P-选择素/P-选择素糖蛋白配体-1与骨髓祖细胞胸腺归巢

骨髓衍生的祖细胞归巢入胸腺是T细胞发育必需的过程,因为胸腺不包含具有自我更新能力的造血干细胞,它需要从血液中添补祖细胞,此过程依赖多级细胞粘附分子和趋化因子的衔接.细胞粘附分子选择素和它的配体PSGL-1在淋巴样祖细胞归巢入胸腺的过程中发挥重要作用.综述了选择素/配体PSGL-1的生物学特征及其相互作用对骨髓祖细胞胸腺归巢及胸腺-骨髓反馈环的影响和作用机制.     

热带轧机轧辊表面氧化膜疲劳脱落的有限元分析

根据热带轧机工作辊与支撑辊之间的接触应力、带钢与工作辊之间的应力,以及轧制过程中的轧辊热应力解析结果,利用大型有限元分析工具ANSYS分析了热轧带钢轧辊的表面氧化膜疲劳脱落问题·结果表明,随着加载次数的增加,氧化膜在原有微裂纹处沿X方向的疲劳应力增加,这将导致在原有微裂纹处沿Y方向产生疲劳裂纹·在氧化膜与轧辊基体的结合面上,由于剪切应力的增加将发生沿轧辊氧化膜与轧辊基体结合部位X方向疲劳裂纹·由于X方向疲劳裂纹和Y方向疲劳裂纹的不断扩展,使得裂纹相遇而导致了轧辊表面氧化膜的脱落·     

IL-8-induced L-selectin shedding regulates its binding kinetics to PSGL-1

L-selectin plays a crucial role in inflammation cascade by initiating the tethering and rolling of leukocytes on endothelium wall. While many L-selectin molecules are rapidly shed from the cell surface upon activation, the remaining membrane-anchored L-selectin may still play an important role in regulating leukocyte rolling and adhesion with different binding kinetics. Here we developed an in vitro model to activate Jurkat cells via interlukin-8 （IL-8） and quantified the two-dimensional （2D） binding kinetics, using a micropipette aspiration assay, of membrane-anchored L-selectin to P-selectin glycoprotein ligand 1 （PSGL-1） ligand coupled onto human red blood cells （RBCs）. The data indicated that L-selectin shedding reduced the amount of membrane-anchored L-selectin and lowered both its reverse and forward rates. These results suggested that the rolling dynamics of activated leukocytes was determined by two opposite impacts： reducing the surface presentation would enhance the rolling but lowering the kinetic rates would decrease the rolling. This finding provides a new insight into understanding how L-selectin shedding regulates leukocyte rolling and adhesion.     

平辊薄件轧制的刚塑性有限元计算

本文用钢塑性有限元方法,对平辊同步和异步薄件轧制进行了计算,求出力能参数、速度场和应力应变场,并对二者加以比较。之后,又对异步轧制的特征进行了分析。     

摩擦系数对支承辊次表层接触疲劳损伤的影响

以正交剪应力作为滚动接触次表层疲劳损伤评价的临界应力,分析了摩擦系数对滚动接触次表层正交剪应力幅及应力比的影响规律.根据疲劳损伤累积理论及非对称循环应力幅修正公式,建立了支承辊次表层接触疲劳应力与寿命计算模型,用于评价支承辊次表层接触疲劳损伤.实例分析了摩擦系数对支承辊次表层接触疲劳损伤的影响,结果表明:随着应力比及摩擦系数增大,支承辊的次表层接触疲劳损伤增大,因此,降低支承辊接触摩擦系数,可改善支承辊的疲劳损伤.     

Leukocyte accumulation promoting fibrin deposition is mediated in vivo by P-selectin on adherent platelets.

The glycoprotein P-selectin is a cell adhesion molecule of stimulated platelets and endothelial cells, which mediates the interaction of these cells with neutrophils and monocytes. It is a membrane component of cell storage granules, and is a member of the selectin family which includes E-selectin and L-selectin. P-selectin recognizes both lineage-specific carbohydrate ligands on monocytes and neutrophils, including the Lewis x antigen, sialic acid, and a protein component. In inflammation and thrombosis, P-selectin may mediate the interaction of leukocytes with platelets bound in the region of tissue injury and with stimulated endothelium. To evaluate the role of P-selectin in platelet-leukocyte adhesion in vivo, the accumulation of leukocytes within an experimental thrombus was explored in an arteriovenous shunt model in baboons. A Dacron graft implanted within an arteriovenous shunt is thrombogenic, accumulating platelets and fibrin within its lumen. These bound platelets express P-selectin. Here we show that antibody inhibition of leukocyte binding to P-selectin expressed on platelets immobilized on the graft blocks leukocyte accumulation and inhibits the deposition of fibrin within the thrombus. These results indicate that P-selectin is an important adhesion molecule on platelets, mediating platelet-leukocyte binding in vivo, that the presence of leukocytes in thrombi is mediated by P-selectin, and that these leukocytes promote fibrin deposition.     

Direct observation of catch bonds involving cell-adhesion molecules

Bonds between adhesion molecules are often mechanically stressed. A striking example is the tensile force applied to selectin-ligand bonds, which mediate the tethering and rolling of flowing leukocytes on vascular surfaces. It has been suggested that force could either shorten bond lifetimes, because work done by the force could lower the energy barrier between the bound and free states ('slip'), or prolong bond lifetimes by deforming the molecules such that they lock more tightly ('catch'). Whereas slip bonds have been widely observed, catch bonds have not been demonstrated experimentally. Here, using atomic force microscopy and flow-chamber experiments, we show that increasing force first prolonged and then shortened the lifetimes of P-selectin complexes with P-selectin glycoprotein ligand-1, revealing both catch and slip bond behaviour. Transitions between catch and slip bonds might explain why leukocyte rolling on selectins first increases and then decreases as wall shear stress increases. This dual response to force provides a mechanism for regulating cell adhesion under conditions of variable mechanical stress.     

冷轧组合式支承辊过盈配合面应力和微动滑移的分布及影响因素

采用ABAQUS软件建立冷轧组合式支承辊的三维模型,通过模拟带钢轧制过程获得不同工艺参数条件下支承辊辊套和辊芯之间过盈配合面的应力及微动滑移分布,并分析了辊套厚度、配合面摩擦系数、过盈量、轧制力、弯辊力等参数对过盈配合面应力分布及微动滑移量的影响规律。结果表明:过盈配合面上周向应力最大,径向应力次之,且二者均在轧辊压扁区达到最大;离支承辊长度方向对称面越远,过盈配合面上的微动滑移量越大,且压扁区边部的周向滑移量最大,压扁区中部的轴向滑移量最大;支承辊外径不变时,辊套厚度与过盈配合面等效应力成正比,与微动滑移量成反比;摩擦系数对等效应力影响很小,但与微动滑移量成反比;当过盈量增大时,配合面上的接触应力和应变都增大,微动滑移量先增加后趋于稳定;轧制力增大导致过盈配合面微动滑移量和轧辊压扁区等效应力增大,但弯辊力对等效应力及微动滑移的影响均较小。     

厚板轧制头部弯曲的有限元分析

采用二维大变形热-力耦合有限元法分析了厚板轧制头部弯曲的现象,得到了不同的轧制线高度、摩擦状况、上下工作辊直径和上下工作辊转速时对厚板轧后头部弯曲的影响。结果表明,在其他条件相同的情况下,合适的轧制线高度范围是22-33 mm;采用下压法轧制时,合适的下工作辊直径与上工作辊直径差范围是0-20 mm。该结果可为厚板轧制过程参数的设定提供参考。     

热轧窄带钢辊缝预设及头尾厚差预报

在实测的基础上得到了适于窄带热轧生产线的辊缝预报模型。经生产性试验表明，本研究给出的辊缝预设值与现场实测非常接近，将其作为控制窄带精度的手段，可取代目前对人工经验“试调”的依赖，具有重要的实际应用价值；对轧件头尾厚度差的计算不但考虑了奥氏体再结晶软化程度对轧机负荷的影响，还考虑了轧辊弹性压扁与轧制压力的耦合对压力及辊缝的综合影响，从而显著提高了带钢头尾厚差的预报效果。这对控制带钢的通条尺寸、提高产品精度具有重要意义。     

冷轧工作辊辊面剥落与使用条件

通过对冷轧厂轧辊损坏两年的跟踪调查．总结了轧辊损坏的规律，并找出了辊面剥落是导致轧辊服役期未满、早期报废的主要原因。根据现场条件及裂纹的产生和接触应力情况，从使用出发，分析了影响辊面剥落的诸因素，为冷轧厂采取措施提高轧辊寿命提供理论依据。最后总结了使用中防止辊面剥落的措施。冷轧厂３年的实践表明，这些措施是有效的，辊耗从１．００２ｋｇ／ｔ下降到０．６１６ｋｇ／ｔ。     

胶层厚度对胶连接接头承载力的影响机理与控制

为了明晰胶层厚度对胶连接接头承载力的影响机理,采用试验、数值模拟和理论分析相结合的方法研究了胶连接接头承载力与胶层厚度的关系,据此提出了控制技术,并通过试验证明了该技术的有效性。试验发现,随着胶层厚度的增加,初期承载力增加,但是进一步增加胶层厚度,接头破坏模式由剪切破坏变为剥离破坏,承载力明显下降。研究表明,当胶层较薄时,剪应力是接头破坏的控制因素,胶层厚度增加会降低剪应力集中,故承载力提高;而当胶层厚度增加到一定程度时,剥离应力成为接头破坏的控制因素,剥离应力明显增加,故承载力下降。     

用边界元法分析轧制压力和摩擦力

本文给出了一种新的求解轧制力和摩擦力分布的方法,利用测量手段对轧制过程中的轧辊进行测量,然后再利用边界无法对轧辊进行分析,从而求解出轧制过程中轧制力和摩擦力。这种方法避开了为求解轧制力对轧制进行弹塑性分析,也解决了用测力销测量带来的困难,使轧制问题的分析求解得到了简化并提高了求解精度。     

圆钢轧制过程中弯曲低头模型

研究了极限规格的圆钢在轧制过程中的低头现象,防止其在飞剪前堆钢.通过研究小圆钢温度、轧制力和电机功率模型,分析了小圆钢在飞剪处由于直径变小,内应力的降低,容易形成低头,使向前运动的小圆钢头部低于挡板造成堆钢的过程.求解出了挠度变化方程,建立了飞剪处小圆钢低头模型.现场实验中对理论研究计算出的多种极小规格圆钢进行了轧制实验,在有飞剪和无飞剪情况下小圆钢低头实验结果与模型和仿真结果一致.     

轧辊弹性变形对中厚板辊缝设定的影响

根据中厚板轧制过程的受力模型 ,将辊缝变化转化为辊系的弹性变形 ,利用影响函数法 ,计算出轧件宽度、工作辊半径、支承辊半径、工作辊凸度、支承辊凸度及轧制力等因素对辊缝设定的影响·仿真结果表明 :①随着支承辊半径的增大 ,轧辊变形量呈线性减少 ;②随着工作辊半径增大 ,轧辊变形量呈线性增加 ;③随着支承辊凸度的增大 ,轧辊变形量呈线性增加 ;④工作辊凸度与轧辊变形量之间呈线性关系 ,轧件宽度的变化直接影响该线性关系的走向 ;⑤随着轧制力增加 ,轧辊变形量线性增加·只要轧制力相等 ,轧辊变形基本不变     

Zr_（55）Al_（10）Cu_（30）Ni_5块体非晶合金轧制塑性变形三维有限元分析

利用ANSYS/LS-DYNA显式动力学分析有限元法对Zr55Al10Cu30Ni5块体非晶合金的室温轧制塑性变形过程进行模拟计算,分析了非晶合金变形区域内的最大剪切应力分布与压下率的关系。计算得出了稳定轧制阶段不同压下率下非晶合金的应力和应变分布。计算结果表明,轧制变形区的最大剪切应力随压下率的增大而增大,并且在最大剪切应力超过屈服应力的局部区域非晶合金发生了非均匀塑性变形。模拟分析的结果与实验研究结果相符合,从而为进一步研究室温轧制变形诱导非晶合金微观结构变化提供理论依据。     

基于支持向量机的轧制过程灵敏度分析

利用支持向量机(SVM)建立轧制力模型,并由该模型分别对各输入变量进行偏微分,以计算轧制过程出口厚度灵敏度系数,从而解决解析方法难以求解的轧制过程模型“代数环”问题．对轧机第一机架试验仿真,结果表明,基于SVM方法获得的灵敏度具有很高的精度,且由灵敏度确定的控制量可以获得很好的控制效果,同时也表明第一机架辊缝对出口厚度的影响比张力要大,以辊缝控制方式调节出口厚度比张力控制方式具有更高精度．     

Forced extension of P-selectin construct using steered molecular dynamics

P-selectin, a 70-nm-long cellular adhesive molecule, possesses elastic and extensible properties when neutrophils roll over the activated endotheliam of blood vessel in inflammatory reaction. Transient formation and dissociation of P-selectin/ligand bond on applied force of blood flow induces the extension of P-selectin and relevant ligands.Steered molecular dynamics simulations were performed to stretch a single P-selectin construct consisting of a lectin(Lec) domain and an epithelial growth factor (EGF)-Iike domain, where P-selectin construct was forced to extend in water with pulling velocities of 0.005-0.05 nm/ps and with constant forces of 1000--2500 pN respectively. Resulting force-extension profiles exhibited a dual-peak pattern on various velocities, while both plateaus and shoulders appeared in the extension-time profiles on various forces. The force or extension profiles along stretching pathways were correlated to the conformational changes, suggesting that the structural collapses of P-selectin Lec/EGF domains were mainly attributed to the burst of hydrogen bonds within the major β sheet of EGF domain and the disruptions of two hydrophobic cores of Lec domain. This work furthers the understanding of forced dissociation of P-selectin/ligand bond.     

轧制制度对闭孔泡沫铝材料塑性的影响

研究了采用熔体发泡法制备的闭孔泡沫铝材料的轧制过程,分析了不同道次压下量条件下泡沫铝的变形特点与破坏方式,探讨了影响泡沫铝轧制能力的主要因素.结果表明:闭孔泡沫铝的轧制应遵循多道次、小变形的原则.道次压下量为0.1 mm时,Si质量分数为12%的泡沫铝(厚度约11 mm)经10道次变形后可实现1 mm的总变形量.道次压下量过大时泡沫铝的破坏方式为典型的脆性断裂,适宜的压下量则有利于发挥泡沫铝良好的吸能性,但小变形时易出现弯曲而使材料最终发生剪切破坏.提高泡沫铝轧制能力的具体方法为降低基体中的Si含量,提高材料组织性能的均一性,轧制工艺中采用适宜的道次压下量和较低的轧制速度.     

基于非稳态润滑理论的金属塑性加工过程动力学特性研究

基于非稳态流体动力润滑理论和相应的轧机辊缝动力学的基本理论,建立了板带轧制时工作区非稳态润滑基本模型,求解了工作区压应力和摩擦应力分布情况.并对某大型公司轧机进行了仿真分析.通过数值计算,定性地分析了后张应力、非稳态变量角频率、压下率等参数对动态辊缝间压应力和摩擦应力分布的影响.验证了所建模型及仿真的正确性,可以对现场实际中轧机颤振的抑制提供指导.