一种新型MAO改性的高活性铬基气相聚乙烯催化剂

制备了一种新型的CrO3／SiO2／MAO(／EtOAlEt2)乙烯聚合催化剂，在微机控制的自动评价装置上进行了乙烯气相聚合评价试验，研究了催化剂制备中有机铝化合物对催化剂的改性作用．结果表明，MAO作为还原剂可以明显提高催化剂的聚合活性，显著影响乙烯聚合反应动力学，得到的聚乙烯树脂融体流动速率较低．同时采用MAO和EtOAlEt2作为还原剂制备催化剂时，二者具有显著的协同效应，催化剂聚合活性高，临氢效应敏感高，树脂的融体流动速率高．     

新的基于条纹投影轮廓测量的系统标定方法

提出一种新的光栅条纹投影轮廓测量术系统标定模型,新模型不要求投影装置和成像系统的光心连线与参考面平行、成像系统的光轴垂直于参考面及投影装置和成像系统的光轴相交。基于该模型得出了新的相位高度映射关系,其待定系数与成像点的坐标无关。实际测量中只需2个高度不同的标准块便可以求得待定系数。对4个标准块进行高度测量,得到的最大相对误差为0.6%。实验证明:该标定方法简单有效,提高了系统标定的可操作性和测量精度。     

THE DYNAMICS OF AN ANIMAL—VEGETATION SYSTEM: SHEEP FARMING

The paper studies the economy and ecology of sheep farming at the farm level in a Nordic context, with a crucial distinction between the outdoors grazing season and the winter indoors feeding season, and where climate conditions fix the length of the grazing season. Two different categories of animals, ewes (adult females) and lambs, and one plant species are included in our ecological model. The farmer is assumed to maximize present‐value profit where the revenue is made up income from meat and wool production. We find that livestock cycles may represent an optimal management policy. We also show that in a possible steady state with a constant number of animals and constant vegetation quantity, slaughtering either only lambs or only ewes is optimal.     

Synthesis,structure, and luminescence properties of sodium and ytterbium complexes with 2-(benzothiazol-2-yl)selenophenolate ligands

Russian Chemical Bulletin - With the aim of designing new heteroorganic ligands capable of sensitizing the metal-centered photoluminescence (PL) of YbIII through the redox mechanism, a new...