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  • American Institute of Physics (AIP)  (26,481)
  • 2000-2004  (26,481)
  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the synchronization of two commercial picosecond Ti:sapphire lasers with unprecedented low temporal jitter between the pulse trains. Pulse jitter is reduced from a few picoseconds to 20 fs with a stability of several hours. The technology enabling the tight pulse synchronization is reviewed in this article. We demonstrate the usefulness of the synchronization scheme by applying the technique to coherent anti-Stokes Raman scattering (CARS) microscopy. It is shown that CARS images can be acquired with a significant improvement in signal-to-noise ratio. This level of performance brings the fluctuations of the CARS signal down to the fundamental photon shot-noise limit. We present detailed statistical analysis of the pulse jitter and CARS noise along with enhanced CARS vibrational images of polymer beads. © 2002 American Institute of Physics.
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  • 2
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2928-2936 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Increasing the imaging speed of tapping mode atomic force microscopy (AFM) has important practical and scientific applications. The scan speed of tapping-mode AFMs is limited by the speed of the feedback loop that maintains a constant tapping amplitude. This article seeks to illuminate these limits to scanning speed. The limits to the feedback loop are: (1) slow transient response of probe; (2) instability limitations of high-quality factor (Q) systems; (3) feedback actuator bandwidth; (4) error signal saturation; and the (5) rms-to-dc converter. The article will also suggest solutions to mitigate these limitations. These limitations can be addressed through integrating a faster feedback actuator as well as active control of the dynamics of the cantilever. © 2002 American Institute of Physics.
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  • 3
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2958-2962 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A newly designed conical spot profile analyzing low-energy electron diffraction (LEED) allows optimized access to the sample up to an angle of 45° with respect to the surface plane. This allows in vivo LEED measurements during deposition or adsorption. The electron optics of the electrostatic deflection unit and the newly designed entrance lens were simulated and optimized using an electron-beam ray-tracing algorithm. Different sample distances can be accommodated by adjusting the deflection voltage between the front and rear section. A new "real-image" SPA-LEED operation mode is presented allowing simple control of the instrument and accurate electron-beam positioning on the sample. © 2002 American Institute of Physics.
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  • 4
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2900-2905 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It is shown that self-heating of electrolytic capacitors causes the output current of a capacitor bank to increase with successive shots even though the charge voltage is held constant. Self heating of only 10 °C can cause a near tripling in the gas output of the gas puffing valves commonly used in spheromak research. By using metallized polypropylene film capacitors instead of electrolytic capacitors the reproducibility is substantially improved (the shot-to-shot variation in gas output is reduced to be 〈0.5%). © 2002 American Institute of Physics.
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  • 5
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2890-2899 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Aperture, pin-hole and collimator detection systems are often used in plasma diagnostics, for example, in soft x-ray detection and bolometer systems. In this article the simultaneous optimization of viewing-beam overlap and light yield is considered in multi-channel aperture and collimator systems for two-dimensional (2D) tomography. This article briefly highlights the relation between beamwidth overlap and spatial aliasing in tomography, and how aliasing can be avoided in theory and in practice. Three-dimensional (3D) single-channel aperture and collimator systems can be approximated by a combination of two planar systems if the aperture is rectangular. Three ways to optimize beamwidth overlap and light yield for planar aperture and collimator systems are considered in detail: overlap of the angular étendue at the full width at half maximum (FWHM), overlap of the geometric function at the FWHM a certain distance from the aperture, and arbitrary overlap for a given maximum beamwidth. The combination of 2D effects from all three optimization methods were used in the design of 3D apertures for a new multi-channel bolometer camera on the Joint European Torus tokamak. The resulting apertures are complex, but the new camera has several advantages over previous cameras. © 2002 American Institute of Physics.
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  • 6
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2923-2927 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A scanning probe microscope, combining a scanning capacitance microscope with a scanning tunneling microscope (STM) using the same probe and input electronics, has been built. The probe is shielded and its stray capacitance is less than 0.5 fF. As an input stage, a wide-bandwidth current-to-voltage converter has been applied. In the capacitance microscope mode, its phase sensitively measures the current flowing through the probe/sample capacitance. The optimum operating frequency is from 1 to 10 MHz. The achieved signal-to-noise ratio is comparable with microscopes using a videodisk pickup as the capacitance sensor. The same amplifier at reduced bandwidth serves in STM mode. Its sensitivity corresponds to standard microscopes, albeit the input bias current is larger than at good STM input stages. It can be used with tunneling currents larger than 100 pA. © 2002 American Institute of Physics.
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  • 7
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2917-2922 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Low light-level ultraviolet and optical imaging with a photon counting image intensifier coupled to a charge coupled device camera generally results in varying levels of fixed pattern noise in the image. Here, we demonstrate that this can be minimized by the appropriate choice of photon event centroiding algorithm. We compare the fixed pattern noise generated by a center of gravity centroiding algorithm, a Gaussian centroiding algorithm, and a hybrid centroiding algorithm which uses center of gravity centroiding when one wing is zero, and Gaussian centroiding otherwise. This approach yields the best image quality with a lower fixed pattern noise parameter (9.99%) than the sole use of Gaussian centroiding (16.4%), and there is no need for a look-up table correction. In addition, the hybrid algorithm also yields maximum detective quantum efficiency by overcoming small pulse centroiding failure associated with Gaussian centroiding. The digitization error when recording the events is modeled with a Monte Carlo simulation and discussed. It is found that a center of gravity algorithm produces not only significant fixed pattern noise, but also pulse height dependent x¯ positions. For a Gaussian centroiding algorithm the x¯ positions are independent of the pulse height, the fixed pattern noise is low and the digitization error only yields a small increase of the fixed pattern noise parameter. This shows that while there is a limit to centroiding accuracy due to the digitization error, the appropriate choice of centroiding algorithm is a much more important factor to minimize fixed pattern noise. © 2002 American Institute of Physics.
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  • 8
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Tip characteristics play an important role in the resolution and sensitivity of scanning probe microscopy. Extensive efforts have been devoted to tip fabrication. Most of the research is focused on scanning tunneling microscopy applications, which require sharp and short tips. Long tips that can be bent into cantilevered tips have great potential in atomic force microscopy/apertureless near-field scanning optical microscopy applications. However, the fabrication of such tips has been rarely reported. The present work is carried out with the aim of optimizing the conditions suitable for fabricating long and sharp tungsten tips. Besides topography, optical, and spectroscopic information, electrical and magnetic measurements can also be carried out with such tips obtained with the recipe reported in this article. The long tips also make it possible to measure deep grooves/trenches. © 2002 American Institute of Physics.
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  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two problems of technological importance for microelectromechanical systems (MEMS) and microelectronics industry are addressed: fatigue of thin films and nanoscale film cracking. A device is described that can (1) conduct biaxial fatigue tests on thin films and (2) be utilized to study fracture patterns in nanoscale coatings under biaxial stress state. Thin-film specimens, in the form of circular membranes, are exposed to cyclic pressures between two fixed pressure limits. Corresponding pressure and specimen deflection are measured. Experimental results, including hysteresis loops spanning deflections of 15–50 μm are presented for 4.6-μm-thick polyimide films. Furthermore, the evolution of crack patterns in a 150-nm-thick Al film deposited on a polyimide substrate is studied. Critical mode I stress intensity factor for Al is extracted from experimental results. © 2002 American Institute of Physics.
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  • 10
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 3022-3026 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A miniature torquemeter for use in a pulsed magnetic field is developed by utilizing a commercially available piezoresistive microcantilever. The high sensitivity of ∼5×10−13 Am2 at 38 T is achieved. The response to faster signals were considerably improved due to high eigenfrequency of the cantilever (f∼250–300 kHz). In this article, we successfully demonstrate the magnetic torque data of samples of sub-μg order in pulsed magnetic fields up to 38 T with pulse duration of less than 60 ms. We also found that the de Haas–van Alphen data are in good agreement with the previous reports obtained in steady magnetic fields. © 2002 American Institute of Physics.
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  • 11
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 3075-3079 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present the design and the results of the evaluation of a fast, low noise, charge preamplifier. This device uses commercial circuits; the advantages over classical circuits based on transistors are presented. These include short development time, high reliability and reproducibility, and easy maintenance. The amplifier has been tested with a position sensitive multiwire proportional counter with a readout system based on delay lines. With an input impedance of 50 Ω, we have obtained a signal to noise ratio better than 40 dB, a gain of 0.42 μV per electron, a pulse rise time of 9.4 ns, and a total pulse duration lower than 120 ns. These values allow detector data acquisition rates in excess of 1 MHz, and a spatial resolution better than 300 μm. © 2002 American Institute of Physics.
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  • 12
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 3089-3092 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The chromium doped spinel crystals, MgAl2O4:Cr3+, have been grown using floating zone technique and its application for the fiber-optic thermometer is discussed on the basis of the temperature dependence of the fluorescence lifetime. Lifetimes of the spinel crystals (τ=10 ms), which decrease with temperature, were about 3 times larger than that of the ruby crystals (τ=4 ms) at room temperature. Temperature coefficients of the photoluminescence (PL) lifetimes for spinel crystals (37 μs/K) are also 3 times longer than that for the ruby crystals (10 μs/K). The spinel crystals are potentially useful sensor probes for the fiber-optic thermometer, which have an advantage of high sensitivity due to long PL lifetime and large temperature coefficient. © 2002 American Institute of Physics.
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  • 13
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 3101-3106 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article presents design equations for calculating the compliance or spring rate of rectangular single-axis hinges and right circular hinges. The design equations are the result of an exact deduction and are concise in their expressions, so it is more convenient to use them in calculating and analyzing flexure hinges and flexure hinge mechanisms. Comparing these with the exact design equations of Paros and Weisboro [Mach. Des. 37, 151 (1965)], it is suggested that the equations of this article are effective. Limitations of the simplified equations of Paros and Weisboro and the approximate equation of Smith et al. [J. Phys E 20, 977 (1987)] are discussed. While calculating the compliance of flexure hinges, several important points are mentioned. © 2002 American Institute of Physics.
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  • 14
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 3122-3124 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report on the continuous measurement of fluorescence lifetimes at low light levels. Fluorescence photons following pulsed excitation generate a pulse sequence with exponentially distributed amplitudes and interphoton times at the output of a time-to-amplitude converter. This sequence is turned into a continuous step function and is time averaged with an adjustable bandwidth. For a single-exponential decay, our approach yields identical results as would be obtained from fitting fluorescence decays, while being a real-time technique. The proposed technique performs especially well at low count rates. We demonstrate the applicability of the method at the example of confocal fluorescence lifetime imaging of single molecules. © 2002 American Institute of Physics.
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  • 15
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    Review of Scientific Instruments 73 (2002), S. 3131-3132 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental investigation of the characteristics of soft x-ray output emitted from a pinch plasma using a laser-induced Au plasma has been performed. The Au plasma is produced by focusing a laser pulse with a focal spot diameter of 100 μm on the tip of an Au pin anode electrode. A pulsed pinch discharge driven by a Marx generator utilizes the plasma as a discharge medium. Soft x-ray output with a pulse duration of ∼120 ns, an energy of ∼1 μJ mm−2, and an effective photon energy of ∼1 keV, has been obtained with the discharge. It is shown that the output characteristics depend strongly on the Marx charging voltage, laser pulse energy, and delay time of the discharge from the laser irradiation. © 2002 American Institute of Physics.
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  • 16
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1998-2010 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We developed a new optical superheterodyne method for light scattering using frequency tunable lasers and succeeded in measuring Brillouin spectra of simple liquids in a wide frequency range from 10 MHz to 3 GHz. In this method the speed of a photodetector and electric circuits does not limit the upper frequency bound, since the superheterodyne detection of the signal allows us to shift the optical beat frequency down to a desired fixed frequency suitable for electric signal processing. Thus an almost ultimate signal-to-noise ratio is realized at any phonon frequency. This is a great advantage over conventional optical beating methods. It is realized by the continuous tunability of the frequency of the laser used as a local oscillator light for superheterodyne detection. Our method provides an extremely high frequency resolution (∼300 kHz), which is determined by the stability of an optical frequency difference between the two lasers under its feedback control. We call this method "superheterodyne Brillouin spectroscopy." The method has a high potential for studying the dynamics in a wide class of transparent condensed matters. © 2002 American Institute of Physics.
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  • 17
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    Review of Scientific Instruments 73 (2002), S. 2020-2027 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact plasma accelerator concept based on plasma production at a magnetic cusp was designed and fabricated. Plume and discharge characteristics of the device were documented using a Faraday probe and a retarding potential analyzer. The discharge current variations with increasing discharge voltage were nonlinear with the discharge current increasing rapidly with voltage. The device demonstrated the capability of generating ion beamlets (∼80 eV) with downstream peak current densities comparable to that of higher power ion thruster devices (7 mA/cm2). In general, the device appeared to operate best at very low flow rates. High propellant utilization fractions (ionization fractions) were measured below 1 SCCM of Xe flow (88% at 0.48 SCCM). Floating potential measurements made downstream of the device were used to estimate the downstream electric field. These measurements, which were used to qualitatively assess beam neutralization, indicated beam neutralization does occur downstream of the device. Based on the measurements, the compact plasma accelerator concept could potentially be used as a low energy ion source for propulsion applications or for low energy plasma/materials processing applications.
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  • 18
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    Review of Scientific Instruments 73 (2002), S. 2038-2043 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes the use of neural networks (NNs) for the on-line computation of the radiated power in JET. The NNs have been trained using a database of about 120 discharges, for which the emitted power had been calculated via tomographic inversion of JET bolometric signals. In addition to the bolometric data, elongation and triangularity have been used as input to the NN, since these provide useful complementary information. Dedicated NNs have been designed for the determination of the total radiated power, the power from the bulk, and from the divertor region. All the NNs have been tested with a set of about 30 discharges with positive results. Moreover, the NNs can operate at full sampling speed and are therefore suited to follow edge localized modes and other rapid phenomena. The sensitivity of the NNs to failures in the input signals has also been tested, proving their robustness. Their possible use in feedback applications is finally briefly discussed. © 2002 American Institute of Physics.
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  • 19
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple optical multiple reflection system is developed with two cylindrical concave mirrors at an appropriate spacing. The two cylindrical mirrors have different focal lengths and their principal sections are orthogonal. The alternate focusing of the two cylindrical mirrors at different direction keep the reflecting spots small. The reflecting spots fall on Lissajous patterns on the cylindrical mirrors. The mathematics for this optical system is described and the calculated coordinates of beam spots are very close matches of the experimental observations. The cylindrical mirror optical system is easy to construct and align, with a suitable method for obtaining long optical paths and a large number of passes in small volumes. In a photoacoustic spectrometer the beam family enhance the effective power in the photoacoustic cell and thus the signal-to-noise ratio of photoacoustic signal. An experimental result for photoacoustic spectrum of HDSe gas is given. © 2002 American Institute of Physics.
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  • 20
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a technique that can determine the viscosity of highly viscous liquids, particularly, undercooled liquids that exist at temperatures below their freezing points. The technique involves levitation of a liquid drop using an ultrasonic standing wave, and elongation of the drop by rotating it beyond the point of bifurcation. The elongated drop is then allowed to be restored to its original shape by surface tension driven relaxation. The time-dependent shape parameters of the relaxing drop are related to the viscosity through a relaxation model. In addition, this technique can also determine the surface tension that has a known relationship with the angular velocity at the bifurcation point. The feasibility of the technique is demonstrated by performing the measurement using sucrose solutions as a model liquid drop. The obtained viscosity values show a good correlation with those determined by a falling ball method. © 2002 American Institute of Physics.
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  • 21
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    Review of Scientific Instruments 73 (2002), S. 2108-2114 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple procedure for testing the bonding strength of adhesives to surfaces is presented. Tests are carried out on highly polished bonded glass slides for a number of adhesives so the adhesion strength can be characterized. Samples are also cycled to liquid nitrogen temperature to test the effect of thermal cycling on the adhesion strength. A few tests were carried out at liquid helium temperatures. Results are presented for a number of commercially available adhesives. © 2002 American Institute of Physics.
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  • 22
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method of measuring molecular diffusion rates in microscopic sample volumes is described. This method utilizes the standing wave interference created by colliding two counterpropagating laser beams at the focus of two opposing microscope objectives, creating a periodic light distribution in a volume on the order of 1 fl. By using a Pockels cell to vary the laser intensity with a time resolution of milliseconds, we show how this experimental geometry can be used to perform ultrahigh resolution fluorescence recovery after patterned photobleaching (FRAPP) experiments. A mathematical treatment of the experiment shows that the laser excitation profile has two characteristic length scales, the width of the focal spot and the period of the standing wave, which permits the simultaneous measurement of dynamics on two separate length scales. This feature may be used to determine whether the measured diffusion is anomalous. We present experimental results using a femtosecond Ti:sapphire laser to create a two-photon excitation profile with a fringe visibility on the order of 100. This standing wave is used to demonstrate FRAPP in both model dye/polymer systems and in more complex systems like living cells stained with a fluorescent dye. By combining the advantages of standing wave microscopy and two-photon fluorescence recovery after photobleaching, this technique permits the measurement of very short length motions in localized sample volumes, which should be useful in both biology and the study of diffusion in microscopically heterogeneous systems. © 2002 American Institute of Physics.
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  • 23
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    Review of Scientific Instruments 73 (2002), S. 2157-2160 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A Paul ion trap has been developed for use as a high-resolution mass spectrometer. It is of small size (r0=10 mm), having a resolution of m/Δm=324, which is limited by the machining accuracy of the trap. It has a demonstrated mass range of 1–300 u, and a sensitivity of 2×1014 counts/Torr s, or to 500 parts per trillion detection sensitivity in a typical vacuum of 10−5 Torr. Ionization of the room-temperature gas within the trap is carried out with an electron beam traversing the trapping volume. The trap operates in a radio frequency only mode, and no dc is required. Trapping is accomplished within the well depth of the dynamic radio frequency potential, and no cooling gas is required, such as helium. This combination of factors makes the trap potentially of use for autonomous operation in harsh environments requiring low power, low weight, and low volume, such as undersea, on the surface of a planet or asteroid, or in a spacecraft. © 2002 American Institute of Physics.
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  • 24
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    Review of Scientific Instruments 73 (2002), S. 2185-2189 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high power fiber delivery system has been developed for a Q-switched Nd:YAG laser. Multimode fibers with a core diameter of 400 μm were tested with a view to transmitting the maximum possible amount of optical energy. The importance of surface finish was investigated by employing a number of different polishing procedures. Atomic force microscopy and laser-induced damage threshold measurements were used to identify a clear correlation between surface finish and transmission capability. Surface roughness measurements as low as 3 nm were made and the transmission of up to 30 J/cm2 achieved. The front face of the fibers would be improved during laser testing due to plasma formation which acts to anneal the surface. The various damage mechanisms that limit the performance of the fiber have been studied and attributed to different optical and physical effects. The nature of the light spot emerging from the fiber was analyzed and quantified by beam profilometry. A number of different methods for altering the beam profile were tried but changing the length of the fiber was found to be the most effective. © 2002 American Institute of Physics.
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  • 25
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A four-pass cell was employed for the multifrequency parametric Raman generation in gaseous hydrogen. More than 18 rotational-vibrational Raman lines from 450 to 830 nm were generated using an 80-mJ, 3-ns pump pulse at a wavelength of 532 nm. The output spectrum broadening was observed by increasing the number of passes of the pump pulse through the Raman cell. © 2002 American Institute of Physics.
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  • 26
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    Review of Scientific Instruments 73 (2002), S. 2208-2210 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for designing open gradient coils for magnetic resonance imaging using a simulated annealing optimization algorithm is described. The algorithm allows the current density toward the open end to be increased, compensating for the "missing" coil section. A semicylindrical transverse z gradient has been designed and built providing a gradient efficiency of 0.82 mT/m/A. The prototype provided good agreement with the theory over the central imaging region. © 2002 American Institute of Physics.
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  • 27
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A low cost interrogation scheme is demonstrated for a refractometer based on an in-line fiber long period grating (LPG) Mach–Zehnder interferometer. Using this interrogation scheme the minimum detectable change in refractive index of Δn∼1.8×10−6 is obtained, which is the highest resolution achieved using a fiber LPG device, and is comparable to precision techniques used in the industry including high performance liquid chromatography and ultraviolet spectroscopy. © 2002 American Institute of Physics.
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  • 28
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The third harmonic generation of light (266 nm) is enhanced, sensitively depending on the time delay between a pair of pulses split from a single 800 nm femtosecond laser pulse, when they are focused and collided in air. This finding offers a convenient and widely applicable technique to detect temporal and spatial overlapping of two femtosecond pulses. This technique has several advantages over the conventional sum frequency generation method using nonlinear optical crystals, since it obviates the need for expensive crystals, free from phase matching, and elimination of temporal walk off. By applying it to "a holographic encoding system using an interference femtosecond laser pulse," a periodic fringe spacing is minimized to ∼430 nm by extending the colliding angle between two-pulse beams up to ∼160 °C. © 2002 American Institute of Physics.
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  • 29
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    Review of Scientific Instruments 73 (2002), S. 1756-1760 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Typical magnetic materials are experimentally characterized. Particularly our efforts are concentrated on deriving a core-loss scaling in operation region with minor B–H loops for highly repetitive voltage modulators. The core losses are evaluated as functions of magnetization rate and flux swing using semiempirical equations based on magnetization models. A prototype induction module has been successfully operated up to 1 MHz and the loss values are adapted well to the core-loss criterion. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1761-1765 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A matched filter analysis has been developed to identify the amplitude and phase of magnetohydrodynamic modes in DIII-D tokamak plasmas using magnetic probe signals (δBp). As opposed to conventional Fourier spatial analysis of toroidally spaced probes, this analysis includes data from both toroidally and poloidally spaced magnetic probe arrays. Using additional probes both improves the statistics of the analysis and more importantly incorporates poloidal information into the mode analysis. The matched filter is a numeric filter that matches signals from the magnetic probes with numerically predicted signals for the mode. The numerical predictions are developed using EFIT equilibrium reconstruction data as input to the stability code GATO and the vacuum field code VACUUM. Changes is the plasma equilibrium that occur on the same time scale as the mode are taken into account by modeling simple matched filter vectors corresponding to changes in total plasma current, plus vertical and horizontal plasma shifts. The matched filter method works well when there is good understanding of a mode and good modeling of its structure. Matched filter analysis results for a fast growing ideal kink mode, where equilibrium change effects are minimal, show the effectiveness of this method. A slow growing resistive-wall mode (RWM) is also analyzed using the matched filter method. The method gives good results for identifying the amplitude and phase of the RWM but the simple equilibrium vectors are insufficient for complete elimination of equilibrium changes on this time scale. An analysis of the computational requirements of the scheme indicates that real-time application of the matched filter for RWM identification will be possible. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1786-1794 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Detection of systematic errors is an important issue in the treatment of measurement data. Existing methods such as the t-detection method and the residual error method are based on the statistics theory that requires large sample sizes and known distributions. For small sample sizes and unknown distributions, these methods could become ineffective. To solve this problem, a new method is proposed to detect the systematic errors in a measurement process, based on fuzzy set theory. In the proposed method, the distribution of measured data may be unknown and the sampling size small. Mathematical models for systematic error detection are presented together with criteria for the detection. Results of the case studies show that the proposed method is effective and the proposed criteria are consistent in identifying monotonic and periodic systematic errors. © 2002 American Institute of Physics.
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  • 32
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    Review of Scientific Instruments 73 (2002), S. 2193-2196 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article, we present a variation on the design of the micromachined flextensional transducer for use to eject liquids. The transducer is constructed by depositing a piezoelectric thin film to a thin, edge clamped, circular annular plate. By placing a fluid behind one face of a vibrating compound plate that has an orifice at its center, we achieve continuous or drop-on-demand ejection of the fluid. We present results of ejection of water and isopropanol. The ejector is harmless to sensitive fluids and can be used to eject fuels, organic polymers, low-k dielectrics, chemical, and biological samples. Micromachined two-dimensional array piezoelectrically actuated flextensional droplet ejectors were realized using planar silicon micromachining techniques. Typical resonant frequency of the micromachined device ranges from 400 kHz to 4.5 MHz. The ejection of water through a 5 μm diameter orifice at 3.5 MHz was demonstrated by using the developed micromachined two-dimensional array ejectors. © 2002 American Institute of Physics.
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  • 33
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    Notes: We report on the generation of a background-free nearly transform-limited picosecond pulse using a simple quenching scheme in a distributed feedback dye laser. The pulsewidth and spectral linewidth were 65 ps and 10 pm, respectively. The product of these values is 0.650, which is close to the transform limit of 0.441 for a Gaussian pulse. © 2002 American Institute of Physics.
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  • 34
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    Review of Scientific Instruments 73 (2002), S. 2211-2213 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this Note, we present a goniometric instrument for measuring the forward angular light scattering behavior of liquid or solid samples with high angular resolution and large dynamic range. The instrument is designed to work in the visible and near-infrared regions. Along with measuring the angular scattering behavior, the instrument functions as a refractometer to determine the refractive index of the sample. © 2002 American Institute of Physics.
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  • 35
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    Review of Scientific Instruments 73 (2002), S. 1697-1701 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article reports on a modified cavity phase-shift (CAPS) method for accurate and reliable characterization of high reflectance mirrors. Our approach relies on using a directly modulated Fabry–Pérot laser to circumvent the difficulties encountered in previous attempts with the CAPS method. The Fabry–Pérot laser diode ensures a constant coupling between the probe laser and test cavity modes. This results in a stable beam intensity transmitted through the test cavity allowing for accurate measurements of the phase shift from which the absolute reflectance can be determined. The experimental arrangement presented in this article is versatile and easy to use. The method is nondestructive and especially suited for the characterization of distributed Bragg reflectors (DBRs) employed in vertical-cavity optoelectronic devices. A premium feature of this method is its capability to probe a relatively small area of less than 1 mm which can be positioned anywhere across the surface of the wafer. We demonstrate the use of the method by measuring the absolute reflectance of metalorganic vapor-phase epitaxy grown AlAs/GaAs DBRs for 1.3 μm vertical-cavity lasers. © 2002 American Institute of Physics.
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  • 36
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Methods to collect two-dimensional time-resolved x-ray diffraction patterns from surfaces/interfaces were developed. Reflection surface x-ray diffraction utilizing high brilliance x rays and a charge coupled device can achieve a time resolution as good as one second. Also, two-dimensional maps of reflectivity rocking curves can be recorded fast enough to monitor growth processes. These methods were demonstrated for the study of Ag and Pb films on Si (111)−(7×7) surfaces. © 2002 American Institute of Physics.
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  • 37
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have built a relatively simple, highly efficient, THz emission and detection system centered around a 15 fs Ti:sapphire laser. In the system, 200 mW of laser power is focused to a 120 μm diam spot between two silverpaint electrodes on the surface of a semi-insulating GaAs crystal, kept at a temperature near 300 K, biased with a 50 kHz, ±400 V square wave. Using rapid delay scanning and lock-in detection at 50 kHz, we obtain probe laser quantum-noise limited signals using a standard electro-optic detection scheme with a 1-mm-thick (110) oriented ZnTe crystal or a (110) oriented 0.1-mm-thick GaP crystal. The maximum THz-induced differential signal that we observe is ΔI/I=7×10−3, corresponding to a THz peak amplitude of 95 V/cm. The THz average power was measured to be about 40 μW, to our knowledge, the highest power reported so far generated with Ti:sapphire oscillators as a pump source. The system uses off-the-shelf electronics and requires no microfabrication techniques. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1724-1727 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A magnetic structure composed of electromagnets and permanent magnets is proposed as an undulator to control the polarization state of synchrotron radiation. The horizontal field is produced by the permanent magnets and tuned by moving them along the undulator axis, while the vertical field is produced by the electromagnets and tuned by changing the coil current. The proposed device has two important degrees of freedom. One is that of the periodic length of the electromagnets and the other is that of the relative phase between the vertical and horizontal fields. Thanks to them, the proposed device works as various types of undulator to realize polarization control. © 2002 American Institute of Physics.
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  • 39
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    Review of Scientific Instruments 73 (2002), S. 1728-1733 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-intensity pulsed ion source of TEMP-type series, operating in bipolar mode, has been developed as a unique pulsed energy source to produce a high-intensity pulsed ion beam (HIPIB) for surface modification of materials. To generate the ion beam, a specially shaped bipolar pulse, consisting of a first negative pulse and a second delayed positive pulse both of nanosecond width, is formed by a double coaxial pulse-forming line (PFL) powered with a Marx generator and supplied to a magnetically insulated ion diode (MID) by a self-magnetic field. It is found that the efficient generation of a HIPIB is mainly dependent on the delay time of the bipolar pulse, adjusted by pressure ratio in the two gas switches of a PFL, and the anode–cathode (A–K) gap distance in the self-magnetic field MID. The delay time determines the effective area on the anode surface for plasma generation and the A–K gap distance ensures the stability of the process. A proper delay time and a proper A–K gap distance are obtained by a series of experimental investigations. Under delay time from 30 to 280 ns and several different A–K gap distances, the typical wave forms of the bipolar pulses at a dc charging voltage of 45 kV to Marx generator are illustrated to clarify the effects of delay time and A–K gap distance on the ion beam generation. The proper A–K gap distance is not uniform, varied from 6 to 8 mm, and the corresponding proper delay time is 250 ns. The most efficient plasma generation leads to a maximum output of HIPIB with a peak ion current density of 350 A cm−2 and a beam pulse width of 75 ns (full width at half maximum), at an accelerating pulse of 220 kV with a pulse width of 100 ns. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1734-1740 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The knowledge of the detection efficiency of the microchannel plate is of upmost importance in many applications using this type of particle detector. However, few attempts have been made to measure the absolute value of the detection efficiency of microchannel plates. In this article, a new way of accurately measuring the absolute value of the detection efficiency is described. When particles hit the detector in the interchannel web of the microchannel plate, secondary electrons are generated. These secondary electrons can be returned to neighboring channels by means of an electric field applied at the front face of the detector. The resulting increase in the detection efficiency has been quantified using the absolute measurement of the detection efficiency. It is found that the value of the returning field has to be carefully set in order to prevent detection artifacts that may lead to a wrong estimation of the detection efficiency. In the best conditions, the detection efficiency increase reaches 40%. © 2002 American Institute of Physics.
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  • 41
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    Notes: A new steady-state, low-energy, and high-flux ion beam test device has been developed to study erosion, re-deposition, and hydrogen retention mechanisms of plasma facing materials under high flux conditions. Source plasma was produced by electron cyclotron resonance discharge with 2.45 GHz microwave. Ion extraction was made by spherical multiaperture triode electrodes to obtain high ion flux at the focal point. Ion extraction aperture geometry was designed so that high current density can be obtained in the case of low energy (〈500 eV) by applying high deceleration voltage. It was demonstrated that low-energy and high-flux ion beam can be produced by increasing deceleration voltage with the fixed acceleration voltage (beam energy). In the case of hydrogen beam energy of 300 eV, beam power density has rapidly increased with a deceleration voltage over accel–decel ratio 4, and maximum beam flux is 4.1×1020 H/m2 s. On the other hand, maximum beam flux of 3.6×1021 H/m2 s was obtained for 3 keV hydrogen beam. These fluxes are much higher than that of conventional mass analyzed ion beam (〈1.0×1020 H/m2 s). © 2002 American Institute of Physics.
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  • 42
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    Notes: A technique of spatial and temporal diagnostics of an electron beam was investigated experimentally by Thomson scattering of the electron beam with a femtosecond laser beam at a 90° configuration. The spatial structure of the electron beam was measured by scanning the laser across the electron beam in the Thomson scattering, and compared with imaging of the beam profile on a phosphor screen using a charge coupled device. By scanning the femtosecond laser beam in time along the electron beam, we measured the temporal density distributions of short and long electron bunches which were produced in a photocathode rf gun with laser injection phases of 30° and 55°. A subpicosecond time slice of the actual electron beam was achieved in the measurement. © 2002 American Institute of Physics.
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  • 43
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    Notes: A simple interference filter spectrometer, together with a modulated neutral diagnostic beam is used on the Tore Supra tokamak for the measurement of carbon impurity profiles by charge exchange spectroscopy. A temporal resolution of 8 ms with a good signal to noise ratio is obtained with a neutral hydrogen beam of about 1 A equivalent neutral current at the plasma edge at 45 kV. Experimental results with ion cyclotron heating show that fast changes of the heating power are followed by transient modifications of the carbon impurity profile. The evolution of the C6+ profile from peaked to hollow and back to normal can be followed step by step and a typical diffusion time of about 30 ms is measured. © 2002 American Institute of Physics.
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  • 44
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes hardware and software solutions to a need which is comprised of (i) acquisition of a large volume of high speed data with multiple time scales, (ii) control of various operational parameters of device and diagnostics, and (iii) processing and management of the acquired data for a large volume plasma device. The solution relies on the base of a VXI bus and uses a standard PC with a Windows 98/NT operating system and C as the programming language. The system is networked with the existing network with the result of allowing a large data storage space of processing facilities from any terminal in the laboratory.© 2002 American Institute of Physics.
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  • 45
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    Notes: We have developed a surface-contact sensor on the basis of a tuning fork which differs from the previously described ones in that it has a high operating speed (up to 100 times as fast as the so-called Q limit), requires no external piezoelectric drive, has a sufficiently high sensitivity, and features a "soft" probe attachment which makes the lifetime of the probe equal to that of the standard atomic force microscopy. When using a "soft" probe with a rigidity of 0.5 N/m, one can reliably detect probe tip-to-sample distance variations as small as 0.1 nm. The resonance frequency resolution attained amounted to 2×10−3 Hz. The rate of transient rise is τ=1.5 ms (this refers to the response time of the sensor proper with the Z-coordinate feedback loop open and not to the response time of the microscope as a whole). We have theoretically substantiated the fact that the Q limit, where Q∼10 000 is the Q factor of the tuning fork proper, is not a fundamental restriction on the operating speed of the sensor. This sensor characteristic is governed by another independent quantity, namely, Q1∼100: the quality factor of the tuning fork preamplifier system that can be varied to suit the experimenter. In that case, the fundamental force limitation on the sensitivity of the sensor, associated with its operating speed and the Q factor of the tuning fork, is Fnoise(approximate)10.4 nN/((square root of)Q(square root of)Q1). © 2002 American Institute of Physics.
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  • 46
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    Review of Scientific Instruments 73 (2002), S. 1821-1827 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A laser-based technique for measuring the curvature of a multilayer/substrate couple is described. Unlike most wafer curvature systems, the instrument described measures the local curvature of the multilayer/substrate couple, correcting for the local topography of the substrate, rather than measuring changes in the average curvature of the multilayer/substrate couple. The apparatus has been designed specifically to perform biaxial zero-creep measurements at elevated temperatures in vacuum. It can also be used to examine the development of biaxial stresses during thermal cycling of thin films deposited on substrates. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1841-1844 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Si–N based membrane calorimeters are a promising technology for the study of thermal properties of small quantities of materials in both pulsed and steady-state magnetic fields to 60 T and beyond. We present results that demonstrate our ability to measure the heat capacity of thin film samples from 2–300 K in steady-state fields up to 8 T. These measurements include the magnetoresistance of the Pt and Nb–Si thermometers and focus on confirming that the thermal conductance of the Si–N membrane does not change significantly in magnetic fields. This means the thermal conductance needs to be measured only in zero field, reducing the measurement time in high field. This is particularly important for future measurements in fields up to 60 T. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1853-1855 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For milling over large areas there is need for broad ion beam sources with a uniform etch rate profile. Currently uniform ion beam density is obtained in the central portion of the ion source by manipulating the grids and the magnets in the ion source. We have designed and implemented specially shaped hard masks to a rotating substrate holder. This mask is able to transform the Gaussian etch rate profile of a 150-mm-diam Oxford ion source to a flat profile. The flat profile decreases the etch rate in the central portion while maintaining the same etch rate along the edge. The deviation in the ion beam etch rate is within 5% in the flat region. © 2002 American Institute of Physics.
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  • 49
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A laser-based instrument is described for the study of femtosecond dissociation dynamics of gas phase molecules via time-resolved vacuum ultraviolet and soft x-ray photoelectron spectroscopy. Visible or UV pump pulses are generated with nonlinear crystal techniques on a Ti:sapphire laser output, while soft x-ray probe pulses are created via high-order harmonic generation of the same laser in rare gases. Here we describe the optical layout of the pump-probe system, the means for separation of the high-order harmonics in the soft x-ray probe beam, including a description of the two grating setup used to compress the high-harmonic pulses and the magnetic bottle photoelectron spectrometer used for data collection. The feasibility of using the generated high-harmonic pulses for an array of gaseous phase photoelectron spectroscopy experiments is established. These include measurements of valence shell and core-level photoelectron transitions in atoms and molecules, the tunability of the soft x-ray harmonic through Rydberg resonances, and the energy bandwidths of the harmonics. Cross correlations between the visible/UV and soft x-ray pulses, by above threshold ionization, are used to establish the pulse timing, pulse duration, and spatial overlap for ultrafast studies. The observed real time photodissociation of Br2 serves as a demonstration of the pump-probe ultrafast technique and the applicability to ultrafast time-resolved chemical dynamics. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1945-1948 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High-speed x-ray radiography is used for the imaging of internal components of a low-voltage air circuit breaker during fast current interruption events. A continuous x-ray source was used to irradiate the circuit breaker during interruption, while a fast camera imaging system recorded the output visible light from the x-ray image intensifier up to a maximum rate of 4000 frames per second. Detailed time-resolved images were obtained of the movable contact position and tripping mechanism components of the circuit breaker during the interruption event. Experimental observations were used to validate numerical simulation results obtained using electromagnetics and dynamics/kinematics analysis software. In addition to imaging of the circuit breaker mechanism, molten metal streams and droplets ejected from the electrodes were also observed. Tracking of these metallic particles can provide valuable information about contact phenomena and gas flow fields in circuit breakers. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1965-1966 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An improved light element driver employing two transistors, one capacitor and one grounded resistor, is presented. It also has the fewest number of possible components and can drive a red light-emitting diode with a supplied voltage as low as 0.8 V. Its power efficiency is about 70% to deliver to a light-emitting element at 1 V supply voltage. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1970-1971 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An angular motion feedthrough capable of supporting a large diameter linear motion feedthrough has been designed and built for the large experiment on instabilities and anisotropies at West Virginia University. With a combination of linear, angular, and rotary motion, a probe can be positioned in the vacuum chamber within a cone-shaped volume. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1117-1120 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two new straightforward methods for the evaluation of optical losses in planar waveguides are proposed and discussed. The first method exploits a single nonsliding isosceles prism and it allows the attenuation to be determined through the measurement of the power exiting the waveguide and the evaluation of the coupled power. It requires a very simple operation procedure, it allows a mode-selective determination of losses, and it presents a good accuracy provided that the sample is not too short. The second method uses end-fire coupling and it is based on the measurement of the output power together with the power back-reflected by the output face of the waveguide. The main advantage of the method is that it can be very accurate also for shorter waveguides and that its accuracy is to a high degree insensitive with respect to the optical depth of the waveguide. It provides better results in the case of high refractive index waveguides that give an intense back-reflected signal. Experimental results obtained with both methods on two different waveguides are presented. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1129-1139 
    ISSN: 1089-7623
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electrostatic energy analyzer is described that allows parallel acquisition of the energy spectrum of charged particles over a wide range of energies and over the complete range of azimuthal directions. The analyzer is similar to the cylindrical mirror analyzer except that a linear potential variation is applied in the axial direction to the outer cylinder. The analyzer can also be used in a second-order focusing mode to analyze a narrow range of energies with higher energy resolution. A position sensitive detector is required, the shape of which depends on the way in which the analyzer is used. Comparisons with existing electron energy analyzers are given. © 2002 American Institute of Physics.
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  • 55
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    Notes: There is nonlinearity in the dynamic characteristics of sensors under some conditions. Previous researchers have presented the nonlinear dynamic models of sensors only using a block, which make it difficult to compensate the nonlinear dynamic responses of sensors. In this article a Hammerstein model is adopted to describe the nonlinear dynamic models of sensors, and a one-stage identification algorithm is proposed to simplify the calculation. On this basis a two-step compensation method is presented for the nonlinear dynamic responses of sensors. The one-stage identification algorithm has advantages as follows: (1) One-stage identification simplifies the algorithm; (2) it depends only on the data of input and output of the system, and does not need to introduce auxiliary variables that could not be measured in practice; (3) it only needs dynamic calibration experimental data of systems, and does not need to do static calibration experiments. The simulation results and its application in the wrist force sensor show the methods proposed by this article are effective. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1962-1964 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The speed measurement system is based on an advanced single buffered method utilizing both the pulse counting and the period measurement. The extremely wide speed range from 5×10−5 to 1830 rpm is independent of the sampling time, chosen between 100 μs and 22 ms. The maximum static relative error is limited to 6.67×10−4 for 1 ms or 6.67×10−3 for 100 μs sampling time. This method is useful for a real-time control and an off-line speed analysis. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1103-1107 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a new automated device for measurement of time-resolved frequency chirp of optical transmitters. It measures chirp in real time by utilizing two temperature-tunable silicon-wafer etalons as frequency discriminators. The time-resolved frequency chirp in a range of ±12 GHz can be measured with a time resolution of approximately 40 ps. © 2002 American Institute of Physics.
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    Review of Scientific Instruments 73 (2002), S. 1125-1128 
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    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A long undulator is a direct way to create a brilliant synchrotron radiation source. However, the length of undulators has been bounded by technical limitations and available space in accelerators. The first long undulator was developed at SPring-8, which is a third-generation synchrotron radiation facility equipped with four 30-m-long straight sections, making it the most brilliant x-ray source in the world. The magnets are placed inside a vacuum chamber and this makes it possible to arrange 780 periods continuously for 25 m. The absolute flux and spectrum of the output radiation were measured and compared with theory. The observed spectrum is in a good agreement with theory once the electron beam orbit was corrected for geomagnetic fields. © 2002 American Institute of Physics.
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    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Experiments have been carried out to optimize the yield of Pb+4 ions from the plasma produced by a 100 J CO2 laser. The laser power density on the target surface was varied between 1010 W/cm2 and 9×1010 W/cm2 by changing the focal spot size. Data on the production of Pb+4 to Pb+10 ions are presented for the 15 and 40 ns laser pulse durations. The 10 mA/80 μs pulses of Pb+4 ions (about 1012 ions per pulse) were directed into an extraction aperture of 3.4 cm in diameter for optimal irradiation conditions. This is comparable with the parameters of the MEVVA ion source. Laser ion sources can be especially attractive due to the absence of the "noise" problem, typical for the MEVVA ion source, and because of the possibility of generating higher charge states. The emittance of the lead ion beam extracted from the laser-produced plasma was measured by using a 5 J laser, which provided plasma parameters (the electron temperature, ion velocities, and the charge state distribution) close to those of the plasma generated by the 100 J CO2 laser under optimized (for the yield of Pb+4 ions) conditions. The emittance was measured for 30 and 50 kV extraction voltages with a 10 μs temporal resolution. The value of about 400 π mm mrad was obtained for the lead ion beam with the total current of 10 mA, and a pulse length of 75 μs for about 75% of the beam ions. © 2002 American Institute of Physics.
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  • 60
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    Review of Scientific Instruments 73 (2002), S. 1224-1228 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The magnetic domain structure of a single crystal of Co (0001) and of polycrystalline AlNiCo was investigated in a photoelectron emission microscope making use of partial restriction of the electron beams. An external movable magnet was used for off-axis deflection of the electron trajectories in the microscope column such that parts of the trajectories are stopped by the apertures of the electron optical elements. As a result, the contrast caused by the stray fields of the magnetic domains is significantly enhanced. The distribution of the local magnetic fields at the surface is reconstructed from the image by means of a theory on the contrast mechanism. © 2002 American Institute of Physics.
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  • 61
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe concept, design, and performance of a novel spin polarimeter based on spin-dependent specular reflection of electrons from a Fe(100) surface. The Fe surface is prepared as an ultrathin film on Ag(100). By tuning the energy of the electrons to a critical point in the Fe band structure, a large spin asymmetry combined with a large scattering efficiency is achieved. The polarimeter yields a figure of merit up to 10−2 for the best Fe(100) surfaces. © 2002 American Institute of Physics.
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  • 62
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the construction of an ultrahigh vacuum chamber that incorporates variable-temperature scanning tunneling microscopy (STM), Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS), Auger electron spectroscopy, low-energy electron diffraction, and temperature programmed desorption, for studying structure and reactivity at surfaces. The chamber and manipulator design enables in situ sample preparation and analysis, and rapid access to several surface-analytical techniques by rotation only. This eliminates sample inconsistencies due to ex situ preparation or the necessity to run parallel experiments. Inclusion of FT-IRAS allows us to characterize surface species and identify adsorbates during studies using STM. © 2002 American Institute of Physics.
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  • 63
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1288-1292 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A nondestructive testing technique for imaging of voids and inclusions in dielectric materials for high-voltage application is described. Void partial discharge occurrence is induced by a narrow pulsed x-ray beam scanning the bulk of epoxy sample. Phase resolved partial discharge analysis is recorded as a function of the beam position. The data matrix is used to construct digital gray scale images, which gives information about location, dimensions, and partial discharge activity in each defect in dielectric materials. This nondestructive technique can be an important tool to evaluate the degradation state of the material. © 2002 American Institute of Physics.
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  • 64
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1193-1197 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design of a user-friendly compact water-window x-ray microscope. The microscope is based on a λ=3.37 nm liquid-jet-target laser-plasma source in combination with a normal-incidence multilayer condenser mirror and high-resolution diffractive optics for the imaging. With its high mechanical and thermal stability, the instrument demonstrates enhanced resolution and potential for compact x-ray imaging with the quality of synchrotron-based microscopes. Furthermore, a new sample handling system, computer control, and other improvements facilitate application-oriented x-ray microscopy outside the synchrotron laboratory. © 2002 American Institute of Physics.
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  • 65
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Millions of single-crystal silicon cantilevers were fabricated by anisotropic etching of silicon by KOH. They could be tailored to measure from 500 nm to 100 μm in length and from 30 to 100 nm in thickness. Since the tips and the cantilevers were formed by a combination of crystal-line facets, they had very high uniformity, well-defined shape, and size. The density of the cantilevers was over 1 mil cantilevers per square centimeter. Typical mechanical characteristics of cantilevers measuring a few microns in length were spring constant a few N/m, natural frequency around 10 MHz, Q factor 5 in air, and 104 in vacuum. The natural frequency of cantilevers within the same row differed by 0.01%. Displacement measurement of the cantilever from the back surface of the silicon substrate by an infrared Fizeau interferometer had a visibility of 0.1. © 2002 American Institute of Physics.
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  • 66
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    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1217-1223 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A reactive oxygen beam generation system is described for the formation of high-quality and high-precision films. This system utilizes pulsed laser evaporation of highly concentrated solidified ozone (O3). The equipment for safely generating and handling a large amount of high-purity liquid and solid O3 was also developed for this purpose. The beam is characterized by its high concentration of oxygen atoms in an excited state [O(1D)], constant flux per laser shot (4×1017 molecules cm−2 shot−1), appropriate level of kinetic energy (KE) for enhancing the surface reaction (mean KE of 0.4 eV, maximum KE of 2 eV) and small angular spread (6°). These characteristics enabled us to precisely control the SiO2 film thickness by the number of laser shots, and achieve an enhanced Si oxidation rate and new local oxidation process. © 2002 American Institute of Physics.
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  • 67
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The basic principle of deflection of a beam of polarizable particles by an inhomogeneous electric field is straightforward, but its application to realistic beams having spatial and velocity distributions of finite widths requires special care. We present a detailed treatment of these issues as developed for a measurement of electric polarizabilities of alkali clusters in a continuous supersonic beam. We begin by describing a general technique for extracting the beam velocity distribution from the time-of-flight profile generated by two separate 50–50 gating choppers. This method yields accurate model-free information directly from the experimental profile, without errors associated with detector delays, and with high signal throughput. We then use a simple but accurate approximation for the deflecting field variation over space, and derive analytical expressions for the deflection of beams of finite width and finite velocity spread. This allows us to evaluate the magnitude of a number of corrections to the ideal formula; the results are applicable to optimization of various electric and magnetic field deflection experiments. Finally, we demonstrate, both theoretically and experimentally, the phenomenon of local velocity variations across the beam profile which arise as a result of deflection. © 2002 American Institute of Physics.
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  • 68
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    Review of Scientific Instruments 73 (2002), S. 1242-1246 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electron spin resonance (ESR) apparatus with a high sensitivity vector network analyzer has been developed for use at ultralow temperatures. The microwave frequency can be varied between 45 and 110 GHz. The resonant cavity was installed in a 3He–4He dilution refrigerator which provides ultralow temperatures down to 160 mK. In order to avoid the heating of the cavity and the sample by microwaves or heat leaks in the cryostat, attenuators and thermal anchors were placed at the most suitable positions. As the first experiment, the ESR was measured for a quantum spin chain Cu benzoate. The breather mode, which is a new ESR mode caused by a field induced gap, has been clearly observed at the lowest temperatures. © 2002 American Institute of Physics.
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  • 69
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    Review of Scientific Instruments 73 (2002), S. 1255-1258 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new type of Kerr effect polarimeter, making use of four detectors, is described. The light is reflected at oblique incidence off each detector in turn, in such a way that the plane of incidence changes on each reflection. Since the reflections are polarization dependent, each detector signal depends on the Kerr rotation and, since the detector outputs can be normalized, this rotation may be obtained without the need of either a particularly stable laser source nor any type of modulation. The method thus provides a cheap alternative to more traditional Kerr techniques. We demonstrate its use in obtaining hysteresis loops for a thin film sample of CoO deposited on Co. © 2002 American Institute of Physics.
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  • 70
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electrospray ion source has been coupled to an accelerator that injects ions into an electrostatic heavy-ion storage ring. Since the dc ion current produced by electrospray ionization is low (∼106 ions/s), ions are accumulated in a cylindrical ion trap filled with a helium buffer gas. The ions are collisionally damped in the buffer gas and confined to the central trap region by a rf field. Extraction from the trap occurs within a few microseconds and after acceleration through 22 kV, the ions of interest are selected by a magnet according to their mass to charge ratio. The ion bunch is subsequently injected into the ring. Both positive and negative ions have been stored, with masses ranging over 3 orders of magnitude (∼102–104 Da). From a pickup signal in the ring, the number of ions in a bunch is estimated to be of the order of 103–104 when the accumulation time is 0.1 s. Our first measurements show that we can store a sufficient number of ions to study the decay of metastable ions and to determine relative destruction cross sections. The technique could be useful to probe conformers differing only in size. Furthermore, our setup can be used for spectroscopic measurements of the ion-photon interaction such as the excitation of [Cytochrome c+17H]17+ protein ions with 532 nm photons. © 2002 American Institute of Physics.
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  • 71
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Refractive and diffractive artifacts can dominate the spatial resolution and affect quantitative measurements by microtomography at the micron level. We have recently developed x-ray computed tomography methods that demonstrated 1 μm resolution in three dimension in the final reconstruction. The first method used a Fresnel zone plate to produce a submicron focal spot which was then rastered across the sample see W. Yun et al., Rev. Sci. Instrum. 70, 2238 (1999). The second method used a collimated beam and a high resolution charge coupled device camera to capture the absorption image of the sample in close proximity see A. Koch et al., J. Opt. Soc. Am. A 15, 1940 (1998). Both methods were applied to study the mineral ultrastructure of individual trabeculae. Using volumetric viewing, the volume, shape, and orientation of osteocyte lacunae and major cannaliculae can be observed. Quantitative measurements and comparison between the two methods will be presented. © 2002 American Institute of Physics.
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  • 72
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A differential heat-conducting double microcalorimeter intended for heat measurements at 300–700 K is described. Platinum resistance thermometers are applied as the heat-flux sensors. The calorimeter is a low-noise instrument with the baseline fluctuations ranging up to 0.02×10−6 V (5×10−6 W); it allows measurements of the heat effects with an error of 1%–1.5% at a recorded scale of about 1×10−2 J/cm2. The design features and the method of the heat-flux transformation to the electric signals, the calorimetric ampoules for measurements and for calibration and the calibrating device, the heat-balance equation and the equation for the temperature dependence of the calorimetric sensitivity, the results of the calibration and the verification of the calorimeter, and a number of illustrative examples of calorimetric measurements are presented. The calorimeters are applicable for studying solid–gas, solid–liquid, and liquid–gas interactions and thermophysical characteristics of solids and liquids. © 2002 American Institute of Physics.
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  • 73
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A linear motion device was designed and built to move small sample cells within the confined space of a liquid nitrogen Dewar cryostat. Instead of the often-used methods of flowing or rotating samples to generate motion, this cryostat insert simply translates the sample cell while maintaining atmospheric isolation. Accurate, repeatable and rapid translation over a 5 cm range with peak linear velocities of 1 m/s is attainable. The insert is constructed mainly from commercially available components and can be built with minimal effort. Another benefit is that the cryostat insert uses commercially available sample cells, allowing for maximal flexibility in satisfying pathlength and volume requirements and the cells can be easily replaced during the duration of the experiment. The motion device system can be easily installed into existing experimental apparatuses with confined volumes with minor modifications and can be used with liquid helium cryostats or for use in high vacuum applications. This motion is demonstrated by collecting temperature dependent ultrafast signals from the laser dye Rhodamine 640 in viscous glycerol at 170 and 293 K. © 2002 American Institute of Physics.
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  • 74
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: To use the unique element-specific nature of polarized x-ray techniques to study a wide variety of problems related to magnetic materia