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  • American Institute of Physics (AIP)  (8)
  • Blackwell Publishing Ltd  (2)
  • 1990-1994  (10)
  • 1965-1969
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7951-7961 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a study of deep-ultraviolet-light-enhanced (4.1〈hν〈5.1 eV) oxygen reactions on GaAs from submonolayer to several monolayers coverage. The reaction is nonthermal and does not involve gas-phase excitation or dissociation of O2. Our experiments show a distinct wavelength and coverage dependence for the photoenhancement. X-ray photoelectron spectroscopy has been used to examine the chemical nature of the oxygen adsorbate and the GaAs oxides in order to find intermediate reaction species and evidence of the reaction pathways. The roles of photons and photogenerated carriers in the reaction enhancement mechanism are discussed. The results indicate that a mechanism based on photoemission of electrons into the growing oxide film is most in accord with the experimental observations. Such electron emission would increase the field-driven transport of oxygen to the GaAs interface.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 3327-3342 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A discrete version of the quaternionic Cauchy–Riemann equation ∂A=F, where F is Gauss–Poisson white noise, is discussed. On the lattice δZ4 random variables Fδ(δn) and Aδ(δn) are constructed which approximate the corresponding random fields F and A, respectively, in the limit δ→0. In the Gaussian case the random variables Aδ(δn) can be interpreted as the lattice approximation of the free electromagnetic Euclidean potential field whereas in the non-Gaussian case one obtains an approximation of nonlinear interacting electromagnetic quantum fields. Convergence to the continuum limit is proven.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 76 (1991), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The exotoxin pertussis toxin (PT) produced by virulent Bordetella pertussis bacteria is regarded as the main virulence factor of the organism and held responsible for most of its pathological effects. Identification of functional sites on PT would greatly facilitate site-specific detoxification and thus also the development of a new vaccine. For the investigation of structure-function aspects of PT we have prepared and characterized eleven monoclonal antibodies (mAbs) (UB-A1, UB-A2, UB-A10, UB-B7, UB-B12, UB-D4, UB-D7, UB-D10, UB-F7, UB-G1, and UB-G12) directed at the native toxin. Only UB-B12 and UB-D10 recognized PT in Western blotting indicating that most of the mAbs were directed against conformational epitopes. The mAbs were assayed for their ability to interfere with the binding of PT in model receptor systems like a solid phase binding assay using fetuin as receptor moiety, hemagglutination of chymotrypsin-sensitized goose erythrocytes, and the PT-mediated induction of the clustered growth pattern (CGP) of Chinese hamster ovary (CHO) cells. Five of the eleven mAbs (UB-A1, UB-A2, UB-B7, UB-B12, and UB-D7) interfered with the binding of PT to fetuin on solid phase and with PT-mediated hemagglutination. UB-A2, UB-B7, and UB-B12 also inhibited the induction of the clustered growth pattern of CHO-cells. This indicates that the determinants recognized by these mAbs are associated with the formation of the carbohydrate recognition sites of PT. Thus, the monoclonal antibodies described in this study will be valuable tools in the further analysis of the structure-function relationship of pertussis toxin with respect to receptor recognition and binding.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 4082-4084 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical contact resistivities of both Al and Cu single layer contacts as well as Cu/Au and Al/Au bilayer metal contacts to YBa2Cu3O7−x (YBCO) thin film have been studied. It was found that aluminum and copper make poor electrical contacts to YBCO due to interface reactions. These contacts have large contact resistivity (10−1–1 Ω cm2), orders of magnitude higher than that of a gold/YBCO contact (10−6 Ω cm2). When an ultrathin Au interlayer (10–30 A(ring)) was inserted between an Al or Cu overlayer and a YBCO film, interface reaction was greatly reduced. The contact resistivities of Al/Au and Cu/Au bilayer-metal contacts dropped by five orders of magnitude when Au interlayer thickness was increased from 0 to 10 A(ring). With the gold interlayer thickness of 15 A(ring), the Al/Au and Cu/Au bilayer-metal contacts reached a minimum contact resistivity, approaching that of a thick single-layer Au metal contact.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4211-4216 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analytical and numerical calculations of threshold behavior and electro-optical characteristics in twisted chiral nematic layers are presented, when weak anchoring in the tilt and twist angle of the director is assumed. An analytical expression for the effective twist angle and the Fréedericksz threshold voltage is derived. In cells with bistabilities, we investigate the influence of the anchoring parameters and device parameters on the width of the hysteresis. Using the 4×4-matrix formalism of Berreman [J. Opt. Soc. Am. 62, 502 (1972)], we demonstrate the influence of the weak anchoring on the transmission-versus-voltage characteristic.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 8417-8419 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The alloy system Six(SnyC1−y)1−x was investigated. The purpose is to form material with reduced strain at silicon heterojunctions. In this work, samples were prepared by coimplantation of tin and carbon ions into silicon wafers within the dosage range 1015–1016 cm−2, followed by rapid thermal annealing. Rutherford backscattering and channeling, Auger sputter profiling, and secondary-ion-mass spectrometry were employed to study the crystallinity, chemical composition, and depth profiles. A near-perfect crystallinity for 0.5 at. % of tin and carbon was achieved. For high-dose implanted samples, tin segregation was observed. This work demonstrates promising features of group-IV semiconductor synthesis by ion implantation.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 616-616 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1143-1145 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface chemistry of GaAs-oxide removal with an electron cyclotron resonance (ECR) hydrogen plasma has been investigated with x-ray photoelectron spectroscopy. It is found that As oxide is efficiently removed at room temperature, and heating expedites the removal of Ga oxide. Band bending changes during ECR hydrogen-plasma oxide reduction are also discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2228-2230 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrafast electromagnetic radiation induced by a femtosecond laser beam from a semiconductor provides determination of the impurity doping concentration, carrier mobility, sign, and strength of the depletion field near the semiconductor surface.
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The adherence mechanisms of enteropathogenic Escherichia coli (EPEC) to epithelial cells are still not understood. To study the molecular basis of the diffuse adherence (DA) phenotype exhibited by diarrhoeagenic E. coli expressing classical EPEC serotypes we investigated strain 2787 (O126:H27) isolated from a case of infantile diarrhoea. A 6.0 kb plasmid-derrved DNA fragment mediates the DA phenotype and encodes the 100 kDa adhesin protein AIDA-I (adhesin involved in diffuse adherence). Sequencing of the entire fragment revealed two open reading frames which encoded proteins of 45 kDa and 132 kDa, respectively. The 132 kDa protein has been identified as an AIDA-I precursor protein. After cleavage of the signal sequence further processing at the C-terminus of the 132 kDa precursor leads to the mature ∼100 kDa AIDA-I. While the exact function of the cytopiasmic 45 kDa protein is not known, preliminary evidence indicates that it is necessary for the correct maturation of AIDA-I. The AIDA-l precursor exhibits significant homology with the virG(icsA) protein of Shigella flexneri which seems to be involved in the intercellular spread of invasive Shigella organisms.
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