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  • 1995-1999  (1)
  • 1990-1994  (2)
  • 1970-1974  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5526-5539 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for the reactions of NO+NH3 and NO+H2 has been developed for simulating the reduction of NO on Pt(100) in the 10−6 mbar pressure range for temperatures between 300 and 700 K. The model consists of seven ordinary differential equations for describing the coverage changes of six adsorbed species as well as an equation for describing the 1×1(arrow-right-and-left)hex phase transformation. Simulations of the N2 and H2O reaction rates for both reaction mixtures reproduced the hysteresis effects and the existence range for kinetic oscillations, which were found in the experiments. In addition, the occurrence of the so-called "surface explosion'' in both reaction systems is well described by the model. In contrast to the NO+CO reaction on Pt(100), where oscillations may also take place on a pure 1×1 substrate, the 1×1(arrow-right-and-left)hex phase transition occurs during oscillations for the NO+NH3 and NO+H2 reactions. The transitions between different adsorbate/substrate phases during one oscillatory cycle which are predicted by the model are in agreement with experimental observations made by photoemission electron microscopy (PEEM) for the NO+NH3 reaction. Using values for the constants which were taken from experiments, the model provided quantitative predictions of the absolute reaction rates as well as the relative rates of the competing reaction channels, e.g., N2 and NH3 production in the case of the NO+H2 reaction. The similar dynamical behavior observed in the NO+H2 and NO+NH3 reactions on Pt(100) is attributed to the insensitivity of NO reduction to the source of the hydrogen atoms.
    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 67 (1996), S. 4000-4004 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This work describes an improved CO2 laser intracavity photoacoustic spectrometer. It can detect and measure small quantities of trace gases in air. The measured absorption sensitivity of 3.3×10−10 cm−1 corresponds to a mixture of 11 pptv (volume parts per trillion) of ethene in nitrogen. The sensitivity and reliability of the instrument were enhanced by reducing the level of background signals originating from optical and acoustical sources. The sensitivity reached is comparable with the best existing continuous measuring instruments while the background signal is two orders of magnitude smaller. The improvements are described in detail and a comparison to previous work is made. A first measurement demonstrates the suitability of the apparatus for biological applications. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 57 (1993), S. 185-191 
    ISSN: 1432-0649
    Keywords: 42.55.Hq ; 42.60.By
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the recent progress in the performance of the CO-overtone Δv=2 laser. We were able to increase both the number of lines and the output power by a significant amount. This laser is now a reliable source for spectroscopic applications in the spectral region from 2500–3800 cm−1. The typical parameters of the laser plasma and a table with the observed laser transitions and their frequencies are given.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 11 (1972), S. 127-136 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We prepared helices with noncomplementary bases by N1-oxidation of poly A, followed by reaction with poly U. Mixing curves indicate that doubly and triply helical structures form, with only the unmodified adenines involved in base pair formation. Circular dichroism spectra were examined particularly at the absorbance maximum of the adenine N1-oxide (A*). In the single strand poly (A,A*), there is a relatively strong pair of positive and negative CD bands from the A*. These are greatly reduced in the double helix, and abolished in the triple helix. We conclude that A* stacks in a conventional manner with A in the single strand, but is rotated out of the double and triple helix. In the double helix the A* probably maintains a preferred orientation with respect to the helix, but rotates randomly in the triple helix.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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