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。     

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。     

Discovery of abundant hydrothermal venting on the ultraslow-spreading Gakkel ridge in the Arctic Ocean

Submarine hydrothermal venting along mid-ocean ridges is an important contributor to ridge thermal structure, and the global distribution of such vents has implications for heat and mass fluxes from the Earth's crust and mantle and for the biogeography of vent-endemic organisms. Previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow-spreading ridges (ridges with full spreading rates <2 cm x yr(-1)-which make up 25 per cent of the global ridge length), and that such vent systems would be hosted in ultramafic in addition to volcanic rocks. Here we present evidence for active hydrothermal venting on the Gakkel ridge, which is the slowest spreading (0.6-1.3 cm x yr(-1)) and least explored mid-ocean ridge. On the basis of water column profiles of light scattering, temperature and manganese concentration along 1,100 km of the rift valley, we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites. Our discovery of such abundant venting, and its apparent localization near volcanic centres, requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow-spreading ridges.     

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。     

Central role of detachment faults in accretion of slow-spreading oceanic lithosphere

The formation of oceanic detachment faults is well established from inactive, corrugated fault planes exposed on sea floor formed along ridges spreading at less than 80 km Myr(-1) (refs 1-4). These faults can accommodate extension for up to 1-3 Myr (ref. 5), and are associated with one of the two contrasting modes of accretion operating along the northern Mid-Atlantic Ridge. The first mode is asymmetrical accretion involving an active detachment fault along one ridge flank. The second mode is the well-known symmetrical accretion, dominated by magmatic processes with subsidiary high-angle faulting and the formation of abyssal hills on both flanks. Here we present an examination of approximately 2,500 km of the Mid-Atlantic Ridge between 12.5 and 35 degrees N, which reveals asymmetrical accretion along almost half of the ridge. Hydrothermal activity identified so far in the study region is closely associated with asymmetrical accretion, which also shows high levels of near-continuous hydroacoustically and teleseismically recorded seismicity. Increased seismicity is probably generated along detachment faults that accommodate a sizeable proportion of the total plate separation. In contrast, symmetrical segments have lower levels of seismicity, which occurs primarily at segment ends. Basalts erupted along asymmetrical segments have compositions that are consistent with crystallization at higher pressures than basalts from symmetrical segments, and with lower extents of partial melting of the mantle. Both seismic evidence and geochemical evidence indicate that the axial lithosphere is thicker and colder at asymmetrical sections of the ridge, either because associated hydrothermal circulation efficiently penetrates to greater depths or because the rising mantle is cooler. We suggest that much of the variability in sea-floor morphology, seismicity and basalt chemistry found along slow-spreading ridges can be thus attributed to the frequent involvement of detachment faults in oceanic lithospheric accretion.     

The importance of water to oceanic mantle melting regimes

The formation of basaltic crust at mid-ocean ridges and ocean islands provides a window into the compositional and thermal state of the Earth's upper mantle. But the interpretation of geochemical and crustal-thickness data in terms of magma source parameters depends on our understanding of the melting, melt-extraction and differentiation processes that intervene between the magma source and the crust. Much of the quantitative theory developed to model these processes has neglected the role of water in the mantle and in magma, despite the observed presence of water in ocean-floor basalts. Here we extend two quantitative models of ridge melting, mixing and fractionation to show that the addition of water can cause an increase in total melt production and crustal thickness while causing a decrease in mean extent of melting. This may help to resolve several enigmatic observations in the major- and trace-element chemistry of both normal and hotspot-affected ridge basalts.     

Vapour undersaturation in primitive mid-ocean-ridge basalt and the volatile content of Earth's upper mantle

The analysis of volatiles in magmatic systems can be used to constrain the volatile content of the Earth's mantle and the influence that magmatic degassing has on the chemistry of the oceans and the atmosphere. But most volatile elements have very low solubilities in magmas at atmospheric pressure, and therefore virtually all erupted lavas are degassed and do not retain their primary volatile signatures. Here we report the undersaturated pre-eruptive volatile content for a suite of mid-ocean-ridge basalts from the Siqueiros intra-transform spreading centre. The undersaturation leads to correlations between volatiles and refractory trace elements that provide new constraints on volatile abundances and their behaviour in the upper mantle. Our data generate improved limits on the abundances of carbon dioxide, water, fluorine, sulphur and chlorine in the source of normal mid-ocean-ridge basalt. The incompatible behaviour of carbon dioxide, together with the CO(2)/Nb and CO(2)/Cl ratios, permit estimates of primitive carbon dioxide and chlorine to be made for degassed and chlorine-contaminated mid-ocean-ridge basalt magmas, and hence constrain degassing and contamination histories of mid-ocean ridges.     

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。