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71.
The results of observations of the optical emission that accompanied the gamma-ray burst GRB 080319B are reported. Observations were made using the TORTORA fast wide-field camera mounted on the REM robotic telescope in Chile. The behavior of the light curve before, during, and after the gamma-ray burst is described. The light curve consists of four, possibly periodic, 5–7 s long peaks 8–9 s apart. The behavior of the burst in the gamma and optical energy ranges are compared and the results of the theoretical interpretation of this comparison are reported.  相似文献   
72.
Garnet geochronology was used to provide the first direct measurement of the timing of eclogitization in the central Himalaya. Lu–Hf dates from garnet separates in one relict eclogite from the Arun River Valley in eastern Nepal indicate an age of 20.7 ± 0.4 Ma, significantly younger than ultra-high pressure eclogites from the western Himalaya, reflecting either different origins or substantial time lags in tectonics along strike. Four proximal garnet amphibolites from structurally lower horizons are 14–15 Ma, similar to post-eclogitization ages published for rocks along strike in southern Tibet. PT calculations indicate three metamorphic episodes for the eclogite: i) eclogite-facies metamorphism at ~ 670 °C and ≥ 15 kbar at 23–16 Ma; ii) a peak-T granulite event at ~ 780 °C and 12 kbar; and iii) late-stage amphibolite-facies metamorphism at ~ 675 °C and 6 kbar at ~ 14 Ma. The garnet amphibolites were metamorphosed at ~ 660 °C. Three models are considered to explain the observed PTt evolution. The first assumes that the Main Himalayan Thrust (basal thrust of the Himalayan thrust system) cuts deeper at Arun than elsewhere. While conceptually the simplest, this model has difficulty explaining both the granulite-facies overprint and the pulse of exhumation between 25 and 14 Ma. A second model assumes that (aborted) subduction, slab breakoff, and ascent of India's leading edge occurred diachronously: ~ 50 Ma in the western Himalaya, ~ 25 Ma in the central Himalaya of Nepal, and presumably later in the eastern Himalaya. This model explains the PTt path, particularly heating during initial exhumation, but implies significant along-strike diachroneity, which is generally lacking in other features of the Himalaya. A third model assumes repeated loss of mantle lithosphere, first by slab breakoff at ~ 50 Ma, and again by delamination at ~ 25 Ma; this model explains the PTt path, but requires geographically restricted tectonic behavior at Arun. The PTt history of the Arun eclogites may imply a change in the physical state of the Himalayan metamorphic wedge at 16–25 Ma, ultimately giving rise to the Main Central Thrust by 15–16 Ma.  相似文献   
73.
74.
The impact of domestic sewage effluent (SE) on the dynamics of phytoplankton assemblages from Bedford Basin was evaluated in the laboratory. Phytoplankton production and chlorophyll a increased proportionally with SE enrichment. Phytoplankton species composition also changed. The potentially harmful diatoms, Pseudonitzschia spp., present initially in small numbers (600 cells 1−1) in Bedford Basin seawater, and became dominant (3–5×106 cells 1−1) when the seawater was enriched with 0.5–5% untreated SE. With higher proportions of SE, other harmful species such as Fragilaria spp. and Euglena spp. became dominant (7−15×106 and 2.2×104 cells 1−1, respectively). Treatment of SE with UV light or activated charcoal seems to favour growth of benign species, such as Chaetoceros socialis, Skeletonema costatum and Thalassiosira spp., but not harmful species such as Pseudonitzschia spp. Further research on UV treatment of domestic sewage is recommended.  相似文献   
75.
Izvestiya, Atmospheric and Oceanic Physics - The Arctic Sea ice area, calculated by the VASIA2 algorithm using the SSMIS data during the most intensive melting of the ice cover in 2019, is compared...  相似文献   
76.
There is now strong evidence that stratal geometries on basin margins are most likely a consequence of multiple controls, not just variations in accommodation. Consequently, correct sequence stratigraphic interpretation of stratal geometries requires an understanding of how multiple different controls may generate similar geometries. Using a simple numerical stratigraphic forward model, we explore the impact of time variable sediment supply and different sediment transport rates on stratal geometries. We demonstrate how four common types of stratal geometry can form by more than one set of controlling parameter values and are thus likely to be non‐unique, meaning that there may be several sets of controlling factors that can plausibly explain their formation. For example, a maximum transgressive surface can occur in the model due to an increase in rate of relative sea‐level rise during constant sediment supply, and due to a reduction in rate of sediment supply during a constant rate of relative sea‐level rise. Sequence boundaries, topset aggradation and shoreline trajectories are also examples of non‐unique stratal geometries. If the model simulations in this work are sufficiently realistic, then the modelled stratal geometries are important examples of non‐uniqueness, suggesting the need for a shift towards sequence stratigraphic methods based on constructing and evaluating multiple hypotheses and scenarios.  相似文献   
77.
Izvestiya, Atmospheric and Oceanic Physics - On the basis of calculations of insolation and insolation characteristics, taking into account changes in solar activity, the causes of global climatic...  相似文献   
78.
79.
A 3000 km2 multibeam survey was carried out on the eastern Anaximander Mountains (Mts), (Eastern Mediterranean). The objective was to obtain detailed bathymetry of known mud volcanoes and identify new sites of active mud volcanism in the area. N-NW of the Amsterdam Mud-Volcano (MV) several mounds and cone-like morphological irregularities with a height of few tens of meters to about one hundred meters were detected and considered as potential MVs on the basis of their distinctive backscattered character. A group of two mounds was selected, the northern mound was sampled, documented as active, and named accordingly Athina MV. These new findings strongly support the presence of extensive active mud volcanism in the Anaximander Mountains especially in the area north of the Amsterdam MV.GEM  相似文献   
80.
The molecular sources, dynamics and analytical characterizations of the phosphorus (P) containing components of marine dissolved and particulate organic matter (OM) are reviewed. Using a combination of 13C and 31P nuclear magnetic resonance spectroscopy on samples collected from a depth profile (20-4000 m) at Station Aloha in the North Pacific subtropical gyre, the biomolecular associations of P functional groups in marine OM are identified. Compositional differences between ultrafiltered dissolved organic matter (UDOM; 1-100 nm size fraction) and ultrafiltered particulate organic matter (UPOM; 0.1-60 μm size fraction) as reflected by NMR and elemental analyses indicate that UDOM does not originate from simple solubilization of UPOM, and the aggregation of UDOM is not the primary source of UPOM. Regression analyses indicated a large fraction of the P in UDOM is associated with carbohydrates and amino acids, but not with lipids. Similar analyses for UPOM indicated that P is associated with carbohydrates, amino acids and lipids. The P functional groups also appear to be balanced in their distribution among molecular classes, because they remain in relatively constant proportion throughout the ocean.  相似文献   
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