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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5903-5905 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ultrafine nickel particles have intriguing physical and chemical properties, which are interesting both in fundamental and applied research. The size of the particle was controlled by gas pressure. X-ray diffraction studies showed that fine Ni particles have fcc crystal structure and are coated with thin Ni oxide on the surface. Electron micrographs showed a spherical particle shape, forming a long chain. Size dependence of magnetic properties were studied. The specific magnetic moment drastically decreases when reducing the diameter d of particles 〈15 nm. The coercivity Hc also approaches zero when d is about 15 nm. Therefore, we can suppose that the critical size for superparamagnetism at room temperature is about 15 nm. According to the superparamagnetic formula KV=25 kT, the value of the magnetic anisotropy constant can be determined, K = −5.8 × 105 (erg/cc). It is found to be larger than bulk Ni [K=−3.4–5.1 × 104 (erg/cc)], the same as Fe particles. The maximum of coercivity at room temperature is about 250 Oe, that is less than the theory value for the coherent rotation model, Hc = 4 K/3Ms=1600 Oe. The mechanism of reversal magnetization can be understood by the sphere chain model. The critical diameter of the single domain is about 65 nm. Curie temperature Tc obviously decreases for 9-nm average diameter particles rather than bulk. It may be in connection with the lattice contraction.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3566-3578 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Space astronomy requires large-area cryogenic infrared focal plane arrays (FPAs) with high quantum efficiency, extremely low dark current, low power dissipation, and background limited noise performance. To meet these requirements, especially at temperatures of 5–15 K, Santa Barbara Research Center designed and fabricated a new multiplexer, CRC-744. The FPAs made by bonding InSb detector arrays to CRC-744 multiplexers were evaluated at the University of Rochester. The best array achieved the read noise of 5 e − with 12 s integration and 7 e − with 200 s integration with Fowler-64 sampling at 15 K, the average dark current of 〈0.2 e−/ s at both 15 and 29 K, and the average quantum efficiency of 87% at both 15 and 29 K. The 10%–90% rise time was 4 μs driving a 600 pF external load. The power dissipation was 0.3–0.4 mW when running flat-out (100% duty cycle). The full well capacity was 105 e− (230 mV) with 400 mV of applied bias. The above test results demonstrate that the FPAs meet background-limited space experiment requirements. The CRC-744 multiplexer works well down to at least 5 K (the lowest temperature of our tests). © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3314-3316 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Iron particles were prepared by a gas evaporation method in a nitrogen atmosphere. The particle size, shape, and magnetic properties were influenced by the nitrogen pressure. Particles prepared by this method were relatively stable in air and were not seriously oxidized. The recoilless fraction is low for the oxide layer, so that it cannot be detected at room temperature by Mössbauer spectrum. A superparamagnetic peak associated with the oxide microcrystal layer did not occur in the Mössbauer spectra due to the action of the magnetic field from the iron core and the interaction between iron particles and the low Debye temperature. From the electron micrography, the magnetic reversal process seems to be determined by a chain-of-spheres mechanism but Hc∼T curve cannot coincide with the Ms∼T curve at low temperatures. An increase of Hc may be associated with magnetic anisotropy. It is found that the magnetization versus temperature shows an anomalous increase in M(T) at higher T. We think that this means that the surface oxide layer was not magnetized to saturation even under 40 kOe at 5.5 K as the surface anisotropy is rather large.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2554-2556 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The low-energy theory for finite long carbon nanotube is derived and numerically examined. It shows that the electronic structure is dominated by the quantum confining, which determines the profile of wave functions as well as the eigen energies; while the details of the wave functions are resolved by the structure of the nanotubes. This behavior is attributed to the peculiar electronic structure of the nanotubes. Because of the slow variation of the profile of electron wave functions, the measured conductance is NOT independent of the position to measure it, which is evident in the multiprobe experiment. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Veterinary radiology & ultrasound 36 (1995), S. 0 
    ISSN: 1740-8261
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: A method for systematic examination of the livers was developed, based on identification of the hepatic and portal veins in sixteen dogs. The right medial, quadrate, left medial and lateral hepatic veins and the hepatic branches of the portal veins were easily located with the dog in dorsal recumbency. The right lateral and caudate hepatic veins were identified more easily from the right side with the transducer positioned between the ninth to the eleventh intercostal spaces. Visibility was affected by the fullness of the stomach but this effect could be minimized by changing the position of the transducer to select a more suitable anatomical approach. Identification of the two systems depended on their echogenicity, the anatomical position of the main branches and their pattern of distribution. As in humans, the portal veins were in general, more echogenic than the hepatic veins and the hepatic veins could be traced from their junctions with the caudal vena cava. Identification of the branches of the hepatic and portal veins was complicated by the anatomical shape, the nutritional status and respiratory stage of the animal. A systemic approach based on a knowledge of the distribution patterns produced by the hepatic and portal veins ensures that all liver lobes are identified and all important structures are assessed.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3718-3732 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two implementations of the backward Euler method for simulating molecular fluids are compared with Brownian dynamics and molecular dynamics simulations of a single diatomic molecule, liquid argon, a single butane molecule, and liquid butane. By comparison with standard molecular dynamics results, backward Euler simulations give different thermodynamic properties for liquids; predict liquid structures which are too solidlike; and incorrectly represent dynamical relaxation processes. The backward Euler methods allows longer time steps to be used in simulations at the cost of an energy minimization at every time step. Even when time steps more than 20 times larger than that required for energy and momentum conservation are used, neither implementation of the backward Euler algorithm is more accurate than standard molecular dynamics calculations with the same time step. We conclude that the new methods offer no computational advantages over more usual methods for simulating molecular fluids and that they often predict incorrect results. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9890-9890 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    The @journal of organic chemistry 58 (1993), S. 5513-5517 
    ISSN: 1520-6904
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 8645-8650 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 8635-8644 
    ISSN: 1520-5126
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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