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  • Springer  (32)
  • American Institute of Physics (AIP)  (7)
  • Cambridge University Press  (3)
  • Sage Publications  (3)
  • Wiley  (3)
  • Taylor & Francis  (2)
  • American Association for the Advancement of Science (AAAS)  (1)
  • Amsterdam : Elsevier
  • Geological Society of London
  • Nature Publishing Group
  • 2000-2004
  • 1990-1994  (53)
  • 1950-1954
  • 1994  (34)
  • 1992  (19)
Collection
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  • 2000-2004
  • 1990-1994  (53)
  • 1950-1954
Year
  • 1
    Electronic Resource
    Electronic Resource
    Fragment rotational state distributions from the dissociation of NeIBr: Experimental and theoretical results (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6262-6275 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump–probe laser-induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I–Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5±1.2 cm−1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8±1.2 cm−1. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck–Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calculations. Analysis of specific rotational distributions in the context of the energy gap law shows poor quantitative agreement. The average fragment rotational energy relative to analogous Ne-containing complexes is, however, qualitatively predicted by the energy gap relations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463688
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational branching ratios from the dissociation of the NeIBr van der Waals molecule (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3536-3541 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The degree of vibrational excitation in the IBr fragment from the vibrational predissociation of NeIBr (A 3Π1) has been measured using two-color pump–probe laser-induced fluorescence spectroscopy. We find that for the lowest initial vibrational states examined, Δv=−1 dissociation pathways dominate the dynamics, while this channel is closed for v≥17. From this result, the A state binding energy (D0) of the complex is determined to be 67±4 cm−1, while that in the X electronic state is found to be 73±4 cm−1. The X state binding energy is identical to that for NeI2 and NeBr2, suggesting that the potential energy surface for NeIBr can be constructed from a summation of atom–atom pair potentials; we present such a model potential energy surface. The variations in the vibrational branching ratios, when combined with the trends in the predissociation rates, point to the importance of fragment rotational excitation in the dynamics of the dissociation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461908
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  • 3
    Electronic Resource
    Electronic Resource
    Nascent product states in the photoinitiated reaction of O3 and H2O (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 952-961 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational, vibrational and fine-structure state distributions for the reaction 16O(1D)+ H218O →16OH +18OH, triggered by 266 nm photolysis of O3, have been measured under conditions where less than 1% of the nascent fragments experienced collisions prior to detection. The distributions are qualitatively different than those reported earlier for 266 nm photolysis, which were evidently affected by collisions. The rotational and vibrational state distributions are similar to recent 248 nm photolysis experiments, but with differences attributed to collisional and/or energetic effects in those experiments. The "new'' 16OH is formed with vibrational populations in the ratio 0.39(v=0):0.29(v=1):0.3(v≥2). Gaussian rotational energy distributions peaked near N=12 give average rotational energies of 〈Erot〉 = 3440 and 2780 cm−1 for 16OH v=0 and v=1, respectively. The "old'' 18OH is much colder with vibrational populations 0.94(v=0):0.06(v=1) and a 18OH v=0 Gaussian rotational energy distribution characterized by 〈Erot〉 = 1920 cm−1.There is negligible rotational alignment of the 16OH fragments [βμJ' = β20(02) = 5A(0)2/4 = 0.06± 0.09], which is significantly less than expected for fragment rotations aligned with respect to the O+H2O relative velocity vector. The spin-orbit propensities deviate slightly from the statistical expectation and are characterized by [F2,N]/[F1,N]=(0.89±0.06) ×N/(N + 1). The Λ-doublet distributions for 18OH (all N) and 16OH (low-to-moderate N) fragments conform to an unconstrained-dynamics prior distribution. A slight propensity for Π(A') in excess of this expectation is seen for the 16OH (high N) fragments. These new results are discussed in terms of possible insertion and abstraction mechanisms for the reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463198
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  • 4
    Electronic Resource
    Electronic Resource
    The extraction of signal to noise values in x-ray absorption spectroscopy : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 856-858 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The assessment of signal to noise (S/N) values in x-ray absorption spectroscopy is important for a number of reasons. Two methods will be described that remove the signal to give the noise. The first uses polynomials and the second Fourier filtering. Having extracted the noise the signal can then be used to calculate the S/N ratio. The method described operates on a background subtracted spectrum and is quick so it can be done on line in an experimental situation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142627
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  • 5
    Electronic Resource
    Electronic Resource
    A femtojoule calorimeter using micromechanical sensors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3793-3798 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a highly sensitive new type of calorimeter based on the deflection of a "bimetallic'' micromechanical sensor as a function of temperature. The temperature changes can be due to ambient changes, giving a temperature sensor or, more importantly, due to the heat absorbed by a coating on the sensor, giving a heat sensor. As an example we show the results of using the sensor as a photothermal spectrometer. The small dimensions and low thermal mass of the sensor make it highly sensitive and we demonstrate a sensitivity of roughly 100 pW. By applying a simple model of the system the ultimate sensitivity is expected to be of the order of 10 pW. The thermal response time of the cantilever can also be determined, giving an estimate of the minimum detectable energy of the sensor. This we find to be 150 fJ and again from our model, expect a minimum value of the order of 20 fJ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144509
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  • 6
    Electronic Resource
    Electronic Resource
    Gallium arsenide surface reconstructions during organometallic vapor-phase epitaxy (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2610-2612 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ surface x-ray scattering studies of the GaAs(001) surface were used to determine whether specific surface reconstructions occur during organometallic vapor-phase epitaxy. Prior to growth, we find that surfaces heated in the presence of As form a c(4×4) structure, while those heated in the absence of organometallics or in Ga form two similar fourfold reconstructions. We find no evidence for the presence of any surface reconstruction during the actual layer-by-layer growth process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106924
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  • 7
    Electronic Resource
    Electronic Resource
    Picosecond time-resolved adsorbate response to substrate heating: Spectroscopy and dynamics of CO/Cu(100) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1704-1716 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The response of the molecular stretch mode of CO/Cu(100) near 2086 cm−1 (ν1) to resonant infrared, and nonresonant visible and ultraviolet pumping is measured on a picosecond time scale. Fourier transform infrared measurements establish that ν1 is anharmonically coupled to the frustrated translation near 32 cm−1 (ν4), so that transient shifts in ν1 indicate population changes in ν4. The ν1 response to visible and ultraviolet pumping is characterized by a spectral shift near zero delay time, which decays with a ≈2 ps time constant to an intermediate value, which then decays on a ≈200 ps time scale. The data agree well with a model whereby ν4 couples to both the photogenerated hot electrons and to the heated phonons. The characteristic coupling times to these two heat baths are found to both be a few picoseconds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467792
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  • 8
    Electronic Resource
    Electronic Resource
    Externally driven countercurrent multiplication in a mathematical model of the urinary concentrating mechanism of the renal inner medulla (1994)
    Springer
    Bulletin of mathematical biology 56 (1994), S. 491-514 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Substitution of measured permeabilities into mathematical models of the concentrating mechanism of the renal inner medulla yields less than the known urine osmolalities. To gain a better understanding of the mechanism we analyse a model in which a force of unspecified origin [expressed as fraction, ɛ, of entering descending thin limb (DTL) concentration] drives fluid from DTL to interstitial vascular space (CORE), thus concentrating the solution in DTL. When flow in the DTL reverses at the hairpin bend of the loop of Henle, the high solute permeability of ascending thin limb (ATL) permits solute to diffuse into the CORE thus permitting ɛ to be multiplied many-fold. Behavior of the model is described by two non-linear differential equations. In the limit for infinite salt permeability of ATL the two equations reduce to a single equation that is formally identical with that for the Hargitay and Kuhn multiplier, which assumes fluid transport directly from DTL to ATL (Z. Electrochem. Angew. Phys. Chem. 55, 539, 1951). Solutions of the equations describing the model with parameters taken from perfused thin limbs show that urine osmolalities of the order of 5000 mosm L−1 can be generated by forces of the order of 20 mosm L−1. It seems probable that mammals including desert rodents use some variant of this basic mechanism for inner medullary concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460468
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  • 9
    Electronic Resource
    Electronic Resource
    Spiral hexagonal circle packings in the plane (1994)
    Springer
    Geometriae dedicata 49 (1994), S. 39-70 
    Details
    ISSN: 1572-9168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We discuss an intriguing geometric algorithm which generates infinite spiral patterns of packed circles in the plane. Using Kleinian group and covering theory, we construct a complex parametrization of all such patterns and characterize those whose circles have mutually disjoint interiors. We prove that these ‘coherent’ spirals, along with the regular hexagonal packing, give all possible hexagonal circle packings in the plane. Several examples are illustrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01263534
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  • 10
    Electronic Resource
    Electronic Resource
    Amphiboles from Dalradian metasedimentary rocks of NE Scotland: environmental inferences and distinction from amphiboles of meta-igneous amphibolites (1994)
    Springer
    Mineralogy and petrology 51 (1994), S. 241-242 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Mehrere Formationen im unteren Teil der Appin Gruppe der Dalradians sind durch karbonatische und kalk-silikatische Lithologien gekennzeichnet. Amphibole treten in diesen metasedimentären Einheiten in verschiedener Ausbildung auf, als feinkörnige, disseminierte Kristalle, als radialstrahlige, die Gesteine durchwachsende Aggregate und in dunkelgrünen, zu mehr als 90% aus Amphibolen bestehenden Lagen. Elektronenstrahl-Mikrosondenuntersuchungen belegen einfache mineralchemische Zusammensetzungen, die Tremolite, tremolitische Hornblende und Magnesio-Hornblende umfassen. Die einzige bedeutende Substitution ist die zwischen Tremolit und Alumino-Tschermakit [MgSi ⇌ AlviAliv] und zwischen Tremolit und Ferri-Tschermakit [MgSi = FeviAliv]. Im Gegensatz dazu zeigen Amphibole aus den nahegelegenen Metavulkaniten und intrusiven Metadoleriten vier Substitutionstrends von Tremolit zu Ferro-Aktinolith, Edenit, Alumino-Tschermakit und Ferri-Tschermakit. Diese unterschiedlichen Trends könnten auch anderswo bei der Unterscheidung zwischen Para- und Orthoamphiboliten behilflich sein. Tremolitische Amphibole machen normalerweise einen Großteil der kalk-silikatischen Gesteine aus, in denen ansonsten nur Quarz ± Phlogopit auftritt. Karbonate fehlen bemerkenswerterweise. Dies weist auf Mg-reiche sedimentäre Protolithe, wie dolomitische Mergel mit möglicherweise etwas Magnesit, hin. Sedimentologische Überlegungen lassen die Ablagerung in abgeschnürten Küstenlagunen tropischer Breiten, die Teil eines weiträumigen stabilen Schelfes waren, vermuten.
    Notes: Summary Several formations within the lower part of the Dalradian Appin Group are characterised by calcareous and calc-silicate lithologies. Amphibole occurs in these metasedimentary units in a variety of habits, from fine-grained disseminated crystals, through radiating aggregates permeating the whole rock, to dark green layers consisting of over 90% amphibole. Electron microprobe analyses of these amphiboles exhibit simple compositional trends from tremolite, through tremolitic hornblende to magnesio-hornblende. The only significant substitutions are from tremolite towards alumino-tschermakite [MgSi ⇌ AlviAliv] and from tremolite towards ferri-tschermakite [MgSi ⇌ FeviAliv]. This is in marked contrast to amphiboles from nearby suites of metavolcanic rocks and intrusive metadolerites which exhibit four coupled substitutions, leading from tremolite towards the ferro-actinolite, edenite, alumino-tschermakite and ferritschermakite end-members. These distinctive compositional trends may aid the distinction between para- and ortho-amphibolites elsewhere. Tremolitic amphibole commonly constitutes a high proportion of the calc-silicate rocks, the only other phases present being quartz ± phlogopite. Carbonate minerals are notably absent. This suggests that the sedimentary protolith was high in Mg, such as a dolomitic marl, possibly containing some magnesite. Sedimentological considerations suggest deposition in tropical latitudes in restricted coastal lagoons forming part of an extensive stable shelf bordering a mature landscape.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159730
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