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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3758-3761 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The spatial resolution of high-accuracy microchannel plate (MCP) detectors has reached the values, where the so-called detector walk (or image blurring) may start to limit any further improvements. Image blurring with gain is studied in detail for detectors incorporating angular-biased MCPs. It was found that the presence of the pore bias at the output MCP results in a variation of the charge footprint position for events with different gains. Events with higher gains are shifted in the direction of the pore bias and the absolute value of this shift is directly proportional to the absolute value of the detector gain. Variation of the detector modal gain from 7.5×106 to 2.5×107 resulted in a ∼100 μm image offset for a 13°-biased MCP positioned at a distance of 8.5 mm from the anode with an accelerating rear field of 75 V/mm. We also extended our previous study of another type of detector walk associated with fluctuations of the accelerating rear field. Image displacements as functions of the rear accelerating field for both 13°- and 19°-biased MCPs were measured and compared with the results of computer simulation based on our charge cloud propagation model presented earlier. A good agreement between the experimental and simulated data verifies the validity of the model for different MCPs. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3282-3288 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The measurements of the electron cloud footprints produced by a stack of microchannel plates (MCPs) as a function of gain, MCP-to-readout distance and accelerating electric field are presented. To investigate the charge footprint variation, we introduce a ballistic model of the charge cloud propagation based on the energy and angular distribution at the MCP output. We also simulate the Coulomb repulsion in the electron cloud, which is likely to cause the experimentally observed increase in the cloud size with increasing MCP gain. Calculation results for both models are compared to the charge footprint sizes measured both in our experiments with high rear-field values (∼200–900 V/mm) and in the experiments of Edgar et al. [Rev. Sci. Instrum. 60, 3673 (1989)] (accelerating electric field ∼30–130 V/mm). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Far Ultraviolet Wideband Imaging Camera (WIC) complements the magnetospheric images taken by the IMAGE satellite instruments with simultaneous global maps of the terrestrial aurora. Thus, a primary requirement of WIC is to image the total intensity of the aurora in wavelength regions most representative of the auroral source and least contaminated by dayglow, have sufficient field of view to cover the entire polar region from spacecraft apogee and have resolution that is sufficient to resolve auroras on a scale of 1 to 2 latitude degrees. The instrument is sensitive in the spectral region from 140–190 nm. The WIC is mounted on the rotating IMAGE spacecraft viewing radially outward and has a field of view of 17° in the direction parallel to the spacecraft spin axis. Its field of view is 30° in the direction perpendicular to the spin axis, although only a 17°×17° image of the Earth is recorded. The optics was an all-reflective, inverted Cassegrain Burch camera using concentric optics with a small convex primary and a large concave secondary mirror. The mirrors were coated by a special multi-layer coating, which has low reflectivity in the visible and near UV region. The detector consists of a MCP-intensified CCD. The MCP is curved to accommodate the focal surface of the concentric optics. The phosphor of the image intensifier is deposited on a concave fiberoptic window, which is then coupled to the CCD with a fiberoptic taper. The camera head operates in a fast frame transfer mode with the CCD being read approximately 30 full frames (512×256 pixel) per second with an exposure time of 0.033 s. The image motion due to the satellite spin is minimal during such a short exposure. Each image is electronically distortion corrected using the look up table scheme. An offset is added to each memory address that is proportional to the image shift due to satellite rotation, and the charge signal is digitally summed in memory. On orbit, approximately 300 frames will be added to produce one WIC image in memory. The advantage of the electronic motion compensation and distortion correction is that it is extremely flexible, permitting several kinds of corrections including motions parallel and perpendicular to the predicted axis of rotation. The instrument was calibrated by applying ultraviolet light through a vacuum monochromator and measuring the absolute responsivity of the instrument. To obtain the data for the distortion look up table, the camera was turned through various angles and the input angles corresponding to a pixel matrix were recorded. It was found that the spectral response peaked at 150 nm and fell off in either direction. The equivalent aperture of the camera, including mirror reflectivities and effective photocathode quantum efficiency, is about 0.04 cm2. Thus, a 100 Rayleigh aurora is expected to produce 23 equivalent counts per pixel per 10 s exposure at the peak of instrument response.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2018-12-14
    Description: Author(s): A.W.T. Gregg, J.N. Hendriks, C.M. Wensrich, A. Wills, A.S. Tremsin, V. Luzin, T. Shinohara, O. Kirstein, M.H. Meylan, and E.H. Kisi Residual stress arising from many manufacturing processes ( e . g . welding, forming, or additive manufacturing) can have a profound effect on mechanical performance. Strain tomography via neutron imaging promises a powerful experimental approach, but has been demonstrated in just a small number of special cases. The authors develop a general algorithm for tomographic reconstruction of residual strain fields in two dimensions, and experimentally demonstrate the technique. Strain tomography has the potential to impact a number of fields within experimental mechanics, and this study represents a significant step toward the ultimate goal: general reconstruction in three dimensions. [Phys. Rev. Applied 10, 064034] Published Thu Dec 13, 2018
    Electronic ISSN: 2331-7019
    Topics: Physics
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  • 5
    Publication Date: 2017-10-26
    Description: Crystal Growth & Design DOI: 10.1021/acs.cgd.7b01048
    Print ISSN: 1528-7483
    Electronic ISSN: 1528-7505
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 6
    Publication Date: 2016-06-28
    Description: Spin-Echo Modulated Small Angle Neutron Scattering (SEMSANS) in Time-of-Flight (ToF) mode has been shown to be a promising technique for measuring (very) small angle neutron scattering (SANS) signals and performing quantitative Dark-Field Imaging (DFI), i.e., SANS with 2D spatial resolution. However, the wavelength dependence of the modulation period in the ToF spin-echo mode has so far limited the useful modulation periods to those resolvable with the limited spatial resolution of the detectors available. Here we present our results of an approach to keep the period of the induced modulation constant for the wavelengths utilised in ToF. This is achieved by ramping the magnetic fields in the coils responsible for creating the spatially modulated beam in synchronisation with the neutron pulse, thus keeping the modulation period constant for all wavelengths. Such a setup enables the decoupling of the spatial detector resolution from the resolution of the modulation period by the use of slits or gratings in analogy to the approach in grating-based neutron DFI.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 7
    Publication Date: 2015-12-18
    Description: High material penetration by neutrons allows for experiments using sophisticated sample environments providing complex conditions. Thus, neutron imaging holds potential for performing in situ nondestructive measurements on large samples or even full technological systems, which are not possible with any other technique. This paper presents a new sample environment for in situ high resolution neutron imaging experiments at temperatures from room temperature up to 1100 °C and/or using controllable flow of reactive atmospheres. The design also offers the possibility to directly combine imaging with diffraction measurements. Design, special features, and specification of the furnace are described. In addition, examples of experiments successfully performed at various neutron facilities with the furnace, as well as examples of possible applications are presented. This covers a broad field of research from fundamental to technological investigations of various types of materials and components.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 8
    Publication Date: 2017-11-21
    Description: Hydrology, Vol. 4, Pages 54: Real-Time Three-Dimensional Imaging of Soil Resistivity for Assessment of Moisture Distribution for Intelligent Irrigation Hydrology doi: 10.3390/hydrology4040054 Authors: Vasily Tremsin An affordable standalone sensor that can provide volumetric information on soil moisture distribution in real time was developed and tested for potential application in irrigation control systems. The moisture content of soil is reconstructed tomographically from electrical resistivity measured between multiple pairs of electrodes, which are installed on two opposite sides of the soil volume. The measurement of relative moisture content reconstructed from the measured resistance values demonstrated in this paper requires a simple, in-situ, two-point calibration (for dry and wet soil conditions) after electrodes are installed in place. This calibration has to be repeated once the soil conditions, such as salinity or fertilizer content, are altered as the season progresses. Historical data collected over a 12-month period can be stored locally or transferred over a wireless network at given intervals or in real time. Although existing single-point sensors can provide more accurate measurements of soil moisture, knowledge on the three-dimensional distribution of moisture around plant roots should allow substantial savings of precious fresh water resources and more intelligent multi-channel irrigation systems. The same system can possibly be extended to estimation of fertilizer distribution.
    Electronic ISSN: 2306-5338
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by MDPI
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  • 9
    Publication Date: 2018-01-13
    Description: Author(s): T. Reimann, A. Bauer, C. Pfleiderer, P. Böni, P. Trtik, A. Tremsin, M. Schulz, and S. Mühlbauer Spatially resolved neutron diffractive imaging with a microchannel plate collimator is used to directly map the nucleation of the skyrmion lattice (SkL) of the B20 compound MnSi at the conical to SkL transition as a function of magnetic field. Our study shows a macroscopic phase separation of the Sk... [Phys. Rev. B 97, 020406(R)] Published Fri Jan 12, 2018
    Keywords: Magnetism
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
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  • 10
    Publication Date: 2019-07-17
    Description: Direct imaging of the magnetosphere by the IMAGE spacecraft will be supplemented by observation of the global aurora. The IMAGE satellite instrument complement includes three Far Ultraviolet (FUV) instruments. The Wideband Imaging Camera (WIC) will provide broad band ultraviolet images of the aurora for maximum spatial and temporal resolution by imaging the LBH N2 bands of the aurora. The Spectrographic Imager (SI), a novel form of monochromatic imager, will image the aurora, filtered by wavelength. The proton-induced component of the aurora will be imaged separately by measuring the Doppler-shifted Lyman-a. Finally, the GEO instrument will observe the distribution of the geocoronal emission to obtain the neutral background density source for charge exchange in the magnetosphere. The FUV instrument complement looks radially outward from the rotating IMAGE satellite and, therefore, it spends only a short time observing the aurora and the Earth during each spin. To maximize photon collection efficiency and use efficiently the short time available for exposures the FUV auroral imagers WIC and SI both have wide fields of view and take data continuously as the auroral region proceeds through the field of view. To minimize data volume, the set of multiple images are electronically co-added by suitably shifting each image to compensate for the spacecraft rotation. In order to minimize resolution loss, the images have to be distort ion-corrected in real time. The distortion correction is accomplished using high speed look up tables that are pre-generated by least square fitting to polynomial functions by the on-orbit processor. The instruments were calibrated individually while on stationary platforms, mostly in vacuum chambers. Extensive ground-based testing was performed with visible and near UV simulators mounted on a rotating platform to emulate their performance on a rotating spacecraft.
    Keywords: Geophysics
    Type: Publilcation Spring AGU Meeting; May 30, 2000 - Jun 03, 2000; Washington, DC; United States
    Format: text
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