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Oct 2000

Volume 71, Issue 10, pp. 3611-3966

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back to top MICROSCOPY and IMAGING

Million frames per second infrared imaging system

Alan T. Zehnder, Pradeep R. Guduru, Ares J. Rosakis, and G. Ravichandran

Rev. Sci. Instrum. 71, 3762 (2000); http://dx.doi.org/10.1063/1.1310350 (7 pages) | Cited 16 times

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An infrared imaging system has been developed for measuring the temperature increase during the dynamic deformation of materials. The system consists of an 8×8 HgCdTe focal plane array, each with its own preamplifier. Outputs from the 64 detector/preamplifiers are digitized using a row-parallel scheme. In this approach, all 64 signals are simultaneously acquired and held using a bank of track and hold amplifiers. An array of eight 8:1 multiplexers then routes the signals to eight 10 MHz digitizers, acquiring data from each row of detectors in parallel. The maximum rate is one million frames per second. A fully reflective lens system was developed, consisting of two Schwarszchild objectives operating at infinite conjugation ratio. The ratio of the focal lengths of the objectives determines the lens magnification. The system has been used to image the distribution of temperature rise near the tip of a notch in a high strength steel sample (C-300) subjected to impact loading by a drop weight testing machine. The results show temperature rises at the crack tip up to around 70 K. Localization of temperature, and hence, of deformation into “U” shaped zones emanating from the notch tip is clearly seen, as is the onset of crack propagation. © 2000 American Institute of Physics.
Show PACS
42.79.Pw Imaging detectors and sensors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.70.Fy Nondestructive testing: optical methods

Experimental determination of scanning probe microscope cantilever spring constants utilizing a nanoindentation apparatus

J. D. Holbery, V. L. Eden, M. Sarikaya, and R. M. Fisher

Rev. Sci. Instrum. 71, 3769 (2000); http://dx.doi.org/10.1063/1.1289509 (8 pages) | Cited 37 times

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A rapid, nondestructive, and accurate method for determining the normal spring constants of scanning probe microscopy cantilevers is presented. Spring constants are determined using a commercial combination atomic force microscope and nanoindentation apparatus configured with a W-indenter tip geometrically configured into either a scanning tunneling microscope pointed tip or chisel shape that may be placed onto the cantilever of interest with high accuracy. A load is applied to the cantilever tip and the corresponding displacement is measured. From the force–displacement curve, the spring constant is determined. For cantilevers with spring constants greater than 1 N/m, the derived spring constants are believed to be accurate to within ±10%, with better accuracy for stiffer levers. This method has been used to measure the stiffness of cantilevers from several manufacturers. © 2000 American Institute of Physics.
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07.79.Lh Atomic force microscopes
07.10.Pz Instruments for strain, force, and torque
06.20.F- Units and standards

A high pressure, high temperature, scanning tunneling microscope for in situ studies of catalysts

Brandon L. Weeks, Colm Durkan, Hiromi Kuramochi, Mark E. Welland, and Trevor Rayment

Rev. Sci. Instrum. 71, 3777 (2000); http://dx.doi.org/10.1063/1.1290043 (5 pages) | Cited 5 times

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We describe the construction and operation of a novel scanning tunneling microscope, which is capable of operating throughout a wide range of pressures (atmospheric—60 bar) and temperatures (300–650 K). The instrument has cylindrical symmetry and is constructed out of materials with low thermal conductivity and low coefficients of thermal expansion that allows imaging the same area over a wide temperature range. With this microscope we present images of the oxidation of polycrystalline nickel. © 2000 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
07.20.Ka High-temperature instrumentation; pyrometers
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Cryogenic magnetic force microscope

M. Roseman and P. Grütter

Rev. Sci. Instrum. 71, 3782 (2000); http://dx.doi.org/10.1063/1.1290039 (6 pages) | Cited 16 times

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We describe our cryogenic magnetic force microscope, operating between 4.2 and 300 K, in fields of 0–8 T. The system uses a fiber optic interferometer to measure cantilever deflections, permitting the tracking of the resonance frequency through the use of a phase locked loop. Piezoelectric positioners, capable of operation in high magnetic fields, perform in situ tip and fiber approaches. As an effective means of vibration isolation, we suspend the microscope from a soft bellows which attenuates vibrations by more than an order of magnitude. A detailed noise analysis indicates that although the microscope is thermally limited, the system frequency resolution is currently limited by the shot noise of the interferometer. © 2000 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.60.Vg Fiber-optic instruments
07.60.Ly Interferometers
07.10.Fq Vibration isolation
06.60.Sx Positioning and alignment; manipulating, remote handling
42.81.Pa Sensors, gyros

Spring constant measurement of a bent near-field optical fiber probe

Sy-Hann Chen, Heh-Nan Lin, and Pang-Ming Ong

Rev. Sci. Instrum. 71, 3788 (2000); http://dx.doi.org/10.1063/1.1290503 (3 pages) | Cited 3 times

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We present a method to determine the spring constant of a bent near-field optical fiber probe based on resonance change. The spring constant of a cylindrical fiber cantilever is first obtained and the fiber is used to measure the mass of a sticky lump around 100 μm in size through resonance change. The known mass is then transferred to the end of a bent fiber probe and its spring constant can be obtained by the same approach. Three different masses have been employed and the spring constant is measured with a total uncertainty of around 10%. The current method has the advantage that particles of uniform sizes and densities are not required. © 2000 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
42.81.Pa Sensors, gyros
42.81.Cn Fiber testing and measurement of fiber parameters
back to top CONDENSED MATTER; MATERIALS

Electromagnetic levitation apparatus for investigations of the phase selection in undercooled melts by energy-dispersive x-ray diffraction

C. Notthoff, H. Franz, M. Hanfland, D. M. Herlach, D. Holland-Moritz, and W. Petry

Rev. Sci. Instrum. 71, 3791 (2000); http://dx.doi.org/10.1063/1.1289508 (6 pages) | Cited 30 times

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The metastable state of an undercooled melt can provide access to the formation of metastable phases whose crystallographic structures differ from their stable counterparts. The electromagnetic levitation technique is used here to undercool bulk melts without containers. This technique, combined with energy dispersive x-ray diffraction of synchrotron radiation, allows in situ study of the rapid crystallization of undercooled Ni–V alloys. The binary Ni–V alloy was chosen as a model system, because it shows phase competition of three different crystallographic phases, bcc, fcc, and an intermetallic phase of tetragonal structure at intermediate concentrations. The diffraction experiments provide for direct identification of the various crystalline phases formed from the nonequilibrium state of the undercooled melt. The phase selection is investigated as a function of undercooling temperature for Ni–V alloys of different concentrations. © 2000 American Institute of Physics.
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61.05.cp X-ray diffraction
85.70.Rp Magnetic levitation, propulsion and control devices
81.30.Fb Solidification
64.60.My Metastable phases
64.70.D- Solid-liquid transitions
64.60.Q- Nucleation
07.85.Qe Synchrotron radiation instrumentation

Polarized reflectometer for the investigation of surface magnetism, the new polarized neutron reflectometer with polarization analysis at the Laboratoire Léon Brillouin

C. Fermon, F. Ott, G. Legoff, H. Glättli, and V. Wintenberger

Rev. Sci. Instrum. 71, 3797 (2000); http://dx.doi.org/10.1063/1.1310342 (4 pages) | Cited 4 times

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We present the new polarized reflectometer for the investigation of surface magnetism, which has been built at the Laboratoire Léon Brillouin. This polarized neutron reflectometer with polarization analysis has been optimized for the study of small magnetic samples (1 cm2 range). We describe the new multilayer monochromator which has permitted us to obtain a wider wavelength distribution (∼4%) and the focusing neutron guide which has allowed the focalization of a 100 mm high beam onto a region 15 mm high. This new optical setup has allowed a large neutron flux increase, which is now of 2×105 n/cm2 s. © 2000 American Institute of Physics.
Show PACS
29.30.Hs Neutron spectroscopy
41.85.Si Particle beam collimators, monochromators
75.70.Rf Surface magnetism
07.77.Ka Charged-particle beam sources and detectors
03.75.Be Atom and neutron optics

Three-configurational surface magneto-optical Kerr effect measurement system for an ultrahigh vacuum in situ study of ultrathin magnetic films

J.-W. Lee, J.-R. Jeong, D.-H. Kim, J. S. Ahn, J. Kim, and S.-C. Shin

Rev. Sci. Instrum. 71, 3801 (2000); http://dx.doi.org/10.1063/1.1310346 (5 pages) | Cited 28 times

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We have constructed a three-configurational surface magneto-optical Kerr effect system, which provides the simultaneous measurements of the “polar,” “longitudinal,” and “transverse” Kerr hysteresis loops at the position where deposition is carried out in an ultrahigh vacuum growth chamber. The present system enables in situ three-dimensional vectorial studies of ultrathin film magnetism with a submonolayer sensitivity. We present three-configurational hysteresis loops measured during the growth of Co films on Pd(111), glass, and Pd/glass substrates. © 2000 American Institute of Physics.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Rf Surface magnetism
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
07.55.Db Generation of magnetic fields; magnets

Nondestructive evaluation of steel structures using a superconducting quantum interference device magnetometer and a neural network system

C. Hall Barbosa, M. Vellasco, M. A. Pacheco, A. C. Bruno, and C. S. Camerini

Rev. Sci. Instrum. 71, 3806 (2000); http://dx.doi.org/10.1063/1.1313796 (10 pages) | Cited 1 time

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This work combines two state-of-the-art techniques in the area of magnetic nondestructive evaluation: the application of the superconducting quantum interference device (SQUID) as the magnetic field sensor; and the use of artificial neural networks as analysis tools applied to the detected magnetic signals. Pioneering measurements using the SQUID sensor have been made in steel samples containing various types of flaws, and a neural network system, based on the time-delay neural network and radial basis function algorithms, has been implemented to characterize the flaws. The neural network system aims to, based on the measured magnetic field, provide information about defect geometry, thus allowing the assessment of defect severity, as a basis for maintenance and repair procedures. © 2000 American Institute of Physics.
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81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.05.Mh Neural networks, fuzzy logic, artificial intelligence

High precision ac susceptometer for measuring the temperature and magnetic field dependence of the penetration depth in superconductor single crystals

C. P. Bidinosti and W. N. Hardy

Rev. Sci. Instrum. 71, 3816 (2000); http://dx.doi.org/10.1063/1.1311945 (6 pages) | Cited 7 times

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An ac susceptometer has been developed for very sensitive measurement of the magnetic moment of small samples as a function of temperature and applied dc field. The system was designed specifically for measurements on small single crystals of the high Tc superconductor YBa2Cu3O7−δ in the Meissner state. The natural platelet geometry of these crystals allows results to be easily transcribed into changes in the material’s magnetic field penetration depth, Δλ, an important quantity in the exploration of the underlying physics of its superconductivity. The resolution of the technique is of the order of one tenth of an angstrom for a sample of area ∼ 2 mm2. © 2000 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.72.-h Cuprate superconductors

Simultaneous measurement of liquid density and viscosity using remote query magnetoelastic sensors

Craig A. Grimes, Dimitris Kouzoudis, and Casey Mungle

Rev. Sci. Instrum. 71, 3822 (2000); http://dx.doi.org/10.1063/1.1315352 (3 pages) | Cited 20 times

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Earlier work [C. A. Grimes et al., Smart Mater. Struct. 8, 639, (1999)] has shown that upon immersion in liquid the resonant frequency of a magnetoelastic sensor shifts linearly in response to the square root of the liquid density and viscosity product. It is shown that comparison between a pair of magnetoelastic sensors with different degrees of surface roughness can be used to simultaneously determine the liquid density and viscosity. © 2000 American Institute of Physics.
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06.30.Dr Mass and density
47.80.-v Instrumentation and measurement methods in fluid dynamics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.55.-w Magnetic instruments and components

High magnetic field corrections to resistance thermometers for low temperature calorimetry

Nathanael Fortune, Gayle Gossett, Lydia Peabody, Katherine Lehe, S. Uji, and H. Aoki

Rev. Sci. Instrum. 71, 3825 (2000); http://dx.doi.org/10.1063/1.1310341 (6 pages) | Cited 3 times

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We present a general analytical method of correcting for magnetic-field-induced changes in both the apparent temperature and the sensitivity of resistive thermometers at dilution refrigerator temperatures. With this method, we are able to reduce magnetic field induced errors in temperature to a level limited only by our ability to regulate the temperature in the absence of a magnetic field. We illustrate the application of our method to two resistive sensors in magnetic fields up to 18 T: a custom-made AuxGe1−x thin film sensor used in calorimetry and a commercially available ruthenium–oxide thick film resistor used in thermometry. © 2000 American Institute of Physics.
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07.20.Dt Thermometers
07.20.Fw Calorimeters
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
02.60.Ed Interpolation; curve fitting

High-energy (e, 2e) spectrometer for the study of the spectral momentum density of materials

M. Vos, G. P. Cornish, and E. Weigold

Rev. Sci. Instrum. 71, 3831 (2000); http://dx.doi.org/10.1063/1.1290507 (10 pages) | Cited 29 times

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A new spectrometer for the study of energy-resolved momentum densities is described. The (e, 2e) spectrometer uses a symmetric configuration and uses incoming energies up to 50 keV. Energy resolution and momentum resolution are 1.8 eV and 0.1 a.u., respectively. Compared to previous spectrometers this spectrometer has rather low levels of multiple scattering, and thus allows for more quantitative analysis of the data and/or the measurement of thicker samples. © 2000 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
79.20.Kz Other electron-impact emission phenomena
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.30.Ep Charged-particle spectroscopy

A modified dual-slope method for heat capacity measurements of condensable gases

S. Pilla, J. A. Hamida, and N. S. Sullivan

Rev. Sci. Instrum. 71, 3841 (2000); http://dx.doi.org/10.1063/1.1290040 (5 pages) | Cited 1 time

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A high resolution nonadiabatic method for measuring the heat capacity (CP) of bulk samples of condensable gases in the range of 7.5–70 K is described. In this method CP is evaluated by directly comparing the heating and cooling rates of the sample temperature for two algebraically independent heat pulse sequences without explicit use of the thermal conductance between sample and thermal bath. A fully automated calorimeter for rapid measurement of CP of molecular solids utilizing this technique is presented. The technique along with the automated calorimeter with a provision to apply external electric and magnetic fields is particularly useful for the study of continuous phase transitions in molecular solids as well as field induced changes in the heat capacity. © 2000 American Institute of Physics.
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07.20.Fw Calorimeters
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
64.70.K- Solid-solid transitions

All-optical technique for measuring thermal properties of materials at static high pressure

G. I. Pangilinan, H. D. Ladouceur, and T. P. Russell

Rev. Sci. Instrum. 71, 3846 (2000); http://dx.doi.org/10.1063/1.1286309 (7 pages) | Cited 4 times

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The development and implementation of an all-optical technique for measuring thermal transport properties of materials at high pressure in a gem anvil cell are reported. Thermal transport properties are determined by propagating a thermal wave in a material subjected to high pressures, and measuring the temperature as a function of time using an optical sensor embedded downstream in the material. Optical beams are used to deposit energy and to measure the sensor temperature and replace the resistive heat source and the thermocouples of previous methods. This overcomes the problems introduced with pressure-induced resistance changes and the spatial limitations inherent in previous high-pressure experimentation. Consistent with the heat conduction equation, the material’s specific heat, thermal conductivity, and thermal diffusivity (κ) determine the sensor’s temperature rise and its temporal profile. The all-optical technique described focuses on room-temperature thermal properties but can easily be applied to a wide temperature range (77–600 K). Measurements of thermal transport properties at pressure up to 2.0 GPa are reported, although extension to much higher pressures are feasible. The thermal properties of NaCl, a commonly used material for high-pressure experiments are measured and shown to be consistent with those obtained using the traditional methods.
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07.20.-n Thermal instruments and apparatus
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Separation of thermal wave induced displacements and thermoreflectance variations using a rotated beamsplitter cube interferometer

C. J. Fiedler, J. W. Wagner, and K. E. Henseler

Rev. Sci. Instrum. 71, 3853 (2000); http://dx.doi.org/10.1063/1.1289677 (7 pages) | Cited 2 times

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A rotated beamsplitter cube interferometer has been developed which can measure both the change in reflectivity and the displacement of nontransparent thin films caused by thermal waves. Thermal waves are used to characterize material properties, especially those of thin films, by monitoring the heat propagation in a specimen. Thermal waves cause both a change in the reflectivity of the specimen and a displacement of the specimen surface. By varying the phase difference between the reference and signal arms of an interferometer, a method for detecting and separating the contributions of each of these effects has been developed. This enables the determination of the thermal expansion coefficient of the thin film independent of substrate properties. Data demonstrating the application of this technique on Cu and TiN thin films are presented.
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07.60.Ly Interferometers
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
68.60.Dv Thermal stability; thermal effects
07.20.-n Thermal instruments and apparatus

Near-field acoustic densimeter and viscosimeter

R. Patois, P. Vairac, and B. Cretin

Rev. Sci. Instrum. 71, 3860 (2000); http://dx.doi.org/10.1063/1.1286308 (4 pages) | Cited 12 times

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We have developed a vibrating microsensor allowing simultaneous measurement of density and viscosity in liquids. A small-sized spherical oscillating probe is immersed in the liquid and is connected to a microcantilever driven in flexural vibration by a piezoelectric transducer. Cantilever resonance parameters (frequency and damping) are used to measure the probe–fluid interaction. The developed analytical model enables us to compute fluid characteristics from measured data by solving the inverse problem. Measurements performed for various fluids are compared to literature data. Investigation depth of the sensor is determined by studying the effect of the presence of an immersed wall in the vicinity of the probe. © 2000 American Institute of Physics.
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43.58.-e Acoustical measurements and instrumentation
06.30.Dr Mass and density
47.80.-v Instrumentation and measurement methods in fluid dynamics
07.10.Cm Micromechanical devices and systems
back to top CHEMISTRY

Real-time precision concentration measurement for flowing liquid solutions

V. Krishna, C. H. Fan, and J. P. Longtin

Rev. Sci. Instrum. 71, 3864 (2000); http://dx.doi.org/10.1063/1.1288236 (5 pages) | Cited 15 times

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The precise, real-time measurement of liquid concentration is important in fundamental research, chemical analysis, mixing processes, and manufacturing, e.g., in the food and semiconductor industries. This work presents a laser-based, noninvasive technique to measure concentration changes of flowing liquids in real time. The essential components in the system include a 5 mW laser diode coupled to a single-mode optical fiber, a triangular optical cell, and a high-resolution beam position sensor. The instrument provides a large range of concentration measurement, typically 0%–100% for binary liquid mixtures, while providing a resolution on the order of 0.05% concentration or better. The experimental configuration is small, reliable, and inexpensive. Results are presented for NaCl and MgCl2 aqueous solutions with concentrations ranging from 0% to 25%, with very good agreement found between measured and true concentrations. © 2000 American Institute of Physics.
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82.80.-d Chemical analysis and related physical methods of analysis
07.60.Hv Refractometers and reflectometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Design and characterization of collimated effusive gas beam sources: Effect of source dimensions and backing pressure on total flow and beam profile

Jeffrey M. Guevremont, Stanley Sheldon, and Francisco Zaera

Rev. Sci. Instrum. 71, 3869 (2000); http://dx.doi.org/10.1063/1.1311939 (13 pages) | Cited 17 times

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The total flux and the flow profile of gas-phase molecular beams generated by a number of assemblies involving different combinations of apertures and capillary arrays were measured for a wide range of backing pressures covering the molecular and viscous flow regimes. Specifically, δ=10 and 50 μm diameter, L = 2 mm thick glass capillary arrays were combined with single apertures of ϕ=0.17, 1.0, and 11.4 mm diameters and L = 0.1, 0.5, and 2 mm thickness in order to design high-flux beam dosers with a high degree of collimation. The variations in the total flux and the spatial profile of the beams were tested as a function of the backing pressure, which was varied between 10−4 and 102 Torr, by a sampling movable skimmer. The data obtained under the molecular flow (low backing pressure) regime corroborate some conclusions from previous reports. In particular, it is shown here that the conductance of the dosers (the ratio of the total flux of the beam to the backing pressure) depends only on their geometry in that regime. The beam profile, on the other hand, deteriorates with increasing backing pressure because of the increase in gas–wall and gas–gas collisions in the intermediate “opaque” flow regime where the mean free path of the gas, λ, is larger than the diameter of the capillaries, δ, but smaller than the length of the tubes, L. As λ approaches δ, a transition “slip” regime is reached, and a drop in the conductance of the doser is observed. Finally, by pressures where λ<0.05δ, a viscous laminar flow is established where the conductance of the doser increases with pressure and its directionality improves as well. The implications of our results to the design of molecular beams for specific applications are briefly discussed. © 2000 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
07.77.Gx Atomic and molecular beam sources and detectors
47.45.-n Rarefied gas dynamics

High-pressure photoacoustic calorimetry

John A. Daffron, Gerard J. Farrell, and Theodore J. Burkey

Rev. Sci. Instrum. 71, 3882 (2000); http://dx.doi.org/10.1063/1.1311941 (4 pages) | Cited 2 times

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A high-pressure photoacoustic calorimeter has been developed to operate up to 200 MPa. Photoacoustic calorimetry can be used to study the microsecond kinetics and thermodynamics of reactions in solution. Both thermal expansion and volume of reaction contribute to the generation of the photoacoustic signal, and the separation of these contributions has been achieved by the variation of pressure. The construction of a stainless-steel flow cell, bellows, and a high-pressure manifold are described. These components enable rapid sample change and sample flow at high pressure. As a test, the enthalpy and volume of reaction were determined for diphenylcyclopropenone decomposition to diphenylethyne and carbon monoxide. © 2000 American Institute of Physics.
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82.80.Kq Energy-conversion spectro-analytical methods (e.g., photoacoustic, photothermal, and optogalvanic spectroscopic methods)
07.20.Fw Calorimeters
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
82.60.Cx Enthalpies of combustion, reaction, and formation
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

A fast-response chemical ionization mass spectrometer for in situ measurements of HNO3 in the upper troposphere and lower stratosphere

J. A. Neuman, R. S. Gao, M. E. Schein, S. J. Ciciora, J. C. Holecek, T. L. Thompson, R. H. Winkler, R. J. McLaughlin, M. J. Northway, E. C. Richard, and D. W. Fahey

Rev. Sci. Instrum. 71, 3886 (2000); http://dx.doi.org/10.1063/1.1289679 (9 pages) | Cited 20 times

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A chemical ionization mass spectrometer instrument has been developed for in situ measurements of nitric acid (HNO3) in the upper troposphere and lower stratosphere from the NASA WB-57 aircraft. Fast and sensitive measurements of HNO3 are achieved by using a low surface area heated Teflon sampling inlet and detection techniques that employ ion-molecule reactions. Sensitivity to HNO3 is determined in flight by adding HNO3 from a calibrated HNO3 permeation source into the sample air flow, and instrument background is measured by displacing ambient air from the sampling inlet with a flow of dry nitrogen in the sampling inlet. Instrument temperatures, pressures, and gas flows are controlled in flight to maintain a constant detection sensitivity in a changing ambient operating environment. The initial performance of this new instrument is evaluated using HNO3 and ozone data obtained between 6 and 19 km during the 1999 NASA Atmospheric Chemistry of Combustion Emissions Near the Tropopause mission. The data reveal a sensitivity of 0.73 Hz/pptv, a detection limit of 30 pptv for 10 s integration times, and a fast time response (<1 s). Further reductions in the background HNO3 signal will improve performance. © 2000 American Institute of Physics.
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93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
07.75.+h Mass spectrometers
07.88.+y Instruments for environmental pollution measurements
92.60.H- Atmospheric composition, structure, and properties
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
back to top BIOLOGY and MEDICINE

High pressure-jump apparatus for kinetic studies of protein folding reactions using the small-angle synchrotron x-ray scattering technique

J. Woenckhaus, R. Köhling, R. Winter, P. Thiyagarajan, and S. Finet

Rev. Sci. Instrum. 71, 3895 (2000); http://dx.doi.org/10.1063/1.1290508 (5 pages) | Cited 26 times

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An apparatus suitable for pressure-jump experiments with variable pressure amplitude and a fast response time to facilitate time-resolved small-angle x-ray scattering at synchrotron facilities is described. The high pressure-jump apparatus is capable of performing bidirectional pressure jumps at a time resolution as high as 5 ms. The high pressure sample cell presented has flat diamond windows and is suited for pressures up to 0.7 GPa operating in the temperature range from −40 to 120 °C. The cell is designed for investigating biological and other soft condensed matter materials. Modifications on the window supports allow also simultaneous wide-angle x-ray scattering data to be taken. We have used the equipment to study the kinetics of protein folding reactions. The performance of the apparatus is demonstrated by presenting data on the pressure-induced un/refolding reaction of the water-soluble protein SNase WT. © 2000 American Institute of Physics.
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87.64.Bx Electron, neutron and x-ray diffraction and scattering
07.85.Qe Synchrotron radiation instrumentation
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
87.15.Cc Folding: thermodynamics, statistical mechanics, models, and pathways

A compact x-ray system for macromolecular crystallography

Mikhail Gubarev, Ewa Ciszak, Igor Ponomarev, Walter Gibson, and Marshall Joy

Rev. Sci. Instrum. 71, 3900 (2000); http://dx.doi.org/10.1063/1.1311937 (5 pages) | Cited 2 times

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We describe the design and performance of a high flux x-ray system for a macromolecular crystallography that combines a microfocus x-ray generator (40 μm full width at half maximum spot size at a power level of 46.5 W) and a collimating polycapillary optic. The Cu Kα x-ray flux produced by this optimized system through a 500 μm diam orifice is 7.0 times greater than the x-ray flux previously reported by Gubarev et al. [M. Gubarev et al., J. Appl. Crystallogr. 33, 882 (2000)]. The x-ray flux from the microfocus system is also 2.6 times higher than that produced by a rotating anode generator equipped with a graded multilayer monochromator (green optic, Osmic, Inc. CMF24-48-Cu6) and 40% less than that produced by a rotating anode generator with the newest design of graded multilayer monochromator (blue optic, Osmic, Inc. CMF12-38-Cu6). Both rotating anode generators operate at a power level of 5000 W, dissipating more than 100 times the power of our microfocus x-ray system. Diffraction data collected from small test crystals are of high quality. For example, 42 540 reflections collected at ambient temperature from a lysozyme crystal yielded Rsym = 5.0% for data extending to 1.70 Å, and 4.8% for the complete set of data to 1.85 Å. The amplitudes of the observed reflections were used to calculate difference electron density maps that revealed positions of structurally important ions and water molecules in the crystal of lysozyme using the phases calculated from the protein model. © 2000 American Institute of Physics.
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61.05.cp X-ray diffraction
07.85.Jy Diffractometers
87.64.Bx Electron, neutron and x-ray diffraction and scattering
61.66.Hq Organic compounds
back to top GRAVITY; GEOPHYSICS; ASTRONOMY and ASTROPHYSICS

Trifilar torsion pendulum for measurement of dissipation caused by an electric field

V. P. Mitrofanov and N. A. Styazhkina

Rev. Sci. Instrum. 71, 3905 (2000); http://dx.doi.org/10.1063/1.1290501 (5 pages) | Cited 1 time

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A trifilar all-fused silica pendulum with a Q factor exceeding 107 is described. This pendulum has been used to study the damping caused by an electric field applied between the suspended mass and a nearby electrode. Among the different loss mechanisms the most interesting one is associated with the surfaces of the electrodes. Application of a field of 106 V/m added an excess loss Qe−1 of at least 10−7. These results are important for laser interferometer gravitational wave detectors since electrostatic actuators are supposed to be used in order to precisely align the cavity mirrors. © 2000 American Institute of Physics.
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07.10.-h Mechanical instruments and equipment
46.40.Ff Resonance, damping, and dynamic stability
04.80.Nn Gravitational wave detectors and experiments

Computer monitoring and control of the GEO 600 gravitational wave detector

M. M. Casey, H. Ward, and D. I. Robertson

Rev. Sci. Instrum. 71, 3910 (2000); http://dx.doi.org/10.1063/1.1310352 (8 pages) | Cited 6 times

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The GEO 600 gravitational wave detector is at an advanced stage of construction at Ruthe, near Hannover in Northern Germany. Successful long-term stable operation of long-baseline interferometers like GEO 600 will critically depend on continuous monitoring and control of the very large number of interdependent feedback systems involved. We present here a description of the control infrastructure developed for this task for GEO 600. Our solution is based on a combination of purpose-built interfacing hardware, standard local area network-connected personal computers, and control software written using LabVIEW. The software techniques developed allow monitoring of all detector systems and also provide the mechanisms for manual and automated control both locally and from remote internet-connected sites. © 2000 American Institute of Physics.
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04.80.Nn Gravitational wave detectors and experiments
07.60.Ly Interferometers
07.05.Dz Control systems
07.07.Tw Servo and control equipment; robots
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