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  • 1
    Electronic Resource
    Electronic Resource
    Silicon-Directed Nazarov Reactions III. Stereochemical and Mechanistic Considerations (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2397-2411 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of remote substituents on the stereochemical outcome of electrocyclization in the silicon-directed Nazarov reaction has been examined. While the degree of stereocontrol was modest (ca. 3:1) the substituent in the major isomer (4,5 or 7-substituted cis-hexahydroind-2-en-1-ones) is always cis to the protons on the ring fusion. Thorough spectroscopic and conformational analysis revealed that divergent senses of electrocyclization are responsible for the observed products. Additional experiments suggest that steric, rather than stereoelectronic forces control the sense of cyclization. A qualitative description of the nature of reactive intermediates in the silicon-directed Nazarov reaction is proposed as well as an explanation for the remarkable efficacy of FeCl3 for inducing the reaction.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660803
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  • 2
    Electronic Resource
    Electronic Resource
    Silicon-Directed Nazarov Reactions II. Preparation and Cyclization of β-Silyl-substituted Divinyl Ketones (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2377-2396 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two general methods for the preparation of β-silyl-substituted divinyl ketones have been developed starting from either α, β-unsaturated aldehydes or simple ketones. Anhydrous FeCl3 induces the cyclization to cyclopentenones under mild conditions and in good yields with predictable and complete control over the position of the double bond in the five-membered ring. The observed effects of substituents on rate can be explained by a rate-determining cationic electrocyclization. Silyl substitution has been shown to retard the reaction.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660802
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  • 3
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    January and July global distributions of atmospheric heating for 1986, 1987, and 1988 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Three-dimensional global distributions of atmospheric heating are estimated for January and July of the 3-year period 1986-88 from the European Center for Medium Weather Forecasts (ECMWF) Tropical Ocean Global Atmosphere (TOGA) assimilated datasets. Emphasis is placed on the interseasonal and interannual variability of heating both locally and regionally. Large fluctuations in the magnitude of heating and the disposition of maxima/minima in the Tropics occur over the 3-year period. This variability, which is largely in accord with anomalous precipitation expected during the El Nino-Southern Oscillation (ENSO) cycle, appears realistic. In both January and July, interannual differences of 1.0-1.5 K/day in the vertically averaged heating occur over the tropical Pacific. These interannual regional differences are substantial in comparison with maximum monthly averaged heating rates of 2.0-2.5 K/day. In the extratropics, the most prominent interannual variability occurs along the wintertime North Atlantic cyclone track. Vertical profiles of heating from selected regions also reveal large interannual variability. Clearly evident is the modulation of the heating within tropical regions of deep moist convection associated with the evolution of the ENSO cycle. The heating integrated over continental and oceanic basins emphasizes the impact of land and ocean surfaces on atmospheric energy balance and depicts marked interseasonal and interannual large-scale variability.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 7; 8; p. 1270-1285
    Format: text
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  • 4
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    Artificial neural network for the determination of Hubble Space Telescope aberration from stellar images (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: An artificial-neural-network method, first developed for the measurement and control of atmospheric phase distortion, using stellar images, was used to estimate the optical aberration of the Hubble Space Telescope. A total of 26 estimates of distortion was obtained from 23 stellar images acquired at several secondary-mirror axial positions. The results were expressed as coefficients of eight orthogonal Zernike polynomials: focus through third-order spherical. For all modes other than spherical the measured aberration was small. The average spherical aberration of the estimates was -0.299 micron rms, which is in good agreement with predictions obtained when iterative phase-retrieval algorithms were used.
    Keywords: OPTICS
    Type: Applied Optics (ISSN 0003-6935); 32; 10; p. 1720-1727.
    Format: text
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  • 5
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    A global analysis of stratospheric-tropospheric exchange during northern winter (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The global and the regional distributions of the time-averaged stratospheric-tropospheric (ST) mass exchange were analyzed. Using a mathematical formulation of ST exchange, the cross-tropopause mass flux was diagnosed globally for January 1979, and contributions by physical mechanisms including the diabatic transport and the quasi-horizontal adiabatic transport along isentropes that intersect the tropopause surface were evaluated. Two regions of mass flux zonally integrated into the stratosphere were found: one over tropical latitudes associated with diabatic transports, and a second one over subpolar latitudes associated with adiabatic transport. The results are consistent with independent analyses of trace atmospheric constituents.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 121; 1; p. 162-172.
    Format: text
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  • 6
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    Atlas of the global distribution of atmospheric heating during the global weather experiment (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Global distributions of atmospheric heating for the annual cycle of the Global Weather Experiment are estimated from the European Centre for Medium-Range Weather Forecasts (ECMWF) Level 3b data set. Distributions of monthly, seasonally, and annually averaged heating are presented for isentropic and isobaric layers within the troposphere and for the troposphere as a whole. The distributions depict a large-scale structure of atmospheric heating that appears spatially and temporally consistent with known features of the global circulation and the seasonal evolution.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-CR-4370 , REPT-91A01339 , NAS 1.26:4370
    Format: application/pdf
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  • 7
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    Global heating distributions for January 1979 calculated from GLA assimilated and simulated model-based datasets (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This study surveys the large-scale distribution of heating for January 1979 obtained from five sources of information. Through intercomparison of these distributions, with emphasis on satellite-derived information, an investigation is conducted into the global distribution of atmospheric heating and the impact of observations on the diagnostic estimates of heating derived from assimilated datasets. The results indicate a substantial impact of satellite information on diagnostic estimates of heating in regions where there is a scarcity of conventional observations. The addition of satellite data provides information on the atmosphere's temperature and wind structure that is important for estimation of the global distribution of heating and energy exchange.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 4; 395-406
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  • 8
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    The three-dimensional distribution of atmospheric heating during the GWE (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The large-scale three-dimensional time-averaged distribution of heating and its temporal evolution as determined from the European Center for Medium-range Weather Forecasts (ECMWF) Global Weather Experiment (GWE) Level IIIb data set are examined. Global distributions of vertically averaged heating for January, April, July, and October 1979 are presented to illustrate the seasonal evolution of the planetary pattern. Horizontal distributions of heating and vertical profiles from various climatological regimes of the planetary circulation are given and provide insight into the four-dimensional structure of the thermal forcing of the atmosphere. Major features of the global distributions include heating in regions of deep moist convection over places such as South America. Seasonal meridional and zonal heating migration are discussed and it is noted that zonal migration is linked with planetary scale distribution of continents and oceans and the land-sea surface temperature distribution. Various degrees of heating in the troposphere and their consequences are investigated.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Tellus, Series A - Dynamic Meteorology and Oceanography (ISSN 0280-6495); 42A; 305-327
    Format: text
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