Effect of food quality on energy uptake     

Jeffrey S. Ren   《Journal of Sea Research》2009,62(2-3):72

The dynamic energy budget (DEB) theory assumes that the feeding of an organism in relation to food density follows the type-II functional response when food consists of purely digestible organic matter. However when faced with a food source high in inorganic content, an organism needs to adapt physiologically to maximise organic extraction. Indeed filter-feeding marine bivalves inhabiting turbid coastal waters cope with large fluctuations in food quality by selectively ingesting and pseudofaeces production. Data from feeding experiments with the New Zealand greenshell mussel Perna canaliculus have demonstrated that inorganic particles contribute some uncertainty to the estimate of the half-saturation coefficient. Incorporating inorganic matter into the functional response would improve the prediction of energy uptake.  相似文献   

Characterization of the lithological contact in the shergottite EETA79001—A record of igneous differentiation processes on Mars     

Deon Van Niekerk  Cyrena Anne Goodrich  G. Jeffrey Taylor  Klaus Keil 《Meteoritics & planetary science》2007,42(10):1751-1762

Abstract— Elephant Moraine (EET) A79001 is the only Martian meteorite that consists of both an olivine‐phyric shergottite (lithology A) and a basaltic shergottite (lithology B). The presence of these lithologies in one rock has previously been ascribed to mixing processes (either magmatic or impact‐induced). Here we present data regarding phase changes across the contact between the lithologies. These data show that the contact is gradational and suggest that it is a primary igneous feature consistent with crystallization of a single cooling magma. We present a model to establish a petrogenetic connection between an olivine‐phyric and a basaltic shergottite through differentiation. The model involves the shallow or surface emplacement of a magma that contained pre‐eruptive solids (phenocrysts and minor xenocrysts). Subsequent differentiation via crystal settling and in situ crystallization (Langmuir 1989) resulted in a layered sequence of lithology A overlain by lithology B, with gradations in modal abundance of maskelynite (increasing from A to B) and pigeonite/maskelynite (decreasing from A to B), and a gradational change in pattern of pyroxene zonation (zones of magnesian augite separating magnesian and ferroan pigeonite appear and thicken into B) across the contact. A pigeonite phenocryst‐bearing zone near the contact in lithology B appears to be intermediate between lithology A and the bulk of lithology B (which resembles basaltic shergottite Queen Alexandra Range [QUE] 94201). Re‐examination of Sr isotopic compositions in lithology A and across the contact is required to test and constrain the model.  相似文献   

The Meteoritical Bulletin,No. 100, 2014 June     

Alex Ruzicka  Jeffrey N. Grossman  Laurence Garvie 《Meteoritics & planetary science》2014,49(8):E1-E101

Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Ko?ice, Silistra, So?tmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondrites, 96 HED achondrites, 25 ureilites, 18 primitive achondrites, 17 iron meteorites, 15 enstatite chondrites, 11 lunar meteorites, 10 mesosiderites, 10 ungrouped achondrites, 8 pallasites, 8 Martian meteorites, 6 Rumuruti chondrites, 3 enstatite achondrites, and 2 angrites, and with 937 from Antarctica, 592 from Africa, 230 from Asia, 95 from South America, 44 from North America, 36 from Oceania, 6 from Europe, and 1 from an unknown location. This will be the last Bulletin published in the current format. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available online at http://www.lpi.usra.edu/meteor/  相似文献   

Mineralogy,petrology, chronology,and exposure history of the Chelyabinsk meteorite and parent body          下载免费PDF全文

K. Righter  P. Abell  D. Agresti  E. L. Berger  A. S. Burton  J. S. Delaney  M. D. Fries  E. K. Gibson  M. K. Haba  R. Harrington  G. F. Herzog  L. P. Keller  D. Locke  F. N. Lindsay  T. J. McCoy  R. V. Morris  K. Nagao  K. Nakamura‐Messenger  P. B. Niles  L. E. Nyquist  J. Park  Z. X. Peng  C.‐Y. Shih  J. I. Simon  C. C. Swisher III  M. J. Tappa  B. D. Turrin  R. A. Zeigler 《Meteoritics & planetary science》2015,50(10):1790-1819

Three masses of the Chelyabinsk meteorite have been studied with a wide range of analytical techniques to understand the mineralogical variation and thermal history of the Chelyabinsk parent body. The samples exhibit little to no postentry oxidation via Mössbauer and Raman spectroscopy indicating their fresh character, but despite the rapid collection and care of handling some low levels of terrestrial contamination did nonetheless result. Detailed studies show three distinct lithologies, indicative of a genomict breccia. A light‐colored lithology is LL5 material that has experienced thermal metamorphism and subsequent shock at levels near S4. The second lithology is a shock‐darkened LL5 material in which the darkening is caused by melt and metal‐troilite veins along grain boundaries. The third lithology is an impact melt breccia that formed at high temperatures (~1600 °C), and it experienced rapid cooling and degassing of S₂ gas. Portions of light and dark lithologies from Chel‐101, and the impact melt breccias (Chel‐102 and Chel‐103) were prepared and analyzed for Rb‐Sr, Sm‐Nd, and Ar‐Ar dating. When combined with results from other studies and chronometers, at least eight impact events (e.g., ~4.53 Ga, ~4.45 Ga, ~3.73 Ga, ~2.81 Ga, ~1.46 Ga, ~852 Ma, ~312 Ma, and ~27 Ma) are clearly identified for Chelyabinsk, indicating a complex history of impacts and heating events. Finally, noble gases yield young cosmic ray exposure ages, near 1 Ma. These young ages, together with the absence of measurable cosmogenic derived Sm and Cr, indicate that Chelyabinsk may have been derived from a recent breakup event on an NEO of LL chondrite composition.  相似文献   

Nutrient Fluxes from Sediments in the San Francisco Bay Delta     

Jeffrey C. Cornwell  Patricia M. Glibert  Michael S. Owens 《Estuaries and Coasts》2014,37(5):1120-1133

In September 2011 and March 2012, benthic nutrient fluxes were measured in the San Francisco Bay Delta, across a gradient from above the confluence of the Sacramento and San Joaquin Rivers to Suisun Bay. Dark and illuminated core incubation techniques were used to measure rates of denitrification, nutrient fluxes (phosphate, ammonium, nitrate), and oxygen fluxes. While benthic nutrient fluxes have been assessed at several sites in northern San Francisco Bay, such data across a Delta–Bay transect have not previously been determined. Average September rates of DIN (nitrate, nitrite, ammonium) flux were net positive across all sites, while March DIN flux indicated net uptake of DIN at some sites. Denitrification rates based on the N₂/Ar ratio approach were between 0.6 and 1.0 mmol m^?2 day^?1, similar to other mesotrophic estuarine sediments. Coupled nitrification–denitrification was the dominant denitrification pathway in September, with higher overlying water nitrate concentrations in March resulting in denitrification driven by nitrate flux into the sediments. Estimated benthic microalgal productivity was variable and surprisingly high in Delta sediments and may represent a major source of labile carbon to this ecosystem. Variable N/P stoichiometry was observed in these sediments, with deviations from Redfield driven by processes such as denitrification, variable light/dark uptake of nutrients by microalgae, and adsorption of soluble reactive phosphorus.  相似文献   

Geochronology and paleoenvironment of pluvial Harper Lake,Mojave Desert,California, USA     

Anna L. Garcia  Jeffrey R. Knott  Shannon A. Mahan  Jordon Bright 《Quaternary Research》2014

Accurate reconstruction of the paleo-Mojave River and pluvial lake (Harper, Manix, Cronese, and Mojave) system of southern California is critical to understanding paleoclimate and the North American polar jet stream position over the last 500 ka. Previous studies inferred a polar jet stream south of 35°N at 18 ka and at ~ 40°N at 17–14 ka. Highstand sediments of Harper Lake, the upstream-most pluvial lake along the Mojave River, have yielded uncalibrated radiocarbon ages ranging from 24,000 to > 30,000 ¹⁴C yr BP. Based on geologic mapping, radiocarbon and optically stimulated luminescence dating, we infer a ~ 45–40 ka age for the Harper Lake highstand sediments. Combining the Harper Lake highstand with other Great Basin pluvial lake/spring and marine climate records, we infer that the North American polar jet stream was south of 35°N about 45–40 ka, but shifted to 40°N by ~ 35 ka. Ostracodes (Limnocythere ceriotuberosa) from Harper Lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the Mojave River, thus confirming the lake was fed by the Mojave River. The ~ 45–40 ka highstand at Harper Lake coincides with a shallowing interval at downstream Lake Manix.  相似文献   

Large impact features on middle-sized icy satellites     

Jeffrey M. Moore  Paul M. Schenk  Erik Asphaug 《Icarus》2004,171(2):421-443

All of the large impact features of the middle-sized icy satellites of Saturn and Uranus that were clearly observed by the Voyager spacecraft are described. New image mosaics and stereo-and-photoclinometrically-derived digital elevation models are presented. Landforms related to large impact features, such as secondary craters and possible antipodal effects are examined and evaluated. Of the large impacts, Odysseus on Tethys appears to have had the most profound effect on its “target” satellite of any of the impact features we examined. Our modeling suggests that the Odysseus impact may have caused the prompt formation of Ithaca Chasma, a belt of tectonic troughs that roughly follow a great circle normal to the center of Odysseus, although other hypotheses remain viable. We identify probable secondary cratering from Tirawa on Rhea. We attribute a number of converging coalescing crater chains on Rhea to a putative, possibly relatively fresh, ∼350 km-diameter impact feature. We examine the antipodes of Odysseus, the putative ∼350 km-diameter Rhean impact feature, and Tirawa, and conclude that evidence from Voyager data for damage from seismic focusing is equivocal, although our modeling results indicate that such damage may have occurred. We propose a number of observations and tests for Cassini that offer the opportunity to differentiate among the various explanations and speculations reviewed and evaluated in this study.  相似文献   

Where does water go when it rains? Moving beyond the variable source area concept of rainfall‐runoff response     

Jeffrey J. McDonnell 《水文研究》2003,17(9):1869-1875

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Blowing in the wind. II. Creation and redistribution of refractory inclusions in a turbulent protoplanetary nebula     

Jeffrey N. Cuzzi  Sanford S. Davis  Anthony R. Dobrovolskis 《Icarus》2003,166(2):385-402

Ca-Al rich refractory mineral inclusions (CAIs) found at 1-6% mass fraction in primitive chondrites appear to be 1-3 million years older than the dominant (chondrule) components which were accreted into the same parent bodies. A prevalent concern is that it is difficult to retain CAIs for this long against gas-drag-induced radial drift into the Sun. We reassess the situation in terms of a hot inner (turbulent) nebula context for CAI formation, using analytical models of nebula evolution and particle diffusion. We show that outward radial diffusion in a weakly turbulent nebula can overcome inward drift, and prevent significant numbers of CAI-size particles from being lost into the Sun for times on the order of 10⁶ years. CAIs can form early, when the inner nebula was hot, and persist in sufficient abundance to be incorporated into primitive planetesimals at a much later time. Small (?0.1 mm diameter) CAIs persist for longer times than large (?5 mm diameter) ones. To obtain a quantitative match to the observed volume fractions of CAIs in chondrites, another process must be allowed for: a substantial enhancement of the inner hot nebula in silicate-forming material, which we suggest was caused by rapid inward drift of meter-sized objects. This early in nebula history, the drifting rubble would have a carbon content probably an order of magnitude larger than even the most primitive (CI) carbonaceous chondrites. Abundant carbon in the evaporating material would help keep the nebula oxygen fugacity low, plausibly solar, as inferred for the formation environment of CAIs. The associated production of a larger than canonical amount of CO₂ might also play a role in mass-independent fractionation of oxygen isotopes, leaving the gas rich in ¹⁶O as inferred from CAIs and other high temperature condensates.  相似文献   

Stellar masses and star formation histories for 10⁵ galaxies from the Sloan Digital Sky Survey     

Guinevere Kauffmann  Timothy M. Heckman  Simon D. M. White  Stéphane Charlot  Christy Tremonti  Jarle Brinchmann  Gustavo Bruzual  Eric W. Peng  Mark Seibert  Mariangela Bernardi  Michael Blanton  Jon Brinkmann  Francisco Castander  Istvan Csábai  Masataka Fukugita  Zeljko Ivezic  Jeffrey A. Munn  Robert C. Nichol  Nikhil Padmanabhan  Aniruddha R. Thakar  David H. Weinberg  Donald York 《Monthly notices of the Royal Astronomical Society》2003,341(1):33-53

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