ALBERT

Notes: Probe tips for scanning tunneling microscopy have been sharpened using focused ion beam milling. Reproducible tips were formed on polycrystalline W and Pt-Ir shanks, but this technique is not limited to these materials. The tips were found to have cone angles of 12±3° and radii of curvature as sharp as 4 nm. Focused ion beam machining allows precise control of the final shape of the tips which is important in metrology measurements of various nanostructure devices.

Notes: Commercial carbon composition resistors have been used as gauges to make dynamic stress measurements in homogeneous and heterogeneous reactive and inert materials. Initial loading was provided by plane wave lenses or shaped charge jets. A series of gas gun and aquarium experiments has been conducted to characterize the behavior of the gauges. Calibrations up to about 14 GPa for nominal 470 Ω resistors and 17 GPa for nominal 4700 Ω resistors are presented. The accuracy of the carbon resistor gauges is limited by response time considerations when submicrosecond rise times are encountered, and there is hysteresis during release. The gauge-to-gauge reproducibility appears to be adequate, and they survive in situations where no other stress transducer has been successfully used, such as in reacting beds of large-particle gun propellants.

Notes: A theoretical analysis of standing waves in a pipe with flow was conducted aimed toward the development of a flowmeter based on a measurement of phase difference between two points on the circumference of a pipe separated axially by an integral multiple of half sound wavelength. Effects of nonzero Mach number, variable ratios of upstream and downstream running waves, choice of location of the sensing pressure taps, and the incorrect spacings were examined numerically. Calculations were also made for steam flow where the maximum Mach number is much smaller than in cold air flows. For an industrial application where steam flow velocities are below 50 m/s, a very accurate sensor is shown to be possible. Experimental data were obtained by using an active aeroacoustic source over the range of 50 m/s to zero in an air flow. Experimental phase plots obtained from several coast-down tests have been compared with analytical results. The agreement with theory is excellent when the spacings are near Nλ/2 and the sensing locations are near the pressure antinodes. Otherwise, some zero shifts are introduced. Theory predicts that for steam flow much better results can be expected because the maximum Mach number is much smaller. Effects due to the (1−M2) factor would be imperceptible for steam flow.

Notes: A flowing solvent reactor for coal liquefaction has been developed, which uses direct electrical resistance heating of the reactor tube wall to achieve rapid, controllable heating. A computerized control system previously developed for a wire-mesh pyrolysis apparatus is used for temperature control; heating rates between 0.1 and 10 K/s, peak temperatures up to 450 °C, and isothermal holding times from 5 to 1600 s have been obtained. Alternating current is used for heating, allowing a simple thyristor bridge to be used for power control. Solvent is fed from a pressurized reservoir at up to 100 bars, obviating the need for a supply pump. Using this apparatus the effects of a variety of parameters on primary coal liquefaction processes can be examined; the design of the system and typical results are presented.

Notes: The hardware and software designs for fast measurement of dielectric properties of different substances over a wide range of characteristic times (10−5–10−10 s) by means of time domain dielectric spectroscopy (TDS) are presented. The characteristic feature of the described installation is the nonuniform time sampling of measured signals, which enables one to cover a wide range of characteristic times with a single measurement. Comparative results for an aqueous solution of lysozyme obtained on the traditional apparatus and on the described one are presented.

Notes: In this article we describe a simple SQUID magnetometer system useful for the magnetic characterization of high temperature superconductors. The system employs a commercial rf SQUID probe with associated electronics located in a 4He gas exchange cryostat. The system is equipped with a copper coil dc magnet for fields up to 50 Gauss. The cryostat is surrounded by a μ-metal shield that keeps the remanent field to less than 20 mGauss. The apparatus has been used extensively to measure both the superconducting transition temperature and width as well as the relative quantities of magnetic flux expulsion and exclusion. It has therefore served as an important first step in the evaluation of sample quality.

Notes: We describe two novel devices for optical beam alignment. One allows for a variable angle, fixed position of incidence upon a target. The other allows for a variable position, fixed angle of incidence upon a target. Cascaded together, these devices allow placement of a laser beam upon a sample with arbitrary angle and arbitrary position of incidence. These devices are particularly useful for experiments and applications involving ultrashort pulses since the time of flight through either of these devices is a constant independent of the angle of incidence and position of incidence.

Notes: We have developed a high-speed method to compress the two-dimensional angular distribution of space particles gathered by space plasma instrumentation into the pitch angle distribution, where the pitch angle is polar angle with respect to the ambient magnetic field. The pitch angle sorter can handle rates of up to 2 MHz and it is designed to accommodate high angular resolution plasma analyzers that are placed on a rotating spacecraft. This compression is achieved by relying on digitally encoded lookup tables to eliminate all arithmetic operations while applying the high symmetry of this compression to reduce the amount of digital memory.

Notes: A novel manometric technique that can be used to measure the inside diameter of otherwise inaccessible vertically aligned bores of known geometry is described. The technique was developed to measure the inside diameter of a long (1.5 m), relatively thin tapered tube with an uncertainty of ±0.5% (±0.2 mm in 40 mm). A substantial reduction in this uncertainty is shown to be achievable. The technique is potentially applicable to a wide variety of bore measurement situations where the desired measurement site is completely inaccessible and/or must be measured in situ.

Notes: Electrical resistance measurements at 4.2 K on an electron-beam welded Cu-Ag joint and a simple screw-fastened Cu-Ag joint are reported. It was found that the welded joint, when annealed, gives a contact resistance that is about three times smaller than the resistances for the best screw-fastened joints.

Notes: In materials testing it is well known that material strengths depend on: loading rate, whether loading is compressive or tensile and, in some cases, previous loading history; a widely useful loading technique should provide adjustable loading rate and reproducible compressive or tensile loading. Further, real-time microscopic studies require localized loading in a predetermined region−the microscope field of view. Symmetrical axial loading of cylindrical specimens can provide predetermined loading localization. Symmetrical loading may also facilitate analysis by localizing loading within a region of specimen material far from interfaces with other material or fixed or free ends. We describe a symmetrical impulse loading technique for compressive or tensile microscopic response studies. The technique is based on the use of magnetically induced stress waves and is capable of microsecond pressure pulse widths, (approximately-greater-than)10 000 psi pressure peaks and nanosecond synchronization of the symmetrical loading pulses. Our goal is to observe in real time the response of structural materials at the micron level with a scanning electron microscope.

Notes: Use is made of the fast response capability of the hot film shear gauge to perform unique shock tube and field test blast wave surface shear measurements. Mean flow turbulent calibration data are presented from three different test facilities: a low speed wind tunnel, a high pressure pipe facility, and a laboratory scale shock tube. Favorable agreement in calibration data between the three facilities is demonstrated. The good correlation in calibration results validates the "established'' formulation procedure and provides a unique verification of available shock tube shear data. Measurements of ground shear under clean wall, i.e., nondusty, flow conditions are reported for blast waves created by high explosive detonations under large scale field test conditions. Satisfactory scaling of results in terms of event yield and overpressure location is demonstrated.

Notes: An alternative form of application of an electric field to semiconductors so as to provide electroreflectance modulation is presented. Two metallic contacts, a large ring-shaped one enclosing a small transparent one, are deposited on the specimen surface and connected to the two leads of a signal generator. Results from a highly doped n-type silicon bulk and from an undoped 4000 nm silicon film on sapphire demonstrate that this technique yields spectra equivalent to traditionally performed electroreflectance or photoreflectance. We also show that electroreflectance response can be obtained with a current generator connected across a single metal contact.

Notes: Using a gamma-ray detector and a television camera system for synchrotron light, high-energy bremsstrahlung and horizontal growth of the synchrotron light source were observed when sudden decrease in the electron-beam lifetime occurred due to dust trapping in the electron beam. Two types of beam current losses were found; one was a continuous beam current loss, and the other was a short-term beam current loss. High-energy bremsstrahlung at a location was observed in a short time and after that, the bremsstrahlung was not detected in spite of the occurrence of dust trapping phenomena. The fact suggests motions of the trapped dust particles in the longitudinal directions. Materials collected in the beam chamber are dust particles from ion pumps and dust particles made during the beam chamber processing for welding. Most of the collected dust particles were less than 2 mm in size and surfaces of some dust particles were melted with the electron beam. Simple analysis was carried out for the conditions necessary for a dust particle to be trapped, for motions of the trapped dust particle, and for interactions between the trapped dust particle and the electron beam. The analysis showed that a dust particle less than 3 mm in size, made of Al, can be trapped and that the trapped dust particle can move in the vertical and longitudinal directions.The analysis also suggested that a dust particle in size of about 2 mm can be continuously trapped around the electron beam without being destroyed by the electron beam. Furthermore, the analysis explained the difference between the two types of beam current losses observed in the ring. Experiments which simulate the electron beam using a Cu wire in an evacuated beam chamber show that a dust particle (less than 70 μm) is trapped sufficiently. The experiments also coincide with theory for an attractive force acting to a conducting small particle. The calculated electric field of the electron beam and the calculated electric charge of dust particles given through the photoelectric effect in the TRISTAN accumulation ring are 100 times and 104–106 times higher than those of the simulated experiments, respectively. In the ring, the attractive force caused with the average electric field and with the expected charge is 10–103 times larger than that of the simulated experiments. Therefore, a dust particle (less than 2 mm) can be trapped sufficiently. An electrostatic dust collector using an electron beam and an electrostatic force are effective in removing all of the sample dust particles in the test chamber for the simulated experiments. A method to remove trapped dust particles using electrostatic electrodes is also discussed. It is expected that such electrodes can be useful for trapped dust particles moving in a longitudinal direction.

Notes: An easy to build, high intensity monochromator for helium II radiation is presented. The design includes a double focusing, nonblazed, toroidal grating with a groove density of 800 l/mm. The adjustment and focusing properties of the design have been studied using an optical simulation program. It is found that all necessary adjustments of the grating may be performed by using only two degrees of freedom; rotation and sidewise shifting. Inner and outer valence photoelectron spectra of N2 and CO have been recorded using monochromatized HeIIα radiation. The study reveals extensive vibrational structures in the inner valence region of both molecules. A new state has been identified in the CO molecule.

Notes: Ion sources can be damaged by arcs between metallic components of the source if these arcs are permitted to last. The negative-biased low-work-function converter in a surface conversion negative ion source is especially susceptible to metal-arc breakdown damage. Here an electronic circuit for minimizing the damage caused by such an arc is described. The circuit uses a transistor switch and an inductor in series with the converter bias power supply to limit the damage during the metal-arc breakdown.

Notes: As with most similar equipment, the method consists in applying a sinusoidal voltage to an unknown impedance and measuring the current through it. The advantage of the developed equipment is that it allows independent and simultaneous measurement of the resistive and reactive components of the current through the sample impedance, thus making possible the determination of impedances in magnitude and phase. The measurements can be controlled with a computer using a digital interface. The instrument may also be controlled with a computer using a digital interface. The instrument may also be controlled manually from a front panel. The apparatus was designed to operate in the audio range 1 Hz–100 kHz for currents even below 1 μA. The analog outputs may either be connected to an X-Y recorder or the data can be acquired with a computer through an analog-to-digital converter. The laboratory tests have shown a good performance according to the design specifications. These tests have been carried out using discrete circuits made of calibrated components.

Notes: A new amplifier, designed to operate with fast semiconducting bolometers, is presented. Based on current detection of the bolometer signal, it allows one to obtain good sensitivity with response times of about 10 ns without using cryogenic electrical components. The amplifier was used to detect heat pulses propagating in a Si crystal.

Notes: A fraction marker-timer controller has been designed that partially automates peak collection and provides event marking during high-performance liquid chromatography of partially purified samples having complex chromatograms. The device is activated via a pushbutton switch when a peak of interest elutes. The apparatus places an event mark on the detector's chart recording, provides a time delay to account for detector-to-fraction-collector dead volume, and then advances a fraction collector to capture the peak in a test tube. If more than one peak elutes in the dead volume window, up to three independent time delays may be triggered.

Notes: A design for a heater stage capable of operating in a high oxygen partial pressure is presented. Substrates attached to the stage may be heated up to 900 °C in oxygen partial pressures from 10−3 to 760 Torr. The design of the heater allows easy replacement of all parts.

Notes: A simple yet reliable laboratory laser microrefractometer is described. A detailed theoretical analysis of the errors is made. The construction permits the utilization of various lasers as light sources. Preliminary investigations on some liquids with a He-Ne laser are carried out. The results confirm the applicability of the configuration, and the practical accuracy is in good agreement with the theoretical one. The possibilities for further improvement of the device in terms of range and accuracy are discussed.

Notes: The distortion of the cylindrical Langmuir probe I-V characteristic, connected with the ohmic resistance of its operating element, is investigated. The relations given in the paper enable one to reconstruct the shape of the undistorted I-V characteristic from the experimental data.

Notes: This article describes the design and operating characteristics of a reasonably compact, semi-sealed-off, high-efficiency transversely excited atmospheric-pressure CO2 laser operating at prfs 〈150 Hz by a stable discharge system using a new type of surface-wire-corona preionizer. An efficient laser operation at a slope efficiency of 10.2% with a maximum average power of 42 W (100 Hz) has been achieved from a discharge volume of 57.5 cc with an active length of 26 cm. With CO and H2 as additive, (approximately-greater-than)2.1×106 shots has been achieved on a single gas fill and an estimated half-power lifetime of 2×107 shots made.

Notes: It is pointed out that a determination of the temperature dependence of the Fermi cutoff in the conduction band of a metal provides a means of measuring the thermal emf of a single metal, as well as the absolute thermoelectric power, without use of a reference substance. The energy of the Fermi cutoff is determined by photoemission. The method is illustrated by a crude determination of the thermal emfs of copper and constantan.

Notes: Many circuit functions can now be realized using digital rather than analog techniques. The application of digital signal processing (DSP) technology for the implementation of the feedback control loop of a scanning tunneling microscope is discussed. A system that utilizes a commercially available PC AT-compatible plug-in card based on the Texas Instruments TMS320 series of digital processing chips to implement a loop controller of the proportional-integral-differential type is described. The advantages afforded by DSP in comparison to analog systems include greater flexibility in the choice of the signal processing algorithm and greater ease of control of loop parameters by the host computer.

Notes: An adapter is described that enables one to use a nonbakable closed-loop helium cryostat in ultrahigh-vacuum experiments. The adapter is fully bakable, simple and cheap, and has been designed specifically for systems where a sample holder is mounted to an x,y,z-rotational manipulator. During bakeout of the ultrahigh-vacuum apparatus the cold head of the cryostat is removed from the system.

Notes: We designed, constructed, and tested at 4.2 K (using two different low phase noise electrical pump generators) a cryogenic double-resonant parabridge motion transducer made out of niobium, whose electrical output was amplified by a two-stage metal-semiconductor field-effect transistor cryogenic amplifier. Most of the experimental results agreed well with the theoretical models. We were able to adjust the two electrical bridge resonant frequencies at the pump frequency, allowing us to obtain an electromechanical coupling as high as 0.054, and we successfully measured the mechanical Brownian motion of this transducer. In one case, we observed a dip in the electrical noise spectrum near the mechanical resonant frequency due to destructive interference between this noise and its "reflection'' from the mechanical resonator. At the bottom of this dip, in a bandwidth of 0.7 Hz, we measured an equivalent displacement noise of 4 × 10−16 m/(square root of)Hz with a systematic error of less than 10%.

Notes: A wobbling mechanism for a secondary mirror has been developed for a balloon-borne infrared telescope. Friction of the wobbling mechanism is negligibly small, and hence the wobbling mechanism is very reliable for the use in a severe environment at balloon altitudes. Motion is controlled by servo electronics, whose transfer function includes the second-order differential term of the error signal in order to improve the waveform. Good performance of the drive mechanism has been confirmed in two balloon flights in 1988 at an altitude of 31 km.

Notes: We describe the design and optical characteristics of a tunable x-ray polarimeter set up at the National Synchrotron Light Source at Brookhaven. Initially, the energy range from 7.0 to 9.2 keV is covered with a polarization extinction ratio greater than 10 000 and a statistically limited sensitivity of 70 μrad in measurements of optical rotary power. First spectroscopic measurements on a wide range of cobalt compounds show optical activity, Faraday rotation, and circular dichroism in the energy region close to the cobalt K edge. More recently we have worked on a variety of samples containing iron near the iron K edge.

Notes: X-ray absorption fine structure (XAFS) measurements in regions less than 20 μm in diameter were realized using an x-ray microprobe employing the fluorescence detection method. To realize an energy tunable intense small x-ray beam, an ellipsoidal mirror was used as the synchrotron radiation focusing element combined with a double-crystal monochromator. Distortion of a XAFS spectrum due to the self-absorption effect is discussed in detail. The degree of the distortion was experimentally evaluated from the measurement of the x-ray fluorescence intensity as a function of takeoff angle, and the distortion was significantly reduced with the small takeoff angle detection geometry. Utilizing this technique, reliable XAFS spectra were obtained from a rock sample containing several minerals.

Notes: The Light Source Building of the Photon Factory was found to distort so much as to induce the displacement of magnets in the storage ring. This resulted in drifting of the beam orbit. It was considered that the building was distorted by the variations of thermal stress, such as diurnal changes of the solar irradiation and atmospheric temperature. To reduce such thermal stress, the rooftop of the building was insulated with a layer of polyethylene foam. The building distortion was measured in terms of vertical floor displacements along the storage ring by using a hydrostatic level measuring system. Results of the measurement were compared with those of a model simulation based on the finite element method. Comparison between measured and simulated results showed good agreement before the insulation applied to the roof. After the insulation, the measured floor displacements reduced to about one half and were also comparable to the simulated results. A full description of the subject is given in T. Katsura, Ed., KEK Internal 90-32 (in Japanese) Jan. (1991).

Notes: Motion of trapped dust particles has been previously analyzed using high-energy bremsstrahlung data obtained during dust trapping in the TRISTAN accumulation ring. Because it is difficult to observe the actual motions of dust particles trapped in an electron beam due to the strong synchrotron light background, we carried out experiments to trap sample dust particles with a Cu wire simulating an electron beam. A negative potential was slowly applied to the wire using a high voltage dc power supply. Motions of dust particles trapped by the wire were recorded with a video camera system. In an experiment using a Cu wire (1.5 mm in diameter) with no magnetic field, the charged dust particle made vertical oscillation about the wire. In another experiment using the same wire but with a vertical magnetic field (0.135 T) simulating a bending magnetic field, both vertical and horizontal oscillating motions perpendicular to the wire were observed. Furthermore, it was found that the dust particle moved in the longitudinal direction of the wire in the bending magnetic field. Therefore, it is expected that charged dust particles trapped by the electric field of the electron beam oscillate vertically where there is no magnetic field in the TRISTAN accumulation ring. It is also expected that trapped dust particles where there is a bending magnetic field oscillate horizontally and vertically as the particle drifts in a longitudinal direction along the ring.

Notes: Design and performance of a newly developed scanning photoelectron microscope based on focused coherent vacuum ultraviolet (VUV) light are described. The VUV light at 118 nm wavelength (10.48 eV photon energy) was generated by the frequency upconversion of a pulsed YAG laser light. The microscope is characterized by its high spatial resolution of a few microns, which is consistent with its high-energy resolution of better than 200 meV. The spatial resolution was provided by focusing the VUV light nearly to its diffraction limit, while the photoelectron energy was resolved by a high efficiency time-of-flight (TOF) energy analyzer. The point-to-point data acquisition, as well as the sample scanning, were controlled by a computer system, and the spectral data were accumulated at every two-dimensional mesh point of the specimen. From the photoemission profile across a processed Ag/Si stripe, the spatial resolution was nominally 6 μm. The energy resolving capability of the present microscope was demonstrated by the observation of crystalline facets formed on a polished copper disk.

Notes: High-energy bremsstrahlung synchronized with the electron beam in the TRISTAN accumulation ring was observed accompanied by a sudden decrease in the electron beam lifetime which occurred due to dust trapping in the electron beam. The bremsstrahlung observed with gamma-ray detectors was obviously different from that caused by interactions between residual gases and the electron beam. Other bremsstrahlung observations showed a trapped dust particle passing through the periphery of the electron beam in the bending magnetic field; the transit time through the periphery of the electron beam was 0.15 ms; the half period of the horizontal oscillation perpendicular to the orbit of the electron beam was about 200 ms and the period of the vertical oscillation was 1 s. Simultaneous observation at two adjacent gamma-ray detectors showed that a trapped dust particle in the bending magnetic field moved in a longitudinal direction at the average speed of about 0.191 m/s. These observations coincide with the results based on our newly developed theory for motions of a trapped dust particle in a bending magnetic field. Furthermore, we introduced sample dust particles into the TRISTAN accumulation ring and carried out an experiment to trap the dust particles in the electron beam, in a straight chamber with no magnetic field and observed their motion with a gamma-ray detector. The beam lifetime suddenly decreased when the sample dust particles directly under the electron beam were caught up into the beam. High-energy bremsstrahlung and a pressure rise caused by the destruction of the dust particles were also observed at the same time. After that, beam lifetime recovered gradually. Our theoretical analysis shows that vertical oscillation of a trapped dust particle with no magnetic field continues and that the dust particle is destroyed by the heat deposited by the electron beam in less than a second. The calculated variation in the beam lifetime coincides approximately with the actual variation in the beam lifetime. Compared results of the observations and experiment show that our theory for motions of a trapped dust particle is useful.

Notes: An optical interferometric instrument for the measurement of distance and position is presented. The system is based on a high-frequency sinusoidal phase-modulation interferometer. Phase modulation of the laser beam in one of the two interferometer arms is obtained by means of an electro-optic modulator operating at frequencies up to 10 MHz. The electronic unit performs synchronous demodulation of the signal coming from the photodetector. The resulting signals are fed to an up-down counting logic that is interfaced to a personal computer. The performance of the instrument has been evaluated by means of a system calibration against a reference high-precision commercial interferometer. The overall accuracy of the system resulted to be within 80 nm, at target speeds up to 1 m/s. In this article, the optical setup, the electronic equipment, and the calibration results are presented.

Notes: A simple trigatron spark-gap chamber is modified to accommodate two cascading high-voltage breakdowns, separated by the time lag of the second spark formation. The time lag is employed as a temporal delay for synchronizing the ultraviolet preionization and the main discharge in the transversely excited atmospheric CO2 laser. Owing to prompt triggering and in situ preionization of the second breakdown, reliable delay up to 500 ns is possible by simply varying the separation of the second spark-gap electrode to that of the first spark gap.

Notes: A two-crystal spectrometer for chemical state analysis of high-resolution x-ray fluorescence spectra employs ball-screw and slide mechanisms rather than gears to obtain a 2θ scanning range of 40°–147° and a Δ2θ scanning step of 10−4 deg under vacuum, and a 2θ resolution of 10−4 deg in determination of an intercrystal angle with encoder-based measurement and servomechanical control of position. The spectrometer, although simple in structure, is a powerful instrument for chemical state analysis, as demonstrated by its high resolution, stability, and repeatability in determination of the Kα lines of first transition metals, aluminum, silicon, and sulfur with Si(220), ADP(101), InSb(111), and Ge(111) as analyzer crystal, respectively.

Notes: We present a system which uses optical feedback from a diffraction grating to provide primary control over the frequency tuning of a diode laser, and employs simultaneous optical feedback from a narrowband Fabry–Perot cavity to reduce the linewidth. The frequencies of the optical feedback from the diffraction grating and narrowband cavity are electronically locked using a novel technique. The reduction in the linewidth is measured as a reduction in the frequency noise seen on the side of a Cs-saturated absorption line. The presence of optical feedback from the narrowband cavity reduces the frequency noise by a factor of 3 compared to the frequency noise obtained using the grating feedback alone.

Notes: A new approach to electro-optical signal modulation is proposed based on the geometrical representation of signal voltages. In the forward biased implementation an assembly consisting of a deposited meander pattern, sinusoidal mask, and microchannel plate (MCP) is shown to perform one-dimensional Fourier analysis. The sinusoidal mask is shown to modulate a biasing voltage pulse as is traverses the meander pattern. In this paper the MCP gain and signal-to-noise models are combined with signal sampling criteria to obtain constraints on the assembly dimensions and biasing voltages. It is shown that a 0.5 mm square meander, coupled with mask wavelengths of order 10 mm, is sufficient to measure about 10 Fourier components of a 400 ps pulse with peak voltage of order 10 V. Experimental issues which have arisen in the course of testing the concept are discussed.

Notes: We have designed and fabricated a miniaturized, light-weight magnetic sector for a focal plane mass spectrograph (Mattauch–Herzog design) by using a new high-energy-product magnet material (Nd-B-Fe alloy), and a high permeability magnet yoke material (V-Co-Fe alloy). The magnetic sector weighs less than 10 kg and has a focal plane of 5.1 cm in length and covers a nominal mass range of 40–240 amu. Such a magnetic sector in conjunction with an array detector and a short microbore capillary column is eminently suited for the development of a field-portable gas chromatograph-mass spectrometer instrument of high performance.

Notes: The coupling of an autoneutralizing SF−6 fast ion-beam gun to a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer is described. The fast neutral beam provides for secondary-ion-type FT/ICR mass analysis [e.g., production of abundant pseudomolecular (M+H)+ ions] of involatile samples without the need for external ion injection, since ions are formed at the entrance to the ICR ion trap. The design, construction, and testing of the hybrid instrument are described. The feasibility of the experiment (for both broadband and high-resolution FT/ICR positive-ion mass spectra) is demonstrated with tetra-butylammonium bromide and a Tylenol(large-closed-square) sample. The ability to analyze high molecular weight polymers with high mass resolution is demonstrated for Teflon(large-closed-square). All of the advantages of the fast neutral beam ion source previously demonstrated with quadrupole mass analysis are preserved, and the additional advantages of FT/ICR mass analysis (e.g., high mass resolving power, ion trapping) are retained.

Notes: Ultrafast microchannel-plate photomultipliers offer picosecond resolution in time-correlated photon counting, provided all additional causes of timing jitter be minimized. Here we analyze the contribution of the electronic circuit noise, mainly dependent on the fast preamplifier and no more negligible at picosecond level. Criteria are derived for minimizing this contribution by proper design or selection of the amplifier. We highlight that it does not make sense to select amplifiers with bandwidths of 3 GHz or more, looking mainly to the rise time of the fast microchannel-plate pulse and paying minor attention to the noise. We demonstrate that (i) the noise spectral amplitude has chief importance, (ii) the bandwidth providing minimum jitter is around 1 GHz, and (iii) satisfactory results are obtained with lower bandwidths, in some cases down to about 500 MHz.

Notes: A new resistor network for an octupole deflector combined with a stigmator is proposed. Improvement on the time constant due to the octupole's stray capacity, which is made by connecting phase-compensative capacitors parallel to the resistors, is also described.

Notes: Atmospheric observations show that ultraviolet absorption ozone monitors used for ambient measurements can, under some conditions, respond to variable water vapor concentrations with quantitative responses varying from instrument to instrument. A combined theoretical and experimental study shows that these monitors should not respond to water vapor. The source of the response appears to be the varying extinction of ultraviolet light by the windows of the optical cells. A change of 6-g H2O kg air−1 gives, at maximum, an extinction equivalent to 800 ppbv ozone. This changing extinction appears to be related to surface contaminants or surface structure on the cell windows. Instruments with such cell windows can give spurious ozone results in some measurement sequences.

Notes: A simple, inexpensive, and flexible sample transfer system is described. The system possesses the advantages of excellent base pressure and the flexibility to study thin films deposited in situ. We have applied the system to study thin-film magnetism with magnetic measurements utilizing optical techniques that require stable sample support.

Notes: We have investigated errors and their sources in exponential-parameter estimation. This investigation was part of ongoing research in thermal metrology using the temperature-dependent fluorescence lifetime of rare-earth-doped ceramic phosphors. We have found that noise and baseline offset are the dominant sources of error in our experiments. In this note, we present the dependence of errors in exponential-lifetime estimates upon baseline offset and noise, as determined by the Monte Carlo simulation of Marquardt least-squared-error algorithms. These simulation results are validated by a Kullback–Leibler stochastic-distance model. We also demonstrate the necessity of estimating the baseline for accurate lifetime estimation.

Notes: We describe a method for covering large apertures of nearly arbitrary size and shape in ion optics with uniformly taut, flat, electroformed metal mesh. An O-ring trapped between two plates in a specially cut, beveled groove provides uniform radial tensioning of the mesh as the plates are bolted together.

Notes: The viscometric thermometer is one of the few simple and inexpensive methods of temperature measurement in the presence of electric or magnetic fields. This work further improves our previous viscometric thermometer design so it now measures the temperature distributions in both steady and transient states with a response time of a few seconds or less.

Notes: We developed a device which allows continuous measurement of the density of low-temperature stabilized atomic hydrogen by means of a bolometer. This density monitor was tested in a large open-storage cell during microwave-induced extraction of polarized atoms.

Notes: An adjustable gas-blending apparatus is hypothesized that would maintain a consistent mixture over a broad range of flowrates. The design equations for the unique valve seat required for such an apparatus are developed and solved numerically. An example seat is calculated and illustrated in table form. For preliminary study, a prototype is constructed and empirical data are presented which substantiate the design.

Notes: A simple and reusable metal sample holder for a hydrogen permeation experiment was made of two standard conflat flanges and gaskets of copper and aluminum.

Notes: A two-frequency laser heterodyne interferometer has been implemented for small displacement measurement. The displacement signal is detected by using a double-heterodyne technique. Vibration amplitudes at 1 kHz on the order of 1 nm and smaller can be detected.

Notes: A holographic relaxation spectrometer is described which incorporates high-frequency phase modulation of the probe or reference beams by means of an electro-optic modulator. Heterodyne detection at the modulation frequency or two times the modulation frequency provides signals that are proportional to the electric field amplitude of the diffracted light. This system permits heterodyne detection of a transient diffraction signal in a single-shot experiment. The requirements for phase stability are somewhat relaxed and samples that deteriorate under laser irradiation can be studied. Diffraction amplitudes for the phase and absorbance components of laser-induced gratings can be recorded separately under certain conditions.

Notes: We have evaluated the performance of a commercially available, completely automated high pressure dilatometer (PVT apparatus) by determining the equation of state of water over the ranges 30 °C–250 °C and 0–200 MPa, using a sample of only 1–2 g. Although the apparatus was designed for the measurement of solid and molten polymers, we conclude that the system is quite capable of measuring PVT properties of water (and presumably other simple liquids) with a reasonable accuracy (0.001 to 0.005 cm3/g, depending on the temperature range), typically five to ten times less accurate than dedicated equipment using 40–250 times larger samples and, in general, smaller pressure and temperature ranges. Two polynomial fits (for separate pressure ranges) with twelve coefficients give 0.0004–0.0005 cm3/g absolute average deviations from the experimental data for the whole range. Comparisons with the NBS/NRC steam tables show deviations within 0.001 cm3/g below 200 °C, reaching their maximum of 0.006 cm3/g at 250 °C.

Notes: When using multichannel SQUID magnetometers for biomagnetic applications, the correct measurement of the Tesla/volt calibration factor of each channel is of extreme importance, in order to avoid gross errors when analyzing the results. We propose a general calibration method valid for all kinds of gradiometer arrays. One of the main properties of this method is that the gradiometer position inside the cryogenic Dewar does not need to be known precisely. When tested, calibration factors with accuracies ranging from 0.3% to 0.8% were obtained. It is based on a spatial Fourier technique and on the fact that the gradiometer acts as a discrete spatial filter.

Notes: Commercially available dimethyl polysiloxane is shown to be an excellent liquid coolant for the containing walls of high power plasmas (≥300 W/cm3) excited with 2.45-GHz microwaves. This stable, nontoxic, and nonflammable fluid has very low microwave absorption (tan δ=ε‘/ε'=3.5×10−4) at this frequency. Fortuitously, it also has excellent ultraviolet, visible, and near infrared (λ≤0.8 μm) transmission. The UV transmission over 1 cm shows 2% transmission at 2000 A(ring), a 30% transmission at 2200 A(ring), 80% at 2400 A(ring), and 100% for λ(approximately-greater-than)2500 A(ring). These features plus its good physical (viscosity, thermal conductivity, specific heat capacity, heat of vaporization, and density) and electrical (resistivity and breakdown) properties make it very unique as a liquid coolant of UV emitting microwave plasma lamps. The clear coolant's infrared absorption for λ≥1.0 μm reduces the radiative (heat) emission from the plasma. In addition, dimethyl polysiloxane has a very wide operating temperature range, −73 °C≤T≤260 °C. Particular procedures required to assure its excellent ultraviolet transmission are described along with different geometrical combinations of liquid cooled plasma lamps and reflector housings. This liquid may also be used to cool microwave excited laser tubes.

Notes: The design, calibration, and performance are described of an apparatus to study the shear response of ultrathin liquid films. The device, a modification of the surface forces apparatus, measures the resistance to shear of liquids confined between two atomically smooth solid surfaces. The surfaces are separated by distances on the order of the size of the liquid molecules (liquid film thickness 〈10 nm). Shear forces with periodic time dependence are applied to one surface while the second is held fixed, and any motion so induced is analyzed to determine the behavior of the liquid film. The frequency and amplitude of the shear forces applied can be varied over a wide range (0.03–60 Hz frequency and 0.1–1000 nm amplitude) to achieve different values for the magnitude of the shear rate. The dynamic response of the device is linear in the applied force at a given frequency; nonetheless, nonlinear dependence of the liquid's shear resistance on the shear rate, net normal pressure, and film thickness can be observed with the technique. The mechanical and electrical characteristics of the device are modeled to gain insight into its behavior and facilitate analysis of the measured data. The central results of this approach are expressions for the magnitude of the shear rate and an effective friction coefficient of the liquid film in terms of easily measured electrical quantities. For convenience the friction coefficient is restated as an apparent dynamic viscosity in analogy to continuum hydrodynamics, but the validity of the approach does not depend on a particular understanding of the structure in the liquid layer. The applications and limitations of the device are discussed, as well as other potential uses to which the apparatus may be applied by rational extension to the approach presented.

Notes: A laboratory coal metering device for the entrainment of pulverized coals is described. The system uses controlled aerodynamic stripping of the powder surface by a carrier gas to effect the coal feed. This device has been used for approximately one year in bench-scale combustion studies requiring exacting feed rates with very satisfactory results.

Notes: A new sensor for optical detection of shear stress field induced by air or gas flow on a rigid surface is reported. The sensor uses the novel effects of shear induced optical switching in ferroelectric liquid crystals. The principle of operation of the sensor is described and a theoretical model for the optical response to shear stress is given. Director dynamics and system-free energy considerations predict a system response time ≈10 ns for an applied shear stress step of ≈700 Torr. A thin (≈1 μm) ferroelectric liquid crystal film coated on a flat glass model surface is exposed to gas flow from a micro wind tunnel attached to the polarizing microscope employed for optical measurements. Schlieren texture of the thin film consists of two stable domains separated by a domain wall. Gas or air flow on the liquid crystal surface induces director reorientation resulting in optical contrast. Transmitted and reflected light intensities from polarization microscopy provide measurement of the flow parameters. System response time τ∼150 μs has been estimated from the material viscosity and the time variation of the applied shear stress in the experiment. Optical response is linear for applied differential pressures up to ≈800 Torr beyond which it tends to saturate. Second-order nonlinear effects are observed for flow rates beyond ≈42 l/min. The configuration used in the present method overcomes many of the limitations of similar measuring techniques including those using cholesteric liquid crystals. The present method offers a preferred alternative for flow visualization and skin friction measurements in wind-tunnel experiments on laminar boundary layer transition investigations.

Notes: An apparatus for making in situ measurements of the magnetic moment of submonolayer through multimonolayer samples deposited in a UHV chamber is described. The UHV chamber is designed to be used with a commercial SQUID magnetometer with a sensitivity of ∼10−8 emu. The component of magnetic moment parallel to the sample surface may be measured over the temperature range 4–400 K and for magnetic fields (applied parallel to the surface) up to 5 T. A thin re-entrant metal tape is used both as an initial substrate for the deposition of any desired films, and as the means of transporting the deposited sample from the evaporation and evaluation regions of the vacuum chamber to the SQUID analysis region. Some results for Fe evaporated on polycrystalline Ag films are presented.

Notes: Significant improvements and extensions have been made to a high Tc superconducting levitation motor with an optical commutator. The primary extension is the development of a heat exchanger that permits high Tc superconductors to be cooled with liquid nitrogen to 77 K and below in vacuums of 10−5 Torr and less. This permits the levitation motor to be operated without the decelerating force of atmospheric drag. The result is an increase of nearly two orders of magnitude in the sustainable rotational frequency from a maximum of 10 s−1 at atmospheric pressure to 500 s−1 (30 000 rpm) at 10−5 Torr. The corresponding tangential velocity of the rotor arms increased from 3 m/s to 155 m/s. Angular frequencies between 100 s−1 and 200 s−1 have been sustained for periods exceeding 6 h. Measurements and analysis of rotor deceleration as a function of pressure and time are presented. Other improvements are discussed.

Notes: A novel method of target manipulation for laser vaporization of metals has been described. The simplicity of fabrication offers a number of advantages over existing techniques. The yield of stable clusters M+x, x=1 to 8 is quite good and mass selection using a Wien (E×B) mass filter has been achieved. Examples of Nb, Co, and Mn mass spectra are presented.

Notes: We describe an apparatus for measuring the biaxial mechanical properties of metallic films. A circular knife-edge support forms a drum-head geometry over which the film to be studied is stretched. The film's tension is obtained from the frequency of its membrane modes, and its strain by using an optical technique. The biaxial modulus is obtained from the ratio of tension and strain. An electronic detection system is developed that regeneratively locks to the film's resonant frequency. The system is also capable of measuring the film's damping when the lock is switched off.

Notes: Measurements of the longitudinal profile of intense electron bunches with an energy of 100 keV, using a button monitor and a 20-GHz sampling oscilloscope, are presented in this paper. At this energy, which is intermediate between nonrelativistic and relativistic, the button response is quite different from the response in either of the two extreme cases. An analytical model of the response is presented. The resolution derived from this model is 80 ps at 100-keV beam energy. For more relativistic beams, a resolution of about 40 ps appears to be feasible. Great care has to be taken in avoiding resonances.

Notes: A multi-element segmented concentric Faraday collector has been developed for measuring the time evolution of the beam half-current radius (a1/2) of an intense relativistic electron beam. Each collector segment measures the total current within its radius. The data analysis procedure fits the data from all five segments at a given time to a prescribed beam profile and calculates a1/2 from the parameters of the fitted curves. The effect of beam centroid offsets on the data analysis was investigated numerically. Beam centroid offsets as large as half the beam radius produce only a 10% error in the experimental measurement of a1/2. The use of a thin graphite overlayer followed by range-thick stainless steel reduces scattering from one collector element to the next. The instrument has been used extensively on the SuperIBEX relativistic electron beam accelerator for measurement of the half-current radius as a function of time. Radius variations in excess of 4:1 have been measured over the duration of the beam pulse for beams with 5-MeV energy, 20-kA peak current and 1-cm final half-current radii.

Notes: A physisorption apparatus with very high sensitivity has been constructed. It is capable of accurately measuring adsorption and desorption isotherms of gases on solids in the pressure range of 10−5–1000 Torr. This is particularly useful for investigating argon sorption on catalysts and catalyst supports, e.g., FCC, reforming and hydroprocessing catalysts; zeolites; and pillared layered materials. The isotherms contain information about micropore and mesopore size distribution, BET surface area, etc. The operation of the unit and the analysis of isotherm data are both fully automated. Details of the equipment and the software are described.

Notes: A new monolithic and linear four-quadrant multiplier allows replacement of traditional hybrid-based circuits used in frequency conversion, and in-phase or amplitude modulation schemes. We demonstrate the advantages of this approach by evaluating the performances of a wideband amplitude and phase modulation unit built around the 500 MHz multiplier AD834. Key specifications of the unit we assembled are an 80 dB attenuation range, a 100 ns response time, a 360° range of phase shift, and an accuracy up to 0.02°. The device suits the phase and amplitude modulation needs of a nuclear magnetic resonance spectrometer.

Notes: Noise voltage and noise current measurements have been carried out at different temperatures on two kinds of low-noise silicon J-FET at moderately high frequencies up to 100 kHz. We have made careful noise current measurements by constructing a very low-loss superconducting resonator working in the kHz frequency range, whose quality factor reaches 3×105. At 10 kHz, the measured noise energy lies between 1.1 and 1.8×10−24 W/Hz for both types of transistors, but the ratio between the noise voltage and the noise current exhibits pronounced differences depending on the device under test.

Notes: We report in this article an analysis of the distortion of the time distribution due to the dead time of the detection chain. The special case of distributions coming from a pulsed source is considered and a relatively simple method for the reconstruction of the true time distribution is given. The method is applicable in both extended and nonextended dead times. It can be applied to correcting an experimental time distribution and, if the shape of the distribution is known, to deducing the true rate of events from that measured by a counter. An experimental method to simulate a pulsed source with a controllable mean production rate is also shown; the time distributions obtained from this source have been used as test distributions to prove the reliability of the reconstruction procedure.

Notes: This note concerns the accuracy of measurement of local particle density (cloud density in number or mass per unit volume) of a gas-solid suspension in pipe flow, inasmuch as such a system is susceptible to fluctuations in density and velocity.

Notes: A technique is presented for the analysis of digitally recorded capacitance transients in order to determine the energy and capture cross section of deep levels. The method is essentially a digital simulation of the measurement carried out by a lock-in amplifier. This technique in principle allows trap parameters to be determined in a single temperature scan. The more efficient use of data brought about by the method permits a detailed study of the Arrhenius plot and in particular gives insight into cases where the capacitance transient is nonexponential. The method may be adapted to allow more efficient data usage in conventional lock-in amplifier deep level transient spectroscopy.

Notes: Using optical spectroscopy we study the spatial and temporal distributions of the Hα, Cs i(4555 A(ring)), Cs ii(4604 A(ring)), and Mo i(3903 A(ring)) emission lines in a Penning surface-plasma source (SPS). A diagnostic slit exposes the entire SPS discharge gap either parallel or perpendicular to the magnetic field. The spatial and temporal distributions of the emitting species are recorded using a 1-m monochromator. In addition, the visible light and the Hα and Cs ii(4604 A(ring)) spatial distributions are recorded with a video camera. The cesium atomic and ionic light, and the molybdenum atomic light, is strongly concentrated near the cathodes; the visible light and the Hα light is almost uniform in both directions. Electron-impact ionization of atoms sputtered from the cathodes and the return of the ions to the cathodes by residual plasma fields is probably the mechanism which concentrates cesium near the cathodes. The Cs0 mean free path is estimated to be 16 and 0.43 mm for 2 and 400 A discharges, respectively.

Notes: A fast "notch'' current has been produced on the (4 μH) hardcore central conductor [C. M. Greenfield, M. E. Koepke, and F. L. Ribe, Phys. Fluids B 2, 133 (1990)] of the high beta Q machine, a 2.6 m theta pinch [S. O. Knox, H. Meuth, E. Sevillano, and F. L. Ribe, 3rd IEEE International Pulsed Power Conf., 1981, IEEE Publ. 81 CH1662/6, paper 3.1]. With the notch circuitry, the current can be slowly (τ1/4 = 14 μs) brought to a crowbarred dc value (20 kA) and then quickly (τ1/4 = 1.3 μs) "notched'' to a different value (typically either 0 kA or twice the dc value) and then quickly returned to the dc value. The use of a new inductively loaded spark gap switch eliminates extraneous ringing in the final crowbarred current waveform. As described here, by driving the hardcore circuit with two isolated capacitor banks, and a voltage stepup transformer, the notch current is created using spark gaps and ignitrons for switching, resulting in an inexpensive and technically simple circuit.

Notes: A two-photon-excited laser-induced fluorescence (LIF) was applied to measurement of atomic hydrogen densities in the edge region of high-temperature plasmas of Heliotron E for the first time. In this application, fluorescence signals were observed coaxially to the laser beam. This was possible because, in two-photon-excitation LIF, the visible fluorescence is localized at the laser focus and stray light can be completely eliminated by optical spatial filters, allowing much easier optical access than in previous LIF experiments. The densities at the initiation of the discharge and at the quasisteady state of the discharge were determined to be 3×1016 and 1×1016 m−3, respectively within an error of a factor of 2. Optimization to maximize the signal-to-noise ratio of the observation and resulting detection limit were discussed and confirmed the above results.

Notes: A new apparatus has been constructed combining free-jet molecular-beam technology and radio-frequency plasma production for reactive-ion etching. The beam is formed in a laval-type nozzle and is skimmed before entering the plasma chamber. The free jet enters a discharge region between two parallel plates, one of which is capacitively powered with 13.56 MHz radio frequency. The goal was to investigate the possibility of creating a high-density plasma with a linear multinozzle array for large-area wafer processing. Experiments were carried out with argon and oxygen as process gases. Jet plasma glows with lengths of about 10 cm downstream of the skimmer were detected. Jet beam profile analysis was performed measuring the distribution of dynamic pressures with the Pitot–Prandtl method.

Notes: Azimuthal arrays of B-dot loops are often used to measure the time-resolved beam centroid location of a pulsed, intense relativistic electron beam propagating in a metallic drift tube. A new analytical analysis is presented which can solve for the beam centroid position exactly, even for large radial displacements near the drift tube wall. This exact method is compared with the traditional first-order analysis.

Notes: A simple, fast, reliable diamagnetically driven gas puff valve is described. It offers an extremely quick rise time (∼100 μs) and a large pressure rise rate (∼270 Pa/μs at a distance of 13.5 cm) with an input energy of only 90 J (600 V on a 500 μF capacitor). Because the valve can be operated with such a small input energy, solid-state switching devices are adequate and the operation of the valve will not produce the amount of electrical noise that other valves needing higher energy often do. Our valve achieves high-density puffs at relatively low plenum pressure (380 kPa, 3.8 atm), permitting it to be extremely simple in design and easy to operate. The entire package (valve plus driving circuit) is small in size; it can fit in a volume 4 in. in diameter by 8 in. long. The valve holds about 60 cm3 of gas and has an outlet opening of 1/4 in. in diameter.

Notes: The construction and single-mode tuning characteristics of a short-external-cavity (SXC) module for InGaAsP and AlGaAs semiconductor diode lasers are presented. The SXC system is a cost effective, simple, and rugged means to achieve single-mode tuning and complete spectral coverage over large spectral regions with normally multimode lasers. With AlGaAs lasers, complete spectral coverage in overlapping ∼5-cm−1 intervals over ∼400 cm−1 is obtained, while with InGaAsP diode lasers, complete spectral coverage in overlapping ∼5-cm−1 intervals of 100–200 cm−1 is obtained.

Notes: Long time, stable operation of a high-power discharge-excited CO laser has been attained by controlling the laser gas composition. Firstly, stable obtainable laser output power was measured against the quantities of CO2 and of O2 added to the laser gas. Next, laser gas composition was recorded during sealed-off operation with various initial gas conditions and cooling conditions. Finally, the detractive effect of O2 (added to enhance attainable output power through discharge stabilization) of quickening CO2 generation and CO depletion, was counteracted through continuous extraction of the laser gas and parallel replacement with fresh gas of predetermined composition. The resulting stabilization of the laser gas composition reduced output power variations to ±3% at 3 kW power level.

Notes: An automatic goniometer has been built in order to simultaneously measure the reflectance and transmittance of films at different angles of incidence of the incoming light. The angle can be varied from 7° to 83° and the incident light can be either s or p polarized. Following a minimization procedure, optical constants for the deposited films can be accurately determined. Results for Nb2O5, WO3, LiBO2 are presented and the precision of the method is discussed.

Notes: A compact electron polarimeter which operates at low scattering energies (100 eV) has been built and characterized. The polarimeter uses spin-dependent diffraction from a W(001) single crystal to measure the electron spin polarization of an incident electron beam. The design obtains reliable operation by attention to the input optics, the crystal mount, and the alignment procedure. The transport lens delivers the electron beam to the analyzer over an acceleration range of at least 2.0–0.33 while simultaneously keeping the angular convergence of the beam less than ±1.5°, and the magnification constant to within ∼30%. The crystal mount allows both orientation of the crystal normal to within 0.2° and flashes to 2500 K. Geometric instrumental asymmetries are linear in displacement (AD = 4%/mm) and angular displacement (Aθ = 3%/deg) of the sample. The alignment procedure and performance of the polarimeter are illustrated using spin-polarized low-energy electron diffraction rotation curves. Preliminary results suggest that the polarimeter may be operated for 1 h between cleaning cycles without degradation of the figure of merit.

Notes: A new tunneling instrument has been developed to observe the anisotropy of the Fermi surface. This instrument has two advantageous mechanisms over the conventional scanning tunneling microscope (STM); a tilt mechanism to keep two crystals parallel to each other and a rotation mechanism of the proven crystal over the sample crystal. We have evaluated its performance.

Notes: The input reactance of a pair of coupled coils is a function of the latter's primary, secondary, and mutual inductances as well as the secondary tuned frequency. It is thus possible to synthesize two appropriate equivalent inductances for use in a double-tuned probe by a judicious choice of these parameters. From a given coil configuration and hence the associated self and mutual inductances, the present note analyzes and derives the essential equations showing the possible values of the tuned secondary frequency to be used to design this type of probe circuit first proposed by Fitzsimmons, Brooker, and Beck [Magn. Resoh. Med. 10, 302 (1989)]. In cases where an intercoil coupling capacitor is needed, its value also can be calculated from a biquadratic equation. A numerical example is given to check the validity of the theoretical results.

Notes: A novel thermal lens spectrophotometer which can be used for simultaneous measurements of thermal lens and absorption has been constructed to verify the developed theories (which were described in the previous paper) and to implement the thermal lens technique for sensitive kinetic determinations. The measured experimental results agree well with the values predicted by the developed theories. Compared to other conventional kinetic methods, the thermal lens technique provides kinetic results which are not only accurate and precise but also can be obtained with reagents whose concentrations are about 100 times lower. Other potential applications of this method, including the kinetic determinations of fast chemical reactions, are discussed.

Notes: Fidelity of waveform reproduction requires constant amplitude ratio and constant time lag of a temperature sensor's indication, at all frequencies of interest. However, heat-transfer type sensors usually cannot satisfy these requirements. Equations for the actual indication of a thermocouple and an optical-fiber pyrometer are given explicitly, in terms of sensor and flowing-gas properties. A practical, realistic design of each type of sensor behaves like a first-order system with amplitude-ratio attenuation inversely proportional to frequency when the frequency exceeds the corner frequency. Only at much higher frequencies does the amplitude-ratio attenuation for the optical fiber sensor become inversely proportional to the square root of the frequency. Design options for improving the frequency response are discussed. On-line electrical lag compensation, using a linear amplifier and a passive compensation network, can extend the corner frequency of the thermocouple 100 fold or more; a similar passive network can be used for the optical-fiber sensor. Design details for these networks are presented.

Notes: Measurements of the quality factor (Q) and period (P0) of two Al 5056 torsional oscillators are presented as a function of temperature from 0.02 to 1.2 K. The 5056 alloy is found to have Q's of order 104 at room temperature and 107 below 4 K. In addition to having an extraordinary high Q, we also find that the temperature dependence of the reduced period, ΔP/P0, is extremely weak at low temperatures, making this material well suited for superfluid helium film studies. A technique for attaching thin dielectric substrates to the torsion member of one of the oscillators is also discussed.

Notes: Resistivity of nonmagnetic metallic cylindrical samples is measured contactlessly with a high-frequency LC (inductance-capacitance) series resonance method by evaluating both frequency shift Δf and change of Q factor ΔQ due to the sample. By this method, sufficient accuracy can easily be achieved without any resistivity standards, although the size of the measuring coil as well as the value of the series capacitor (and hereby the operating frequency) are arbitrary and not part of the calculation. Results obtained for Cu, Al, Mg, Zn, Pd, Sn, Zr, and Bi are in agreement with the literature values.

Notes: This paper presents the results of a study of pecan spectral reflectances. It describes an experiment for measuring the contrast between several components of raw pecan product to be sorted. An analysis of the experimental data reveals high contrast ratios in the infrared spectrum, suggesting a potential improvement in sorting efficiency when separating pecan meat from shells. It is believed that this technique has the potential to dramatically improve the efficiency of current sorting machinery, and to reduce the cost of processing pecans for the consumer market.

Notes: A directional energy analyzer, capable of quickly responding to fast signal changes as well as having a good angular resolution, is developed. Results have shown that owing to a current amplifier prepared in it, the analyzer can respond to a small and rapidly changing ion current with a rise time as short as 2 μs, as observed in plasma shock experiments.

Notes: The question of an optimum exposure time for an event counting charge coupled device electron detection system is discussed [B. D. Hall, M. Flüeli, J. -P. Borel, and R. Monot, Rev. Sci. Instrum. (in press)]. The system is a null-event detector, providing a single piece of information per exposure: whether an event has not been detected. It is shown that when the number of exposure periods is fixed, optimum operation conditions require high exposures, in spite of the loss of information due to multiple events being detected as single ones.

Notes: A very simple construction of a linear-motor-driven XYaitch-theta positioner has been developed. The velocities can be controlled up to 4 mm/s. Positioning accuracy of better than 0.05 μm can easily be obtained.

Notes: An experiment for direct measurement of the atomic mass unit is proposed. A mononuclidic ion flux is collected and accumulated to an amount that can be weighed with high accuracy. Simultaneously, the ion current is measured and integrated. By means of voltage and resistance references based on the Josephson and the quantum Hall effect, the mass is then related to atomic mass by frequency counting over a certain time interval. This experiment may enable a new, physical definition of the kilogram.

Notes: A folded-path two-detector photopolarimeter for measuring all four Stokes parameters of light is described. The light beam, whose state of polarization is to be measured, strikes the two (windowless and reflective) detector surfaces at oblique incidence and with noncoincident planes of incidence. After reflection from the second detector, the beam is folded back on itself by a mirror and the feedback is interrupted periodically with a light chopper. This intermittent feedback causes square-wave modulation of the two detector outputs which provides a 4×1 current vector I. The unknown 4×1 Stokes vector S of incident light is determined by S=A−1 I, where A is a wavelength-dependent 4×4 instrument matrix which is fixed by calibration. Based on an explicit expression for det A, all potential singularities of A are investigated and are found to be readily avoidable. Optimum parameters are also specified that make A as far from singular as possible by maximizing its determinant.

Notes: A multichannel single photon counting detection system for steady state, time-resolved luminescence spectra, time-gated imaging, or time-gated Raman is described. This system, which has approximately 80 ps time resolution, is based on a microchannel plate photomultiplier with a position-sensitive anode (Mepsicron). This detector can operate at very low light levels with excitation wavelengths from 200 nm to the near infrared. For time-resolved luminescence applications, the system simultaneously collects 1024 decays of up to 1024 spectral channels. The measured time dispersion for spectral bandwidths greater than 100 nm are shown to be negligible.

Notes: An acousto-optic (AO) element made of As2Se3 glass was used for spectroscopic gas sensing. With the AO element, desired wavelengths in the infrared can be monitored by simply switching the oscillation frequency of the ultrasonic transducer. The concentration of the CO2 gas was measured by using the absorption band at 4.3 μm wavelength. To avoid measurement error due to the fluctuation in the sensing system, a probe light of 4.3 μm and a reference light of 4.7 μm were measured alternatively by switching the acoustic frequency between 50 and 54 MHz. It has been demonstrated in a preliminary experiment that the AO element is a promising device for constructing a fast, compact, and inexpensive measurement system for monitoring pollutants.

Notes: The initiation of many physiologically important biochemical reactions is dependent on the binding of a molecule or molecules from solution to an appropriate solid surface such as a cell membrane. The quantitative study of dynamic interactions of molecules in solution with immobilized surfaces under physiologically relevant conditions presents a significant physical problem. Traditionally these measurements have been performed by discontinuous, nonequilibrium assays that cannot accurately model in vivo reaction mechanisms. Total internal reflection fluorescence spectroscopy (TIRFS) is an analytical technique that is based on the excitation of fluorescence by means of an exponentially decaying surface energy wave called the evanescent wave. The limited "penetration depth'' of the evanescent wave leads to excitation of fluorescent molecules at or near the surface. This phenomena makes TIRFS uniquely qualified for the dynamic fluorescence study of liquid-solid interface binding reactions. The instrument described here permits the powerful technique of TIRFS to be used by biomedical researchers in their investigation of biochemical interface reactions. The fully automated, menu driven instrument allows the real time dynamic measurement of binding of fluorescent-labeled molecules in solution at physiologically relevant concentrations to appropriate immobilized surfaces.The novel design of the total internal reflection element enables the study of binding from essentially opaque and highly scattering solutions such as whole blood. Measurements may be performed under static, stirred, or flow conditions. The presently described TIRFS instrument is capable of tracking a binding reaction with evanescent fields established by two identical reflecting light beams with different reflection angles. This instrumental feature allows the dynamic measurement not only of the primary binding event but also of fluctuations in the distance between the optical interface and the point of signal generation. Data from experiments involving fluorescently labeled molecules binding to cell monolayers as well as binding experiments performed in whole blood are shown to verify the instrument performance. Due to its extraordinary capabilities and its user friendly design, the developed TIRFS instrument opens up a large number of relevant but previously unmeasurable experimental systems for investigation.

Notes: A versatile electron-impact time-of-flight mass spectrometer (EI-TOFMS) in a pulsed molecular beam has been constructed. The instrument contains a fast rise time, square pulse generator, biased at high voltage, which simplifies the implementation of EI-TOFMS. Power field effect transistors are used as the active switching element, which afford compact size and simplified circuit construction. The effect of the shape of the repelling pulse on the flight time and space focusing condition is estimated by numerical calculation. Preliminary test results are provided for pulsed molecular beams of ammonia and hydrogen iodide.

Notes: A ring of accurately placed and matched printed circuit coils is placed at the center of the DIII-D tokamak vacuum vessel, aligned magnetically with the toroidal field and used to measure the nonaxisymmetric magnetic field of each of the 18 poloidal field coils. [Toroidal and poloidal variations can be of mode n and m, respectively, with helical variations of form cos(nφ−mθ).] From the error fields, it is computed that the most irregular poloidal field coil is one of the outer vertical field coils having a shift of 1.9 ±0.2 cm (compared to a diameter of 482 cm), and having an ellipticity 1.0027. All the 18 poloidal field coils together make a resonant, helical, radial error field for m=2, n=1 of about 1.4 × 10−4 of the toroidal field.

Notes: Important information about physical characteristics of clays can be inferred from the distribution of the orientations of straight lines in photographs of cross sections of its samples. This article describes the development of a semiautomated system for clay analysis that is based on the application of computer vision techniques. Due to the inherent complexity of these techniques, two strategies have been used in order to reduce the execution time: an effective technique, the binary Hough transform, is applied for detection of straight lines and the transputer is used to enhance the system processing power. The article includes the characterization of the clay analysis application, the description of the binary Hough transform for detection of straight line segments, the presentation of the semiautomated system, and a complete illustrative example.