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41.
Erlandson JM Rick TC Braje TJ Casperson M Culleton B Fulfrost B Garcia T Guthrie DA Jew N Kennett DJ Moss ML Reeder L Skinner C Watts J Willis L 《Science (New York, N.Y.)》2011,331(6021):1181-1185
Three archaeological sites on California's Channel Islands show that Paleoindians relied heavily on marine resources. The Paleocoastal sites, dated between ~12,200 and 11,200 years ago, contain numerous stemmed projectile points and crescents associated with a variety of marine and aquatic faunal remains. At site CA-SRI-512 on Santa Rosa Island, Paleocoastal peoples used such tools to capture geese, cormorants, and other birds, along with marine mammals and finfish. At Cardwell Bluffs on San Miguel Island, Paleocoastal peoples collected local chert cobbles, worked them into bifaces and projectile points, and discarded thousands of marine shells. With bifacial technologies similar to those seen in Western Pluvial Lakes Tradition assemblages of western North America, the sites provide evidence for seafaring and island colonization by Paleoindians with a diversified maritime economy. 相似文献
42.
Montañez IP Tabor NJ Niemeier D Dimichele WA Frank TD Fielding CR Isbell JL Birgenheier LP Rygel MC 《Science (New York, N.Y.)》2007,315(5808):87-91
The late Paleozoic deglaciation is the vegetated Earth's only recorded icehouse-to-greenhouse transition, yet the climate dynamics remain enigmatic. By using the stable isotopic compositions of soil-formed minerals, fossil-plant matter, and shallow-water brachiopods, we estimated atmospheric partial pressure of carbon dioxide (pCO2) and tropical marine surface temperatures during this climate transition. Comparison to southern Gondwanan glacial records documents covariance between inferred shifts in pCO2, temperature, and ice volume consistent with greenhouse gas forcing of climate. Major restructuring of paleotropical flora in western Euramerica occurred in step with climate and pCO2 shifts, illustrating the biotic impact associated with past CO2-forced turnover to a permanent ice-free world. 相似文献
43.
Lupus, a multigenic autoimmune condition in which a breakdown of tolerance results in the development of autoantibodies, leads to a variety of pathologic outcomes. Despite the heterogeneity of factors influencing disease susceptibility, we demonstrate that the partial restoration of inhibitory Fc receptor (FcgRIIB) levels on B cells in lupus-prone mouse strains is sufficient to restore tolerance and prevent autoimmunity. FcgRIIB regulates a common B cell checkpoint in genetically diverse lupus-prone mouse strains, and modest changes in its expression can result in either tolerance or autoimmunity. Therefore, increasing FcgammaRIIB levels on B cells may be an effective way to treat autoimmune diseases. 相似文献
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Although it is well established that mammalian class switch recombination is responsible for altering the class of immunoglobulins, the mechanistic details of the process have remained unclear. Here, we show that stable RNA/DNA hybrids form at class switch sequences in the mouse genome upon cytokine-specific stimulation of class switch in primary splenic B cells. The RNA hybridized to the switch DNA is transcribed in the physiological orientation. Mice that constitutively express an Escherichia coli ribonuclease H transgene show a marked reduction in RNA/DNA hybrid formation, an impaired ability to generate serum immunoglobulin G antibodies, and significant inhibition of class switch recombination in their splenic B cells. These data provide evidence that stable RNA/DNA hybrids exist in the mammalian nuclear genome, can serve as intermediates for physiologic processes, and are mechanistically important for efficient class switching in vivo. 相似文献
47.
Kilimanjaro ice core records: evidence of holocene climate change in tropical Africa 总被引:1,自引:0,他引:1
Thompson LG Mosley-Thompson E Davis ME Henderson KA Brecher HH Zagorodnov VS Mashiotta TA Lin PN Mikhalenko VN Hardy DR Beer J 《Science (New York, N.Y.)》2002,298(5593):589-593
Six ice cores from Kilimanjaro provide an approximately 11.7-thousand-year record of Holocene climate and environmental variability for eastern equatorial Africa, including three periods of abrupt climate change: approximately 8.3, approximately 5.2, and approximately 4 thousand years ago (ka). The latter is coincident with the "First Dark Age," the period of the greatest historically recorded drought in tropical Africa. Variable deposition of F- and Na+ during the African Humid Period suggests rapidly fluctuating lake levels between approximately 11.7 and 4 ka. Over the 20th century, the areal extent of Kilimanjaro's ice fields has decreased approximately 80%, and if current climatological conditions persist, the remaining ice fields are likely to disappear between 2015 and 2020. 相似文献
48.
Stefano Casalegno Giuseppe Amatulli Annemarie Bastrup-Birk Tracy Houston Durrant Anssi Pekkarinen 《European Journal of Forest Research》2011,130(6):971-981
Proactive forest conservation planning requires spatially accurate information about the potential distribution of tree species.
The most cost-efficient way to obtain this information is habitat suitability modelling i.e. predicting the potential distribution
of biota as a function of environmental factors. Here, we used the bootstrap-aggregating machine-learning ensemble classifier
Random Forest (RF) to derive a 1-km resolution European forest formation suitability map. The statistical model use as inputs
more than 6,000 field data forest inventory plots and a large set of environmental variables. The field data plots were classified
into different forest formations using the forest category classification scheme of the European Environmental Agency. The
ten most dominant forest categories excluding plantations were chosen for the analysis. Model results have an overall accuracy
of 76%. Between categories scores were unbalanced and Mesophitic deciduous forests were found to be the least correctly classified
forest category. The model’s variable ranking scores are used to discuss relationship between forest category/environmental
factors and to gain insight into the model’s limits and strengths for map applicability. The European forest suitability map
is now available for further applications in forest conservation and climate change issues. 相似文献
49.
The feasibility of autologous intrarenal mesenchymal stem cell (MSC) therapy in cats with chronic kidney disease (CKD) was investigated. Six cats (two healthy, four with CKD) received a single unilateral intrarenal injection of autologous bone marrow-derived or adipose tissue-derived MSC (bmMSC or aMSC) via ultrasound guidance. Minimum database and glomerular filtration rate (GFR) via nuclear scintigraphy were determined pre-injection, at 7 days and at 30 days post-injection. Intrarenal injection did not induce immediate or long-term adverse effects. Two cats with CKD that received aMSC experienced modest improvement in GFR and a mild decrease in serum creatinine concentration. Despite the possible benefits of intrarenal MSC injections for CKD cats, the number of sedations and interventions required to implement this approach would likely preclude widespread clinical application. We concluded that MSC could be transferred safely by ultrasound-guided intrarenal injection in cats, but that alternative sources and routes of MSC therapy should be investigated. 相似文献
50.
BACKGROUND: In pest management research, harmonic radar systems have been largely used to study insect movement across open or vegetation‐poor areas because the microwave signal is attenuated by the high water content of vegetation. This study evaluated whether the efficacy of this technology is sufficient to track insects in vegetative landscapes. RESULTS: Field efficacy data were collected using portable harmonic microwave radar and electronic dipole tags mounted on adults of three economically important pests: Leptinotarsa decemlineata (Say), Diabrotica virginifera virginifera (LeComte) and Conotrachelus nenuphar Herbst. Detection and recovery of tagged Colorado potato beetles, plum curculios and western corn rootworms was high within and among potato plants, moderate within apple trees and high within, but not between, corn plants respectively. The efficacy of the radar depends on the ability of the operator to move around the host, scanning for a signal ‘sightline’ with the tagged insect among plant structures. CONCLUSION: The detection rate of tagged insects by harmonic radar systems is high enough to track the walking path of pests through low row crops such as potato, tall row crops such as corn or tall but well‐separated trees of orchard‐type crops by adapting the scanning procedure to the vegetative architecture. Copyright © 2010 Crown in the right of Canada. Published by JohnWiley & Sons, Ltd 相似文献