北温带干旱地区土壤-大气界面CO2通量的变化特征

采用箱法对栗钙土、灰钙土、粗骨土和山地灰褐土4种有代表性的干旱土壤表面CO2通量进行观测和研究。结果表明:森林土壤（粗骨土和山地灰褐土）的通量显著大于草原土壤（栗钙土和灰钙土）。干旱区土壤表面CO2通量的平均值为230.05 μmol/(m2·h),变化范围为-147.27～2 319.55 μmol/(m2·h)。不同土壤类型之间存在差异,粗骨土(351.82 μmol/(m2·h))山地灰褐土(347.33 μmol/(m2·h))栗钙土(193.36 μmol/(m2·h))灰钙土(162.37 μmol/(m2·h))。土壤表面CO2通量存在季节变化,趋势呈“S”形。9月份最高(516.79 μmol/(m2·h)),以土壤向大气释放为主;1月份最低(－7.09 μmol/(m2·h)),以大气进入土壤为主;具有春夏秋冬交替规律,与气候变化趋势基本一致,土壤表面CO2通量稍有后滞。全天候土壤表面CO2通量呈“山峰”形变化,04:00最小(154.13 μmol/(m2·h)),12:00最大(349.65 μmol/(m2·h)),具有昼夜交替规律,比气候日变化稍有滞后。影响土壤表面CO2通量的环境因子有地表空气温度、土壤温度（0～10 cm、10～20 cm和20～30 cm）、土壤含水量（0～10 cm、10～20 cm和20～30 cm）;其中,地表空气温度、土壤温度（0～10 cm、10～20 cm和20～30 cm）和土壤含水量（0～10 cm）分别与土壤表面CO2通量呈正相关关系,而10～20 cm和20～30 cm深度的土壤含水量与土壤表面CO2通量呈负相关关系,地表空气相对湿度与土壤表面CO2通量的关系不显著。大气与土壤之间的CO2存在双向转移机制,CO2不仅从土壤向大气转移,而且也从大气向土壤转移,热量在地球表面的差异性分布,导致温带和寒带地区的土壤具有平衡大气CO2浓度的功能,是温带、寒带地区的显著特征。      

湖南5种园林地被植物蒸腾耗水特征初探

该研究旨在掌握湖南5种园林地被植物在缺水季节的耗水特性,为制定科学合理的灌溉制度及配置方式提供依据。采用盆栽控水法,从8—11月,通过模拟实际栽植中植物所处的不同光照状况,测定了马尼拉草、细叶萼距花、麦冬、吉祥草和葱兰在不同光照条件下土壤水分不断降低过程中的蒸腾速率。结果为:①根据植物在控水期间蒸腾速率的变化及生长状况划分了4种土壤水分梯度,即水分充足、轻度胁迫、中度胁迫和重度胁迫,土壤水势分别为-0.20～-0.03 MPa、-0.54～-0.20 MPa、-1.38～-0.54 MPa和＜-1.38 MPa。②不同月份在前3种土壤水分梯度下,全光照时,细叶萼距花的日均蒸腾速率大于马尼拉草;半光照时,蒸腾速率大、入选前2位较多的是细叶萼距花和葱兰,蒸腾速率低、处于最后一位较多的是马尼拉草;全遮荫时,麦冬、吉祥草和葱兰的蒸腾速率相差不大。③控制土壤水分、光照强度所达到的节水效果是不同的,可根据节水效益和实际需要来选择优化的节水方式。      

单作与间作条件下核桃根系分布特征研究

以河北平山县退耕区核桃林为研究对象,通过自制取根器取样,研究间作对核桃根系分布的影响。结果表明:单作条件下核桃根系在垂直方向上呈负指数型分布,根系主要集中在10～60 cm;在水平方向上,89.75%的根长密度集中在0～110 cm。间作条件下核桃根系在垂直方向上,主要集中在20～70 cm;在水平方向上,95.15%的根长密度集中在0～110 cm;间作物黄芩在垂直方向上主要分布于 0～50 cm,水平方向上主要分布于100～150 cm处,其对核桃根系分布具有一定的影响。      

东北枸杞多糖分离纯化及鉴定

研究了东北枸杞多糖的提取、分离纯化及其组分和结构的鉴定,结果表明:枸杞多糖水提的最佳条件为提取温度100℃,pH值11,料液比1:20,浸提2h;通过DEAE-SephadexA-50柱层析得到纯度较高的LBP-4,薄层分析LBP-4主要是由鼠李糖、木糖、葡萄糖、甘露糖和半乳糖醛酸组成.红外光谱和刚果红实验分析LBP-4具有糖类的特征吸收峰,是多种单糖通过α糖苷键及β糖苷键连接组成的杂多糖,不具有三股螺旋结构.     

桐城市农村户用沼气建设综述

通过对桐城市实施户用沼气池建设项目取得成效和存在问题的分析,提出了解决问题的措施与对策。     

半主动悬架山地拖拉机姿态控制系统设计与仿真

为提高山地拖拉机在复杂农田环境中的作业平稳性,基于Matlab/Simulink仿真平台,搭建了半主动悬架拖拉机七自由度时域仿真模型,包括四轮路面激励模型、半主动悬架振动模型、半主动悬架拖拉机车体受力分析模型、车身姿态分析模型以及半主动悬架拖拉机时域仿真模型,以车身垂向位移、车身倾斜角和车身俯仰角作为拖拉机的姿态变化参数进行仿真试验。通过构建增量式比例积分微分（Proportion integration differentiation, PID）控制器和反向传播（Back propagation, BP）神经网络PID控制器仿真模型实现对半主动悬架拖拉机车身姿态的自动控制,并分别对两种控制器的控制性能进行测试与评价。利用车身垂直向加速度和车轮相对动载作为半主动悬架系统性能的评价指标,对两种控制方式下的半主动悬架性能进行了评价。仿真结果表明：基于传统增量式PID控制算法的半主动悬架拖拉机,其车身垂直位移均方根减少42.17%、侧倾角均方根减少36.76%、俯仰角均方根减少57.85%,其车身垂向加速度为0.0177m/s2,4个车轮的动载荷均方根分别为0.0284、0.0346、0.0239、0.0304N。基于BP神经网络PID控制算法的半主动悬架拖拉机,其车身垂直位移均方根减少74.54%、侧倾角均方根减少74.66%、俯仰角均方根减少75.03%,其车身垂向加速度为7.5758×10-5m/s2,4个车轮的动载荷均方根值分别为0.0197、0.0235、0.0166、0.0198N。相比增量式PID控制的半主动悬架拖拉机,基于BP神经网络PID控制的半主动悬架拖拉机,其车体平稳性得到了较好的提高。     

冬小麦条锈病内外菌源的原理和效应研究

调查研究表明,冬小麦条锈病发生晚的麦田,病叶主要分布在上部,与早发麦田相比,同部位叶片发病轻,因而形成的本田菌源量低,不利于后期小麦条锈病暴发,控病效果明显。因此对早发麦田要早期挑治和中期控制,对晚发麦田要中期控制,阻止外部菌源的落户和本田菌源的形成,有效减轻后期发病程度, 中度以上发病年份,齐穗扬花期普防病田     

“Time” in the Process of Building Formation

Looking for the “soul” the buildings have lost, and considering the meaning of the society and culture for the building formation on a particular site, there are rigorous and urgent tasks in construction development nowadays to transfer theoretical unders     

A Calculating Method of Non Linear Earth Pressure Behind Retaining Walls

Based on equilibrium analysis of forces and moment with inclined soil element, an analytical solution of earth pressure with inclined surface of fill and rough retaining wall was proposed, and the influence of slope angle of fill on earth pressure also was discussed. It is shown that the classical Rankine's earth pressure theory is a special case of the analytical solution with horizontal surface of fill and a smooth retaining wall. The results also show that the limiting rupture angle of a sliding wedge behind a retaining wall decreased with increasing slope angle of fill or friction angle between soil and a retaining wall, with the settled value of the internal friction angle of fill. The non linear character of earth pressure exhibited distinctly for the earth pressure along a retaining wall was obtained by an analytical solution. The value of earth pressure is 0 at the toe of retaining wall, consistent with the testing results. In addition, the value of earth pressure at the toe of the retaining wall will increase rapidly with increasing slope angle of fill. The analytical solution of earth pressure behind a retaining wall with fill of clay soils can be further studied with the investigative method we developed.     

Correlation of Algae Growth with Nitrogen and Phosphorus Concentrations at the Mouth of the Jialing River

Correlation analysis was used to evaluate the influencing factors and relationship of algae growth and nitrogen and phosphorus concentration in order to determine the algae growth change rule at the mouth of the Jialing River in Chongqing, P. R. China. The results indicate that algae grows rapidly during June and July. Under the same climate conditions and small differences of nutrient concentration, there is a negative correlation between algae cell density and flow velocity. Areas having tranquil water flows are advantageous for algae multiplication. Algae cell density has a positive linear relationship to nitrogen and phosphorus concentrations. Phosphorus has a greater influence weight than nitrogen, however, indicating that phosphorus is the restrictive factor for algae growth．Phosphorus affects algae growth more strongly in areas with tranquil water flows where the algae is more active. Fast flow velocity, abundant sediment content, low water temperature, and other factorss will affect the correlation of algae growth with nitrogen and phosphorus concentrations. This correlation is not obvious during rising flood stages. The results provide important parameters for understanding the changing water quality patterns of the Jialing River and the conditions and mechanism analysis of water eutrophication.