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排序方式: 共有447条查询结果,搜索用时 15 毫秒
441.
Ma'ayan A Jenkins SL Neves S Hasseldine A Grace E Dubin-Thaler B Eungdamrong NJ Weng G Ram PT Rice JJ Kershenbaum A Stolovitzky GA Blitzer RD Iyengar R 《Science (New York, N.Y.)》2005,309(5737):1078-1083
We developed a model of 545 components (nodes) and 1259 interactions representing signaling pathways and cellular machines in the hippocampal CA1 neuron. Using graph theory methods, we analyzed ligand-induced signal flow through the system. Specification of input and output nodes allowed us to identify functional modules. Networking resulted in the emergence of regulatory motifs, such as positive and negative feedback and feedforward loops, that process information. Key regulators of plasticity were highly connected nodes required for the formation of regulatory motifs, indicating the potential importance of such motifs in determining cellular choices between homeostasis and plasticity. 相似文献
442.
Doyle LR Carter JA Fabrycky DC Slawson RW Howell SB Winn JN Orosz JA Prša A Welsh WF Quinn SN Latham D Torres G Buchhave LA Marcy GW Fortney JJ Shporer A Ford EB Lissauer JJ Ragozzine D Rucker M Batalha N Jenkins JM Borucki WJ Koch D Middour CK Hall JR McCauliff S Fanelli MN Quintana EV Holman MJ Caldwell DA Still M Stefanik RP Brown WR Esquerdo GA Tang S Furesz G Geary JC Berlind P Calkins ML Short DR Steffen JH Sasselov D Dunham EW Cochran WD Boss A Haas MR Buzasi D Fischer D 《Science (New York, N.Y.)》2011,333(6049):1602-1606
We report the detection of a planet whose orbit surrounds a pair of low-mass stars. Data from the Kepler spacecraft reveal transits of the planet across both stars, in addition to the mutual eclipses of the stars, giving precise constraints on the absolute dimensions of all three bodies. The planet is comparable to Saturn in mass and size and is on a nearly circular 229-day orbit around its two parent stars. The eclipsing stars are 20 and 69% as massive as the Sun and have an eccentric 41-day orbit. The motions of all three bodies are confined to within 0.5° of a single plane, suggesting that the planet formed within a circumbinary disk. 相似文献
443.
Carter JA Fabrycky DC Ragozzine D Holman MJ Quinn SN Latham DW Buchhave LA Van Cleve J Cochran WD Cote MT Endl M Ford EB Haas MR Jenkins JM Koch DG Li J Lissauer JJ MacQueen PJ Middour CK Orosz JA Rowe JF Steffen JH Welsh WF 《Science (New York, N.Y.)》2011,331(6017):562-565
The Kepler spacecraft has been monitoring the light from 150,000 stars in its primary quest to detect transiting exoplanets. Here, we report on the detection of an eclipsing stellar hierarchical triple, identified in the Kepler photometry. KOI-126 [A, (B, C)], is composed of a low-mass binary [masses M(B) = 0.2413 ± 0.0030 solar mass (M(⊙)), M(C) = 0.2127 ± 0.0026 M(⊙); radii R(B) = 0.2543 ± 0.0014 solar radius (R(⊙)), R(C) = 0.2318 ± 0.0013 R(⊙); orbital period P(1) = 1.76713 ± 0.00019 days] on an eccentric orbit about a third star (mass M(A) = 1.347 ± 0.032 M(⊙); radius R(A) = 2.0254 ± 0.0098 R(⊙); period of orbit around the low-mass binary P(2) = 33.9214 ± 0.0013 days; eccentricity of that orbit e(2) = 0.3043 ± 0.0024). The low-mass pair probe the poorly sampled fully convective stellar domain offering a crucial benchmark for theoretical stellar models. 相似文献
444.
DNA polymerase activities associated with smooth membranes and ribosomes from rat liver and hepatoma cytoplasm 总被引:2,自引:0,他引:2
Deoxyribonucleic acid polymerase activity that prefers denatured DNA primer concentrates with the smooth membranes during sucrose gradient centrifugation of rat liver and hepatoma cytoplasmic extracts. The activity in this fraction is eightfold higher in hepatoma tissue. Deoxyribonucleic acid polymerase activity that prefers native DNA primer concentrates with the free ribosome fraction from both tissues. 相似文献
445.
J.?L.?WillersEmail author J.?N.?Jenkins W.?L.?Ladner P.?D.?Gerard D.?L.?Boykin K.?B.?Hood P.?L.?McKibben S.?A.?Samson M.?M.?Bethel 《Precision Agriculture》2005,6(5):431-452
When insect population density varies within the same cotton field, estimation of abundance is difficult. Multiple population
densities of the same species occur because cotton fields (due to edaphic and environmental effects) are apportioned into
various habitats that are colonized at different rates. These various habitats differ temporally in their spatial distributions,
exhibiting varying patterns of interspersion, shape and size. Therefore, when sampling multiple population densities without
considering the influence of habitat structure, the estimated population mean represents a summary of diverse population distributions
having different means and variances. This single estimate of mean abundance can lead to pest management decisions that are
incorrect because it may over- or under-estimate pest density in different areas of the field. Delineation of habitat classes
is essential in order to make local control decisions. Within large commercial cotton fields, it is too laborious for observers
on the ground to map habitat boundaries, but remote sensing can efficiently create geo-referenced, stratified maps of cotton
field habitats. By employing these maps, a simple random sampling design and larger sample unit sizes, it is possible to estimate
pest abundance in each habitat without large numbers of samples. Estimates of pest abundance by habitat, when supplemented
with ecological precepts and consultant/producer experience, provide the basis for spatial approaches to pest control. Using
small sample sizes, the integrated sampling methodology maps the spatial abundance of a cotton insect pest across several
large cotton fields. 相似文献
446.
Summary Effects of three rates of fertilizer nitrogen, viz. 80, 160 and 240 kg N/ha, on tuber yield and dry-matter percentage in potato
cv. Record were compared in two experiments. Crop nitrogen uptake increased with application rate but total uptake differed
between experiments. Tuber yield was highest following application of 160 or 240 kg N/ha but differences between these two
rates were not significant. Tuber dry-matter percentage was reduced in one experiment with increasing nitrogen rate, but in
the second experiment final dry- matter percentage was highest following application of 240 kg N/ha. In all treatments, positive
linear relationships were found between dry matter percentage and mean fresh weight of tubers >30 mm, but within experiments,
the regression coefficients were generally reduced by increased crop nitrogen uptake. 相似文献
447.
Geraldine V. Mitchell Mamie Young Jenkins Erich Grundel 《Plant foods for human nutrition (Dordrecht, Netherlands)》1989,39(1):53-58
As a part of a cooperative study initiated to assess bothin vitro andin vivo protein quality methods, the protein efficiency ratio (PER) and net protein ratios (NPR) of 15 different protein sources were determined. Male weanling Sprague-Dawley rats were fed a 10% protein diet. Fourteen-day NPR and relative NPR (RNPR) values and 14- and 28-day PER and relative PER (RPER) values were calculated for each protein source. When protein quality values were expressed relative to ANRC casein, the 14- and 28-day PER data ranked the protein sources essentially in the same order. RPER values of nonfat dried skim milk (unheated) and tuna were more than 100% that of casein; nonfat dried skim milk (heated), chickpeas, and breakfast sausage were between 50 and 70% of that of casein; and pinto beans and rice-wheat gluten cereal did not support substantial growth of the rat. The NPR method did not always rank the protein sources in the same order as the PER method. For the poor quality proteins, RNPR values were much higher than the RPER values; however, the RNPR and RPER values agreed closely for high quality protein sources.A preliminary report of this work was given at the Annual Meeting of the Federation of American Societies for Experimental Biology, Washington, D.C., March 29–April 2, 1987. Fed. Proc. 1987; 46: 889. 相似文献