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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 7 (1972), S. 29-53 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary It is shown that the Gouy-Chapman double layer analysis adequately describes the variation of the surface potential of monolayers of acidic natural lipids over a wide range of surface charge density and salt concentration. It is also shown that the potential which initially appears when an electrolyte gradient is rapidly imposed across a bilayer membrane is due to a difference in the double layer potentials on the two sides of the membrane. This conclusion follows from the fact that the observed bilayer potentials arise much more rapidly than can be accounted for by charge migration across the membrane and from the observation that the bilayer membrane concentration potentials, when measured immediately after establishment of a gradient, are equal to the surface potential change observed when the subphase concentration of a monolayer of the same lipid is changed by an amount equal to the gradient across the bilayer. The bilayer potential and monolayer potential changes, so measured, agree in a number of different electrolyte solutions over a wide range of electrolyte concentrations and surface charge densities. Because of this agreement and the applicability of the Gouy theory to monolayers, initial bilayer potentials may be calculated if the composition of the mixture used to form the membrane is known, provided that the pK's and areas of such components are available. In the absence of this information, membrane potentials may be calculated from electrophoretic data on the membrane lipid mixture; the conditions under which the latter approach is possible have been determined. The experimental results indicate that the composition of monolyers and bilayers spread from the same lipid mixture in decane are very similar, that the composition of the two types of film closely resembles the composition of the solution used to generate them, and that bilayer membranes are close-packed. The evidence further indicates that if any hydrocarbon solvent remains in these bilayers, it must be so situated that it contributes little, if anything, to the surface area. The steady state potential in the bilayer membrane system is frequently not identical with the initial potential which supports the hypothesis that in many cases only a fraction of the electrical conductance of unmodified membranes is caused by the ions which constitute the bulk electrolyte. An expression for the relationship between diffusion and double layer potentials has been derived which shows that, in the absence of any intrinsic selectivity of the hydrocarbon region of the membrane for hydrogen, hydroxyl, or impurity, the two potentials should be identical.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 8 (1989), S. 189-190 
    ISSN: 1432-0789
    Keywords: Nitrogen ; Ammonium ; Nitrate ; Nitrogen extraction ; Soils ; Nitrogen mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A roller bed and rotary end-over-end shaker were compared for the extraction of mineral N from a variety of soil types; both were equally efficient with an optimum extraction time of 30 min. However, the roller bed permitted a greater operational capacity, a faster throughput of samples, and easier identification of sample bottles compared with the end-over-end shaker. More NH4 +-N and NO3 −-N (P〈0.001) was recovered from soil by 2 M KCl than by any other extractant, in a soil: extractant ratio of 1 to 5 (w:v), except water, which was equally efficient at removing NO3 −-N from soils.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6508-6518 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-resolved cross sections for the inelastic scattering of OH(X 2Π) with CO and N2 have been measured in a crossed molecular beam apparatus over the energy range from 0.5 to 5.5 kcal mol−1. The magnitude and shape of the excitation functions for the same OH final states were virtually independent of the two targets except near threshold. Both spin–orbit conserving and spin–orbit changing transitions have been investigated. Cross sections for spin–orbit changing transitions of large ΔN were approximately the same magnitude as those for spin–orbit conserving transitions. For small ΔN, however, the spin–orbit conserving transitions became more favorable. The Λ-doublet ratio, Π(A')/Π(A‘), in the Π3/2 (F1) manifold differed from unity only for the N2 target for which the ratio became increasingly larger than unity as N' increased. The observed fine-structure effects were nearly the same as those from the corresponding (reverse) reactive collisions, and a close connection between the inelastic and reactive events has been conjectured.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1478-1479 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction CN+O2→NCO+O has been investigated in a crossed-molecular beam experiment at a collision energy of 0.76 kcal/mole. Internal state distributions of the ground state NCO(X˜ 2Π3/2, 0010,J,e/f) products have been measured by laser-induced fluorescence. The rotational excitation is small. There is an observed preference in the population of the K doublet fine-structure states, 1f〉1e, and this preference is even stronger for low J states.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2443-2459 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-to-state integral cross sections for the isotopic exchange reaction of CH(X 2Π) with D2 to produce CD(X 2Π) have been measured in a crossed-beam apparatus by the laser-induced fluorescence method. Two types of measurements were performed: (1) the translational energy dependence of an individual quantum state of the product and (2) the state distribution of the products at fixed and well-defined translational energy. To understand some of the finer details of the reaction dynamics similar experiments were also carried out on the reaction CD(X 2Π) with H2 to give CH(X 2Π). For the isotopic exchange channel, the cross section decreased rapidly with increasing translational energy, signifying a complex formation reaction mechanism. The CD(CH) product rotational level distributions are substantially colder than a statistical expectation and are interpreted as the result of a multiple-impact collision between the receding products in the exit channel. A novel frequency-locking mechanism, similar to that proposed to understand the dynamics of inelastic collisions between CH and D2 (the preceding paper), is suggested to explain anomalous peaks in the product rotational level distribution for the isotopic exchange channel. However, the fine-structure state distributions for the reactive process, which are very different from that for the inelastic channel, cannot be rationalized by conventional interpretation. Some basic concepts about fine-structure selectivity in chemical reactions have been developed. With these concepts, it is conjectured that the fine-structure state distributions of open-shell molecules arising from reactive encounters could provide a "fingerprint'' of the electronic wave function at the transition state.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 821-838 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-to-state integral cross sections for the inelastic scattering of CH(X 2Π) with He were measured in a newly constructed crossed molecular beam machine. Use of laser-induced fluorescence in an unconventional flux mode of detection provided single fine-structure state specific detection of the products. Two types of measurements were performed to further our understanding of the collision dynamics of open shell systems: (1) the product state distribution at a fixed and well-defined collision energy and (2) the dependence on collision energy of product state-resolved cross sections. A qualitative understanding of the collision dynamics can be obtained by properly factoring out features dependent on the fine-structure states, i.e., effects involving individual Λ-doublet states and features dependent on the rotational level alone, i.e., effects remaining after summing over all four fine-structure states associated with a given rotational quantum number. As for the fine-structure effects, a preferential population of product Λ-doublet states with reflection symmetry Π(A‘) was observed. The physical origin of this observed electronic orbital alignment can be attributed to a quantum interference phenomenon, as detailed in the accompanying paper. At the rotational level, the dominance of rotational rainbow scattering is unambiguously identified from both the existence of dynamical thresholds and a strong correlation between rotational level distributions at fixed translational energy and level specific excitation functions. These effects combined with other experimental observations lead us to visualize the CH+He scattering dynamics in a novel fashion. The collision can be regarded as a series of approximately independent sequential events each mediated by different regions of the interaction potential during the course of the whole encounter.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4443-4444 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The title reaction was studied in a new crossed molecular beam apparatus. Laser-induced-fluorescence was used to characterize both the reactant CH radical and the product CD radical in a state-resolved manner. Two types of dynamical information are reported here: (1) the excitation function for a specific reaction product state and (2) the product rotational state distribution at a well-defined collision energy.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2431-2442 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The state-to-state integral cross sections for the inelastic scattering of CH(X 2Π) and D2 to produce rotationally excited CH(X 2Π) product have been measured in a crossed-beam apparatus by the laser-induced fluorescence method. Two types of measurements were performed: (1) the translational energy dependence of an individual quantum state of the product and (2) the state distribution of the products at fixed and well-defined translational energy. For the inelastic scattering channel, the cross sections gradually increased from a dynamical threshold to a broad maximum and then slowly decreased as the translational energy increases. Evidence for multiple-impact rotational rainbows was found and a possible frequency-locking phenomenon between the two receding rotors resulted. Moderate orbital alignment was observed except for the highest rotational levels of the product. By comparing and contrasting the kinematically similar system CH(X 2Π)+He, the influence of a strongly attractive potential energy surface on the inelastic scattering of CH+D2 was inferred. Combining the results of the inelastic scattering and the isotopic exchange channels (the following paper) provide an unprecedented look into the dynamics of collisions between CH(X 2Π) and D2.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6689-6699 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the reactions of translationally energetic H atoms with BrCN, ClCN, and (CN)2 was studied by determining both the rotational state distribution and the translational energy disposition of the CN product ground vibrational level. The reaction was carried out using H atoms with a most probable translational energy of 92 kJ mol−1. The CN radical was monitored by time- and frequency-resolved absorption spectroscopy using the CN red system (A 2Π←X 2Σ) (2,0) band near 790 nm. Sub-Doppler resolution spectroscopy was used to determine the initial translational temperature of the CN(0,J) product. The fraction of the available reaction exothermicity that appeared as CN(0) rotational energy, fR, for H+XCN→HX+CN was 0.034±0.006, 0.061±0.02, and 0.13±0.007, for X=Br, Cl, and CN, respectively. Likewise, the fraction of the available reaction exothermicity that appeared as relative product translational energy, fT, was 0.52±0.25, 0.52±0.20, and 0.59±0.05, for X=Br, Cl, and CN, respectively. The absolute reaction cross sections for the H+XCN→HX+CN reactions were also measured to be 0.03, 0.02, and 0.3×10−16 cm2 for X=Br, Cl, and CN, respectively. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 101 (1994), S. 0 
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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