“线下生”与“线上生”学业状况的比较分析

随着高校招生自主权的不断扩大 ,一部分低于统一录取分数线的考生进入了校园。这部分“线下生”入校后的学业状况如何 ?他们与“线上生”相比较有何差异 ,能否跟上学校的学业要求 ?围绕这些问题 ,我们以电气工程学院 99级新生为对象 ,进行了近一年的跟踪调查。通过调查 ,以期掌握“线下生”的学业状况 ,发现存在的主要问题 ,并有针对性地提出解决办法 ,同时也为学校招生及教学管理部门的决策提供参考依据。

低碳马氏体强化工艺在汽车板簧上的应用

近十多年来低碳马氏体强化工艺虽已在国内有较多应用,但在汽车板簧上应用还是一种尝试。1983年11月以来,我厂利用28MnSiB钢,采用低碳马氏体强化工艺,试制了美国联合发展有限公司（U.D.I）的E3～1750型、09475—01型、466017C91—01型、E6—4000型出口板簧。严品质量均达到美国“S.A.E”标准,疲劳寿命10万次未断,已于1984年6月开始销往美国。1.28MnSi 钢的强化用低碳马氏体强化工艺制作汽车板簧,工艺简单、容易掌握,可在原有的60Si2Mn 钢生产线上生产。它的技术关键在于低碳马氏体的形成及强化,也就是说以淬火来得到低碳马氏体。钢的淬透性、含碳量,奥氏体化温度及淬火介质因素,

日本企业市场竞争新招

长期以来,日本企业依靠产品的过硬质量、卓越的性能和优良的售后服务,形成了极强的国际竞争能力。近年来,日本企业又推出市场竞争的新招,从而,进一步拉大了与追赶者的距离。一、“灵活生产体系”。就是根据市场需求,在同一生产线上生产出批量小、型号或品种多的“

Estimation of the Above-ground Biomass of Tamarix Species along a Transect at the Tarim River's Middle Reaches

[Objective] The purpose was to research the distribution characteristics of Tamarix species above-ground biomass of Tarim River＇s middle reaches and to find out best-fit linear-regression model of Tamarix species in this area.[Method] By dint of the most common sampling method PCQ,five samples in the middle reaches of Tarim River were collected.The best-fit linear-regression model of Tamarix species of this area was set up,based on the fieldwork and the model of Evangelista and obtained the distribution rules of Tamarix species of Tarim River＇s middle reaches.[Result] The result indicated that this model fitted for the estimation of aboveground biomass of the study area.According to the distribution rules of aboveground biomass,it was clear that underground water was the major element which decided the distribution of aboveground biomass.[Conclusion] The study provided theoretical basis for the calculation of biomass of Tamarix.

Response of Marine Microalgae,Heterotrophic Bacteria and Their Relationship to Enhanced UV-B Radiation

Ozone depletion in the stratosphere has enhanced solar UV-B radiation reaching the Earth surface and has brought about significant effects to marine ecosystems. The effects of enhanced UV-B radiation on marine microalgae, heterotrophic bacteria and the interaction between them are discussed. The effects on marine microalgae have been proved to occur at molecular, cellular and population levels. Enhanced UV-B radiation increases microalgal flavonoid content but decreases their chlorophyll content and pho- tosynthesis rate; this radiation induces genetic change and results in DNA damage and change of protein content. There have been fewer studies on the effects of UV-B radiation on marine heterotrophic bacteria. Establishment of a microalgal ecological dynamic model at population and commuity levels under UV-B radiation has gradually become a hotspot. The effects of enhanced UV-B radiation on microalgae commtmities, heterotrophic bacterial populations and interaction between them will become a focus in the near future. This paper will make an overview on the studies concerning the effects of enhanced UV-B radiation on marine microalgae and heterotrophic bacteria and the interaction between them.

Allometric prediction of above-ground biomass of eleven woody tree species in the Sudanian savanna-woodland of West Africa

Allometric models are necessary for estimating biomass in terrestrial ecosystems. Generalized allometric relationship exists for many tropical trees, but species- and region-specific models are often lacking. We developed species-specific allometric models to predict aboveground biomass for 11 native tree species of the Sudanian savanna- woodlands. Diameters at the base and at breast height, with species means ranging respectively from 11 to 28 cm and 9 to 19 cm, and the height of the trees were used as predictor variables. Sampled trees spanned a wide range of sizes including the largest sizes these species can reach. As a response variable, the biomass of the trees was obtained through destructive sampling of 4 754 trees during wood harvesting. We used a stepwise multiple regression analysis with backward elimination procedure to develop models separately predicting, total biomass of the trees, stem biomass, and biomass of branches and twigs. All species- specific regression models relating biomass with measured tree dimen- sions were highly significant （p 〈 0.001）. The biomass of branches and twigs was less predictable compared to stem biomass and total biomass, although their models required fewer predictors and predictor interac- tions. The best-fit equations for total above-ground biomass and stem biomass bad R2 〉 0.70, except for the Acacia species; for branches including twig biomass, R2-values varied from 0.749 for Anogeissus leiocarpa to 0.183 for Acacia macrostachya. The use of these equations in estimating available biomass will avoid destructive sampling, and aid in planning for sustainable use of these species.

Validation of a Critical Nitrogen Curve for Summer Maize in the North China Plain

The concept of critical N concentration(N_c)has been widely used in agronomy as the basis for diagnosis of crop N status,and allows discrimination between field situations of sub-optimal and supra-optimal N supply.A critical N dilution curve of N_c=34.0W^(-0.37),where W is the aboveground biomass(Mg DM ha^(-1))and N_c the critical N concentration in aboveground dry matter(g kg^(-1)DM),was developed for spring maize in Europe.Our objectives were to validate whether this European critical N dilution curve was appropriate for summer maize production in the North China Plain(NCP)and to develop a critical N dilution curve especially for summer maize production in this region.In total 231 data points from 16 experiments were used to test the European critical N dilution curve.These observations showed that the European critical N dilution curve was unsuitable for summer maize in the NCP,especially at the early growth stage.From the data obtained,a critical N dilution curve for summer maize in the NCP was described by the equation of N_c=27.2W^(-0,27),when aboveground biomass was between 0.64 and 11.17 Mg DM ha^(-1).Based on this curve,more than 90%of the data for the N deficiency supply treatments had an N nutrition index(NNI)<1 and 92%of the data for the N excess supply treatments had an NNI>1.

Bottom-up synthesis of ultrathin straight platinum nanowires： Electric field impact

We present a study of the electric field effect on electrochemically grown ultrathin, straight platinum nanowires with minimum diameter of 15 nm and length in the micrometer range, synthesized on a silicon oxide substrate between metal electrodes in H2PtC16 solution. The influence of the concentration of the platinum- containing acid and the frequency of the applied voltage on the diameter of the nanowires is discussed with a corresponding theoretical analysis. We demonstrate for the first time that the electric field profile, provided by the specific geometry of the metal electrodes, dramatically influences the growth and morphology of the nanowires. Finally, we provide guidelines for the controlled fabrication and contacting of straight, ultrathin metal wires, eliminating branching and dendritic growth, which is one of the main shortcomings of the current bottom-up nanotechnology. The proposed concept of self-assembly of thin nanowires, influenced by the electric field, potentially represents a new route for guided nanocontacting via smart design of the electrode geometry. The possible applications reach from nanoelectronics to gas sensors and biosensors.