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  • 1
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of acetonitrile clusters [CH3CN]N, N=2–256: Melting transitions and even/odd character of small clusters (N=2–9), heat capacities, density profiles, fractal dimension, intracluster dimerization, and dipole orientation (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3791-3802 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamic and structural properties of acetonitrile clusters [CH3CN]N, N=2–15, 20, 30, 60, 128, and 256 have been investigated using Monte Carlo simulation. Interactions in the small clusters (N≤9) are dominated by antiparallel pairing of the molecular dipoles. The simulations reveal rigid ↔ fluid (melting) transitions with a remarkable even–odd alternation in the transition temperatures for the N=2–9 clusters. The higher melting temperatures of the even-N clusters arise as consequences of the antiparallel paired dipoles which provide favorable electrostatic interactions. Even–odd alternation has also been observed in the configurational energies and heat capacities and the percentage of molecules possessing an antiparallel nearest neighbor. These observations are consistent with the fact that Coulomb potential terms dominate the interaction energies in clusters with N〈12. The average density in clusters with N(approximately-greater-than)60 is fairly well represented by the bulk liquid density. Order parameters characterizing dipole orientation indicate that the molecular dipoles tend to lie flat on the cluster surface for N≥30. Significant dimerization within the clusters suggests evaporation of molecules via dimers and an enhancement of evaporative loss over condensation and this may explain the slower nucleation rates observed for acetonitrile compared to the predictions of the classical nucleation theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466367
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  • 2
    Electronic Resource
    Electronic Resource
    An all-acoustic parametric amplifier in superfluid helium (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4438-4445 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies of nonlinear acoustic interactions in superfluid helium at temperatures below 0.2 K have culminated in the construction of an all-acoustic parametric amplifier at gigahertz frequencies. This device represents the shortest wavelength parametric amplifier ever made, with signal wavelengths shorter than 1000 A(ring) and pump wavelengths shorter than 600 A(ring). In the experiment, plane waves are mixed at a predefined angle in the superfluid helium. Two gain regimes are observed. The first regime is a noncollinear phase-matched process, in which the signal phonon stimulates decay of the pump phonon to create gain at the signal frequency. The second regime is a four-phonon collinear process, in which gain on the signal is created by the second harmonic of the pump. This four-phonon process is unusual and is shown to be a combination of three-phonon processes wherein the lack of conservation of energy and momentum in one process is mostly compensated by the other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346194
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  • 3
    Electronic Resource
    Electronic Resource
    Homogeneous nucleation in supersaturated vapors of polar molecules: Acetonitrile, benzonitrile, nitromethane, and nitrobenzene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3356-3368 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The critical supersaturations (Sc) required for the homogeneous nucleation of acetonitrile, benzonitrile, nitromethane, and nitrobenzene vapors have been measured over wide temperature ranges using a thermal diffusion cloud chamber. At Tr=0.44, the experimental results are higher than the predictions of the classical nucleation theory by 20% (CH3NO2), 50% (CH3CN), 57% (C6H5NO2), and 112% (C6H5CN). This trend correlates well with the dipole moments and to a lesser extent with the polarizabilities of these substances. Corresponding states of simple fluids and scaled nucleation law show that CH3CN and CH3NO2 have similar nucleation behavior which is different from that of C6H5CN and C6H5NO2. Correlations with other less polar substances are examined. The scaled law, with Ω (the excess surface entropy per molecule) determined from the temperature dependence of the bulk surface tension, gives a better description of the experimental results than the classical theory with the exception of nitromethane. The results suggest that the classical theory does not take proper account of the dipole–dipole interaction in calculating the free energy of the embryonic droplets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464108
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of homogeneous nucleation data of polar molecules: Vapor association, dipole orientation, and elongated clusters (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3369-3379 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present the results of several theoretical models examined in order to explain the observed systematic deviations of the homogeneous nucleation of highly polar substances from the predictions of the classical nucleation theory (CNT). It is found that molecular association in acetronitrile or nitromethane vapor cannot explain the observed higher supersaturations. Similarly, the use of virial coefficient data to obtain a size dependent surface energy correction factor does not reproduce the experimental results. It is shown that orientation of the surface dipoles within the spherical droplets results in higher supersaturations in agreement with the experimental findings. We also generalize the CNT for elongated clusters and show that these clusters can allow for favorable end-to-end and antiparallel alignments of the dipoles. It is found that for reasonable agreement with experiment, acetonitrile, and benzonitrile clusters require a larger degree of elongation compared to nitromethane and nitrobenzene clusters. These results are discussed in relation to molecular simulations of bulk liquids and clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464109
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  • 5
    Electronic Resource
    Electronic Resource
    The incidence of three virus diseases of winter oilseed rape in England and Wales in the 1991/92 and 1992/93 growing seasons (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant pathology 43 (1994), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The incidence and severity of three diseases of oilseed rape, caused by beet western yellows luteovirus (BWYV), cauliflower mosaic caulimovirus (CaMV) and turnip mosaic potyvirus (TuMV), were assessed in England and Wales in the springs of 1992 and 1993. In 1992, 62% of oilseed rape crops examined were found to contain BWYV, with an average of 28% plants infected; 14% of crops contained CaMV, with an average of 5% plants infected; and TuMV with 3% crops and 〈 1% plants infected. In 1993, BWYV was found in 42% of crops and 12% of plants infected; CaMV in 25% of crops and 7% of plants infected; and TuMV in 14% of crops and 5% plants infected. The yields of plants showing severe virus symptoms were reduced by an estimated 70 to 79%. The high incidence of CaMV and TuMV in oilseed rape crops could have important consequences for rapeseed production in the UK and also serve as a source of virus for vegetable brassicae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3059.1994.tb01656.x
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  • 6
    Electronic Resource
    Electronic Resource
    Structural Characterisation of Corrosion Inhibiting Zinc Nickel Electroplate by Rietveld Methods (1993)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 133-136 (Jan. 1993), p. 501-506 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/00/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.133-136.501.pdf
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of mercury on unidirectional sodium and calcium influx inAsellus aquaticus (1991)
    Springer
    Archives of environmental contamination and toxicology 21 (1991), S. 567-570 
    Details
    ISSN: 1432-0703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Notes: Abstract The effect of mercuric chloride (HgCl2) and monomethyl mercury chloride (CH3HgCl) on unidirectional22Na and45Ca influx were measured in the freshwater isopodAsellus aquaticus. Flux measurements involved short-term (20 min) exposure to22Na or45Ca following 2 h pre-exposure to Hg. Experiments were conducted at two different Na and Ca concentrations, 0.025 mmol L−1 and 0.25 mmol L−1. HgCl2 and CH3HgCl inhibited Na influx at both Na concentrations although Na influx at 0.25 mmol L− was always higher. This reflected the uptake kinetics of the Na pump which was determined to be saturable with a kmax values of 32 μmol Na g−1 h−1 and a Km value of 0.8 mmol L−1. CH3HgCl generally resulted in relatively greater inhibition of Na influx. At 0.025 mmol NaL−1 all CH3HgCl concentrations tested were inhibitory to Na influx, i.e., the lowest observed effect concentration (LOEC) was 〈0.04 μmol L−1. Ca influx was inhibited by HgCl2 at all concentrations tested (LOEC 〈0.04). The degree of inhibition was unaffected by Ca concentration, which was seen as evidence for non-competitive inhibition. However, CH3HgCl, which inhibited Ca influx from 0.025 mmol Ca L−1 by 〉68% at molar Hg concentrations ≥1 μmol L−1 showed no significant inhibitory affect at 0.25 mmol Ca L−1. Elimination of CH3HgCl inhibition at the higher Ca concentration suggests competition in this case, possibly at the level of access to the Ca pump.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183879
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  • 8
    Electronic Resource
    Electronic Resource
    Structure of bis(pentamethyldiethylenetriamine)disodium hexasulfide (1993)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 1482-1483 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270193001167
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  • 9
    Electronic Resource
    Electronic Resource
    A note on quaternary climate modelling using Boolean delay equations (1990)
    Springer
    Climate dynamics 4 (1990), S. 263-267 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Boolean delay equation model of Ghil et al. for the study of Quaternary ice ages has been re-examined and also extended to include a hydrological feedback mechanism that directly influences the thermohaline circulation. For the basic Ghil et al. model (with the original and with corrected time delays), we show that the maximum duration for a high ice volume state depends continuously but not monotonically on the time delays of the problem. In particular, both short spiky glacials and longer glacials can be obtained from identical parameter values by simply choosing different initial conditions. In the extended model, we find that an additional temperature-hydrology-ocean feedback mechanism tends to generate longer glacials, but in neither case do the average time scales of model variability compare favourably with those of the major Quarternary glacials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211063
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  • 10
    Electronic Resource
    Electronic Resource
    The cardiovascular and central nervous system effects in the human of U-62066E (1994)
    Springer
    European journal of clinical pharmacology 46 (1994), S. 203-207 
    Details
    ISSN: 1432-1041
    Keywords: U-62066E ; Opioid antagonist ; blood pressure ; heart rate ; plasma catecholamines ; naloxone ; Doppler regional blood flow ; kappa receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The cardiovascular and central nervous system effects of the kappa opioid receptor agonist U-62066E were investigated in ten normal male subjects who received U-62066E or placebo with low or high dose naloxone in a randomized, double blind study. Blood pressure and heart rate in the supine and standing position, plasma adrenaline and noradrenaline, regional Doppler blood velocity indices and psychometric assessments were recoreded for 1.25 h before and 6 h following injection. U-62066E caused sedation and dysphoria but no euphoria. Plasma noradrenaline was increased by U62066E when compared with basal levels. This action of U62066E was prevented by high but not low dose naloxone. U-62066E had no significant effect on blood pressure, heart rate or regional blood flow indices in the vessels studied and no effect on plasma adrenaline levels. Since U62066E at a dose known to have marked kappa effects was not found to influence cardiovascular indices our results do not support a major role for kappa opioids in the control of the circulation. However, U62066E may influence noradrenaline release or clearance and cause sedation and psychotomimetic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192549
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