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  • 1
    Electronic Resource
    Electronic Resource
    Phase separation in segmented polyurethanes derived from mixtures of polyether polyols with different functionality (1996)
    Springer
    Journal of polymer research 3 (1996), S. 221-225 
    Details
    ISSN: 1572-8935
    Keywords: Segmented polyurethanes ; Phase separation ; Compatibility ; Polyol mixture ; Thermal transitions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A series of segmented polyurethanes containing 60 wt° of hard segments (HS) was prepared from MDI (4,4′-diphenylmethane diisocyanate) ethylene glycol and mixtures of a polyoxyethylene end-capped polyoxypropylene triol and a polyoxyethylene end-capped polyoxypropylene diol. The effects of the content of polyether diol in polyether polyols on phase separation and properties was investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and investigation of tensile properties. The DSC and DMA results indicate that the polyurethane derived from only polyether triol exhibits obvious phase separation and that the HS is immiscible with the SS, but that the HS is compatible with the HS for the polyurethane derived from polyether diol. As the content of polyether diol increases, the compatibility between HS and SS increases. As the content of polyether diol increases, the tensile strength. elongation. toughness and tear resistance of the polyurethanes increases. but their moduli decrease. The modulus-temperature dependence in the temperature region of −30 to 65 °C increases as the polyether diol content increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01493491
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  • 2
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    Oscillations in D-region absorption at periods of one to two months (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: One to two month oscillations in D-region absorption are found in seven years of daily f-min data from low latitude stations at Singapore (1N, 104E) and Rarotonga (21S, 160W). Coherency (cross-spectral) analyses reveal that solar flux variations account for much of the f-min variance at these periods. Over the range of periods from 10 to 200 days, statistically significant linear correlation is found between the f-min time series and contemporaneous 10.7 cm solar flux mearurements at periods of 16 to 19 days, the 26 to 29 day solar rotation band, and a broad band covering 43 to 80 day periods.
    Keywords: GEOPHYSICS
    Type: NASA-CR-184684 , NAS 1.26:184684
    Format: application/pdf
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  • 3
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    Rossby-gravity waves in tropical total ozone (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Randel (1992) has recently reported evidence for Rossby-gravity waves in tropical data fields produced by the European Centre for Medium Range Weather Forecasts (ECMWF). The purpose of this paper is to show that similar features are observable in fields of total column ozone from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The observed features are episodic, have zonal (east-west) wavelengths of approximately 6,000-10,000 km and oscillate with periods of 5-10 days. The modes exhibit westward phase progression and eastward group velocity. A simple linear model is used to estimate the magnitude of total ozone perturbations induced by Rossby-gravity waves. The model is able to account for the magnitude of observed TOMS features as well as their asymmetry about the equator. The significance of finding Rossby-gravity waves in total ozone fields is that: (1) the report of similar features in ECMWF tropical fields is corroborated with an independent data set; and (2) the TOMS data set is demonstrated to possess surprising versatility and sensitivity to relatively smaller scale tropical phenomena.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 20; p. 2239-2242
    Format: text
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  • 4
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    Time-varying zonal asymmetries in stratospheric nitrous oxide and methane (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: Previously analyses of Stratospheric And Mesospheric Sounder (SAMS) data of atmospheric constituent gases have dealt almost exclusively with zonal means (and mostly monthly means), owing perhaps to concern over data quality. The purpose of this note is to show that, with care, time-dependent zonally-asymmetric features may be recovered from the SAMS nitrous oxide and methane data. As an example, we demonstrate the existence of zonal wave-1 constituent perturbations with periods of a few weeks in the middle and upper stratosphere. When the perturbations are normalized by the constituent zonal-mean mixing ratio to compensate for the slowly varying (in both space and time) background concentration of constituents, wavepacket-like features are found over all latitudes and seasons in the three-year SAMS record. One specific low-latitude case discussed had features which appear to be consistent with constituent oscillations induced by episodic equatorial Kelvin waves. Further studies are needed to better identify the nature of the plethora of observed wave-like phenomena.
    Keywords: GEOPHYSICS
    Type: Royal Meteorological Society, Quarterly Journal (ISSN 0035-9009); 119; 511; p. 591-598.
    Format: text
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  • 5
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    Kelvin waves in total column ozone (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Tropical Kelvin waves have been observed previously in ozone mixing ratio data from the SBUV (Solar Backscatter Ultraviolet) and LIMS (Limb Infrared Monitor of the Stratosphere) instruments on board the Nimbus-7 satellite. The present study investigates Kelvin wave features in total column ozone, using version 6 data from the Total Ozone Mapping Spectrometer (TOMS) instrument (also on Nimbus-7). Results show eastward-propagating zonal waves 1-2 with periods approx. 5-15 days, amplitudes approx. 3-5 Dobson Units (1-2% of the time mean), and latitudinal symmetry typical of Kelvin waves. The analyses and a linear model in this study suggest that the primary source of the perturbations is slow Kelvin waves in the lower-to-middle stratosphere. Maximum Kelvin wave signatures occur in conjunction with westward lower-to-middle stratospheric equatorial zonal winds (a quasi-biennial oscillation (QBO) wind modulation effect). The significance of these results is that the TOMS data are shown to be useful for investigations with global coverage of a major component of tropical stratospheric dynamics, Kelvin waves. The TOMS data set with its excellent coverage and high quality should be useful in validating model studies in the relatively data sparse and dynamically difficult tropical region.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 2; p. 105-108
    Format: text
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  • 6
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    CH4 and N2O photochemical lifetimes in the upper stratosphere - In situ estimates using SAMS data (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Upper stratospheric photochemical lifetimes are estimated in situ for CH4 and N2O for the first time, based on an analysis technique using 3 years of satellite measurements from the Stratospheric And Mesospheric Sounder (SAMS) instrument. The technique involves investigation of the time dependence of tracers injected into high northern latitudes in late winter and their subsequent photochemical decay during the dynamically quiescent summer stratosphere. Dynamical corrections are made for mean meridional circulation contributions. The lifetimes for N2O at 2 and 7 hPa (about 43 and about 35 km altitude) are found to be 1.7 and 8.3 months, respectively. For CH4, 0.6 (about 52 km altitude) and 2 hPa lifetimes are 3.3 and 3.4 months, respectively. These observed values are in good agreement with model calculations by Solomon et al. (1986).
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 677-680
    Format: text
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  • 7
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    Low-frequency oscillations in total ozone measurements (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Low frequency oscillations with periods of approximately one to two months are found in eight years of global grids of total ozone data from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The low frequency oscillations corroborate earlier analyses based on four years of data. In addition, both annual and seasonal one-point correlation maps based on the 8-year TOMS data are presented. The results clearly show a standing dipole in ozone perturbations, oscillating with 35 to 50 day periods over the equatorial Indian Ocean-west Pacific region. This contrasts with the eastward moving dipole reported in other data sets. The standing ozone dipole appears to be a dynamical feature associated with vertical atmospheric motions. Consistent with prior analyses based on lower stratospheric temperature fields, large-scale standing patterns are also found in the extratropics of both hemispheres, correlated with ozone fluctuations over the equatorial west Pacific. In the Northern Hemisphere, a standing pattern is observed extending from the tropical Indian Ocean to the north Pacific, across North America, and down to the equatorial Atlantic Ocean region. This feature is most pronounced in the NH summer.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 13797-13
    Format: text
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  • 8
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    Oscillations in D-region absorption at periods of one to two months (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: One to two month oscillations in D-region absorption are found in seven years of daily f-min data from low latitude stations at Singapore (1 deg N, 104 deg E) and Rarotonga (21 deg S, 160 deg W). Coherency (cross-spectral) analyses reveal that solar flux variations account for much of the f-min variance at these periods. Over the range of periods from 10 to 200 days, statistically significant linear correlation is found between the f-min time series and contemporaneous 10.7 cm solar flux measurements at periods of 16-19 days, the 26-29 day solar rotation band, and a broad band covering 43-80 day periods.
    Keywords: GEOPHYSICS
    Type: Journal of Atmospheric and Terrestrial Physics (ISSN 0021-9169); 51; 975-981
    Format: text
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  • 9
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    Possible feedback path for low-frequency atmospheric oscillations (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Four years of satellite-derived microwave radiance data have been analyzed, providing evidence for the possiblity of a feedback route in the Southern Hemisphere. The present propagation path extends from the central equatorial Pacific across lower South America, heads equatorward after passing south of Africa, and finally reenters the equatorial Indian Ocean with correct phase to enhance the primary equatorial dipole structure. The Southern Hemisphere propagation path migrates northward in April-September and southward in October-March, and it may constitute a feedback mechanism which could stabilize the low frequency oscillations.
    Keywords: GEOPHYSICS
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 45; 1425-143
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  • 10
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    Short meridional scale anomalies in the lower stratosphere and upper troposphere (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Consequences of the discovery of short-meridional scale anomalies (SMSAs) in the lower stratospheric temperature field in the analyses of Microwave Sounding Unit channel 4 data are examined. The time scales of these features, their presence in the u-wind, v-wind, and geopotential, and the heat and momentum fluxes resulting from the SMSAs are investigated. The SMSAs are not regularly propagating features. Latitudinal movement occurs in both northern and southern directions. Both eastward movement and stationarity are observed in the zonal direction. In episodes, SMSAs require a few days to grow, persist from a few days to two weeks, and then decay over a few days. Heat fluxes are small. It is suggested that the SMSAs are possibly caused by secondary effects of baroclinic disturbances.
    Keywords: GEOPHYSICS
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 42; 2081-209
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