Landscape change and sandy desertification in arid areas: a case study in the Zhangye Region of Gansu Province, China   总被引：3，自引：0，他引：3  

F. Luo  S. Z. Qi  H. L. Xiao 《Environmental Geology》2005,49(1):90-97

The Zhangye Region of Gansu Province is an important agricultural base in arid northwestern China. During the twentieth century, especially in the last five decades, the region has experienced sandy desertification. To document the status and causes of this deterioration, satellite images, meteorological and socioeconomic data to assess landscape change from 1993 to 2002 were interpreted and analyzed. The results show that during the intervening 9-year period the area of sandy lands has increased by 642.2 km², which consist of aeolian sand dune (357.1 km²) and potential sandy land (216.3 km²). Although the development and reversion of sandy desertification co-exist, the sandy desertification in this area seems serious and is attributable to the irrational use of water and land.  相似文献   

Gamma-ray bursts from a close pulsar binary system?     

Ya. N. Istomin 《Astronomy Reports》2005,49(6):446-449

The close neutron-star binary system comprised of the radio pulsars PSR J0737-3039 A,B is discussed. An analysis of the observational data indicates that the wind from pulsar A, which is more powerful than the wind from pulsar B, strongly distorts the magnetosphere of pulsar B. A shock separating the relativistic wind from pulsar A and the corotating magnetosphere of pulsar B should form inside the light cylinder of pulsar B. A weakly diverging “tail” of magnetic field is also formed, which stores a magnetic energy on the order of 10³⁰ erg. This energy could be liberated over a short time on the order of 0.1 s as a result of reconnection of the magnetic-force lines in this “tail,” leading to an outburst of electromagnetic radiation with energies near 100 keV, with an observed flux at the Earth of 4 × 10^?11 erg cm^?2 s^?2. Such outbursts would occur sporadically, as in the case of magnetic substorms in the Earth’s magnetosphere.  相似文献   

The afterglow of a dense molecular cloud after the passage of a cosmological gamma-ray burst     

M. V. Barkov  G. S. Bisnovatyi-Kogan 《Astronomy Reports》2005,49(8):611-623

Bolometric light curves for the afterglow resulting from the passage of a gamma-ray burst through a molecular cloud are computed. The profile and duration of the afterglow light curve depend strongly on the distribution of matter in the cloud, the degree of collimation of the gamma-ray radiation, and the observing conditions. The peak can be reached as soon as seven days (the gamma-ray burst is located at some distance from the center of a molecular cloud with small-scale density enhancements), or as long as one to three years (the gamma-ray burst is located at the center of a uniform molecular cloud) after the burst. The bolometric luminosity of the re-radiated signal can reach 6.5 × 10⁴² erg/s.  相似文献   

Polymorphic phase transition in Superhydrous Phase B     

M. Koch-Müller  P. Dera  Y. Fei  H. Hellwig  Z. Liu  J. Van Orman  R. Wirth 《Physics and Chemistry of Minerals》2005,32(5-6):349-361

We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200°C (LT) and 1400°C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to −180°C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.  相似文献   

Nicolaus Steno and Sessions of the International Geological Congress     

V. K. Kuznetsov 《Lithology and Mineral Resources》2005,40(5):483-486

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The role of socio-environmental networking in the sustainability of rain-fed agriculture in the coastal savanna of Ghana     

Michael O’Neal Campbell 《GeoJournal》2005,61(1):79-88

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Uraninite recrystallization and Pb loss in the Oklo and Bangombé natural fission reactors, Gabon   总被引：1，自引：0，他引：1  

Lena Z. Evins  Keld A. Jensen  Rodney C. Ewing 《Geochimica et cosmochimica acta》2005,69(6):1589-1606

The Oklo and Bangombé natural fossil fission reactors formed ca. 2 Ga ago in the Franceville basin, Gabon. The response of uraninite in the natural reactors to different geological conditions has implications for the disposal of the UO₂ in spent nuclear fuel. Uraninite and galena from two reactor zones, RZ16 at Oklo and RZB at Bangombé, were studied to clarify the chronology and effect of alteration events on the reactor zones. In addition, ion microprobe U-Pb analysis of zircons from a dolerite dyke in the Oklo deposit were completed to better constrain the age of the dyke, and thereby testing the link between the dyke and an important alteration event in the reactor zones.The analyzed uraninite from RZ16 and RZB contains ca. 6 wt% PbO, indicating a substantial loss of radiogenic Pb. Transmission electron microscopy showed that microscopic uraninite grains in the reactor zones consist of mainly defect-free nanocrystalline to microcrystalline aggregates. However, the nanocrystalline regions have elevated Si contents and lower Pb contents than coarser uraninite crystallites. Single stage model ages of large, millimeter-sized galena grains at both RZ16 and RZB correlate well with the age of the Oklo dolerite dyke, 860 ± 39 Ma (2σ). Thus, the first major Pb loss from uraninite occurred at both Oklo and Bangombé during regional extension and the intrusion of a dyke swarm in the Franceville basin, ∼860-890 Ma ago. Uraninite Pb isotopes from RZ16 and RZB give lower ages of ca. 500 Ma. These ages agree with the “chemical” ages of the uraninite, and show that an ancient Pb loss occurred after the intrusion of the dolerite dykes. The presence of nanocrystallites in the reactor uraninite indicates internal recrystallization, which may have occurred around 500 Ma, resulting in the 6wt% PbO uraninite. It is suggested that leaching by fluid interaction triggered by the Pan-African orogeny was important during this second Pb-loss event. Thus, there are indications that uraninite at both the Oklo and Bangombé natural reactors has experienced at least two ancient episodes of Pb loss associated with internal recrystallization. These recrystallization events have occurred without significantly depleting the 2 Ga fission products compatible with the uraninite structure.  相似文献   

Kinematic structure and mesoscale variability of the rim current near the coast of Crimea (according to the data of instrumental measurements in September 2008)     

G. F. Dzhiganshin  A. B. Polonsky 《Physical Oceanography》2011,21(1):23-32

By using the results of processing of the instrumental data with high space resolution obtained in September 2008, we analyze the structure of the Rim Current in the upper 100-m layer near the coast of Crimea. We determine the statistical characteristics of the mesoscale fluctuations of currents according to the data of 1165 vertical probes. It is shown that the kinetic energy of intense mesoscale perturbations observed in the vicinity of the Rim Current is of the same order of magnitude as the kinetic energy of the mean current.  相似文献   

Workplace environmental demands and energizers at two Kuwait oil companies     

A. Al-Hemoud  W. Behbehani 《International Journal of Environmental Science and Technology》2017,14(5):983-992

The Work Compatibility Improvement Framework was developed and used to assess the environmental and ergonomic work conditions at two oil companies in Kuwait: One is a government-owned company, while the other is a private subcontractor of the government-owned company. The work compatibility presents demand–energizer environmental factors that act upon the individuals in the workplace. The reliability coefficients were tested and considered good (0.752) and excellent (0.855) for two domain conditions environment and ergonomics, respectively. Results reveal that in all of the three regions of the government-owned company (north, southwest, east) the ‘overall’ compatibility data for the ‘environment’ is perceived to be poor. The ‘ergonomics’ compatibility data seem to be average in the southeast and west, while it is considered to be poor in the north. As for the private subcontractor, the perceived ‘environment’ is considered to be poor for two departments out of four (slickline and wellhead maintenance), while considered moderate for the remaining two (maintenance and crude/chemical handling). The ‘ergonomics’ compatibility is reported to be poor for crude/chemical handling and wellhead maintenance jobs; while the conditions seem to be moderate for the maintenance and slickline jobs. The major conclusion extracted from this study is that the oil sector organizations in Kuwait are not managed as ergo-environmental enterprises where there is disharmony in the ergonomics system, environmental system, and the ergo-environmental interface interaction. These gaps in the enterprise-wide systems have a significant impact on work productivity and the environment conditions.  相似文献   

Retraction Note to: Depositional environments and porosity distribution in regressive limestone reservoirs of the Mishrif Formation,Southern Iraq     

M. Al-Dabbas  J. Al-Jassim  S. Al-Jumaily 《Arabian Journal of Geosciences》2017,10(9):200

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