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Apr 2003

Volume 74, Issue 4, pp. 2255-2616

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back to top CONDENSED MATTER; MATERIALS

Combined rheometry and small-angle x-ray scattering

P. Panine, M. Gradzielski, and T. Narayanan

Rev. Sci. Instrum. 74, 2451 (2003); http://dx.doi.org/10.1063/1.1556943 (5 pages) | Cited 15 times

Online Publication Date: 26 March 2003

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We have developed an apparatus to simultaneously monitor rheological parameters with high-resolution small-angle x-ray scattering (SAXS). The device is based on a commercial rheometer coupled to concentric cylindrical shear flow geometry. The shear cell can be operated from 20 °C–180 °C without significant evaporation loss of the sample. The apparatus has wide ranging applications in the field of complex fluids such as colloidal suspensions, surfactant phases, liquid crystals, and polymer solutions. In addition, it allows performing SAXS in combination with a wide variety of rheological tests including simple shear flows, creep, recovery, as well as oscillatory deformation. The performance of the equipment is demonstrated through experiments involving shear-induced ordering of complex fluids. © 2003 American Institute of Physics.
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83.85.Hf X-ray and neutron scattering
61.05.cf X-ray scattering (including small-angle scattering)
83.50.Ax Steady shear flows, viscometric flow
83.85.Cg Rheological measurements—rheometry

Improving sensitivity of a small angle x-ray scattering camera with pinhole collimation using separated optical elements

Th. Zemb, O. Taché, F. Né, and O. Spalla

Rev. Sci. Instrum. 74, 2456 (2003); http://dx.doi.org/10.1063/1.1556954 (7 pages) | Cited 8 times

Online Publication Date: 26 March 2003

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We show that a significant improvement in the sensitivity of a Huxley–Holmes design for a small angle x-ray scattering camera is obtained by separating the mirror and the monochromator. The design of the camera involves a long x-ray mirror close to a point x-ray source associated with a curved focusing crystal located close to the sample. The sample area is located at half the distance between the source and detector planes. Diffuse scattering produced by the mirror is not incident on the focusing crystal, thus reducing the background signal. Complete elimination of hard x rays allows precise calibration and hence absolute determination of sample cross section by means of a semitransparent beam stop. In pinhole geometry, the flux corresponds to a ∼ 107 photons/s through the sample, collimated to 10−2 Å−1 in q range. This allows determination of scattered intensities on the order of 10−3 cm−1, corresponding to the scattering related to isothermal compressibility of less than 0.1 mm of pure water. As a reference sample, the widely used Lupolen™, a semicrystalline polymer, is calibrated. The high-q limit (q ≈ 4.5 nm−1) of a porous calcite sample can be used as a secondary standard for specific area determination of solid/solid or solid–liquid dispersions. © 2003 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ag Apertures, collimators

Neutron lens by superposition of glancing reflections

A. D. Stoica and X.-L. Wang

Rev. Sci. Instrum. 74, 2463 (2003); http://dx.doi.org/10.1063/1.1556946 (4 pages)

Online Publication Date: 26 March 2003

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A neutron lens can lead to substantial intensity gains in neutron scattering experiments by imaging a source directly onto the sample. A design is proposed for a compact neutron lens made of a stack of silicon wafers, each coated with a neutron-reflective supermirror on one side and a neutron-absorbing layer on the other. We show that for imaging, the length of each mirror is a function of its distance from the optical axis, y, following a simple 1/y relationship. Uniform bending of the mirror assembly decreases the spatial aberration. The optimal design to minimize the optical spatial aberrations is discussed and Monte Carlo simulation results are presented. © 2003 American Institute of Physics.
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41.85.-p Beam optics
42.79.Bh Lenses, prisms and mirrors

Magnetic susceptibility measurements at high pressure using designer diamond anvils

D. D. Jackson, C. Aracne-Ruddle, V. Malba, S. T. Weir, S. A. Catledge, and Y. K. Vohra

Rev. Sci. Instrum. 74, 2467 (2003); http://dx.doi.org/10.1063/1.1544084 (5 pages) | Cited 20 times

Online Publication Date: 26 March 2003

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High pressure magnetic susceptibility experiments can yield valuable insights into the changes in magnetic behavior and electron correlation properties which can accompany extreme compressions of matter. However, magnetic susceptibility experiments with ultrahigh pressure diamond anvil cells are extremely challenging due to the very small size of the high-pressure sample (≈75 μm diameter) and the difficulty of obtaining good coupling between the sample and the sensing coil. As a result, measurement sensitivity and poor signal-to-background ratios tend to be serious concerns which limit the applicability of these experiments. We present here a new approach to high-pressure ac magnetic susceptibility experiments that involve specially fabricated diamond anvils with diamond encapsulated sensing microcoils which are located just 10–20 μm from the high-pressure sample. We also present some test results taken with a gadolinium sample in order to demonstrate the viability of this high-pressure ac susceptibility technique. © 2003 American Institute of Physics.
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07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells

High-pressure spectroscopic measurement on diffusion with a diamond-anvil cell

K. Aoki, Eriko Katoh, H. Yamawaki, H. Fujihisa, and M. Sakashita

Rev. Sci. Instrum. 74, 2472 (2003); http://dx.doi.org/10.1063/1.1556955 (5 pages)

Online Publication Date: 26 March 2003

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We report a diamond-anvil-cell (DAC) technique developed for spectroscopic measurement on the diffusion process in molecular solids at high pressure. The diffusion processes of atoms, molecules, or their ionic species are investigated for a bilayer specimen by measuring the variation of infrared vibrational spectra with time. The experimental procedures for the protonic and molecular diffusion measurements on ice at 400 K and 10.2 GPa are presented as an example study. The in situ spectroscopic technique with a DAC significantly extends the pressure range accessible for diffusion measurement. The diffusion process at a rate of 10−16–10−14 m2/s can currently be observed at temperatures of 300–600 K and pressures up to several tens of gigaPascals. © 2003 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells

Torsion pendulum method to evaluate the internal friction and elastic modulus of films

Z. S. Li, Q. F. Fang, S. Veprek, and S. Z. Li

Rev. Sci. Instrum. 74, 2477 (2003); http://dx.doi.org/10.1063/1.1544079 (4 pages) | Cited 3 times

Online Publication Date: 26 March 2003

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The formulas for the evaluation of the internal friction and shear elastic modulus of a film deposited on a cylindrical substrate using the torsion pendulum method are derived in this article. The internal friction and the shear modulus of the film, especially their variation with temperature, can be easily deduced by measuring the internal friction and the resonance frequency of the pendulum with the bare substrate and with the composite, respectively. As an example, the shear modulus and the internal friction of a TiN/Ti(C,N) multilayer film deposited on a Mo wire are measured in the temperature range from room temperature to 400 °C. © 2003 American Institute of Physics.
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46.80.+j Measurement methods and techniques in continuum mechanics of solids
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
07.10.Pz Instruments for strain, force, and torque

Electronic sample-and-hold circuit to minimize artifacts during high-temperature Auger electron spectroscopy measurements

R. P. Henson, E. C. Viljoen, J. J. Terblans, and J. du Plessis

Rev. Sci. Instrum. 74, 2481 (2003); http://dx.doi.org/10.1063/1.1556974 (2 pages)

Online Publication Date: 26 March 2003

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The accurate control of sample temperature during Auger electron spectroscopy measurements was obtained in this laboratory using a pulsed heater current. This setup is favored instead of adjusting the dc level of the heater current not only because of its simplicity—it also provides the opportunity to measure the Auger signal during the “off” cycle, thus avoiding possible magnetic effects. The output of the lock-in-amplifier responds to this pulsed current as a differentiation circuit: It spikes on the positive and negative going edges. To eliminate this problem, a sample-and-hold circuit synchronized to the pulsed heating current frequency and a low-pass filter were inserted after the lock-in amplifier. © 2003 American Institute of Physics.
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07.81.+a Electron and ion spectrometers
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
07.20.Ka High-temperature instrumentation; pyrometers
07.68.+m Photography, photographic instruments; xerography

Development of an interactive molecular dynamics simulation software package

P. Knoll and S. Mirzaei

Rev. Sci. Instrum. 74, 2483 (2003); http://dx.doi.org/10.1063/1.1544419 (5 pages) | Cited 1 time

Online Publication Date: 26 March 2003

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Computer experiments play a significant role in science today. Molecular dynamic (MD) simulations are extremely powerful tools not only to understand and interpret the experiments at the microscopic level, but also to study regions that are not accessible experimentally. In the last few years interactive visualization of MD simulations has been proven invaluable while developing models and computational techniques. In this work a platform independent code for interactive MD simulations, which can be run either as a stand alone application or can be distributed by a master process among a number of workers by means of JavaSpaces, is presented. This approach is of interest because the parallel mode enables the user to perform serious research work, whereas the stand alone application can be used for educational purposes. The dynamical representation of the simulation is done with the Java3D application-programming interface, which makes it possible for the user to immediately visualize phenomena under study and therefore brings a new level of understanding to the work. © 2003 American Institute of Physics.
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07.05.Tp Computer modeling and simulation
02.70.Ns Molecular dynamics and particle methods
back to top CHEMISTRY

An ion beam reflectron/single-photon infrared emission spectrometer for the study of gas-phase polycyclic aromatic hydrocarbon ions: Testing proposed carriers of the unidentified infrared emission bands

Hack-Sung Kim and Richard J. Saykally

Rev. Sci. Instrum. 74, 2488 (2003); http://dx.doi.org/10.1063/1.1544418 (7 pages) | Cited 2 times

Online Publication Date: 26 March 2003

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We describe the design and performance of an electron-impact ion beam reflectron system coupled to our “single-photon infrared emission spectrometer” for measurement of infrared emission from excited gas-phase polycyclic aromatic hydrocarbon (PAH) cations. This experiment provides for direct comparison of laboratory infrared emission spectra of gaseous ionized PAHs with the “unidentified infrared emission bands,” the origin of which is still debated. © 2003 American Institute of Physics.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
41.75.Ak Positive-ion beams

Application of time-sliced ion velocity imaging to crossed molecular beam experiments

Jim J. Lin, Jingang Zhou, Weicheng Shiu, and Kopin Liu

Rev. Sci. Instrum. 74, 2495 (2003); http://dx.doi.org/10.1063/1.1561604 (6 pages) | Cited 107 times

Online Publication Date: 26 March 2003

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A three-dimensional (3D) ion velocity imaging method was developed to measure the product velocity distributions in crossed molecular beam experiments. While maintaining conventional two-dimension velocity mapping, the third velocity component was mapped linearly to the ion time of flight. A weak extraction field was used to spread the ion turnaround time to several hundred nanoseconds, which permits good resolution for selection of the longitudinal velocity. A fast gated (⩾5 ns) intensified charge coupled device camera was used to record time-sliced ion images. Calibration of the apparatus was done by measuring O+ images from the multiphoton dissociation/ionization of O2. The resolution in velocity achieved was about 1% (Δv/v) in slicing through the center of a Newton sphere. The overall performance was examined by observing product ion images from the F+CD4→DF+CD3 reaction. To detect CD3+ with kinetic energy release of about 1 eV, 50 ns time slicing provides sufficient velocity resolution, such that resolution of the image is mainly limited by the spread in velocity of the two molecular beams. These ion optics can focus on a large volume of ion cloud, which is crucial in crossed molecular beam experiments. Direct 3D imaging also simplifies data analysis. This direct 3D ion imaging method provides a powerful tool with which to study systems with no cylindrical symmetry. © 2003 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
41.85.-p Beam optics

Zetameter for microelectrophoresis studies of the oxide/water interface at temperatures up to 200 °C

X. Y. Zhou, X. J. Wei, M. V. Fedkin, K. H. Strass, and S. N. Lvov

Rev. Sci. Instrum. 74, 2501 (2003); http://dx.doi.org/10.1063/1.1556957 (6 pages) | Cited 7 times

Online Publication Date: 26 March 2003

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The zeta potential (ZP) is an important and measurable parameter related to the electrical double layer structure at a solid-aqueous solution interface. A high temperature zetameter based on the microelectrophoresis technique was developed to determine the zeta potential and the isoelectric point (IEP) of the metal oxide/water interfaces at temperatures up to 200 °C and pressures up to 50 bar. Design of the microelectrophoresis cell, the main unit of the zetameter, utilized a flow-through concept and the cell internals were made from corrosion resistant materials in order to minimize materials degradation and solution contamination. Two sapphire windows were installed to the microelectrophoresis cell to enable observation of the particle movement under an imposed electrical field. A ZrO2 powder was used to test the zetameter. The ZP for the ZrO2/water system was measured over wide ranges of temperature and pH. The IEP of the ZrO2/water system was found equal to 6.05 at room temperature, 5.00 at 120 °C, and 4.67 at 200 °C. Thus, at room temperature, the IEP obtained was within the confidence interval of the averaged literature data. In addition, it was found that the IEP of ZrO2 was sensitive to temperature and the difference between the IEP and 0.5pKw remained constant (1.00±0.2) with temperatures up to 200 °C. © 2003 American Institute of Physics.
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82.45.-h Electrochemistry and electrophoresis

Spark combustion reactor for 13-carbon isotope enrichment analysis of gases

Michael May, Michael Gray, John E. Kuo, and C. T. Tan

Rev. Sci. Instrum. 74, 2507 (2003); http://dx.doi.org/10.1063/1.1544089 (5 pages)

Online Publication Date: 26 March 2003

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A novel spark combustion reactor was designed, built, and utilized for quantitative 13-carbon isotope determination of highly enriched permanent gases. The analytical methodology developed is straightforward and begins by loading the reactor with hydrocarbon and oxygen using a steel gas manifold. High voltage is applied to the platinum electrode spark plug incorporated into the reactor, which rapidly converts hydrocarbon to carbon dioxide (and other products). Carbon dioxide species are then quantitated by quadrupole mass spectrometry. The primary reactor consists of a three-way stainless steel tee, plus the following components connected to threaded ports: (1) a platinum electrode spark plug sealed with a Viton O ring, (2) a steel gas storage cylinder, and (3) a manual bellows valve terminated with a VCO type connector. Making use of the spark combustion reactor, the 13-carbon fraction of highly enriched 13CH4 was measured to be ≥ 99.5 at. % 13C. This portable, static reactor permits determination of the 13C/12C isotope fraction for permanent gases utilizing mass spectrometric detection. The analytical system presented is relatively rapid (due to spark ignition), straightforward, and flexible (applicable to hydrocarbon gases using various gas detectors). Its limitation in performance for 13C isotope work is probably due to carbon embedded in the reactor interior. © 2003 American Institute of Physics.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
32.10.Bi Atomic masses, mass spectra, abundances, and isotopes
82.33.Vx Reactions in flames, combustion, and explosions
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Experimental procedure for fundamental studies of reinforcing steel corrosion processes

F. J. Martin and J. Olek

Rev. Sci. Instrum. 74, 2512 (2003); http://dx.doi.org/10.1063/1.1544082 (5 pages)

Online Publication Date: 26 March 2003

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An experimental procedure is presented for use in fundamental studies of reinforcing steel corrosion. An electrochemical corrosion cell is presented that incorporates a cement paste film cast against a polished section of reinforcing steel surface, while isolating other portions of the reinforcing steel surface from corrosion activity. The cement paste is prepared without admixed chlorides, then allowed to hydrate in a curing chamber for a period of three days prior to introduction of chlorides to the cell. The cell is transferred from a humid curing chamber to chloride solution exposure, where chlorides diffuse through the cement paste film to the steel surface and causes corrosion damage. This experimental procedure is well suited for detecting subtle changes in the passive state of reinforcing steel by either ac or dc electrochemistry. Ac impedance spectroscopy can also monitor the continuing hydration of cement paste. Chemical and microstructural analysis of the steel/cement paste interface is also possible upon disassembly of the cell. © 2003 American Institute of Physics.
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82.45.Bb Corrosion and passivation

Stray capacitance contribution to the electrical measurement of contact angles and areas

Anthony Quinn and Phil Attard

Rev. Sci. Instrum. 74, 2517 (2003); http://dx.doi.org/10.1063/1.1537046 (6 pages)

Online Publication Date: 26 March 2003

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The capacitance of two parallel disks of finite unequal size is calculated by a variational procedure based on the electrostatic energy. It is found that effects due to the edges and the asymmetry can be substantial unless the radii of the disks are very much greater than the thickness of the dielectric interlayer. The trends predicted by the calculations are confirmed by measurements of the capacitance of electrodes deposited on polymer films and of water droplets. The implications for the electrical measurement of the contact angle or contact area of a droplet, and for the dependence of the contact angle on the applied potential in electrowetting, are discussed. © 2003 American Institute of Physics.
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68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
02.30.Xx Calculus of variations

Pressure cell for time-resolved calorimetric measurements of photoinitiated reactions on the fractional millisecond and longer time scale

Gregory J. Edens, Yan Liu, Joseph Grzymski, and David Mauzerall

Rev. Sci. Instrum. 74, 2523 (2003); http://dx.doi.org/10.1063/1.1556950 (7 pages) | Cited 1 time

Online Publication Date: 26 March 2003

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Photoacoustics is an excellent method to obtain enthalpy and volume changes of photochemical reactions. It is particularly useful for photobiological or other reactions in water where the thermal and inherent volume changes can be separated by measurement at the temperature of maximum density. However, its time range is limited to less than ∼10 μs because the amplitude of the observed pressure wave is proportional to the rate of volume change. We describe a closed pressure cell which perfectly complements the usual photoacoustic methodology. It has a rise time of 20 μs and a thermal decay time of several seconds. Its single pulse sensitivity [signal/noise (S/N) = 1] is 10 pL or 15 μJ absorbed energy in water. The assembly and calibration of the instrument is described along with its verification by measurement of the enthalpy and volume change of the photodissociation of CO-myoglobin. The apparatus is eminently suited for the study of proton pumping in bacteriorhodopsin and oxygen formation in photosynthesis. © 2003 American Institute of Physics.
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07.20.Fw Calorimeters
82.50.-m Photochemistry
78.47.-p Spectroscopy of solid state dynamics
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Direct current slice imaging

Dave Townsend, Michael P. Minitti, and Arthur G. Suits

Rev. Sci. Instrum. 74, 2530 (2003); http://dx.doi.org/10.1063/1.1544053 (10 pages) | Cited 99 times

Online Publication Date: 26 March 2003

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We report a new variation of the velocity map ion imaging method that allows the central section of the photofragment ion cloud to be recorded exclusively. The relevant speed and angular distributions for a molecular photodissociation or scattering event may therefore be obtained without need to utilize inversion methods such as the inverse Abel transform. In contrast to the recently reported “slicing” technique of Kitsopoulos and co-workers [C. R. Gebhardt et al., Rev. Sci. Instrum. 72, 3848 (2001)], our method makes no use of grids or pulsed electric fields which can distort the photofragment cloud and therefore compromise the resolution of velocity mapping. We find that by operating a multilens velocity mapping assembly at low voltages, the ion cloud stretches in the acceleration region owing to the kinetic energy release in the fragments. Furthermore, this inherent stretching is sufficient to allow the central section of the distribution to be recorded exclusively by application of a narrow time gate (∼40 ns) to a position sensitive detector. We have performed extensive ion trajectory simulations to understand this “direct current (dc) slice imaging” technique, and experimentally we have applied it to the 355 nm dissociation of Cl2 and NO2 as well-understood test cases. In the Cl2 studies the velocity resolution obtained for the 35Cl fragments is on the order of Δν/ν=2.8% and for the first time we are able to directly observe dissociation via the weak B 3Π0u+ state channel whilst imaging the ground state Cl(2P3/2)-atom distribution. For the case of NO2 dissociation the internal state distributions of the NO fragment are extracted more cleanly using slicing than is possible with the Abel inversion and our resolution is sufficient to resolve some of the NO rotational structure in the kinetic energy release for the first time. Overall, we find our data to compare very favorably with previously reported results and conclude that dc slice imaging offers an important, easily implemented refinement to the velocity mapping approach. We also demonstrate a second dc slice imaging method that records only the central section of an expanded photofragment distribution by using a probe laser displaced off-axis from the molecular beam. This approach, which we term “raster imaging,” may be particularly advantageous in two-color experiments where the probe laser also makes a significant contribution to the initial photolysis of the molecular species under investigation. © 2003 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
back to top BIOLOGY and MEDICINE

Design of a compact synchrotron for medical applications

Nader Al Harbi and S. Y. Lee

Rev. Sci. Instrum. 74, 2540 (2003); http://dx.doi.org/10.1063/1.1561598 (6 pages) | Cited 1 time

Online Publication Date: 26 March 2003

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An optimal design of a low energy (300 MeV) proton synchrotron for medical applications is addressed. The machine has the following properties: (1) The transition energy is higher than the targets final proton beam energy of 300 MeV; (2) the betatron tunes are chosen such that the machine is free of systematic resonances; (3) the machine can accommodate both slow and fast extraction systems; and (4) the machine can provide rapid cycling operations depending on the rf cavity voltage. Applications of this low energy synchrotron are discussed. © 2003 American Institute of Physics.
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87.56.B- Radiation sources

Laser transfer of biomaterials: Matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE Direct Write

P. K. Wu, B. R. Ringeisen, D. B. Krizman, C. G. Frondoza, M. Brooks, D. M. Bubb, R. C. Y. Auyeung, A. Piqué, B. Spargo, R. A. McGill, and D. B. Chrisey

Rev. Sci. Instrum. 74, 2546 (2003); http://dx.doi.org/10.1063/1.1544081 (12 pages) | Cited 50 times

Online Publication Date: 26 March 2003

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Two techniques for transferring biomaterial using a pulsed laser beam were developed: matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE direct write (MDW). MAPLE is a large-area vacuum based technique suitable for coatings, i.e., antibiofouling, and MDW is a localized deposition technique capable of fast prototyping of devices, i.e., protein or tissue arrays. Both techniques have demonstrated the capability of transferring large (mol wt>100 kDa) molecules in different forms, e.g., liquid and gel, and preserving their functions. They can deposit patterned films with spatial accuracy and resolution of tens of μm and layering on a variety of substrate materials and geometries. MDW can dispense volumes less than 100 pl, transfer solid tissues, fabricate a complete device, and is computed aided design/computer aided manufacturing compatible. They are noncontact techniques and can be integrated with other sterile processes. These attributes are substantiated by films and arrays of biomaterials, e.g., polymers, enzymes, proteins, eucaryotic cells, and tissue, and a dopamine sensor. These examples, the instrumentation, basic mechanisms, a comparison with other techniques, and future developments are discussed. © 2003 American Institute of Physics.
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87.85.J- Biomaterials
81.15.Fg Pulsed laser ablation deposition
42.62.Be Biological and medical applications

Production of standardized air bubbles: Application to embolism studies

Peggy Palanchon, Jan Klein, and Nico de Jong

Rev. Sci. Instrum. 74, 2558 (2003); http://dx.doi.org/10.1063/1.1561596 (6 pages) | Cited 5 times

Online Publication Date: 26 March 2003

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Gaseous emboli may arise and enter into the circulation system during various clinical procedures. In order to better understand their immediate and long-term consequences, clinical investigations following the insertion of air bubbles into the body as well as new detection techniques need to be carried on. To this end, a device has been developed to generate a uniform stream of microbubbles with diameters ranging between 20 and 300 μm. This device comprises a glass micropipette connected to an air pressure source. The micropipette tip crosses a variable liquid flow and the bubbles produced are carried away by the flow. These bubbles have a very narrow size and density distribution: 90% of the bubbles lie within ±6% of the mean radius and the number of bubbles does not vary more than 10%. The size and density of the produced bubbles can be controlled by adjusting three independent parameters: the liquid flow, the gas pressure level, and the micropipette shape. For a given micropipette, increasing the liquid flow or decreasing the gas pressure level leads to a reduction of bubble size while the number of bubbles produced increases. As an example, doubling of the liquid flow results in a variation in bubble size up to 40%. This technique offers the advantage of generating uniform bubbles of known size and number depending on the settings selected. It appears to be a valuable tool for embolism studies such as the development of ultrasonic methods for detection of gaseous emboli. © 2003 American Institute of Physics.
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87.80.-y Biophysical techniques (research methods)
43.80.Qf Medical diagnosis with acoustics
back to top GRAVITY; GEOPHYSICS; ASTRONOMY and ASTROPHYSICS

A camera based position control of a suspended optical bench used in a gravitational wave detector

F. Beauville, D. Buskulic, R. Flaminio, F. Marion, A. Masserot, L. Massonnet, B. Mours, J. Ramonet, E. Tournefier, D. Verkindt, O. Veziant, and M. Yvert

Rev. Sci. Instrum. 74, 2564 (2003); http://dx.doi.org/10.1063/1.1561603 (6 pages) | Cited 1 time

Online Publication Date: 26 March 2003

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The VIRGO gravitational wave detector uses several optical benches suspended inside a large vacuum system. One of these benches is placed at the interferometer output port and it includes all of the optics required to collect and filter the interferometer dark fringe beam. The position of this bench is controlled with respect to ground by means of a charge coupled device camera and 400 light-emitting diodes placed outside the vacuum tank. The read-out sensitivity is a few 10−8 m/√Hz for the translations degrees of freedom and 10−7 rad/√Hz for the rotational degrees of freedom. Displacements as large as ±10 mm and rotations at the level of ±5 mrad can be measured. The feedback is based on a digital architecture and it has been fully tested at the VIRGO site. It is able to control all the six degrees of freedom of the bench with a precision better than 1 μm for the translations and 0.5 μrad for all the rotations. © 2003 American Institute of Physics.
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04.80.Nn Gravitational wave detectors and experiments
95.55.Ym Gravitational radiation detectors; mass spectrometers; and other instrumentation and techniques
42.79.Pw Imaging detectors and sensors
07.05.Dz Control systems
07.60.Ly Interferometers

Adaptive optics approach for prefiltering of geometrical fluctuations of the input laser beam of an interferometric gravitational waves detector

E. Calloni, J. T. Baker, F. Barone, R. DeRosa, L. Di Fiore, L. Milano, and S. R. Restaino

Rev. Sci. Instrum. 74, 2570 (2003); http://dx.doi.org/10.1063/1.1537043 (5 pages) | Cited 5 times

Online Publication Date: 26 March 2003

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In this article we present a preliminary study and experimental results on the use of an adaptive optics (AO) system for the reduction of geometrical fluctuations in a laser beam. The AO system is based on a Shack–Hartmann wave front sensor and a micromachined deformable mirror as a corrective element. The aim of this work is to investigate the applicability of such technologies to improving wave front clean-up conditions in long baseline interferometric gravitational wave detection. © 2003 American Institute of Physics.
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04.80.Nn Gravitational wave detectors and experiments
07.60.Ly Interferometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.79.Bh Lenses, prisms and mirrors
back to top THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL and PHOTOACOUSTIC

Design of an experimental setup to achieve sinusoidal temperature oscillation in ultrahigh vacuum

F. Pesty and P. Garoche

Rev. Sci. Instrum. 74, 2575 (2003); http://dx.doi.org/10.1063/1.1544420 (5 pages) | Cited 2 times

Online Publication Date: 26 March 2003

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We designed an experimental setup to produce a temperature oscillation at the surface of a sample, in ultrahigh vacuum. The heating device, a tungsten wire, uses infrared radiation to heat the sample. A regular sine wave cannot produce a harmonic power oscillation, due to the nonlinear character of the Stefan–Boltzmann law of radiation. To achieve it we generate a complex wave form to take into account the thermal behavior of the heating filament as well as its electronic transport properties. An example of temperature oscillation is shown in the case of a tantalum sample, at a 0.12 Hz frequency. It exhibits harmonic behavior with an oscillation amplitude of about 1 K. This method opens the field to new experiments in surface science, to study reversible surface phase transitions. © 2003 American Institute of Physics.
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07.20.Hy Furnaces; heaters
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Recent work in shape-based methods for diffusive inverse problems

Gregory Boverman, Mohamed Khames ben Hadj Miled, and Eric L. Miller

Rev. Sci. Instrum. 74, 2580 (2003); http://dx.doi.org/10.1063/1.1517183 (3 pages) | Cited 3 times

Online Publication Date: 26 March 2003

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We consider geometric inversion methods designed to directly determine information concerning the size, shape, location, and perhaps number of anomalies in a region of interest [E. L. Miller, M. E. Kilmer, and C. M. Rappaport, IEEE Trans. Geosci. Remote Sens. 38, 1682 (2000); O. Dorn, E. L. Miller, and C. Rappaport, Inverse Probl. 16, 1119 (2000)] for diffusive inverse problems arising in medical imaging and environmental remediation. First, a parametric approach to the problem is derived and validated using a diffuse optical tomography sensing example. A second technique to identify boundaries of an unknown number of objects is based on the idea of curve evolution. This approach mathematically “shrink wraps” a deformable surface in 3D or curve in 2D to the boundary of one or more objects. We demonstrate the utility of this method using an electrical resistance tomography sensing example in three dimensions. © 2003 American Institute of Physics.
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87.63.L- Visual imaging
93.85.Bc Computational methods and data processing, data acquisition and storage
02.30.Zz Inverse problems
42.30.Wb Image reconstruction; tomography
87.57.N- Image analysis
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Real-time wavelet-transform spectrum analyzer for the investigation of 1/fα noise

Doriano Brogioli and Alberto Vailati

Rev. Sci. Instrum. 74, 2583 (2003); http://dx.doi.org/10.1063/1.1556945 (10 pages) | Cited 3 times

Online Publication Date: 26 March 2003

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A wavelet-transform spectrum analyzer operating in real time within the frequency range 3×10−5–1.3×105 Hz has been implemented on a low-cost digital signal processing (DSP) board operating at 150 MHz. The wavelet decomposition of the signal allows one to efficiently process nonstationary signals dominated by large amplitude events fairly well localized in time, thus providing the natural tool to analyze processes characterized by 1/fα power spectrum. The parallel architecture of the DSP allows the real-time processing of the wavelet transform of the signal sampled at 0.3 MHz. The bandwidth is about 220 dB, almost 10 decades. The power spectrum of the signal is processed in real time from the mean square value of the wavelet coefficients within each frequency band. The performances of the spectrum analyzer have been investigated by performing dynamic light scattering experiments on colloidal suspensions and by comparing the measured spectra with the correlation functions data obtained with a traditional multitau correlator. In order to assess the potentialities of the spectrum analyzer in the investigation of processes involving a wide range of time scales, we have performed measurements on a model system where fluctuations in the scattered intensities are generated by the number fluctuations in a dilute colloidal suspension illuminated by a wide beam. This system is characterized by a power-law spectrum with exponent −3/2 in the scattered intensity fluctuations. The spectrum analyzer allows one to recover the power spectrum with a dynamic range spanning about 8 decades. The advantages of wavelet analysis versus correlation analysis in the investigation of processes characterized by a wide distribution of time scales and nonstationary processes are briefly discussed. © 2003 American Institute of Physics.
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07.68.+m Photography, photographic instruments; xerography
02.30.Uu Integral transforms
82.70.Dd Colloids
42.25.Fx Diffraction and scattering
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids

OPL-3D: A novel, portable optical digitizer for fast acquisition of free-form surfaces

Giovanna Sansoni, Alessandro Patrioli, and Franco Docchio

Rev. Sci. Instrum. 74, 2593 (2003); http://dx.doi.org/10.1063/1.1561602 (11 pages) | Cited 9 times

Online Publication Date: 26 March 2003

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The paper presents OPL-3D, a novel, powerful three-dimensional optical digitizer based on structured, incoherent light illumination, developed in our laboratory for noncontact acquisition and digitization of free forms in space. The system exploits active stereovision using time multiplexing based on a combination of Gray code and phase-shifting techniques. The system has been specifically designed for applications to reverse engineering and rapid prototyping of free-form shapes, as well as for applications to measurement and quality control. Suitable estimation of the measurement parameters, as well as specifically developed two-dimensional image analysis, allows us to retrieve very dense point clouds in a few seconds. Special care has been devoted to the implementation of easy-to-use fast calibration procedures, and to enhancement of the flexibility of the system to the measuring problem as well as its portability. A kernel for elaboration of the views and for their alignment is provided. OPL-3D exhibits low-measurement uncertainty (120 μm) over large measurement areas (450 mm×340 mm), linearly scalable in the case of smaller areas. The output formats of the data files are fully compatible with the formats commonly used by elaboration environments dedicated to the production of polygonal models and to computer-aided design models of the shapes. The performance of OPL-3D has been tested in a number of applications, ranging from industry to biomedicine and virtual reality. © 2003 American Institute of Physics.
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42.79.Ls Scanners, image intensifiers, and image converters
42.30.-d Imaging and optical processing
07.05.Hd Data acquisition: hardware and software
06.20.F- Units and standards
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