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  • American Chemical Society  (393,169)
  • American Institute of Physics  (129,796)
  • Cell Press  (35,351)
  • 1995-1999  (203,461)
  • 1990-1994  (229,170)
  • 1970-1974  (125,685)
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  • 1
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    Gas Hydrates: Review of Physical/Chemical Properties (1998)
    American Chemical Society
    In:  Energy & Fuels, 12 (2). pp. 191-196.
    Details
    Publication Date: 2020-07-31
    Description: An overview is provided of time-independent physical/chemical properties as related to crystal structures. The following two points are illustrated in this review:  (1) Physical and chemical properties of structure I (sI) and structure II (sII) hydrates are well-defined; measurements have begun on sH. Properties of sI and sII are determined by the molecular structures, described by three heuristics:  (i) Mechanical properties approximate those of ice, perhaps because hydrates are 85 mol % water. Yet each volume of hydrate may contain as much as 180 volumes (STP) of the hydrate-forming species. (ii) Phase equilibrium is set by the size ratio of guest molecules within host cages, and three-phase (Lw−H−V) equilibrium pressure depends exponentially upon temperature. (iii) Heats of formation are set by the hydrogen-bonded crystals and are reasonably constant within a range of guest sizes. (2) Fundamental research challenges are (a) to routinely measure the hydrate phase (via diffraction, NMR, Raman, etc.), and (b) to formulate an acceptable model for hydrate formation kinetics. The reader may wish to investigate details of this review further, via references contained in several recent monographs.
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  • 2
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    Iridoid glycosides of Leonurus persicus (1999)
    American Chemical Society
    In:  Journal of Natural Products, 62 (6). pp. 811-816.
    Details
    Publication Date: 2020-07-22
    Description: Two new iridoid glucosides, 6-O-acetylajugol (1) and 7,8-epoxy-8-epi-loganic acid (2), together with five known iridoid glucosides, galiridoside (3), ajugoside (4), 10-deoxygeniposidic acid (5), 7-deoxy-8-epi-loganic acid (6), and 8-O-acetylharpagide (7), have been isolated from the aerial parts of Leonurus persicus. Leucosceptoside A (8), eugenyl β-rutinoside (9), and kaempferol 3-O-glucoside (10) were also isolated. The structures of 1 and 2 were elucidated by extensive 1D- and 2D-NMR spectroscopy and molecular modeling. The structure of 3 was confirmed by single-crystal X-ray diffraction. Antimicrobial activity of compounds (1−10) was also evaluated against a panel of Gram-positive and Gram-negative bacteria and two strains of fungi.
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  • 3
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    New furanoid and seco-labdanoid diterpenes from Leonurus persicus (1996)
    American Chemical Society
    In:  Journal of Natural Products, 59 (2). pp. 131-134.
    Details
    Publication Date: 2020-07-22
    Description: Six new labdane diterpenoids, leopersin C (1), 15-epi-leopersin C (2), leopersin D (3), leopersin E (4), leopersin F (5), and 7-epi-leopersin F (6) were isolated from the aerial parts of Leonurus persicus. Their structures were elucidated by extensive use of 1D and 2D homonuclear and heteronuclear shift-correlated 1H−13C-NMR spectroscopic methods. Leopersin C (1) and 15-epi-leopersin C (2) were obtained as a C-15 epimeric mixture, and their structures were elucidated on this basis.
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  • 4
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    Further labdane diterpenoids isolated from Leonurus persicus (1997)
    American Chemical Society
    In:  Journal of Natural Products, 60 (9). pp. 874-879.
    Details
    Publication Date: 2020-07-22
    Description: Seven new labdane diterpenoids, leopersin G−L (1−4, 6−7) and 15-epi-leopersin J (5), and two known ones, 13-hydroxyballonigrinolide (8) and ballotenol (9), were isolated from the aerial parts of Leonurus persicus along with β-sitosterol and stigmasterol. The structure determinations were mainly based on 1D and 2D NMR spectra. The stereochemical configuration of ballotenol (9) was reestablished by 2D ROESY spectroscopy and by single-crystal X-ray diffraction analysis.
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  • 5
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    Detailed 1H- and 13C-nmr investigations of some diterpenes isolated from Leonurus persicus (1995)
    American Chemical Society
    In:  Journal of Natural Products, 58 (10). pp. 1543-1554.
    Details
    Publication Date: 2020-07-22
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  • 6
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    Classification of heterogeneous seafloor topography through surface slope distributions (1991)
    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 90 (4, Pt. 2). pp. 2255-2256.
    Details
    Publication Date: 2020-07-16
    Description: Seafloor topography is neither spatially homogeneous, nor does it obey Gaussian statistics; deviations from both of these assumptions are important from a geological and acoustic point of view. It has been found that the distribution of topographic slopes can be used as a primary tool for understanding the sources and extent of spatial heterogeneities and patterns on the seafloor. The covariance function has been widely used to characterize seafloor topography, but requires the assumption of Gaussian joint probability statistics to be valid. For heterogeneous topography characterized by large transient signals such as steep scarps and volcanoes, the covariance becomes dominated by the transients; in contrast the family slope distributions can still be used to derive stable descriptors for regions with large transient signals, as well as regions containing asymmetric features, and regions with only limited sampling. Knowledge of slopes is useful because a direct relation exists between the covariance and the slope distributions at different spatial scales. Studies of the slope distribution provide a means of identifying the presence of the non‐Gaussian elements in the topography, and flagging their spatial locations. The methods used here are demonstrated by applying them to three small patches of topography located within 20 km of each other in the Eastern Pacific. It is found that dominant azimuthal directions and dip angles differ widely between the patches. In addition, asymmetries in the cross‐sectional shapes of faulted abyssal hills are documented. [Work supported by ONR.]
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  • 7
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    High‐frequency bottom backscattering: Roughness versus sediment volume scattering (1992)
    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 92 (2). pp. 962-977.
    Details
    Publication Date: 2020-07-16
    Description: High‐frequency bottom acoustic and geoacoustic data from three well‐characterized sites of different bottom composition are compared with scattering models in order to clarify the roles played by interface roughness and sediment volume inhomogeneities. Model fits to backscattering data from two silty sites lead to the conclusion that scattering from volume inhomogeneities was primarily responsible for the observed backscattering. In contrast, measured bottom roughness was sufficient to explain the backscattering seen at a sandy site. Although the sandy site had directional ripples, the model and data agree in their lack of anisotropy.
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  • 8
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    New equation for the speed of sound in natural waters (with comparisons to other equations) (1974)
    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 56 (4). p. 1084.
    Details
    Publication Date: 2020-07-16
    Description: A new equation for the speed of sound in sea water has been developed with validity not only for realistic combinations of the parameters salinity, temperature, and pressure, but with extension to pure water as well. This new equation, referred to as NRL II, has a standard deviation of 0.05 m/sec. Tables are presented comparing calculations using this new model to each of eight earlier equations. Graphs are also included indicating approximate corrections that could be applied to existing sound speed profiles, but it is recommended that such profiles be recalculated and new ones obtained according to NRL II.
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  • 9
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    Depth-pressure relationships in the oceans and seas (1998)
    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 103 (3). pp. 1346-1352.
    Details
    Publication Date: 2020-07-16
    Description: Two sets of equations, covering all world oceans and seas, are presented to calculate pressure from depth for the computation of sound speed, and depth from pressure for use in ocean engineering. They are based on the algorithm of UNESCO 1983 [N. P. Fofonoff and R. C. Millard, Jr., Unesco Tech. Papers in Mar. Sci. No. 44 (1983)], and on calculations from temperature and salinity profiles. The pressure to depth conversion is presented first. The equations can be used in those cases where the desired accuracy is reduced to ±0.8 m. The equations to convert depth to pressure provide an overall accuracy between ±8000 Pa and ±1000 Pa. This leads to errors in sound speed consistently smaller than ±0.02 m/s. The discussion, and comparisons with results and other formulas, suggest that the new equations are a substantial improvement on the previous simplified ones, which should now be abandoned.
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  • 10
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    Vertinoid Polyketides from the Saltwater Culture of the FungusTrichodermalongibrachiatumSeparated from aHaliclonaMarine Sponge† (1998)
    American Chemical Society
    In:  The Journal of Organic Chemistry, 63 (26). pp. 10011-10014.
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    Publication Date: 2020-05-11
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