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  • 1
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tomographic imaging of the ionosphere is a recently developed technique that uses integrated measurements and computer reconstructions to determine electron densities. The integral of electron density along vertical or oblique paths is obtained with radio transmissions from low-earth-orbiting (LEO) satellite transmitters to a chain of receivers on the earth's surface. Similar measurements along horizontal paths can be made using transmissions from Global Position System (GPS) navigation satellites to GPS receivers on LEO spacecraft. Also, the intensities of extreme ultraviolet (EUV) emissions can be measured with orbiting spectrometers. These intensities are directly related to the integral of the oxygen ion and electron densities along the instrument line of sight. Two-dimensional maps of the ionospheric plasma are produced by analyzing the combined radio and EUV data using computerized ionospheric tomography (CIT). Difficulties associated with CIT arise from the nonuniqueness of the reconstructions, owing to limited angle measurements or nonoptimal receiver location. Improvements in both reconstruction algorithms and CIT measurement systems are being implemented to overcome these difficulties. New imaging systems being developed employ CIT for large area mapping of the plasma densities in the ionosphere. © 1998 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 69 (1998), S. 2747-2756 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A capacitive-discharge spot welder is described which is primarily intended for making electrical connections between small (〈25–150 μm diameter) wires and samples of metallic materials, although it can be used in many applications where miniature welds must be made. It has been particularly useful in allowing low resistance (several mΩ) contacts to be created on samples of rare earth and actinide intermetallic compounds which are highly resistant to soldering. The device has a minimum time constant of about 25 μs and can deliver a maximum of between 700 μJ and 400 mJ of energy to the weld region, depending on the resistance of the latter. A suitable electrode holder is also described, and considerations for choosing the electrode materials, selecting the contact wires, preparing the sample, and creating a weld are discussed. © 1998 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 564-578 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A clearance-sealed piston pump has been developed which can be used to move high pressure gases in a closed loop for the purpose of purification, mixing, or phase equilibration. It has been designed primarily with the former role in mind, so that inert gases may be used in the preparation of high purity intermetallic compounds to suppress the evaporation of volatile constituents without introducing contamination. To this end, the device is made in such a way as to minimize outgassing, leakage, the formation of dead volumes, and the creation of debris. The pump is intended for use at pressures of up to 200 bar. Its structural materials are highly resistant to corrosion, and this should enable the device to be used with a wide variety of reactive gases. Flow rates of between 4.3 and 0.043 l min−1 can be sustained without difficulty using realistic loads, although larger and smaller ones are possible. The pump is capable of producing a head of 0.23 bar. A novel system has been developed for sensing and controlling the position of the piston. This makes it possible to monitor and vary the instantaneous flow rate while minimizing wear and vibration. The arrangement does not require the presence of a transducer or any kind of feedthrough in the clean, high pressure environment. It may find applications in other areas where positioning is needed under hostile or demanding conditions, such as inside ultrahigh vacuum apparatus. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 247-250 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method is described for making electrical contacts to metallic materials which, because of their hardness and reactivity, can be very difficult to attach leads to using other techniques. These metals, including some of the heavy fermion materials, form inert and tightly bonded oxide layers which hinder the use of ordinary soldering methods. It has been found that a simple modification to an ordinary soldering iron, involving the replacement of the standard copper tip with one made of tungsten carbide, enables these oxide layers to be penetrated and electrical contact to be made without the use of flux. The size of the resulting contacts can be very small and their electrical resistance very low. Other, less viable, techniques for making contacts are also discussed, and a means of holding samples in place during soldering is described. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3402-3412 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A piston–cylinder cell has been constructed which makes it possible to achieve pressures of over 35 kbar at room temperature, and more than 29 kbar in a cryogenic environment. The use of a nonmagnetic cobalt–nickel alloy with an unusually high yield strength (1.97 GPa at 293 K) allows the cell to be used in the presence of large magnetic fields. It seems likely that the cobalt–nickel material can be used as a direct replacement for the celebrated (but largely unavailable) Russian nickel alloy in many applications where nonmagnetic pressure cells are needed. Such applications may also include other kinds of high pressure apparatus, such as diamond anvil and sapphire anvil cells. The pressure cell described in the present article employs the "Teflon cap" technique, and detailed information concerning the application of this method is given which can be used with a wide variety of cells of the piston–cylinder type. © 1999 American Institute of Physics.
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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In a conventional superconductor, the binding of electrons into the paired states that collectively carry the supercurrent is mediated by phonons — vibrations of the crystal lattice. Here we argue that, in the case of the heavy fermion superconductors CePd2Si2 and ...
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Acta biotheoretica 44 (1996), S. 165-168 
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The argument is put forward that genetic mutations are viable then only, when the changed pattern of growth and/or metabolism is accommodated by the taxon-specific biochemistry of the organisms, i.e. by adaptive, somatic/physiological plasticity. The range of somatic plasticity under changing environmental conditions, therefore, has a certain predictive value for the kind of mutations that are likely to be viable.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 1250-1251 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A special high-resolution routine of the EISCAT radar has been used to investigate the structure and development of the poleward wall of a deep trough in electron density. The feature was tracked by the radar during a 7-hour period under very quiet geomagnetic conditions. The field-aligned nature of the structure enabled an estimate to be made of the inclination of the geomagnetic field above EISCAT that was in good agreement with the current model. Observations of narrow field-aligned enhancements in electron temperature demonstrated that the wall of this trough is a dynamic feature, reforming regularly as the electron density responds on a time scale of tens of minutes to energy input from soft-particle precipitation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 16 (1998), S. 1169-1179 
    ISSN: 0992-7689
    Keywords: Ionosphere-magnetosphere interactions ; Polar ionosphere ; Radio science ; Ionospheric propagation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.
    Type of Medium: Electronic Resource
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