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  • Articles  (233)
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  • 2000-2004  (241)
  • 2003  (78)
  • 2002  (91)
  • 2001  (72)
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  • Articles  (233)
  • Other Sources  (8)
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  • 2000-2004  (241)
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  • 2003  (78)
  • 2002  (91)
  • 2001  (72)
  • 2004  (89)
  • 2000  (89)
Journal
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 1361-1369 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic energy transfer pathways that occur following collisions between I2 in the E ion-pair electronic state (v=0, J=55) and He and Ar atoms have been determined. The nearby D, D′, and β ion-pair states are populated, but with relative branching ratios that vary with the rare gas collision partner. In He/I2 collisions, the D state is preferentially populated, while Ar/I2 collisions preferentially populate the β electronic state. Bimolecular rate constants and effective hard sphere collision cross sections have been determined for each channel; the cross sections range from 7.0±1.0 Å2 for populating the β state with Ar collisions to 0.9±0.2 Å2 for populating the D′ state with He collisions. For both rare gas collision partners, and all three final electronic states, low vibrational levels are populated, in rough accord with the relevant Franck–Condon factors. There is little propensity observed for population of vibrational levels that are in near resonance with the initially prepared level in the E state. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1214-1232 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The mechanism of the reaction CH4+O(1D2)→CH3+OH was investigated by ultrafast, time-resolved and state-resolved experiments. In the ultrafast experiments, short ultraviolet pulses photolyzed ozone in the CH4⋅O3 van der Waals complex to produce O(1D2). The ensuing reaction with CH4 was monitored by measuring the appearance rate of OH(v=0,1;J,Ω,Λ) by laser-induced fluorescence, through the OH A←X transition, using short probe pulses. These spectrally broad pulses, centered between 307 and 316 nm, probe many different OH rovibrational states simultaneously. At each probe wavelength, both a fast and a slow rise time were evident in the fluorescence signal, and the ratio of the fast-to-slow signal varied with probe wavelength. The distribution of OH(v,J,Ω,Λ) states, Pobs(v,J,Ω,Λ), was determined by laser-induced fluorescence using a high-resolution, tunable dye laser. The Pobs(v,J,Ω,Λ) data and the time-resolved data were analyzed under the assumption that different formation times represent different reaction mechanisms and that each mechanism produces a characteristic rovibrational distribution. The state-resolved and the time-resolved data can be fit independently using a two-mechanism model: Pobs(v,J,Ω,Λ) can be decomposed into two components, and the appearance of OH can be fit by two exponential rise times. However, these independent analyses are not mutually consistent. The time-resolved and state-resolved data can be consistently fit using a three-mechanism model. The OH appearance signals, at all probe wavelengths, were fit with times τfast(approximate)0.2 ps, τinter(approximate)0.5 ps and τslow(approximate)5.4 ps. The slowest of these three is the rate for dissociation of a vibrationally excited methanol intermediate (CH3OH*) predicted by statistical theory after complete intramolecular energy redistribution following insertion of O(1D2) into CH4. The Pobs(v,J,Ω,Λ) was decomposed into three components, each with a linear surprisal, under the assumption that the mechanism producing OH at a statistical rate would be characterized by a statistical prior. Dissociation of a CH4O* intermediate before complete energy randomization was identified as producing OH at the intermediate rate and was associated with a population distribution with more rovibrational energy than the slow mechanism. The third mechanism produces OH promptly with a cold rovibrational distribution, indicative of a collinear abstraction mechanism. After these identifications were made, it was possible to predict the fraction of signal associated with each mechanism at different probe wavelengths in the ultrafast experiment, and the predictions proved consistent with measured appearance signals. This model also reconciles data from a variety of previous experiments. While this model is the simplest that is consistent with the data, it is not definitive for several reasons. First, the appearance signals measured in these experiments probe simultaneously many OH(v,J,Ω,Λ) states, which would tend to obfuscate differences in the appearance rate of specific rovibrational states. Second, only about half of the OH(v,J,Ω,Λ) states populated by this reaction could be probed by laser-induced fluorescence through the OH A←X band with our apparatus. Third, the cluster environment might influence the dynamics compared to the free bimolecular reaction.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4132-4138 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The collision-induced electronic energy transfer that occurs when I2 in the E(0g+) ion-pair electronic state collides with ground electronic state I2 has been investigated. We prepare I2 in single rotational levels in v=0 of the E state using two-color double resonance laser excitation. The resulting emission spectrum shows that the nearby (ΔTe=−385 cm−1) D(0u+) electronic state is populated. The cross section for collision-induced E→D energy transfer is found to be 18±3 Å2. A range of D state vibrational levels are populated, consistent with a model in which overlap between the initial and final vibrational wave functions is important, but modulated by propensities for small vibrational energy gaps and those energy gaps that are closely matched to the v=0→v=1 energy separation in the I2(X) collision partner. © 2001 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 58 (2001), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The ratios of stable isotopes 18O/16O and 13C/12C, in sagittal otolith carbonate from two tropical demersal teleosts, red emperor Lutjanus sebae and Rankin cod Epinephelis multinotatus, from several locations in northern Western Australia, differed between sites. On a broad scale, fish from the four locations, Shark Bay, Ningaloo, Pilbara, and Broome had stable isotope values that were sufficiently different to indicate separate stocks, and it is appropriate to manage these populations of the two species independently in these areas. On a smaller scale, there may be limited mixing of these species between the Pilbara trawl fishery and the trap and line fisheries operating out of Onslow and Broome. Values of stable oxygen isotopes were strongly related to sea surface temperature, although there were some sites in shallow water where low values of stable oxygen isotopes indicated that fish were living in warm water. The use of stable oxygen and carbon isotope values is a valuable, cost effective method of determining the degree of mixing of fish stocks.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 44 (2002), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Spo0A~P is the essential response regulator and transcription factor for sporulation initiation in Bacillus subtilis. The phosphorylation level of Spo0A in the cell is determined by the sensor kinase activity of the phosphorelay, donating phosphoryl groups, and the antagonistic effects of dephosphorylation mediated by the Rap and Spo0E families of phosphatases. In this study, spo0A mutations were generated that encoded proteins less sensitive to the activity of Spo0E than the wild-type protein. The Spo0A substitutions N12K, P60S, L62P and F88L are surface exposed and localize to the same face of the molecule as the active site and in its close proximity on the β1–α1, β3–α3 and β4–α4 loops. The corresponding surface in the Spo0F response regulator was shown previously to be involved in the interaction with the RapB phosphatase, as well as the KinA histidine kinase and the Spo0B phosphotransferase. Thus, residues occupying the same position (N12:Q12, F88:Y84) and the same loops in Spo0A or Spo0F are involved in the interaction with the structurally unrelated Spo0E and RapB phosphatases, respectively, in addition to kinases and phosphotransferase. The specificity in phosphatase target recognition must be the result of side-chain variability within the response regulators and the interactions they promote. The residues involved in Spo0E interaction are identical in all Spo0A orthologues from spore-forming Bacilli encoding Spo0E phosphatases.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1367-1367 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This talk will describe proposed studies of atomic- and nanoscale dynamics in condensed matter which take advantage of the high coherent x-ray flux to be produced by future x-ray free-electron laser (FEL) sources, such as the Linac Coherent Light Source at Stanford. In particular, I will focus on the current status and future prospects for photon correlation spectroscopy using coherent x-rays (XPCS), and the use of the ultrashort pulse structure of the x-ray FEL to observe dynamics into the femtosecond range. © 2002 American Institute of Physics.
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique for selective characterization of the structure of free and buried thin-film interfaces by vibrationally resonant sum frequency generation spectroscopy is described. Manipulation of Fresnel coefficients by choice of film thickness on a reflecting substrate allows simultaneous optimization of the signal from the desired interface and minimization of the signal from other interfacial sources. This technique is demonstrated for the free polystyrene (PS)/air and the buried PS/spin-on glass interfaces. Our spectra show that the pendant phenyl group orientation is similar at the buried and free interfaces, with the phenyls pointing away from the bulk PS at each interface.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1809-1811 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present in situ surface x-ray scattering measurements of PbTiO3 epitaxy by metal–organic chemical-vapor deposition. Oscillations in crystal truncation rod intensity corresponding to layer-by-layer growth are observed under a variety of growth conditions. At lower PbO overpressures, we observe a transition to step-flow growth and an increased rate of recovery after growth, indicating a higher surface mobility. © 2002 American Institute of Physics.
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  • 9
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of mycorrhizal infection, soil P availability and fruit production on the male function of reproduction were examined in two cultivars of tomato (Lycopersicon esculentum Mill.). Tomato plants were grown in a greenhouse under three treatment combinations: non-mycorrhizal, low P (NMPO); non-mycorrhizal, high P (NMP3); and mycorrhizal, low P (MPO). In addition, all treatment combinations were grown both with and without fruit. Fruit production decreased final leaf biomass, flower production and in vitro pollen tube growth rates, often reducing the beneficial effects of increased P uptake. Thus, fruit production diverted resources from subsequent vegetative growth, flower production and pollen development. As the growing season progressed, mean pollen production per flower and in vitro germination and tube growth decreased. Mycorrhizal infection and high soil P conditions increased final leaf biomass, flower production, mean pollen production per flower (in one cultivar) and in vitro pollen tube growth rates. Thus, mycorrhizal infection and high soil P conditions increased pollen quantity and quality, thereby enhancing fitness through the male function. Similar trends in these treatments suggested that mycorrhizal effects on the male function were largely the result of improved P acquisition.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Water and environment journal 16 (2002), S. 0 
    ISSN: 1747-6593
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: An organism diversity index for use with mixed liquor or wastewater samples was developed to assess the species richness and diversity of activated sludge. The index was used in several studies and was found to be fast and simple to perform using basic laboratory equipment. Two bench-scale and two pilot-scale studies found that the resulting ‘organism diversity index’value was a good indicator of process performance and was not influenced by the total concentration of the mixed-liquor suspended solids but by their nature alone. The technique rapidly yielded pertinent information about the health of the sludge and could be used instead of genetic investigations to obtain population information quickly enough for wastewater-treatment plant process control.
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