速生杨木单板高频加热层积弯曲胶合工艺研究

利用速生杨木单板,采用高频加热层积弯曲胶合工艺生产弯曲构件,探讨速生杨木代替优质阔叶材生产曲木家具的可行性,并对影响弯曲构件性能指标的因素进行分析。结果表明:速生杨木单板高频加热层积弯曲胶合构件的各项性能指标均超过了企业相关标准,完全可以代替优质阔叶材,用于曲木家具生产。方差及直观分析结果显示, 单板含水率13%,热压压力1.7 MPa,热压时间5 min,保压冷却时间12 min,即可获得满意的弯曲构件性能指标。     

Post-fire tree stress and growth following smoldering duff fires

Understanding the proximate causes of post-fire conifer mortality due to smoldering duff fires is essential to the restoration and management of coniferous forests throughout North America. To better understand duff fire-caused mortality, we investigated tree stress and radial growth following experimental fires in a long-unburned forest on deep sands in northern Florida, USA. We burned basal fuels surrounding 80 mature Pinus palustris Mill. in a randomized experiment comparing the effects of basal burning treatments on stem vascular meristems; surficial roots; root and stem combinations; and a non-smoldering control. We examined the effects of duration of lethal temperatures (>60 °C) on subsequent pine radial growth and root non-structural carbohydrates (starch and sugar). Duff and mineral soil temperatures in the experimental fires consistently exceeded 60 °C for over an hour following ignition, with lethal temperatures of shorter duration recorded 20 cm below the mineral soil surface. Duff heating was best explained by day-of-burn Oe horizon moisture (P = 0.01), although little variation was explained (R² = 0.24). Post-fire changes in latewood radial increment in the year following fires was related to duration of temperatures >60 °C 10 cm deep in the mineral soil (P = 0.07), but explained little variability in post-fire growth (R² = 0.17). In contrast, changes in non-structural carbohydrate content in coarse roots (2–5 mm diameter) 120 days following burning were more strongly correlated with the duration of lethal heating 5 cm below the mineral soil surface (P = 0.02; R² = 0.53). Results from this study implicate the role of mineral soil heating in the post-fire decline of mature longleaf pine following restoration fires in sandy soils.     

苦荬菜汁提取工艺的研究

采用热榨法和热浸提法对苦荬菜汁进行提取试验。通过对出汁率、可溶性固形物含量和感官质量等进行综合分析与评价,探讨2种提取方法的工艺条件,同时将2种提取方法与鲜榨法进行比较分析,最终筛选出1种较合理的苦荬菜汁提取方法。结果表明,热榨法提取苦荬菜汁的最适工艺条件为:热烫温度90℃,热烫时间1 min;热浸法提取苦荬菜汁的最适工艺条件为:料水比1∶2,浸提时间2 h,浸提温度60℃;热榨法提取苦荬菜汁工艺合理,出汁率达61.84%,可溶性固形物含量达4.24%,所得苦荬菜汁苦香味浓郁、无异味,颜色青绿,稳定性好。     

Atmospheric Environmental Impact Simulation of Gas Fired Boilers as Peak Load Heat Sources

Heating with gas can reduce air pollutant emission and therefore becomes a new sort of peak load heat source. To study the atmospheric environmental impact, we adopted a newly built combined heating system and simulated its pollutant dispersion for centralized and distributed peak heating. The simulations were based on the improved regulatory environmental impact assessment (EIA) guidelines for atmospheric environment. The model developed an algorithm for infill wind direction simulation and exported pollutant contours for comparisons. Simulation results show that the system's atmospheric environmental impact is related not only to the pollution emission quantity per quantificational heating, but also to the distribution of heat resource in the gas fired boilers. The centralized peak heating has comparatively small environmental impact; for distributed peak heating, the more concentration of gas fired boilers distribution is applied, the more serious environmental impact will be. In addition, the optimum setting proportion of gas fired boilers should be between 0.2 and 0.6 from the perspective of environmental impact.     

豫西脂尾羊体尺与体重的相关性分析

运用SPSS软件对139只豫西脂尾羊体尺、体重的测定结果进行相关分析和通径分析,并建立最优回归方程。结果表明:豫西脂尾羊的体重(-Y)与体高(X1)、体长(X2)、胸围(X3)、胸宽(X4)、胸深(X5)、尾宽(X6)、尾长(X7)均呈极显著正相关。胸深、体高、胸宽的直接作用和间接作用对体重的影响都极大。得到最优回归方程为-Y=0.438X1+(-0.209)X2+0.554X5;经t检验,方程具有极显著的真实性和拟合度。     

论鲜活农产品直配模式的形成机理及交易效率——以河北省为例

随着我国农业产业化程度的提高和农产品流通体制的健全,鲜活农产品在其生产和流通领域正在发生一些变化。通过对河北各地的实地考察,文章对河北省鲜活农产品配送模式中两种典型的直配模式进行了分析和比较,认为"合作经济组织+超市"模式具有较高的组织化程度和交易效率,但由于其市场目标一般为高端市场,其规模不宜太大;"生产基地+终端消费市场"模式计划性很强,是目前组织化程度最高的配送模式之一,但其外生交易费用较高。     

双离合器变速器简介

汽车变速箱发展经历了100多年,从最初采用侧链传动到手动变速箱,及至液力自动变速箱和电控机械式自动变速箱,再到现在无级自动变速箱的普遍使用,在汽车工业技术不断前进的同时,变速箱也向着更平顺、更省油、更富驾驶乐趣的方向不断发展。直至双离合自动变速箱的出现,将汽车带进了一个更加环保低碳的境界。本文通过对大众迈腾双离合器自动变速器的介绍,让人们更加充分地认识双离合器自动变速器的优越性。     

多孔毛管温室冠层空间热风增温实验

为研究微孔散热条件下,多孔毛管沿程温度分布规律、温室冠层以下空间的垂直温度梯度及其与主要影响因素之间的关系,构建了多孔毛管温室空间热风增温实验系统。对多孔毛管进行保温围护,以毛管进口温度、进风压力、出风孔径等为实验参数,采集毛管前端孔口、中间孔口与末端孔口围护空间内温度数据,分析其在毛管沿程方向上和垂直空间内的分布规律。实验结果表明,毛管沿程出风孔口围护空间温升略有降低;垂直空间内温升呈先上升后下降的驼峰状变化趋势。不同进口温度、进风压力条件下,构建的热风增温系统可以使围护空间内距地面800～1 200 mm高度空间内的温度升高2.5～6.2℃。     

804P拖拉机液压系统热平衡问题的解决

804P拖拉机提升器液压系统在增加液压输出后,出现油温高的问题。通过分析和实验的方法,进行简约的热平衡计算,对液压系统进行局部调整和改进,解决油温高的问题。     

Microwave-enhanced alkali treatment of Pinus yunnanensis: Physiochemical characterization of the dissolved lignins

Pinus yunnanensis was subjected to water-bath and microwave treatments in 1% NaOH aqueous solutions at 100 °C with various ratios of bath heating time to microwave heating time (0/120, 20/100, 40/80, 60/60, 80/40, 100/20 and 120/0 min). The lignins dissolved in the alkali liquors were separated and purified, and their physicochemical features were comparatively characterized by sugar analysis, GPC, FT-IR, ¹³C and HSQC NMR, as well as thermogravimetric analysis (TGA). The results showed that the lignin fractions extracted with microwave heating (20-120 min) had high molecular weights and polydispersities (M_w 3150-5710 g/mol, M_n 2130-3020 g/mol, M_w/M_n 1.48-2.00) as compared to those prepared without microwave heating (M_w 3080 g/mol, M_n 2080 g/mol, M_w/M_n 1.48). The most striking characteristic of all lignin fractions was the almost absence of associated sugars (0.16-3.25%). The TGA results indicated that the thermal stability of the lignin fraction increased with the increment of the molecular weight. FT-IR and NMR spectra suggested that the lignin fractions showed similar structures which were mainly composed of guaiacyl (G) and minor amounts of p-hydroxyphenyl (H) units. Moreover, HSQC NMR spectrum of a typical lignin fraction (prepared with microwave heating for 120 min) revealed that it contained dominant amounts of β-O-4′ linkages (64.6%) and phenylcoumaran (β-5′) substructures (25.8%) together with small amounts of resinol (β-β′) substructures (6.7%) and coniferyl alcohol end groups (2.9%).