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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10034-10041 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulations are used to study two-dimensional hard rod fluids consisting of spherocylinders confined to lie in a plane. The phase behavior is mapped out as a function of the aspect ratio (L/D) of the particles, from the hard disc limit at one extreme (L/D=0) to the thin hard needle limit at the other (L/D=∞). For long rods, a 2D nematic phase is observed at high density in which the orientational correlation functions decay algebraically, indicating that the phase does not possess true long range orientational order. The simulation data indicate that the transition from this phase to the low density isotropic phase is continuous, via a Kosterlitz–Thouless disclination unbinding type mechanism, rather than first order. For short rods the nematic phase disappears so that, on expansion, the solid phase undergoes a first order transition directly to an isotropic phase. Although the latter phase is globally isotropic, we find evidence for strong local positional and orientational correlations between the particles. Where possible, the simulation results are compared and contrasted to experimental, simulation and theoretical data for other two-dimensional liquid crystalline systems. © 2000 American Institute of Physics.
    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 92 (2002), S. 1555-1563 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoacoustic spectroscopy is an absorption spectroscopy technique that is currently used for low-level gas detection and catalyst characterization. It is a promising technique for chemical analysis in mesoscale analysis systems because the detection limit scales favorably with miniaturization. This work focuses on the scaling properties of photoacoustic spectroscopy, and on the miniaturization of gas-phase photoacoustic detection of propane in a nitrogen ambient. The detection system is modeled with a transmission line analogy, which is verified experimentally. The model includes the effects of acoustic leaks and absorption saturation. These two phenomena degrade the performance of the photoacoustic detector and must be controlled to realize the scaling advantages of photoacoustic systems. The miniature brass cells used to verify the model employ hearing aid microphones and optical excitation from a mechanically chopped, 3.39 μm He–Ne laser, transmitted into the cells with an optical fiber. These cells are able to detect 10 ppm of propane in nitrogen (a signal level of ∼1 Pa/W). We also describe the development of a miniaturized photoacoustic system formed by microfabrication. In this case, the pressure-driven deflection of the detection membrane is measured optically. These systems show that photoacoustic detection may be inappropriate for systems with large variations in gas concentration because of absorption saturation and changing gas acoustic properties. Nevertheless, photoacoustic spectroscopy is a promising technique for the analysis of dilute mixtures in miniature chemical systems. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1329-1336 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the past, minimal improvements have been predicted for efficiency enhancement of solar cells using the impurity photovoltaic (IPV) effect, where optical excitation through midgap defect levels allows the use of long wavelength photons to increase the conversion efficiency of sunlight to electricity. In the present work, the principle of detailed balance is used to calculate the limiting efficiency of solar cells with the inclusion of the impurity photovoltaic effect, in the idealized case when all transitions are assumed to be radiative. Based on these calculations, the limiting efficiency of the IPV device with a large number of different defect species is determined to be 77.2%. The terrestrial performance of the IPV device is also investigated by comparing its spectral sensitivity with that of tandem solar cell designs. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7217-7224 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The bulk thermodynamic properties of membrane proteins originate from a complex combination of molecular interactions. We propose a simple model based on the pair interactions between a model membrane protein, annexin V. The experimental observations of a honeycomb (p6) and a triangular (p3) phase are successfully reproduced with Monte Carlo computer simulations. Grand canonical simulations and a newly developed "strip"-move constant pressure technique reveal the stability of a dilute fluid phase and a dense solid phase, not observed with the current experimental technology. While this model is extremely simple in that it relies only on hard-body and short-range directional interactions, it nevertheless captures the essential physics of the interactions between the protein molecules and reproduces the phase behavior observed in experiments. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 80 (1958), S. 5329-5332 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 80 (1958), S. 5332-5333 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 29 (1957), S. 79-81 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 30 (1958), S. 233-237 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1246-1248 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chromium-doped aluminum nitride (AlN:Cr) films were grown on p-doped silicon (111) by rf magnetron sputtering in a nitrogen atmosphere at a pressure of 10−4 Torr. Film thickness was typically 200 nm. After growth, the films were "activated" at ∼1300 K for 30 min in a nitrogen atmosphere. Films activated in this manner exhibit intense cathodoluminescence and photoluminescence emission. Spectral evidence demonstrates conclusively that the luminescent centers are Cr3+ ions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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