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81.
R. Ganapathy Grace M. Papia Lawrence Grossman 《Earth and Planetary Science Letters》1976,29(2):302-308
The concentrations of zirconium and hafnium have been determined in Orgueil, Murchison, Allende, Bruderheim and Alais by RNAA. The mean Zr/Hf weight ratio in the first four of these meteorites is 31.3 ± 2.2 indicating no major fractionation of Zr from Hf. Alais contains anomalously high amounts of many refractory lithophile elements, including Zr and Hf. Orgueil contains 3.1 ppm Zr and 0.11 ppm Hf, corresponding to 9.0 and 0.16 atoms, respectively, relative to 106 Si atoms. 相似文献
82.
Lawrence A. Curtis 《Estuaries and Coasts》1978,1(2):73-84
Aspects of the population dynamics of the polychaeteSabellaria vulgaris Verrill 1874 were studied by observing the temporal occurrence of larvae in the plankton of Delaware Bay. Vertical plankton samples were collected monthly from July 1970 to October 1971. Four 25-hour plankton studies were conducted within this time period, and on one occasion samples were collected on a transect across the mouth of the bay.Sabellaria vulgaris larvae were present in the bay only from mid-April through October. July (1970) and August (1971) 25-hour plankton studies showed larvae present in the water column at virtually all times of the day and night. Horizontal dispersion of larvae in the plankton was clearly aggregated. However, correlation of larval presence, absence or abundance with the measured physical factors in the estuary was not apparent except on a seasonal scale. Six developmental stages were defined based upon observation of laboratory-reared larvae. Young larvae appeared in the plankton on numerous occasions, indicating that spawning occurred repeatedly during the April–October time period in Delaware Bay. Relative to other habitats within the geographic range ofS. vulgaris, Delaware Bay is a particularly well-suited environment for the construction of massive colonies by the species. Adults living in large aggregates would exhibit greater fitness because of the higher probability of eggs being fertilized. Indications are that a portion of the larvae produced in the Bay are retained in the estuary and undergo settlement there. Delaware Bay may be a population center for the species. A comparison of reproductive phenomena among sabellariid species is presented. It is apparent that the species,S. vulgaris, consists of several physiologically distinct populations, and that this is true of certain other sabellariid species as well. 相似文献
83.
Judith M. Capuzzo Joel C. Goldman John A. Davidson Sarah A. Lawrence 《Marine pollution bulletin》1977,8(7):161-163
The effects of free chlorine and chloramine on stage I lobster larvae and juvenile killifish were investigated in continuous flow bioassay units. In comparing mortality and changes in standard respiration rates during and after exposure to either chlorine form, significant respiratory stress was observed with exposure to sublethal levels. Sublethal responses to free and combined chlorine should be considered when establishing regulations for chlorine residuals in cooling waters. 相似文献
84.
Higuchiet al. (1977) proposed the existence of Tl-rich and Tl-poor “mysterite” to explain Tl and Bi contents of dark clasts in the Supuhee H6 chondrite and of bulk Supuhee. They suggested that these two components formed by gas-dust fractionation during condensation. An aliquot of one of the clasts studied by Higuchi et al. and found to contain Tl-poor mysterite was analyzed by instrumental neutron activation in this paper. A complex assortment of element fractionations was found. Data for rare earth and other refractory lithophiles and refractory and moderately volatile siderophiles are consistent with random separation and reunification of gas and dust throughout the condensation sequence. Independent evidence thus exists that processes like those invoked by Higuchi et al. to explain mysterite did occur in the region of the nebula sampled by this clast. 相似文献
85.
P. Lira R. A. Johnson A. Lawrence R. Cid Fernandes 《Monthly notices of the Royal Astronomical Society》2007,382(4):1552-1590
We present optical and infrared broad-band images, radio maps, and optical spectroscopy for the nuclear region of a sample of nearby galaxies. The galaxies have been drawn from a complete volume-limited sample for which we have already presented X-ray imaging. We modelled the stellar component of the spectroscopic observations to determine the star formation history of our targets. Diagnostic diagrams were used to classify the emission-line spectra and determine the ionizing mechanism driving the nuclear regions. All those sources classified as active galactic nuclei present small Eddington ratios (∼10−3 –10−6 ) , implying a very slow growth rate of their black holes. We finally investigate the relative numbers of active and normal nuclei as a function of host galaxy luminosity and find that the fraction of active galaxies slowly rises as a function of host absolute magnitude in the M B ∼−12 to −22 range. 相似文献
86.
Anna Lawrence 《Global Environmental Change》2009,19(2):173-179
Biological recording is a long-established feature of amateur natural history in Britain. Phenology (the recording of seasonal events) in particular has provided scientists with important long-term data sets. These data are of increasing interest as indicators of climate change and its impacts. Most scientists treat the data as the object of interest, while less attention has been paid to the two-way process of knowledge creation, and the significance of the inner, personal part of that. Phenological recording provides an interesting window on this because it is relatively straightforward (and therefore involves a wider range of people than more technically demanding recording), and because it is linked to the climate change discourse (and therefore connected with emotional and moral framings of the situation). This paper describes the rise of popular phenology in the UK and explores these dynamically related aspects of knowledge creation by drawing on accounts in the media and by participants. It concludes that reflexivity and credibility are important aspects of both personal and interpersonal meaning-making, and suggests that attention to both subjective integration of data, and the scale of local cultures of knowledge, are important in understanding the potential for connecting networks of citizen science. Phenology therefore appears to have a particular role to play in public understanding of climate change, which extends beyond the merely extractive collection of data to a more deeply integrated connection between observation and meaning. 相似文献
87.
Lawrence M. Mayer Linda L. Schick Thomas S. Bianchi Laura A. Wysocki 《Marine Chemistry》2009,113(1-2):123-128
Several chemical markers of organic matter source and age are shown to be susceptible to light-induced alteration. To test for the photochemical lability of markers previously employed for sediments from the Louisiana coastal zone, we subjected sediments under resuspension conditions to simulated sunlight, and monitored changes in C:N and Br:OC ratios, δ13C, Δ14C, and lignin composition. Markers of terrigenous origin (high C:N, lignin) decreased and δ13C became enriched in sediments containing primarily terrigenous organic matter, while a marker of marine organic matter (Br:OC) decreased in samples containing significant contributions from this source. Preferential loss of 14C from all sediments indicated enhanced photochemical lability of organic matter of relatively recent origin, consistent with the changes in chemical markers. Most, but not all, experimental alterations are consistent with field distributions of these markers. Relatively small experimental changes in the markers in combination with confounding processes in the environment, however, prevent these parallel trends from providing any more than a consistency test for the importance of photochemical reactions in this region. 相似文献
88.
Lawrence E. Krumenaker 《Icarus》1978,34(1):215-219
Longitudes of surface marking observed on Mercury by E.M. Antoniadi are determined. The most frequent of the locations are used to determine the most probable positions on Mercury's surface for the names defined on Antoniadi's 88-day planisphere. It is suggested that these locations can serve as a valid and accurate basis for Mercurian nomenclature. 相似文献
89.
Evidence for high‐temperature fractionation of lithium isotopes during differentiation of the Moon
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James M. D. Day Lin Qiu Richard D. Ash William F. McDonough Fang‐Zhen Teng Roberta L. Rudnick Lawrence A. Taylor 《Meteoritics & planetary science》2016,51(6):1046-1062
Lithium isotope and abundance data are reported for Apollo 15 and 17 mare basalts and the LaPaz low‐Ti mare basalt meteorites, along with lithium isotope data for carbonaceous, ordinary, and enstatite chondrites, and chondrules from the Allende CV3 meteorite. Apollo 15 low‐Ti mare basalts have lower Li contents and lower δ7Li (3.8 ± 1.2‰; all uncertainties are 2 standard deviations) than Apollo 17 high‐Ti mare basalts (δ7Li = 5.2 ± 1.2‰), with evolved LaPaz mare basalts having high Li contents, but similar low δ7Li (3.7 ± 0.5‰) to Apollo 15 mare basalts. In low‐Ti mare basalt 15555, the highest concentrations of Li occur in late‐stage tridymite (>20 ppm) and plagioclase (11 ± 3 ppm), with olivine (6.1 ± 3.8 ppm), pyroxene (4.2 ± 1.6 ppm), and ilmenite (0.8 ± 0.7 ppm) having lower Li concentrations. Values of δ7Li in low‐ and high‐Ti mare basalt sources broadly correlate negatively with 18O/16O and positively with 56Fe/54Fe (low‐Ti: δ7Li ≤4‰; δ56Fe ≤0.04‰; δ18O ≥5.7‰; high‐Ti: δ7Li >6‰; δ56Fe >0.18‰; δ18O <5.4‰). Lithium does not appear to have acted as a volatile element during planetary formation, with subequal Li contents in mare basalts compared with terrestrial, martian, or vestan basaltic rocks. Observed Li isotopic fractionations in mare basalts can potentially be explained through large‐degree, high‐temperature igneous differentiation of their source regions. Progressive magma ocean crystallization led to enrichment in Li and δ7Li in late‐stage liquids, probably as a consequence of preferential retention of 7Li and Li in the melt relative to crystallizing solids. Lithium isotopic fractionation has not been observed during extensive differentiation in terrestrial magmatic systems and may only be recognizable during extensive planetary magmatic differentiation under volatile‐poor conditions, as expected for the lunar magma ocean. Our new analyses of chondrites show that they have δ7Li ranging between ?2.5‰ and 4‰. The higher δ7Li in planetary basalts than in the compilation of chondrites (2.1 ± 1.3‰) demonstrates that differentiated planetary basalts are, on average, isotopically heavier than most chondrites. 相似文献
90.
Peter J. ISAACSON Amit BASU SARBADHIKARI Carlé M. PIETERS Rachel L. KLIMA Takahiro HIROI Yang LIU Lawrence A. TAYLOR 《Meteoritics & planetary science》2011,46(2):228-251
The lunar rock and mineral characterization consortium (LRMCC) has conducted coordinated mineralogy/petrography/spectroscopy analyses of a suite of pristine lunar basalts. Four basalt slabs (two low‐Ti, two high‐Ti) and paired thin sections were analyzed. Thin sections were analyzed for mineralogy/petrography, while the slabs were used to prepare particulate separates of major mineral phases and bulk samples. Mineral separates and particulate bulk samples were crushed to controlled grain sizes and their reflectance spectra measured in the NASA RELAB at Brown University. The resulting data set provides an essential foundation for spectral mixing models, offers valuable endmember constraints for space weathering analyses, and represents critical new ground truth results for lunar science and exploration efforts. 相似文献