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Element Ratios (element + ratio)
Selected AbstractsFirst and second optical transitions in single-walled carbon nanotubes: a resonant Raman studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007H. Telg Abstract Resonant Raman spectroscopy was performed to study electron,phonon coupling in single-walled carbon nanotubes separated in solution. By varying the excitation energy from 1.26 eV to 1.93 eV we obtained radial breathing mode resonance profiles of the first and second optical transitions E11 and E22 of the (9,1) and (8,3) tubes. We observe up to 16 times stronger Raman intensities for the E11 transitions which can mostly be attributed to a two times broader linewidth of the E22 transition. Comparison of the matrix element ratio ,11/,22 to theoretical predictions on the electron,phonon coupling show a deviation of a factor 1.7 which might be associated with the change of the exciton,photon matrix element. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crustal thickness and adakite occurrence in the Philippines: Is there a relationship?ISLAND ARC, Issue 4 2008Carla B. Dimalanta Abstract Adakites are increasingly being recognized worldwide in a variety of tectonic settings. Models on the formation of this geochemically distinct class of volcanic rocks have evolved from partial melting of subducted young, hot oceanic slabs to magmatism resulting from oblique subduction, low-angle or flat subduction, or even slab-tearing. Some workers have also pointed to the partial melting of thickened crust to explain the generation of adakitic melts. Rare earth element ratios from adakites and adakitic rocks in the Philippines were used in this study to obtain approximations of the levels where they were generated. These were tied to available geophysical data that defines the crustal thickness of the areas where the samples were collected. High Sm/Yb and La/Yb ratios denote the involvement of amphiboles, and in some cases garnet, in the generation of adakites and adakitic magmas. The presence of amphibole and garnet as residual phases suggests high pressures corresponding to thicker crust (,30 to 45 km). Adakites and adakitic rocks formed through processes other than melting of subducted young oceanic crust would need ,30 km to account for the heavy rare earth element signatures. If mantle fractionation is not the process involved, crustal thickness is critical to generate adakites and adakitic rocks. [source] TOF-SIMS analysis of cometary matter in Stardust aerogel tracksMETEORITICS & PLANETARY SCIENCE, Issue 1-2 2008Thomas Stephan While single grains >1 ,m are highly variable in their chemical composition, nanometer-scale material found in the wall of one track has within a factor of 1.22 bulk CI chondritic element ratios relative to Fe for Na, Mg, A1, Ti, Cr, Mn, and Co. Compared to CI, a depletion in Ca by a factor of four and an enrichment in Ni by a factor of two was observed. These results seem to confirm recent reports of a CI-like bulk composition of Wild 2. The analysis of organic compounds in aerogel samples is complicated by the presence of contaminants in the capture medium. However, polycyclic aromatic hydrocarbons that could possibly be attributed to the comet were observed. [source] THE TECHNOLOGY OF ,GLAZED' RESERVED SLIP WARE,A FINE CERAMIC OF THE HARAPPAN PERIOD*ARCHAEOMETRY, Issue 4 2005K. KRISHNAN ,Glazed' Reserved Slip Ware (RSW) is a high-quality glossy bichrome pottery of the Indus Valley civilization, and dates to the mature Harappan period (c. 2600,1900 bc). Scanning electron microscopy with energy-dispersive X-ray analysis indicates that the surface coat on RSW is composed of a pale grey vitrified clay slip, which overlies a black slip with significantly higher iron oxide. Hence the term ,sintered' Reserved Slip Ware is to be preferred. X-ray diffraction analysis indicates that both the pale and black slips contain hercynite, mullite and quartz, but observation by scanning electron microscopy shows that the black slips contain higher amounts of coarser-grained hercynite. The elemental data suggest that different clays were used to make the bodies and the slips. However, key element ratios are very close in associated black and pale slips. The grey slip may have been produced by elutriation of the fine, iron oxide-rich clay that was used to prepare the black slip. The pale grey slip was laid over the black and removed by combing to produce a bichrome effect, which evoked semi-precious materials such as agate. RSW was a specialist product that required significantly higher input skill and resources than the majority of Harappan clay-based ceramics. It is a further example of the range of sophisticated Harappan ceramic wares, which included faience, fired steatite and stoneware. [source] Use of non-limiting substrates to increase size; a generic strategy to simultaneously optimize uptake and minimize predation in pelagic osmotrophs?ECOLOGY LETTERS, Issue 7 2005T. Frede Thingstad Abstract Coexistence of two organisms competing for the same nutrient is possible if one is an ,uptake', and the other a ,predation defence' specialist. In pelagic food webs this principle has been linked to cell size. Small osmotroph cells, with their high surface : volume ratio, have been argued to be uptake specialists, while larger osmotrophs avoiding the intense grazing pressure from small protozoan predators might represent ,predation defence' specialists. This may seem like an obligatory trade-off situation that necessitates a choice of either being small or being large, and thus being potentially dominant in oligotrophic or in eutrophic environments, respectively. However, in a more precise form, the theory for nutrient diffusion states that it is the ,surface : cell requirement of limiting element' ratio, rather than the ,surface : volume' ratio, that is important. The distinction is crucial, since it opens up the possibility of there being life strategies that use a non-limiting element to increase size. Hypothesized to maximize uptake and predator defence simultaneously, such strategies should be particularly successful. We suggest that this strategy is exploited by osmotrophs with different size and physiology, such as heterotrophic bacteria, unicellular cyanobacteria and diatoms. Since the strategy implies a shift in organism stoichiometry, the biogeochemical implications are strong, illustrating the tight relationships between physical micro-scale processes, organism life strategies, biodiversity, food web structure, and biogeochemistry. [source] Seasonal records of climatic change in annually laminated tufas: short review and future prospects,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2005J. E. Andrews Abstract Many Recent and fossil freshwater tufa stromatolites contain millimetre-scale, alternating laminae of dense micrite and more porous or sparry crystalline calcites. These alternating laminae have been interpreted to represent seasonally controlled differences in the biotic activity of microbes, and/or seasonally controlled changes in the rate of calcification. Either way, couplets of these microbially mediated alternating calcified laminae are generally agreed to represent annual seasonality. Combined stable isotope (,18O and ,13C) and trace element (Mg, Sr, Ba) geochemistry from Recent tufa stromatolites show that seasonal climatic information is available from these calcites. Variability in ,18O (and in one case Mg concentration) has been shown to be controlled primarily by stream temperature change, usually driven by solar insolation. In arid climates, seasonal evaporation can also cause ,18O enrichment by at least 1,. Variability in ,13C results potentially from: (1) seasonal change in plant uptake of 12C-enriched CO2; (2) seasonal change in degassing of 12C-enriched CO2 in the aquifer system; and (3) precipitation of calcite along the aquifer or river flow path, a process that increases ,13C of dissolved inorganic carbon (DIC) in the remaining water. Mechanisms 2 and 3 are linked because calcite precipitates in aquifers where degassing occurs, e.g. air pockets. The latter mechanism for ,13C enrichment has also been shown to cause sympathetic variation between trace element/Ca ratios and ,13C because trace elements with partition coefficients much greater than 1 (e.g. Sr, Ba) remain preferentially in solution. Since degassing in air pockets will be enhanced during decreased recharge when water saturation of the aquifer is lowest, sympathetic variation in trace element/Ca ratios and ,13C is a possible index of recharge and therefore precipitation intensity. High-resolution geochemical data from well-dated tufa stromatolites have great potential for Quaternary palaeoclimate reconstructions, possibly allowing recovery of annual seasonal climatic information including water temperature variation and change in rainfall intensity. However, careful consideration of diagenetic effects, particularly aggrading neomorphism, needs to be the next step. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||