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91.
L. S. Dubrovinsky P. Lazor S. K. Saxena P. Häggkvist H.-P. Weber T. Le Bihan D. Hausermann 《Physics and Chemistry of Minerals》1999,26(7):539-545
Iron pressurized to 60 gigapascal (GPa) was heated with laser up to temperatures of over 2200 K. The structural changes were
determined in-situ using third generation synchrotron X-ray source; the changes were recorded on an imaging plate with a monochromatic beam.
The results strongly support the existence of a phase transformation of the hexagonal close-packed (hcp) structure to the
new polymorph (β-phase of iron) at high pressure and temperature. We interpret the X-ray data as belonging to the double hexagonal
close-packed (dhcp) structure distorted by stress due to laser heating.
Received: 2 February 1998 / Accepted: 23 August 1998 相似文献
92.
In this paper we have proposed certain generalizations of anomalous diffusion equations for fractional order. These diffusion equations are solved by the method of Laplace transform with respect to the time variable and Fourier transform with respect to the space variable. The solutions of some known diffusion equations are also shown to be derived here. 相似文献
93.
Sandeep Singh Munendra Singh A. K. Choudhary Anju Saxena I. B. Singh A. K. Jain 《International Journal of Earth Sciences》2010,99(8):1991-1997
The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan
rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial
Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the
transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient
zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the
Ganga River, draining nearly 30,500 km2 area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport
its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati
River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about
335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher
than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average
runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface
is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon
than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon
precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the
alluvial plain rivers. This study establishes that elevated 87Sr/86Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain. 相似文献
94.
S. K. Sharma A. K. Singh T. Saud T. K. Mandal M. Saxena S. Singh S. K. Ghosh S. Raha 《Meteorology and Atmospheric Physics》2012,118(1-2):37-51
Aerosol (PM10) samples were collected and its precursor gases, i.e., NH3, NO, NO2, and SO2 measured over Bay of Bengal (BoB) during winter months of December 2008 to January 2009 to understand the relationship between particular matter (PM) and precursor gases. The observations were done under the winter phase of Integrated Campaign on Aerosols, gases and Radiation Budget (W_ICARB). The distribution of water-soluble inorganic ionic composition (WSIC) and its interaction with precursor gases over BoB are reported in present case. Average atmospheric concentration of NH3, NO, NO2, and SO2 were recorded as 4.78?±?1.68, 1.89?±?1.26, 0.31?±?0.14, and 0.80?±?0.30?μg?m?3, whereas WSIC component of PM10, i.e., NH4 +, SO4 2?, NO3 ?, and Cl? were recorded as 1.96?±?1.66, 8.68?±?3.75, 1.92?±?1.75, and 2.48?±?0.78?μg?m?3, respectively. In the present case, abundance of nss-SO4 2? in the particulate matter is recorded as 18?%. It suggests the possibility of long-range transport as well as marine biogenic origin. Higher SO4 2?/(SO2?+?SO4 2?) equivalent molar ratio during the campaign indicates the gas-to-particle conversion with great efficiency over the study region. 相似文献
95.
David Morrill Anderson Bruce A. Bauer Charles R. Buckner Edward Gille Wendy S. Gross Michael Hartman Carrie Morrill Anju M. Shah Eugene R. Wahl 《Earth Science Informatics》2011,4(4):161-167
Reducing uncertainty in global temperature reconstructions of the past millennium remains the key issue in applying this record
to society’s pressing climate change problem. Reconstructions are collaborative, built on the research of hundreds of scientists
who apply their diverse scientific expertise and field and laboratory skill to create the individual proxy reconstructions
that underlie the multi-proxy, global average temperature time series. Web 2.0 features have enabled collaborative efforts
that improve the characterization of uncertainty. Raw data shared via a repository (the World Data Center for Paleoclimatology)
enable new reconstructions from the collection of user-generated data. Standards propagated by expert communities facilitate
quality control and interoperability. Open access to data and computer code promote transparency and make the science accessible
to a broader audience. Blogs, wikis, and listservs share background information and highlight contentious as well as unique
aspects of paleo science. A novel approach now underway, titled the Paleoclimate Reconstruction Challenge, and based on the
sharing of simulated data (pseudo-proxies) and reconstruction results, seeks to facilitate method development, further reducing
uncertainty. Broadly-useful aspects of the Challenge may find application in other fields. 相似文献
96.
Yamuna Singh Anubhooti Saxena A K Bhatt R Viswanathan T S Shaji L K Nanda 《Journal of Earth System Science》2018,127(1):4
Crystallochemical data on metamict davidite from albitites and albitised rocks from the Bichun area (Jaipur district, Rajasthan, India) of Banded Gneissic Complex (BGC) are provided. Davidite occurs as euhedral, subhedral to anhedral crystals in the form of disseminated grains and also as fracture filled veins. The crystals of davidite are up to 8 cm in length and 6 cm in width. The powder X-ray diffraction (XRD) pattern of the heat-treated davidite (at \(900{^{\circ }}\hbox {C}\)) reveals well-defined reflections of crystallographic planes. The calculated unit-cell parameters of the heat treated davidite are: \(\hbox {a}_{0} = \hbox {b}_{0} = 10.3556 \, \text {\AA }\) and \(\hbox {c}_{0} = 20.9067 \, \text {\AA }\), with unit-cell volume \(\hbox {(V)} = 1941.6385 \, \text {\AA }^{3}\); and \({\upalpha }={\upbeta }= 90^{\circ }\) and \({\upgamma }= 120^{\circ }\), which are in agreement with the values of davidite standard. Geochemical data reveals that the investigated davidite contains 51.5–52.6% \(\hbox {TiO}_{2}\), 14.8–15.1% \(\hbox {Fe}_{2} \hbox {O}_{3}\), 9.8–10.2% FeO, 6.97–7.12% \(\hbox {U}_{3} \hbox {O}_{8}\), 6.72–6.92% \(\hbox {RE}_{2} \hbox {O}_{3}\), 3.85–3.61% \(\hbox {K}_{2}\hbox {O}\), 0.9–1.4% \(\hbox {Al}_{2} \hbox {O}_{3}\), and 0.8–1.2% \(\hbox {SiO}_{2}\). The calculated structural formulae of the two davidite crystals are: D-1: \(\hbox {K}_{0.0044/0.004} \hbox {Ba}_{0.0044/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.053/0.053} \hbox {Mg}_{0.14/0.14} \hbox {Pb}_{0.0076/0.008} \hbox {Fe}_{2.675/2.675} \hbox {Fe}_{1.59/1.59} \hbox {Y}_{0.1175/0.118} \hbox {P}_{0.053/0.053} \hbox {Nb}_{0.008/0.008} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.033/0.033} \hbox {U}_{0.468/0.468} \hbox {Th}_{0.009/0.009} \,\,\hbox {REE}_{0.6829/0.683})_{6.05/6.05} (\hbox {Ti}_{12.15/12.15}\,\, \hbox {Fe}_{1.9022/1.903} \hbox {Si}_{0.372/0.372}\,\, \hbox {Al}_{0.517/0.517}\,\, \hbox {Cr}_{0.018/0.018} \hbox {Co}_{0.009/0.009} \hbox {Ni}_{0.027/0.027})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.319/0.319[]1.681/1.681})_{2/2}\) and D-2: \((\hbox {K}_{0.004/0.004} \hbox {Ba}_{0.005/0.005} \hbox {Ca}_{0.20/0.20} \hbox {Na}_{0.012/0.012} \hbox {Mn}_{0.05/0.05} \hbox {Mg}_{0.094/0.094} \hbox {Pb}_{0.007/0.007} \hbox {Fe}_{2.58/2.58} \hbox {Fe}_{1.71/1.71} \hbox {Y}_{0.112/0.112} \hbox {P}_{0.106/0.106} \hbox {Nb}_{0.006/0.006} \hbox {Sn}_{0.001/0.001} \hbox {Zr}_{0.03/0.03} \hbox {U}_{0.48/0.48} \hbox {Th}_{0.009/0.009} \hbox {REE}_{0.665/0.665})_{6.088/6.088} (\hbox {Ti}_{12.48/12.48} \hbox {Fe}_{1.87/1.87} \hbox {Si}_{0.249/0.249} \hbox {Al}_{0.334/0.334} \hbox {Cr}_{0.019/0.019} \hbox {Co}_{0.008/0.008} \hbox {Ni}_{0.04/0.04})_{15/15} \hbox {O}_{36/36} (\hbox {OH}_{0.098/0.098[]1.90/1.90})_{2/2}\). The calculated structural formulae are not fully stoichiometric, which could be due to metamict nature of davidite. The characteristic feature of distribution pattern of REE in davidite is unusually high concentration of LREE and HREE and substantially low content of MREE. It may be due to the occupation of REEs in two distinct crystallographic sites in davidite structure, i.e., M(1) and M(O) sites. Chondrite-normalised plot of davidite reveals a pronounced negative Eu-anomaly (\(\hbox {Eu}/\hbox {Eu}^{*} = 0.30{-}0.39\)), which suggests extremely fractionated nature of the metasomatising fluids from which davidite had crystallized. Metamict davidite-bearing U ores not only from Rajasthan, but also from other parts of India are likely to yield very high U leachability, thereby making them attractive sources of U, which otherwise are ignored by mineral engineers as uneconomic U ores. 相似文献
97.
98.
The southeastern fringe of the Precambrian Aravalli fold belt has been designated as Jahazpur Belt, which includes two greenschist facies metasedimentary lithopackages, Hindoli (Late Archean/Paleoproterozoic) and Jahazpur (Paleoproterozoic) Groups. We present geochemical data on metapelite (phyllite) and metagreywackes from the Hindoli Group. Metapelites are enriched in alumina while metagreywackes show a wide range and higher abundance of silica. Covariance between TiO2 — Al2O3, K2O — Al2O3 pairs and moderate to high SiO2/MgO ratios indicate a strong weathering control. Chemical Index of Alteration (CIA = 68 for metagraywackes; 75 for metapelites) reveals moderately weathered protoliths for them. Fractionated LREE pattern with almost flat HREE trend and moderate to high Eu anomalies (Eu/Eu* = 0.66 to 0.8) indicate feldspar bearing granite — granodiorite as probable compositions in the provenance. Very high PIA values (93) for metapelites reflect almost complete feldspar dissolution while the corresponding values for metagraywackes (68) are relatively lower. The diagnostic immobile trace elements (Sc, Zr, Th) can be interpreted as a variable felsic source (mainly granitic and subordinate granodioritic) for metagreywackes and a granodioritic (more mafic) one for metapelites. Considering the broad Precambrian geological set-up of NW India, the Banded Gneiss Complex (BGC), which predominantly comprises TTG gneisses and granites, amphibolite, etc. seems to be the most likely provenance for Hindoli sediments. 相似文献
99.
The production rate of H2O molecules at a heliocentric distance of 1 AU for comet Halley and the abundance ratio with respect to water (H2O) of parent molecules at the cometary nucleus from the paper of Yamamoto (1987) have been used to compute the number densities of positive ions viz. H3O+, H3S+, H2CN+, H3CO+, CH3OH
2
+
and NH
4
+
at various cometocentric distances within 600 kms from the nucleus.The role of proton transfer reactions in producing major ionic species is discussed. A major finding of the present investigation is that NH
4
+
ion which may be produced through proton transfer reactions is the most abundant ion near the nucleus of a comet unless the abundance of NH3 as a parent is abnormally low. Using the quoted value of Q(NH3)/Q(H2O) for comet Halley and the life times of NH3 and H2O molecules, the abundance ratio N(NH3)/N(H2O) is found to be one-third of that used in the present paper. The consequent proportionate decrease in the NH
4
+
ions does not, however, affect its superiority in number density over other ions near the nucleus.The number density of the next most abundant ion viz. H3O+ is found to be 4 × 104 cm-3 at the nucleus of comet Halley and decreases by a factor of two only upto a distance of 600 K ms from the nucleus. The ionic mass peak recorded by VEGA and GIOTTO spacecrafts atm/q = 18 is most probably composite of the minor ionic species H2O+, as its number density = 102 cm-3 remains virtually constant in the inner coma and of NH
4
+
, the number density of which at large cometocentric distances may add to the recorded peak atmlq = 18. The number densities of other major ions produced through proton transfer from H3O+ are also discussed in the region within 600 K ms from the nucleus of comet Halley. 相似文献
100.
Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm-1. The observed line profiles from 1.1 to 1.7 R⊙ with a spatial resolution of 10 × 22 arcsec2, give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 106 K. If temperature of the order of 1.3 × 106 K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s-1 to -17 km s-1. Most of the locations have velocities less than ±5 km s-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down. 相似文献