木质素/聚氯乙烯膜的制备及其亲水性研究

为提高聚氯乙烯(PVC)膜的亲水性,通过聚合物共混法制备了木质素/PVC膜.通过扫描电子显微镜(SEM)表征了膜的断面形貌;通过膜的吸水率、孔隙率、膜通量和膜表面接触角测试探讨了木质素用量、致孔剂种类和用量对膜亲水性能的影响.研究结果表明:木质素/聚氯乙烯膜的内部呈多级孔;加入木质素后,膜的吸水率、孔隙率、亲水性以及膜...     

Four-node Membrane Element of Vector Form Intrinsic Finite Element for Large Deformation Analysis of Membrane Structures

Based on fundamental principles of the vector form intrinsic finite element (VFIFE), the basic formulas of 4-node quadrilateral membrane element were first derived in this paper. The procedure for the determination of pure nodal deformation through reverse movement was elaborated, and the method for the calculation of internal nodal forces through deformation coordinate system was presented. Feasible approaches were also proposed for several issues for 4-node membrane element, including the location statuses and the numerical integration for internal forces. A computer program of 4-node membrane element was developed. By the analysis of the numerical example, the correctness and validity of the membrane element theory and the computer program were verified. Then the approach was applied for more analysis of large deformation and large rotation problems of membrane structures, including cushion inflating and cloth draping.     

Strength-permeability Model of Pervious Cement Concrete

High permeability is an important characteristic of pervious concrete. For the existing permeability testing devices of pervious concrete, the specimen sidewall leakage is serious due to the large numbers of open pores on the surface of specimens. To solve the problem, a new permeability testing method for pervious concrete was developed and a composite sidewall structure with waterproof daub, flexible rubber cushion and rigid sleeve sidewall was proposed. Meanwhile, the strength and permeability of pervious cement concrete are incompatible with a reciprocal relationship. However, limited research has been conducted on the relationship between them. Effects of water-cement ratio (W/C), aggregate-cement ratio and porosity on the properties of pervious concrete, including strength and permeability, were studied. Furthermore, strength-porosity model, permeability-porosity model and strength-permeability model were established. Tests reveal that: a) There is an optimum W/C of pervious concrete, at which strength reaches the maximum; b) The relationship between the strength and W/C shows a downward quadratic curve, and the permeability is proportional to porosity and aggregate-cement ratio; c) The relationship between strength and permeability of pervious cement concrete can be well fitted with the Lorentzian function, and the strength decreases when the permeability increases, but the rate of reduction decreases gradually. The optimum combination of strength and permeability should be determined based on the specific engineering requirements in design.     

Experimental study on adaptability of well pattern using sandstone plate model with ultra-low permeability

Because the porous flow state is difficult to be simulated by one-dimensional cores and two-dimensional sand filled models,this paper proposes a method of making large-scale natural outcrop flat model and defines two parameters to evaluate adaptability of different well pattern on the ultra-low permeability sandstone flat model. With natural sandstone plate model,production of different well patterns in homogeneous oil reservoirs is simulated. A concept of pressure sweep efficiency and deliverability index for researches on adaptability of well patterns are put forward. Through experiments,plane pressure gradient field of different well patterns under different drawdown pressures are measured,and then seepage areas of the models are divided into immobilized seepage area,nonlinear seepage area,and quasi-linear seepage area,with the help of small core nonlinear seepage curve. Experiments show that adaptability of inverted nine-spot equilateral well pattern is better than those of inverted nine-spot rhombus well pattern and rectangular well pattern. With the increase of drawdown pressure,deliverability index of all well patterns increases,immobilized seepage area reduces,and quasi-linear seepage area expands. At the same time,nonlinear seepage area of inverted nine-spot equilateral well pattern reduces,while those of inverted nine-spot rhombus well pattern and rectangular well pattern fluctuate as expanding first and then reducing.     

松树皮原花青素的超声提取、超滤膜分离中试研究

通过松树皮原花青素的超声提取、膜分离纯化技术中试试验,考察了超声波提取温度、料液比、提取时间等单因素对原花青素得率的影响,试验得到了超滤膜工作压力、截留分子量的最佳工艺参数。结果表明,采用超声波强化逆流提取松树皮原花青素的最佳参数为：料液比1：12,超声温度60℃,提取时间30min;超滤膜分离纯化工艺参数为：膜工作压力0．2MPa,截留分子量5000。试验获得的松树皮原花青素经检测含量可达95％以上。     

Some factors influencing susceptibility to discoloring fungi and water uptake of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and Oriental spruce (Picea orientalis)

Abstract

The heartwood and sapwood from Scots pine (PS), Norway spruce (PA), and Oriental spruce (PO) were tested for susceptibility to discoloring fungi and water uptake. In addition, annual ring width and density were measured. The methods used were Mycologg for testing growth of fungi and a modified version of EN 927-5 to investigate water uptake. For pine, the heartwood showed a lower water uptake and no discoloring fungi growing in the tests. The heartwood had a significantly higher density and smaller annual ring width than the sapwood. In PA the heartwood had significantly lower discoloration than sapwood. The total water uptake in g/m² was significantly higher in sapwood, but not the calculated moisture content. As for wood properties, the density was significantly higher in sapwood compared to heartwood, although there were no differences in annual ring width. Regarding PO, differences in water uptake could be seen between sapwood and heartwood although the densities were similar. These results show that susceptibility to discoloring fungi and water uptake is hard to correlate to a single inherent property when looking at different wood species.     

Cracks in bread crust cause longer crispness retention

Crispness is among the most important factors that the consumer uses to assess the quality of crispy bread. However, this quality attribute is rapidly lost after baking. It is known that crispness retention can be increased more than eight times by enhancing the water vapor permeability of the crust. Current methods to achieve this, i.e., puncturing the bread before baking, require an extra process step. We hypothesize that cracks that appear spontaneously on the crust surface after baking can also enhance water vapor permeability and therefore improve crispness retention. We were able to confirm this hypothesis by preparing composite breads containing the same crumb but different crusts, with crust recipes of varying starch/protein ratios. Crusts systems that were generally high in gelatinized starch content and poor in evenly distributed gluten were more prone to crack after the whole process of part-baking, freezing, and baking off. These cracks led to an increased water vapor permeability of the crust and an eight times longer instrumental crispness retention compared to standard bread. In this paper we also discuss possible causes for crack formation in the crust. We hypothesize that effective cracks are caused by thermal shock in materials with a low ability to dissipate energy.     

基于蒙皮效应钢梁的静力性能研究

采用数值试验的方法分析了基于蒙皮效应的钢梁在静力情况下的力学性能.给出了该新型钢梁的应力分布情况,并与H型钢梁、箱型钢梁的承载能力进行了比较.研究表明,相同跨度、相同质量的新型钢梁具有更高的承载能力,并且随着跨度的增加,合理设计的新型梁的承载力具有更加明显的优势.     

日光温室茄子膜面集雨微灌施肥一体化技术研究

日光温室茄子膜面集雨微灌施肥一体化技术研究结果表明,膜面集雨微灌施肥一体化技术与传统大水漫灌技术比较,节水量为4 875 m3/hm2,节水55.08%,节肥457 kg/hm2;有效降低温室内空气湿度和土壤湿度,抑制了茄子的病害发生;提高室温和地温有利于形成长柱花,有效抑制短柱花和畸形果,使温室茄子产量提高了773 kg/hm2,水分生产效率提高10.19 kg/m3。     

家蚕卵黄膜蛋白基因BmVMP23的3'-UTR变异对其表达的影响

BmVMP23已被预测为一种编码家蚕卵黄膜蛋白的基因,该基因在家蚕"明"死卵突变体(l-em)中呈显著下调表达,并已证明其终止密码子后的序列发生了变异。为研究变异位点是否位于BmVMP23的3'-UTR区段及序列变异对该基因表达的影响,通过RACE扩增获得BmVMP23的全长cDNA序列,证实突变位点位于BmVMP23的3'-UTR区段。在此基础上,以突变体l-em及正常型的BmVMP23 3'-UTR序列为实验模型,构建以EGFP为报告基因的重组载体pMD18-T(A3-EGFP-SV40)、pMD18-T[A3-EGFP-3'UTR(WT)]和pMD18-T[A3-EGFP-3'UTR(l-em)],并将其分别转染BmN细胞观察EGFP的表达。结果显示,转染pMD18-T(A3-EGFP-SV40)和pMD18-T[A3-EGFP-3'UTR(WT)]质粒的细胞均能检测到绿色荧光,而转染pMD18-T[A3-EGFP-3'UTR(l-em)]质粒的细胞检测不到绿色荧光。上述结果证实BmVMP23的正常表达须具有完整的3'-UTR,由此认为"明"死卵突变体中BmVMP23基因表达量的降低是因其3'-UTR的变异引起的。