bluuebunny/crossref_metadata_2025 huggingface dataset:
Tetragonal germanium flims deposited by the cluster-beam evaporation technique
Authors: Sato S. , Nozaki S. , Morisaki H. , Iwase M.
Published: July 2002

Germanium (Ge) films have been fabricated by the cluster-beam technique. In transmission electron microscope (TEM) micrographs, the film deposited on a substrate at room temperature appears smooth and uniform, while that deposited at liquid nitrogen temperature consists of nanostructures with diameters from 4 to 40 nm. The x-ray diffraction (XRD) patterns show that the crystalline structure for either deposition temperature is not the ordinary diamond structure but is tetragonal. The absorption spectra are distinct from that of bulk Ge. The photo-oxidized Ge nanostructures exhibit blue light emission, which is strong enough to be recognized with the naked eye even under a room light.
Charge exchange recombination spectroscopy measurements of ion temperature and plasma rotation in PBX
Authors: Jaehnig K. P. , Fonck R. J. , Ida K. , Powell E. T.
Published: July 2002

The primary diagnostic on PBX for ion temperature measurements is charge exchange recombination spectroscopy of low Z ions, wherein fast neutrals from the heating neutral beams excite spectral lines from highly excited states (n>4) of hydrogenic O, C, and He via charge exchange collisions with the respective fully stripped ions. Since the neutral beams on PBX provide relatively low-velocity neutrals (i.e., D° beams at 44 keV), best signals are obtained using the near-UV lines of O7+ (e.g., n=8–7, 2976 Å). Off-line analysis of the Doppler broadened and shifted line profiles includes nonlinear least-squares fitting to a model line profile, while a simplified on-line fast analysis code permits between-shot data analysis.
A goniometer using a continuously rotating grating
Authors: Barnes T. H.
Published: July 2002

Goniometers incorporating continuously rotating gratings offer great potential for high-accuracy angular measurement. Simple mathematical relations describing the limitations of this type of instrument are presented together with results showing 6 arc s accuracy from an experimental model.
Peltier oven for thermistor mounts
Authors: Peters J. E.
Published: July 2002

Thermistor mounts are widely used for microwave power measurement, but suffer from drift caused by ambient temperature fluctuations. A Peltier oven has been developed which can be easily fitted to a thermistor mount to stabilize the mount temperature near the ambient temperature, thereby reducing the drift substantially.
Improved differential optical position detector for magnetic suspension systems
Authors: Murgatroyd P. N. , Carmichael A. T. , Thomas S. J. P.
Published: July 2002

A split-beam position detector for single-axis magnetic suspension systems has been modified by including a narrow-angle prism to produce symmetrical deflection of the two beams. The modified system is relatively insensitive to positioning of the components, and has a wider range of linear response.
High-speed motor for use in an ultrahigh-vacuum environment
Authors: Engel Thomas , Braid Donald
Published: July 2002

Modification of a commerical motor to drive a chopper blade in UHV is described. The motor has performed satisfactorally at a frequency of 200 Hz over prolonged periods. The observed pressure rise which is due primarily to outgassing of the bearings is less than 1×10−9 Torr.
‘‘Glow-discharge’’ ionic anemometer
Authors: Yamanaka M. D. , Hirosawa H. , Matsuzaka Y. , Tanaka H.
Published: July 2002

We have developed an ionic anemometer utilizing a glow discharge for the purpose of observing stratospheric turbulence. The anemometer has a three-electrode structure; two electrodes made of Ni mesh hold a glow discharge between them and act as the source of ion tracers. The third electrode collects the ions interacting with wind. The minimum detectable wind speed is less than 1 cm/s over a pressure range of 15–35 Torr. The lifetime of this device is more than 50 h. The anemometer has been successfully operated on balloon-borne experiments carried out in 1983 and 1984.
Microcomputer-based data-acquisition system for the Langmuir probe
Authors: Wong C. S.
Published: July 2002

I/V characteristics in a plasma have been recorded by means of a Langmuir probe interfaced to an Apple II computer.
Determination of correct reference fluorescence lifetimes by self-consistent internal calibration
Authors: Castelli Francesco
Published: July 2002

A method of internal calibration is developed that allows one to ascertain the monexponentiality of a reference compound fluorescence decay and to determine its lifetime with high accuracy. It is shown that when the fluorescence decays of several samples are analyzed as a function of the reference lifetime, which is used to calculate the ‘‘lamp profile,’’ all the data are consistent with each other only if the fluorescence of all the used compounds decays monoexponentially and the correct lifetime for p-terphenyl, which is used as reference compound, is between 1.02 and 1.03 ns.
Fast heterodyne interferometer with electronically stabilized initial phase
Authors: van der Geer C. A. J. , van der Meer A. F. G. , Mastop W. J.
Published: July 2002

A heterodyne interferometer setup with initial-phase stabilization is described, which allows the full range of ‘‘half a fringe’’ to be used without ambiguity, using only one phase comparator. This phase stabilization is achieved by the insertion of a voltage-controlled delay line in the reference path of the phase comparator. The system is used to measure the electron line density of pulsed plasmas (with pulse lengths of 1 ms) in the range 5×1019–2×1021 m−2 with a time resolution of 200 ns. The resolution of the electronic system is approximately (half a fringe)/200.
Effect of gas mixing on H− production in a multicusp source
Authors: Leung K. N. , Ehlers K. W. , Pyle R. V.
Published: July 2002

The effect of gas mixing on volume H− production in a magnetically filtered multicusp source has been investigated. By applying the proper bias voltage on the plasma electrode, the addition of xenon or argon gases to a hydrogen discharge can enhance the H− yield. This increase in H− output is closely related to the increase in plasma electron density in the filter and extraction chamber regions.
Complex conductivity measurements between 26 and 110 GHz using complex impedance bridges
Authors: Sridhar S. , Reagor D. , Gruner G.
Published: July 2002

A method is described of measuring complex conductivity based upon the measurement of the impedance of a sample placed in a waveguide using a complex impedance bridge. From the observed changes in the bridge parameters, viz., attenuation and phase shift, the impedance and, hence, the complex conductivity are inferred. The principles and details of operation of three bridges covering the frequency range 26 to 110 GHz are discussed. The measurement technique was verified for lossless samples and for lossy resistive wires. An example of temperature and frequency dependent complex conductivity measurements on a linear chain material is presented.
Detector for measuring energy- and angle-resolved neutral-particle (EARN) distributions for material desorbed from bombarded surfaces
Authors: Kobrin Paul H. , Schick G. Alan , Baxter James P. , Winograd Nicholas
Published: July 2002

The design and application of a detector is described, which is capable of simultaneously measuring energy and angular distributions of neutral particles desorbed from surfaces. Specific applications to ion bombardment studies are presented. The detector utilizes the state selectivity, sensitivity, and pulsed characteristics of multiphoton resonance ionization as a time-of-flight sensitive postionization technique. A microchannel-plate element allows position-sensitive detection of the laser-ionized particles. Sample data are presented for ground-state Rh atoms desorbed from clean, ion-bombarded Rh foil and Rh(111) surfaces.
Video system for quantitative measurements of RHEED patterns
Authors: Bölger B. , Larsen P. K.
Published: July 2002

Two different signal-processing systems are described for the conversion of reflection high-energy electron diffraction (RHEED) patterns, displayed on a phosphor screen, into quantitative data. Both systems are based on the use of a sensitive video camera. One system using a multichannel boxcar integrator is particularly suited to simultaneous temporal measurements of different RHEED beams and integrated line intensities, while the other can be applied to fast data acquisition of line profiles. The system performance is illustrated and discussed.
Fiber-optic absorption temperature sensor using fluorescence reference channel
Authors: Grattan K. T. V. , Selli R. K. , Palmer A. W.
Published: July 2002

In this work a fiber-optic thermometer is demonstrated, using the change in absorption characteristics of a doped glass plate as the principle of operation of the transducer. A novel reference channel, generated at the sensor element itself is used, based on the fluorescence induced in a piece of neodymium/glass. Operation from −60 to 200 °C is reported and the potential for higher temperature operation is discussed.
Development of radio frequency induction plasma generators for neutral beams
Authors: DiVergilio W. F. , Goede H. , Fosnight V. V.
Published: July 2002

The techniques, operational aspects, and experimental results of a radio frequency induction plasma generator, with an internal rf power coupler, intended for intense neutral beam applications are described. One of the development sources suitable for 10×10-cm2 extraction optics was operated to a deuterium ion current density of 250 mA/cm2, uniform to 5%, over a circular extraction area 15 cm in diameter with a coupled rf power of 20 kW. Temporal fluctuation levels in the extracted ion current were measured to be typically 1% of the dc level. A second developmental source suitable for 10×40-cm2 grid sets was operated to 200 mA/cm2, uniform to ±8% over a 10×40 cm2 area, with 40-kW coupled rf power.
Spacecraft mass spectrometer ion source employing field emission cathodes
Authors: Curtis C. C. , Hsieh K. C.
Published: July 2002

An ion source that uses field emission cathodes to provide a 200-eV, 0.1-mA electron beam has been incorporated into three spacecraft mass spectrometers. The source is rugged, compact, and dissipates less than 30 mW.
High-flux normal incidence monochromator for circularly polarized synchrotron radiation
Authors: Schäfers F. , Peatman W. , Eyers A. , Heckenkamp Ch. , Schönhense G. , Heinzmann U.
Published: July 2002

A 6.5-m normal incidence monochromator installed at the storage ring BESSY, which is optimized for a high throughput of circularly polarized off-plane radiation at moderate resolution is described. The monochromator employs two exit slits and is specially designed and used for low-signal experiments such as spin- and angle-resolved photoelectron spectroscopy on solids, adsorbates, free atoms, and molecules. The Monk–Gillieson mounting (plane grating in a convergent light beam) allows for large apertures with relatively little astigmatism. With two gratings, a flux of more than 1011 photons s−1 bandwidth−1 (0.2–0.5 nm) with a circular polarization of more than 90% in the wavelength range from 35 to 675 nm is achieved.
Low-cost high-resolution laser spectrometer system in the near infrared region using a GaAlAs diode laser
Authors: Gustavsson T. , Martin H.
Published: July 2002

A commercial low-cost GaAlAs diode laser, operating at room temperature, was used as the tunable monochromatic light source in a high-resolution laser spectrometer for the near-infrared spectral region. This laser was found to have qualities fully comparable to those of the thousandfold more expensive single-mode dye lasers commonly used in high-resolution laser spectroscopy. Molecular spectra, obtained both in absorption and in laser-induced emission, and optogalvanic atomic spectra clearly demonstrate the power of this extremely simple and cheap laser spectroscopic system.
Ion temperature profile measurements using the far line wings of Hα
Authors: Bengtson Roger D. , Boédo J. , Rowan W. L.
Published: July 2002

We present ion temperature profiles for the outer half of the TEXT plasma using the Doppler broadened far line wings of the Hα line profile. The technique depends on the assumption that the hydrogen neutrals have equilibrated with the ions through charge-exchange collisions. Data reduction depends upon going far enough out on the line wing that the remaining intensity in the profile originates in the hottest portion of the line of sight, thus removing the need for an inversion procedure. A scanning Fabry–Perot interferometer is used to measure the line profiles because of its superior instrumental profile. This technique and its results will be compared with the charge-exchange technique and impurity Doppler broadening results. The application to ion temperature measurements using a diagnostic neutral beam will also be discussed.
rf-probe method for measurements of electron densities in plasmas at high neutral densities
Authors: Johnsen Rainer
Published: July 2002

A radio frequency (rf) method has been developed for measurements of the electron density in weakly ionized gases at high (∼atmospheric) neutral density. The technique relies on passing an rf current ( f=15 MHz) between two concentric cylindrical electrodes and relating the measured electrical conductivity to the electron density. The physical principles of the technique and quantitative theory are presented in detail. Test measurements in photoionized helium gas mixtures indicate that the method performs well in the electron density range from about 105 to 1010 cm−3 and that it may also be applicable for measurements of ion densities in plasmas composed predominantly of positive and negative ions.
Auto-switching filter array for frequency measurement of unstable signals
Authors: Kashiwagi Junji , Aoki Tadashi
Published: July 2002

A bandpass filter whose center frequency is switched automatically is described. The frequency filter makes it possible to measure the frequency of the signal which has fluctuating amplitude and is accompanied by considerable noise. Twelve bandpass filters whose center frequencies are located slightly apart from each other and connected in parallel, discriminate the signal and the noise. From the bandpass filters paralleled, only the output with the largest amplitude among all is selected by photocoupler switches. The frequency range of the filter array is two decades and easily expandable. An application to laser-Doppler anemometer is also described.
Baseline compensation circuit for measurement of transient signals
Authors: Janata E.
Published: July 2002

An automatic compensation circuit (back-off circuit) is described which incorporates a sample-and-hold amplifier with a digital memory in order to avoid droop problems at long durations of measurement. This device is helpful in pulse radiolysis and laser-flash photolysis experiments on the nanosecond to second timescale. The range of current compensation is ±5 mA. The resolution is ±1.27 μA and the accuracy is better than ±1% for a range of compensation of 0.15 to 5 mA. A voltage output is provided as a measure (1 V/mA) of the compensated current.
Computer-controlled apparatus for measuring complex elastic, dielectric, and piezoelectric constants of polymer films
Authors: Furukawa T. , Date M. , Ishida K. , Ikeda Y.
Published: July 2002

Principles and design details are described for a fully automatic system measuring frequency and temperature spectra of the complex elastic, dielectric, and piezoelectric constants of polymer films. A microcomputer is used to control all processes including wave generation, sampling, and calculations. A sinusoidal excitation wave is written onto a RAM, readout by an external clock, and applied to a sample via a D/A converter. The resulting signals related to force, deformation, charge, and voltage are simultaneously sampled using the same clock and are determined as complex quantities through Fourier transformation. Their ratios give corresponding complex response functions. A multifrequency signal consisting of eight sinusoidal waves with frequencies of common ratio 2 is used to obtain frequency spectra over two decades at a time. This system operates over a frequency range from 0.01 to 100 Hz for elastic and piezoelectric measurements and from 0.01 Hz to 10 kHz for dielectric measurements at temperatures from −160 to 250 °C with an accuracy of 0.1% in tan δ.
Wide-angle beam condensor for recording IR transmission spectra of strongly scattering samples in the 3000 cm−1 region
Authors: Brunner G. O. , Reifler H. , Kleber E.
Published: July 2002

A condensor system consisting of two or three concentric rings with aspheric reflecting surfaces (elliptic or hyperbolic) for the outer part of the beam and a lens (CaF2) for the central part of the beam is described. A considerable increase in energy throughput to the detector and a much improved baseline are obtained for transmission experiments involving high-scatter samples.
Neutral beam probe spectroscopy for the measurement of local plasma density fluctuations
Authors: Komori A. , Yamagiwa K. , Mitarai O. , Yamaoka H. , Kadota K. , Fujita J.
Published: July 2002

A neutral Li beam probing combined with a spectroscopic technique to measure local electron-density fluctuations is experimentally demonstrated in an ECR test plasma. The density fluctuations of up to 180 kHz are excited and controlled by applying periodic bursts of sinusoidal waves to a grid. The electron-density fluctuation levels thus obtained are found to agree well with those measured with a Langmuir probe. It is also suggested that this method can be applied to plasmas whose densities are in a wide range of 1010–1013 cm−3.
Microcomputer-controlled chemiluminescence spectrometer for solid phase samples
Authors: Pronko J. G. , Chapman I. V.
Published: July 2002

An effective, low-cost microcomputer-controlled chemiluminescence detection system was developed for use in correlating the stability and aging of materials to the chemiluminescence emitted from the surface of these materials. The system is completely automated to record data as a function of time and sample temperature. In addition, spectra over the visible light region can be obtained under microcomputer control. A description of the hardware, computer interface, and programs as well as the use of the system are presented.
Auroral and airglow Fabry–Perot spectrometer
Authors: Hecht J. H. , Christensen A. B. , Pranke J. B. , Chater W. T. , Howey C. K. , Lott R. L. , Sivjee M. G.
Published: July 2002

A microcomputer-controlled and piezoelectrically scanned Fabry–Perot spectrometer capable of being transported to remote field sites has been constructed. The Fabry–Perot has a 70-mm aperture and has a provision for computer control of the cavity drift. The instrument has been operated at resolutions from 0.06–1.5 Å in making high-speed observations of the aurora from 7500–8500 Å. A separate filter-wheel photometer section provides information on other auroral and airglow emissions such as N+2(4278) and OI(6300). The apparatus is portable and has been operated at Poker Flat, Alaska and Churchill, Canada.
Hall effect measurement in the diamond anvil high-pressure cell
Authors: Patel Dinesh , Crumbaker Todd E. , Sites James R. , Spain Ian L.
Published: July 2002

Hall effect measurements have been carried out in the diamond anvil cell to pressures of 6 GPa. A plasma sprayed coating has been used to insulate the electrical leads from the gasket, similar to the configuration employed by Tozer and King [Rev. Sci. Instrum. 56, 260 (1985)], but a van der Pauw geometry was used to make the Hall and mobility measurements. Application of the technique to GaAs at 300 K is described, for which the Γ-X conduction band crossover is observed at 4.0 GPa, in good agreement with recent photoluminescence measurements.
Development of an x-ray framing camera
Authors: Stearns D. G. , Wiedwald J. D. , Cook W. M. , Hanks R. L.
Published: July 2002

An ultrafast x-ray framing camera is being developed at Lawrence Livermore National Laboratory to be used as a diagnostic instrument in laser experiments. The framing camera is designed to provide temporal resolution of 50 ps and spatial resolution of 30 μ at the image plane. The unique design incorporates the x-ray photocathode directly into a suspended-strip transmission line. The photocathode is gated using a high-voltage (−5 kV) pulse of short duration generated with a photoconductive switch. The photoelectrons are extracted through an unbiased microchannel plate and are directly detected with a charge-coupled device in the electron-bombardment mode. We report on current progress in the fabrication, characterization, and integration of the various components of the instrument.
New probe for high-temperature nuclear-magnetic-resonance spectroscopy with ppm resolution
Authors: Stebbins J. F. , Schneider E. , Murdoch J. B. , Pines A. , Carmichael I. S. E.
Published: July 2002

A new type of instrument has been designed and built to make Fourier transform nuclear-magnetic-resonance (NMR) spectroscopic measurements at temperatures to at least 1200 °C, with a resolution of about 1 ppm. A sample is rapidly and repeatedly shuttled between the furnace and the radio frequency (rf) coil of the NMR probe (both located within a high field superconducting magnet), spending most of the time in the furnace. During each cycle, a series of rf pulses may be given and a single free-induction decay sampled. The rf coil is located outside of the furnace and is maintained at room temperature despite its close proximity to the sample. Electronic stability and coil ‘‘filling factor’’ are thus both optimized. The sample temperature drops below that of the furnace when cycling begins, but rapidly approaches a nearly constant value with only small fluctuations. 99% BN has been successfully used as a sample container in experiments on 27Al, 29Si, and 23Na in molten silicates in the system Na2O–Al2O3–SiO2.
Delayed and continuous nucleation of islands in GaAs molecular beam epitaxy revealed by in situ scanning electron microscopy
Authors: Osaka J. , Inoue N. , Homma Y.
Published: July 2002

In situ scanning electron microscopy reveals delayed and continuous nucleation of two-dimensional islands in the molecular beam epitaxy of GaAs. It is found that the islands do not appear until about 1/3 of a monolayer is deposited. The mechanism is discussed in terms of site dependent successive atomic layer growth processes. Nucleation continues till the islands start to coalesce.
Miniature, solid-state gas compressor
Authors: Lawless W. N. , Arenz R. W. , Cross L. E.
Published: July 2002

A concept for a miniature, solid-state gas compressor is examined. The device operates by the phased activation of voltage-driven, electrostrictive ceramic blocks along a compression channel wherein a confined elastomer provides a motion-amplifying medium for peristaltically closing the compression channel. The device is also self-valving. Model estimates based on the nonlinear electromechanical parameters for paraelectric BaTiO3 suggest that a small (∼5×5×9-cm3), lightweight (∼1-kg) device would supply ∼0.3 cm3 per cycle at a compression ratio of 25:1 employing modest electric fields (∼20 kV/cm). At 500 Hz this corresponds to 38 mW of ideal Joule–Thompson refrigeration at 4.2 K using He gas. The efficiency of the device is estimated to be ∼85% (not including the power supply). A three-cell mechanical simulator of the concept was built and tested, and it was demonstrated that compression and self-valving can be achieved by peristaltically extruding an elastomer against a gas channel. An electronic power supply to drive the electrostrictive ceramics was designed, and a three-cell supply was built and tested which demonstrated that voltages up to 150 V could be switched at frequencies up to 10 kHz using small, inexpensive components. A critique of practical considerations is given, and it is concluded that the concept is feasible but additional research is required in elastomeric materials and in fabricating relatively large ceramic capacitors (∼2×2×1 cm3). Currently available electrostrictive actuators are inadequate.
Aperture intensity ratio fiber-optic displacement sensor
Authors: Wobschall Darold , Hejazi Shahram
Published: July 2002

A displacement sensor based on the ratio of fiber-optic light emitted from two fixed position optical fibers into a third, movable fiber connected to a photodetector is described. Square-wave modulated light of opposite phases produces a corresponding square wave at the detector which has zero ac amplitude at the center position and an amplitude proportional to displacement on either side of the detection fiber. A phase-sensitive detector produces a positive dc output voltage for positive displacements and negative for negative displacements.
Practical preparation of copper oxide superconductors
Authors: Chen Xiao-Dong , Lee Sang Young , Golben John P. , Lee Sung-Ik , McMichael R. D. , Song Yi , Noh Tae W. , Gaines J. R.
Published: July 2002

We present a thorough yet simple approach for synthesizing high Tc superconductors of substantial quality. The approach is accompanied by a step-by-step discussion of possible pitfalls as well as a correlation of the sample characteristics to the various preparation procedures. A procedure sufficiently accurate for characterizing the resistance as a function of temperature for a Tc determination is also described.
Scanning tunneling microscope with micrometer approach and thermal compensation
Authors: Jericho M. H. , Dahn D. C. , Blackford B. L.
Published: July 2002

A scanning tunneling microscope that uses a micrometer coarse approach mechanism is described. The approach mechanism can be decoupled from the rest of the microscope to result in a thermally compensated instrument. Thirty minutes after establishing tunneling, lateral thermal drift in our instrument is down to 0.5 Å/min. Construction details of the microscope and high resolution images of pyrolytic graphite and 2H-NbSe2 samples are presented.
Pellet injection on the ZT-40M reversed field pinch
Authors: Watt R. G. , Wurden G. A. , Weber P. G. , Büchl K. , Spanos E. K.
Published: July 2002

The four barrel pneumatic pellet injector originally used on the Alcator C tokamak at MIT has been reconfigured for use on the ZT-40M reversed field pinch (RFP) at Los Alamos National Laboratory. The lower temperature and density in this device require operation at velocities significantly lower than on Alcator. Allowing a 2-s warmup prior to firing the injector has enabled operation with pressures as low as 40 psig and velocities ranging as low as 200 m/s with H2 pellets, without major cryostat modification. Initial injection experiments in the ZT-40M plasma have verified that pellet refueling is effective for density control, but the net particle inventory increase is less than might be expected based on simple models. Indications of nonoptimal penetration and curvature of the pellet trajectory, in addition to comparable time scales for particle confinement and pellet transit, may account for this.
Time-of-arrival photoelectron correlator
Authors: Dhadwal H. S. , Chu Benjamin , Xu Renliang
Published: July 2002

A photoelectron correlator based on the measurement of the joint probability distribution function in the arrival times of eight stop pulses following a single start pulse is described. This correlator has a measurement interval of 5 μs and delay time resolution of 2.5 ns. With an eight-stop capability, much higher count rates can be used without fear of distorting the intensity–intensity time correlation function due to saturation. Thus the accumulation time becomes tolerable for acceptable signal-to-noise ratios in time correlation function measurements with such a short delay time increment.
Pressure, velocity, and temperature sensitivities of a bleed-type pressure sensor
Authors: Giovanangeli J. P. , Chambaud P.
Published: July 2002

This paper presents the results of a complete series of tests and calibrations of a bleed-type pressure sensor used in order to determine in-stream static pressure fluctuations in a turbulent boundary layer just above a pure laboratory wind–wave field. The static calibrations show that for air flow mean velocities lower than 15 m/s, the sensor response depends not only upon the pressure but also upon the velocity and the temperature of the air flow. Dynamic calibrations prove that the temperature and velocity sensitivities depend strongly upon the frequency. They are important for low frequencies and equal to zero only for frequencies greater than 0.1 Hz if the sensor is operated in an isothermal turbulent flow and greater than 1 Hz for a nonisothermal flow. Pressure sensitivity doesn’t depend upon frequency for a range from dc to 600 Hz.
Pressure-pulse measurements in electrode kinetics
Authors: Jovancicevic V. , Bockris J. O’M.
Published: July 2002

An apparatus is described whereby physicochemical measurements which involve pressure changes up to about 2 kbar can be made in times of the order of 102 s. Pressure changes in short times are achieved by the evolution of a large supply of hydrogen gas into a very small volume.
Development of a controlled spray generator
Authors: Ashgriz N. , Yao S. C.
Published: July 2002

A multiorifice spray generator with two different modes of operation is developed. The impulse jet operation mode covers a wide range of droplet frequencies and produces arrays of droplets with controllable spacing, but with a wide size spectrum. This ejector also operates in pressurized flow mode. In this mode, optimum disturbance frequency breaks up the liquid jets into uniform size droplets, resulting in a monosized spray. Precise control of fuel flow rate and droplet size is achieved.
Instrumented pseudofruit for acquisition of impact damage data for agricultural perishables
Authors: Siyami S. , Zapp R. , Tennes B. , Brown G.
Published: July 2002

Impact bruising during harvesting, manual and mechanical handling, and during transportation of agricultural perishables results in major crop loss and/or commodity quality loss. An instrumented pseudofruit has been developed which permits automatic measurement and recording of vector accelerations (impacts) along with the time of occurrence. This device will assist in identifying time and amplitude of damaging impacts. The features of this device are: (1) It is a miniaturized, totally integrated, portable digital system which is cast in a 15-cm rigid cube or 10-cm-diam sphere. (2) It is calibrated to provide an adequate degree of accuracy for the measurement of impact it will experience. (3) Serial communication is provided to permit program initialization and data transfer to an independent processing computer, where custom-developed routines convert the measured impacts into equivalent bruising and/or drop heights for the fruit of interest (e.g., apple).
Electrodeless measurement of ionic conductivity of RbAg4I5: Temperature dependence
Authors: Ishida T. , Nakada I. , Koike M.
Published: July 2002

An electrodeless method has been applied to the measurement of an ionic conductivity of a single crystalline RbAg4I5 as a function of temperature. The activation energy obtained by this method is in good agreement with those of earlier works.
Device for controlled intensification of the light output of xenon flash tubes
Authors: Baba Shoji A. , Mogami Yoshihiro
Published: July 2002

A circuit has been designed for the operation of commercial xenon tubes with flexible application to stroboscopic micrography in biological researches. This operation system enables intensification of the light output for successive flashes in a short time for high-resolution photography.
CO2 laser scintillation interferometer for the measurement of density fluctuations in plasma confinement devices
Authors: Nazikian R. , Sharp L. E.
Published: July 2002

Density fluctuations in magnetically confined plasmas have been measured from the phase scintillations impressed onto a 10.6-μm wavelength laser beam probe, using a Mach–Zender interferometer operating in the optical near field. By careful design, the effects of vibration and air-borne sound waves, which limit the instrument’s sensitivity, have been reduced to a level such that the minimum detectable signal is 10−6 rad in the frequency range 10 kHz–1 MHz, corresponding to a plasma density fluctuation level (δN/N) of 10−4.
Elimination of the induced current error in magnetometers using superconducting flux transformers
Authors: Dummer D. , Weyhmann W.
Published: July 2002

The changing magnetization of a sample in a superconducting flux transformer coupled magnetometer induces a current in the transformer which in turn changes the field at the sample. This ‘‘image’’ field and the error caused by it can be eliminated by sensing the current in the loop and nulling it by feedback through a mutual inductance. We have tested the technique on the superconducting transition of indium in an applied magnetic field and shown that the observed width of the transition is greatly reduced by maintaining zero current in the flux transformer.
Surface dynamics during CdTe growth by molecular beam epitaxy
Authors: Arnoult A. , Cibert J.
Published: July 2002

The dynamics of growth of CdTe by molecular beam epitaxy is studied by RHEED intensity oscillations. The transition to growth by step propagation is observed at lower temperature (i.e., the diffusion length is larger) on the Te-rich (2×1) surface than on the Cd-rich c(2×2)–(2×1) one. A strong anisotropy is found, which suggests that growth islands are elongated in the [11̄0] direction. In addition, sublimation cannot be neglected, with at least two mechanisms with different activation energies.
Simple and direct method to determine the single or polydomain status of the particles in a uniaxial ferromagnetic polycrystal: Measure of the coercive and anisotropy fields
Authors: Turilli G. , Pareti L. , Paoluzi A.
Published: July 2002

We present a method and the corresponding apparatus which allow one to determine the single or polydomain status of the particles in a uniaxial ferromagnetic polycrystal. The method is based on the measurement of the field dependence of the transverse susceptibility χt(H). The proposed technique also allows for the measure of the coercive field of the specimen. Furthermore, the anisotropy field can be measured for the single-domain particle samples.
Precision limits of lifetime estimation algorithms as determined by Monte Carlo simulation: A comparison of theory and experiment
Authors: Dowell L. J. , Gillies G. T.
Published: July 2002

The estimation of exponential decay lifetimes is important in many areas of physics, but often difficult if the waveform produced by some particular process (say, fluorescence decay) is noisy. We have used a simulation technique which makes it possible to model accurately two common waveform analysis methods. Results from actual experiments can be compared with those produced by the simulation in order to investigate the nature of the measurement system’s precision limits and thereby effect a reduction of the measurement error. Specifically, an algorithm calculating decay lifetime from two data points exhibited a one-sigma error of 4% when the measurement signal-to-noise ratio was 40:1, compared with a 0.1% error of a least-squared error algorithm under similar conditions.
On-line gas electron diffraction identification of gas chromatography effluents (GC-GED)
Authors: Ewbank John D. , Paul David W. , Schäfer Lothar , Siam Khamis , Monts David L. , Faust Walter L.
Published: July 2002

Experiments are described which document the utility of gas electron diffraction (GED) as a means of detecting analytes emerging from the column of a gas chromatograph (GC). In these experiments electron diffraction patterns from GC effluents are made visible on a phosphor screen, and the intensities of each GC peak are recorded on line by a 1024-channel linear photodiode array detector. The technique not only indicates the presence of elutants but also provides auxiliary information on their molecular structures under favorable conditions. Minimum sample sizes of about 1 μl per component are currently required for GC-GED, but indications are that further detector enhancements will allow the recording of electron intensities from smaller samples.
Simple laser refractometer for liquids
Authors: Zaidi A. A.
Published: July 2002

A method for the determination of the refractive index of liquids using a He–Ne laser is presented. The experimental setup is simple and utilizes equipment which is normally available in most optics laboratories. Measurements carried out on water and several organic liquids are reported. The values of the refractive indices obtained by this method are in good agreement with those given in literature. The accuracy of results is of the order of ±5×10−3 and can be improved by the use of a scale of higher precision.
Four-probe single-crystal holder for conductivity measurements
Authors: Papaioannou John , Dye James L.
Published: July 2002

The development and testing of a four-probe small single-crystal holder for conductivity studies down to liquid-helium temperature is described. A single crystal of the reactive sodide, Na+C222⋅Na–, was successfully mounted, but its resistance was too high to permit determination of the conductivity. The method should be useful for single-crystal conductivity measurements of reactive and/or thermally unstable crystals.
Steady-state discharge test of coaxial LaB6 cathode
Authors: Tanaka S. , Leung K. N. , Purgalis P. , Williams M. D.
Published: July 2002

Results of steady-state discharge test of coaxial LaB6 cathodes in a multicusp plasma generator are described. After a single-unit test of a compact, 6.4-mm-diam coaxial LaB6 cathode, a discharge test of two cathodes with one heater power supply was carried out with success. In addition, a new tapered coaxial cathode, which was designed to prevent overheating of LaB6 due to ohmic heating by discharge current, was investigated. During steady-state plasma source operation, a discharge current as high as 180 A was obtained with this tapered cathode.
Rutherford magnetic spectrograph for intense ion beam measurements on PBFA-II
Authors: Leeper R. J. , Stygar W. A. , Kensek R. P. , Lee J. R. , Johnson D. J. , Lockner T. R. , Maenchen J. , Hebron D. E. , Wenger D. F.
Published: July 2002

A time-resolved magnetic spectrograph employing a gold Rutherford-scattering foil has been constructed to measure the parameters of the intense ion beams generated by Sandia National Laboratories’ PBFA-II accelerator. The spectrograph operates by allowing the direct intense beam of PBFA-II to scatter from a thin gold foil to reduce its intensity for magnetic analysis. Details of the spectrograph’s construction, detector package, and recent PBFA-II proton data are included in the paper.
Superthermal electron distribution measurements from polarized electron cyclotron emission (invited)
Authors: Luce T. C. , Efthimion P. C. , Fisch N. J.
Published: July 2002

Measurements of the superthermal electron distribution can be made by observing the polarized electron cyclotron emission. The emission is viewed along a constant magnetic field surface. This simplifies the resonance condition and gives a direct correlation between emission frequency and kinetic energy of the emitting electron. A transformation technique is formulated which determines the anisotropy of the distribution and number density of superthermals at each energy measured. The steady-state distribution during lower hybrid current drive and examples of the superthermal dynamics as the runaway condition is varied are presented for discharges in the PLT tokamak.
Automated system for the measurement of fluctuation phenomena in FETs
Authors: Abidi A. A.
Published: July 2002

A computer-controlled system to measure the flicker noise spectra in MOSFETs up to 1 MHz is described. The field-effect transistor (FET) is automatically biased in all its regions of operation, and the current noise spectral density is measured. The system has several advantages, principally that of accuracy, in this application, and does not exact any additional penalty in noise performance over previously reported systems. An analysis of the resolving power of the noise amplifier, as well as the limitations to its performance, are discussed.
System for simultaneous count/current measurement with a dual-mode photon/particle detector
Authors: Kristo Michael J. , Enke Christie G.
Published: July 2002

A microcomputer-based control system for a dual-output Channeltron (TM) detector has been developed and implemented. This system is capable of collecting ion current and ion-counting information simultaneously. Ion current and ion-counting data are scaled in software and provide consistent ion intensity values from both outputs. Calculation of the ion current/ion count rate ratio at each peak in the mass spectrum allows the system to compensate for variations in gain from peak to peak. The data collection system maximizes the data collection rate and extends the useful dynamic range of electron multiplier-based detection to nine orders of magnitude with no change in any of the multiplier conditions. Measurement of such a wide range of ion intensities in a single spectrum is particularly useful for applications in tandem mass spectrometry.
Automated outgassing facility with inductive heating
Authors: Simpkins J. E. , Mioduszewski P. K.
Published: July 2002

The use of graphite for both first walls and limiters in fusion experiments has increased during recent years. However, graphite contains large amounts of gaseous contaminants that affect the plasma adversely. To study the vacuum characteristics of various candidate graphites and to evaluate conditioning techniques for these materials, we have built an outgassing facility, which is described in this paper. Induction heating is used to heat the sample to 2000 °C. This heating technique was chosen to avoid heating other components in the vacuum chamber. Since the walls are heated by radiation from the sample at the higher temperatures, they are kept at a constant elevated temperature of 100 °C by thermostatically controlled heaters throughout the experiment. The entire system is automated. Some results that compare POCO and pyrolytic graphites are shown.
Comparison between two-wire and three-wire models for shielded twisted-pair cables used in Johnson noise thermometry
Authors: Roberts M. J.
Published: July 2002

Using typical values of cable parameters and typical connections used in Johnson noise thermometry, a comparison was made between a two-wire and a three-wire transmission line model of a 30-m-long, shielded, twisted-pair cable over a range of frequencies from 0 to 300 kHz. For a 200-Ω source impedance and a 1-MΩ load impedance, the maximum difference between the voltage transfer functions calculated from the two models was 0.415%. For a 500-Ω source impedance, the maximum difference was 0.607%. For a 200-Ω source impedance and a 1-Ω load impedance, the maximum difference between the current transfer functions calculated from the two models was 4.24%. For a 500-Ω source impedance, the maximum difference was approximately 4.47%.
Compact vacuum ultraviolet source for photoelectron spectroscopy
Authors: Tonkyn Russell G. , White Michael G.
Published: July 2002

A simple source chamber is described which enables the introduction of laser-generated, vacuum ultraviolet (VUV) radiation below 102 nm into most existing photoelectron and photoion spectrometers. A long capillary light guide provides a conductance barrier between the VUV source and experimental chambers, and also provides a small, well-collimated VUV beam at the interaction region. A platinum photodiode is found to provide a useful measure of the VUV intensity with minimal interference from the unconverted UV light. The performance and capabilities of the source are demonstrated by several applications using photoelectron spectroscopy.
Description and performance of a new electron scattering spectrometer involving multiangle parallel detection
Authors: Tremblay D. , Dubé D. , Roy D.
Published: July 2002

This paper describes the realization of a new electrostatic electron spectrometer, called MAPDESS, for the parallel measurement of angular distributions in gas-phase electron scattering experiments. The electron beam originates from a filament and a standard 127° cylindrical monochromator, and the beam is carried to the collision center at the desired energy by three successive cylindrical electron lenses that partly compensate for the high dissymmetry of the beam. The electrons scattered off the gaseous target are filtered by a 19-aperture angle selector (from 18° to 162°) and injected into the energy analyzer by means of an annular zoom lens. This lens allows one to keep control of the beam in the retarding or accelerating process, which is necessary to get a good resolution and/or intensity. The analyzer is a novel truncated spherical mirror symmetric about the scattering center and whose ring-shaped exit is coupled to 19 channel electron multipliers, thereby allowing parallel multiangle detection. This spectrometer thus directly gives the angular distribution of an energy-resolved scattering event in a plane. The angular resolution is shown to be ±3°. Some measurements in rare gases are presented, showing an energy resolution of 25 meV at a pass energy of 7 eV.
An algorithm for the compound Poisson analysis of histogram data
Authors: Cobb Carolus M. , Bjorkholm Paul , Cobb Carolus M.
Published: July 2002

An algorithm is presented for fitting histogram data which may be considered the sum of several different Poisson sources (compound Poisson distribution). The average values and the fractions of the population associated with each average value are calculated from the moments of the experimental histogram. It is believed that the algorithm obtains the maximum possible information from the data.
Flow meter based on the trapped vortex pair fluidic oscillator
Authors: Mansy Hussein , Williams David R.
Published: July 2002

A new type of fluidic flow meter is presented, which relies on the hydrodynamic instability resulting from the interaction of a pair of vortices for its operation. The vortices are confined to a convergent channel section of the device and oscillate along approximately elliptical trajectories. The output of the oscillator is a fluctuating pressure signal whose frequency is linearly proportional to the flowrate. One particular configuration of the fluidic oscillator operates over the range 0.227–7.135 (m3/h) with a maximum pressure drop of 63 mm of water and a calibration linearity better than±2.9%. Experiments with both air and water have shown that the fluidic oscillator calibrations are similar when plotted as Strouhal number against Reynolds number.
Echographic technique-based apparatus to detect structure and anomalies in the subsoil
Authors: Cannelli G. B. , D’Ottavi E.
Published: July 2002

An apparatus based on acoustic wave–echographic technique has been developed to detect shallow structure and inhomogeneities of the earth. The apparatus consists of a carefully assembled pair of paraboloidal transducers which are used for transmission and for reception of seismic signals. The transmitting transducer is an electroacoustic pulse source in which the acoustic wave is produced by a high-energy electric spark-gap set at the focus of the paraboloidal reflector which is filled with a suitable liquid. The receiving transducer is similar to the transmitter except for a piezoelectric-ceramic device at its focus. Both transducers have mechanisms for adjusting the positions of the spark gap and the piezoelectric ceramic around the respective foci in order to optimize performance. The experimental results reported in this paper, in conjuction with those of the same authors in a previous work, show that this echographic system can be used successfully in shallow prospecting on land as well as under water, and even more profitably in exploration of near-surface zone where traditional techniques are inadequate.