二阶非线性微分方程的一个振动准则

本文给出了二阶非线性微分方程的一个新的振动准则。所得结果改进了若干熟知的振动准则。     

Regulation in the heart field of zebrafish

In many vertebrates, removal of early embryonic heart precursors can be repaired, leaving the heart and embryo without visible deficit. One possibility is that this 'regulation' involves a cell fate switch whereby cells, perhaps in regions surrounding normal progenitors, are redirected to the heart cell fate. However, the lineage and spatial relationships between cells that are normal heart progenitors and those that can assume that role after injury are not known, nor are their molecular distinctions. We have adapted a laser-activated technique to label single or small patches of cells in the lateral plate mesoderm of the zebrafish and to track their subsequent lineage. We find that the heart precursor cells are clustered in a region adjacent to the prechordal plate, just anterior to the notochord tip. Complete unilateral ablation of all heart precursors with a laser does not disrupt heart development, if performed before the 18-somite stage. By combining extirpation of the heart precursors with cell labeling, we find that cells anterior to the normal cardiogenic compartments constitute the source of regulatory cells that compensate for the loss of the progenitors. One of the earliest embryonic markers of the premyocardial cells is the divergent homeodomain gene, Nkx2.5. Interestingly, normal cardiogenic progenitors derive from only the anterior half of the Nkx2.5-expressing region in the lateral plate mesoderm. The posterior half, adjacent to the notochord, does not include cardiac progenitors and the posterior Nkx2.5-expressing cells do not contribute to the heart, even after ablation of the normal cardiogenic region. The cells that can acquire a cardiac cell fate after injury to the normal progenitors also reside near the prechordal plate, but anterior to the Nkx2.5-expressing domain. Normally they give rise to head mesenchyme. They share with cardiac progenitors early expression of GATA 4. The location of the different elements of the cardiac field, and their response to injury, suggests that the prechordal plate supports and/or the notochord suppresses the cardiac fate.     

Relationship of the Yttrium Compounds with the Alloying Method in ODS Ferritic Stainless Steel

ＲｅｌａｔｉｏｎｓｈｉｐｏｆｔｈｅＹｔｔｒｉｕｍＣｏｍｐｏｕｎｄｓｗｉｔｈｔｈｅ　ＡｌｌｏｙｉｎｇＭｅｔｈｏｄｉｎＯＤＳＦｅｒｒｉｔｉｃＳｔａｉｎｌｅｓｓＳｔｅｅｌＺｈａｎｇＹｏｎｇ（张勇）；ＣｈｅｎＭｉｎｇｂｉａｏ（陈明彪）；ＷｕＣｈｅｎｇＪｉａｎ...     

Slag of the production of aluminum alloys from secondary resources as a raw material for the refractory industry

Results of chemical, x-ray phase, and petrographic investigations of slag are presented. It is established that slag from the production of aluminum alloys from secondary raw materials can be classified as a high-alumina refractory material (85–95% Al₂O₃ + SiO₂, refractoriness 1670–1770°C). The refractory properties of the slag can be retained by magnetic separation. There is a practical possibility of using this slag in the production of refractories. Semidry pressing of a charge based on the slag can give a refractory of grade ShA in accordance with GOST 390-83.Translated from Ogneupory, No. 2, pp. 24 – 26, February, 1996.     

Laboratory Experiments on Electroosmotic Dewatering of Vegetable Sludge and Mine Tailings

Vegetable wastes in the food industry are costly lo handle because of their high moisture content. while mill plant tailings in the mining industry contain large quantities of ultralines which are difficult io dewater.This paper describes the results of small scale electmosmotic dewatering (EOD) and combined field dewatering (CFD) measurements with model vegetable sludges and mine tailings.     

β″－Al_2O_3陶瓷的强化和韧化

研究了稳定ＺｒＯ＿２和部份稳定ＺｒＯ＿２对β″－Ａｌ＿２Ｏ＿３陶瓷的强化和韧化作用，观察了不同种类、不同含量的ＺｒＯ＿２对β″－Ａｌ＿２Ｏ＿３陶瓷的显微结构、力学性能和电导率的影响，探讨了β″－Ａｌ＿２Ｏ＿３的韧化机理。     

Enhanced electron emission from phosphorus-doped diamond-cladsilicon field emitter arrays

Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities     

TiAl基合金表面改性对高温抗氧化性的影响

研究了渗碳处理ＴｉＡｌ基合金试样的高温氧化行为，发现渗碳处理可以在ＴｉＡｌ基合金试样表层形成致密的多层结构的渗碳层，并发生表层Ａｌ、Ｔｉ重新分配。致密的渗碳层具有良好的高温抗氧化性和高温热稳定性，同时，Ｔｉ、Ａｌ重新分配形成的富Ａｌ最外层也能进一步提高合金的抗氧化性。