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691.
Dezsö Nagy 《Journal of Geodesy》1978,52(2):159-164
A Direct Gravity Formula, polynomial in latitude, has been obtained from the series expansion of the closed gravity formula
of Somigliana by a telescoping procedure. The use of the 7 coefficient formula gives a result as accurate as the closed expression.
With 6 coefficients it gives an order of magnitude better accuracy than that of the widely used Chebyshev approximation and
with 5 coefficients a result that is accurate to better than that of the conventional form of computing theoretical gravity.
The derived approximation is not only simpler than other forms, but also at least 11 and 17 times faster on the CDC CYBER
74 computer than the Chebyshev approximation and the closed gravity formula respectively.
Contribution from the Earth Physics Branch No 720. 相似文献
692.
693.
Zusammenfassung Es wurden zwei indische Lateritprofile untersucht. Die Lateritproben wurden soweit unverfestigt, in Korngrößenklassen zerlegt. Mit röntgenographischen. differentialthermoanalytischen und optischen Methoden wurde der Mineralbestand quantitativ bestimmt. Die Änderungen des Mineralbestandes und die Änderungen der Mineralverteilung wurde in den Lateritprofilen verfolgt.Die Lateritprofile sind auf quarzhaltigen Gesteinen, einem grobkörnigen Granit und einem feinkörnigen Quarz-Glimmer-Sandstein, entstanden. Als Ursache der Lateritbildung ist bei beiden Profilen die Verwitterung und Kaolinisierung des Ausgangsgesteins anzusehen. Bei dem Granit wurden die Feldspäte sowie die Hornblende und der Biotit, bei dem Sandstein wurde der Muskowit kaolinisiert. Der Quarz wurde mehr oder weniger stark korrodiert.Durch die Anreicherung von oxydischen und hydroxydischen Eisenmineralen in bestimmten Zonen der Verwitterungsprofile kam es zur Ausbildung typischer Lateritprofile mit konkretionsführenden bzw. pisolithischen Horizonten. Die Anreicherung von Eisenmineralen in diesen Horizonten ist durch Zufuhr von Eisen aus Verwittrungslösungen erfolgt. Das Eisen entstammt bei dem ersten Profil den verwitternden eisenhaltigen Mineralen des Granites, der Hornblende und dem Biotit. Bei dem zweiten Profil ist die Herkunft des Eisens aus verwitternden hämatitreichen Rindern des Sandsteines abzuleiten. An hydroxydischen Aluminiummineralen sind in beiden Lateritprofilen nur geringe Mengen Diaspur vorhanden.Auflösung von Kaolinit, Wanderung der Kaolinsubstanz und Neubildung von Fireclaymineral wurde in beiden Profilen nachgewiesen. 相似文献
694.
Minor and trace elements in HF-soluble zircons 总被引:2,自引:0,他引:2
Electron probe analysis of a group of HF-soluble zircons from porphyroids of the Thuringian Forest, Germany, established yttrium, phosphorus, and iron to be the significant minor constituents. It is believed that these elements render the zircon structure HF-soluble. The Y content varies from about 6500–48000 ppm=0.83–6.10% Y2O3; the P concentrations range from a low of about 790 to a maximum of 4000 ppm=0.18–0.92% P2O5; the Fe content varies from about 400–15000 ppm=0.06–2.10% Fe2O3. Although both Y and P are distributed throughout each given grain, they are sometimes mutually enriched in growth zones. These zones are also resolved in reflected light micrographs and the electron images. 相似文献
695.
Principal components analysis is used to study the chemistry of 639 calcic amphiboles. Eigenvectors representing multiple partial correlation coefficients give various sets of substitutional relationships. The relative significance of each set can be noted by the percent variation of the data it represents. The highest percent variation (36%) is associated with the substitutions $$Si + Mg \rightleftharpoons Al^{IV} + Al^{VI} + Ti + Fe^{3 + } + Fe^{2 + } + Na + K$$ . Other expected substitutions among the ions such as AlIV + Na ? Si, the positive correlation between AlIV and AlVI etc. are shown statistically. The substitution of Al in T 1 and T 2 positions imposes an ordering in the M 1, M 2 and M 3 sites. Variability of OH in the amphiboles is found to be significant. There is no definite correlation between OH and Fe3+ but OH and Ti are positively correlated. Under certain conditions and provided the concentration of AlIV does not change significantly, Fe and Mg may be assumed to mix ideally in the amphibole solid solution. 相似文献
696.
Ghylaine Quitté Christopher Latkoczy Maria Schönbächler Alex N. Halliday Detlef Günther 《Geochimica et cosmochimica acta》2011,75(23):7698-7706
Eucrites are basaltic meteorites that cooled rapidly but are in many instances thermally metamorphosed and impact brecciated. The exact timing of these events remains unclear. In this study, Ni isotopic compositions and Fe/Ni elemental ratios are presented for two non-cumulate eucrites, Bouvante and Juvinas, including mineral separates from the latter. The samples are characterized by variable, well-resolved 60Ni-excesses consistent with the former presence of live 60Fe (t1/2 = 2.62 Ma) at the time of eucrite crystallization. A significant fraction of Ni with a terrestrial-like composition appears to be surface correlated. This Ni may be the product of terrestrial contamination or was introduced by a chondritic impactor during brecciation. Altogether, the data provide evidence for a complex and probably multi-stage history of Fe and/or Ni redistribution, which impedes the interpretation of the chronological data. 相似文献
697.
The molecular fingerprints of the chemosynthesis based microbial communities at methane seeps tend to be extremely well preserved in authigenic carbonates. The key process at seeps is the anaerobic oxidation of methane (AOM), which is performed by consortia of methanotrophic archaea and sulphate reducing bacteria. Besides the occurrence of 13C depleted isoprenoids and n-alkyl chains derived from methanotrophic archaea and sulphate reducing bacteria, respectively, 13C depleted triterpenoids have been reported from a number of seep deposits. In order to evaluate the significance of these apparently non-AOM related molecular fossils, the biomarker inventories of one Campanian and two Miocene methane seep limestones are compared. These examples provide strong evidence that methane was not solely oxidized by an anaerobic process. Structural and carbon isotope data reveal that aerobic methanotrophy was common at some ancient methane seeps as well. The Miocene Marmorito limestone contains abundant 3β-methylated hopanoids (δ13C: −100‰). Most likely, 3β-methylated hopanepolyols, prevailing in aerobic methanotrophs, were the precursor lipids of these compounds. A series of isotopically depleted 4-methylated steranes (lanostanes; δ13C: −80‰ to −70‰) and similarly isotopically depleted 17β(H),21β(H)-32-hopanoic acid in the Miocene Pietralunga seep limestone also are derived probably from aerobic methanotrophs. Lanosterol, which is known to be produced by aerobic methanotrophs, is the most likely precursor of 4-methylated steranes. Less obvious is the origin of 8,14-secohexahydrobenzohopanes (δ13C: −110‰ to −107‰) in Late Cretaceous seep limestones. These hopanoids probably reflect early degradational products of precursor lipids locally produced by seep endemic aerobic methanotrophs. 相似文献
698.
699.
W. Roland Gehrels Katie Szkornik Jason R. Kirby William A. Marshall Jørn B.T. Pedersen 《Quaternary Research》2006,66(2):288-302
Cores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to 14C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP. 相似文献
700.
Tom K. Ekström 《Contributions to Mineralogy and Petrology》1973,38(4):329-338
Hydrothermal syntheses of chlor-hydroxyapatite have been carried out between 300 and 700° C at a constant pressure of 1000
bar. The substitution of OH for Cl varies as a function of the amount of added CaCl2, temperature, and pH. In the main reaction the incorporation of Cl is negligible at 300° C but increases to over 40 mole
percent Cl-apatite at 700° C. A simple X-ray method for determining the Cl/Cl+OH ratio has been developed and this is also
extended to fluorine-bearing chlor-hydroxyapatites. A number of natural chlor-fluorhydroxyapatites are discussed in the light
of the X-ray method and the result of the synthesis. 相似文献