BP网络应用于黄河水质的预测研究

利用黄河兰州段水质指标浓度时间序列作为学习样本，选取了DO、COD、氨氮、重金属离子等l0项指标作为输出参数，运用人工神经网络BP模型中的Levenberg—Marguardt优化算法对学习样本优化建模，将优化好的网络的预测结果与实测结果进行了比较，表明BP网络可以很好地用于黄河水质指标值及水质类别的预测。     

A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse

In horses, graying with age is an autosomal dominant trait associated with a high incidence of melanoma and vitiligo-like depigmentation. Here we show that the Gray phenotype is caused by a 4.6-kb duplication in intron 6 of STX17 (syntaxin-17) that constitutes a cis-acting regulatory mutation. Both STX17 and the neighboring NR4A3 gene are overexpressed in melanomas from Gray horses. Gray horses carrying a loss-of-function mutation in ASIP (agouti signaling protein) had a higher incidence of melanoma, implying that increased melanocortin-1 receptor signaling promotes melanoma development in Gray horses. The Gray horse provides a notable example of how humans have cherry-picked mutations with favorable phenotypic effects in domestic animals.     

Identification of angiogenic activity and the cloning and expression of platelet-derived endothelial cell growth factor

Cloning and sequencing of the complementary DNA for platelet-derived endothelial cell growth factor indicates that it is a novel factor distinct from previously characterized proteins. The factor, a protein with a relative molecular mass of about 45,000, stimulates endothelial cell growth and chemotaxis in vitro and angiogenesis in vivo.     

Possible positive autocrine feedback in the prereplicative phase of human fibroblasts

The growth of normal diploid fibroblasts is generally thought to be tightly controlled by exogenous growth factors such as platelet-derived growth factor (PDGF) and epidermal growth factor (EGF). Subversion of a growth factor pathway at a regulatory point is considered to be a key event in neoplastic transformation and tumorigenesis. Thus, simian sarcoma virus has acquired the gene encoding the B-chain of PDGF and there is direct experimental proof that SSV-transformation is mediated by a PDGF-like growth factor. There is accumulating evidence that PDGF-like molecules are also synthesized and released by certain normal cells, suggesting an important role of cellularly produced PDGF in development and tissue regeneration. We now present evidence that a transient expression of the gene encoding the PDGF A-chain, and the synthesis and release of functional A-chain homodimers, is an early event in the prereplicative phase of normal human foreskin fibroblasts exposed to PDGF or EGF. Since these cells are PDGF-responsive, the results imply the existence of a positive autocrine signal that may serve as an amplifier of the mitogenic response under certain conditions.     

Gemini表面活性剂在气/液界面上的微区形貌随表面压的变化

测定了Gemini表面活性剂在pH值为10．86,NaBr浓度为1．0mol／L的溶液气／液界面上的表面压一分子面积的等温线。用自制的Brewster角显微镜(BAM)观察了由Gemini表面活性剂在界面上所形成单分子膜的微区形貌随表面压的变化。结果表明：当pH值为10．86时,Gemini表面活性剂在1．0mol／L NaBr溶液的气／液界面上生成了凝聚态的单分子膜;当表面压较低时,观察到在界面上形成了同心圆结构;随着表面压的增加,这些同心圆可发生聚并而形成多中心结构。     

石羊河流域空气传播孢粉的初步研究

为了确定风长距离搬运的孢粉对干旱区尾闾型湖泊沉积物孢粉谱的贡献率，对干旱区典型的小流域--石羊河流域空气中的孢粉进行了分析．石羊河流域云杉树盛花期时，3个样点8个空气样孢粉分析显示，空气样孢粉组合与取样点植被状况大致相当，孢粉组合的空间变化基本上受现代植被分布状况控制，影响空气样孢粉谱和孢粉浓度的因素主要是取样时间和地点．在一定的范围内，干旱区风搬运孢粉的能力很强，可大量地搬运孢粉；但风长距离搬运孢粉的能力有限，超过一定距离，风搬运的孢粉数量还是很小的，风搬运的流域上游森林带的孢粉对中下游地区空气样孢粉谱的贡献率很小．     

磁性隧道结中自旋相关输运的势垒影响

为了研究势垒对铁磁/绝缘层/半导体/绝缘层/铁磁(FM/I/SM/I/FM)双隧道结中自旋相关电子输运特性的影响,提出了在半导体层厚度合适的情况下,非对称势垒对于提高平行结构磁性双隧道结的自旋注入效率SIE(spin injection efficiency)更具优势.数值计算结果表明,当两势垒强度的比率达到合适数值时双结的SIE和隧穿磁电阻TMR(tunneling magnetore resistance)都将达到最大,这给提高从铁磁到半导体的SIE带来新选择.研究还表明,非对称势垒结构磁性隧道结中增大铁磁交换能对提高SIE和TMR都是有益的,而且铁磁交换能的增加对SIE的提高要比对TMR的提高更显著.     

关于加强青年农民工的思想道德建设的思考

青年农民工是我国工业化、城市化进程中的一支重要力量,他们在为我国经济社会发展做出巨大贡献的同时,却遭受着不公正的待遇,不能取得与拥有城镇户口身份的劳动者平等的地位并享受相应权益等等,这些问题在一定程度上造成青年农民工在思想和道德素质上表现出种种不足,给社会和谐稳定带来了隐患。为此,加强青年农民工的思想道德建设,成为和谐社会发展中的一个重要课题。     

斜螺旋面的近似展开

本文用计算法论述了斜螺旋面展开图的近似画法，为斜螺旋面展开图提供亍一个较简便的方法。