The Gamow-Teller strength distribution function, B(GT), for the odd Z parent 51V, N?Z=5, up to 30 MeV of excitation energy in the daughter 51Ti is calculated in the domain of proton-neutron Quasiparticle Random Phase Approximation (pn-QRPA) theory. The pn-QRPA results are compared against other theoretical calculations, (n, p) and high resolution (d, 2He) reaction experiments. For the case of (d, 2He) reaction the calibration was performed for 0≤Ej≤5.0 MeV, where the authors stressed that within this excitation energy range the ΔL=0 transition strength can be extracted with high accuracy for 51V. Within this energy range the current pn-QRPA total B(GT) strength 0.79 is in good agreement with the (d, 2He) experiment’s total strength of 0.9±0.1. The pn-QRPA calculated Gamow-Teller centroid at 4.20 MeV in daughter 51Ti is also in good agreement with high resolution (d, 2He) experiment which placed the Gamow-Teller centroid at 4.1±0.4 MeV in daughter 51Ti. The low energy detailed Gamow-Teller structure and Gamow-Teller centroid play a sumptuous role in associated weak decay rates and consequently affect the stellar dynamics. The stellar weak rates are sensitive to the location and structure of these low-lying states in daughter 51Ti. The calculated electron capture rates on 51V in stellar matter are also in good agreement with the large scale shell model rates. 相似文献
Gamow-Teller (GT) transitions play a preeminent role in the collapse of stellar core in the stages leading to a Type-II supernova. The microscopically calculated GT strength distributions from ground and excited states are used for the calculation of weak decay rates for the core-collapse supernova dynamics and for probing the concomitant nucleosynthesis problem. The B(GT) strength for 57Zn is calculated in the domain of proton-neutron Quasiparticle Random Phase Approximation (pn-QRPA) theory. No experimental insertions were made (as usually made in other pn-QRPA calculations of B(GT) strength function) to check the performance of the model for proton-rich nuclei. The calculated B(GT) strength distribution is in good agreement with measurements and shows differences with the earlier reported shell model calculation. The pn-QRPA model reproduced the measured low-lying strength for 57Zn better in comparison to the KB3G interaction used in the large-scale shell model calculation. The stellar weak rates are sensitive to the location and structure of these low-lying states in daughter 57Cu. The structure of 57Cu plays a sumptuous role in the nucleosynthesis of proton-rich nuclei. The primary mechanism for producing such nuclei is the rp-process and is believed to be important in the dynamics of the collapsing supermassive stars. Small changes in the binding and excitation energies can lead to significant modifications of the predictions for the synthesis of proton rich isotopes. The ??+-decay and electron capture (EC) rates on 57Zn are compared to the seminal work of Fuller, Fowler and Newman (FFN). The pn-QRPA calculated ??+-decay rates are generally in good agreement with the FFN calculation. However at high stellar temperatures the calculated ??+-decay rates are almost half of FFN rates. On the other hand, for rp-process conditions, the calculated electron capture (??+-decay) rates are bigger than FFN rates by more than a factor 2 (1.5) and may have interesting astrophysical consequences. 相似文献
A Staged Z-pinch (H.U. Rahman, F.J. Wessel, N. Rostoker, Phys. Rev. Lett. 74:714, 1995), configured for a 100 ns, 2 MJ implosion accelerator, is studied using the 2-1/2 D, radiation-MHD code, MACH2. The Z-pinch
is configured as a cylindrical, high-atomic number plasma shell that implodes radially onto a co-axial, plasma target, for
example: Xenon onto a 50:50 mixture of Deuterium-Tritium. During implosion a shock develops in the plasma liner, producing
a conduction channel at the Xe/DT interface as the mass Xe accumulates, and preheating the DT target. During subsequent acceleration
and compression the Xe/DT interface remains stable, even as the outer surface of the Xe shell develops RT instabilities. At
peak implosion the simulated fusion-energy yield is 7.6 MJ, producing an energy gain of 3.8. 相似文献
Mafic–ultramafic sequences in the Jebel Rahib fold-and-thrust belt of NW Sudan comprise the metamorphosed equivalents of obducted oceanic lithosphere. Primary features like pillow-structures, quenchtextures, igneous layering and primary minerals like chromian spinels and pyroxenes are partly preserved. Geochemical investigations confirm the field evidence and reveal the occurrence of harzburgites, ophiolitic chromites, gabbros, gabbroic cumulates and basalts of primitive tholeiitic compositions resembling transitional MORBs. The age of low-grade overprint of the basaltic rocks can be limited to 860–740 Myr (K–Ar). The existence of an ophiolite, as well as its close interfingering with highly deformed basin sediments, provides unambiguous evidence for a cycle of extensional and compressional tectonics in NW Sudan during Pan-African times. Consequently, the concept of an older, stable Proterozoic, or even Archaean, ‘African Craton’onto which the juvenile Pan-African Nubian Shield assemblages were accreted, needs revision. 相似文献
The concentrations of n-alkanes, unresolved complex mixture (UCM), petroleum molecular markers, other tracers of cooking and burning emissions, and
natural background in atmospheric particles and roadside dust particles were measured at eight locations in the city center
and the suburbs of Kuala Lumpur, Malaysia. Atmospheric particles were collected using high-volume filtration (PM-10, GFF)
over 24 h average periods. Road dusts were swept up, dried and sieved. Both types of samples were extracted with dichloromethane/methanol
mixture (3:1 v/v) by ultrasonic agitation. The extracts were then fractionated by column chromatography and the alkanes subjected
to gas chromatography–mass spectrometry (GC–MS). Total extracts were also analyzed directly by GC–MS after silylation. The
molecular distributions of compounds as well as diagnostic geochemical ratios were determined in order to identify the sources
of the organic compounds. Samples collected from a rural area and lubricating oils were also analyzed for comparisons. Anthropogenic
and biogenic sources such as vehicular emissions, waxes of higher plants, food cooking operations, and biomass and domestic
refuse burning processes contributed to the organic matter content of atmospheric and to lesser extent, roadside dust particles. 相似文献
Atmospheres of different oxidation potentials were used to equilibriate samples at 1300°C starting with a stoichiometric composition xFe2TiO4·(1 ? x) Fe3O4 where x = 0.3 and 0.6. Samples were selected which appeared homogeneous in polished section and gave only spinel-type X-ray reflections. All specimens were found to have small amounts of included material of higher Curie point than the bulk material. Specimens were made by dispersing grains of known size in a non-magnetic matrix and the hysteresis properties were measured for these speciméns. 相似文献
Grains from a natural titanomagnetite are found to contain fine ex-solved regions with a higher Curie point than the host oxide. Experimental results are given, in which tests have been made of the influence of the magnetization of the ex-solution regions on the overall magnetization of specimens which contain a dispersion of the titanomagnetite grains in an inert matrix. The results are compared with those predicted by Stephenson for a model of similar properties. 相似文献
The Bengal Basin, in the north-eastern part of the Indian subcontinent, contains a thick (± 22 km) early Cretaceous-Holocene
sedimentary succession. The Neogene succession in the Sylhet Trough of the basin reaches a thickness of more than 6 km of
which the Surma Group contains important sandstone reservoirs. Lithologically, the group consists of a succession of alternating
shales, siltstones, sandy shales and sandstones, with minor conglomerates. This research work is a sedimentological analysis
of the subsurface Neogene succession encountered in the petroleum exploration wells in the Sylhet Trough of the Bengal Basin.
Detailed lithologic logs of the cores, based on considering texture and sedimentary structure, permit a subdivision into eight
lithofacies, e.g., a shale-dominated facies, interbedded fine sandstones and mudstones, ripple-laminated sandstones, parallel-laminated
sandstones, massive sandstones, cross-bedded sandstones, cross-bedded sandstones with pebble/granule lag and conglomerates.
Characteristic sedimentary structures of the Surma Group, such as flaser-, wavy- and lenticular-bedding, bipolarity of ripple
cross-stratification, evenly laminated sand/silt-streaked shales, reactivation surfaces within cross-bedded sandstone sets,
mud-drapes on foreset laminae and herringbone cross-stratification as well as small-scale vertical sequences (several fining-upward
cycles) are diagnostic for tidal influence. On the basis of the lithofacies associations and prograding character of the deposits
revealed from the electrofacies associations, the Surma Group sediments have been interpreted as representing deposits of
tide-dominated deltaic depositional setting. 相似文献
The present study deals with the geochemistry of Late Quaternary ironstones in the subsurface in Rajshahi and Bogra districts, Bangladesh with the lithological study of the boreholes sediments. Major lithofacies of the studied boreholes are clay, silty clay, sandy clay, fine to coarse grained sand, gravels and sands with (fragmentary) ironstones. The ironstones contain major oxides, Fe2O3* (* total Fe) (avg. 66.6 wt%), SiO2 (avg. 15.3 wt%), Al2O3 (avg. 4.0 wt%), MnO (avg. 7.7 wt%), and CaO (avg. 3.4 wt%). These geochemical data imply that the higher percentage of Fe2O3* along with Al2O3 and MnO indicate the ironstone as goethite and siderite, which is also validated by XRD data. A comparatively higher percentage of SiO2 indicates the presence of relative amounts of clastic quartz and manganese-rich silicate or clay in these rocks. These ironstones also have significant amounts of MnO (avg. 7.7 wt%) suggesting their depositional environments under oxygenated condition. Chemical data of these ironstones suggest that the source rock suffered deep chemical weathering and iron was mostly carried in association with the clay fraction and organic matter. Iron concretion was mostly formed by bacterial build up in swamps and marshes, and was subsequently embedded in clayey mud. Within the coastal environments, the water table fluctuates and goethite and siderite with mud and quartz became dry and compacted to form ironstone.