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  • GEOPHYSICS  (162)
  • Life and Medical Sciences  (126)
  • Analytical Chemistry and Spectroscopy  (118)
  • 1990-1994  (406)
  • 1980-1984
  • 1994  (406)
Collection
Keywords
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  • 1990-1994  (406)
  • 1980-1984
Year
  • 1
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    Landau damping of auroral hiss (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A2; p. 2471-2488
    Format: text
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  • 2
    Electronic Resource
    Electronic Resource
    Nongenomic regulation of extracellular matrix events by vitamin D metabolites (1994)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 56 (1994), S. 331-339 
    Details
    ISSN: 0730-2312
    Keywords: 1,25-(OH)2D3 ; 24,25-(OH)2D3 ; matrix vesicles ; nongenomic regulation ; extracellular matrix ; alkaline phosphatase ; phospholipase A2 ; Protein kinase C ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Vitamin D metabolites appear to regulate chondrocytes and osteoblasts via a combination of genomic and nongenomic mechanisms. Specificity of the nongenomic response to either 1,25-(OH)2D3 or 24, 25-(OH)2D3 may be conferred by the chemical composition of the target membrane and its fluid mosaic structure, by the presence of specific membrane receptors, or by the interaction with classic Vitamin D receptors. Nongenomic effects have been shown to include changes in membrane fluidity, fatty acid acylation and reacylation, arachidonic acid metabolism and prostaglandin production, calcium ion flux, and protein kinaase C activity. Chondrocytes metabolize 25-(OH)D3 to 1,25-(OH)2D3 and 24,25-(OH)2D3; production of these metabolites is regulated by both growth factors and hormones and is dependent on the state of cell maturation. 1,25-(OH)2D3 and 24,25-(OH)2D3 may interact directly with extracellular matix vesicles to regulate their function in the matrix, including protease activity, resulting in matrix modefication and calcification. Isolated matrix vesicles, produced by growth zone chondrocytes, can activate latent transforming growth factor-β when incubated with exogenous 1,25-(OH)2D3. These observations suggest that nongenomic regulation of martix vesicle structure and function may be a mechanism by which mesenchymal cells, like osteoblasts and chndrocytes, may modulate events in the extracellular matrix at sites distant from the cell surace.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240560309
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  • 3
    Electronic Resource
    Electronic Resource
    Increase in copy number of an integrated vector during continuous culture of Hansenula polymorpha expressing functional human haemoglobin (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 10 (1994), S. 1569-1580 
    Details
    ISSN: 0749-503X
    Keywords: Hansenula ; haemoglobin ; integration ; continuous culture ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Recombinant human haemoglobin A (rHbA) was produced by a leucine-requiring strain of Hansenula polymorpha which had been transformed with an integration vector containing the Saccharomyces cerevisiae LEU2 gene and cDNAs for the expression of α and β globin each driven by the H. polymorpha MOX promoter. After 40 generations in a chemostat it was found that the integrated vector had become amplified in the host strain. In some cases this led to an increase in LEU2 gene dosage, but a loss of globin expression cassettes. In other cases the globin gene dosage also increased. These changes coincided with an increase in rHbA production in the culture, which was reversed when the dilution rate was increased. Isolates from a chemostat culture producing elevated levels of rHbA were grown in fed-batch fermentations, resulting in higher productivities than when inoculated with the parent strain. The rHbA produced was purified and characterized. Oxygen binding studies and electrospray mass spectrometry showed that the rHbA had been processed and assembled correctly, and behaved as a fully functional co-operative tetramer.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/yea.320101206
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  • 4
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    Relativistic electron acceleration and decay time scales in the inner and outer radiation belts: SAMPEX (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: High-energy electrons have been measured systematically in a low-altitude (520 x 675 km), nearly polar (inclination = 82 deg) orbit by sensitive instruments onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX). Count rate channels with electron energy thresholds ranging from 0.4 MeV to 3.5 MeV in three different instruments have been used to examine relativistic electron variations as a function of L-shell parameter and time. A long run of essentially continuous data (July 1992 - July 1993) shows substantial acceleration of energetic electrons throughout much of the magnetosphere on rapid time scales. This acceleration appears to be due to solar wind velocity enhancements and is surprisingly large in that the radiation belt 'slot' region often is filled temporarily and electron fluxes are strongly enhanced even at very low L-values (L aprroximately 2). A superposed epoch analysis shows that electron fluxes rise rapidly for 2.5 is approximately less than L is approximately less than 5. These increases occur on a time scale of order 1-2 days and are most abrupt for L-values near 3. The temporal decay rate of the fluxes is dependent on energy and L-value and may be described by J = Ke-t/to with t(sub o) approximately equals 5-10 days. Thus, these results suggest that the Earth's magnetosphere is a cosmic electron accelerator of substantial strength and efficiency.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 6; p. 409-412
    Format: text
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  • 5
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    Perpendicular electron heating by absorption of auroral kilometric radiation (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We investigate the possibility of perpendicular heating of electrons and the generation of '90 deg -electron conics' by particle diffusion in velocity space due to wave-particle interaction with intense auroral kilometric radiation. This interaction is made possible by the downward shift in the R-X cutoff below the electron cyclotron frequency that occurs in the presence of warm plasma. We stimulate this condition and solve the diffusion equation using a finite difference algorithm. The results show strong perpendicular electron heating and indicate that the main characteristics of an electron conic distribution can be reproduced under these conditions.
    Keywords: GEOPHYSICS
    Type: NASA-198815 , NAS 1.26:198815
    Format: application/pdf
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  • 6
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    The response of C1O radical concentrations to variations in NO2 radical concentrations in the lower stratosphere (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The respose of ClO concentrations to changes in NO2 concentrations has been inferred from simultaneous observations of (ClO), (NO), (NO2) and (O3) in the midlatitude lower stratosphere. This analysis demonstrates that (ClO) is inversely correlated with (NO2), consistent with formation and photolysis of (ClONO2). A factor of ten range in the concentration if NO2 was sampled (0.1 to 1 x 10(exp 9) mol/cu cm), with a comparable range in the ratio of (ClO) to total available inorganic chlorine (1% less than or equal to (ClO)/(Cl(sub y)) less than or equal to 5%. This analysis leads to an estimate of (ClONO2)/(Cl(sub y)) = 0.12 (x/2), in the mid-latitude, lower-stratospheric air masses sampled.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 23; p. 2543-2546
    Format: text
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  • 7
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    Relativistic electron flux comparisons at low and high altitudes with fast time resolution and broad spatial coverage (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Analyses are presented for the first high-time resolution multisatellite study of the spatial and temporal characteristics of a relativistic electron enhancement event with a rapid onset. Measurements of MeV electrons were made from two low-altitude polar orbiting satellites and three spacecraft at synchronous altitude. The electron fluxes observed by the low-altitude satellites include precipitating electrons in both the bounce and drift loss cones as well as electrons that are stably trapped, whereas the observations at geosynchronous altitude are dominated by the trapped population. The fluxes of greater than 1 MeV electrons at low-satellite altitude over a wide range of L shells tracked very well the fluxes greater than 0.93 MeV at synchronous altitude.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A9; p. 17,421-17,426
    Format: text
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  • 8
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    Plasma flow and magnetic field characteristics near the midtail neutral sheet (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Using IMP 6, 7, and 8 magnetic field and plasma data, we have determined statistical occurrance properties of bulk flow and magnetic field orientation near the midtail neutral sheet. Characteristics of bulk plasma flow and magnetic field significantly change according to the radial distance down the tail. High-speed flow events (v greater than 300 km/s) are essentially restricted to the region tailward of X = -2.5 R(sub E) and are predominatly sunward or tailward. The low-speed flows were nearly equally likely to be in any direction, with the occurace rate of dustward and sunward flow being larger than that of tailward and dawnward flow. Dustward flow occurrence is highest in the region Earthward of X = -2.5 R(sub E), while sunward flow occurrence is highest in the region tailward of X = -2.5 R(sub E). The significance of the dawn-to-dust flow in the near-Earth region obtained in our study supports the idea that there exists a very effective mechanism to accelerate ions in the dawn-to-dust direction and hence the relief of pressure buildup in the near-Earth region. During high-speed flow events the relationship between B(sub Z) polarity and plasma flow direction is largely consistent with that expected from the magnetic reconnenection processes associted with substorms. There are also significant numbers of negative B9sub Z) events that are not associated with tailward flow. Mechanism other than substorm neutral line should therefore also taken into account to explain general B(sub Z) polarity in the midtail region.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A12; p. 23,591-23,601
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  • 9
    Electronic Resource
    Electronic Resource
    Formation of multiply charged ions from large molecules using massive-cluster impact (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 403-406 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Massive-cluster impact is demonstrated to be an effective ionization technique for the mass analysis of proteins as large as 17 kDa. The design of the cluster source permits coupling to both magnetic-sector and quadrupole mass spectrometers. Mass spectra are characterized by the almost total absence of chemical background and a predominance of multiply charged ions formed from 100% glycerol matrix. The number of charge states produced by the technique is observed to range from +3 to +9 for chicken egg lysozyme (14 310 Da). The lower m/z values provided by higher charge states increase the effective mass range of analyses performed with conventional ionization by fast-atom bombardment or liquid secondary ion mass spectrometry.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290080513
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  • 10
    Electronic Resource
    Electronic Resource
    Matrix-free desorption of biomolecules using massive cluster impact (1994)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 996-1000 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Massive-cluster impact (MCI) ionization was found to be capable of producing high secondary-ion yields from biological samples without the use of a liquid matrix. Dry samples of molecules as large as cytochrome c were observed to be efficiently desorbed without significant fragmentation by the MCI beam of glycerol clusters. In addition, signals from protonated molecules retained a significant proportion of their initial intensity even after several minutes exposure to the primary beam. It was determined that these remarkable phenomena are not the result of the build-up of a layer of glycerol caused by the cluster bombardment.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290081218
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