并行MLFMA分布层的构造及其负载均衡

研究了并行多层快速多极子算法（MLFMA）的分布层,提出了一种衡量其负载不均衡程度的方法,并在此基础上提出了分布树的一种新的构造算法。通过预先估算按分布层的不同层均分所得分布层的负载不均衡度,选取了一种负载不均衡度较小的方法来构造分布树。实验结果表明,该算法相比传统的按分布层的最细层均分所得分布树的算法,能更为有效地提高整个多层快速多极子算法的并行效率。     

Effect of Freezing/Thawing Temperature on the Viscoelastic and Nutritional Qualities of Carrots

This study evaluated and correlated the viscoelastic and nutritional properties of carrots after freezing (–20, –70, and –196^oC) and thawing (4 and 18^oC) treatments. Results showed that all samples exhibited a solid behavior (storage modulus G′ > loss modulus G″) dominating the viscoelastic response. After treatments, G′, G″, hardness, fracturability, springiness, and chewiness of carrots significantly decreased, whereas loss tangent (Tanδ) increased. Compared with other treatments, fast freezing (–196^oC) and thawing (18^oC) better maintained G′, G″, hardness, and fracturability of carrots, and intermediate freezing (–70^oC) better retained springiness, cohesiveness, and chewiness. For nutritional parameters, fast freezing and thawing conditions also contributed to preserving the contents of carotenoids of carrots. Partial least squares regression analysis revealed that β- and α-carotene, lycopene, and soluble sugars were positively correlated with hardness, fracturability, G′, and G″, and negatively with Tanδ in carrots. The variation of viscoelastic parameters could well predict the changes at nutritional levels.     

Sorption isotherms and thermodynamic properties of freeze‐dried colostral whey powders with different additives

Moisture adsorption isotherms of colostral whey (CW) powders with different additives (maltodextrin and sucrose) were determined using gravimetric static method at 15–35 °C in the water activity range of 0.067–0.76. The moisture adsorption isotherms obtained were typical sigmoid curves, and the modified‐Halsey and Guggenheim–Anderson–de Boer (GAB) equations gave the best fit to experimental data among five well‐known equations. Addition with maltodextrin into CW powders could effectively decrease equilibrium moisture content (EMC), whereas addition with sucrose increased EMC in the water activity of 0.43–0.76 at 15 and 25 °C and in the water activity of 0.21–0.76 at 35 °C, respectively. Thermodynamic properties including net isosteric heat of sorption and differential entropy were determined from adsorption data using Clausius–Clapeyron equation. The results showed that net isosteric heat of sorption of all the samples decreased exponentially with increasing EMC. Enthalpy–entropy compensation theory was applicable for adsorption process of all the samples, and the adsorption processes were enthalpy‐driven.     

简单复合岩体中TBM多滚刀破岩机理离散元分析

采用引入考虑胶结尺寸的微观接触模型的PFC^2D离散元软件,对全断面岩石掘进机（TBM）盘形滚刀作用下简单形式的复合岩体破岩机理进行数值模拟研究。进行了单滚刀、双滚刀和三滚刀作用下的复合岩体破碎过程的模拟。模拟结果表明：滚刀破岩过程可以分为三个阶段：加载阶段、卸载阶段和残余跃进阶段。通过双滚刀和三滚刀侵入复合岩体的推力-侵深曲线分析,软岩上的滚刀比硬岩上的滚刀进入各阶段稍慢,略有滞后;不同滚刀间的峰值法向推力相差较大,易造成滚刀磨损。对于花岗岩-绿片岩复合岩体,破岩时接触力链被岩体分界面分割,硬岩区胶结破坏数目较多,双滚刀、三滚刀侵入时易形成贯通裂缝;破岩效率由大到小为双滚刀效率、三滚刀效率、单滚刀效率,而且双滚刀能够将效率提高一倍左右。     

掺杂的SrAl2O4:Eux2+,Dyy3+长余辉粉的合成、表征及发光性质

采用自蔓延高温合成法制备了组成为SrAl2O4:Eu2+x,Dy3+y的2组(x:y=1:1,x:y=1:2)12种铝酸锶长余辉发光粉,测试结果表明,组成为SrAl2O4:Eu2+0.0125,Dy3+0.0125的发光亮度最好。以上述配比为依据,又分别引入了可以用于制备荧光材料的阳离子Li+、Be2+,以及既可以用于制备荧光材料也可以用于制备自激活荧光材料的阳离子Zn2+、Cd2+、Pb2+,共制得5个系列22种铝酸锶(SrAl2O4)长余辉发光粉。Zn2+0.0125的掺杂使得SrAl2O4:Eu2+0.0125,Dy3+0.0125的余辉亮度得到大幅度提高,而且SrAl2O4:Eu2+0.0125,Dy3+0.0125,Zn2+0.0125的衰减速度也明显慢于SrAl2O4:Eu2+0.0125,Dy3+0.0125。X射线衍射结果表明,掺杂少量稀土离子(Eu2+和Dy3+)不会改变SrAl2O4基质的晶体结构。另外,透射电镜分析和粒度分布结果表明,产物为疏松多孔的蘑菇云状固体,粒度在10μm左右。     

Synthesis of magnetic two-dimensional materials by chemical vapor deposition

The development of magnetic two-dimensional (2D) materials in its infancy has generated an enormous amount of attention as it offers an ideal platform for the exploration of magnetic properties down to the 2D limit, paving the way for spintronic devices. Due to the nonnegligible advantages including time efficiency and simplified process, the facile bottom-up chemical vapor deposition (CVD) is regarded as a robust method to fabricate ultrathin magnetic nanosheets. Recently, some ultrathin magnets possessing fascinating properties have been successfully synthesized via CVD. Here, the recent researches toward magnetic 2D materials grown by CVD are systematically summarized with special emphasis on the fabrication methods. Then, heteroatoms doping and phase transition induced in CVD growth to bring or tune the magnetic properties in 2D materials are discussed. Characterizations and applications of these magnetic materials are also discussed and reviewed. Finally, some perspectives in need of urgent attention regarding the development of CVD-grown magnetic 2D materials are proposed.

     

平行双孔水工隧道相互作用的时效解答

地下工程中常遇到流变岩体中双线近距离隧道施工问题。隧道施工位移的预测和控制,特别是新建隧道的施工对既有隧道产生的影响,是工程中面临的重要问题。针对流变岩体中深埋双圆形水工隧道的问题,笔者采用复变函数方法和Laplace变换技术建立了考虑施工过程时黏弹性应力、位移与弹性复位势之间的关系,然后运用黏弹性叠加原理得到了整个施工过程各个阶段围岩应力和位移全量和增量理论解答,并据此进行新建隧道对既有隧道的影响分析。为验证解答的正确性,对一算例进行了有限元解答和理论解答的比对,两者吻合很好。与数值与实验方法相比,本文解答可以较为便利地对岩体应力、位移进行参数分析,进一步可以指导工程的初步设计。     

Large‐Scale Growth and Field‐Effect Transistors Electrical Engineering of Atomic‐Layer SnS2

2D layers of metal dichalcogenides are of considerable interest for high‐performance electronic devices for their unique electronic properties and atomically thin geometry. 2D SnS₂ nanosheets with a bandgap of ≈2.6 eV have been attracting intensive attention as one potential candidate for modern electrocatalysis, electronic, and/or optoelectronic fields. However, the controllable growth of large‐size and high‐quality SnS₂ atomic layers still remains a challenge. Herein, a salt‐assisted chemical vapor deposition method is provided to synthesize atomic‐layer SnS₂ with a large crystal size up to 410 µm and good uniformity. Particularly, the as‐fabricated SnS₂ nanosheet‐based field‐effect transistors (FETs) show high mobility (2.58 cm² V^?1 s^?1) and high on/off ratio (≈10⁸), which is superior to other reported SnS₂‐based FETs. Additionally, the effects of temperature on the electrical properties are systematically investigated. It is shown that the scattering mechanism transforms from charged impurities scattering to electron–phonon scattering with the temperature. Moreover, SnS₂ can serve as an ideal material for energy storage and catalyst support. The high performance together with controllable growth of SnS₂ endow it with great potential for future applications in electrocatalysis, electronics, and optoelectronics.     

斜坡下浅埋偏压隧道地层响应的解析解答

针对斜坡下浅埋偏压隧道的开挖问题,考虑重力梯度作用,根据有限元模拟结果对现有解析偏压初始应力场进行修正,通过理论推导给出隧道开挖引发的地层响应解析解。求解采用复变函数法和Laurent级数解法,采用两种荷载释放方式建立隧道开挖边界的应力边界条件。结合地表边界条件求解得到完整的复位势表达,进而得到全域开挖增量应力和位移的理论解答。考虑到实际工程中隧道边界不存在不平衡力影响,采用洞心释放的理论解答分析了斜坡角度对隧道开挖后的地表位移和洞周应力、位移的影响。结果表明:随斜坡角度增大,偏压影响更加显著,地表位移整体向浅埋侧移动,浅埋侧隆起现象越加明显,地表最大沉降量减小,沉降槽整体向深埋侧移动。环向全应力在90°和270°区域出现拉应力极值,并随偏压角度增加向顺时针方向移动。研究成果对浅埋偏压隧道的初步设计具有参考价值。     

砂埋管道上浮地基破坏机理的离散元模拟

本文采用离散单元法(DEM)建立的砂土中管道上浮模型来研究管道上浮时地基的破坏机理。首先考察不同密实度砂土在不同围压下的宏观力学特性,然后通过土体局部变形和颗粒位移场等微观变量分析不同密实度和不同埋深比对管道上浮地基破坏模式和上浮抗力的影响。结果表明:伴随土体变形,上覆土体的渐进破坏主要分布在上覆土体区域和管道周围;松砂中,与应力-应变关系类似,上浮抗力随着上浮位移的增长呈硬化性增长,管道周围土体回填进管道下部形成的空隙中,呈现局部流动破坏模式;密砂中,上浮抗力随着上浮位移的增加先上升后下降,规律与应变软化一致,管道上方先剪切形成倒梯形的上覆土楔,然后管道周围土体回填下部空隙形成流动,呈现先整体剪切破坏后局部流动的破坏模式;随着埋深的增加,上浮抗力增加,密砂中以先整体剪切破坏为主,同时局部流动破坏有明显的趋势。