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Sep 2007

Volume 78, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 78, 091301 (2007); http://dx.doi.org/10.1063/1.2783112 (11 pages)

Jean-Claude Labiche, Olivier Mathon, Sakura Pascarelli, Mark A. Newton, Gemma Guilera Ferre, Caroline Curfs, Gavin Vaughan, Alejandro Homs, and David Fernandez Carreiras
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Invited article: The fast readout low noise camera as a versatile x-ray detector for time resolved dispersive extended x-ray absorption fine structure and diffraction studies of dynamic problems in materials science, chemistry, and catalysis

Jean-Claude Labiche, Olivier Mathon, Sakura Pascarelli, Mark A. Newton, Gemma Guilera Ferre, Caroline Curfs, Gavin Vaughan, Alejandro Homs, and David Fernandez Carreiras

Rev. Sci. Instrum. 78, 091301 (2007); http://dx.doi.org/10.1063/1.2783112 (11 pages) | Cited 98 times

Online Publication Date: 17 September 2007

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Originally conceived and developed at the European Synchrotron Radiation Facility (ESRF) as an “area” detector for rapid x-ray imaging studies, the fast readout low noise (FReLoN) detector of the ESRF [ J.-C. Labiche, ESRF Newsletter 25, 41 (1996) ] has been demonstrated to be a highly versatile and unique detector. Charge coupled device (CCD) cameras at present available on the public market offer either a high dynamic range or a high readout speed. A compromise between signal dynamic range and readout speed is always sought. The parameters of the commercial cameras can sometimes be tuned, in order to better fulfill the needs of specific experiments, but in general these cameras have a poor duty cycle (i.e., the signal integration time is much smaller than the readout time). In order to address scientific problems such as time resolved experiments at the ESRF, a FReLoN camera has been developed by the Instrument Support Group at ESRF. This camera is a low noise CCD camera that combines high dynamic range, high readout speed, accuracy, and improved duty cycle in a single image. In this paper, we show its application in a quasi-one-dimensional sense to dynamic problems in materials science, catalysis, and chemistry that require data acquisition on a time scale of milliseconds or a few tens of milliseconds. It is demonstrated that in this mode the FReLoN can be applied equally to the investigation of rapid changes in long range order (via diffraction) and local order (via energy dispersive extended x-ray absorption fine structure) and in situations of x-ray hardness and flux beyond the capacity of other detectors.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Pw Imaging detectors and sensors
78.47.-p Spectroscopy of solid state dynamics
78.70.Dm X-ray absorption spectra
61.05.cp X-ray diffraction
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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Scanning optical pyrometer for measuring temperatures in hollow cathodes

J. E. Polk, C. M. Marrese-Reading, B. Thornber, L. Dang, L. K. Johnson, and I. Katz

Rev. Sci. Instrum. 78, 093101 (2007); http://dx.doi.org/10.1063/1.2774828 (8 pages)

Online Publication Date: 10 September 2007

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Life-limiting processes in hollow cathodes are determined largely by the temperature of the electron emitter. To support cathode life assessment, a noncontact temperature measurement technique which employs a stepper motor-driven fiber optic probe was developed. The probe is driven inside the hollow cathode and collects light radiated by the hot interior surface of the emitter. Ratio pyrometry is used to determine the axial temperature profile. Thermocouples on the orifice plate provide measurements of the external temperature during cathode operation and are used to calibrate the pyrometer system in situ with a small oven enclosing the externally heated cathode. The diagnostic method and initial measurements of the temperature distribution in a hollow cathode are discussed.
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07.20.Ka High-temperature instrumentation; pyrometers
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.20.Dt Thermometers
07.60.Vg Fiber-optic instruments
84.47.+w Vacuum tubes
06.20.fb Standards and calibration

Relative detection efficiency of back- and front-illuminated charge-coupled device cameras for x-rays between 1 keV and 18 keV

J. Szlachetko, J.-Cl. Dousse, J. Hoszowska, M. Berset, W. Cao, M. Szlachetko, and M. Kavčič

Rev. Sci. Instrum. 78, 093102 (2007); http://dx.doi.org/10.1063/1.2779214 (11 pages) | Cited 5 times

Online Publication Date: 10 September 2007

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High-resolution x-ray measurements were performed with a von Hamos-type bent crystal spectrometer using for the detection of the diffracted photons either a back-illuminated charge-coupled device (CCD) camera or a front-illuminated one. For each CCD the main x-ray emission lines (e.g., Kα, Kβ, Lα, and Lβ) of a variety of elements were measured in order to probe the performances of the two detectors between 1 and 18 keV. From the observed x-ray lines the linearity of the energy response, the noise level, the energy resolution, and the quantum efficiency ratio of the two CCDs were determined.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Vacuum electron acceleration and bunch compression by a flat-top laser beam

W. Wang, P. X. Wang, Y. K. Ho, Q. Kong, Y. Gu, and S. J. Wang

Rev. Sci. Instrum. 78, 093103 (2007); http://dx.doi.org/10.1063/1.2780816 (5 pages) | Cited 1 time

Online Publication Date: 10 September 2007

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The field intensity distribution and phase velocity characteristics of a flat-top laser beam are analyzed and discussed. The dynamics of electron acceleration in this kind of beam are investigated using three-dimensional test particle simulations. Compared with the standard (i.e., TEM00 mode) Gaussian beam, a flat-top laser beam has a stronger longitudinal electric field and a larger diffraction angle. These characteristics make it easier for electrons to be trapped and accelerated by the beam. With a flat-top shape, the laser beam is also applicable to the acceleration of low energy electron and bunch compression.
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41.75.Jv Laser-driven acceleration
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Fringe counting method for synthetic phase with frequency-modulated laser diodes

Ribun Onodera, Munechika Sakuyama, and Yukihiro Ishii

Rev. Sci. Instrum. 78, 093104 (2007); http://dx.doi.org/10.1063/1.2778628 (6 pages) | Cited 1 time

Online Publication Date: 19 September 2007

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Fringe counting method with laser diodes (LDs) for displacement measurement has been constructed. Two LDs are frequency modulated by mutually inverted sawtooth currents on an unbalanced two-beam interferometer. The mutually inverted sawtooth-current modulation of LDs produces interference fringe signals with opposite signs for respective wavelengths. The two fringe signals are fed to an electronic mixer to produce a synthetic fringe signal with a reduced sensitivity to the synthetic wavelength. Synthetic fringe pulses derived from the synthetic fringe signal make a fringe counting system possible for faster movement of the tested mirror.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly Interferometers
42.55.Px Semiconductor lasers; laser diodes

Precision thickness and refractive index imaging of molecular films

T. E. Balmer and M. Heuberger

Rev. Sci. Instrum. 78, 093105 (2007); http://dx.doi.org/10.1063/1.2777369 (10 pages) | Cited 3 times

Online Publication Date: 20 September 2007

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We present an interferometric contrasting technique that allows visualizing the thickness and refractive index of a molecular film being part of an optical multilayer structure (etalon). Small wavelength shifts of the comblike etalon spectrum are transformed into measurable intensity variations using a second reference etalon (optical correlator), illuminated in series. A charge-coupled device camera acting as two-dimensional photometer is utilized to measure the optical spectral correlation (OSC) image. The performance of the here proposed optical spectral correlation method is demonstrated using very thin confined liquid films. We give a detailed signal-to-noise analysis. Subangstrom film thickness resolution is experimentally verified with single exposure images acquired at frame rates comparable to video standards ( ∼ 25 Hz). Finally, we describe the calibration procedures necessary to obtain an absolute quantification of the OSC image.
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42.79.Wc Optical coatings
42.25.Gy Edge and boundary effects; reflection and refraction
42.30.-d Imaging and optical processing
68.15.+e Liquid thin films
07.60.Ly Interferometers

A heated vapor cell unit for dichroic atomic vapor laser lock in atomic rubidium

Daniel J. McCarron, Ifan G. Hughes, Patrick Tierney, and Simon L. Cornish

Rev. Sci. Instrum. 78, 093106 (2007); http://dx.doi.org/10.1063/1.2785157 (5 pages) | Cited 11 times

Online Publication Date: 26 September 2007

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The design and performance of a compact heated vapor cell unit for realizing a dichroic atomic vapor laser lock (DAVLL) for the D2 transitions in atomic rubidium is described. A 5 cm long vapor cell is placed in a double-solenoid arrangement to produce the required magnetic field; the heat from the solenoid is used to increase the vapor pressure and correspondingly the DAVLL signal. We have characterized experimentally the dependence of important features of the DAVLL signal on magnetic field and cell temperature. For the weaker transitions both the amplitude and gradient of the signal are increased by an order of magnitude.
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03.75.Pp Atom lasers
32.60.+i Zeeman and Stark effects
42.60.Fc Modulation, tuning, and mode locking
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Continuous measurements of bronchial exposure induced by radon decay products during inhalation

Kazuki Iwaoka, Shinji Tokonami, Hidenori Yonehara, Tetsuo Ishikawa, Masahiro Doi, Yosuke Kobayashi, Yoshinori Yatabe, Hiroyuki Takahashi, and Yuji Yamada

Rev. Sci. Instrum. 78, 093301 (2007); http://dx.doi.org/10.1063/1.2786270 (4 pages)

Online Publication Date: 24 September 2007

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The deposition of radon decay products is not equal in each of the respiratory regions and as the presence of radon has been linked with an increase in lung cancer risk, it is important to calculate the deposition of radon decay products in each of the respiratory regions. Recently, many studies on the deposition of radon in respiratory regions have been simulated using wire screens. The systems and equipment used in those studies are not suitable for field measurements as their dimensions are relatively massive, nor can they measure continuously. We developed a continuous bronchial dosimeter (CBD) which is suitable for field measurements. It was designed with specifications that allow it to be remain compact. The CBD simulates the deposition of radon decay products in the different respiratory regions by the use of a combination of wire screens. Deposition in the simulated regions of the lung can be continuously estimated in various environments. The ratio of activities deposited in a simulated nasal cavity (N) and tracheobronchial (TB) regions was calculated from the results of simultaneous measurements using CBD-R (reference), CBD-N (nasal), and CBD-TB (tracheobronchial) measurement units. After aerosols were injected into the radon chamber, the ratio of N and TB depositions decreased. This results indicate that the CBD gave a good response to changes in the environment. It was found that the ratio of N and TB deposition also varied with time in each actual environment.
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87.56.Da Ancillary equipment
87.55.N- Radiation monitoring, control, and safety
89.60.Ec Environmental safety
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Poloidal beta and internal inductance measurement on HT-7 superconducting tokamak

B. Shen, Y. W. Sun, B. N. Wan, and J. P. Qian

Rev. Sci. Instrum. 78, 093501 (2007); http://dx.doi.org/10.1063/1.2779213 (6 pages) | Cited 1 time

Online Publication Date: 7 September 2007

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Poloidal beta βθ and internal inductance li measurements are very important for tokamak operation. Much more plasma parameters can be inferred from the two parameters, such as the plasma energy confinement time, the plasma toroidal current profile, and magnetohydrodynamics instability. Using diamagnetic and compensation loop, combining with poloidal magnetic probe array signals, poloidal beta βθ and internal inductance li are measured. In this article, the measurement system and arithmetic are introduced. Different experimental results are given in different plasma discharges on HT-7 superconducting tokamak.
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52.70.Ds Electric and magnetic measurements
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
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Novel approach to Abel inversion

R. K. Paul

Rev. Sci. Instrum. 78, 093701 (2007); http://dx.doi.org/10.1063/1.2777159 (5 pages) | Cited 3 times

Online Publication Date: 4 September 2007

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Simple yet versatile, physically valid emissivity functions for peaked and hollow profiles with only two determinable parameters are proposed for performing Abel inversion. The advantages of the proposed functions have been explored. The inversion is very fast, accurate, convenient, and viable, in contrast to the existing methods. The validation of these functions has been confirmed by using simulated data under various conditions. The error in the process has been computed and found to depend on the functional form of the model emissivity. A comprehensive comparison has been drawn with the existing method and it has been found to offer a definite advantage over the existing technique in some respects, especially for real time applications. Limitation of this technique has also been discussed. The soft x-ray and visible light emissivity profile of SINP tokamak has been successfully obtained by using this method.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.55.Fa Tokamaks, spherical tokamaks
02.30.Rz Integral equations

Comparison of different methods to calibrate torsional spring constant and photodetector for atomic force microscopy friction measurements in air and liquid

Torbjörn Pettersson, Niklas Nordgren, Mark W. Rutland, and Adam Feiler

Rev. Sci. Instrum. 78, 093702 (2007); http://dx.doi.org/10.1063/1.2779215 (8 pages) | Cited 24 times

Online Publication Date: 5 September 2007

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A number of atomic force microscopy cantilevers have been exhaustively calibrated by a number of techniques to obtain both normal and frictional force constants to evaluate the relative accuracy of the different methods. These were of either direct or indirect character—the latter relies on cantilever resonant frequencies. The so-called Sader [Rev. Sci. Instrum. 70, 3967 (1999) ] and Cleveland [Rev. Sci. Instrum. 64, 403 (1993) ] techniques are compared for the normal force constant calibration and while agreement was good, a systematic difference was observed. For the torsional force constants, all the techniques displayed a certain scatter but the agreement was highly encouraging. By far the simplest technique is that of Sader, and it is suggested in view of this validation that this method should be generally adopted. The issue of the photodetector calibration is also addressed since this is necessary to obtain the cantilever twist from which the torsional force is calculated. Here a technique of obtaining the torsional photodetector sensitivity by combining the direct and indirect methods is proposed. Direct calibration measurements were conducted in liquid as well as air, and a conversion factor was obtained showing that quantitative friction measurements in liquid are equally feasible provided the correct calibration is performed.
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07.79.Lh Atomic force microscopes
07.10.Pz Instruments for strain, force, and torque
06.20.fb Standards and calibration

Simple fiber-optic confocal microscopy with nanoscale depth resolution beyond the diffraction barrier

Ilko Ilev, Ronald Waynant, Israel Gannot, and Amir Gandjbakhche

Rev. Sci. Instrum. 78, 093703 (2007); http://dx.doi.org/10.1063/1.2777173 (4 pages) | Cited 6 times

Online Publication Date: 19 September 2007

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A novel fiber-optic confocal approach for ultrahigh depth-resolution ( ⩽ 2 nm) microscopy beyond the diffraction barrier in the subwavelength nanometric range below 200 nm is presented. The key idea is based on a simple fiber-optic confocal microscope approach that is compatible with a differential confocal microscope technique. To improve the dynamic range of the resolving laser power and to achieve a high resolution in the nanometric range, we have designed a simple apertureless reflection confocal microscope with a highly sensitive single-mode-fiber confocal output. The fiber-optic design is an effective alternative to conventional pinhole-based confocal systems and offers a number of advantages in terms of spatial resolution, flexibility, miniaturization, and scanning potential. Furthermore, the design is compatible with the differential confocal pinhole microscope based on the use of the sharp diffraction-free slope of the axial confocal response curve rather than the area around the maximum of that curve. Combining the advantages of ultrahigh-resolution fiber-optic confocal microscopy, we can work beyond the diffraction barrier in the subwavelength (below 200 nm) nanometric range exploiting confocal nanobioimaging of single cell and intracellular analytes.
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42.81.Wg Other fiber-optical devices
07.60.Pb Conventional optical microscopes
42.15.Eq Optical system design
87.64.mk Confocal
87.80.-y Biophysical techniques (research methods)
87.17.-d Cell processes

Atomic force microscopy of protein films and crystals

Eugenia Pechkova, Marco Sartore, Luca Giacomelli, and Claudio Nicolini

Rev. Sci. Instrum. 78, 093704 (2007); http://dx.doi.org/10.1063/1.2785032 (7 pages) | Cited 1 time

Online Publication Date: 21 September 2007

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A customized atomic force microscopy (AFM) instrument optimized for imaging protein crystals in solution is described. The device was tested on crystals and Langmuir-Blodgett (LB) films of two proteins with quite different molecular weights. This approach enables the periodicity and morphology of crystals to be studied in their mother liquid, thereby preserving the native periodic protein crystal structure, which is typically destroyed by drying. Moreover, the instrument appears to distinguish protein crystals from salt crystals, which under the optical microscope are frequently quite similar, the difference between them often being revealed only during x-ray analysis. AFM estimates of the packing, order, and morphology of the given single proteins appear quite similar in the LB thin film and in the crystals, which means that routine crystal measurements can be performed at high resolution. The AFM consists of a custom-built measuring head and a homemade flexible SPM controller which can drive the head for contact, noncontact and spectroscopy modes, thus providing the user with a high degree of customization for crystal measurement.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
87.15.B- Structure of biomolecules
87.14.E- Proteins
36.20.Hb Configuration (bonds, dimensions)
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Spring constant calibration of atomic force microscopy cantilevers with a piezosensor transfer standard

E. D. Langlois, G. A. Shaw, J. A. Kramar, J. R. Pratt, and D. C. Hurley

Rev. Sci. Instrum. 78, 093705 (2007); http://dx.doi.org/10.1063/1.2785413 (10 pages) | Cited 21 times

Online Publication Date: 24 September 2007

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We describe a method to calibrate the spring constants of cantilevers for atomic force microscopy (AFM). The method makes use of a “piezosensor” composed of a piezoresistive cantilever and accompanying electronics. The piezosensor was calibrated before use with an absolute force standard, the NIST electrostatic force balance (EFB). In this way, the piezosensor acts as a force transfer standard traceable to the International System of Units. Seven single-crystal silicon cantilevers with rectangular geometries and nominal spring constants from 0.2 to 40 N/m were measured with the piezosensor method. The values obtained for the spring constant were compared to measurements by four other techniques: the thermal noise method, the Sader method, force loading by a calibrated nanoindentation load cell, and direct calibration by force loading with the EFB. Results from different methods for the same cantilever were generally in agreement, but differed by up to 300% from nominal values. When used properly, the piezosensor approach provides spring-constant values that are accurate to ±10% or better. Methods such as this will improve the ability to extract quantitative information from AFM methods.
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89.20.Kk Engineering
06.20.fb Standards and calibration
46.32.+x Static buckling and instability

Control of tip-to-sample distance in atomic force microscopy: A dual-actuator tip-motion control scheme

Younkoo Jeong, G. R. Jayanth, and Chia-Hsiang Menq

Rev. Sci. Instrum. 78, 093706 (2007); http://dx.doi.org/10.1063/1.2785158 (7 pages) | Cited 6 times

Online Publication Date: 26 September 2007

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The control of tip-to-sample distance in atomic force microscopy (AFM) is achieved through controlling the vertical tip position of the AFM cantilever. In the vertical tip-position control, the required z motion is commanded by laser reading of the vertical tip position in real time and might contain high frequency components depending on the lateral scanning rate and topographical variations of the sample. This paper presents a dual-actuator tip-motion control scheme that enables the AFM tip to track abrupt topographical variations. In the dual-actuator scheme, an additional magnetic mode actuator is employed to achieve high bandwidth tip-motion control while the regular z scanner provides the necessary motion range. This added actuator serves to make the entire cantilever bandwidth available for tip positioning, and thus controls the tip-to-sample distance. A fast programmable electronics board was employed to realize the proposed dual-actuator control scheme, in which model cancellation algorithms were implemented to enlarge the bandwidth of the magnetic actuation and to compensate the lightly damped dynamics of the cantilever. Experiments were conducted to illustrate the capabilities of the proposed dual-actuator tip-motion control in terms of response speed and travel range. It was shown that while the bandwidth of the regular z scanner was merely a small fraction of the cantilever’s bandwidth, the dual-actuator control scheme led to a tip-motion control system, the bandwidth of which was comparable to that of the cantilever, where the dynamics overdamped, and the motion range comparable to that of the z scanner.
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07.79.Lh Atomic force microscopes

Inspection of refractive x-ray lenses using high-resolution differential phase contrast imaging with a microfocus x-ray source

Martin Engelhardt, Joachim Baumann, Manfred Schuster, Christian Kottler, Franz Pfeiffer, Oliver Bunk, and Christian David

Rev. Sci. Instrum. 78, 093707 (2007); http://dx.doi.org/10.1063/1.2786273 (5 pages) | Cited 7 times

Online Publication Date: 26 September 2007

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A refractive x-ray lens was characterized using a magnifying cone beam setup for differential phase contrast imaging in combination with a microfocus x-ray tube. Thereby, the differential and the total phase shift of x rays transmitted through the lens were determined. Lens aberrations have been characterized based on these refractive properties.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.87.-d Optical testing techniques
42.79.Bh Lenses, prisms and mirrors
42.15.Fr Aberrations
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Soft x-ray coherent scattering: Instrument and methods at ESRF ID08

Guillaume Beutier, Alain Marty, Frédéric Livet, Gerrit van der Laan, Stefan Stanescu, and Peter Bencok

Rev. Sci. Instrum. 78, 093901 (2007); http://dx.doi.org/10.1063/1.2779218 (11 pages) | Cited 10 times

Online Publication Date: 6 September 2007

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An experimental setup has been developed to perform soft x-ray coherent scattering at beamline ID08 of the European Synchrotron Radiation Facility. An intense coherent beam was obtained by filtering the primary beam with the monochromator and a circular pinhole. A pinhole holder with motorized translations was installed inside the UHV chamber of the diffractometer. The scattered intensity was recorded in reflection geometry with a back-illuminated charge coupled device camera. As a demonstration we report experimental results of resonant magnetic scattering using coherent beam. The degree of coherence is evaluated, and it is shown that, while the vertical coherence is much higher than the horizontal one at the source, the situation is reversed at the diffractometer. The intensity of the coherent beam is also discussed.
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07.85.-m X- and γ-ray instruments

Three dimensional drop tracking flow chamber for coalescence studies

Anne M. Grillet, Carlton F. Brooks, Chris J. Bourdon, and Allen D. Gorby

Rev. Sci. Instrum. 78, 093902 (2007); http://dx.doi.org/10.1063/1.2780160 (5 pages) | Cited 1 time

Online Publication Date: 12 September 2007

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We have developed a novel flow chamber which imposes a controlled axisymmetric stagnation flow to enable the study of external flow effects on coalescence dynamics. This system allows for the first time the precise positioning of a drop in a three dimensional flow and additionally enforces a highly symmetric flow around the drop. We focus on the study of a single drop approaching a stationary flat plane as this is analogous to two drops approaching each other. A single drop is created and then guided along the unsteady center line of a stagnation flow. The real time computer control algorithm analyzes video images of the drop in two orthogonal planes and manipulates flow restricting valves along the four outlets of the flow. We demonstrate using particle image velocimetry that the computer control not only controls the drop position but also ensures a symmetric flow inside the flow chamber. This chamber will enable a detailed investigation of the drainage of the thin film between the drop and the lower surface in order to probe the effect of external flow on coalescence.
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47.85.L- Flow control
47.80.Cb Velocity measurements

Simple adaptation of the Bridgman high pressure technique for use with liquid media

E. Colombier and D. Braithwaite

Rev. Sci. Instrum. 78, 093903 (2007); http://dx.doi.org/10.1063/1.2778629 (5 pages) | Cited 8 times

Online Publication Date: 19 September 2007

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We present a simple novel technique to adapt a standard Bridgman cell for the use of a liquid pressure transmitting medium. The technique has been implemented in a compact cell, able to fit in a commercial Quantum Design PPMS system, and would also be easily adaptable to extreme conditions of very low temperatures or high magnetic fields. Several media have been tested and a mix of fluorinert FC84:FC87 has been shown to produce a considerable improvement over the pressure conditions in the standard steatite solid medium, while allowing a relatively easy setup procedure. For optimized hydrostatic conditions, the success rate is about 80% and the maximum pressure achieved so far is 7.1 GPa. Results are shown for the heavy fermion system YbAl3 and for NaV6O15, an insulator showing charge order.
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07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
62.50.-p High-pressure effects in solids and liquids

Characterization of thermoelectric elements and devices by impedance spectroscopy

Adam D. Downey, Timothy P. Hogan, and Bruce Cook

Rev. Sci. Instrum. 78, 093904 (2007); http://dx.doi.org/10.1063/1.2775432 (12 pages) | Cited 2 times

Online Publication Date: 20 September 2007

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This article describes a new measurement technique that utilizes impedance spectroscopy for the characterization of thermoelectric materials and devices. Two circuit models were developed and used to help explain the impedance spectroscopy data using transmission line theory and a coupled electrothermal model. Two testing configurations have been investigated including one based on a sinusoidal source (ac lock-in technique) and one based on a pulsed wave source. Methods for reducing the measurement times for this technique are discussed. In addition, the influence of radiation losses on this measurement technique has also been analyzed to further understand the limitations of this technique at higher temperatures.
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85.80.Fi Thermoelectric devices
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.30.Ka Basic electromagnetic quantities

Experimental technique for reducing contact and background noise in voltage spectral density measurements

C. Barone, A. Galdi, S. Pagano, O. Quaranta, L. Méchin, J.-M. Routoure, and P. Perna

Rev. Sci. Instrum. 78, 093905 (2007); http://dx.doi.org/10.1063/1.2786271 (6 pages) | Cited 8 times

Online Publication Date: 26 September 2007

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Electric noise measurements can give useful information on the conduction mechanisms and the dynamic behaviors of the charge carriers in new materials. However, it is well known that not all the electronic fluctuations are originated from the material itself, but some noise sources depend on the experimental procedures used for the measurements. In this article, an experimental technique to reduce “external” noise components, not associated with the bulk system, is presented. The proposed method is based on measurements of the voltage spectral density, using in sequence a four- and a two-probe technique. From the measurements it is possible to evaluate the contact and the background noise contributions and to recover the real spectral trace of the sample. The proposed procedure is demonstrated to be valid in spectral density measurements performed on La0.7Sr0.3MnO3 thin films.
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72.70.+m Noise processes and phenomena
78.20.-e Optical properties of bulk materials and thin films
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Apparatus for measuring the finite load-deformation behavior of a sheet of epithelial cells cultured on a mesoscopic freestanding elastomer membrane

John C. Selby and Mark A. Shannon

Rev. Sci. Instrum. 78, 094301 (2007); http://dx.doi.org/10.1063/1.2777180 (12 pages) | Cited 3 times

Online Publication Date: 4 September 2007

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Details are given for the design, calibration, and operation of an apparatus for measuring the finite load-deformation behavior of a sheet of living epithelial cells cultured on a mesoscopic freestanding elastomer membrane, 10 μm thick and 5 mm in diameter. Although similar in concept to bulge tests used to investigate the mechanical properties of micromachined thin films, cell-elastomer composite diaphragm inflation tests pose a unique set of experimental challenges. Composite diaphragm (CD) specimens are extremely compliant (E<50 kPa), experience large displacements when subject to small inflation pressures ( ∼ 100 Pa), and must be continuously immersed in a bath of liquid culture medium during the acquisition of load-deformation measurements. Given these considerations, we have constructed an inflation apparatus consisting of an air-piston-cylinder pump integrated with a modular specimen mounting fixture that constitutes a horizontally semi-infinite reservoir of liquid culture medium. In a deformation-controlled inflation test, pressurized air is used to inflate a CD specimen into the liquid reservoir with minimum disturbance of the liquid-air interface. Piston displacements and absolute pump chamber air pressures are utilized as feedback to cycle the displaced (or inflated) CD volume V in a 0.05 Hz triangular or sinusoidal wave form (VMIN = 0 μl, VMAX ⩽ 40 μl) while simultaneously recording the inflation pressure acting at the fixed boundary of the specimen, p(r = a). Using a carefully prescribed six-cycle inflation test protocol, the apparatus is shown to be capable of measuring the [V,p(r = a)] inflation response of a cell-elastomer CD with random uncertainties estimated at ±0.45 μl and ±2.5 Pa, respectively.
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87.80.-y Biophysical techniques (research methods)
87.16.D- Membranes, bilayers, and vesicles
06.20.fb Standards and calibration
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Controller-area-network bus control and monitor system for a radio astronomy interferometer

David P. Woody, Bradley Wiitala, Stephen L. Scott, James W. Lamb, Ronald P. Lawrence, Curt Giovanine, Sancar J. Fredsti, Andrew Beard, Clem Pryke, Michael Loh, Christopher H. Greer, John K. Cartwright, Colby Gutierrez-Kraybill, Alberto D. Bolatto, and Stephen J. C. Muchovej

Rev. Sci. Instrum. 78, 094501 (2007); http://dx.doi.org/10.1063/1.2780135 (11 pages)

Online Publication Date: 6 September 2007

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We describe the design and implementation of a controller-area-network bus (CANbus) monitor and control system for a millimeter wave interferometer. The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is a 15-antenna connected-element interferometer for astronomical imaging, created by the merger of two university observatories. Its new control system relies on a central computer supervising a variety of subsystem computers, many of which control distributed intelligent nodes over CANbus. Subsystems are located in the control building and in individual antennas and communicate with the central computer via Ethernet. Each of the CAN modules has a very specific function, such as reading an antenna encoder or tuning an oscillator. Hardware for the modules was based on a core design including a commercial CANbus-enabled single-board computer and some standard circuitry for interfacing to peripherals. Hardware elements were added or changed as necessary for the specific module types. Similarly, a base set of embedded code was implemented for essential common functions such as CAN message handling and time keeping and extended to implement the required functionality for the different hardware. Using a standard CAN messaging protocol designed to fit the requirements of CARMA and a well-defined interface to the high-level software allowed separate development of high-level code and embedded code with minimal integration problems. Over 30 module types have been implemented and successfully deployed in CARMA, which is now delivering excellent new science data.
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95.75.Mn Image processing (including source extraction)
95.55.Br Astrometric and interferometric instruments
95.75.Kk Interferometry

A laboratory apparatus for streaming potential and resistivity measurements on soil samples

M. R. Sheffer, P. M. Reppert, and J. A. Howie

Rev. Sci. Instrum. 78, 094502 (2007); http://dx.doi.org/10.1063/1.2782710 (8 pages) | Cited 3 times

Online Publication Date: 14 September 2007

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We describe an apparatus designed to perform streaming potential and resistivity measurements on unconsolidated soil samples. The apparatus enables the use of both unidirectional and oscillatory flow methods to measure the streaming potential coupling coefficient (C); the direct current resistivity method is used to measure the bulk resistivity (ρ) of the soil sample. Measuring both of these parameters on the same sample under the same conditions enables us to properly characterize the streaming current cross-coupling coefficient (L). The apparatus is designed to test reconstituted saturated soil samples up to a maximum grain size of 9.5 mm, and hydraulic gradients from less than 0.1 up to a maximum of 4 m of H2O/m in flow-through experiments. Excellent agreement between C values measured using the unidirectional and oscillatory flow methods validates the oscillatory flow method for unconsolidated samples.
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07.68.+m Photography, photographic instruments; xerography
91.60.Pn Magnetic and electrical properties
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Time interval measurement device based on surface acoustic wave filter excitation, providing 1 ps precision and stability

Petr Panek and Ivan Prochazka

Rev. Sci. Instrum. 78, 094701 (2007); http://dx.doi.org/10.1063/1.2779217 (4 pages) | Cited 8 times

Online Publication Date: 5 September 2007

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This article deals with the time interval measurement device, which is based on a surface acoustic wave (SAW) filter as a time interpolator. The operating principle is based on the fact that a transversal SAW filter excited by a short pulse can generate a finite signal with highly suppressed spectra outside a narrow frequency band. If the responses to two excitations are sampled at clock ticks, they can be precisely reconstructed from a finite number of samples and then compared so as to determine the time interval between the two excitations. We have designed and constructed a two-channel time interval measurement device which allows independent timing of two events and evaluation of the time interval between them. The device has been constructed using commercially available components. The experimental results proved the concept. We have assessed the single-shot time interval measurement precision of 1.3 ps rms that corresponds to the time of arrival precision of 0.9 ps rms in each channel. The temperature drift of the measured time interval on temperature is lower than 0.5 ps/K, and the long term stability is better than ±0.2 ps/h. These are to our knowledge the best values reported for the time interval measurement device. The results are in good agreement with the error budget based on the theoretical analysis.
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06.30.Ft Time and frequency
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
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