bluuebunny/crossref_metadata_2025 huggingface dataset:
Directional velocity analyzer for measuring electron distribution functions in plasmas
Authors: Stenzel R. L. , Gekelman W. , Wild N. , Urrutia J. M. , Whelan D.
Published: March 2003

A directional velocity analyzer has been developed for measuring electron distribution functions in plasmas. It contains a collimating aperture which selects particles from a narrow cone in velocity space and a retarding potential analyzer. The distribution function f(v, θ, φ) is obtained from a large number of analyzer traces taken at different angles θ, φ. In addition, the small analyzer can be moved in space and the measurements are time resolved so as to obtain the complete phase space information f (v, r, t). The large data flow of this seven-variable function is processed with a high-speed digital data-acquisition system. The new electron velocity analyzer is applicable over a wide parameter range in electron energies and densities. Various cases of anisotropic distributions such as beams, shells, tails, and drifts have been successfully investigated.
Mössbauer velocity calibration with an (Al, Ga)As laser diode
Authors: Otterloo Bert F. , Stadnik Zbigniew M. , Swolfs Ad E. M.
Published: March 2003

Velocity calibration of a Mössbauer spectrometer operating in a constant acceleration mode has been obtained with a Michelson interferometer using an (Al, Ga)As laser diode. The very small size of the laser diode makes it possible to construct a very compact optical system for velocity calibration.
Magnetically coupled digital motor for producing vortical motion in liquids in tubes
Authors: Jewett Douglas
Published: March 2003

Vortical motion of liquids in tubes, for the purpose of mixing or evaporation in small-scale chemical process streams, is produced by a magnetically coupled digital drive mechanism. The latter consists of an eight-pole stator, to which a continuously commutating magnetization is applied, one pole at a time, and a rotor consisting of a magnetically soft steel ring surrounding and fixed to the liquid-containing tube. The power to the stator windings is controlled by MOSFET transistors driven directly by a CMOS counter decoder. The clock signal is derived from the 60-Hz ac line, eliminating the need for a filtered power supply.
Low-temperature, high-pressure cell for Raman studies of gases and liquids
Authors: Mazzinghi P. , Zoppi M.
Published: March 2003

An optical cell for gases or liquids, with three windows, for pressures up to 1000 bar and temperatures between 10 and 300 K is described. Design criteria and results of performance tests are also presented.
High-pressure low-temperature locknut cell for both EPR and NMR studies to 10 kilobars and 77 K
Authors: Sinha Shantanu , Srinivasan R.
Published: March 2003

A locked high-pressure cell with working pressure range up to 10 kbars suitable for low-temperature studies to 77 K has been described. It can be used for both EPR and NMR studies of single crystals (and other solid samples). The high-pressure seal and all other aspects of the cell remain the same for either application. Only a change of the bottom plug is required for a switch from a nuclear-magnetic-resonance (NMR) to an electron-paramagnetic-resonance (EPR) experiment. Details of the procedure for the calibration of pressure inside the cell at various temperatures are discussed. The performance of the cell in EPR (Cr3+ion) and NMR (27Al nucleus) studies is reported.
Compact 1-GW pulse power source
Authors: Ivers J. D. , Nation J. A.
Published: March 2003

A compact 1-GW pulsed power source, developed for use in a collective acceleration experiment, is described. The system utilizes seven artificial Blumlein pulse forming networks which are charged in parallel and discharged in a series configuration. The generator has been used to produce a 300-kV, 3-kA, 0.5-μs electron beam.
Detonation products gun
Authors: Presles H. N. , Bauer P.
Published: March 2003

To obtain a projectile velocity of about 1500 m/s with a powder gun or a compressed gas gun the barrel must be a few meters long in the former case and roughly 15 m in the latter one. In the present study a new device is proposed, based on the mechanical and thermodynamic properties of detonation products used as propelling gas and created by the detonation of a gaseous explosive mixture at a high initial pressure (100 bar). Results of computation of the projectile velocity using the detonation products of a C2H4–O2–N2 mixture are presented. They show that a high-velocity projectile (1500 m/s) might be obtained in a rather short barrel (4 m long). Moreover, this setup allows a wide range of velocities.
Comparison between constant-current and constant-temperature hot-wire anemometers in high-speed flows
Authors: Bestion D. , Gaviglio J. , Bonnet J. P.
Published: March 2003

A comparison is made between the performance of constant-current (C.C.A.) and constant-temperature (C.T.A.) anemometers in measuring various characteristics of turbulence in supersonic flows. The two systems are comparable, with regard to the bandwidth and to the signal-to-noise ratio, provided that the overheat is not too low in the case of the C.T.A. system, and that suitable corrections be applied to the C.C.A. system. Besides, the two types of apparatus are similar in that their use is very time consuming, a separate adjustment being required for each point of measurement in the flow and each overheat, especially adjustment of the C.T.A. bandwidth, using a sine wave technique, and adjustment of the thermal lag compensating circuit of the C.C.A. system. They differ in that rigorous corrections, dealing for example with electrical noise and insufficiency of the bandpass, are more easily determined in situ and applied with the last system, while the former is better adapted to rapid measurements in blow-down facilities, or when only high overheats are required. As for the level of the electronic noise, it seems to be equivalent in the two systems. Besides, when turbulent intensities and spectral densities are measured in a continuously running tunnel, the results are more reliable if they are obtained with the C.C.A. system, except for measurements of transverse fluxes of heat or momentum performed using an inclined hot wire. Hence the two types of apparatus appear to be complementary.
Data-acquisition system for photoelectron and electron energy loss spectrometers
Authors: Schmidt Manfred
Published: March 2003

A data-acquisition system for the automatic control of photoelectron and electron energy loss spectrometers, based on a commercially available microcomputer, is presented. High versatility is achieved by the introduction of a new bus system, specially designed for laboratory applications. With this bus more than 20 external devices such as analog-to-digital converters, counters, digital-to-analog converters, and stepper-motor interfaces can be controlled. A detailed description of the bus and the circuitry of the interfaces is given.
Application of the linear-resistance flowmeter for low Reynolds numbers two-phase flowrate measurements
Authors: Vallascas Rinaldo
Published: March 2003

In this work the possibility of measuring two-phase flowrate by means of filtering systems when the volumetric flow ratio is known has been verified. Furthermore, for the elements examined, the validity of a linear relationship between flow and pressure drop for low Reynolds numbers has been confirmed. The experiments were carried out with two filtering systems consisting of lead balls with a diameter of 1.9 and 2.9 mm, respectively, in the two-phase flow range comprised between 0.8 and 20 cm3/s for volumetric flow ratios of up to 50%. Taking for granted the necessity of calibration of the measuring device in single-phase flow conditions of air alone and water alone, the experimental observations have shown excellent agreement with the equation proposed, and unless particularly close approximations are required, resort to calibration with two-phase fluids seems superfluous. Moreover, the validity of the correlation between the resistance index number and the Reynolds number for two-phase flow is also corroborated.
Thermometry in high magnetic fields at low temperatures
Authors: Naughton M. J. , Dickinson S. , Samaratunga R. C. , Brooks J. S. , Martin K. P.
Published: March 2003

We have investigated the behavior of carbon resistor and capacitive thermometers from 4.2 to below 0.1 K and to 19 T. We observe, in agreement with previous work at higher temperatures, a nonmonotonic magnetoresistance in a standard carbon resistor for thermometry below 1.0 K. We provide the reader with an expression for the magnetoresistance which may be used, with proper precalibration for a particular sensor, to determine the temperature from a reading of the resistance and the magnetic field. In addition, we discuss epoxy mixing chambers for dilution refrigerators and discuss results which indicate that certain materials can be magnetized and demagnetized at low temperatures. Finally, we report measurements on two types of capacitive temperature sensors which also exhibit magnetoeffects.
Cryopump and sample holder for clean reconstructed surface observations in a transmission electron microscope
Authors: Wilson R. J. , Petroff P. M.
Published: March 2003

The design and construction of a simple cryopump and sample holder which allow imaging of clean reconstructed surfaces prepared in situ in a transmission electron microscope are described. Applications to the Si(111)7×7 surface imaging are presented.
Measurement using a current-axis-independent Josephson sampler
Authors: Hatano Y. , Yamashita K. , Asano A. , Harada Y. , Kotera N. , Hirano M.
Published: March 2003

We have improved measurement of the current-axis-independent Josephson sampler. We use a new chopping detection circuit in the feedback system for sampling point control. Two channels of the sampling head are utilized to cancel drift in the time base. Drift is about 3 ps. We have measured the output of a short pulse generating circuit and obtained a transition duration of 15 ps.
Simple radiometer for net infrared sky irradiance measurements
Authors: Andretta A. , Bartoli B. , Coluzzi B. , Cuomo V.
Published: March 2003

A simple and rugged polythene shielded radiometer is described. The instrument measures the net hemispherical thermal infrared irradiance of the sky even during daylight hours, using white and black sensors to separate solar from long-wave thermal radiation. A compensation radiometer used to calibrate our instrument is also described, the calibration procedure permits measurements of the hemispherical thermal infrared irradiance of the sky with an error of ∼5% during the night and of less than 10 W/m2 during daylight hours.
Microcomputer-controlled gravimetric adsorption apparatus
Authors: Rasmussen M. D. , Akinc M.
Published: March 2003

A microcomputer-controlled gravimetric adsorption apparatus was designed and constructed. Components and software of the system are described. A microcomputer is used to control the experiment and to acquire data. The system is capable of conducting a complete adsorption–desorption run for various adsorbate/adsorbent systems quite accurately and efficiently. Results of the sorption of water and nitrogen on oxide and hydroxide powders are presented to demonstrate the performance of the apparatus.
Digitally controlled measurement of sonic elastic moduli and internal friction by phase analysis
Authors: O’Brien Michael H. , Hunter Orville , Rasmussen Mark D. , Skank Harold D.
Published: March 2003

An automated system is described for measuring internal friction and elastic moduli using sonic resonance techniques. This mirocomputer-controlled device does phase angle analysis in addition to traditional decay and peak-width internal friction measurement. The apparatus may be programmed to make measurements at any sequence of temperatures between room temperature and 1600 °C.
Automatic DNA sequencer: Computer-programmed microchemical manipulator for the Maxam–Gilbert sequencing method
Authors: Wada Akiyoshi , Yamamoto Masahiro , Soeda Eiichi
Published: March 2003

A computer controlled microchemical robot which carries out a series of chemical reaction steps in DNA sequence analysis of Maxam and Gilbert’s scheme is described. Within a 2-h operation of this apparatus, one of the four types of solutions for G, A+C, C+T, or C analysis for a DNA restriction fragment is prepared and is ready for subsequent electrophoretic analysis. It is proven that the chemical robot operated by a computer command is capable of speedily accomplishing the fragmentation reaction for DNA sequencing with accuracy similar to that of a well-trained technician.
Synchronous ECL divider for reduced jitter in laser pulse studies
Authors: Moesle Dolph
Published: March 2003

A fully synchronous five-decade ECL counter is described, operable to beyond 75 MHz and producing two distinct TTL-level outputs separated by presettable N+1 and M+1 input pulses. Intended primarily for laser pulse studies, the counter allows precise Q-switch–mode-lock synchronization, yielding greater optical pulse stability than with a- or semisynchronous synchronizer designs. In addition, the dual modulo feature allows easy selection of one particular optical pulse in the Q-switched output train for close study.
Development of a new UV resonance Raman spectrometer for the 217–400-nm spectral region
Authors: Asher Sanford A. , Johnson Craig R. , Murtaugh James
Published: March 2003

The design and construction of a new UV resonance Raman spectrometer continuously tunable between 217–750 nm are described. The excitation source is based on a YAG laser which is frequency doubled or tripled to pump a dye laser. UV light is generated by nonlinear frequency doubling and mixing of the dye laser output or doubled output with the 1.06-μm YAG fundamental. The detection system utilizes an intensified Reticon multichannel array. Commercially available monochromators are modified to make them useful for UV resonance Raman spectroscopy. Some sampling methodologies important for UV resonance Raman measurements are described. Examples of the sensitivity of UV resonance Raman spectroscopy are illustrated.
Triple point of succinonitrile and its use in the calibration of thermistor thermometers
Authors: Mangum B. W.
Published: March 2003

Results are reported of an investigation of the triple point of succinonitrile as a temperature-fixed point and of its use in the calibration of thermistor thermometers. The average value of the triple point of several samples of this material was determined to be 58.0805 °C, with an estimated uncertainty of ±0.0015 °C relative to the International Practical Temperature Scale of 1968. Three-point calibrations of thermistor thermometers, using temperature-fixed points provided by succinonitrile, gallium, and water were compared with 15-point comparison calibrations performed with a standard platinum resistance thermometer (SPRT). Equations, solved by simultaneous solution using data obtained at the three calibration points, yield values of temperatures in the range from 0° to 70 °C which agree to within about ±1 mK with those obtained by calibration with a SPRT in a bath.
Effect of gusts of wind on a thermal detector of radiation
Authors: Stock K. D.
Published: March 2003

At windy weather air turbulences (gusts of wind) occur close to the ground. These turbulences result in adiabatic air pressure changes (∼10−2 mbar). The incident temperature fluctuations (∼mK) may cause strong disturbances in temperature-sensitive measuring devices. By the example of a so-called cavity detector the influence of wind on the measurement signal of a detector for optical radiation is demonstrated. A quantitative estimation of the uncertainty of measurement as a function of the wind velocity is given and confirmed by experiments. In addition, measures to reduce this disturbing influence are discussed.
Accurate calculations of electrostatic potentials for cylindrically symmetric lenses
Authors: Edwards D.
Published: March 2003

Improved methods are described for determining electrostatic potentials within cylindrically symmetric lenses. At fixed number of mesh points, increases in the obtainable precision of approximately a factor of 100 are found by using the present relaxation method. This type of improvement in the precision implies decreases in computational times of a factor of ∼104 when compared with previous relaxation techniques for equivalent precisions.
Laué diffraction hard x-ray spectrometer for laser fusion diagnostics
Authors: Priedhorsky W. C. , Lier D. W. , Day R. H.
Published: March 2003

We show that a crystal spectrometer used in the Laué mode is a useful diagnostic of high-energy x-ray emission from laser fusion plasmas. It has good collection efficiency and adequate energy resolution for continuum measurements. The instrument measures time integrated x-ray spectra with a resolving power E/ΔE≊10 for photon energies between 60 and 300 keV. A strong signal and no detectable background are obtained in laser fusion experiments where ∼15 J of x rays are released in a pulsed (1 ns), hard (kT≊200 keV) spectrum. A Lanex/Tri-X phosphor/film combination is used as a focal plane detector; we report its relative energy calibration. Because of the imperfection of available crystals, detailed measurements of reflectivity along the crystal are required to achieve absolute calibration.
Improved self-calibrating rubidium magnetometer accurate to 0.01 nT rms
Authors: Ware Randolph H.
Published: March 2003

Self-calibrating Rb87 magnetometers, designed for high-accuracy geomagnetic field measurements, have been improved to attain 0.008 nT rms absolute accuracy. Previous designs were limited to accuracies of 0.04 nT rms or less as a consequence of diurnal temperature drifts and high-frequency noise. We describe a modification to the magnetometer housing that eliminates the temperature drift. We also describe improvements in the 5-Hz servo and radio frequency electronics that lead to an increase in high-frequency stability.
CRISIS detector: The gas system
Authors: Goloskie D. A. , Stoughton T. B.
Published: March 2003

A low-pressure, high-flow, recirculating gas system has been designed and constructed for use on a large volume (250 ft3) ionization sampling drift chamber (CRISIS), which operates at an absolute pressure of less than 1 in. of water relative to atmospheric pressure. The system was also designed to control and monitor the detector gas mixture and to reduce the oxygen level in the detector below 4 ppm. In operation the system demonstrated very stable long and short term stability and also demonstrated the gas cost savings inherent in recirculating systems.
Development of a point-electrode conductivity salinometer with high spatial resolution for use in very saline solutions
Authors: Grimmer D. P. , Jones G. F. , Tafoya J. , Fitzgerald T. J.
Published: March 2003

A conductivity probe and circuit were developed to measure salinities in sodium chloride salt-gradient solar ponds. A point-electrode salinometer design was chosen to give spatial resolution approximately 0.039 in. (1 mm). Such high spatial resolution was necessary to study the behavior of thermohaline columns in the vicinity of convective/conductive zone interfaces. The point-electrode conductivity instrument was designed for use in up to 25% (by weight) salinities with immersion times on the order of magnitude of 0.1 year or longer. Drift in the instrument, caused principally by changes in the surface condition of the platinum probe tip and reflected by changes in the probe cell constant, required periodic in situ calibration against the measured specific gravity of withdrawn fluid samples.
Analysis of ruminal fluids with the ammonia electrode
Authors: Phillips William A.
Published: March 2003

The ammonia concentration of samples collected from the rumen of beef steers was determined by both the Conway and ammonia electrode procedures. Rumen fluid had to be centrifuged and diluted for the electrode procedure to function properly. When only one animal was used as a source of rumen fluid and multiple determinations were made on each sample, the mean ammonia concentration was significantly lower for the electrode procedure than the Conway procedure. The correlation between the two procedures was greater than 0.8 in 78% of the comparisons. In 44% of the comparisons with a concentration range of 3–117 mg/100 ml, the electrode procedure yielded a higher concentration value than the Conway procedure. Two methods of employing the electrode were also compared. Although the known addition method yielded significantly lower ammonia concentration than the direct method, these differences were less than 5% of the mean and probably reflect the sensitivity of the electrode to generate a low standard error.
Probe for studying wall charges in electrodeless discharges at 60 Hz
Authors: Ma Rui-Lin , Curzon F. L.
Published: March 2003

A probe is described, which together with a high-resistance buffer and differential amplifier, has been used to study wall charge effects in a 60-Hz electrodeless discharge in neon at a pressure of 10 Torr. The device makes use of the external fields produced by the wall charges and shows that, in typical conditions, the wall charges take several milliseconds to come to an equilibrium after a breakdown has occurred. A major feature of the device is the use of the small external electrodes which localize the region where the wall charges tend to accumulate.
Excited-state lifetime measurements: Linearization of the Förster equation by the phase-plane method
Authors: Love J. C. , Demas J. N.
Published: March 2003

The Förster equation describes excited-state decay curves involving resonance intermolecular energy transfer. A linearized solution based on the phase-plane method has been developed. The new method is quick, insensitive to the fitting region, accurate, and precise.
Wide-range Langmuir probe sweep circuit
Authors: Cartier Steven , Bosch Robert
Published: March 2003

A circuit is described which facilitates measurements of Langmuir probe currents from 1 μA to 400 mA with sweep voltages as high as 70 V.
Magnetic susceptibility of Stycast 1266 epoxy
Authors: Azevedo L. J.
Published: March 2003

The magnetic susceptibility of Stycast 1266 epoxy, a commonly used low-temperature material, has been measured from 2.5 to 400 K. The susceptibility is diamagnetic over the entire temperature range studied with a small Curie contribution at low temperatures.
Bragg-reflection profiles of graphite and alkali–graphite intercalation compounds: Comparison of double-axis and triple-axis spectrometer results
Authors: Hardcastle S. E. , Misenheimer M. E. , Zabel H.
Published: March 2003

Double-axis x-ray spectrometer measurements at flat, low-absorbing mosaic crystals produce broad and asymmetric Bragg-reflection profiles. If the absorption coefficient changes during the sample preparation process, as in the case of graphite and graphite intercalation compounds, a determination of the instrumental profile is almost impossible. Using triple-axis spectrometers, the Bragg-reflection profiles are independent of the sample transparency, and peak profiles can be determined with high resolution and minor corrections.
Instrument measuring temperature dependence of minority-carrier lifetime without contact
Authors: Ohsawa Akira , Honda Kouichirou , Takizawa Ritsuo , Toyokura Nobuo
Published: March 2003

An instrument measuring the temperature dependence of minority-carrier lifetimes without contacts is described. The temperature range is 100 to 420 K, and the shortest decay time observed is about 2 μs. The instrument utilizes the photo decay of microwave power reflected from the sample, therefore, it is a contactless method. As an example, the instrument was applied to high-quality silicon crystals used in very large scale integrated circuit fabrication. The measured temperature dependence could be explained by the Shockley–Read–Hall theory by assuming a level for the recombination centers at 0.18 eV from the valence band.
Versatile sample holder assembly for P.A.R. Foner-type vibrating sample magnetometer mated with Janis supervaritemp cryostat
Authors: DeFotis Gary C.
Published: March 2003

The lower section of the sample drive rod and sample holder of a P.A.R. Model 155 vibrating sample magnetometer has been modified in order to allow measurements to be made on both powder and variously shaped and sometimes large single-crystal samples, and to allow a carbon-glass thermometer to be mounted very near the sample.
Improved cataphoretic deposition methods for lanthanum hexaboride
Authors: Delmore J. E.
Published: March 2003

The cataphoretic deposition method for preparing lanthanum hexaboride coatings has been modified to permit the preparation of several different types of surfaces. Some of these surfaces had good adhesion to the substrate, overcoming a major drawback to earlier methods. The surfaces ranged from smooth and dense, which were excellent electron emitters but poor halide ion producers, to porous, which were excellent halide ion producers.
S1 photocathode designed for streak camera image converter tubes
Authors: Gex F. , Alexandre R. , Horville D. , Cavailler C. , Fleurot N. , Nail M. , Mazataud D. , Mazataud E.
Published: March 2003

Semitransparent S1 photocathodes have been developed on a low-resistivity SnO2 layer for streak camera image converter tubes. The 50-Ω/⧠ resistivity combined with good photocathode sensitivity prevents parasitic effects and provides an efficient diagnosis tool for 1.06-μm laser–plasma interaction experiments. Furthermore, the lifetime in the 1-μm range has been greatly increased by a rebaking process which may reestablish the 1.06-μm sensitivity.
Fast position-sensitive shadowmeter
Authors: Seagrave John D. , Laird Allie M. , Jones L. A. , Wood C. W.
Published: March 2003

A simple optical detector of position versus time providing submillimeter spatial and nanosecond time resolution is described. The spatial beam profile of a nanosecond-pulse-width nitrogen laser is sampled simultaneously when the UV light strikes multiple turns of a spiral fiber-optic delay line. Fluorescent light coupled into the fiber converts the profile samples into serial bursts of light. These bursts are detected by avalanche photodiodes; electrical pulses are recorded on fast oscilloscopes. An interposed absorbing or refracting material casts a ‘‘shadow’’ which is measured by comparison with a reference recording. Applications are suggested, and two long-time-base recording methods are described.
Generation of plasma targets for a negative ion neutralizer
Authors: Hershcovitch A. I. , Kovarik V. J.
Published: March 2003

Hollow cathode discharge plasmas have been generated in a closed-loop, D-shaped solenoidal magnetic field. This configuration, which is adequate to serve as a neutralizer in a negative ion based neutral beam line, was used to generate argon and hydrogen plasma neutralizer targets. Based on scaling of the observed power dependence of target thickness, this neutralizer concept should be very attractive for application to neutral beam systems.
Dynamical in situ nuclear-magnetic-resonance tensile apparatus
Authors: Hackelöer H. J. , Kanert O. , Tamler H. , De Hosson J. Th. M.
Published: March 2003

A combination of a servohydraulic tensile machine and NMR pulse spectrometer is described enabling nuclear-spin relaxation rates to be recorded simultaneously with stress-strain data incorporating tension as well as compression of nonmetallic as well as of metallic samples. The data of the mechanical system are as follows: Maximum load: 5000 N; minimum deformation speed: 10 μm s−1, maximum deformation speed: 3×105 μm s−1; deformation stroke: digitally controlled between 1 and 8×103 μm; bandwidth: dc to 1 kHz; resolution: 2–4 μm; temperature conditions of the sample: from 80 to 570 K. The operation and performance of the system is described by means of experiments observing nuclear-spin relaxation rates which are induced by the movement of dislocations due to the finite deformation rate of the sample.
Rotating ring-disc electrode with a removable disc
Authors: Kennedy W. , Linge H.
Published: March 2003

The construction of a compact rotating ring-disc electrode with a removable disc electrode is described and performance characteristics measured for rotational speeds up to 4900 rpm between 25° and 94 °C using the ferrocyanide–ferricyanide couple. The electrode is spun with a conventional laboratory stirrer and includes several electrode tips with different ring materials. Each tip can accommodate demountable discs of the material required for study. The electrode tips demonstrated in this paper have a high collection efficiency (0.55) which is remarkably insensitive to mismatch between the ring and disc plane. The electrode has a proven leak-free operation even in very hot solutions.
High-sensitivity resistivity technique for studies of defect behavior
Authors: Tzanetakis P. , Birnbaum H. K.
Published: March 2003

An experimental method for measurement of the contribution to the electrical resistivity due to solutes or defects is described. This technique, which is based on an ac Kelvin Double Bridge may be used at elevated temperatures and does not require the use of liquid helium. The resistivity caused by solutes or defects, ρxs, can be determined at temperatures near 300 K with an accuracy of better than Δρxs/ρxs≊10−3; with the major source of error being the accuracy to which the material resistivity is known. Relative changes in the solute (defect) resistivity can be measured with a precision of 5×10−10 Ω cm. A specimen design and mounting procedure, which takes advantage of the high bridge sensitivity, is described.
Method to increase the bandwidth of heat fluxmeters
Authors: Malcorps H.
Published: March 2003

Meteorological observations may be more profoundly exploited by digitalization and the application of modern statistical methods. These techniques impose more rigorous conditions on the measuring devices; the results may be biased by aliasing or by the frequency response of the measuring instrument itself. Most heat fluxmeters, used in radiometry, do not respond in the same way as a filter with lumped parameters and as a consequence the compensation of their frequency response by electronic filtering is not straightforward. A method to approach the response of this type of sensor by a filter with judicious chosen poles and zeros is described and compensation is obtained by the inversion of this filter. In this way the bandwidth of a particular thermal fluxmeter was increased from 0.07 to 5 Hz.
Mathematical model of beam intensity dispersion at the detector plane in a molecular-beam apparatus
Authors: Perram Glen P. , Dorko Ernest A.
Published: March 2003

A mathematical model of intensity dispersion at the detector plane in a molecular-beam apparatus has been developed for the case of a ribbon-shaped beam effusing from a narrow rectangular slit. The model is developed in terms of position probability distribution functions and Maxwellian velocity distribution functions. The relation derived for the axial flux density is nv̄(Δx′)(Δx′)/4π2L2 in units of number of particles per unit area per unit time. A plot of flux density versus off-axis position agrees with the reported distributions obtained experimentally.
High-performance transient absorption spectrometry on the nanosecond scale
Authors: Weisman R. B. , Selco J. I. , Holt P. L. , Cahill P. A.
Published: March 2003

A flexible apparatus has been constructed to measure the spectra and time dependence of weak optically induced absorption changes in gas phase samples. The instrument uses a pulsed Nd:YAG-pumped dye laser for excitation and a second, independent YAG/dye laser for probing in a coaxial counter-propagating geometry. The excitation wavelength, probe wavelength, and time delay between the two pulses may be separately varied. An on-line laboratory computer acquires induced absorbance data as a function of probe wavelength and delay, and helps to suppress ratiometric noise to the point that induced probe absorptions as low as 2×10−4 absorbance units may be routinely detected in a path length of 75 cm. The sample cell forms part of a gas handling system that permits a wide range of sample and buffer gas mixtures to be prepared. The width of the instrumental time response is approximately 4 ns; it may be deconvoluted from kinetic data to provide an effective resolution of ∼1 ns. This combination of sensitivity and time resolution allows the study of collision-free as well as collision-induced effects in many molecular systems.
Automatic photocoupled trigger for discrete nebulization in flame atomic spectrometry
Authors: Goto K. , Uchida T. , Iida C.
Published: March 2003

An automatic trigger for the discrete nebulization in a flame atomic spectrometry was improved to be compatible with any sample solutions irrespective of the electric conductivity and optical transparency. The sample solution in a Teflon tube can be detected by the specifically made photocoupler and electronics.
Improved light-scattering cavitation nuclei classifier
Authors: Moyer William W.
Published: March 2003

The scattered light approach to classification of cavitation nuclei provides speed and resolution advantages over holographic direct observation methods, but the conventional light-scattering system has been unable to discriminate between bubbles and dirt particles. A two-channel classification system has been developed to process information carried in bursts of light scattered along two different paths by candidate nuclei passing through an illuminated test volume. Processing is based upon an analysis of light-scattering properties of spherical and nonspherical particles. The dual-detector classifier has demonstrated its ability to accomplish the desired differentiation in initial water tunnel tests.
High-power-density electron-beam-sustained laser
Authors: Casey M. , Smith P. W. , Hutchinson M. H. R.
Published: March 2003

A high optical power-density excimer laser pumped by an electron-beam-sustained discharge has been developed. The electron-beam generator comprised a 200-kV pulse transformer-driven power supply and an electrostatically focused electron-beam diode. The careful design and optimization of this generator has allowed very reliable, reproducible operation of the complete laser system with a high enhancement ratio of 4.8. An average output power density of 0.63 MW cm−2 in a 250-ns (FWHM) pulse has been obtained from an e-beam-sustained discharge XeCl* laser with an extraction efficiency of 1.5%.
Laser-power fluctuations: An analog signal-correction technique
Authors: Kumar D. , Nauman R. V. , Mohanty R. , McGlynn S. P. , Findley G. L.
Published: March 2003

A simple and inexpensive analog technique which corrects spectroscopic signals for pulse-to-pulse fluctuations in the output power of an excitation laser is described. The technique is applicable to both linear and nonlinear spectroscopy and, in the latter case, requires no fast electronic function generator. This design yields an improved time-constant characteristic which parallels the approach of the effective time constant toward RC. Furthermore, since this improvement does not require any preintegration, pulse shape information is preserved. A description of a photoacoustic (PA) spectrometer which incorporates the signal-correction device and which relies on the photogalvanic effect for wavelength calibration is presented as an example. Finally, signal-corrected PA spectra of the S1←S0 transition in azulene are presented.
Performance of a laser beam wave-front sensor
Authors: Wang C. P.
Published: March 2003

Laser beam wave-front measurement is important for laser beam quality evaluation and beam control. In this paper we report on a laser beam wave-front sensor consisting of a phase detector and a scanner. With the use of this sensor, the wave-front phase profile across a hydrogen fluoride (HF) laser beam has been obtained. The major advantages of this technique are that it is fast, sensitive, and compact. Other features are electric scanning, self-alignment, noise cancellation, and no drift. Wave-front sensor operational principles, features, and experimental results are presented. The sensitivity of the sensor was 5°. This sensitivity corresponds to the change of beam quality parameter, the Strehl ratio, by 1%. Hence it is a sensitive beam quality measurement technique.
Low-cost microprocessor-based photon correlator
Authors: Murthy N. S. , Choudhary D. M.
Published: March 2003

A simple cost-effective microprocessor-based correlator is described which can be used for Gaussian as well as non-Gaussian light sources. Error calculations are presented to show that there is no significant improvement in accuracy by adopting 4-bit word length in preference to 3-bit word length. The instrument can also be used in Raman and Raleigh scattering experiments. A few experimental results are presented bringing out the importance of correlation averaging in S/N enhancement. Some autocorrelograms for fluctuations in the scattered light from polystyrene spheres suspended in water are also presented. The instrument can sample 1500 points and calculate 85 correlations in each scan. All the parameters such as number of samples, number of correlations, number of scans, and the sampling time are user programmable.
Inexpensive low temporal jitter laser triggering circuit
Authors: Leal Fabio A. M. , Gomes A. S. L. , Rios Leite J. R. , de Araujo Cid B.
Published: March 2003

We present a simple and inexpensive triggering circuit which provides a laser pulse jitter of 0.5 ns.
Inexpensive moderate speed input processor and buffer memory for NMR instrumentation
Authors: Kunz Sara D. , Redfield Alfred G.
Published: March 2003

An inexpensive, moderately fast input converter, adder, and buffer memory is described for use with an NMR instrument. Speed is a few microseconds per 12-bit data point and word length and size are essentially unlimited.
Three-electrode electrostatic deflection plates for low-energy charged beams
Authors: Grisenti R. , Zecca A.
Published: March 2003

A simple system of electrostatic deflection plates with three electrodes is described.
Improved system for energy-dispersive x-ray diffraction with synchrotron radiation
Authors: Skelton E. F. , Qadri S. B. , Webb A. W. , Lee C. W. , Kirkland J. P.
Published: March 2003

A number of improvements in a facility developed over the past three years at the Stanford Synchrotron Radiation Laboratory for the study of pressure and/or temperature effects on materials are described. These include improved beam collimation to both reduce background and eliminate gasket scatter, a remote, pneumatically operated pressurizer, and introduction of a variety of electronics hardware to allow both computer control of experiments and on-line data analyses. Considerations are given to the possible effects of heating of the pressure cavity by the incident beam and to possible fluctuations of the incident beam intensity/energy profile. In both cases, there was no evidence to indicate that these phenomena warranted any further consideration, i.e., they are not considered to be problems in terms of analyzing the data. Extended measurements of a well-defined diffraction peak indicated that a considerable improvement over our earlier work has been realized in terms of the precision in the determination of the energy of the peak, viz., a precision of better than 0.04% for measurement periods as short as 10 s; the estimated precision in the net peak area is less than 3%. The system was used to examine the kinetics of the B1-to-B2 pressure-induced phase transition in KBr. The volume change in the two-phase region is measured to be 10.41%±0.10%, in excellent agreement with most of the previous measurements. A plot of the time dependence of the growth rate of the high-pressure phase indicates that the phase transformation can be described by the Avrami equation. Constants for the phase transition kinetics are given.
Design and preparation of high-Q niobium reentrant cavities for physics measurements
Authors: Oelfke W. C. , Hamilton W. O.
Published: March 2003

Some techniques are given for the design, construction, and chemical surface treatment of niobium uhf reentrant cavities. These techniques ensure that when these cavities are operated at helium temperatures they will consistently display unloaded Q values above 107.
Calibration system for satellite and rocket-borne ion mass spectrometers in the energy range from 5 eV/charge to 100 keV/charge
Authors: Ghielmetti A. G. , Balsiger H. , Bänninger R. , Eberhardt P. , Geiss J. , Young D. T.
Published: March 2003

A new system has been developed for calibration of space plasma analyzers, in particular ion mass spectrometers. The system provides a large-area (∼250 cm2), highly parallel (±0.5°), and spatially uniform (±5%) beam of ions over the energy per charge range from 5 eV/charge to 100 keV/charge. Other special features include variable energy spread from ΔE∼1 eV to ∼3 keV/charge and multiple charge state ions such as He2+ or Xe9+. Among several key ion optical elements are a high-efficiency electron bombardment ion source capable of delivering ∼10−8 A, a 90° crossed electric and magnetic field mass spectrometer designed to produce either a mixed or a mass-selected beam, and a unique beam expansion system which produces the uniform large-area beam. The system also includes automatic beam monitoring and control via a feedback loop, as well as provisions for semiautomatic control of angle and energy analysis. Use of the calibration system during its development phases has made possible the rapid calibration of five complex satellite ion mass spectrometers already flown. Data from one of these calibrations are discussed here.
CAMAC controller for a conventional and pseudorandom time-of-flight system
Authors: Ducorps A. M. , Yashinovitz C. J.
Published: March 2003

Time-of-flight methods are valuable in measurements of the velocity distribution of low-energy atoms and molecules whose energies are difficult to measure directly. A system is described which uses pseudorandom beam chopping and a CAMAC compatible computer interface to provide energy resolution as good as conventional time-of-flight techniques, but with a duty factor of 50%. This system was designed for ice sputtering experiments.
Use of carbon felt as a cold cathode for a pulsed line x-ray source operated at high repetition rates
Authors: Erickson George F. , Mace Phillip N.
Published: March 2003

Tests to determine the usefulness of carbon felt as a cold cathode in high repetition rate x-ray systems are described. Application of these test results to design and operation of an x-ray preionizer for an excimer laser system has resulted in a simple, reliable x-ray source which can be used at pulse rates up to 500 Hz for >2×107 shots before the carbon felt must be replaced.
Peak sampled vibrating-reed for the measurement of electric fields in the presence of space charge
Authors: Horenstein Mark N.
Published: March 2003

An electronically sampled vibrating-reed dc electric field sensor of the chopping field-mill variety is described. The compact, battery powered, self-contained sensor, which can be imbedded in any electrode surface, is capable of measuring true dc fields up to the 106 V/m range over an indefinite period of time; however, continuous peak sampling of the chopped periodic signal allows transients on the order of 10 ms to be monitored. Measurement in the presence of ionic space charge is made possible by keeping all structural components exposed to the field at a single equipotential.
Infrared measurement of specimen temperature profiles during fatigue crack propagation tests
Authors: Hahn M. T. , Hertzberg R. W. , Manson J. A.
Published: March 2003

Hysteretic heating of the crack tip often occurs during tests of fatigue crack propagation. If hysteretic heating occurs to a significant extent at and ahead of the crack tip in a notched polymer specimen, fatigue crack propagation behavior may be altered in a complex way. It is, therefore, important to monitor the temperature at crack tips during testing. Methods of temperature measurement are reviewed, and a semiautomated apparatus incorporating an infrared microscope for measuring temperature profiles during fatigue tests is described.
Commodore PET computer used as a programmable gated integrator
Authors: DeRosa F.
Published: March 2003

A Commodore PET computer with analog-to-digital and digital-to-analog converters may be used as a programmable gated integrator with gate lengths ≥1 ms. Multiple gates and delays of programmed length may be obtained with suitable machine language code accessed from basic.
Angular resolution in total cross-section measurements
Authors: Lazzizzera I. , Zecca A.
Published: March 2003

This paper deals with the calculation of the detection efficiency in total cross-section measurements for two geometries: rectangular beam–rectangular detector of equal (finite) dimensions and circular beam–circular detector. The solutions are given in analytical and graphical form. The use of the term ‘‘angular resolution’’ is discussed and a new definition is proposed.
Accurate i
n s
i
t
u measurement of near-surface volume dilatation in irradiated silica through capacitance monitoring of cantilever deflection
Authors: Norris C. B. , EerNisse E. P.
Published: March 2003

Irradiating a solid with short-range particle often induces a net volume change in the range zone which results in a shallow layer of stressed material. Micron-depth volume dilatations in the part-per-million range can be studied using cantilever mounting of a long, thin, metallized specimen, whose stress-induced bending perturbs the capacitance between the cantilever and a small counterelectrode mounted close to the unirradiated face. This approach has been used successfully by many workers for more than 20 yrs. Elsewhere we have reported the construction of a highly sensitive caltilever/capacitor apparatus and its application in the first accurate measurements of ionization dilatation phenomena in fused silica and grown SiO2 at low-electron energies. In this paper we outline key details of apparatus design and experimental technique for successful cantilever/capacitor work. Many contrasts with the work of Primak and Monahan [Rev. Sci. Instrum. 54, 544 (1983) (preceding paper)] are pointed out. We also highlight previous short-term annealing results which make it clear that the compaction of silica will appear to be significantly less in optical measurements made hours after irradiation than in our cantilever/capacitor measurements made minutes after irradiation.
Simple quasi-two-crystal x-ray spectrometer
Authors: Taniguchi Kazuo
Published: March 2003

A simple two-crystal spectrometer was constructed using a commercial single-crystal spectrometer, i.e., the second crystal and the detector were attached on the 2θ arm of a single-crystal spectrometer. The angle between the second crystal and the detector is preset to an optimum angle for the measurement region of interest. The condition for geometrically ideal analysis can be satisfied by rotating the θ axis and detector arm (2θ arm) at a rotation ratio of 1:3 using an external pair of gears whose ratio is 3:1. The wavelength can be directly read according to Bragg’s diffraction law, like a commercial two-crystal spectrometer. We measured sulphur-Kβ spectra for several sulphur compounds. We conclude, from several measurements, that the spectra obtained with a high-resolution can be an important and powerful tool for the study of the valence band and can also be applied to chemical-state analysis.
Time-resolved two-dimensional imaging of ground-state species using laser-induced fluorescence
Authors: Dougal R. A. , Williams P. F. , Pease D. C.
Published: March 2003

Laser-induced fluorescence has been employed to obtain two-dimensional images of the spatial distribution of a vapor in the ground state with nanosecond resolution. The method has a wide range of potential applications, as it can be used to observe any species which has energy levels accessible to tunable laser systems. In the application we describe, aluminum vapor was observed jetting from spark gap electrodes and diffusing throughout the gap volume.