bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing metabolic activity in aging Caenorhabditis elegans: concepts and controversies
Authors: Braeckman Bart P. , Houthoofd Koen , Vanfleteren Jacques R.
Published: March 2003

It is widely believed that normal by‐products of oxidative metabolism and the subsequent molecular damage inflicted by them couple the aging process to metabolic rate. Accordingly, high metabolic rates would be expected to accelerate aging, and life‐extending interventions are often assumed to act by attenuating metabolic rate. Notorious examples in Caenorhabditis elegans are food restriction, mutation in the Clock genes and several genes of the insulin‐like signalling pathway. Here we discuss how metabolic rate can be accurately measured and normalized, and how to deal with differences in body size. These issues are illustrated using experimental data of the long‐lived mutant strains clk‐1(e2519) and daf‐2(e1370). Appropriate analysis shows that metabolic rates in wild‐type and in the clk‐1 mutant are very similar. In contrast, the metabolic rate profiles point to a metabolic shift toward enhanced efficiency of oxidative phosphorylation in the daf‐2 worms.
The mitochondrial theory of aging: dead or alive?
Authors: Jacobs Howard T.
Published: March 2003

The mitochondrial theory of aging is based around the idea of a vicious cycle, in which somatic mutation of mtDNA engenders respiratory chain dysfunction, enhancing the production of DNA‐damaging oxygen radicals. In turn, this is proposed to result in the accumulation of further mtDNA mutations. Finally, a bioenergetic crisis leads to overt tissue dysfunction and degeneration. A substantial body of circumstantial evidence seems to support this idea. However, the extent of detectable mtDNA mutation is far less than can easily be reconciled to this hypothesis, unless it is assumed that a subset of cells with much higher than average mtDNA mutation load is systematically lost by apoptosis. A rigorous test of the hypothesis remains to be undertaken, but would require a direct manipulation of the rate of mtDNA mutagenesis, to test whether this could alter the kinetics of aging.
Mitochondrial DNA mutations as a fundamental mechanism in physiological declines associated with aging
Authors: Pak Jeong W. , Herbst Allen , Bua Entela , Gokey Nolan , McKenzie Debbie , Aiken Judd M.
Published: March 2003

The hypothesis that mitochondrial DNA damage accumulates and contributes to aging was proposed decades ago. Only recently have technological advancements, which facilitate microanalysis of single cells or portions of cells, revealed that mtDNA deletion mutations and, perhaps, single nucleotide mutations accumulate to physiologically relevant levels in the tissues of various species with age. Although a link between single nucleotide mutations and physiological consequences in aging tissue has not been established, the accumulation of deletion mutations in skeletal muscle fibres has been associated with sarcopenia. Different, and apparently random, deletion mutations are specific to individual fibres. However, the mtDNA deletion mutation within a phenotypically abnormal region of a fibre is the same, suggesting a selection, amplification and clonal expansion of the initial deletion mutation. mtDNA deletion mutations within a muscle fibre are associated with specific electron transport system abnormalities, muscle fibre atrophy and fibre breakage. These data point to a causal relationship between mitochondrial DNA mutations and the age‐related loss of muscle mass.
Reduced age‐related plasticity of neurotrophin receptor expression in selected sympathetic neurons of the rat
Authors: Cowen T. , Woodhoo A. , Sullivan C. D. , Jolly R. , Crutcher K. A. , Wyatt S. , Michael G. J. , Orike N. , Gatzinsky K. , Thrasivoulou C.
Published: March 2003

Selective vulnerability of particular groups of neurons is a characteristic of the aging nervous system. We have studied the role of neurotrophin (NT) signalling in this phenomenon using rat sympathetic (SCG) neurons projecting to cerebral blood vessels (CV) and iris which are, respectively, vulnerable to and protected from atrophic changes during old age. RT‐PCR was used to examine NT expression in iris and CV in 3‐ and 24‐month‐old rats. NGF and NT3 expression in iris was substantially higher compared to CV; neither target showed any alterations with age. RT‐PCR for the principal NT receptors, trkA and p75, in SCG showed increased message during early postnatal life. However, during mature adulthood and old age, trkA expression remained stable while p75 declined significantly over the same period. In situ hybridization was used to examine receptor expression in subpopulations of SCG neurons identified using retrograde tracing. Eighteen to 20 h following local treatment of iris and CV with NGF, NT3 or vehicle, expression of NT receptor protein and mRNA was higher in iris‐ compared with CV‐projecting neurons from both young and old rats. NGF and NT3 treatment had no effect on NT receptor expression in CV‐projecting neurons at either age. However, similar treatment up‐regulated p75 and trkA expression in iris‐projecting neurons from 3‐month‐old, but not 24‐month‐old, rats. We conclude that lifelong exposure to low levels of NTs combined with impaired plasticity of NT receptor expression are predictors of neuronal vulnerability to age‐related atrophy.
Doppler-independent selective heterodyne radiometry for detection of remote species
Authors: Teich Malvin Carl
Published: March 2003

A multiple-frequency heterodyne radiometer is proposed for the detection of radiation from known species moving with unknown velocities. Expressions for the signal-to-noise ratio and the minimum detectable total power are obtained for sinusoidal signals and for Gaussian signals with both Gaussian and Lorentzian spectra. In distinction to the conventional system, knowledge of absolute line rest frequencies and a stable, tunable local oscillator are not required. The system may find use in the detection of certain remote species such as interstellar molecules and pollutants. A number of potential applications are examined.
A high energy (keV), large angular range, precision electron spectrometer for atomic and molecular targets
Authors: Wellenstein H. F. , Schmoranzer Hans , Bonham Russell A. , Wong Tuck C. , Lee Jun Sing
Published: March 2003

An electron impact spectrometer for operation in the keV incident−electron energy range is described. The spectrometer operates between 20 and 60 keV incident−electron energy, utilizing both a low−resolution silicon surface barrier detector (5 keV FWHM), and a high−resolution (0.7 eV FWHM) Möllenstedt energy analyzer over a 1.7 keV energy loss range. It features a large angular scan range (0⩽ϑ<120°), high target gas throughput (i.e., 19000 l/sec for He and 13000 l/sec for N2 through a tube of 0.15 mm diam), and a wide range of incident−electron beam currents (0.1−400 μA) with a focused electron beam size of less than 200 μ FWHM over most of the current range. Careful measurements of the gas density profile of the target gas emanating from the nozzle are also reported. Results are presented for the Bethe surface of He and N2. The latter example is reported here for the first time. In addition, the observation of the angular dependence of the Lyman−Birge−Hopfield band in N2 (dipole forbidden) is compared with the dependence of a neighboring dipole allowed transition.
Continuously displayed emittance measurements
Authors: Billen J. H.
Published: March 2003

A device is described to display continuously on a CRT the emittance of an ion beam. The system uses electrostatic deflectors and small apertures to scan the beam’s phase−space position and momentum coordinates. Measurements are reported of the emittance and brightness of the following beams produced by five different ion sources: H−, D−, He+, He−, C−, D2−, O−, NH2−, A+, and Cu−. Also investigated was the emittance of an H− beam from a duoplasmatron direct−extraction source as a function of the radial displacement of the zwischen electrode, and the phase−space particle density distribution of an H− beam was measured.
An integrated circuit pile−up rejector
Authors: Daniels C. J.
Published: March 2003

The pile−up circuit described has been tested at random rates to 80 000 pps with a pulse pair resolution of 20 nsec. The unit features integrated circuits for decision−making logic.
Simple, efficient, clean−steam generator for oxidation of semiconductor wafers
Authors: Olmstead John A. , Ronen R. S.
Published: March 2003

A simple, efficient generator of clean steam for the oxidation of semiconductor wafers is described. The generator employs infrared radiation to evaporate large quantities of water from the boiler’s surface without visible agitation. A water overflow reservoir and simple valving arrangement is also described which provides for continuous as well as intermittent operation of the generator and for the possible introduction into the furnace tube of other gases such as oxygen, nitrogen, HCL, etc.
A Tesla transformer high−voltage generator
Authors: Hoffmann C. R. J.
Published: March 2003

A Tesla transformer similar to that suggested for transformer−type pulsed accelerators is described. The theory is outlined and computational results presented for representative losses under various conditions of tuning and coupling. The behaviour of an experimental transformer housed in an SF6−filled pressure vessel is discussed. The device has a tuning ratio of 1.1, a voltage coefficient of 0.85, and a coupling coefficient of 0.37. The influence of eddy currents induced in the pressure vessel wall on the coupling coefficient and tuning ratio is noted. The particular transformer described can provide a 2.5 MV peak at the third half cycle of the secondary output voltage.
Hygrometer based on the corona effect
Authors: Daddi L. , Latrofa E.
Published: March 2003

The behavior of a hygrometer based on the dependence of corona current on the humidity in air is described. The device is based on a wire–rod–wire system. The choice of this geometry is discussed. The dependence on changes in atmospheric pressure, temperature, and absolute humidity is examined.
Apparatus for rapid measurement of optical rotation changes
Authors: Tsuda Motoyuki
Published: March 2003

An apparatus for rapid measurement of optical rotation changes has been developed in the face of large absorption changes with time resolutions of 10 μsec (sensitivity 0.018°) and 4 msec (sensitivity 0.0016°). Applications are briefly described for the study of rapid transient processes of reduction reaction of cytochrome c with dithionite with the stopped-flow technique. The method can be combined with stopped-flow, temperature-jump, and flash photolysis and allows direct observation of rapid conformation events of biomolecules.
Simple method for Josephson critical current control of solder drop junctions
Authors: Iguchi I. , Hara K.
Published: March 2003

A simple method, which controls the Josephson critical current of a solder drop junction smoothly and quickly with the junction immersed in liquid helium, is presented.
Phase-locked automatic vibroscope
Authors: Caffin R. N.
Published: March 2003

A vibroscope is an instrument designed to measure the mass per unit length or changes in the mass per unit length of a fiber. While a variety of mechanical transducers have been used in the past, all automatic vibroscopes have used conventional oscillator feedback, and this has often proved unsatisfactory. A new form of feedback involving phase detection has been applied to yield a very reliable system.
Temperature measurement errors with type K (Chromel vs Alumel) thermocouples due to short-ranged ordering in Chromel
Authors: Kollie T. G. , Horton J. L. , Carr K. R. , Herskovitz M. B. , Mossman C. A.
Published: March 2003

After annealed, type K (Chromel vs Alumel) thermocouples were heated above 200 °C, their temperature measurements were in error up to 1.3%, as determined by comparison calibrations to working standard 90% Pt–10% Rh/Pt thermocouples or platinum resistance thermometers. Reannealing the type K thermocouples removed the errors. The errors were due to changes in the thermal emf vs temperature relationship of the type K thermocouples, which from previous work of others can be attributed to short-ranged ordering of the Chromel thermoelements. Reannealing the thermocouples removed the errors because the order–disorder transformation is reversible; that is, short-ranged ordering of the Ni and Cr atoms of the Chromel alloy occurs between 200° and 600 °C, and disordering occurs above 600 °C. The traveling gradient method was used to determine the effects of heat treatment on the thermal emf of type K thermocouples, to investigate the kinetics of ordering of Chromel, and to determine the amount of order produced by heat treatments. Though the order–disorder transformation could not be stopped, our results demonstrate that there exists an optimum amount of order in the Chromel thermoelement to yield a repeatable thermal emf vs temperature relationship for a type K thermocouple in a specific application. When the experimental conditions of the application were controlled carefully, isothermal heat treatment to produce the optimum order in the Chromel thermoelements and calibration of the type K thermocouples prior to use essentially eliminated the temperature measurement errors due to order. The optimum amount of order depended on the application and was determined experimentally. Variations from the optimized heating or cooling cycles, changes in the depth of thermocouple immersion during use, or modification of the temperature gradient on the thermocouple caused temperature measurement errors of up to 1% with ordered and calibrated type K thermocouples.
Recording capacitance dilatometer
Authors: Seymour Raymond B. , Stahl G. Allan
Published: March 2003

A capacitance dilatometer is described which automatically records the height of a mercury column as a function of time. Changes as small as 10−4 ml have been detected, with an instrumental stability allowing experiments of several days’ duration. The technique is based on the measurement of the capacitance of an aluminum foil-covered, precision bore, glass column containing Hg. The dilatometer has been used to measure coefficients of expansion and rates of polymerization and hydrolysis.
TTL pulse sequence generator for ultrasonic pulse-superposition measurements
Authors: Fritz I. J.
Published: March 2003

A simple, versatile pulse sequence generator for use with the McSkimin pulse-superposition technique of measuring ultrasonic velocities is described. Standard TTL integrated circuits are used in construction of the unit. The generator produces a sequence either of two pulses followed by 2, 6, 14, or 30 spaces, or of four pulses followed by 4, 12, 28, or 60 spaces. The pulse repetition frequency is determined by an external oscillator operating at a multiple (one, two, five, or ten) of this frequency. Testing and operation of the unit is described.
Influence, detection, and measurement of depolarization in Hertzian reflecto-polarimetry and reflecto-ellipsometry
Authors: Sardos R.
Published: March 2003

Radar specialists know that during the reflection of waves the phenomenon of depolarization appears in a more or less intense manner depending upon atmospheric conditions. The measurement of depolarization in a laboratory setting is difficult because the problem involves measuring a weak, incoherent energy superimposed upon a strong, coherent energy, and standard instruments have not been conceived to effect such a measurement. The author first studies the influence of wave depolarizations upon reflectometric measurements made at normal incidence in standard rectangular guides, then he indicates how, by using an interferometer, one can perform the measurement of the coherent and incoherent energy. In the second part of his report, he studies the influence of wave depolarizations made during reflection at an oblique angle (for example, the measurement of the Brewster angle). He then indicates a type of interferential analyzer (a two- or a three-wave) employed with a polarization duplexer which enables one to measure, or to record (with a three-wave interferometer), depolarization as well as the rotation and ellipticity of the reflected coherent energy. Finally, in the third part, the author considers the case of reflection made at normal incidence in circular waveguides (mode TE11). He is led to propose an interferential reflecto-polarimeter–ellipsometer having as its principal element a ’’lossy’’ turnstile junction, the properties of which he outlines briefly. He shows that this instrument will enable one to achieve the measurement and recording (when associated with a three-wave interferometer) of depolarization as well as of the rotation and ellipticity of the coherent part of the reflected wave.
Pulsed EPR spectrometer, II
Authors: Percival P. W. , Hyde James S.
Published: March 2003

Further improvements to the pulsed EPR spectrometer of Huisjen and Hyde [Rev. Sci. Instrum. 45, 669 (1974)] are described. Special attention is given to techniques for separation of free-induction-decay and saturation-recovery signals. The instrument is suitable for determination of spin-lattice relaxation times as short as 10−7 sec, and is designed particularly for measurements on dilute solutions of free radicals and of spin-labeled biomolecules. Analytical solutions of the Bloch equations are obtained that are appropriate for this instrument. The predictions of the equations have been verified by comparison with experiments on the tetracyanoethylene (TCNE) radical anion.
Prescaling effects in random-event counting and application to multiscaler measurements
Authors: Cova S. , Gambarini G. , Longoni A.
Published: March 2003

In order to reduce the systematic errors due to count losses caused by deadtimes in the counting of pulses randomly distributed in time, a prescaler, having a much shorter deadtime than the main scaler which records the counts, is often used. The demultiplication due to the prescaler may in turn cause other systematic errors and an increase in the statistical fluctuations in the recorded pulse numbers. Calculations of these effects have been performed, and the results are given for two basic cases, i.e., for a prescaler reset to zero as the main scaler and for a free-running prescaler. Consideration is given to the consequences of these effects in measurements obtained by single or repeated counting runs, with particular attention to the case of measurements of distributions by multichannel analyzers in the multiscaler mode.
Device for the direct measurement of fluid densities
Authors: Keramati B. , Wolgemuth C. H.
Published: March 2003

A density measuring device which operates on the principle of buoyancy is described. The density of liquid SF6 was measured with this device from 0° to 35 °C, and from the saturation pressure to 170 bar. The saturated liquid density is compared with the measurement of other investigators.
High frequency signal tracking lock-in system
Authors: Moresco M. , Zilli E.
Published: March 2003

A lock-in system, able to operate at frequencies higher than those of commercially available lock-in amplifiers, is described; it can tolerate noise and frequency fluctuations in the reference channel.
Low-frequency dielectric bridge
Authors: Lakes R. S. , Harper R. A.
Published: March 2003

This circuit may be used to measure the complex dielectric function (admittance) between 0.01 Hz and 1 kHz in the frequency domain in either the guarded three-terminal or four-terminal probe mode, as well as step-function response (voltage creep or current relaxation) in the time domain. Signals from the unknown impedance and the standard impedance are processed using dc coupled operational amplifiers, the gains of which are varied to balance the bridge.
Programmable power supplies useful for electrostatic analyzers
Authors: Ratcliffe C. A.
Published: March 2003

Two voltage sources are described which can be used with electrostatic analyzers in automated ion–atom collision experiments. One is a 0 to −6 kV supply; the other is a dual (±) 0 to 300 V supply. Circuit diagrams are provided and accuracies discussed.
Improved stressing apparatus for photoelasticity measurements
Authors: Feldman Albert , McKean William J.
Published: March 2003

An improved, direct reading stressing apparatus has been constructed for measuring photoelastic constants. Highly uniform stresses are obtained with minimal specimen tilt.
Technique for mapping the geometry of the flow channel of nozzles
Authors: Savanick George A. , Rosenquist Rollie C.
Published: March 2003

A simple, nondestructive method is described for measuring the roughness of the flow channel of a nozzle. This method involves replicating the flow channel with a silicone rubber cast and measuring the relief on the surface of the cast with a profilometer.
Trap current regulated ion source power supply for a mass spectrometer
Authors: Yinon Jehuda , Ganz Moshe
Published: March 2003

A simple trap current regulated ion source power supply for an isotope ratio mass spectrometer has been built, consisting mainly of commercially available voltage power supplies. Short term stability of 0.01% has been obtained with this system.
Dynamic high pressure seal for low temperatures
Authors: Chua Jaime O. , Terry Robert E. , Ruoff Arthur L.
Published: March 2003

A dynamic high pressure seal is described which operates successfully for numerous cycles to 7 kilobar at liquid nitrogen temperature with helium gas as the pressure medium.
Characterization of two commercially available Hall effect sensors for high magnetic fields and low temperatures
Authors: Rubin L. G. , Nelson D. R. , Sample H. H.
Published: March 2003

A series of measurements were performed on two groups of transverse-configuration Hall effect sensors, each group consisting of devices available from a particular commercial supplier. The Hall voltage output of the probes was measured as a function of magnetic field to 18 T at temperatures of 300, 77, and 1.5–4.2 K; at the same time, the probes were subjected to a program of abrupt thermal cycling and magnetic field cycling. With the aid of computer analysis of the data the following conclusions could be drawn: (1) the outputs of one group of probes were linear with magnetic field within a worst-case value of ∼±1% up to 8 T, and for the second group, to within ±0.5% up to 8 T and ±1.4% up to 18 T; (2) statement (1) was true for any of the selected temperatures; in general, variations of sensor output with temperature proved to be an unimportant factor; (3) the degree of measurement repeatability between thermal cycles varied somewhat from probe to probe within a group, but was significantly different between the two groups; (4) for a limited number of thermal cycles (∼25), it is clear that a simple calibration procedure would suffice to maintain a field measurement accuracy of ±0.2% up to 14 T, at least for one group of probes.
Tunable low-temperature optical-EPR gaussmeter
Authors: Sabisky E. S. , Call P. J. , Anderson C. H.
Published: March 2003

Two methods, utilizing the optical detection of the ground state paramagnetism of ions in solids for field calibration and measurement of the homogeneity of superconducting magnets at liquid helium temperature, are described and demonstrated. This technique has an accuracy comparable to that of NMR and has advantages in simplicity and in measuring homogeneity.
Technique for background elimination in infrared measurements
Authors: Moore Kenneth L.
Published: March 2003

A technique has been devised for electronically eliminating background signals in chopped infrared measuring systems by subtracting a reference signal of proper frequency, phase, and amplitude from the background signal. Subsequently acquired point-source or distant-small-source signals are converted to dc voltage levels which are directly related to incident flux. The system, based on operational amplifier principles, permits measurements of weak radiant emissions in the far ir under signal-to-noise conditions beyond the capabilities of previous field portable instruments.
Dielectric and state behavior of cyclohexane under shock loading
Authors: Hayes Bernard
Published: March 2003

An electrical technique that uses the peaks and troughs of a sine wave source voltage is employed to measure the relative capacitance of a dynamic admittance cell containing cyclohexane at 2.1 and 6.3 GPa. Parameters for the linear shock-particle velocity equation of motion of the liquid are deduced, and a procedure for measuring the shock temperature of selected materials is proposed. A model for shock electrification is given indicating that electrification is a consequence of a normal-state material undergoing a species change. Cyclohexane is an unusual material under shock loading in that it does not exhibit a species change in the pressure range considered.
I
n s
i
t
u devices for the measurement of anelastic effects under neutron irradiation
Authors: Masson M. , Warlop R. , Bisogni E. , Halbwachs M.
Published: March 2003

Two devices for the direct measurement of the anelastic properties of metals in a reactor are described. First, a resonant cavity system has been adapted for the in-pile determination of dimensional changes, with application to strain relaxation measurements at and above room temperature. Second, an inverted torsion pendulum operated at 130 Hz at a constant amplitude has been devised for the study of internal friction in metals exposed to a fast neutron flux. The relevant detection systems and the mechanical arrangements for both apparatus are given, together with typical recorded curves.
Flow system for the production of diatomic metal oxides and halides
Authors: West J. B. , Bradford R. S. , Eversole J. D. , Jones C. R.
Published: March 2003

A flow system for production of diatomic metal oxides and halides is described. Molecules are produced by reacting metal vapor in a flowing, inert gas with a suitable oxidizer. Product molecules are frequently formed in electronically excited states, making this system particularly useful for optical emission spectroscopic studies. Specific advantages are: (a) large number of reactant products; (b) little thermal excitation in the reaction region; (c) spectra uncluttered by emission from undesirable species; and (d) in many cases, formation of molecules in electronically excited states not produced or detected in other sources. Also discussed is a variation of the design which is used to produce small metallic particles. These particles are formed by homogeneous nucleation of the metal vapor and range in size from 5 to 500 nm.
A simple, fast−closing, metallic contact switch for high voltage and current
Authors: Bleys C. A. , Lebely D. , Rioux−Damidau F.
Published: March 2003

A simply installed and operated metal−to−metal contact switch, closed by a magnetic field, is described. Delay times of 13 μsec with a jitter of 0.15 μsec have been measured. The switch has been used to close a high−voltage capacitor bank with currents of 1.3 MA rising in 30 μsec.
Phase measurements in chopped particle beams
Authors: Haberland Hellmut
Published: March 2003

It is shown that phase and amplitude of a chopped particle beam as measured with a lock−in amplifier are given by the Fourier transform of the time−of−flight spectrum, independent of the exact form of the chopper. The information extractable from a measurement of the phase as a function of the chopping frequency is discussed.
Two high resolution velocity vector analyzers for cosmic dust particles
Authors: Auer Siegfried
Published: March 2003

Two new methods are described to measure velocities and angles of incidence of charged cosmic dust particles with precisions of about 1% and 1°, respectively. Both methods employ four one−dimensional position−sensitive detectors in series. The first method utilizes a charge−dividing technique while the second utilizes a time−of−flight technique for determining the position of a particle inside the instrument. The velocity vectors are measured although mechanical interaction between the particle and the instrument is completely avoided. Applications to cosmic dust composition and collection experiments are discussed. The range of radii of measurable particles is from about 0.01 to 100 μ at velocities from 1 to 80 km/sec.
Some applications of GM counters in the vacuum ultraviolet spectral region
Authors: Ederer D. L. , Dhez P.
Published: March 2003

The applicability of GM and proportional counters naturally extends into the vacuum ultraviolet (vuv) spectral region. A simple modification to this detector enables GM counters to be used to measure very small cross section variations or to be used as high efficiency detectors over a narrow spectral range with excellent second order discrimination.
Measurement of the steady−state potential difference across a thin insulating film in a corona discharge
Authors: Weinberg Z. A. , Matthies D. L. , Johnson W. C. , Lampert M. A.
Published: March 2003

A comparison method has been developed for measurement of the potential difference across a thin insulating film under steady−state charging conditions in a corona discharge. The method is based on the dynamics of charged particles (ions or electrons) when drifting under collision−dominated conditions: their trajectories follow, to a close approximation, the electrostatic field lines. The method is simple, accurate, and reliable, and it is particularly valuable where the surface potential, following cessation of charging, decays too rapidly to permit use of the conventional Kelvin probe techniques. The method has been applied successfully to the study of the electrical behavior of thermally grown SiO2 films on Si and thermoplastic materials.
Sample temperature measurement in the PAR vibrating sample magnetometer oven
Authors: Sill Larry R. , Drensky Stephen M.
Published: March 2003

A method is described which allows direct measurement of sample temperature in the high−temperature oven accessory of a Princeton Applied Research vibrating sample magnetometer.
Extension of lock−in operation to vhf frequencies
Authors: Moresco M. , Zilli E.
Published: March 2003

A simple dual frequency converter is described which applies the lock−in technique to frequencies much higher than that of commercially available lock−in amplifiers.
Dielectric measurements at radio frequencies in the presence of a strong static field
Authors: Hopmann Rudolf
Published: March 2003

A differential dielectric bridge is described for the measurement of small changes in the real and imaginary part of the dielectric permittivity effected by the application of a strong static field to a liquid. The apparatus is based on the resonant bridge principle and operates in the rf range (0.7−120 MHz). A dc field up to 250 kV/cm can be superimposed on the rf field. Chemical increments in the dielectric loss factor characteristic for chemical relaxation experiments of less than 1×10−7 are detectable. The apparatus can also be used as a conventional dielectric bridge whereby changes in the real part of 5×10−5 and in the imaginary part of the permittivity as low as 1×10−4 are measurable. The technique of the measurements is discussed and illustrative examples are provided.
Operation of tuned fork light choppers at liquid helium temperatures
Authors: Frodsham Gary
Published: March 2003

A model L40 American Time Products standard ambient temperature light chopper has been adapted to operate at liquid helium cooled temperatures. The application was in a 2−13 μ three−channel rocketborne infrared radiometer. The chopper tines were copper plated and indium gasket material was inserted between the adjoining tine mount surfaces. These two mechanical modifications, combined with the development of a high−efficiency, chopper−drive circuit, made the adaptation to operation at liquid helium temperatures complete. Locating the chopper in a focal plane away from the detector−preamplifier assembly made it possible to effectively eliminate chopper related capacitive, magnetic, and microphonic coherent noise.
High stability operational amplifier current source
Authors: Carter Ronald L.
Published: March 2003

A high stability current source based on commercially available operational amplifiers and electronic components is developed. Criteria are discussed for applications from 10 μA to 1 A with stability approaching 1ppm/h. An inexpensive working model is presented for a 10 mA current source with 2 ppm/h stability.
Polarimetric stopped-flow apparatus
Authors: Goodall D. M. , Cross M. T.
Published: March 2003

A stopped-flow apparatus is described for the measurement of millidegree changes in optical rotation and absorbance changes at wavelengths between 230 and 800 nm. The design utilizes Faraday modulation at 2.5 kHz and signal processing by selective filtering and phase sensitive detection. Observed rms noise levels are reported for the wavelength range 230–450 nm: representative values for nonabsorbing solutions are 0.2 mdeg at 450 nm (15 nm bandpass, 9 msec time constant) and 3 mdeg at 260 nm (8 nm bandpass, 9 msec time constant). It is shown that these figures correspond to the theoretical shot-noise limited performance of the instrument. The use of the apparatus is exemplified by studies of the hydroxide ion-catalyzed mutarotation of glucose, and the displacement of NADH by NAD+ from the NADH-liver alcohol dehydrogenase complex.
Accurate determination of the electrical resistivity from mutual inductance measurements
Authors: Rosenthal M. D. , Maxfield B. W.
Published: March 2003

When a conducting specimen is placed inside a coil, the coil impedance changes. For simple coil and specimen geometries, the impedance change can be related to the electrical resistivity of the specimen. This paper describes a variety of methods for the accurate determination of the resistivity of a cylindrical specimen from the measured change in mutual inductance of a cylindrically symmetric coil assembly. The useful range of resistivity extends from about 3 nΩ⋅cm to above 100 μΩ⋅cm. Using the calibration methods that are described, 1% absolute accuracy is not difficult to obtain even when using a coil system only five coil diameters in length. When compared with calculations for the corresponding infinite specimen and coil problem, the measurements are in disagreement by much more than 1%. Approximate calculations and numerical estimates show that axial field gradients are responsible for these differences when the specimen is more than about twice as long as the coils, and that end effects in the specimen are responsible for the differences when the specimen is short compared to the coil length. The effect of losses other than those in the specimen being studied has also been investigated extensively. We find that in many important experimental circumstances, the conventional procedure of subtracting coil system losses with the specimen absent from those with specimen present can be seriously in error. For instance , if the tail of a metal Dewar, a vacuum can, or the pole faces of an electromagnet are placed so that they intercept some of the return flux of the primary coil, the system losses may not be additive. This occurs because the magnitude of the return flux depends upon the screening currents in the specimen (and hence on the presence or absence of the specimen). This problem is discussed from both an analytical and experimental point of view. An experimental system having very small background losses is described and numerous results on specimens of different lengths and diameters are presented. It can be shown that a radial conductivity variation of about 50% or more can be determined by making measurements at a few frequencies, but that the results are not very sensitive to the functional form of the conductivity variation.
Direct NO2 photolysis rate monitor
Authors: Jackson J. O. , Stedman D. H. , Smith R. G. , Hecker L. H. , Warner P. O.
Published: March 2003

An optically thin actinometer is described which measures the rate of photolysis of NO2 in air. Operating details of the device are reported together with a test in downtown Detroit. The result was that the instrument was more accurate than some of the other test parameters in the range 0–0.5 min−1. Applications to photochemical smog and stratospheric pollution problems are discussed.
Retraction system for multi-anvil presses
Authors: Hall H. Tracy
Published: March 2003

A hollow guide-pin system is described for retraction of the hydraulic rams of multi-anvil presses that saves weight and machining costs and improves mechanical proportions. The system also unclutters the anvil region, providing more access. The use of inverted rams and right/left-hand thread tie-bars and bases further reduces weight and cost.
Prism coupler mount for thin-film optical measurements
Authors: McIntier J. R. , Watts R. K.
Published: March 2003

A mount is described which allows easy positioning of input and output prism couplers for measurement of mode parameters of optical guided waves in thin films.
Phase fluorometer with a continuously variable frequency
Authors: Hauser M. , Heidt G.
Published: March 2003

Primarily to investigate nonexponentially decaying fluorences, a phase fluorometer has been developed with a frequency continously variable between 0.5 and 72 MHz.
Low temperature mechanical testing machine
Authors: Hartwig G. , Wüchner F.
Published: March 2003

A machine was constructed and installed for testing the mechanical properties of materials down to liquid helium temperatures. The facility is designed to perform static and dynamic measurements, and is rigid and fast enough to measure the work of fracture or other fast running processes. The parameters of the machine are so selected that plastics, resins, etc. can be tested, but it may also be adapted to the measurement of electrical or thermal properties of conductors (superconductors) under static or dynamic load. Some results of measurements on unfilled and filled resins are included.
’’Hot,’’metastable atom, molecular beam source
Authors: Leasure E. L. , Mueller C. R. , Ridley T. Y.
Published: March 2003

A molecular beam source for high-energy metastable atoms, utilizing a corona discharge, is described. It was designed for scattering experiments where accurate alignment of beam components is required. The metastable atoms produced in this source have kinetic energies from 5 to 74 eV dependent on the species and sufficient velocity selection to reveal structure in the differential cross sections. These high-energy metastables were previously reported as photons. When the molecular beam source was operated at 200–300 Torr, a supersonic beam of metastables was produced. An optimization of operating conditions produced a supersonic beam flux two orders of magnitude greater than previously reported.
Optical components mount
Authors: Ruby R. H.
Published: March 2003

A mount for optical components is described which allows for the rapid interchange of components in an optical system.
Development of a dc sputtering unit for the production of GaAs devices
Authors: Engemann J.
Published: March 2003

The conventional way of producing GaAs devices such as field-effect transistors or Gunn devices becomes more and more difficult with decreasing device dimensions. These difficulties are due, for example, to the poor adhesion of evaporated metal films and/or to high series and spreading resistance of thin and narrow metal stripes (e.g., gates for FETs). The maximum thickness of such stripes is limited by chemical underetching and the resolution of photo resists. By using a modified dc sputtering unit the adhesion of metal films to GaAs was improved. No underetching was observed. The construction of the sputtering unit is described, especially the modification which was developed for etching the semiconductor surfaces by ion bombardment. Details for the precise control of the etch process are given.
Simple calibration procedures for platinum resistance thermometers from 2.5 to 14 K
Authors: McCrackin F. L. , Chang S. S.
Published: March 2003

Calibration procedures are developed for platinum resistance thermometers in the temperature range 2.5–14 K. Two recommended methods require calibration points at the boiling point of liquid helium (4.215 K) and the triple point of hydrogen (13.81 K); in addition, the first method requires a point at 7.201 K while the second method requires the slope of the calibration curve at 13.81 K. For temperatures from 3.5 to 14 K, the calibrations are accurate to within 0.01 K for the first method and 0.025 K for the second method. For temperatures from 2.5 to 3.5 K, the calibrations are somewhat less accurate. Therefore, if a thermometer has been calibrated for temperatures of 13.81 K and above, its calibration may be easily extended to lower temperatures with sufficient accuracy for many applications. These calibration procedures were developed from two-way structural analysis of the accurate calibrations of 12 platinum resistance thermometers.
High sensitivity piezoelectric accelerometer
Authors: Tims A. C. , Davidson R. L. , Timme R. W.
Published: March 2003

A high-sensitivity piezoelectric accelerometer has been developed to monitor and characterize low-level vibration spectra in large structures. The theory of accelerometer design is traced and applied to a specific problem to develop a set of design criteria. The construction and calibration of the accelerometer is described. The accelerometer has a sensitivity of 2.82 V/g (9.0 dB re 1 V/g) at frequencies to 1 kHz. The use of the accelerometer in conjunction with a real-time spectrum analyzer to identify vibration sources and characterize their ’’signatures’’ is described.
New detector for ions and metastable atoms
Authors: Joshi S. B. , Prince R. H. , Ward T. V.
Published: March 2003

A detector for ions and metastable atoms has been designed and evaluated which utilizes a conversion from particle to photon detection. The device is ’’solar blind’’ and currently used in shock-tube research in conjunction with a quadrupole mass spectrometer where the insensitivity of the gain to pressure fluctuations is highly advantageous. Preliminary observations of the performance of the detector and its conversion efficiency for various ion species are reported. Values of overall gain are typically 5×105 for conversion electrode potentials of 10 kV and a characteristic time constant < 1 μsec.
Channeltron efficiency for counting of H+ and H− at low energy
Authors: Crandall D. H. , Ray J. A. , Cisneros Carmen
Published: March 2003

The counting efficiency of a channel electron multipier is measured for H+ and H− impact with the input of the Channeltron grounded and for impact energies between 0.3 and 5 keV. The counting efficiency is found to be about 30% greater for H− than for H+ at energies below 1 keV. This difference and an observed difference between H− and H+ in the variation of counting efficiency across the Channeltron opening are attributed to the surface potential of the Channeltron near the opening, which can accelerate or decelerate the incident particles.
Hall coefficient measurements in materials of extremely small Hall angle using a modified helicon technique
Authors: Rosenthal M. D. , Maxfield B. W.
Published: March 2003

A novel modification of the helicon resonance method permits the Hall coefficient RH to be determined in materials having a Hall angle smaller than 10−3 with an absolute accuracy of 20%, while changes can be determined to better than 1%. Details of a measurement method are given which allow RH to be determined from swept field measurements at a few fixed frequencies well below resonance. The necessary calibration procedures are described.
Simple device for measurements of the sticking coefficient of cryopumps
Authors: Habets A. H. M. , Verster N. F. , van Vlimmeren Q. A. G.
Published: March 2003

An apparatus is described which allows direct measurements of the reflection coefficient of cryopumps, the complement of the sticking coefficient. The reflected fraction of a gas flow directed towards a cryopump is measured directly. This gives accurate results especially for high sticking coefficients. Measured values ? 0.995 of the sticking coefficient of nitrogen gas on a 16 K cryopump are presented as a function of the gas flow per unit area of the pump. The density of the condensed layer is nearly the same as for solid nitrogen ice.
Effects on focusing properties due to field fringing near the ends of the electrostatic cylindrical mirror analyzer
Authors: Renfro G. M. , Fischbeck H. J.
Published: March 2003

The electrostatic potential field has been calculated numerically near the ends of the electrostatic cylindrical mirror analyzer. The effects of various guard ring configurations on the field distortion are calculated. The trajectories of electrons passing through the guarded and unguarded fields are calculated, and it is shown how field distortions influence the focusing properties of the analyzer. A coincidence spectrometer is proposed, based on the action of guard rings upon the fringing field.
Surface temperature measurements for ion-bombarded Si and GaAs at 1.0 to 2.0 MeV
Authors: Lowe L. F. , Kennedy J. K. , Davies D. E. , Deane M. L. , Eyges L. J.
Published: March 2003

Surface temperatures of ion-bombarded silicon and gallium arsenide have been measured using an infrared detector. Ion beams of N+, N+2, O+, O+2, C+, CO+, and H+ were used at energies from 1–2.0 MeV and at current densities up to 12 μA⋅cm−2. No temperature dependence was found on ion species, energy, or current. The change in temperature depended only on beam power, target material, and sample mounting technique. With proper mounting temperature increases of 20 °C for silicon and 65 °C for gallium arsenide were observed for a beam power density of 1.0 W⋅cm−2.
NMR Q-meter detectors
Authors: Code R. F.
Published: March 2003

An improved analysis of continuous wave (cw) NMR detection by Q-meters is presented which explicitly includes parallel resistive loading of the sample coil and frequency dependent losses caused by the rf skin effect. A versatile MOSFET Q-meter is described which operates at frequencies up to 60 MHz and rf input levels between 2 and 100 mV peak-to-peak. The noise figure is shown to be less than 3 dB at 8 MHz and a 7 mV peak-to-peak rf level. A comparison of Q-meters with other types of cw NMR detectors is given, and their advantages for accurate line-shape and susceptibility experiments are discussed.
Differential light scattering technique for the study of conformational changes in macromolecules
Authors: Cannell David S. , Dubin Stuart B.
Published: March 2003

We present the design and development of a differential laser spectrometer capable of the accurate measurement of very small changes in the translational diffusion coefficients (DT) of macromolecules. Since DT depends solely on the translational frictional coefficient of a macromolecule, this parameter is a direct measure of macromolecular conformation, and thus detection of small changes in the translational diffusion coefficient can reveal very slight conformational alterations. The differential laser probe we present is a differential optical mixing laser spectrometer capable of the direct measurement of the difference in the spectra of the light scattered by two solutions of macromolecules and hence, the difference in the translational diffusion coefficients of the macromolecular species under investigation. In its present form, the instrument has a precision of 3 parts in 103, that is, the differential laser probe can measure a change in DT of 3% with a precision of 10%. Discussion is provided for the system improvements required to increase the precision one additional order of magnitude.
Automated system for measurements of gas volume changes at constant pressure
Authors: Zimmels Yoram
Published: March 2003

The system described functions as a sensitive gas volume meter while automatically keeping the pressure at a constant level. It is based on the simplest hydraulic principles and may be adjusted to work at different pressure levels. Accuracy is better than 0.5% at atmospheric pressure. As the system is cheap to construct, significant experimental time may be saved by incorporating several units in parallel. Reference is also made to possible fields of application.