用有限元法分析木材中的温度分布

在木材应用中,了解温度在木材中的分布情况,掌握木材在受热时的温度场,才能有效地控制解冻,才能对干燥和防腐问题进行深入的研究,才能合理使用建筑围护材料。近年来,随着计算机应用和计算技术的发展,用数值方法求解木材中的热传导问题将成为有效、实用的方法。在许多种数值方法中,有限差分法和有限元法是目前较为成熟和用得普遍的方法。其中的有限元法是对古典近似计算的归纳和总结,它吸取了有限差     

双垄全膜马铃薯套种豌豆对马铃薯生育期及病害的影响

在双垄全膜马铃薯套种针叶豌豆的栽培模式下,研究了其对马铃薯的生育期及病害的影响。结果表明,马铃薯在双垄全膜栽培条件下出苗、现蕾、开花及成熟都较露地有所提前。在病害方面,覆膜使马铃薯早疫病的发生加重,但对晚疫病的发生有很好的抑制作用。     

土壤水势测定方法的选择及准确性研究

通过对土壤水势常用的3种测定方法探讨,发现测定土壤水势的方法存在差别,压力膜的准确度为最高,其次是离心机,张力计的准确度较低.压力膜测定土壤水分特征曲线的形状与原状土壤的特征曲线大致相符,但要完整地测出某土壤的特征曲线需要长达半年之久.离心机测定土壤水分特征曲线较压力膜测定有偏离,离心机测定过程中土壤容重的不断变化、土...     

红外光谱结合多元线性回归法快速测定木塑复合材料中木粉含量

采用KBr压片法对杉木/聚丙烯(PP)复合材料样品进行了红外光谱分析,确定杉木特征吸收谱带为1740~1730、1610~1590、1270~1260、1060~1050以及1040~1030 cm-1,以PP在1377 cm-1处吸收强度(I)为内标,对木塑复合材料(WPC)中木粉含量和杉木特征峰相对吸收强度进行相关性分析,并采用逐步多元线性回归法建立木粉含量与相对峰强间的多元线性回归方程。结果表明,选取I(1060-1050)/I1377、I(1270-1260)/I1377为回归变量建立的二元线性回归方程和以I(1060-1050)/I1377、I(1040-1030)/I1377及I(1270-1260)/I1377为回归变量建立的三元线性回归方程,具有较高的预测精度。木粉含量的预测值和参照值之间具有强烈的相关性,校正决定系数(R2c)超过0.98,验证决定系数(R2p)超过0.96。外部验证结果表明,线性回归方程预测准确性较高,预测相对偏差范围为0.9%至7.4%,其中三元线性回归方程预测准确性稍好于二元线性回归方程。     

再生聚丙烯与木刨花复合材料的密度和木塑比对复合材料主要性能的影响

研究了用异氰酸酯树脂为胶粘剂,木材刨花与回收聚丙烯为主要材料的复合材料的主要力学性能和尺寸稳定性。结果表明,密度对复合材料的性能有很大的影响,密度越大,力学强度越高,吸水厚度膨胀率基本越低;木塑配比对复合材料的力学性能有一定的影响,力学性能均随着配比的增加呈现不同程度的下降趋势;配比对吸水厚度膨胀率影响明显,配比越大,吸水厚度膨胀率越低,且密度大时,影响就越显著。     

果园无公害管理

针对我国果品生产普遍存在的农药、化肥、塑料污染等问题，提出无公害管理的主要措施：通过采取农业措施，搞好病虫预测预报和适当药剂防治等控制病虫害，以有机肥和果园覆草为主，结合少量施用化肥建立科学的肥水管理制度，控制塑料污染和环境污染，建立标准化的生产技术规程。     

滴灌下氮盐交互对加工番茄荧光特性及产量品质的影响

【目的】新疆有着全中国最大面积的盐碱地和加工番茄的种植基地。在新疆开展两年试验以研究加工番茄在氮盐交互下生长、生理、产量和品质的变化规律,获得适宜新疆盐碱地种植加工番茄的合理施氮量和土壤盐分范围,为新疆扩大加工番茄种植面积和合理施氮提供科学的理论依据及技术途径。【方法】试验于2017和2018年在石河子大学现代节水灌溉兵团重点实验基地进行,以当地主栽品种3166为试验材料,2017年试验共设置4个土壤含盐量水平：1.5、4.0、7.0和10.0 g·kg ^-1及4个氮素水平：201、166、131和96 kg·hm ^-2,2018年在2017年的基础上去除10.0 g·kg ^-1的土壤含盐量,增加5.0 g·kg ^-1的土壤含盐量和不施氮量处理。试验测定和分析加工番茄的荧光叶绿素参数、产量和品质指标。【结果】在氮盐交互下,加工番茄荧光参数及产量等指标均呈现出复杂的变化规律。绝大多数的荧光参数及产量受土壤盐分的主导作用较氮素强,在同等氮素水平下,7.0 g·kg ^-1和10.0 g·kg ^-1的土壤盐分对加工番茄荧光指标抑制程度最大;低盐分水平下,166 kg·hm ^-2的中等偏高的施氮量对加工番茄的荧光指标促进作用最大,其次是施氮201 kg·hm ^-2的处理;在中等偏高的盐分水平下,96 kg·hm ^-2的低氮对加工番茄的最好,其次为不施氮水平。加工番茄的鲜果产量总体上符合“盐高产低”的规律,但低氮高盐处理的产量明显高于其他同盐度的氮素水平下的产量。可溶性固形物、VC、可溶性糖和可滴定酸均随着土壤含盐量的增大逐渐增大,糖酸比的最大值均出现在低盐处理,盐分对加工番茄品质的影响远高于氮素,二者交互对加工番茄的品质并无显著性影响。通过图形叠加分析方法,得出了加工番茄获得相对最优产量和品质的合理施氮范围和土壤含盐量区间。【结论】在盐碱程度偏高的土壤可通过少施氮素来提高加工番茄产量;加工番茄获得相对最优产量和品质的合理施氮范围和土壤含盐量区间为N：98.12—119.60 kg·hm ^-2,S：3.57—5.58 g·kg ^-1。     

Response of labile organic C and N pools to plastic film removal from semiarid farmland soil

To examine the effects of plastic film removal on grain yield and soil organic matter (SOM), a spring maize (Zea may L.) field experiment was conducted for 5 yr at Changwu Agricultural and Ecological Experimental Station of Northwest China. Compared with traditional plastic film mulching during entire growing stages (FM), plastic film removal at the silking stage (RM) resulted in a 6.3% higher average maize yield. Under the RM treatment, soil organic carbon and total nitrogen significantly increased after the 5‐yr cultivation in the 0‐ to 20‐cm layer. Significant increases in extractable organic C (EOC), KMnO₄‐oxidizable C (KMnO₄‐C) and C management index (CMI) in the 0‐ to 20‐cm layer, and light fraction organic C and EOC in the 20‐ to 40‐cm layer were observed in response to plastic film removal after the 1‐yr treatment; the responses were more significant after 5 yr. Under the RM treatment, significant increases in microbial biomass C, light fraction organic N, extractable organic N, KMnO₄‐C and CMI were also observed after five years in the 20‐ to 40‐cm layer. Moreover, KMnO₄‐C and EOC were much more sensitive than other labile SOM fractions to the application of RM, even after only 1 yr of cultivation. Therefore, compared with mulching for the whole growing season, plastic film removal at the maize silking stage is an effective option for increasing yields and enhancing SOM concentration and soil sustainability in the regions with semiarid monsoon climates that have sufficient rainfall during maize reproductive stages.     

超高效液相色谱-质谱/质谱法同时测定蔬菜中7种磺胺的残留量

为建立超高效液相色谱-质谱/质谱法(UPLC-MS/MS)同时测定蔬菜中7种磺胺残留量的方法。样品用1%乙酸乙腈提取，以C18色谱柱分离待测物，采用多反应监测(MRM)离子扫描模式，外标法进行定量，线性良好，相关系数均大于0.999。结果显示：7种磺胺的检出限为0.000 4～0.000 6 mg/kg，样品添加回收率为67.5%～94.1%，相对标准偏差均少于5.3%(n＝6)。该方法简单快捷、定量准确，可满足多种蔬菜中7种磺胺的残留检测要求。     

An investigation into the grazing efficiency of perennial ryegrass varieties

The objective of this study was to compare the grazing efficiency of 30 perennial ryegrass varieties, differing in ploidy and heading date. Plots were grazed by lactating dairy cows and managed under a rotational grazing system with 19 grazing events occurring over two years. Pre-grazing and post-grazing compressed sward heights were measured with a rising plate meter. A mixed model was used to predict the post-grazing sward height of each variety based on year, grazing event, block and pre-grazing sward height. Residual grazed height (RGH) was derived as the difference between the actual and predicted post-grazing sward height and was used as the measure of grazing efficiency. Negative RGH values indicated that the actual herbage removed was greater than that predicted and so indicated a superior grazing efficiency. Varieties differed in their level of grazing efficiency (p < .001), with RGH values ranging from −0.38 to +0.34 cm. Tetraploid varieties exhibited significantly greater grazing efficiency performance than diploids (p < .001), with average RGH values of −0.13 and +0.13 cm respectively. A significant difference in grazing efficiency was found among recommended perennial ryegrass varieties that are not being recorded by mechanically harvested simulated grazing protocols. A variety reappraisal that included grazing efficiency could identify varieties capable of improving on-farm livestock productivity from grass.