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Peter R Griffiths
The development of Fourier transform infrared (FT-IR) spectrometers in the mid-1960s followed along three lines. Interferometers for far-infrared FT spectrometry typically had a slow scan speed and the beam of radiation was modulated by a rotating chopper. Several instruments based on this system were developed commercially. Very high-resolution near-infrared FT spectrometers were based on cats-eye retroreflectors mounted in a step-scan interferometer; the beam of radiation was usually modulated by dithering one of the cats-eyes (phase modulation)...
March 2017: Applied Spectroscopy
Tanja Hochstrasser, Gianna Lisa Exner, Stella Nyamoya, Christoph Schmitz, Markus Kipp
The chopper chelator cuprizone serves as a valuable chemical tool to induce consistent and reproducible demyelination in the central nervous system. However, the daily preparation of fresh cuprizone powder mixed in finely ground rodent chow might well be a particular health problem. Alternative methods, such as the fabrication of cuprizone-containing pellets, are available. The effectiveness of this method is, however, not known. In the present study, we compared whether intoxication of C57BL/6 mice with 0...
February 25, 2017: Journal of Molecular Neuroscience: MN
Aurel Radulescu, Noemi Kinga Szekely, Marie-Sousai Appavou, Vitaliy Pipich, Thomas Kohnke, Vladimir Ossovyi, Simon Staringer, Gerald J Schneider, Matthias Amann, Bo Zhang-Haagen, Georg Brandl, Matthias Drochner, Ralf Engels, Romuald Hanslik, Günter Kemmerling
The KWS-2 SANS diffractometer is dedicated to the investigation of soft matter and biophysical systems covering a wide length scale, from nm to µm. The instrument is optimized for the exploration of the wide momentum transfer Q range between 1x10(-4) and 0.5 Å(-1) by combining classical pinhole, focusing (with lenses), and time-of-flight (with chopper) methods, while simultaneously providing high-neutron intensities with an adjustable resolution. Because of its ability to adjust the intensity and the resolution within wide limits during the experiment, combined with the possibility to equip specific sample environments and ancillary devices, the KWS-2 shows a high versatility in addressing the broad range of structural and morphological studies in the field...
December 8, 2016: Journal of Visualized Experiments: JoVE
S Patch, M Kireeff Covo, A Jackson, Y Qadadha, K Campbell, R Albright, P Bloemhard, A Donoghue, C Siero, T Gimpel, S Small, B Ninemire, M Johnson, L Phair
PURPOSE: The potential of particle therapy has not yet been fully realized due to inaccuracies in range verification. The purpose of this work was to correlate the Bragg peak location with target structure, by overlaying thermoacoustic localization of the Bragg peak onto an ultrasound image. METHODS: Pulsed delivery of 50 MeV protons was accomplished by a fast chopper installed between the ion source and the inflector of the 88″ cyclotron at Lawrence Berkeley National Lab...
June 2016: Medical Physics
Ming Ding, Qianlong Zhu
Hardware protection and control action are two kinds of low voltage ride-through technical proposals widely used in a permanent magnet synchronous generator (PMSG). This paper proposes an innovative clustering concept for the equivalent modeling of a PMSG-based wind power plant (WPP), in which the impacts of both the chopper protection and the coordinated control of active and reactive powers are taken into account. First, the post-fault DC link voltage is selected as a concentrated expression of unit parameters, incoming wind and electrical distance to a fault point to reflect the transient characteristics of PMSGs...
2016: SpringerPlus
N B Roozen, C Glorieux, L Liu, M Rychtáriková, T Van der Donck, A Jacobs
One hundred and thirty-five years after Alexander Graham Bell and his assistant Charles Sumner Tainter explored the photoacoustic effect, and about 40 years after Rosencwaig and Gersho modeled the effect in a photoacoustic cell configuration, the phenomenon is revisited in a "Heliophone" device that converts sunlight into sound. The light is focused on a carbon blackened copper coated Kapton foil in an acoustic cell by means of a compound parabolic collimator, and its intensity is modulated by a mechanical chopper...
September 2016: Journal of the Acoustical Society of America
Ben Marwick, Chris Clarkson, Sue O'Connor, Sophie Collins
Jerimalai is a rock shelter in East Timor with cultural remains dated to 42,000 years ago, making it one of the oldest known sites of modern human activity in island Southeast Asia. It has special global significance for its record of early pelagic fishing and ancient shell fish hooks. It is also of regional significance for its early occupation and comparatively large assemblage of Pleistocene stone artefacts. Three major findings arise from our study of the stone artefacts. First, there is little change in lithic technology over the 42,000 year sequence, with the most noticeable change being the addition of new artefact types and raw materials in the mid-Holocene...
December 2016: Journal of Human Evolution
Elliot Greenwald, Ernest So, Qihong Wang, Mohsen Mollazadeh, Christoph Maier, Ralph Etienne-Cummings, Gert Cauwenberghs, Nitish Thakor
We present a bidirectional neural interface with a 4-channel biopotential analog-to-digital converter (bioADC) and a 4-channel current-mode stimulator in 180 nm CMOS. The bioADC directly transduces microvolt biopotentials into a digital representation without a voltage-amplification stage. Each bioADC channel comprises a continuous-time first-order ∆Σ modulator with a chopper-stabilized OTA input and current feedback, followed by a second-order comb-filter decimator with programmable oversampling ratio. Each stimulator channel contains two independent digital-to-analog converters for anodic and cathodic current generation...
October 2016: IEEE Transactions on Biomedical Circuits and Systems
Mariana Landin
The results presented in this article demonstrate the potential of artificial intelligence tools for predicting the endpoint of the granulation process in high-speed mixer granulators of different scales from 25L to 600L. The combination of neurofuzzy logic and gene expression programing technologies allowed the modeling of the impeller power as a function of operation conditions and wet granule properties, establishing the critical variables that affect the response and obtaining a unique experimental polynomial equation (transparent model) of high predictability (R(2) > 86...
January 2017: Journal of Pharmaceutical Sciences
M Trapp, R Steitz, M Kreuzer, M Strobl, M Rose, R Dahint
We present an upgrade to the time-of-flight neutron reflectometer BioRef at the research reactor BER II of the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB). Through the integration of an additional chopper into the existing setup, the available wavelength resolution is significantly extended. Now two distinct operation modes can be used: a high resolution mode with Δλ/λ ranging from 1% to 5%, which allows for the investigation of thick films up to 4000 Å, and a high flux mode with Δλ/λ = 7%-11%...
October 2016: Review of Scientific Instruments
G Ehlers, A A Podlesnyak, A I Kolesnikov
The first eight years of operation of the Cold Neutron Chopper Spectrometer (CNCS) at the Spallation Neutron Source in Oak Ridge is being reviewed. The instrument has been part of the facility user program since 2009, and more than 250 individual user experiments have been performed to date. CNCS is an extremely powerful and versatile instrument and offers leading edge performance in terms of beam intensity, energy resolution, and flexibility to trade one for another. Experiments are being routinely performed with the sample at extreme conditions: T ≲ 0...
September 2016: Review of Scientific Instruments
J A Dávila-Pintle, E Reynoso-Lara, Y E Bravo-García
This paper reports an improvement to the chopper z-scan technique for elliptic Gaussian beams. This improvement results in a higher sensitivity by measuring the ratio of eclipsing time to rotating period (duty cycle) of a chopper that eclipses the beam along the main axis. It is shown that the z-scan curve of the major axis is compressed along the z-axis. This compression factor is equal to the ratio between the minor and major axes. It was found that the normalized peak-valley difference with respect to the linear value does not depend on the axis along which eclipsing occurs...
September 5, 2016: Optics Express
N Tsapatsaris, R E Lechner, M Markó, H N Bordallo
In this work, we present the conceptual design of the backscattering time-of-flight spectrometer MIRACLES approved for construction at the long-pulse European Spallation Source (ESS). MIRACLES's unparalleled combination of variable resolution, high flux, extended energy, and momentum transfer (0.2-6 Å(-1)) ranges will open new avenues for neutron backscattering spectroscopy. Its remarkable flexibility can be attributed to 3 key elements: the long-pulse time structure and low repetition rate of the ESS neutron source, the chopper cascade that tailors the moderator pulse in the primary part of the spectrometer, and the bent Si(111) analyzer crystals arranged in a near-backscattering geometry in the secondary part of the spectrometer...
August 2016: Review of Scientific Instruments
Eric M Dufresne, Robert W Dunford, Elliot P Kanter, Yuan Gao, Seoksu Moon, Donald A Walko, Xusheng Zhang
The performance of a cooled Be compound refractive lens (CRL) has been tested at the Advanced Photon Source (APS) to enable vertical focusing of the pink beam and permit the X-ray beam to spatially overlap with an 80 µm-high low-density plasma that simulates astrophysical environments. Focusing the fundamental harmonics of an insertion device white beam increases the APS power density; here, a power density as high as 500 W mm(-2) was calculated. A CRL is chromatic so it does not efficiently focus X-rays whose energies are above the fundamental...
September 1, 2016: Journal of Synchrotron Radiation
Katalin Kristó, Orsolya Kovács, András Kelemen, Ferenc Lajkó, Gábor Klivényi, Béla Jancsik, Klára Pintye-Hódi, Géza Regdon
In the literature there are some publications about the effect of impeller and chopper speeds on product parameters. However, there is no information about the effect of temperature. Therefore our main aim was the investigation of elevated temperature and temperature distribution during pelletization in a high shear granulator according to process analytical technology. During our experimental work, pellets containing pepsin were formulated with a high-shear granulator. A specially designed chamber (Opulus Ltd...
December 1, 2016: European Journal of Pharmaceutical Sciences
Tian Li, Brian E Anderson, Travis Horrom, Kevin M Jones, Paul D Lett
Many optical applications depend on amplitude modulating optical beams using devices such as acousto-optical modulators (AOMs) or optical choppers. Methods to add amplitude modulation (AM) often inadvertently impart phase modulation (PM) onto the light as well. While this PM is of no consequence to many phase-insensitive applications, phase-sensitive processes can be affected. Here we study the effects of input phase and amplitude modulation on the output of a quantum-noise limited phase-sensitive optical amplifier (PSA) realized in hot <sup>85</sup>Rb vapor...
August 22, 2016: Optics Express
Liang Guo, Daniele M Monahan, Graham Fleming
Spectrometers and cameras are used in ultrafast spectroscopy to achieve high resolution in both time and frequency domains. Frequency-resolved signals from the camera pixels cannot be processed by common lock-in amplifiers, which have only a limited number of input channels. Here we demonstrate a rapid and economical method that achieves the function of a lock-in amplifier using mechanical choppers and a programmable microcontroller. We demonstrate the method's effectiveness by performing a frequency-resolved pump-probe measurement on the dye Nile Blue in solution...
August 8, 2016: Optics Express
S K Patch, M Kireeff Covo, A Jackson, Y M Qadadha, K S Campbell, R A Albright, P Bloemhard, A P Donoghue, C R Siero, T L Gimpel, S M Small, B F Ninemire, M B Johnson, L Phair
The potential of particle therapy due to focused dose deposition in the Bragg peak has not yet been fully realized due to inaccuracies in range verification. The purpose of this work was to correlate the Bragg peak location with target structure, by overlaying the location of the Bragg peak onto a standard ultrasound image. Pulsed delivery of 50 MeV protons was accomplished by a fast chopper installed between the ion source and the cyclotron inflector. The chopper limited the train of bunches so that 2 Gy were delivered in [Formula: see text]...
August 7, 2016: Physics in Medicine and Biology
Anna Fedrigo, Daniele Colognesi, Mads Bertelsen, Monika Hartl, Kim Lefmann, Pascale P Deen, Markus Strobl, Francesco Grazzi, Marco Zoppi
VESPA, Vibrational Excitation Spectrometer with Pyrolytic-graphite Analysers, aims to probe molecular excitations via inelastic neutron scattering. It is a thermal high resolution inverted geometry time-of-flight instrument designed to maximise the use of the long pulse of the European Spallation Source. The wavelength frame multiplication technique was applied to provide simultaneously a broad dynamic range (about 0-500 meV) while a system of optical blind choppers allows to trade flux for energy resolution...
June 2016: Review of Scientific Instruments
Arezu Bagheri, Muhammad Tariqus Salam, Jose Luis Perez Velazquez, Roman Genov
We review integrated circuits for low-frequency noise and offset rejection as a motivation for the presented digitally-assisted neural amplifier design methodology. Conventional AC-coupled neural amplifiers inherently reject input DC offset but have key limitations in area, linearity, DC drift, and spectral accuracy. Their chopper stabilization reduces low-frequency intrinsic noise at the cost of degraded area, input impedance and design complexity. DC-coupled implementations with digital high-pass filtering yield improved area, linearity, drift, and spectral accuracy and are inherently suitable for simple chopper stabilization...
February 2017: IEEE Transactions on Biomedical Circuits and Systems
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