Conversion of zinc oxide nanobelts into superlattice-structured nanohelices

A previously unknown rigid helical structure of zinc oxide consisting of a superlattice-structured nanobelt was formed spontaneously in a vapor-solid growth process. Starting from a single-crystal stiff nanoribbon dominated by the c-plane polar surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the formation of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of alternating and periodically distributed long crystal stripes, which were oriented with their c axes perpendicular to each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar (0110) surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests possible uses in electromechanically coupled sensors, transducers, and resonators.     

4D electron diffraction reveals correlated unidirectional behavior in zinc oxide nanowires

The confined electronic structure of nanoscale materials has increasingly been shown to induce behavior quite distinct from that of bulk analogs. Direct atomic-scale visualization of nanowires of zinc oxide was achieved through their unique pancake-type diffraction by using four-dimensional (4D) ultrafast electron crystallography. After electronic excitation of this wide-gap photonic material, the wires were found to exhibit colossal expansions, two orders of magnitude higher than that expected at thermal equilibrium; the expansion is highly anisotropic, a quasi-one-dimensional behavior, and is facilitated by the induced antibonding character. By reducing the density of nanowires, the expansions reach even larger values and occur at shorter times, suggesting a decrease of the structural constraint in transient atomic motions. This unanticipated ultrafast carrier-driven expansion highlights the optoelectronic consequences of nanoscale morphologies.     

广西山水林田湖生命共同体的耦合协调性评价

[目的] 分析区域山水林田湖生命共同体各要素的耦合协调状态,为更精准开展国土空间规划、生态修复和自然资源要素综合监测提供科学依据。[方法] 以综合评价指数、协调度指数、耦合度指数和关联度指数为基础构建评价分析框架。基于PSR模型,从“山、水、林、田、湖”5个方面构建评价指标体系,运用综合评价模型、耦合协调模型和灰色关联模型探究广西壮族自治区2005—2017年山水林田湖生命共同体的耦合协调时空分异特征及其驱动因素。[结果] ①山水林田湖生命共同体的综合评价指数由2005年的0.918上升至2017年的0.931,具体表现为：水系统 > 田系统 > 林系统 > 湖系统 > 山系统。②山水林田湖生命共同体的耦合协调度由2005年的0.909下降至2017年的0.861,虽然为良好耦合协调状态,但有下降态势。两要素间耦合协调度较高的为“水—田”,3要素间较高的为“水—林—田”,4要素间较高的为“水—林—田—湖”。③影响山水林田湖生命共同体耦合协调发展的主要驱动因素是水要素,灰色关联度为0.723,具体指标因子为水土流失治理。[结论] 山水林田湖生命共同体是一个开放性的“山水林田湖+”的概念范畴,可依据各要素的典型性进行耦合叠加重组,其中水要素是山水林田湖生命共同体各要素耦合关联的核心,水土流失治理是关键因素。广西区内山水林田湖生命共同体综合水平虽然有所改善,但耦合协调情况不容乐观,应以水土流失治理为出发点,串联山水林田湖各要素,进行统筹规划与生态整治,搭建自然资源要素综合监测与质量管理体系,提高耦合协调状态,实现高质量的可持续发展。     

Empirical models of calcium and magnesium uptake in Dieffenbachia amoena

The objective of this work is the development of empirical models that permit the prediction of the calcium (Ca) and magnesium (Mg) nutritional needs of Dieffenbachia amoena “Tropic Snow.” In order to achieve this goal, Ca and Mg uptake has been correlated to temperature, vapor pressure deficit, global radiation, and leaf area index. Seasons (winter and spring) generate important differences in Ca and Mg concentration changes in the recycled solution. In winter, Mg concentration remains constant, while in spring conditions there is a high increase. In both seasons, Ca concentration decreases but this drop is higher in spring than in winter. The study also indicates the possibility of predicting Ca and Mg uptake using the proposed models. Calcium uptake and magnesium uptake can be estimated with a model dependent on water uptake and leaf area index.     

菠萝蜜的染色体制片优化及核型分析

应用改良的去壁低渗法研究比较了不同预处理剂对菠萝蜜染色体制片的效果及其染色体数目和核型。结果表明：以0.002 mol/L 8-羟基喹啉与0.2%秋水仙素（1:1）混合液作为预处理剂,预处理3 h效果较好。菠萝蜜的染色体数目为2n=2x=56,为二倍体,主要由中部和近中部着丝点染色体构成,9号染色体上附着一对随体;最长染色体/最短染色体为2.08:1,臂比大于2的染色体占全组染色体的3.5%,属2A核型,核型公式为2n=2M+50m（2SAT）+4sm。该文首次发现菠萝蜜可能存在B染色体。     

木塑复合材料主要组分定量分析方法研究进展

作为一种绿色环保型复合材料,木塑复合材料（WPC）具有较好的尺寸稳定性及力学性能,在室内装饰、室外园林景观、建筑、汽车内饰及包装运输等领域有着广泛应用。WPC主成分定量分析对于其市场监管、生产过程中的质量控制及消费者合法权益保证至关重要。文中总结WPC的主要组分,系统梳理目前国内外WPC主要组分定量分析方法的研究现状,分析各方法的优势与劣势,并针对今后的研究提出建议,以期为WPC主成分定量分析方法的进一步研究和推广应用提供参考。     

日光温室番茄长季节栽培条件下植株的肥水管理

在日光温室内以卡鲁索 (Caruso)和辽粉杂 3号为试验品种 ,进行长季节栽培 ,在整个生育期中 ,灌水次数为 18～ 2 1次 ,每 667m2 每次灌水量为 15～ 17m3,总灌水量为 2 92 .3 2～ 3 2 4 .4 6m3,2 0cm土层土壤含水量始终保持在田间持水量的 70 %～ 10 0 %。试验过程中除了施基肥外 ,分别在番茄的坐果期、果实膨大期、采收初期和采收中期进行追肥 ,每次追肥量相同 ,即 667m2 追施尿素 10kg,磷酸二铵 15kg ,硫酸钾 15kg     

乙烯利对木薯某些生理特性的影响

在木薯生长后期,施乙烯利能抑制生长,促进成熟。对新生叶的生长有前控后促的作用。对植株上的叶片能加速黄落和降低呼吸消耗,同时能使叶片的蔗糖酶活性增强,还原糖量增加,光合效率提高,叶片内物质输出量和茎皮层泌乳量增多,并提高块根的淀粉含量。     

船拖船体完全泥水膜润滑滑行阻力理论分析

通过理论分析和推导,计算出船体在完全泥水膜润滑状态下的滑行阻力,并与实验结果加以比较,结果表明建立泥水膜能大大降低船体的滑行阻力。