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研究了一种带治疗的病媒传播疾病的流行模型.得到了模型的基本再生数R_0,模型的平衡点和阈值由R_0确定.利用Bendixson-Dulac定理,证明了当R_01时,该模型的唯一正平衡点是全局稳定的.该结果可以帮助探索控制媒介传染病传播的方法.最后对模型进行了数值模拟,验证了该结论. 相似文献
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Lobov IB Rao S Carroll TJ Vallance JE Ito M Ondr JK Kurup S Glass DA Patel MS Shu W Morrisey EE McMahon AP Karsenty G Lang RA 《Nature》2005,437(7057):417-421
Macrophages have a critical role in inflammatory and immune responses through their ability to recognize and engulf apoptotic cells. Here we show that macrophages initiate a cell-death programme in target cells by activating the canonical WNT pathway. We show in mice that macrophage WNT7b is a short-range paracrine signal required for WNT-pathway responses and programmed cell death in the vascular endothelial cells of the temporary hyaloid vessels of the developing eye. These findings indicate that macrophages can use WNT ligands to influence cell-fate decisions--including cell death--in adjacent cells, and raise the possibility that they do so in many different cellular contexts. 相似文献
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Zusammenfassung Aus dem Samen vonAlbizzia procera Benth wurden ausser Machaerinsäure 4 triterpenoide Sapogenine isoliert (Verbindung A und B, Proceragenin A und B). Es wurde bewiesen, dass die Verbindung A das 28 21-Lacton der Machaerinsäure mit einer Konformationsänderung am Ring D oder E ist, während die Verbindung B als Äthylmachaerinat identifiziert wurde. Bei Proceragenin A und B handelt es sich um Dihydroylactone.
A part of the work was carried out at the Department of Chemistry, Bose Institute, Calcutta-9, India, and was supported in part by the Ministry of Education, Government of India. — The authors desire to express their sincere thanks to Dr.A. K. Barua, Reader in Chemistry, Bose Institute, Calcutta and to the Rev. Dr.H. Santapau, Director, Botanical Survey of India, Calcutta for their keen interest and encouragement. 相似文献
A part of the work was carried out at the Department of Chemistry, Bose Institute, Calcutta-9, India, and was supported in part by the Ministry of Education, Government of India. — The authors desire to express their sincere thanks to Dr.A. K. Barua, Reader in Chemistry, Bose Institute, Calcutta and to the Rev. Dr.H. Santapau, Director, Botanical Survey of India, Calcutta for their keen interest and encouragement. 相似文献
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Stefater JA Lewkowich I Rao S Mariggi G Carpenter AC Burr AR Fan J Ajima R Molkentin JD Williams BO Wills-Karp M Pollard JW Yamaguchi T Ferrara N Gerhardt H Lang RA 《Nature》2011,474(7352):511-515
Myeloid cells are a feature of most tissues. Here we show that during development, retinal myeloid cells (RMCs) produce Wnt ligands to regulate blood vessel branching. In the mouse retina, where angiogenesis occurs postnatally, somatic deletion in RMCs of the Wnt ligand transporter Wntless results in increased angiogenesis in the deeper layers. We also show that mutation of Wnt5a and Wnt11 results in increased angiogenesis and that these ligands elicit RMC responses via a non-canonical Wnt pathway. Using cultured myeloid-like cells and RMC somatic deletion of Flt1, we show that an effector of Wnt-dependent suppression of angiogenesis by RMCs is Flt1, a naturally occurring inhibitor of vascular endothelial growth factor (VEGF). These findings indicate that resident myeloid cells can use a non-canonical, Wnt-Flt1 pathway to suppress angiogenic branching. 相似文献
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Several nonmonotonic logic systems together with their algebraic semantics are discussed. NMalgebra is defined. An elegant construction of an NMalgebra starting from a Boolean algebra is described which gives rise to a few interesting algebraic issues. 相似文献
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