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  • 1990-1994  (5)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 814-820 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In the field of condensed matter physics, it is frequently necessary to produce motion at low temperatures. While this can often be done using a mechanical linkage which connects the cryogenic and ambient environments, space constraints sometimes render such a solution impractical. The following paper describes a miniature dc electric motor which can be used to produce motion under these conditions, and also presents a novel scheme for monitoring its position. The motor is a skew-wound ironless device with a coaxial gearhead, and is capable of operating at a temperature of 4 K, in a vacuum, and in a magnetic field of several hundred gauss. The position monitoring arrangement requires no modifications to the motor or the addition of extra hardware, such as rotary encoders or potentiometers. Based on the angular dependence of the rotor inductance, it has been found to work with a number of different motors of the skew-wound ironless type, both at room temperature and at 4°. Provisions have been made to allow the motor and position monitor to be operated by computer control. The author anticipates that they will find applications in other areas where motion is needed and space is at a premium.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Pollen, diatom and chironomid fossils from the sediments of a core from Brier Island Bog Lake, Nova Scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in Atlantic Canada correlative with the European Younger Dryas ca. 10 to 11 ka. Our paleolimnological data were then compared to similar types of data from Splan Pond, New Brunswick to determine if there were any significant differences between a coastal and a more inland site. Nonarboreal pollen was dominant throughout the Brier Island core and the interval 10.0–11.0 ka did not show the typical decline in Picea and increases in tundra-like vegetation characteristic of many sites in Atlantic Canada. However, the limnological indicators did undergo marked changes in taxon composition. The chironomid assemblage was initially dominated by shallow-water, warm-adapted chironomid taxa followed by abundant Sergentia (a cold stenotherm) during 10–11 ka. Sergentia disappeared in the “post Younger Dryas” interval and the warm-adapted genera resumed dominance. Chironomid-inferred paleotemperature reconstructions revealed that at both Brier Island Bog Lake and Splan Pond, summer surface-water temperatures dropped abruptly to between 13 and 17°C during the 10–11 ka interval, suggesting that a cooler climate was present in Atlantic Canada correlative with the European Younger Dryas. Diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 90 (1993), S. 205-241 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Quantum oscillatory effects provide particularly unambiguous information about the properties of quasiparticles in metals, and have consequently been used for the purpose of understanding the low temperature behaviour of a wide variety of metallic elements and compounds, including the recently discovered heavy fermion materials. Unfortunately, the signals which are produced by these oscillations are often so weak as to be undetectable, because of the high effective masses of the quasiparticles, or the presence of imperfections in the samples, or otherwise. In order to improve our ability to measure these effects, the author has developed a system for the detection of resistance oscillations which uses a SQUID as the amplifying element and which fits inside a toploading dilution refrigerator probe. It has proven possible to use this instrument to investigate very elusive phenomena in samples which have been cooled to 0.02 K in magnetic fields of 13.7 tesla. For example, although no resistance oscillations have previously been seen in aluminum, except under conditions of magnetic breakdown, the new system has made it possible to detect resistance oscillations in this material under relatively arbitrary conditions. In the case of the heavy fermion compound CeRu2Si2, oscillations of 10−9 Ω have been detected against a background resistance of about 10−5 Ω, using excitation currents of around 10−2 A.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-7357
    Keywords: 71.28 ; 75.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent studies of properties of heavy quasiparticles have helped to establish thatf electrons and conduction electrons in the normal states of certain U and Ce compounds are characterised by Fermi volumes consistent with Luttingeris Theorem and by integrated qnasiparticle masses which agree with measured linear coefficients of the specific heat. Evidence is presented that this Fermi Liquid picture may, however, break down when the ground state is near pressure or magnetic field induced phase transitions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic ecology 26 (1992), S. 527-531 
    ISSN: 1573-5125
    Keywords: palaeolimnology ; Chironomidae ; taxonomy ; larval subfossils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Collections of adults ofParakiefferiella nigra Brundin indicate that this chironomid occurs widely in arctic and subarctic zones. In addition, it has occasionally been collected in cool temperate and boreal forest lakes of both North America and Europe. Although widely distributed, the larva and its habitat have not previously been described. Identity of the larva ofP. nigra has been established by studying associated reared specimens. The distinctive larva, with reduced second lateral mental teeth, is stenotopic, and on the basis of modern collections appears to be most abundant in cold, oligotrophic lakes. More data is required to establish the range of thermal environments inhabited by the larva. Larval head capsule remains ofP. nigra are common in late-glacial sediments of southwestern British Columbia lakes and provide important evidence for oligotrophic conditions during late-glacial time.
    Type of Medium: Electronic Resource
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