纳米纤维素涂层软包装材料的制备及其隔氧性能评价

为了将纳米纤维素优良的阻隔性能在食品包装材料上进行应用研究,该试验通过将纳米纤维素(cellulose nanocrystals,CNs)涂层在4种软包装基材上进行涂覆并对其性能进行评价。研究结果表明,纳米纤维素均匀的涂覆在4种基材表面,且与原始基材相比,带涂层材料表面的摩擦系数显著降低,隔氧能力得到了显著的提升,但是CNs涂覆方式并未能很好的改善复合膜的光学性能。试验结果表明带CNs涂层的取向聚酰胺薄膜(oriented polyamide,OPA)制得的复合膜隔氧效果最好,其隔氧系数为0.003 cm3·μm/(m2·24h·k Pa),相比于聚对苯二甲酸乙二醇酯薄膜(poly ethylene terephthalate),PET),赛璐玢薄膜(cellophane,CELL),定向聚丙烯薄膜(oriented polypropylene,OPP)3种基材,其隔氧系数显著降低。应用隔氧系数最高的取向聚酰胺薄膜(oriented polyamide,OPA)制作的隔氧膜对鲜切苹果进行包装保鲜,在温度为3~5℃条件下贮藏4 d,与对照组相比,以OPA为基底的隔氧复合膜在第4 d时的亮度值提高了11.7%,且其营养成分指标可滴定酸、维生素C含量和可溶性固形物含量分别提高了1.05倍、42.6%和36.2%。本研究制得的复合膜隔氧性能优异,可以较为显著的增强原始基材的隔氧效果进而延长了对氧气较为敏感食品的货架期。     

三聚氰胺-脲醛树脂改性木基石膏复合材料的效果及机理

为提高木基石膏复合材料的力学性能,以杉木刨花为增强相,以建筑石膏为连续相,采用三聚氰胺-脲醛树脂(melamine-urea-formaldehyde MUF)粘结初步成型和增湿固化2阶段的免加石膏缓凝剂制备方法,开展了MUF用量和木材/石膏质量比对木基石膏复合材料物理力学性能影响试验,并与相应产品标准、结构板材标准及现有文献进行对比。结果表明,试验范围内,MUF用量与木基石膏复合材料力学性能呈正相关关系,木材/石膏质量比的影响较小;MUF用量为15%以上时,木基石膏复合材料的力学性能满足《石膏刨花板:LY/T 1598-2011》产品标准的要求;MUF用量为21%及以上时,除顺纹抗弯强度,其余性能符合《定向刨花板:LY/T 1580-2010》结构板材标准的规定;MUF用量为33%及以上时,木基石膏复合材料达到《结构胶合板:GB/T 35216-2017》结构板材标准中E5.0~F16.0强度等级。抗弯性能试验中,石膏板为脆性破坏,木基石膏刨花板具有一定的延性性能。综合强度和成本,MUF用量为33%、木材/石膏质量比为0.30为较优的原材料配比。优化原材料配比条件下,木基石膏复合材料的内结合强度、静曲强度、弹性模量、位移延性系数和24 h吸水厚度膨胀率分别为1.28 MPa、16.5 MPa、7 350 MPa、1.64和1.23%。采用该2阶段制备方法,木基石膏复合材料中石膏晶体形态细长,且随着MUF用量的增加,晶体交错搭接、叠合现象明显,接触面积增加,晶体结构更加致密,石膏连续相强度增加;MUF用量提高,石膏在刨花表面的覆盖量明显增加,刨花增强相与石膏连续相之间界面性能显著改善。研究结果可为木基石膏复合材料力学性能的进一步提升提供参考,并为其产品的工程应用提供数据支撑。     

花棒根-土复合体直剪试验的有限元数值模拟与验证

为深入了解花棒(Hedysarum scoparium)根系在增强土壤抗剪强度中的作用机理,同时减少试验成本和挖掘根系对环境的破坏,该文采用有限元数值模拟的方法研究了宁夏毛乌素沙地5 a生人工种植花棒根系的根截面积比(root area ratio,RAR)和垂直荷载对根-土复合体抗剪强度的影响,并对模拟结果进行了试验验证。研究表明:花棒根-土复合体的抗剪强度与垂直荷载的关系符合摩尔库伦(Mohr–Coulomb)屈服准则,花棒根系对土壤的抗剪强度有显著的提高作用。随RAR的增加,花棒根系表观黏聚力(root apparent cohesion,SR)呈线性增加(R20.9)。在相同的RAR下,花棒根-土复合体抗剪强度相对于素土抗剪强度的增长率随垂直荷载的增加逐渐降低,符合对数函数变化规律(R20.9);在相同的垂直荷载下,随RAR的降低,花棒根-土复合体抗剪强度相对于素土抗剪强度的增长率呈线性递减(R20.9);在较低垂直荷载的情况下,花棒根系提高土壤抗剪强度的作用更明显。研究发现与素土相比花棒根-土复合体的剪应力峰值出现较晚,当土壤出现明显塑性变形时,花棒根系的固土能力才能体现出来。数值模拟结果和室内试验结果显示:利用该文所建立的花棒根-土复合体直剪试验的有限元数值模型,模拟计算的根-土复合体抗剪强度与室内试验结果基本一致,相对误差绝对值的平均值1.87%,花棒根-土复合体的直剪试验可以通过该研究所建立的有限元数值模型来模拟。研究结果对于深入了解植物根系加固土壤的作用机理和推进根-土相互作用的数值模拟研究具有重要参考意义。     

Formation of aflatoxin derivatives on thin layer chromatographic plates.

Rapid confirmation of the presence of aflatoxins B-1 and G-1 in foods is provided by reaction with trifluoroacetic acid at the origin of a thin layer chromatographic plate. The procedure has been used successfully with various nuts, grains, coffee and cocoa beans, and other foods.     

Grouping of soil bacteria by analysis of colony formation on agar plates

Summary The colony formation of soil bacteria was studied in relation to incubation time. The process was simulated by a colony-forming curve (CFC) which was a superposition of several component curves (cCFC) given theoretically by the first-order reaction (FOR) model. This model had been previously proposed to define the colony formation of cells of a single culture. Soil bacteria were divided into several groups by these cCFC, as different types of bacteria produced their own colonies. Bacteria belonging to a single group grew at a similar rate on the plating medium and each group was characterized by a different growth rate. Most copiotrophic bacteria were fast growers and most oligotrophic bacteria slow growers.     

仿生推土板减粘降阻机理初探

试验证明,仿蜣螂头前部“推土板”形状而设计的仿生推土板,具有较明显的减粘降阻效果。为了进一步研究、优化和开发仿生推土板,本文建立了推土板的力学模型,对土壤与推土板接触界面进行了动态分析,并初步探讨了其减粘降阻的机理。     

Quantitative determination of dietary lectin activities by enzyme-linked immunosorbent assay using specific glycoproteins immobilized on microtiter plates

An immunoenzymatic method for the quantitative determination of dietary lectin activities employing immobilized glycoproteins was studied. Lectins from wheat germ (WGA), peanut (PNA), and jack bean (ConA) were added to microtiter plates coated with ovalbumin or asialofetuin and quantified by enzyme-linked immunosorbent assay (ELISA) with lectin-specific antibodies. ELISA responses for lectin activity were dose-dependent in the concentration range 30-1000 ng/mL for WGA and 80-1000 ng/mL for both PNA and ConA. Inhibition assays carried out with different saccharides confirmed that the binding of lectins to immobilized glycoproteins was specific. The proposed method is specific and sensitive, allowing the quantitative determination of lectin activities on raw samples by simple dilution of the extracts. Examples of application to wheat germ and roasted peanut extracts are reported.     

An experimental and numerical study on flow and transport in a field soil using zero-tension lysimeters and suction plates

Zero-tension lysimeters are widely applied to study the fate of chemicals in the subsurface environment. However, conditions in lysimeters differ from the field situation, because local saturation is required at the lower boundary to collect leachate. The objective was to characterize the influence of the lower boundary on the flow and transport behaviour of bromide observed in six 1.2-m-long lysimeters and in the field by 30 suction plates installed at 1.2-m depth, which were operated with a time-variable suction equal to the ambient soil water potential. A bromide pulse was applied at the bare surface of a silty soil in autumn 1997 and monitored for 2.5 years. The mean leachate flux was 0.98 mm day⁻¹ for the lysimeters versus 0.66 mm day⁻¹ for the suction plates. The lysimeters had a slightly slower effective mean pore-water velocity, expressed as transport distance per unit of leaching depth, and exhibited more solute spreading than the suction plates. Numerical simulations revealed that the amount of water collected with the suction plates was sensitive to the hydraulic conductivity of the plates. The spatial variability in hydraulic properties in the model explained the observed variability in cumulative leachate, at least qualitatively. The arrival time and spreading of the breakthrough curves (BTCs) were well described by the simulations in the lysimeters, but were underestimated in the suction plates. Preferential flow through macropores, which is not an effective carrier for bromide, might be the reason for this discrepancy. Molecular diffusion contributed significantly to solute spreading and enhanced lateral mixing. Both the experiments and the simulations revealed that the dispersivity derived from BTCs is significantly influenced by the observation method and experimental conditions.     

推土板表面形态对土壤动态行为影响的离散元模拟

土壤行为的变化过程直接受触土部件结构的影响，研究不同表面推土板作用下土壤动态行为的变化规律和影响因素对于触土部件的优化设计具有重要意义。根据液桥对土壤微观力学结构的影响，在传统离散单元法理论的基础上，建立了土壤颗粒接触非线性力学模型，并对光滑和波纹形表面形态推土板前端土壤的动态行为进行了离散元模拟。结果表明：离散元模拟不仅准确再现了实验中表面形态对板面前端土壤动态行为影响的定性和定量结果，而且通过离散元细观分析从土壤内部土壤颗粒运动合理解释了土壤宏观形态的变化规律以及推土板表面形态对土壤动态行为的影响，即波纹形表面使板面前端土壤波动频率变大，而波动幅度变小。该研究为土壤－机械相互作用分析提供了新的研究思路和手段。     

Leaching of carbon and nitrogen from a sandy soil substrate: A comparison between suction plates and ion exchange resins

To determine boundary effects on leaching, we investigated (1) how filter materials affect the concentrations of dissolved organic carbon (DOC) and nitrate (NO₃‐N) in soil percolates and (2) whether ion exchange resins and suction plates are equally suited to capture NO₃‐N. DOC leaching was higher with PE suction plates and plate material did not affect NO₃‐N leachate concentrations. Cumulative NO₃‐N leaching was similar for glass suction plates and ion exchange resins.