lowell P. , Stone Jack A.
Published: July 2002

A simple interferometer for matching the wavelengths of tunable lasers is described. Our interferometer uses the angular dispersion of a diffraction grating at the Littrow angle to produce a tilted wavefront with respect to a reference mirror in an opposing arm of a Michelson interferometer. As a first step, the resulting interference pattern is adjusted to produce a null fringe using a reference laser as a wavelength standard. When a tunable laser, such as a laser diode, is used to illuminate the system, the laser is simply tuned to reproduce the null fringe pattern established using the reference laser. When so tuned, the wavelength of the tunable laser is matched to that of the reference laser within about 3 GHz, close enough for optical heterodyning.
Development of high voltage step-up transformer as a substitute for a Marx generator
Authors: Masugata K. , Saitoh H. , Maekawa H. , Yatsui K. , Shibata K. , Shigeta M.
Published: July 2002

A new type of pulse transformer has been developed as a substitute for a Marx generator. In the transformer amorphous metallic cores are utilized with windings of cylindrical conductors. As a result, low leakage inductance is realized with high breakdown strength. The coupling coefficient of the transformer is estimated to be more than 0.99. By using the transformer of winding ratio of 1:3, a Blumlein pulse forming line of capacitance 20 nF is successfully charged up to 270 kV by using a capacitor bank of 240 nF, 90 kV. High speed charging of charging time=250 ns is realized with high efficiency of energy transfer (energy transfer efficiency from the capacitor bank to the pulse forming line was evaluated to be 76%).
Picosecond domain electromagnetic pulse measurements in an exposure facility: An error compensation routine using deconvolution techniques
Authors: Bao Jian-Zhong
Published: July 2002

This article presents a two-step deconvolution routine to compensate for the measurement distortions of transient electrical fields in the picosecond domain in an electromagnetic pulse exposure facility. Because of the low-pass nature of connection cables and the limited bandwidth of a transient digitizer (Tektronix SCD 5000), the measured signal is a distorted output of D-dot (dD/dt, where D is the electric displacement) sensors. An empirical transfer function of the cable-digitizer system was evaluated using a reference impulse generated by a picosecond pulse generator. The reference impulse was injected into the connection cable at the D-dot sensor end and measured with the SCD 5000 while the cable was kept in the same position as for making D-dot measurements to ensure an in-position compensation. Two types of asymptotic conical dipole (ACD) D-dot sensors were utilized as the electrical field sensing devices: an axial model ACD-1(A) and a radial model ACD-1(R). Due to its right-angle structures, the ACD-1(R) gives a different output from that of ACD-1(A) to the same pulse, especially to the fast leading edge. The right-angle bends in ACD-1(R) cause reflections of a sensed signal in the sensor. To correct the errors due to the reflections, the impulse response of the ACD-1(R) D-dot sensor was proposed as a summation of the δ function and the parameters were determined with a pulse measurement using the ACD-1(A) D-dot sensor and an optimization procedure with the Levenberg–Marguardt algorithm. With this routine the measurement accuracy for the electrical pulse in picosecond domain has been improved significantly.
Resonance enhanced multiphoton ionization/time-of-flight measurements of the velocity and internal energy content of thermal and photochemical methyl radical sources
Authors: Fairbrother D. Howard , Briggman K. A. , Dickens K. A. , Stair P. C. , Weitz Eric
Published: July 2002

A single-stage time-of-flight mass spectrometer used in conjunction with resonance enhanced multiphoton ionization has been employed to study the dynamics of surface photodissociation processes as well as methyl radicals produced from a continuous source. By utilizing ion rather than neutral flight times, species that have an impressed velocity along the detection axis can be readily distinguished from species that exhibit an isotropic velocity distribution. This allows for experimental discrimination between photofragments produced from adsorbate photolysis and those produced as a result of probe laser photolysis of gas-phase species photodesorbed from the surface. For species generated in continuous sources, such as methyl radicals produced from azomethane pyrolysis, the same approach permits an unambiguous determination of the total-energy content, despite the presence of additional radicals within the ionizing volume that have scattered from the chamber walls.
Effect of broadband wave number and frequency spectra on E×B particle flux in plasmas
Authors: Crowley T. P.
Published: July 2002

The effect of a broadband wave number (k) and frequency (ω) spectrum S(k,ω), on particle flux due to electrostatic fluctuations in a plasma is examined. Effect of the broadband spectrum on density-potential coherence is also calculated. Particle flux results are compared with a standard quasilinear transport estimate that has been used to interpret heavy ion beam probe and Langmuir probe measurements in fusion plasmas. Situations in which the quasilinear estimate is probably inaccurate are illustrated, including edge shear layer measurements and interior measurements from the TEXT tokamak.
Experimental study on an electron-beam energy recovery system using a multistage collector
Authors: Roy Prabir Kumar , Moon Ahsa , Mima Kunioki , Nakai Sadao , Fujita Masayuki , Imasaki Kazuo , Yamanaka Chiyoe , Tanaka Hidehiro , Sano Eisaku , Tsunawaki Yoshiaki
Published: July 2002

An electron-beam energy recovery system was experimentally investigated using a multistage electron collector designed by a numerical simulation. In our previous experiments, the potential of each electrode was provided through a voltage divider of several hundred megaohms resistance. Experimentally, it was observed that a part of the beam current was lost to ground through the resistance, and inferred that the electrostatic effect of the electrodes was changed from the initial operating condition. In order to overcome the drawback of voltage divider resistance, two high-voltage power supplies have been provided for the electrodes, and the charge collecting electrodes have been kept at a little higher potential than that of the cathode by using a battery. The recovery currents of the system have been directly measured by an ammeter. The maximum charge recovery efficiency of the collector was almost 100% with a beam current of 0.2 mA. It was, however, seen that this efficiency reduced to 73% for a beam current of about 0.85 mA due to the secondary emission. The maximum energy recovery efficiency, 74%, was calculated for 0.2 mA beam current, and this efficiency was reduced to 58% for a beam current of 0.85 mA.
Diagnosis of electron density in magnetized plasmas using lower hybrid waves
Authors: Sheehan D. P.
Published: July 2002

A simple electron density diagnostic for low-temperature, magnetized plasmas is described which relies on the propagation angle of lower hybrid waves. Experiments are discussed in which the diagnostic is used to determine residual electron densities in negative ion plasmas.
Application of sound-absorbent plastic to weak-shock-wave attenuators
Authors: Ootsuta Katsuhisa , Matsuoka Kei , Sasoh Akihiro , Takayama Kazuyoshi
Published: July 2002

A device for attenuating weak shock waves propagating in a duct has been developed utilizing sound-absorbent plastic which is usually used for attenuating sound waves. The device has a tube made of the sound-absorbent plastic installed coaxially to a surrounding metal tube with a clearance between them. The clearance acts as an air layer to enhance the performance of the shock wave attenuation. When a weak shock wave propagates through this device, the pressure gradient of the shock wave is gradually smeared and hence its overpressure is decreased. The performance of the device was examined using a 1/250-scaled train tunnel simulator which simulated the discharge of weak shock waves created by high-speed entry of trains to tunnels. The overpressure of the shock waves ranged up to 5 kPa. The shock wave overpressure was decreased by 90% with the present attenuator attached. This device can be applied to various industrial noise suppressions which are associated with unsteady compressible flows.
A low-cost multichannel Thomson scattering system for CDX-U
Authors: Munsat T. , LeBlanc B.
Published: July 2002

A multichannel Thomson scattering system has been developed for the CDX-U spherical torus. The system is designed for 10 eV<Te<400 eV, ne>1018 m−3, which includes typical and predicted central and edge conditions in CDX-U. The system uses two laser passes to double the scattered photons from a 5 J ruby laser. The beam path is vertical through the ∼66 cm (elongated) diameter of the plasma and is movable in the major-radial direction, enabling coverage of nearly 70% of the major-radial plasma extent. Twelve channels over the vertical minor radius provide ∼2.5 cm spatial resolution. The main collecting lens, located 45 cm from the laser beamline, provides high solid angle (ΔΩ∼0.01) light collection using a 15 cm diam lens. The system makes maximum usage of an optically fast (f/1.8) compact imaging spectrometer. An intensified charge coupled device with a GaAs photocathode provides quantum efficiency of ∼20% at 6943 Å. The combination of plasma access, multiple beam passes, high-throughput spectrometer, and high quantum efficiency detector provide for very high total photon statistics in a relatively simple and inexpensive system.
He
3
refrigerator based very low temperature scanning tunneling microscope
Authors: Pan S. H. , Hudson E. W. , Davis J. C.
Published: July 2002

We describe the design and development of a scanning tunneling microscope (STM) which can operate at temperatures down to 240 mK and in magnetic fields up to 7 T with high spatial and energy resolution. The compact and rigid STM head is mounted directly on a low vibration, single shot, He3 refrigerator. This refrigerator can be operated at its base temperature continuously for several days before the He3 needs to be recondensed. The system is equipped with a sample transport manipulator from room temperature, and a cleavage device at low temperature, so that the cryogenic ultrahigh vacuum condition inside the cryostat can be utilized. A superconducting magnet provides a magnetic field of up to 7 T at the sample along the STM tip direction. Test results have shown that, at the base temperature, this instrument has better than 0.5 pm z-direction resolution in imaging mode, and better than 20 μV energy resolution in spectroscopy mode.
Circuit to cancel ac displacement current to reveal dissipative and nonlinear conduction phenomena
Authors: Li Lillian T. , Boggs Steven A.
Published: July 2002

Conduction and dissipative phenomena which result in a small current compared to a displacement current are important in many contexts but are very difficult to measure as the displacement current may be a million times larger than the resistive and harmonic currents of interest. In principle, a dual phase lock-in amplifier can measure the average value of the rectified fundamental resistive current wave form; however, the accuracy of the phase reference and phase stability of the lock-in would have to be much greater than is practical. Further, such a measurement does not reveal the actual wave form or allow the measurement of harmonic current components which indicate nonlinear phenomena and may be of greater interest or of larger magnitude than the fundamental. The present circuit employs a dual phase lock-in amplifier in a feedback configuration which actively cancels the in-phase component of the current wave form to reveal the remaining current wave form components as well as provide a measure of the fundamental quadrature component via the lock-in. The active nature of the feedback assures long-term cancellation of the displacement current so that the nondisplacement current wave form can be monitored over time during evolution of the system as a result of aging, electrochemistry, etc.
Preset count moving average digital algorithm with faster response to an increasing count rate
Authors: Arandjelović V. Dj. , Koturović A. M. , Vukanović R. B.
Published: July 2002

The preset count unweighted moving average (MA) algorithm for digital rate meters has been analyzed and compared to the preset count weighted MA algorithm. The correction factor applicable to the unweighted MA algorithm in order to obtain a final result identical to that of the weighted MA algorithm has been found. It is shown that the response time of the corrected unweighted MA algorithm to an increasing count rate is shorter than that of the weighted MA algorithm. This makes the corrected unweighted MA algorithm suitable for nuclear engineering applications where the slower response of this algorithm to a decreasing count rate need not be considered a shortcoming. The statistical fluctuations in a steady state of the unweighted MA algorithm are found to be somewhat higher than those of the weighted MA algorithm. However, this difference becomes negligibly small for a sufficiently high value of the preset count.
Detection of laser excited surface acoustic waves by infrared radiation
Authors: Kubyshkin A. , Paul M. , Arnold W.
Published: July 2002

Remote detection of ultrasonic waves is shown experimentally by measuring the infrared (IR) radiation accompanying the adiabatic propagation of surface waves. The Rayleigh waves were excited by a pulsed Nd:yttrium–aluminum–garnet laser on the surface of a steel sample at temperatures up to 700 °C. The observed time-of-flight data of the Rayleigh waves correspond to values obtained by optical interferometry and the measured signal-to-noise ratio of ≈0.1 agrees with the estimated value using an IR detector with a sensitivity of D*=1.7×109 mm √Hz/W. Further improvements of IR detection may lead to a viable tool for laser ultrasonics.
Accuracy of error propagation exemplified with ratios of random variables
Authors: Winzer Peter J.
Published: July 2002

The method of error propagation provides a convenient tool for calculating mean and variance of a measurand from means and variances of primarily measured quantities. However, being based on a (usually first-order) Taylor approximation of the measurement function, it only yields approximate results with unknown accuracy. We develop a method for estimating the accuracy of (Nth-order) error propagation for an arbitrary number of correlated random quantities, and apply our findings to the ratio of two random variables (RVs). A comparison with some analytically solved expressions for certain probability density functions (PDFs) as well as with some computer simulations reveals the excellent quality of our estimates as long as the involved PDFs are not significantly skew. For the ratio of two RVs it turns out that conventional, first-order error propagation is safely applicable (with about 1% accuracy) as long as the denominator’s mean is larger than about 12 times its standard deviation. Using second-order error propagation, the approximation for the ratio’s mean can be refined, yielding 1% accuracy if the denominator’s mean is larger than about four times its standard deviation.
Variable temperature superconducting microscope
Authors: Cheng Bo , Yeh W. J.
Published: July 2002

We have developed and tested a promising type of superconducting quantum interference device (SQUID) microscope, which can be used to detect vortex motion and can operate in magnetic fields over a large temperature range. The system utilizes a single-loop coupling transformer, consisting of a patterned high Tc superconducting thin film. At one end of the transformer, a 20 μm diam detecting loop is placed close to the sample. At the other end, a large loop is coupled to a NbTi coil, which is connected to a low Tc SQUID sensor. Transformers in a variety of sizes have been tested and calibrated. The results show that the system is capable of detecting the motion of a single vortex. We have used the microscope to study the behavior of moving vortices at various positions in a YBa2Cu3O7 thin film bridge.
An apparatus for supersonic jet epitaxy of thin films
Authors: Ustin S. A. , Brown K. A. , Ho W.
Published: July 2002

An ultrahigh vacuum chemical beam epitaxy growth system has been built using multiple supersonic jets as precursors. Supersonic jets provide very high flux to the growth front while maintaining low growth pressures (10−5 Torr). Activation barriers to chemisorption are overcome by using hyperthermal (1–10 eV) precursors for heteroepitaxial growth. Improvement in growth rates and higher degrees of structural orientation are obtained at lower temperatures. Wide band gap semiconductors (SiC, GaN, and AlN) are deposited on silicon substrates using neutral chemical precursors. Epitaxial growth of SiC on silicon has been obtained at the lowest temperatures reported to date using a supersonic jet of methylsilane.
Compact low field magnetic resonance imaging magnet: Design and optimization
Authors: Sciandrone M. , Placidi G. , Testa L. , Sotgiu A.
Published: July 2002

Magnetic resonance imaging (MRI) is performed with a very large instrument that allows the patient to be inserted into a region of uniform magnetic field. The field is generated either by an electromagnet (resistive or superconductive) or by a permanent magnet. Electromagnets are designed as air cored solenoids of cylindrical symmetry, with an inner bore of 80–100 cm in diameter. In clinical analysis of peripheral regions of the body (legs, arms, foot, knee, etc.) it would be better to adopt much less expensive magnets leaving the most expensive instruments to applications that require the insertion of the patient in the magnet (head, thorax, abdomen, etc.). These “dedicated” apparati could be smaller and based on resistive magnets that are manufactured and operated at very low cost, particularly if they utilize an iron yoke to reduce power requirements. In order to obtain good field uniformity without the use of a set of shimming coils, we propose both particular construction of a dedicated magnet, using four independently controlled pairs of coils, and an optimization-based strategy for computing, a posteriori, the optimal current values. The optimization phase could be viewed as a low-cost shimming procedure for obtaining the desired magnetic field configuration. Some experimental measurements, confirming the effectiveness of the proposed approach (construction and optimization), have also been reported. In particular, it has been shown that the adoption of the proposed optimization based strategy has allowed the achievement of good uniformity of the magnetic field in about one fourth of the magnet length and about one half of its bore. On the basis of the good experimental results, the dedicated magnet can be used for MRI of peripheral regions of the body and for animal experimentation at very low cost.
Computer-controlled instrumentation for fast voltammetry at ultramicroelectrodes
Authors: Pospı́šil L. , Fiedler J. , Fanelli N.
Published: July 2002

In this article we describe an electrochemical experimental setup for cyclic voltammetry operating from low (1 V/s) to very high (200 kV/s) scan rates. The system is designed to achieve an acceptable cost and to be user friendly for nonexperts. The instrumentation is based on a commercial arbitrary wave form generator, a digital oscilloscope, a general purpose interface bus interface to a PC, and a laboratory-built potentiostat. There are no complicated manual operations, instead the software creates dialog with an operator to control commands for the instruments. Requirements for the wave form synthesis and the data acquisition are given. Various data-smoothing methods for treating 8-bit fast scan data are evaluated. The performance was tested on the oxidation of ferrocene in acetonitrile. The estimated value of the standard heterogeneous rate constant, k0=0.8±0.1 cm s−1, is in reasonable agreement with the most recent reports from other laboratories.
Nonuniform doping of the collector in avalanche transistors to improve the performance of Marx bank circuits
Authors: Mallik Kanad
Published: July 2002

It is shown that the avalanche multiplication factor of transistors, which plays a key role in the functioning of the Marx bank circuit, can be considerably enhanced when the collector has a Gaussian doping profile, compared to uniform doping. The limiting of the maximum field in the collector, and the base push out are the events involved in the occurrence of the current mode second breakdown of avalanche transitors in the Marx circuit. Calculations show that the limiting of the maximum field, followed by the base push out, is the sequence conducive to the enhancement of the avalanche gain. Preliminary experimental assessment of the doping profiles of the same model of transistors from two different manufacturers supports the proposed idea.
Measurements of the velocity and temperature in a turbulent flow by the laser photothermal effect with the new compulsorily phase locked interferometer
Authors: Nakatani Noboru
Published: July 2002

This article describes measurements of the velocity and temperature in a turbulent flow by means of a photothermal effect. We developed a new differential interferometer for detecting small phase variation caused by the photothermal effect without influence of turbulent phase fluctuation. The detected fringe point of the interferometer is scanned repeatedly by moving a photomultiplier. An electric system is constructed for compulsorily operating the interferometer at the maximum inclination point of the fringe intensity curve. Using a turbulent jet of nitrogen gas mixed with ethylene gas, we confirmed that this measurement system is useful to measure the velocity and temperature in the turbulent flow.
Spectral analysis: A new method to measure the spontaneous polarization of ferroelectric liquid crystals
Authors: Martins O. Gimenes , Neto A. M. Figueiredo
Published: July 2002

A new method to measure the spontaneous polarization density PS of ferroelectric liquid crystals as a function of the temperature is described. It is based on the spectral decomposition of the polarization and measurement of the different temporal harmonics using a lock-in amplifier. It is particularly adapted to measure small values of PS in regions where different nonlinear process compete. This condition is fulfilled at temperatures around the SmC*–SmA transition temperature in liquid crystals. The method has a quantitative procedure to evaluate the saturation state of the sample’s polarization at a given applied electric field. It overcomes the difficulty of the subjective evaluation of the hysteresis loop present in the usual methods. The accuracy in the measurement of PS of the ZLI-3654 ferroelectric liquid crystal in the region of about 0.5 nC/cm2 is approximately one order of magnitude larger than that obtained with conventional hysteresis loop methods.
Raman shifting a tunable ArF laser to wavelengths of 190–240 nm
Authors: Balla R. Jeffrey , Herring G. C.
Published: July 2002

Tunable radiation at far-ultraviolet wavelengths is produced by Raman shifting a modified (285 mJ at 1–100 Hz repetition rate) ArF excimer laser. Multiple Stokes outputs are observed in H2(20%), CH4(22%), D2(53%), N2(21%), SF6(2.1%), and CF4(0.35%). Numbers in parentheses are the first vibrational Stokes energy conversion efficiencies. We can access 70% of the frequency range 42 000–52 000 cm−1 (190–240 nm), with Stokes pulse energies that vary from 0.2 μJ to 58 mJ inside the Raman cell. One of our better results, using 110 mJ of pump energy and D2, is an energy conversion efficiency of 53% and a tunable Stokes energy that varies over the range 29–58 mJ/pulse for the wavelength range 204–206 nm.
Polymer microparticle arrays from electrodynamically focused microdroplet streams
Authors: Ng K. C. , Ford J. V. , Jacobson S. C. , Ramsey J. M. , Barnes M. D.
Published: July 2002

We describe instrumentation for forming two-dimensional arrays of polymer microparticles produced from electrodynamically focused microdroplet streams. A single-stage linear quadrupole was used to focus droplets/particles onto silanated glass slides mounted on a computer-driven two-dimensional translation stage. Center-to-center position stability was on the order of 1 μm. Applications to molecular sorting with polymer particles as host carriers are discussed.
Postphotobleaching method for the control of coupling constant in an electro-optic polymer directional coupler switch
Authors: Hwang Wol-Yon , Kim Jang-Joo , Zyung Taehyoung , Oh Min-Cheol , Shin Sang-Yung
Published: July 2002

A method to control the coupling constant of a directional coupler switch made of electro-optic polymer after completing the device fabrication is demonstrated. The method utilizes the selective postphotobleaching of the gap region to lower its effective refractive index while monitoring optical output power from each arm. The output power changes gradually and the crossover states are successively observed as the postphotobleaching proceeds. It is shown that the method can be utilized to tune the initial output to the crossover state to have a good switching extinction.
Strain relaxation in silicon-germanium microstructures observed by resonant tunneling spectroscopy
Authors: Zaslavsky A. , Milkove K. R. , Lee Y. H. , Ferland B. , Sedgwick T. O.
Published: July 2002

We have measured the resonant tunneling current–voltage I(V) characteristics of strained p-Si/Si1−xGex double-barrier microstructures ranging from 1.0 to 0.1 μm in lateral extent. The bias spacing between resonant current peaks in the I(V) reflects the energy separation of the Si1−xGex quantum well subbands, which is partially determined by the strain. As the lateral size of the structures decreases, we observe consistent shifts in the I(V) peak spacing corresponding to strain energy relaxation of ∼30% in smaller structures. An additional I(V) fine structure is observed in the 0.1 μm device, consistent with lateral quantization due to nonuniform strain.
Optical and dielectric properties of photochromic dye in amorphous state and its application
Authors: Kawai Tsuyoshi , Koshido Takashi , Yoshino Katsumi
Published: July 2002

Preparation of amorphous phase of a photochromic dye, cis-1,2-dicyano-1,2- bis(2,4,5-trimethyl- 3-thienyl) ethene, has been investigated and its photochromic properties have been studied. This photochromic dye shows clear photochromism in the amorphous solid state accompanying reversible changes in absorption spectrum, refractive index, and dielectric properties. Clear optical pattern formation has been achieved on the amorphous dye layer.