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排序方式: 共有821条查询结果,搜索用时 31 毫秒
811.
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
812.
Bertram TH Perring AE Wooldridge PJ Crounse JD Kwan AJ Wennberg PO Scheuer E Dibb J Avery M Sachse G Vay SA Crawford JH McNaughton CS Clarke A Pickering KE Fuelberg H Huey G Blake DR Singh HB Hall SR Shetter RE Fried A Heikes BG Cohen RC 《Science (New York, N.Y.)》2007,315(5813):816-820
We present a statistical representation of the aggregate effects of deep convection on the chemistry and dynamics of the upper troposphere (UT) based on direct aircraft observations of the chemical composition of the UT over the eastern United States and Canada during summer. These measurements provide unique observational constraints on the chemistry occurring downwind of convection and the rate at which air in the UT is recycled. These results provide quantitative measures that can be used to evaluate global climate and chemistry models. 相似文献
813.
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
814.
Concepta McManus Giane Regina Paludo Helder Louvandini Rosilene Gugel Luiz Cláudio Bastos Sasaki Samuel Rezende Paiva 《Tropical animal health and production》2009,41(1):95-101
Thirty Santa Ines adult, non-lactating, non-pregnant ewes, ten with a brown coat, ten black coated and ten white coated, as well as ten Bergamasca and ten of mixed breed were used to evaluate the effect of climate on physiological and blood parameters in sheep. Two sample collections were taken (6 am and 2 pm) on six days. Sweating rate (SR), heart (HR) and breathing rates (BR), complete hemogram, rectal (RT) and skin temperatures (ST) were measured. Variance analyses were carried out using SAS®. In general, there were significant differences between animals due to skin type, time and day of collection. White coated animals showed lower HR, BR and RT, with afternoon parameters higher than morning. Correlations between HR, BR, RT, SR and ST were medium and positive. Correlations between physiological and blood traits were in general negative and medium. Packed Cell Volume (PCV), total plasma proteins, red blood cell count and hemoglobin concentration had high positive correlations between each other. The first two autovectors explained 49% of variation between traits. White coated Santa Ines animals were shown to be better adapted to climatic conditions in Central Brazil and wool sheep more affected by heat. 相似文献
815.
Juteau-Vigier A Atlan S Deleris I Guichard E Souchon I Trelea IC 《Journal of agricultural and food chemistry》2007,55(9):3577-3584
Aroma compound properties in food matrices, such as volatility and diffusivity, have to be determined to understand the effect of composition and structure on aroma release and perception. This work illustrates the use of mass transfer modeling to identify diffusion and partition properties of ethyl hexanoate in water and in carrageenan matrices with various degrees of structure. The comparison of results obtained with a diffusive model to those obtained with a convective model highlights the importance of considering the appropriate transfer mechanism. Modeling of the preliminary experimental steps ensures correct estimation of the conditions for the main aroma release step. The obtained values of partition and diffusion coefficients are in agreement with those found in the literature (either experimentally determined or predicted by theoretical equations) and demonstrate that the structure level of carrageenan matrices has little influence on diffusion properties of ethyl hexanoate (less than 20%). 相似文献
816.
Colin G. Scanes Douglas Lazarus Samuel Bowen Frances C. Buonomo Rex L. Gilbreath 《Domestic animal endocrinology》1987,4(4):253-257
Plasma concentrations of growth hormone (GH), somatomedin (SmC), thyroxine (T4) and triiodothyronine (T3) were determined from birth to post weaning in pigs (Yorkshires). Plasma samples were obtained from the smallest, median and largest piglet from 11 litters. No differences in the circulating concentrations of any of the hormones were observed between piglets of different sizes. However, there were changes in circulating concentrations of hormones during postnatal development. Plasma concentrations of GH decreased between 2 and 8 to 10 days of age. A progressive increase in the circulating concentrations of SmC was observed with concentrations rising (3.83-fold between 2 days and 40 days of age). Plasma concentrations of T4 and T3 were maximal at 23 and 16 days of age, respectively. 相似文献
817.
Samuel Cruz-Esteban Irais Brito-Bonifacio David Estrada-Valencia Edith Garay-Serrano 《Journal of Pesticide Science》2022,47(2):93
Orius insidiosus, known as the pirate bug, is widely distributed throughout the Americas. It is employed for the biological control of Frankliniella occidentalis in organic berry crops in Mexico. In conventional crops, spinosad is the main control method for this pest. The LD50 of spinosad on O. insidiosus was determined. In addition, we monitored the population density of F. occidentalis in blackberry crops under two types of management (biochemical+mass trapping, and biological control). The LD50 was 225.65 ppm 3.8 times greater than the 60 ppm dose commonly used in blackberry crops. Both types of control are efficient; however, spinosad is less effective and should be combined with other environmentally friendly strategies. The possibility of combining chromatic traps+spinosad application and chromatic traps+strategic release of O. insidiosus to effectively control thrips without compromising fruit quality is discussed. 相似文献
818.
Jenni Bridges Rebecca Windsor Samuel D. Stewart Lori FuerherSenecal Chand Khanna 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2022,36(4):1365
BackgroundIntervertebral disc‐associated epidural hemorrhage (EH) in dogs is a poorly understood neurological condition.ObjectiveTo compare the clinical presentation, magnetic resonance imaging (MRI) changes, and clinical outcome of dogs with acute thoracolumbar intervertebral disc herniation (TL‐IVDH) with and without EH.AnimalsOne hundred sixty client‐owned dogs that underwent MRI and hemilaminectomy for acute TL‐IVDH at a private practice in Colorado, including 63 dogs with EH and 97 dogs without EH.MethodsRetrospective review of medical record data from 160 dogs presenting sequentially to a single practice with acute TL‐IVDH that underwent MRI and hemilaminectomy surgery.ResultsSixty‐three of 160 (39%) dogs had confirmed EH. French Bulldogs were significantly overrepresented (23/63; odds ratio [OR]: 4.1; 95% confidence interval [CI]: 1.8‐9.0; P < .001) of the EH cases. Dogs with EH were more likely to present with clinical signs less than 48 hours than were dogs without EH (24‐48 vs 48‐72 hours; OR: 2.4; 95% CI: 1.2‐4.6; P = .02) and were more likely to be nonambulatory on presentation (OR: 2.1; 95% CI: 1.0‐4.1; P = .04). Dogs with EH were more likely to have <50% cross‐sectional spinal cord compression than dogs without EH (OR: 2.3 vs. 0.4; 95% CI: 1.2‐4.4 and 0.2‐0.9, respectively), longer longitudinal spinal cord compression (3 spaces vs 1 space, P < .001), and greater intrinsic spinal cord change (grade 3/severe vs grade 1/mild; P < .001) based on MRI. The location of the intervertebral disc herniation in French Bulldogs with EH was more likely to be thoracolumbar (OR: 10.8; 95% CI: 2.1‐55.7; P = .03).Conclusions and Clinical ImportanceFrench Bulldogs have a high prevalence of intervertebral disc‐associated EH. Dogs with EH have a shorter clinical course and are more likely to be nonambulatory on initial presentation. 相似文献
819.
Samuel A. Ofori Sunanda K. A. Kodikara Loku P. Jayatissa Sanduni K. Madarasinghe T. W. G. F. Mafaziya Nijamdeen Farid Dahdouh-Guebas 《水产资源保护:海洋与淡水生态系统》2023,33(1):15-28
- Among the several threats to the conservation of mangrove ecosystems in most South Asian countries, shrimp farming is predominant. Since the introduction of shrimp farming in Sri Lanka in the 1980s, mangroves on the island’s north-western coast have been continually cleared to create new shrimp farms, leading to a decline in the social-ecological services provided by the mangrove ecosystems.
- Using aerial (1973) and satellite (1996–2020) images, this study assessed areal changes in mangroves and shrimp farms in the Pambala-Chilaw lagoon complex and Ihala Mahawewa, as well as the ecological footprint of shrimp farming in the study area.
- Mangroves around the Chilaw lagoon had decreased in areal extent by 45% from 1973 to 2020 of which 92% of this change was attributed to shrimp farming. There was, however, a decrease in the areal extent of shrimp farms from 2001 to 2020, and a corresponding increase in mangroves from 2006 to 2020.
- The ecological footprint of shrimp farming was assessed by comparing the expected surface ratios with those recorded for shrimp farms with mangroves and surface water bodies in the study area from 1973 to 2020. The results showed that the current shrimp farming was unsustainable (i.e. high ecological footprint).
- While the results support the current view that there is cause for cautious optimism with mangrove conservation (as evidenced by an increase in mangrove areal extent), it also reveals that semi-intensive shrimp farming in Sri Lanka and probably other similar tropical countries is unsustainable.
- If immediate actions such as effective regulation of shrimp farming activities and mangrove restoration are not taken, the mangrove ecosystem will continue to decline.
820.
Samuel Westrelin Julien Cucherousset Romain Roy Laurence Tissot Frdric Santoul Christine Argillier 《Ecology of Freshwater Fish》2022,31(1):129-142
The diversity of predatory species plays a key role in ecosystem functioning but our understanding of the mechanisms underlying their coexistence is limited, particularly in freshwater ecosystems. Northern pike Esox lucius, European perch Perca fluviatilis and pikeperch Sander lucioperca are three widespread predatory species in European lakes, where they often coexist. As potential competitors, we hypothesised that partitioning habitat is a determinant of species coexistence. This was tested by quantifying the variability of their habitat use in tracking adult individuals in the Bariousses reservoir (France, 86.6 ha, mean depth 7.1 m). Specifically, we investigated their distribution along the littoral–pelagic and depth axes along the daily cycle and across seasons. From littoral to pelagic waters were first found pike, then perch and finally pikeperch. Pike was the closest to the surface while pikeperch was the deepest. This general pattern was, however, variable across seasons with the three species located in the upper layer in summer during reservoir stratification. Individuals were more evenly distributed along the littoral–pelagic axis and closer to the bottom when water was mixing (autumn, winter). In summer, perch used more intensively in the pelagic zone during the daytime. Other species did not show any diel change of habitats. Our results highlighted that species coexistence is associated with habitat partitioning among these three predators, with perch showing a more variable behaviour regarding habitat characteristics. Now more than ever, in the context of global change which modifies habitats, it is of crucial importance to understand the coexistence mechanisms of species that shape ecosystems. 相似文献