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81.
Lipid biomarker assemblages preserved within the bitumen and kerogen phases of sedimentary rocks from the ca. 780–729 Ma Chuar and Visingsö Groups facilitate paleoenvironmental reconstructions and reveal fundamental aspects of emerging mid‐Neoproterozoic marine communities. The Chuar and Visingsö Groups were deposited offshore of two distinct paleocontinents (Laurentia and Baltica, respectively) during the Tonian Period, and the rock samples used had not undergone excessive metamorphism. The major polycyclic alkane biomarkers detected in the rock bitumens and kerogen hydropyrolysates consist of tricyclic terpanes, hopanes, methylhopanes, and steranes. Major features of the biomarker assemblages include detectable and significant contribution from eukaryotes, encompassing the first robust occurrences of kerogen‐bound regular steranes from Tonian rocks, including 21‐norcholestane, 27‐norcholestane, cholestane, ergostane, and cryostane, along with a novel unidentified C30 sterane series from our least thermally mature Chuar Group samples. Appreciable values for the sterane/hopane (S/H) ratio are found for both the free and kerogen‐bound biomarker pools for both the Chuar Group rocks (S/H between 0.09 and 1.26) and the Visingsö Group samples (S/H between 0.03 and 0.37). The more organic‐rich rock samples generally yield higher S/H ratios than for organic‐lean substrates, which suggests a marine nutrient control on eukaryotic abundance relative to bacteria. A C27 sterane (cholestane) predominance among total C26–C30 steranes is a common feature found for all samples investigated, with lower amounts of C28 steranes (ergostane and crysotane) also present. No traces of known ancient C30 sterane compounds; including 24‐isopropylcholestanes, 24‐n‐propylcholestanes, or 26‐methylstigmastanes, are detectable in any of these pre‐Sturtian rocks. These biomarker characteristics support the view that the Tonian Period was a key interval in the history of life on our planet since it marked the transition from a bacterially dominated marine biosphere to an ocean system which became progressively enriched with eukaryotes. The eukaryotic source organisms likely encompassed photosynthetic primary producers, marking a rise in red algae, and consumers in a revamped trophic structure predating the Sturtian glaciation. 相似文献
82.
Leuschner F Dutta P Gorbatov R Novobrantseva TI Donahoe JS Courties G Lee KM Kim JI Markmann JF Marinelli B Panizzi P Lee WW Iwamoto Y Milstein S Epstein-Barash H Cantley W Wong J Cortez-Retamozo V Newton A Love K Libby P Pittet MJ Swirski FK Koteliansky V Langer R Weissleder R Anderson DG Nahrendorf M 《Nature biotechnology》2011,29(11):1005-1010
Excessive and prolonged activity of inflammatory monocytes is a hallmark of many diseases with an inflammatory component. In such conditions, precise targeting of these cells could be therapeutically beneficial while sparing many essential functions of the innate immune system, thus limiting unwanted effects. Inflammatory monocytes-but not the noninflammatory subset-depend on the chemokine receptor CCR2 for localization to injured tissue. Here we present an optimized lipid nanoparticle and a CCR2-silencing short interfering RNA that, when administered systemically in mice, show rapid blood clearance, accumulate in spleen and bone marrow, and localize to monocytes. Efficient degradation of CCR2 mRNA in monocytes prevents their accumulation in sites of inflammation. Specifically, the treatment attenuates their number in atherosclerotic plaques, reduces infarct size after coronary artery occlusion, prolongs normoglycemia in diabetic mice after pancreatic islet transplantation, and results in reduced tumor volumes and lower numbers of tumor-associated macrophages. 相似文献
83.
Triplet Excitons in Highly Efficient Solar Cells Based on the Soluble Small Molecule p‐DTS(FBTTh2)2
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Stefan Väth Kristofer Tvingstedt Andreas Baumann Michael C. Heiber Andreas Sperlich John A. Love Thuc‐Quyen Nguyen Vladimir Dyakonov 《Liver Transplantation》2017,7(7)
Triplet exciton formation in neat 7,7‐(4,4‐bis(2‐ethylhexyl)‐4H‐silolo[3,2‐b:4,5‐b′] dithiophene‐2,6‐diyl)bis(6‐fluoro‐4‐(5′‐hexyl‐[2,2′‐bithiophen]‐5‐yl)benzo[c][1,2,5]thiadiazole) (p‐DTS(FBTTh2)2) and blends with [6,6]‐Phenyl C70 butyric acid methyl ester (PC70BM), with and without the selective solvent additive 1,8‐diiodooctane, is investigated by means of spin sensitive photoluminescence measurements. For all three material systems, a significant amount of long living triplet excitons is detected, situated on the p‐DTS(FBTTh2)2 molecules. The characteristic zero‐field splitting parameters for this state are identified to be D = 42 mT (1177 MHz) and E = 5 mT (140 MHz). However, no triplet excitons located on PC70BM are detectable. Using electrically detected spin resonance, the presence of these triplet excitons is confirmed even at room temperature, highlighting that triplet excitons form during solar cell operation and influence the photocurrent and photovoltage. Surprisingly, the superior performing blend is found to have the largest triplet population. It is concluded, that the formation of triplet excitons from charge transfer states via electron back transfer has no crucial impact on device performance in p‐DTS(FBTTh2)2:PC70BM based solar cells. 相似文献
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85.
Jacob Love 《American anthropologist》2003,105(2):437-438
Traditionalism and Modernity in the Music and Dance of Oceania: Essays in Honour of Barbara B. Smith. Helen Reeves Lawrence and Don Niles. eds. Oceania Monograph 52. Sydney: University of Sydney, 2001. 267 pp. 相似文献
86.
In vitro fertilization (IVF) was performed on in vitro-matured equine oocytes in three experiments. Frozen-thawed sperm were prepared using swim-up separation and heparin treatment. In Experiment 1, fertilization was achieved with sperm from only one frozen ejaculate of four obtained from the same stallion. Within this ejaculate, fertilization rates were higher with fresh media, as compared to media held for 6-8 days before use (39.6% versus 7.3%, respectively; P<0.001). The type of bovine serum albumin used affected fertilization rates (4% versus 39.6%; P<0.001). To determine if IVF rates were influenced by factors associated with the freezing process (Experiment 2), a single ejaculate from a second stallion was frozen using eight variations in timing of steps in the freezing protocol. There were no differences among treatments in fertilization rates (range, 0-3%). In Experiment 3, fertilization rates of semen frozen in an extender containing 21.5% egg yolk were lower than fertilization rates of semen from the same ejaculate but frozen with a 3% egg-yolk extender (0% versus 15%, respectively; P<0.01). We inferred that rates of equine IVF with frozen-thawed sperm were influenced by ejaculate, the composition and age of the media used, and freezing extender. To our knowledge, this is the first report of ejaculate or extender differences affecting in vitro fertilization in this species. These factors may help to explain the great variability in fertilization rates reported with equine IVF, both among and within laboratories. 相似文献
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89.
Shorebird predation of horseshoe crab eggs in Delaware Bay: species contrasts and availability constraints 总被引:2,自引:0,他引:2
Gillings S Atkinson PW Bardsley SL Clark NA Love SE Robinson RA Stillman RA Weber RG 《The Journal of animal ecology》2007,76(3):503-514
1. Functional responses -- the relationship between resource intake rate and resource abundance -- are widely used in explaining predator-prey interactions yet many studies indicate that resource availability is crucial in dictating intake rates. 2. For time-stressed migrant birds refuelling at passage sites, correct decisions concerning patch use are crucial as they determine fattening rates and an individual's future survival and reproduction. Measuring availability alongside abundance is essential if spatial and temporal patterns of foraging are to be explained. 3. A suite of shorebird species stage in Delaware Bay where they consume horseshoe crab Limulus polyphemus eggs. Several factors including spawning activity and weather give rise to marked spatial and temporal variation in the abundance and availability of eggs. We undertook field experiments to determine and contrast the intake rates of shorebird species pecking for surface and probing for buried eggs. 4. Whether eggs were presented on the sand surface or buried, we demonstrate strong aggregative responses and rapid depletion (up to 80%). Depletion was greater at deeper depths when more eggs were present. No consistent give-up densities were found. Type II functional responses were found for surface eggs and buried eggs, with peck success twice as high in the former. Maximum intake rates of surface eggs were up to 83% higher than those of buried eggs. 5. Caution is needed when applying functional responses predicted on the basis of morphology. Our expectation of a positive relationship between body size and intake rate was not fully supported. The smallest species, semipalmated sandpiper, had the lowest intake rate but the largest species, red knot, achieved only the same intake rate as the mid-sized dunlin. 6. These functional responses indicate that probing is rarely more profitable than pecking. Currently, few beaches provide egg densities sufficient for efficient probing. Areas where eggs are deposited on the sand surface are critical for successful foraging and ongoing migration. This may be especially true for red knot, which have higher energetic demands owing to their larger body size yet appear to have depressed intake rates because they consume smaller prey than their body size should permit. 相似文献
90.
Staying out in the cold: glacial refugia and mitochondrial DNA phylogeography in ancient European brown bears 总被引:4,自引:1,他引:3
Valdiosera CE García N Anderung C Dalén L Crégut-Bonnoure E Kahlke RD Stiller M Brandström M Thomas MG Arsuaga JL Götherström A Barnes I 《Molecular ecology》2007,16(24):5140-5148
Models for the development of species distribution in Europe typically invoke restriction in three temperate Mediterranean refugia during glaciations, from where recolonization of central and northern Europe occurred. The brown bear, Ursus arctos, is one of the taxa from which this model is derived. Sequence data generated from brown bear fossils show a complex phylogeographical history for western European populations. Long-term isolation in separate refugia is not required to explain our data when considering the palaeontological distribution of brown bears. We propose continuous gene flow across southern Europe, from which brown bear populations expanded after the last glaciation. 相似文献