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951.
Angiogenesis does not only depend on endothelial cell invasion and proliferation: it also requires pericyte coverage of vascular sprouts for vessel stabilization. These processes are coordinated by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) through their cognate receptors on endothelial cells and vascular smooth muscle cells (VSMCs), respectively. PDGF induces neovascularization by priming VSMCs/pericytes to release pro-angiogenic mediators. Although VEGF directly stimulates endothelial cell proliferation and migration, its role in pericyte biology is less clear. Here we define a role for VEGF as an inhibitor of neovascularization on the basis of its capacity to disrupt VSMC function. Specifically, under conditions of PDGF-mediated angiogenesis, VEGF ablates pericyte coverage of nascent vascular sprouts, leading to vessel destabilization. At the molecular level, VEGF-mediated activation of VEGF-R2 suppresses PDGF-Rbeta signalling in VSMCs through the assembly of a previously undescribed receptor complex consisting of PDGF-Rbeta and VEGF-R2. Inhibition of VEGF-R2 not only prevents assembly of this receptor complex but also restores angiogenesis in tissues exposed to both VEGF and PDGF. Finally, genetic deletion of tumour cell VEGF disrupts PDGF-Rbeta/VEGF-R2 complex formation and increases tumour vessel maturation. These findings underscore the importance of VSMCs/pericytes in neovascularization and reveal a dichotomous role for VEGF and VEGF-R2 signalling as both a promoter of endothelial cell function and a negative regulator of VSMCs and vessel maturation.  相似文献   
952.
The increasing ability to control light-matter interactions at the nanometre scale has improved the performance of semiconductor lasers in the past decade. The ultimate optimization is realized in semiconductor microcavities, in which strong coupling between quantum-well excitons and cavity photons gives rise to hybrid half-light/half-matter polariton quasiparticles. The unique properties of polaritons-such as stimulated scattering, parametric amplification, lasing, condensation and superfluidity-are believed to provide the basis for a new generation of polariton emitters and semiconductor lasers. Until now, polariton lasing and nonlinearities have only been demonstrated in optical experiments, which have shown the potential to reduce lasing thresholds by two orders of magnitude compared to conventional semiconductor lasers. Here we report an experimental realization of an electrically pumped semiconductor polariton light-emitting device, which emits directly from polariton states at a temperature of 235 K. Polariton electroluminescence data reveal characteristic anticrossing between exciton and cavity modes, a clear signature of the strong coupling regime. These findings represent a substantial step towards the realization of ultra-efficient polaritonic devices with unprecedented characteristics.  相似文献   
953.
954.
Isolation of cDNA clones encoding T cell-specific membrane-associated proteins   总被引:32,自引:0,他引:32  
S M Hedrick  D I Cohen  E A Nielsen  M M Davis 《Nature》1984,308(5955):149-153
Of 10 distinct cloned DNA copies of mRNAs expressed in T lymphocytes but not in B lymphocytes and associated with membrane-bound polysomes, one hybridizes to a region of the genome that has rearranged in a T-cell lymphoma and several T-cell hybridomas. These characteristics suggest that it encodes one chain of the elusive antigen receptor on the surface of T lymphocytes.  相似文献   
955.
无机膜应用于废润滑油再生   总被引:1,自引:0,他引:1  
废润滑油污染对环境的潜在危害正日益显现,传统的废润滑油再生方法产生大量的酸性淤泥,造成二次污染,故提出膜分离应用于废润滑油再生的新思路,根据废油的特点来选取合适的膜来处理废润滑油,并利用降低油液黏度和压力膜过程来提高膜的渗透通量,使膜的渗透通量明显增加.  相似文献   
956.
“经济数学”课程教学模式改革实践与分析评估 3   总被引:1,自引:1,他引:0  
以促进学生的全面发展和潜能开发为目标的"经济数学"课程教学模式改革,在"三个一工程"实践中,分别实施了分层教学、学生任选教师教学、分层+任选教师的教学模式;通过对不同教学模式的实践及效果评价,分析总结了不同教学模式在人才培养中的作用与意义,提出了提高教学质量的教学模式及其改进措施.  相似文献   
957.
基于计算机三维建模的“工程制图”课程测绘实践研究 3   总被引:3,自引:1,他引:2  
分析了计算机三维建模运用于制图测绘环节的必要性,以锻炼学生的实践能力、设计思维及团队精神为目的,提出了运用项目教学法引领测绘训练的全过程,并将计算机三维建模作为测绘训练的主线;实践表明,该教学方法的改革不仅使得课程设计质量较好,学生对机械设计专业的认识也有了较大的提高.  相似文献   
958.
This note reports the first discovery of Middle-Late Ordovician acritarchs from the Buqingshan ophiolite complex of the southern ophiolite zone of East Kunlun. The acritarch assemblage is dominated with acanthomorphids (approx. 32%) and sphaeromorphds (approx. 63%) and contains more characteristic forms, such as Lophosphaeridium edenense, L. varum, Nothooidium sp.,? Buedingiisphaaeridium sp., Visbysphaera sp., Strophomorpha sp., etc. In addition, some tube-like fragments and tetrads, which are recognized as affinity to terrestrial plants and usual occurrence in Late Ordovician-Early Silurian strata, are preserved together with acritarchs. All the known fossil evidence indicates that the strata should be Middle-Late Ordovician in age. It not only provides paleontological proof for the existence of Ordovician ophiolite, but also challenges the usual ideas on strata composition of the studied area and the southern ophiolite zone of East Kunlun, and the models on tectonic framework and evolution of this area and the northern part of the Qinghai-Tibetan Plateau.  相似文献   
959.
P-and S-wave velocities in eclogites and granulites from the Dabie ultrahigh pressures (UHP) meta morphic belt, China, were measured at room temperature under the hydrostatic pressures up to 1.0 GPa. The ultrahigh pressure eclogites had the highest densities (3.3 ~ 3.6 g.cm-3) , high velocities and the lowest anisotropy (1.4%c ~ 2.6 % ) . The lowest densities (2.8 ~ 3.1 g. cm-3 ) and the highest Poisson' s ratios (0.28 ~ 0.29) were found in gran ulites, whereas the strongest anisotropies (6. 1 % ~8.4% ) were found in the high-pressure (HP) eclogites. Compari son of the velocities in rocks with that observed in the deep seismic sounding profile crossing Dabieshan suggests that e clogites might exist in the lower crust of Dabieshan, but the quantity might be small. The upper mantle has very similar velocities as the UHP eclogites and serpentinizated/water-bearing dunite. The formation of eclogite represents the crust mantle recycling processes. Crustal material is delaminated and sinks into the mantle by way of eclogite, whereas only a small part of the eclogite could return to the crust.  相似文献   
960.
软件结构级上的需求变化处理   总被引:2,自引:0,他引:2  
为处理需求变化,提出一种基于软件结构引入技术的变化处理机制(Variant Handing Based on Software Architecture Introduction,VHBSAI)和它的4个具体的与软件开发相关的实施步骤(需求变化的分析和识别,变化对象的转化,软件结构的引入,软件结构的调整),以达到对其他变化处理技术进行指导,以及以模块上的操作手段,有效地进行软件系统维护,VHBSAI为软件系统生命周期、开发效益等问题提供了新的解决方法,最后以成功的实例验证说明了VHBSAI的有效性。  相似文献   
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