bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattered electron counting system for nozzle beam studies of small clusters
Authors: Kim Sang S. , Stein Gilbert D.
Published: March 2003

A single-channel scintillation detection system has been developed for the study of the physical properties and structure of small atomic and molecular particles with size g⩽5000 atoms (or molecules) per cluster. A multistage, molecular beam apparatus is used to produce a beam of noninteracting clusters which is crossed with a 40-keV electron beam. The detection system is used to record the resultant electron diffraction patterns from the clusters. Its high sensitivity can be employed for the detection of low-intensity patterns characteristic of cluster beams having small mean size. Synchronous detection (i.e., digital up–down pulse counting) is used to overcome the unfavorable signal-to-noise limitations encountered when g⩽1000. The lock-in detection technique, in conjunction with cluster beam chopping, provides a substantial advantage over dc film recording of these patterns. The electron scattering from background gas is greatly reduced, compared to film detection, and the uncertainties due to film quality and exposure are eliminated. The diffraction patterns are obtained in real time, both as analog and digital presentations which facilitates experimental optimization. Finally, the data in digital form are directly accessible for theoretical computations necessary to derive the physical quantities. This system has been used in several studies to obtain diffraction data for cluster beams of SF6, Ar, Kr, and Xe.
Design of a continuous guard ring and its application to swarm experiments
Authors: Iinuma K. , Takebe M. , Satoh Y. , Seto K.
Published: March 2003

A new type of drift tube was designed and constructed for the study on the behavior of slow ions in gases. The guard ring, made up only of an aluminous porcelain tube, is different from those of conventional thin or thick types. Thick-film resistor for microcircuits was coated over the inner surface of the tube. With this guard ring a new swarm experiment was carried out: the drift distance scanning method. Spectra representing the spatial distribution of ions for fixed drift times were obtained. Mobilities and longitudinal diffusion coefficients of K+ ions in oxygen were measured in a trial and compared with the data obtained by a conventional analysis of the arrival time spectra.
Contactless conductivity and rotational hysteresis measurements using a gas turbine
Authors: Flanders P. J.
Published: March 2003

Contactless measurements of electrical conductivity σ and rotational hysteresis WR are made with a high-speed, low-power gas turbine as samples rotate about an axis which is perpendicular to a magnetic field H. The field induces a retarding torque which decreases the rotor frequency from f0 to f, (Δf). When starting from the same f0, σ is found by equating the eddy current torque kfσB2, to that of a standard sample after adjusting the field applied to each specimen until an equal value for f is obtained. For small values of Δf/f0, Δf is proportional to kσB2, where k is a constant that depends on the sample geometry. The conductivity can be measured for regularly shaped specimens such as spheres, hollow and solid cylinders, discs, and rectangular parallelepipeds. Since Δf closely scales with the retarding torque, rotational hysteresis in magnetic samples can be measured by plotting Δf against field.
Method for measurement of capacitance, series and shunt resistances of semiconductor junctions, and their voltage dependence
Authors: Popkirov George , Tabov Nikola
Published: March 2003

A method and an electronic circuit for measurement of capacitance, series and shunt resistances of semiconductor junctions, and their dependence on the voltage applied across the junction are described. The method is based on comparing the current transient waveforms of the sample under test and of a reference capacitor, with series and shunt resistors connected to it, obtained with square-wave voltage pulses.
Laser triggered Cr:GaAs HV sparkgap with high trigger sensitivity
Authors: Williamson S. , Albrecht G. F. , Mourou G.
Published: March 2003

Bulk Cr:GaAs in a sparkgap-type arrangement has switched 4 kV pulses into 50 Ω with <1 ns rise time. The required trigger energy from the laser was ⩾ 35 nJ; the timing jitter was ⩽ ±150 ps.
Automation of a calorimetric system
Authors: Cheung T. D. , Chan W. K. , Kouvel J. S.
Published: March 2003

The data-acquisition and data-reduction procedures of an existing system designed for precise adiabatic calorimetry at cryogenic temperatures in strong magnetic fields were automated with a microprocessor (μp) based controller. A M6800 μp is used for handling the logic control functions, and the numerical calculations are handled by a MM57109 number processor (♯P, a calculator-type integrated circuit). This combination of μp and ♯P provides a very cost-effective design for an instrument controller with minimal hardware and software requirements. With on-line data processing capability, the heat capacity results are readily available to the operator during the experiment. A generalized algorithm was developed to handle multiple-order curve fitting without the need for double-precision arithmetic. The basic electronic system and the data-reduction procedures are described.
Rapid measurement of thermal conductivity of polymer films
Authors: Lee Hoosung
Published: March 2003

A simple and rapid technique to measure the thermal conductivity and resistance has been developed using common laboratory equipment. It has been applied to measure thermal conductivities of polymer films as thin as 12 μm, for which the time required for a single measurement was as short as 3 s. Thermal conductivities measured for polystyrene, (polymethyl metacrylate), and Mylar films are 0.169±0.001, 0.201±0.004, and 0.189±0.004 (Wm−1K−1), respectively. It has been demonstrated that the true conductivity should be calculated after correction for the resistance at zero sample thickness.
Simple medium power stepper motor logic sequencer and phase driver
Authors: Erdman P. W. , Zipf E. C.
Published: March 2003

We have constructed a logic sequencer for a four-phase stepper motor with only two medium scale integration TTL devices. The design can easily be expanded to accommodate eight-phase motors. Of special advantage is the sequencer’s ability to directly drive the final power transistors which are each capable of delivering several amperes per motor phase.
Sample holder for measurement of small magnetic moments using SQUID magnetometers
Authors: Roy Apurba , Buchanan D. Scott , Ginsberg D. M. , Roach P. R.
Published: March 2003

A self-compensating sample holder, suitable for making precise measurements of the magnetic moments of very small samples in SQUID magnetometers, has been developed. The design calculations for this holder are outlined, and its observed performance is described. The compensated holder exhibits a signal whch is only 1.5% of the signal from a noncompensated holder.
Adaptation of an electrochemical system for measurement and regulation of oxygen partial pressure to a symmetrical thermogravimetric analysis system developed using a Cahn 1000 electrobalance
Authors: Caneiro A. , Bavdaz P. , Fouletier J. , Abriata J.P.
Published: March 2003

We report equipment consisting of the coupling of an electrochemical system for measurement and regulation of oxygen partial pressure (PO2) to a symmetrical thermogravimetric analysis system built on the basis of a Cahn 1000 electrobalance. The electrochemical system allows the measurement and regulation of PO2 within a few percent, and has the additional advantage that it can be checked against systematic errors in an absolute way by means of the ’’Faraday’s law test.’’ The performance of the whole experimental setup is demonstrated by the resolution of a narrow hysteresis loop shown by PO2 as a function of composition in the U3O8 phase of the uranium–oxygen system.
Low-noise rf capacitance bridge transducer
Authors: Linsay Paul S. , Shoemaker David H.
Published: March 2003

We have designed a low-noise servo system to both damp the motion of a high Q pendulum as well as measure the ground noise that drives it. The servo is based on a high-frequency low-noise capacitance bridge which is used as a displacement transducer for sensing the position of the pendulum. The bridge itself is servoed to minimize the need to adjust its components because of slow mechanical thermal drifts. Used as a displacement transducer we have achieved a position sensitivity of 4×10−11 cm/√Hz.
Time and position-sensitive detector for dissociative processes in fast beams
Authors: de Bruijn D. P. , Los J.
Published: March 2003

A microchannel-plate detector has been developed to detect the time and position of two particles simultaneously. High resolution in position and timing is achieved with 100 μm FWHM and 0.5 ns FWHM, respectively. The detector is designed to measure dissociative processes of molecules in fast beams. The released kinetic energy and the direction of the associated momentum with respect to the beam direction in the center of mass can be determined directly. This method offers big advantages over the determination by means of a mass spectrometer which is common practice in the field of ’’translational spectroscopy.’’ The efficiency is increased by a factor of 103–105 with comparable energy resolution. Measurements are performed on the dissociative charge exchange of H+2 with Mg atoms. In the range of 7.2–10.2 eV 17 discrete energies are observed due to the predissociation of the c3πu state in H2 and presumably also the c1πu state.
New electron energy analyzer for magnetized plasmas
Authors: Arion D. N. , Ellis R. F.
Published: March 2003

A single selecting electrode device for the measurement of electron energy distributions parallel to a strong magnetic field in a plasma is described. A series of parallel plates eliminates ion entry into the analyzer and selectively retards electrons for energy analysis. The device was tested in a hot cathode discharge in the University of Maryland Mirror Machine. Results compare favorably with data taken with a conventional four-grid energy analyzer.
New technique for direct measurement of electron temperature
Authors: Kaya Nobuyuki
Published: March 2003

The Langmuir probe is frequently used as a conventional method in laboratories and space observations to measure an electron temperature. However, the method needs a complicated analysis to determine the electron temperature. A new technique which automatically determines the electron temperature is proposed in this paper. Its principle is: two potentials at which a preset electron current is collected by the probe are automatically measured and the difference of the two potentials is simply proportional to the electron temperature. Merits of this technique are high accuracy, quick response, direct display of an electron temperature independent of electron density, and diagnostic simplicity. Results of experiments of electron temperature measurements on a sounding rocket and in a space chamber proved the usefulness of this technique.
Instrument to measure wave numbers of cw and pulsed laser lines: The sigmameter
Authors: Juncar P. , Pinard J.
Published: March 2003

We report the first absolute wave number measurements made using a sophisticated version of the sigmameter. This apparatus is composed of four double Michelson type interferometers with fixed path differences. All path differences are calibrated using four reference lines given by single-mode lasers stabilized on iodine lines whose absolute wave numbers are known to better than one part in 109. This permits us to make absolute wave number measurements of radiation from a cw laser to a precision of the order of one part in 108 (≊5 MHz) and from a pulsed laser to a precision limited only by its spectral width. As examples, using a cw tunable dye laser, several new measurements of 20Ne lines have been achieved with the expected precision (10−8). Measurement of a pulsed laser frequency has also been done with an accuracy of the order of one part in 106.
Simple switching circuit to improve vidicon (OMA2) linearity
Authors: Cascio Horace E. , Smith Paul D. , Liesegang Gerard W.
Published: March 2003

A simple switching circuit which allows a change of the target scan voltage to a new value at the end of the preparation frames in OMA2 vidicon detectors is described. This voltage change reduces lag significantly and leads to a linear response of the vidicon to pulsed illumination. The circuit is readily incorporated into OMA2 detectors.
Fast polarization modulated ellipsometer using a microprocessor system for digital Fourier analysis
Authors: Drevillon B. , Perrin J. , Marbot R. , Violet A. , Dalby J. L.
Published: March 2003

A new type of spectroscopic automatic ellipsometer using a piezobirefringent element for polarization modulation at 50 kHz is described. Instead of lock-in amplifiers the data-acquisition system consists of a 12.8-MHz digital sampling of the detected signal with a high word rate 8-bit ADC, followed by on line Fourier transformation of the accumulated data with a short instruction cycle (∼200 ns) microprocessor, driven by a commercial microcomputer. The absolute minimum time required for measuring one set of Fourier coefficients is thus reduced to the modulation period of 20 μs. For digital error reduction purposes and signal-to-noise ratio improvement a basic 5 ms sequence of 256 accumulated periods per point is chosen. At this data-acquisition rate a precision of 5×10−4 is obtained. Further accumulation over 10 s leads to 10−5 precision capability. A detailed analysis of various sources of inaccuracy leads to an estimate of 0.5° maximum systematic error on the ellipsometric angles and ψ and Δ. Applications to the in situ study of a-Si:H plasma deposited films are also presented.
Cryostat for microspectroreflectometry by use of a microminiature refrigerator
Authors: Yakushi K. , Kuroda H. , Hollman R. , Little W. A.
Published: March 2003

By use of a microminiature refrigerator, a small and inexpensive cryostat was constructed for the purpose of measuring the specular reflectance spectrum of small single-crystal specimens with a microspectrophotometric technique. The design of the cryostat system and its performance are described.
Modification of instrumentation for research on lingual vibrotactile sensitivity: Elimination of the tongue clamping procedure
Authors: Fucci Donald , Petrosino Linda , Wallace Daniel , Small Larry H.
Published: March 2003

A simplified modification in lingual vibrotactile instrumentation involving elimination of the tongue clamping procedure is presented. Reasons for this modification and the advantages are discussed in terms of facilitating clinical testing.
Neutral beam profiles and a computer-controlled emittance measuring device for a cyclotron beam
Authors: Haddock Christopher , Anderson James , De Jong Mark , Konopasek Francis , Smith Charles Anthony
Published: March 2003

The beam scanner at the University of Manitoba Cyclotron Facility is a device which images the position of a cyclotron proton beam using a rapidly rotating wire. The paper reports that the scanner will also give a profile of a neutral beam of low-energy deuterium particles and describes the application of the scanner to measure the emittance at the accelerated cyclotron beam.
Response of a split film probe under electrical perturbations
Authors: Ho Chih-Ming
Published: March 2003

The split film probe is designed for simultaneous measurements of streamwise and transverse velocity components. However, difficulties in obtaining reliable results have been experienced by many researchers. The problems are attributed mainly to static and dynamic cross talk through the substrate. In this paper, the static cross talk is examined in the first part by deliberately operating the film with different overheats. In the second part, both films are statically balanced, one of the films is subjected to an electrical perturbation, the other film will respond to the dynamic perturbation due to the imperfect insulation of the substrate. At low frequencies, the thermal response can be as high as 37%. At high frequencies, the frequency response is a function of the substrate characteristic frequency and the circuit characteristic frequency. The reasons for the thermal response are examined at the low-frequency limit. The dynamical unbalanced resistance generated by the electrical perturbation will set up an instantaneous temperature gradient across the substrate which produces the cross talk. Furthermore, if azimuthal asymmetry exists, the communication between the two films will also appear due to the azimuthal asymmetric temperature distribution.
Laboratory measurements of ultralow permeability of geologic materials
Authors: Trimmer D.
Published: March 2003

A new apparatus is described for determining permeability (water) in geologic materials as a function of confining pressure (to 200 MPa), pore pressure (to 25 MPa), and deviatoric stress (500–800 MPa). The samples are relatively large (0.15 m diameter ×0.28 m long) and may be intact or contain a single through-going fracture. Permeabilities of 10−11–10−24 m2 (10–10−12 D) may be measured, simultaneously, with electrical conductivity and acoustic velocity and amplitude. Crack closure is also monitored for the fractured samples. All experimental control and data-acquistion functions are performd by a microcomputer. A discussion of data-analysis techniques and typical data are also presented.
Measurement of the wear properties of metallic solids with a Falex Lubricant Testing Machine
Authors: Hale Edward B. , Meng Chun-Ping , Kohser Ronald A.
Published: March 2003

A modified Falex Lubricant Testing Machine has been used to determine wear properties of metallic solids. In particular, wear mass loss, wear volume loss, wear rates, and other parameters have been determined for a basic steel, as heat treated and after ion implantation. Wear rate improvements of more than an order of magnitude were found in a nickel–chrome steel (SAE 3135) implanted with 2.5×1017 N+2/cm2. Wear tests were conducted with a cylinder-in-groove geometry in a mild lubricating oil with loads greater than 540 N, which corresponded to pressures which exceeded 108N/m2. A detailed analysis of the data is presented.
Deep level transient spectroscopy using CAMAC components
Authors: Jervis T. R. , Teter W. M. , Cole T. , Dunlavy D.
Published: March 2003

Apparatus for computer-controlled acquisition of capacitance transient data for deep level analysis is described. The system is configured for either electrical or optical excitation of deep levels in GaAs and is based on the highly flexible CAMAC interface. The system is designed to collect transient spectroscopy data in as simple a form as possible and to make use, as much as possible, of commercially available apparatus of resonable cost. Hardware requirements and connections are described as are software for data acquisition and analysis.
Helium-temperature beam source of atomic hydrogen
Authors: Walraven J. T. M. , Silvera Isaac F.
Published: March 2003

We describe a technique for producing a high-flux beam of atomic hydrogen with a velocity distribution corresponding to liquid-helium temperatures. We have studied how a gas of hydrogen atoms (H) may be cooled to low temperatures through interaction with cold walls. The gas was analyzed by forming an atomic beam. We obtained fluxes φH≃2.4×1016 atoms/s at T≃8 K, which corresponds to an increase in flux of low-velocity atoms by a factor of 20 over that of the same source operated at room temperature. The degree of dissociation and the translational temperature of the gas were determined using a quadrupole mass spectrometer and time-of-flight techniques. A beam modulation technique advantageous for such a system is discussed and analyzed. General design considerations for the transport and cooling of H are presented and illustrated with examples. The methods of data analyses are discussed in detail.
Device for combined studies at the metal/solution interface by an alternating current bridge
Authors: Raev N. , Kazakov I.
Published: March 2003

This work deals with a device attached to a circuit for carrying out combined capacitance–electrocapillary measurements using a metal dropping electrode. The circuit involves an alternating current bridge of Wien type, an electronic device, and a digital time meter. The electronic device converts the bridge signal into current impulses determining the time intervals: τ—the lifetime of the metal drops, and τ′—the time from the moment of fall of the preceding drop to the balance moment of the bridge. The differential capacitance and the interference tension are, simultaneously, determined at the same interface. The time intervals are measured with an accuracy of ±1×10−3 and ±5×10−3 s for τ′ and τ, respectively.
Application of an optical data link in an airborne scanning system
Authors: Green M. J.
Published: March 2003

One of the principal impediments to a more widespread use of airborne remote sensing has been the lack of availability of research aircraft. In order to circumvent this problem, the University of Wisconsin Marine Studies Center has developed a system which enables their Texas Instruments RS-18A Thermal Scanner to be used with any P-3 patrol aircraft. A key element in this system is the application of a commercially available optical data link that provides communications between the scanner, which is mounted in a wing pod, and the data-acquisition system which operates inside the aircraft. Signals from the scanner are beamed via an optical transmitter in the pod, through one of the aft observation windows, to a receiver inside. This arrangement allows the scanner to be flown with no necessary modifications to the airplane. This technique seems readily transferrable to other types of instrumentation and acquisition requirements.
Computer-interfaced digital pulse counting circuit
Authors: Gilbert Richard E. , Cox David F. , Hoflund Gar B.
Published: March 2003

An electronic circuit is presented which can be used in digital pulse counting applications such as ESCA, Auger spectroscopy, UPS, etc. It consists of a quartz crystal clock and integrated circuits, and can be interfaced easily to a laboratory computer through a parallel board. A modification allows this circuit to be used as a counter with a time delay, thus making it useful in applications involving time-of-flight mass spectrometry.
Automatic temperature compensating apparatus for measurement of thin films during deposition
Authors: Generosi R. , Miriametro A.
Published: March 2003

This work describes the construction of a quartz resonator capable of measuring the thickness of deposited thin films with very high precision. A voltage-to-frequency converter is used as a reference oscillator. Temperature variations during the evaporation process, produced by both thermal irradiation and atomic bombardments, are monitored by an iron-constantan thermocouple which is used to generate a compensating signal at the input of the converter. The system also allows accurate measurement of the growth rate.
Electrohydrodynamic ion source with a reservoir and an emitter tip heated by electron bombardment
Authors: Noda T. , Okutani T. , Yagi K. , Tamura H. , Okano H. , Watanabe H.
Published: March 2003

An electrohydrodynamic ion source with a reservoir and an emitter tip heated by electron bombardment was constructed. This ion source can produce a variety of ion species including materials with high melting points for a long time, owing to the heating method and the reservoir. This ion source was operated with metals such as gold and indium, and has successfully produced an intense and stable ion beam from each material.
Radially uniform electron source
Authors: McComas D. , Bame S. J.
Published: March 2003

A thermionic electron source capable of producing uniform count rates in a number of channel electron multipliers simultaneously was required for conditioning multipliers for an extended space mission. It was found that a straight tungsten filament in the center of a cylindrically symmetric geometry surrounded by an array of multipliers emits a radially asymmetric distribution of electrons that changes with time. A source was developed which successfully produces a time-independent radially uniform distribution of electrons by moving the filament out of the direct line of sight and replacing it with a centrally located electron ’’cloud.’’
Possible error in the use of a mass flux gauge for the calibration of the dimer population in a molecular beam
Authors: Gentry W. Ronald
Published: March 2003

The mass spectrometric measurement of van der Waals dimer population in a molecular beam is complicated by fragmentation of the dimeric species to give the monomer ion. In a recent article, Lee and Fenn [Rev. Sci. Instrum. 49, 1269 (1978)] suggested the use of a ’’mass flux gauge’’ measurement to correct for this effect. A re-analysis of this method shows that the mass flux gauge is not very useful for this purpose.
Detection coil, sensitivity function, and sample geometry effects for vibrating sample magnetometers
Authors: Zieba A. , Foner S.
Published: March 2003

A general description based on the sensitivity function is presented for the effects of detection coil geometry and sample geometry on the output of a vibrating sample magnetometer (VSM). This function gives the VSM output versus position of a vibrating dipole. Calculations of the sensitivity function for axial and transverse detection coil configurations are presented using exact results and approximations including a spherical harmonic expansion. For axial, thick, rectangular cross-section coils, the design yielding the output with a minimum sensitivity to sample position, sample shape, and sample size is presented. For the transverse geometry the small coil approximation is used. Various designs yielding maximum output and output insensitive to variations of sample geometry are reviewed. The signal-to-noise for various coil configurations is also discussed. Corrections for the VSM output are calculated for ’’large’’ samples with regular geometries (thin rod, circular cylinder, cube, and rectangular parallelepiped). The calculations were verified experimentally for a rod-like sample for different orientations. The effects of applied field homogeneity, sample position errors, and sample support contributions are also discussed. Finally, applications of the analysis to other types of induction and force type magnetometers are discussed briefly.
Effect of additive noise and bandpass filter on the performance of a Josephson junction noise thermometer
Authors: Soulen R. J. , Vechten Deborah Van , Seppä H.
Published: March 2003

A Josephson junction may be used to convert the voltage fluctuations generated by Johnson (i.e., thermal) noise in a resistor into frequency fluctuations. The variance of the frequency fluctuations is thus a measurement of the Johnson noise and, therefore, of the temperature. This particular type of noise thermometer has been used at the National Bureau of Standards as part of a program to define a cryogenic temperature scale. We have studied the detailed influence of two types of post-detection bandpass filters (square and one-pole Butterworth) on the measured variance. We report here on these measurements and the circuit model used to fit them. The conclusion is that small but well understood corrections must be applied to the measured variance whenever the measurement time (i.e., gate time) of the frequency becomes comparable with the response time (defined as the inverse of the bandwidth) of the bandpass filter.
Optimization of the performance of a tandem microchannel plate detector as a function of interplate spacing and voltage
Authors: Rogers Douglas , Malina Roger F.
Published: March 2003

The effect of varying the size of the gap and the voltage between two microchannel plates (MCP’s) in a tandem configuration has been investigated. It was found that increasing the voltage in the gap increased the gain of the pair and also produced a narrower Gaussian pulse-height distribution. Beyond a critical voltage the gain of the channel plate pair was found to plateau. These observations can be explained in terms of a model involving both the nonlinear gain behavior of individual microchannels and the behavior of the electron cloud emitted from the first MCP as it spreads out between the two MCP’s and hits the surface of the second. From this model the plateau voltage is calculated as a function of the gap size, the gain of each MCP, and the diameter of the channels, and is found to match the observed results. It is concluded that interplate gaps of up to several millimeters can be accommodated without a significant degradation in pulse-height distribution.
Setup for the simultaneous measurement of quasistatic and high-frequency C–V characteristics of MOS capacitors
Authors: Greeuw G. , Hillen M. W. , Köhnke G. H. P.
Published: March 2003

A new apparatus for the simultaneous measurement of quasistatic and high-frequency (100 kHz) capacitance–voltage curves of MOS (metal-oxide semiconductor) structures is presented. The electronic circuit is relatively simple because of an extensive use of operational amplifiers; the main feature is a wide band amplifier (HA-2065) which converts both the dc (quasistatic) and the ac (100 kHz) signal. Also presented are experimental results of one of the applications of this setup.
Bidirectional hot-wire anemometer
Authors: Mahler D. S.
Published: March 2003

A simple hot-wire anemometer based device has been designed and developed which is capable of measuring flow reversals. The instrument has a useful range of 0 to ±150 cm/s.
New approach to the measurement of the thermal conductivity of electrical conductors
Authors: Cook J. G. , Herman P. R.
Published: March 2003

A novel method for measuring the thermal conductivity of an electrical conductor is described. The heat flow is radial, giving important advantages for high-temperature studies. It is an electrical method and is, therefore, most suited to resistive materials which have a high temperature coefficient of resistance, such as semiconductors. Since the outside temperature of the sample need not be determined directly, and the sample is best kept thin, the method holds promise for studies of liquids, especially where convection problems have occurred in the past. In many of these aspects, the proposed method works best where the conventional axial guarded heat flow method fails.
Spectrometer for momentum-resolved bremsstrahlung spectroscopy
Authors: Fauster Th. , Himpsel F. J. , Donelon J. J. , Marx A.
Published: March 2003

A spectrometer for momentum-resolved and polarization-dependent bremsstrahlung spectroscopy (inverse photoemission) in the vacuum UV range is described and the performance of the apparatus is discussed. A Seya–Namioka monochromator combined with a position-sensitive channel plate device for parallel detection of a wavelength range of 165 Å is used as a photon detector and covers an energy regime from 10 to 40 eV with a resolution of 5 Å. Due to the polarization-dependent reflectivity of the gold-coated gratings, the monchromator is also inherently an analyzer for the polarization of the detected light. A space-charge-limited Pierce-type electron gun comprising a BaO dispenser cathode is used as an electron source with 0.1-Å−1 momentum resolution. The overall energy resolution of the apparatus is 0.3 eV at 20 eV photon energy. The sensitivity is 1.8×104 counts per Coulomb and eV for the unoccupied s, p bands of a polycrystalline gold sample.
Rapid-sampling system for dusts and gases
Authors: Conti R. S. , Hertzberg M. , Duda F. T. , Cashdollar K. L.
Published: March 2003

The Bureau of Mines has developed a system for the rapid grab sampling of heterogeneous mixtures of gases and dusts during the preignition and postignition stages of dust explosions. The combustion chamber in which the explosion occurs is first fitted with a hypodermic sampling needle with its inlet end at the desired sampling point within the chamber and its sharp, injecting end protruding outside of the chamber. Rapid sampling (approximately 25 to 50 ms) is achieved with a double-acting, air-pressure-actuated cylinder. The forward stroke of the cylinder thrusts the rubber septum seal of an evacuated glass sampling tube onto the protruding needle which punctures the septum, filling the tube with gas and dust from the combustion chamber. The return stroke of the cylinder reseals the sampling tube by returning the mechanism to its original position. The initial time of sampling and the duration of sampling are independently variable and controlled by a microprocessor. Results obtained with a trimodal distribution of coal dust show no significant size discrimination at least up to 70 μm. Data obtained from laboratory-scale coal dust explosion tests are also presented. Such data provide valuable insights into the basic phenomena involved in explosions.
Localized metallic melting and hole boring by laser guided discharges
Authors: Gilgenbach R. M. , Ulrich O. E. , Horton L. D.
Published: March 2003

We demonstrate a new technique for localized melting and boring of materials using discharges guided by laser induced breakdown of atmospheric pressure air. This technique has important applications to a novel method for machining and welding materials, since the melting location can be controlled by adjusting the path of the focused laser beam. These experiments have demonstrated several features of localized metallic melting by laser guided discharges: (1) the melted spot can be scanned by changing only the position of the laser focal spot on the metal sample; (2) the melted spot diameter and profile depend upon the relative timing of the laser pulse and the discharge; (3) defocusing the laser beam has an effect upon the melted spot pattern; and (4) hole boring has been accomplished in aluminum foils which cover the stainless-steel electrode.
Laser system for two pulse and multiple position Thomson scattering
Authors: Sudo S. , Kondo K. , Mutoh T. , Zushi H. , Iiyoshi A. , Uo K. , Komatsu I.
Published: March 2003

We developed a special laser system for two pulse (about 100 ms interval) and multiple position (10 different points) Thomson scattering. A special feature of this laser system is that the beam quality is improved by adjusting the condition of the cavity wall. For two pulses, the power supplies are doubled and thyristor switches are used.
Technique for determining second-sound attenuation near the superfluid transition in 4He
Authors: Crooks Michael J. , Robinson Bradley J.
Published: March 2003

A procedure has been developed to measure the attenuation of second sound in liquid helium at temperatures near Tλ. The decay rate of a second-sound resonance in a high-Q cavity is determined, and data for more than one harmonic is obtained allowing the separation of the attenuation due to bulk fluid from losses at the cavity walls. This method has proven particularly successful near Tλ, where the second-sound velocity is strongly dependent on temperature and a high degree of temperature stability is needed. Results are given for the temperature range 40 μK<Tλ-T<40 mK at saturated vapor pressure. With minor modifications the apparatus can be used for measurements at elevated pressure and over a much wider range of temperatures.
Application of a personal computer for control and data acquisition in an Auger electron spectrometer
Authors: Chornik Boris
Published: March 2003

A digital system was designed to control a Varian Auger spectrometer to perform automatic data acquisition and data reduction. It is based on the Apple II personal computer. The advantages of the system are: low cost, simple design and construction of interface circuits, and great flexibility and power for different setups. A detailed description is given for the interface circuits, the analog-to-digital converter, and the digital-to-analog converters. Finally, it is discussed how to make changes in the original design to suit different needs.
Laser interferometer for measuring microwave-induced motion in eye lenses in vitro
Authors: Brown Peter V. K. , Wyeth N. Convers
Published: March 2003

A system was designed to optically measure the physical motion induced by a microwave pulse on a rat eye lens immersed in saline. After consideration of several possible techniques, a Michelson interferometer using a HeNe laser and normal reflection from the lens surface was constructed. The system uses wavefronts matched to the curved lens surface, a vibrating reference mirror for calibration and signal discrimination, a sample chamber mechanically isolated from the microwave waveguide, and a fast photodetector and signal averager. A rotatable half-wave plate and two polarizers were used to smoothly vary the intensity of the reference beam while maintaining the spatial integrity of its wavefronts. The system was able to measure motion down to 2 nm and performed successfully in the microwave pulse exposure experiments.
Interferometric measurements of very small electrostrictive strains
Authors: Luymes B. J.
Published: March 2003

Electrostrictive dilatations in the order of 10−13 m are measured in dielectric crystals by an interferometric method based on the Michelson interferometer. The electrostriction constants γ1111 of quartz, diamond, and LiF are found to be (−0.6±0.2), (+0.17±0.03), and (−7.9±0.8) 10−21m2/V2, respectively.
Visualization of evaporative convection in minute drops by laser shadowgraphy
Authors: Zhang N. , Yang Wen-Jei
Published: March 2003

A very simple optical procedure is developed to investigate the morphology of natural convection and the dynamic behavior of drops evaporating on a plate by means of a laser shadowgraphic system. This method is the only nonintrusive means of visualizing flow patterns in a time-varying ‘‘lens’’ shaped system. Its uniqueness and superiority are discussed.
Multipulse sequences in electron-spin echoes
Authors: Eliav Uzi , Freed Jack H.
Published: March 2003

A method is described whereby Carr–Purcell (CP) multipulse sequences may be generated at a rate rapid enough for electron-spin echoes ESE and in a manner consistent with constraints of typical ESE spectrometers. Both Carr–Purcell–Meiboom–Gill and alternating phase-CP sequences may be produced. It is shown how such sequences may be utilized (1) to increase the rate of data collection, which is especially important in laser photo-induced experiments, and (2) to study slow motions. They are respectively illustrated with results on transient spin-polarized photoelectrons and electrons trapped in irradiated quartz.
Scanning microwave interferometer for ELMO bumpy torus
Authors: Uckan Taner
Published: March 2003

A simple 4-mm scanning microwave interferometer has been developed and employed for electron density profile measurements on the ELMO bumpy torus (EBT). By making use of a pair of horizontally moving 45° mirrors that are located at the top and bottom of the plasma volume, the system avoids the deleterious effects of plasma sputtering and wall material flaking, since the microwave transmission and receiving horns do not view the plasma directly.
Microprocessor-based digital correlator
Authors: Thomas John C. , Lum Y. T. , Kennett David
Published: March 2003

We describe the design, construction, and operation of a low-cost, microprocessor-based digital correlator. The device has 128 channels, operates in either the single clipping or single scaling mode, and allows selection of the sample interval with 2-digit precision over the range 100 ns to 9.9 s. The device can be operated in the autocorrelate or cross-correlate mode and may easily be expanded to more than 128 correlation channels.
Microwave–microwave double resonance using a Fabry–Perot cavity spectrometer
Authors: Nandi Rabindra N. , Murray Alice M. , Choe Jong-In , Harmony Marlin D.
Published: March 2003

The design and operation of a relatively simple, yet versatile spectrometer for microwave–microwave double resonance (MMDR) studies is described. The system consists of a high-Q, semiconfocal Fabry–Perot cavity resonator which is crossed at right angles by a second free-space microwave beam. We excite the cavity with a low-power unmodulated signal source, while the free-space irradiation source is square-wave frequency modulated and is of moderately high power (several hundred milliwatts). Both microwave sources are scannable; the signal source is locked to the cavity while the pumping klystron is free running. The signal (cavity) frequency has been operated in the 15–40-GHz range, and pump frequencies can be selected and easily implemented above or below the signal microwave frequency.
New contactless method for lifetime measurement in semiconductor wafers
Authors: Hlávka J.
Published: March 2003

It has previously been demonstrated that a magnetic field caused by the photomagnetoelectric (PME) short-circuit current makes contactless measuring of recombination characteristics of a semiconductor wafer possible. In this paper, the general expression for the magnetic flux of this magnetic field is derived. The results are presented in graphical form showing magnetic flux as a function of absorption coefficient, bulk lifetime, and surface recombination velocity, with other wafer characteristics as parameters. The presented experimental results for germanium wafers are in agreement with the results calculated. A simple apparatus exploiting the method makes simple and rapid comparative measurement (with respect to a reference sample) of bulk lifetime as short as 10−7 s in wafers of arbitrary form possible. Lifetimes shorter than the one mentioned above can be measured under conditions discussed in the paper.
Determination of transducer damping ratio by frequency domain analysis
Authors: Simonen P. , Olkkonen H. , Korhonen T.
Published: March 2003

A new frequency domain method for determination of the damping ratios of the second-order transducer systems by the Fourier transform was developed. The damping ratios were calculated for several analytic functions representing the transducer system and compared to the theoretical values. The damping ratios produced by this method were in good agreement (average error 0.7%) with the theoretical ones. The method has numerous adaptations in the analysis of the physical transducers and instrumentation systems.
Improved and simplified diaphragm cell design and analysis technique for calibration
Authors: Asfour Abdul-Fattah A.
Published: March 2003

The diffusion diaphragm cell is considered the simplest and most reliable device for determining liquid-phase diffusion coefficients. Modifications were introduced to a diffusion diaphragm cell patterned after that described earlier by Stokes, to make it simpler in design and easier to use and handle. A new analysis technique made it possible to obtain cell constants faster and with much higher precision than before. Cell constants using the modified cell and the new analysis technique were reproducible to within ±0.07%.
Spherical field meter for measurement of the electric field vector
Authors: Kamra A. K.
Published: March 2003

A spherical field meter has been designed, constructed, and calibrated for the measurement of the atmospheric electric field vector above the ground surface. Three different insulated quadrants of a conductive sphere are used to measure the electric field normal to the quadrants. These three outputs together with nine field-distortion coefficients, determined experimentally, are used to determine the three components of the electric field, and hence, the electric field vector. The instrument can detect electric field changes of 2 V/m or more in any one component of the electric field and is reasonably stable for continuous operation. Preliminary observations show that variations in the vertical components of the electric field measured with the spherical field meter are parallel to the ones measured by a radioactive probe and the horizontal field components may be appreciable. Limitations of the apparatus and some possible modifications to it are discussed.
Step-loading technique for tungsten carbide opposed anvil high-pressure setup
Authors: Singh A. K. , Divakar C. , Mohan M.
Published: March 2003

A method is described to achieve a step loading of a tungsten carbide opposed anvil setup. The rise time of the pressure pulse is nearly 200 ms and the maximum height of the pressure pulse is 2 GPa. The use of this method in the study of the kinetics of pressure induced transformations under isobaric conditions is illustrated with the help of the data on fcc→bcc (face-centered-cubic and body-centered-cubic) transformation in ytterbium.
Convenient method for the synthesis of rare-earth hydrides by the use of a conventional very high pressure technique
Authors: Wakamori Koji , Filipek Stanisl/aw M. , Sawaoka Akira
Published: March 2003

This paper describes a new method for synthesizing massive rare-earth hydrides with high hydrogen contents. The method can substantially reduce the time for synthesizing rare-earth hydrides compared to a conventional method. Thermally decomposed gas from a hydride was used to synthesize another hydride under very high pressure. AlH3 and MgH2 were used as hydrogen sources. When AlH3 was used as a solid source of hydrogen, SmH2.95 was obtained under the pressure of 4.0 GPa at 300 °C in 30 min. When MgH2 was used, SmH2.95 was obtained under 3.0 GPa at 250 °C for 1 h, or under 4.0 GPa at 200 °C for 1.5 h.
Low-cost tubular sapphire optical cells for study of phase separation in fluid mixtures
Authors: Davis Harry A.
Published: March 2003

The construction of low-cost optical cells using thin-walled sapphire tubing, which are used for observation of phase separation in fluid mixtures, is described. The three different designs shown have been successfully used in our laboratory.
Pulsed plasma source spectrometry in the 80–8000-eV x-ray region
Authors: Henke B. L. , Yamada H. T. , Tanaka T. J.
Published: March 2003

The general characteristics are compared for the plane, convex, and concave fixed crystal analyzers which may be applied to the spectrometry of concentrated, intense plasma sources of x radiation involved, for example, in fusion energy and x-ray laser research. The unique advantages of the elliptical analyzer for precise and absolute spectral measurements are noted and detailed descriptions of its geometrical and physical optics are presented. With a source point at one of the foci of the elliptical analyzer profile, the spectrum is Bragg reflected (45°<2θ<135°) at normal incidence upon a detection circle with its center at the second focal point, at which an effective scatter aperture and filter window is located. A primary monochromator consisting of a cylindrical, grazing-incidence mirror is placed between the source and the analyzer to provide an efficient cutoff for high-order diffracted background radiation and to focus the divergent rays so as to obtain an adjustable spectral line length at the detection circle. Photographic film may be transported along the detection circle. Linear position-sensitive electronic detection arrays or a streak camera slit window may be placed along a chord of the detection circle. Calibration procedures for absolute line and continuum intensity measurement are described and examples of calibrating spectra are presented as measured with elliptical analyzers of LiF, PET, KAP, and molecular multilayers for the 80–8000-eV photon energy region. The instrumental effects that contribute to the spectral line shape as measured by the elliptical analyzer spectrograph are defined and a simple line-shape analysis procedure is presented for the determination of the line-broadening contributions of the source. The effects of an off-axis positioning of a source point and of an extended source are analyzed and the application of the elliptical analyzer spectrograph for one- and two-dimensional imaging or an extended source at a given photon energy is discussed. Finally, methods and materials for the construction of the elliptical analyzers are described.