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11.
Kenneth B. Schwartz Derek B. Leong Richard L. McConville 《Physics and Chemistry of Minerals》1994,20(8):563-574
The structure, crystal chemistry, and microstructure of disordered and ordered Mg-cordierites synthesized in a bismuth oxide flux system have been studied by a combination of x-ray and neutron powder diffraction and quantitative x-ray microanalysis using analytical electron microscopy. Microchemical data obtained on Bi-flux cordierites using energy-dispersive x-ray analysis is interpreted through comparison with data collected on stoichiometric Mg2Al4Si5O18 glass and α- and β-cordierite samples synthesized by subsolidus crystallization of the glass. Bi-flux cordierites crystallize in both the hexagonal and orthorhombic polymorphs and contain 5 to 10 at% occupancy of bismuth on the C1 and C2 channel sites. The microstructure of Bi-flux α-cordierite is characterized by the existence of local domains of disordered cordierite solid solutions with variable composition and significant vacancy concentrations on the octahedral site. The β-cordierites have a more homogeneous microstructure but are still Al-deficient, Si-rich solid solutions. 相似文献
12.
13.
A large sample of radar reflectivity data from essentially a full summer of operation was analyzed to determine the horizontal
extents and internal structure of rain areas observed at altitude levels from 2 to 10 km. Results are given on the size distributions
of individual cells or patches defined by reflectivity thresholds approximately 4 dBz apart, on the dependence of mean size
on altitude and reflectivity threshold, and on the interior structure of the patches as characterized by the number and sizes
of higher-threshold patches contained in each echo. In a more detailed analysis of internal structure, the data were restricted
to convective echoes in which certain prescribed reflectivities, ranging from about 30 to 50 dBz, were exceeded. It was found
that the dependence of mean quantities, such as patch area, on reflectivity and altitude could be approximately described
by simple functions, but that the scatter of observations about the mean was usually large. 相似文献
14.
The solution to the problem of the motion of the Moon relative to spatial irregularities in the interplanetary magnetic field is found. The lunar electrical conductivity is modeled by a two-layer conductivity profile. For the interaction of the Moon with the corotating sector structure of the interplanetary magnetic field it is found that the magnetic field in the lunar shell is the superposition of an oscillatory uniform field, an oscillatory dipole field and anoscillatory field that is toroidal about the axis of the motional electric field. With various lunar conductivity models and the theory of this paper, lunar surface magnetometer data can be quantitatively interpreted to yield information on the conductivity and consequently the temperature of the lunar core.Presently visiting the Max-Planck-Institut für Physik und Astrophysik, München, Germany. 相似文献
15.
Tracer experiments were carried out in groyne fields (GF) of the river Elbe near Havelberg (Germany) in order to estimate the hydraulic connectivity with the river channel. The characteristic times of the five groyne fields, which were estimated from the exponentially declining tracer curves in 43 runs, ranged between 15 min and 69 min and did not correlate with the water level. Methodological investigations show that single point injection and two measurements (in the outflowing water and in the dominant region) are sufficient to provide robust in‐situ tracer curves. Using simplified mathematical simulations with connected stirred tanks, the conditions are investigated for the development of breaks in tracer curves and for the occurrence of significant errors in the estimation of intrinsic residence times. It was shown that an initial uniform dye distribution is not mandatory for the estimation during steady states. In special cases, point injections are more advisable. Moreover, the mean hydraulic residence time was found to be not equivalent to the estimated characteristic time. In fact, it is mostly overestimated by tracer experiments. The degree of overestimation depends on mixing and the volumetric proportions between the different parts of the GF and can be calculated from measured dye concentration differences. For example, an overestimation of 32% was calculated for a groyne field with a commonly found circulation flow pattern. 相似文献
16.
Ninety rock samples from the La Granja porphyry copper in northern Peru have been analyzed for 30 elements, 10 of which are discussed here. Although intense weathering has produced a leached capping up to 200 m thick, the distribution of Mg, Ca, Na, K, Rb and Sr can still be correlated with different phases of hydrothermal alteration.There has been complete supergene leaching of sulphides; Cu has been depleted 10 to 30 times and Mo up to twice with respect to hypogene ore, Fe has been enriched in some parts of the leached capping, whereas Au remained stable. The coincidence of low Fe, high Mo and high Au contents with a high Cu/Fe ratio in the capping indicates the approximate centre of the underlying orebody. Also, high K, Rb, Mg and low Sr indicate high-grade copper ore. 相似文献
17.
18.
Share G.H. Murphy R.J. Dennis B.R. Schwartz R.A. Tolbert A.K. Lin R.P. Smith D.M. 《Solar physics》2002,210(1-2):357-372
The RHESSI high-resolution spectrometer detected γ-ray lines and continuum emitted by the Earth's atmosphere during impact
of solar energetic particles in the south polar region from 16:00–17:00 UT on 21 April 2002. The particle intensity at the
time of the observation was a factor of 10–100 weaker than previous events when gamma-rays were detected by other instruments.
This is the first high-resolution observation of atmospheric gamma-ray lines produced by solar energetic particles. De-excitation
lines were resolved that, in part, come from 14N at 728, 1635, 2313, 3890, and 5106 keV, and the 12C spallation product at ∼ 4439 keV. Other unresolved lines were also detected. We provide best-fit line energies and widths
and compare these with moderate resolution measurements by SMM of lines from an SEP event and with high-resolution measurements
made by HEAO 3 of lines excited by cosmic rays. We use line ratios to estimate the spectrum of solar energetic particles that
impacted the atmosphere. The 21 April spectrum was significantly harder than that measured by SMM during the 20 October 1989
shock event; it is comparable to that measured by Yohkoh on 15 July 2000. This is consistent with measurements of 10–50 MeV protons made in space at the time of the γ-ray observations. 相似文献
19.
The RHESSI Spectrometer 总被引:2,自引:0,他引:2
Smith D.M. Lin R.P. Turin P. Curtis D.W. Primbsch J.H. Campbell R.D. Abiad R. Schroeder P. Cork C.P. Hull E.L. Landis D.A. Madden N.W. Malone D. Pehl R.H. Raudorf T. Sangsingkeow P. Boyle R. Banks I.S. Shirey K. Schwartz Richard 《Solar physics》2002,210(1-2):33-60
RHESSI observes solar photons over three orders of magnitude in energy (3 keV to 17 MeV) with a single instrument: a set of
nine cryogenically cooled coaxial germanium detectors. With their extremely high energy resolution, RHESSI can resolve the
line shape of every known solar gamma-ray line except the neutron capture line at 2.223 MeV. High resolution also allows clean
separation of thermal and non-thermal hard X-rays and the accurate measurement of even extremely steep power-law spectra.
Detector segmentation, fast signal processing, and two sets of movable attenuators allow RHESSI to make high-quality spectra
and images of flares across seven orders of magnitude in intensity. Here we describe the configuration and operation of the
RHESSI spectrometer, show early results on in-flight performance, and discuss the principles of spectroscopic data analysis
used by the RHESSI software. 相似文献
20.
Alex Schwartz 《The Professional geographer》1987,39(2):166-172
An increasing number of studies of business start-ups, closings, and relocations rely on a single data base, DUNS Market Identifiers. This data file to U.S. business establishments provides researchers with essential information about individual firms and establishments. It also exhibits serveral idiosyncracies and requires careful consideration of the meaning of such basic terms as “location”and “firm.”Drawing from a recent survey of 500 New Jersey firms. I consider some of the methodological amd conceptual issues Dun and Bradstreet data pose for industrial location analysts. The Dun and Bradstreet listings exaggerate the exaggerate the incidence and magnitude of establishment openings and closing. 相似文献