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71.
72.
A molecular face-on view of the Galactic Centre region 总被引:1,自引:0,他引:1
73.
M. Cohen 《Astrophysics and Space Science》2001,275(1-2):103-111
The rather rare class of central stars of planetary nebulae thatshow Wolf-Rayet spectra have been a subject of great interest,particularly in the infrared, since their discovery in the late1960s. I will focus on further peculiarities found within thepast 1-2 years with the advent of infrared spectroscopy fromISO. Notably, these stars simultaneously betray the presenceof regions of carbon-rich and oxygen-rich dust chemistry. Icompare and contrast complete ISO spectra from 2 to 200 micronsof a small sample of [WC9] to [WC11] central stars. 相似文献
74.
A.B. Galvin C.M.S. Cohen F.M. Ipavich R. von Steiger J. Woch U. Mall 《Planetary and Space Science》1993,41(11-12)
During the inbound segment of the Ulysses flyby of Jupiter, there were multiple incursions into the dawnside low-latitude boundary layer, as identified by Bame et al. (Science257, 1539–1542, 1992) using plasma electron data. In the present study, ion composition and spectral measurements provide independent collaborative evidence for the existence of distinct boundary layer regions. Measurements are taken in the energy-per-charge range of 0.6–60 keV/e and involve mass as well as mass-per-charge identification by the Ulysses/SWICS experiment. Ion species of Jovian magnetospheric origin (including O+, O2+, S2+, S3+) and sheath origin (including He2+ and high charge state CNO) have been directly identified for the first time in the Jovian magnetospheric boundary layer. Protons of probably mixed origin and He+ of possibly sheath (ultimately interstellar pickup) origin were also observed in the boundary layer. Sheath-like ions are observed throughout the boundary layer; however, the Jovian ions are depleted or absent for portions of two boundary layer cases studied. Ions of solar wind origin are observed within the outer magnetosphere. and ions of magnetospheric origin are found within the sheath, indicating that transport across the magnetopause boundary can work both ways, at least under some conditions. Although their source cannot be uniquely identified, the proton energy spectrum in the boundary layer suggests a sheath origin for the lower energy protons. 相似文献
75.
Donald S. Mussel White Heather A. Dalton Walter S. Kiefer Allan H. Treiman 《Meteoritics & planetary science》2006,41(9):1271-1290
Abstract— The Martian meteorite Yamato (Y‐) 980459 is an olivine‐phyric shergottite. It has a very primitive character and may be a primary melt of the Martian mantle. We have conducted crystallization experiments on a synthetic Y‐980459 composition at Martian upper mantle conditions in order to test the primary mantle melt hypothesis. Results of these experiments indicate that the cores of the olivine megacrysts in Y‐980459 are in equilibrium with a melt of bulk rock composition, suggesting that these megacrysts are in fact phenocrysts that grew from a magma of the bulk rock composition. Multiple saturation of the melt with olivine and a low‐calcium pyroxene occurs at approximately 12 ± 0.5 kbar and 1540 ± 10°C, suggesting that the meteorite represents a primary melt that separated from its mantle source at a depth of ?100 km. Several lines of evidence suggest that the Y‐980459 source underwent extensive melting prior to and/or during the magmatic event that produced the Y‐980459 parent magma. When factored into convective models of the Martian interior, the high temperature indicated for the upper Martian mantle and possibly high melt fraction for the Y‐980459 magmatic event suggests a significantly higher temperature at the core‐mantle boundary than previously estimated. 相似文献
76.
Heather Crow Daniel Paradis Elliot Grunewald Xiao Xia Liang Hazen A.J. Russell 《Ground water》2022,60(3):377-392
This study examined the application of slim-hole nuclear magnetic resonance (NMR) tools to estimate hydraulic conductivity (KNMR) in an unconsolidated aquifer that contains a range of grain sizes (silt to gravel) and high and variable magnetic susceptibilities (MS) (10−4 to 10−2 SI). A K calibration dataset was acquired at 1-m intervals in three fully screened wells, and compared to KNMR estimates using the Schlumberger-Doll research (SDR) equation with published empirical constants developed from previous studies in unconsolidated sediments. While KNMR using published constants was within an order of magnitude of K, the agreement, overprediction, or underprediction of KNMR varied with the MS distribution in each well. An examination of the effects of MS on NMR data and site-specific empirical constants indicated that the exponent on T2ML (n-value in the SDR equation, representing the diffusion regime) was found to have the greatest influence on KNMR estimation accuracy, while NMR porosity did not improve the prediction of K. KNMR was further improved by integrating an MS log into the NMR analyses. A first approach detrended T2ML for the effects of MS prior to calculating KNMR, and a second approach introduced an MS term into the SDR equation. Both were found to produce similar refinements of KNMR in intervals of elevated MS. This study found that low frequency NMR logging with short echo times shows promise for sites with moderate to elevated MS levels, and recommends a workflow that examines parameter relationships and integrates MS logs into the estimation of KNMR. 相似文献
77.
In a warming climate, atmospheric wave activity and associated weather patterns may change, although conflicting results have been reported on this topic. Additionally, atmospheric wave changes in a future climate have mainly focused on waves of a specified spatial scale, rather than a particular spatiotemporal scale. Here, changes in the variability of Rossby waves of multiple spatiotemporal scales are analyzed using the wavenumber-frequency power spectrum, a tool commonly applied to analyze atmospheric equatorial waves. Daily 500 hPa geopotential height data over 40°–60°N from historical (1950–2005) and future (2006–2099) simulations from 20 models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) under the RCP8.5 scenario were analyzed. When compared to the historical period, the late 21st century climate projections showed a decline in spectral power for both eastward and westward propagating waves with wavenumbers greater than 8 that spanned over all frequencies in all seasons, but an increase in mean power for eastward propagating waves with wavenumbers 1–7 over all frequencies was shown in winter and spring. This increase in power was accompanied by increased variance, i.e., an increased meridional extent of 500 hPa ridges and troughs, and was the result of increases in the mean number of high amplitude events and duration of activity within this wave band. These results indicate that large-scale (~ 104 km) eastward propagating weather systems may intensify with higher amplitudes for ridges and troughs, while short-scale (102–103 km) weather systems may decrease in their intensity due to reduced variability in the late 21st century under the high emissions scenario. Potential mechanisms for these changes are discussed, including enhanced Arctic warming and midlatitude-tropical interactions. 相似文献
78.
Jim Cohen 《Astrophysics and Space Science》2005,295(1-2):27-36
Magnetic field strengths and directions can be estimated using many different observational techniques that span a wide range of wavelengths. Each observational method favours different regimes of scale size, density and other physical conditions. The available techniques and their ranges of applicability are briefly described and the current status of observations is reviewed, with particular emphasis on high-resolution observations of star-forming regions. 相似文献
79.
Phase-referenced observations of 13 star-forming regions in the 2 Π1/2 , J = 1/2 transition of rotationally excited OH at 4765 MHz have been carried out using MERLIN. Two of the regions were also observed at 4750 MHz and one at 4660 MHz. There were 10 maser detections at 4765 MHz and three non-detections. There were no detections at 4750 and 4660 MHz. The 4765-MHz masers have brightness temperatures of ∼107 K at MERLIN resolution (∼50 mas). Several cases of 4765-MHz masers overlapping in position and velocity with 1720- and 1665-MHz masers are reported. There are also isolated 4765-MHz masers with peak flux densities ≥30 times that of any ground-state counterpart. Most of the 4.7-GHz maser spots are unresolved at 50-mas angular resolution, but in four of the nearest sources the maser spots are resolved, indicating a characteristic size for 4765-MHz maser regions of ∼100 au. In W3(OH) we discovered that 20 per cent of the 4765-MHz emission comes from a narrow low-brightness filament that stretches north–south for ∼1.0 arcec (∼2200 au) between two previously known 4765-MHz maser spots. The filament appears in projection against the H ii region and has a brightness temperature of ∼4 × 105 K . There are matching absorption features in mainline transitions of highly excited OH. The filament may trace a shock front in a rotating disc. 相似文献
80.