“授之以渔”,不忘“授之以鱼”——如何对中下水平的学生进行学习策略训练

初中阶段是学生形成学习策略的重要阶段，要重视学习策略使用能力的培养，而对中下水平的学生来说尤其如此。在课堂教学中，教师应因材施教，帮助他们进行学习策略训练，“授之以渔”，同时，不忘“授之以鱼”。

Groundwater Contamination with NO_3-N in a Wheat-Corn Cropping System in the North China Plain

The North China Plain,where summer corn(Zea mays L.)and winter wheat(Triticum aestivum L.)are the major crops grown,is a major agricultural area in China.Permeable soils make the region susceptible to groundwater pollution by NO_3-N,which is applied to fields in large amounts of more than 400 kg NO_3-N ha^(-1)as fertilizer.A field experiment was established in 2002 to examine the relationship among N fertilization rate,soil NO_3-N,and NO_3-N groundwater contamination.Two adjacent fields were fertilized with local farmers' N fertilization rate(LN)and double the normal application rate(HN),respectively,and managed under otherwise identical conditions.The fields were under a traditional summer corn/winter wheat rotation.Over a 22-month period,we monitored NO_3-N concentrations in both bulk soil and soil pore water in 20-40 cm increments up to 180 cm depth.We also monitored NO_3-N concentrations in groundwater and the depth of the groundwater table.No significant differences in soil NO_3-N were observed between the LN and HN treatment.We identified NO_3-N plumes moving downward through the soil profile.The HN treatment resulted in significantly higher groundwater NO_3-N,relative to the LN treatment,with groundwater NO_3-N consistently exceeding the maximum safe level of 10 mg L^(-1),but groundwater NO_3-N above the maximum safe level was also observed in the LN treatment after heavy rain.Heavy rain in June,July,and August 2003 caused increased NO_3-N leaching through the soil and elevated NO_3-N concentrations in the groundwater.Concurrent rise of the groundwater table into NO_3-N- rich soil layers also contributed to the increased NO_3-N concentrations in the groundwater.Our results indicate that under conditions of average rainfall,soil NO_3-N was accumulated in the soil profile.The subsequent significantly higher- than-average rainfalls continuously flushed the soil NO_3-N into deeper layers and raised the groundwater table,which caused continuous groundwater contamination with NO_3-N.The results suggest that under common farming practices in the North China Plain,groundwater contamination with NO_3-N was likely,especially during heavy rainfalls,and the degree of groundwater contamination appeared to be proportional to the N application rates.Decreasing fertilization rates, splitting fertilizer inputs,and optimizing irrigation scheduling had potential to reduce groundwater NO_3-N contamination.

Evaluation of nitrate source in groundwater of southern part of North China Plain based on multi-isotope

Nitrate pollution in groundwater is a serious water quality problem that increases the risk of developing various cancers.Groundwater is the most important water resource and supports a population of 5 million in Anyang area of the southern part of the North China Plain. Determining the source of nitrate pollution is the challenge in hydrology area due to the complex processes of migration and transformation. A new method is presented to determine the source of nitrogen pollution by combining the composition characteristics of stable carbon isotope in dissolved organic carbon in groundwater. The source of groundwater nitrate is dominated by agricultural fertilizers, as well as manure and wastewater. Mineralization, nitrification and mixing processes occur in the groundwater recharge area, whereas the confined groundwater area is dominated by denitrification processes.

Liquid film falling behaviour on horizontal circular cylinder

The flow pattern behaviour of falling liquid film over three horizontal cylinders was evaluated.These flows can take three forms:discrete droplets,individual jets,and continuous sheet,and special attention is paid to the effects of the physical properties and geometrical parameters of the first two forms(droplets and jets) because these forms are more important in heat-transfer behaviour and less research has been published for these forms,The flow modes and experimental results were successfully compared with previous experimental literatures,and also the effects of liquid flow rate,tube diameter,and tube spacing on departure site spacing,in both drop and jet modes,were evaluated in the low Galileo number and high viscosity fluid(cooking oil),to help developing criteria for determining falling film modes and their transitions,and to understand the heat transfer characteristics associated with each mode.

做好父母

女儿说她配不上我这样的妈妈Q:我毕业于“985”学校,在一家大型企业做中层,事业小有成就。但女儿从小就不爱学习,成绩一直是中下水平,我们软硬兼施都没什么用。为了陪她过13岁生日,前不久我放弃了去香港学习的机会。没想到女儿来了句:“何苦呢?我这样的孩子配不上你这么好的妈妈!”我愕然、伤心,不知她为何会这么说?

老师,我也想试一下

二年级要举行跳绳比赛,经过两轮班级选拔,最终确定男、女生各10名可以参加比赛。在接下来的一个月里,体育老师将对这20名即将参加比赛的学生进行强化训练。小婧在两轮选拔中的成绩是一分钟130下左右,这个成绩对于二年级的学生来说属于中下水平。为了使参赛选手有足够的动力坚持训练,不断提升自己的跳绳水平,也为了激励其他学生继续努力,我对全班学生说:“虽然20名参赛选手已经确定,但这不是最终名单,其他同学如果能够超过他们,也能入选。”说完,我看到了几个孩子的脸上露出欣喜之情,小婧就是其中一个。

女儿刚上小学二年级,我就由“佛妈”变“狼妈”

上小学二年级的女儿,语文单元测试考了81.5分,在班里属中下水平。我马上坐立不安起来女儿今年8岁,上小学二年级。两周前,她的语文单元测试考了81.5分,在班里属中下水平。从看到成绩和排名的那一刻起,我就坐立不安起来,没想到女儿考得这么差。我看了几遍试卷,又请教了高分同学的家长,发现对小学低年级学生而言,要想取得好成绩,需要有一定的词汇量,并且要多做题。

力戒饶幸,合作共赢

这次考试,小A有了明显进步,尤其是数学成绩大幅提升。有一道题目难度很大,班里很多“高手”都没能拿到满分,小A却拿到了,这有些出乎我的意料。小A性格内向,不善交流,但学习态度很认真,只不过成绩一直处于中下水平。这次他的成绩突然名列前茅,不免让人有所杯疑。但我没有证据,不好妄下结论,况且内向的人自尊心更强,如果处理不当,后果无法想象。