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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7022-7024 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that GaAs grown by molecular beam epitaxy on silicon has ideal characteristics for THz receiver applications. The lattice mismatch between silicon and GaAs causes a disordered growth of GaAs, reducing the carrier lifetime to 1.8 ps. This is similar to the characteristics observed in low temperature grown GaAs. Furthermore, the high resistivity silicon substrate has a very low absorption and dispersion in the far infrared. This makes it an ideal material in THz system applications, and we show that a maximum frequency of 5 THz and a sixfold increase in sensitivity can be obtained using a GaAs-on-silicon based THz detector.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 349-359 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a conducting wire of finite length illuminated by an incident electromagnetic wave, induced surface current is represented as the sum of a driven term and resonant traveling waves, for which free-space propagation behavior is slightly modified by a perturbation m. Requiring current to vanish at the ends of the wire, both m and the resulting amplitude are obtained for normal incidence by applying Galerkin's method to the resulting trial function. In the Rayleigh limit cross sections are expressed analytically. For wires up to one-half wavelength long, we find equivalence with Tai's variational results [J. Appl. Phys. 23, 909 (1952)]. Beyond this point, the driven term goes over to the infinite cylinder current, as wire length increases. At the same time, for highly conducting wires one finds an explicit formula for m, in which ||m−1||(very-much-less-than)1; for moderate conductivity, m reduces to the attenuated propagation behavior found by Sommerfeld [J. A. Stratton, Electromagnetic Theory (McGraw-Hill, New York, 1941), pp. 524ff] for infinite-length wires.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 99 (1992), S. 0 
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Objective To investigate whether fetal weight estimation by ultrasound in diabetic pregnancy might be based upon fetal abdominal circumference (AC) alone.Design A retrospective study.Setting Diabetes Center, Rigshospitalet and Ultrasound Laboratory, Glostrup Hospital, Copenhagen.Subjects Eighty-six diabetic pregnant women who had an ultrasound study within 2 days before delivery.Results We assessed in 73 fetuses various formulas based upon biparietal diameter and AC against formulas based upon AC alone, and these were only marginally less effective than the more complex ones. In 86 fetuses an AC was available. These fetuses were divided into a study population and a test population. The linear model was customized for the study population. Evaluation on the test population showed that the relative error (error as a percentage of birthweight) in predicting birthweight had a Standard deviation of 7–8%. The efficacy of AC in detecting fetuses 〉4000 g was examined in the test population; If AC〉36–0 cm was chosen as riterion for macrosomia the positive and negative predictive values were 80% (8/10) and 91% (30/33), respectively.Conclusion Formulas for estimating fetal weight in diabetic pregnancy based on AC alone are almost as effective as more complex ones. We recommend a simple linear formula of fetal weight as a function of AC.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The heavy fermion superconductor UPt3 is thought to have a d-wave pairing ground state. The principal experimental evidence for this consists of the anisotropy of the power-law behavior observed in transverse ultrasound and μ+ SR measurements. The observation of a complex phase diagram in the superconducting state in ultrasound, torsional oscillator, and specific heat measurements may be a further indication of an unconventional pairing state. Theoretical investigations suggest the possibility of vortex lattices that are unconventional in their symmetry, their quantization, or the structure of their composite vortex cores. Transitions between such exotic vortex lattices are in principle allowed and could explain the observed features at H≈0.6 Hc2 (for H(parallel)cˆ) and H≈0.3Hc2 (for H⊥cˆ). Neutron diffraction is an ideal bulk probe of the microscopic properties of the vortex lattice. We have studied the vortex lattice with H⊥cˆ and T≈50 mK in the field range 0.75〈H〈10 kG. The structure of the vortex lattice and the quantization of the vortices, in addition to the London penetration depth, λL, the coherence length, ξ, and the effective mass anisotropy are all well determined by our measurements. The lattice is oblique hexagonal with conventional quantization. Its anisotropy can be explained by considering a combination of Fermi surface and gap anisotropy. However, the lattice does not appear to change near the transition between superconducting phases identified by other techniques.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 791-792 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extinction efficiency was measured for fibrous aerosol particles arrayed on a diaphragm in a plane orthogonal to the Poynting vector of the incident radiation. Very small quantities of material can be characterized in this static fashion. Two-dimensional extinction efficiencies for a series of graphitic fibers of various resistivities are shown to agree with results of a variational theory. Particle interaction distances initiate at approximately the value of the length of the particle.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1372-1374 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report an unexpected observation of strong terahertz pulses, radiated perpendicular to semiconductor-air interfaces illuminated by femtosecond laser pulses at normal incidence. Symmetry arguments preclude radiation emitted strictly along the direction of the surface electric field and the dipoles, normal to the interface. We attribute our observations to the strong interface-induced angular redistribution of the radiation being collected by a small dielectric lens. For detection, a small symmetry breaking displacement within the terahertz diffraction spot is sufficient.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 1265-1267 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate a new ultrafast pump-probe technique using terahertz pulses to investigate carrier transport and screening in semiconductors. As an example we have studied the temporal evolution of the local electric field in a dipole antenna, used for generation of ultrafast terahertz pulses. Ultrafast screening effects are shown to be important for both carrier transport and the emission of THz radiation. At high carrier densities the external bias field is screened on a time scale comparable to the duration of the THz pulse, giving rise to changes in the shape and bandwidth of the radiated pulses.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 45 (1990), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 26 (1993), S. 5350-5364 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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