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  • 1995-1999  (119)
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  • 1
    Electronic Resource
    Electronic Resource
    Fabry-Perot interferometer measurements of neutral winds and F2 layer variations at the magnetic equator (1998)
    Springer
    Annales geophysicae 16 (1998), S. 731-737 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (Equatorial ionosphere; Ionosphere-atmosphere interaction) ; Meteorology and Atmospheric Dynamics (General circulation)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This letter presents some night-time observations of neutral wind variations at F2 layer levels near the dip equator, measured by the Fabry-Perot interferometer set up in 1994 at Korhogo (Ivory Coast, geographic latitude 9.25°N, longitude 355°E, dip latitude -2.5°). Our instrument uses the 630 nm (O1D) line to determine radial Doppler velocities of the oxygen atoms between 200 and 400 km altitude. First results for November 1994 to March 1995 reveal persistent eastward flows, and frequent intervals of southward winds of larger than 50 ms−1 velocity. Compared with the simultaneous ionospheric patterns deduced from the three West African equatorial ionosondes at Korhogo, Ouagadougou (Burkina-Faso, dip latitude +1.5°) and Dakar (Sénégal, dip latitude + 5°), they illustrate various impacts of the thermospheric winds on F2 layer density: (1) on the mesoscale evolution (a few 103 km and a few 100 minutes scales) and (2) on local fluctuations (hundreds of km and tens of minutes characteristic times). We report on these fluctuations and discuss the opportunity to improve the time-resolution of the Fabry-Perot interferometer at Korhogo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0731-4
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  • 2
    Electronic Resource
    Electronic Resource
    Observations of thermospheric neutral winds within the polar cusp and the auroral oval using a Doppler imaging system (DIS) (1998)
    Springer
    Annales geophysicae 16 (1998), S. 1461-1474 
    Details
    ISSN: 0992-7689
    Keywords: Ionosphere (Polar ionosphere) ; Meteorology and atmospheric dynamics (thermospheric dynamics; instruments and techniques)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two Doppler imaging systems (DIS) or wide-field imaging Fabry-Perot interferometers (FPI), have recently been commissioned, one at the Auroral Station, Adventdalen, Longyearbyen, Svalbard, and the second at the IRF, Kiruna, Sweden. These instruments can provide wide-field (600 * 800 km) images of neutral wind flows in the upper thermosphere, by measuring the Doppler shift of the atomic oxygen forbidden near 630 nm, which is emitted from an altitude of approximately 240 km. From the instrument in Svalbard, at mid-winter, it is possible to observe the dayside polar cusp and the polar cap throughout the entire day, whereas from Kiruna, the night-time auroral oval is observable during the hours of darkness. Measurements of thermospheric dynamics from the DIS can be used in conjunction with observations of ionospheric plasma flows and thermal plasma densities by the EISCAT-Svalbard radar (ESR) and by EISCAT, along with other complementary observations by co-located instruments such as the auroral large-scale imaging system (ALIS). Such combined data sets will allow a wide range of scientific studies to be performed concerning the dynamical response of the thermosphere and ionosphere, and the important energetic and momentum exchange processes resulting from their complex interactions. These processes are particularly important in the immediate vicinity of the polar cusp and within the auroral oval. Early results from Svalbard in late 1995 will be discussed. The DIS in Kiruna observed two interesting geomagnetic disturbances in early 1997, the minor geomagnetic storm of 10, 11 January, and the disturbed period from 7–10 February. During these events, the thermospheric wind response showed some interesting departures from the average behaviour, which we attribute to the result of strong and variable Lorenz forcing (ion drag) and Joule and particle heating during these geomagnetic disturbances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-1461-3
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  • 3
    Electronic Resource
    Electronic Resource
    Gravity wave generation and propagation during geomagnetic storms over Kiruna (67.8°N, 20.4°E) (1995)
    Springer
    Annales geophysicae 13 (1995), S. 358-366 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Atmospheric gravity waves, detected over Kiruna (67.8°N, 20.4°E) during geomagnetic storms, are presented and analysed. The data include direct measurements of the OI 630.0 nm emission line intensity, the x-component of the local geomagnetic field and thermospheric (meridional and zonal) wind velocities derived from the OI 630.0 nm Doppler shift observed with an imaging Fabry-Perot interferometer (IFPI). A low pass band filter technique was used to determine short-period variations in the thermospheric meridional wind velocities observed during geomagnetic storms. These short-period variations in the meridional wind velocities, which are identified as due to gravity waves, are compared to the corresponding variations observed in the OI 630.0 nm emission line intensity, x-component of the local geomagnetic field and the location of the auroral electrojet. A cross-correlation analysis was used to calculate the propagation velocities of the observed gravity waves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0358-7
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  • 4
    Electronic Resource
    Electronic Resource
    A simple pressure cell and delivery system for the preparation of Xe derivatives for protein crystallography : The 9th National conference on synchrotron radiation instrumentation (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3365-3365 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed a simple device for preparing Xe derivatives under moderate gaseous pressure (1–100 atm). The device employs a Cajon ultra-torr fitting to ensure a gas-tight seal around a standard x-ray capillary. As such, the cell can accommodate standard x-ray capillaries up to 1.5 mm in diameter without any modification. The device is straightforward to utilize, and samples can be mounted and pressurized in a matter of seconds. In addition, a simple and safe purging and pressurization system has been designed and constructed for the use at beamline 7-1 at the Stanford Synchrotron Radiation Laboratory (SSRL). We describe the construction of both the pressure cell and the delivery system and present results on the cells use in the preparation of xenon derivatives. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147473
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  • 5
    Electronic Resource
    Electronic Resource
    Successful flash-cooling of xenon-derivatized myoglobin crystals (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 190-194 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper demonstrates for the first time a method for preparing cryocooled xenon-derivatized protein crystals. The method is based upon the hypothesis and subsequent observation that the diffusion of a xenon atom from a tight binding site following depressurization occurs on a timescale of minutes. We have observed significant changes in diffraction intensities from myoglobin crystals for up to 5 min following depressurization from 1 MPa of xenon. In accordance with this observation, a xenon-derivatized myoglobin crystal was cryocooled at 9̃5 K within 20 s of complete depressurization. A crystallographic data set was then collected to 2.0 Å resolution and isomorphous and anomalous difference Patterson maps revealed the presence of a well ordered xenon site with an occupancy of approximately 0.5. Phasing statistics for this site were of good quality and demonstrate the practicality of this method. The ability to cryocool xenon-derivatized crystals will make this heavy-atom substitution method even more useful for single-isomorphous-replacement and multiple-isomorphous-replacement phasing of macromolecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889896012939
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  • 6
    Electronic Resource
    Electronic Resource
    A simple device for studying macromolecular crystals under moderate gas pressures (0.1–10 MPa) (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 29 (1996), S. 608-613 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A simple device for studying crystalline samples under moderate gas pressure (0.1–10 MPa) has been developed. The device employs a modified Cajon ultra-torr fitting to ensure a gas-tight seal around an X-ray capillary. The cell accommodates standard X-ray capillaries that require no modification. The device is straightforward to utilize and samples can be mounted with routine techniques and pressurized in a matter of seconds. In a subsequent development, a complete purging and pressurization system has been designed and constructed for use on beamline 7-1 at the Stanford Synchrotron Radiation Laboratory. This paper describes the construction of both the pressure cell and the delivery system and presents results of the use of this cell for the preparation of xenon derivatives to be used in phase determination by the multiple isomorphous replacement method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889896004712
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  • 7
    Electronic Resource
    Electronic Resource
    Wheat Yield Progress Associated with Higher Stomatal Conductance and Photosynthetic Rate, and Cooler Canopies (1998)
    Springer
    Crop science 38 (1998), S. 1467-1475 
    Details
    ISSN: 1435-0653
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Grain yields of eight representative semidwarf spring wheat (Triticum aestivum L.) cultivars released in northwest Mexico between 1962 and 1988 have increased linearly across years as measured in this region during 6 yr under favorable management and irrigation. To understand the physiological basis of this progress and possibly assist future selection for grain yield, leaf traits were determined during 3 yr in the same study. Stomatal conductance (g s), maximum photosynthetic rate (Amax), and canopy temperature depression (CTD), averaged over the 3 yr, were closely and positively correlated with progress in the 6-yr mean yield. The correlation was greatest with g s (r=0.94, P〈0.01). Compared with the overall yield increase of 27%, g s, increased 63%, Amax increased 23%, and canopies were 0.6° cooler. Carbon-13 isotope discrimination was also positively associated with yield progress (r=0.71, P〈0.05), but other leaf traits such as flag leaf area, specific leaf weight, percentage N and greeness were not, nor was crop growth rate around anthesis. The causal basis of the leaf activity interrelationships is reasonably clear, with both increased intercellular CO2 concentration and increased mesophyll activity contributing to the increase in Amax. However, causal links to the yield progress, and the accompanying increase in kernels per square meter, are not clear. It is concluded that g s and CTD should be further investigated as potential indirect selection criteria for yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/
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  • 8
    Electronic Resource
    Electronic Resource
    Role of the active-site cysteine of Pseudomonas aeruginosa azurin. Crystal structure analysis of the CuII(Cys112Asp) protein (1997)
    Springer
    JBIC 2 (1997), S. 464-469 
    Details
    ISSN: 1432-1327
    Keywords: Key words Azurin ; Cytochrome c551 ; Electron transfer ; Site-directed mutagenesis ; Protein crystallography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  Replacement of the cysteine at position 112 of Pseudomonas aeruginosa azurin with an aspartic acid residue results in a mutant (Cys112Asp) protein that retains a strong copper-binding site. CuII(Cys112Asp) azurin can be reduced by excess [RuII(NH3)6]2+, resulting in a CuI protein with an electronic absorption spectrum very similar to that of wild-type CuI azurin. Cys112Asp azurin exhibits reversible interprotein electron-transfer reactivity with P. aeruginosa cytochrome c 551 (μ = 0.1 M sodium phosphate (pH 7.0);E°(CuII/I) = 180 mV vs NHE); this redox activity indicates that electrons can still enter and exit the protein through the partially solvent-exposed imidazole ring of His117. The structure of CuII(Cys112Asp) azurin at 2.4-Å resolution shows that the active-site copper is five coordinate: the pseudo-square base of the distorted square-pyramidal structure is defined by the imidazole Nδ atoms of His46 and His117 and the oxygen atoms of an asymmetrically-bound bidentate carboxylate group of Asp112; the apical position is occupied by the oxygen atom of the backbone carbonyl group of Gly45. The CuII–Asp112 interaction is distinguished by an approximately 1.2-Å displacement of the metal center from the plane defined by the Asp112 carboxylate group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050157
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  • 9
    Electronic Resource
    Electronic Resource
    The molybdenum-cofactor: a crystallographic perspective (1997)
    Springer
    JBIC 2 (1997), S. 773-781 
    Details
    ISSN: 1432-1327
    Keywords: Key words Molybdopterin ; Molybdoenzymes ; Tungstoenzymes ; Molybdenum-cofactor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The molybdenum-cofactor (Mo-co) consists of a mononuclear molybdenum or tungsten ion coordinated by one or two molybdopterin ligands. Crystallographic analyses have demonstrated that the molybdopterin ligands are tricyclic and nonplanar, and that they coordinate the metal through their dithiolene sulfurs. Additional ligands to the metal may be provided by amino acid side chains (including serine, cysteine and selenocysteine), as well as one or more nonprotein O or S ligands, such as oxo, hydroxo, and sulfido. The molybdopterin ligand may participate in the various electron transfer reactions associated with the catalytic mechanism of these proteins, as suggested by both oxidation state-dependent changes in the metal coordination environment and the molybdopterin structure, and by the interaction of the molybdopterin with other redox groups within Mo-co-containing enzymes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050194
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  • 10
    Electronic Resource
    Electronic Resource
    Crystal structure of rubredoxin from Pyrococcus furiosus at 0.95 Å resolution, and the structures of N-terminal methionine and formylmethionine variants of Pf Rd. Contributions of N-terminal interactions to thermostability (1998)
    Springer
    JBIC 3 (1998), S. 484-493 
    Details
    ISSN: 1432-1327
    Keywords: Key words Rubredoxin ; Iron-sulfur proteins ; Hyperthermostability ; Protein structure ; Metalloproteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The high-resolution crystal structure of the small iron-sulfur protein rubredoxin (Rd) from the hyperthermophilic archeon Pyrococcus furiosus (Pf) is reported in this paper, together with those of its methionine ([_0M]Pf Rd) and formylmethionine (f[_0M]Pf Rd) variants. These studies were conducted to assess the consequences of the presence or absence of a salt bridge between the amino terminal nitrogen of Ala1 and the side chain of Glu14 to the structure and stability of this rubredoxin. The structure of wild-type Pf Rd was solved to a resolution of 0.95 Å and refined by full-matrix least-squares techniques to a crystallographic agreement factor of 12.8% [F〉2σ(F) data, 25 617 reflections], while those of the [_0M]Pf and f[_0M]Pf Rd variants were solved at slightly lower resolutions (1.1 Å, R=11.5%, 17 213 reflections; 1.2 Å, R=13.7%, 12 478 reflections, respectively). The quality of the data was such that about half of the hydrogen atoms of the protein were clearly visible. All three structures were ultimately refined using the program SHELXL-93 with anisotropic atomic displacement parameters for all non-hydrogen protein atoms, and calculated hydrogen positions included but not refined. In this paper we also report thermostability data for all three forms of Pf Rd, and show that they follow the sequence wild-type 〉[_0M]Pf〉formyl[_0M]Pf. Comparison of the three Pf Rd structures in the N-terminal region show that the structures of wild-type Pf Rd and f[_0M]Pf are rather similar, while that of [_0M]Pf Rd shows a number of additional hydrogen bonds involving the extra methionine group. While the salt bridge between the Ala1 amino group and the Glu14 carboxylate is not the primary determinant of the thermostability of Pf Rd, alterations to the amino terminus do have a moderate influence on the thermostability of this protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050258
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