边坡勘察若干重要问题——《工程地质勘察规范》(DBJ50-043-2005)讲座之二

引言重庆市的工程建设经常遇到边坡问题,边坡勘察是工程地质勘察的重要内容。重庆市工程建设标准《工程地质勘察规范》(DBJ50-043-2005)(以下简称本标准)用专章对边坡勘察进行了规定,在多个方面对原标准《工程地质勘察规范》(DB50/5005-1998)作了调整。为帮助勘察工程师更好地理解本标准关于边坡勘察的规定,本文对编制岩质边坡岩体分类、边坡强度参数、边坡坡率允许值和斜坡勘察等方面规定的背景和思路进行介绍。1岩质边坡的岩体分类1.1分类的修改情况本标准修订的岩质边坡的岩体分类方案见表1。边坡岩体分类是岩质边坡勘察中非常重要的内…     

Surface plasma resonance spectra of Au nanoparticles formed from dewetted thin films

We investigated surface plasma resonance (SPR) properties of gold (Au) nanoparticles formed by step-by-step thermal annealing of Au films deposited onto substrates. We found that the averaged sizes of the Au particles formed in the annealing process depend on the initial thicknesses of the films. Using the geometric parameters extracted from the images of Au particles, the optical transmission spectra measured can be completely described in terms of SPR in the particles. The results suggest that annealing of Au films can be a simple and effective approach for producing Au nanoparticles with desired optical transmission properties, and the approach can be easily integrated into thin film fabrication processes.     

露地土壤-芹菜体系噻虫嗪及其代谢产物噻虫胺残留与消长规律研究

目的 探明露地土壤-芹菜体系噻虫嗪及其代谢产物噻虫胺的残留与消长规律。方法 在河北张家口开展露地芹菜噻虫嗪、噻虫胺的最终残留和消解动态试验,样品通过10 mL乙腈提取,提取溶液经50 mg N-丙基乙二胺和3 mg多壁碳纳米管净化后,采用气相色谱-串联三重四极杆质谱法在质谱多反应监测模式下检测噻虫嗪和噻虫胺的残留量。结果 噻虫嗪和噻虫胺在芹菜上的回收率范围分别为 80.7%~90.5%、76.1%~103.0%;在土壤上分别为74.0%~96.4%、84.9%~86.7%,最终残留实验中,用药后第10 d噻虫嗪在芹菜残留量为0.188 mg/kg,低于国家规定的最大残留限量(maximum residue limit, MRL),噻虫胺为0.112 mg/ kg,超出其MRL值。噻虫嗪在芹菜上的消解动力学方程为C=2.7244 e-0.246 t,r2为0.9094,半衰期为2.82 d。噻虫嗪在土壤中沉积量呈现先上升再下降趋势,峰值为0.33 mg/kg;噻虫胺在土壤中未见明显趋势。结论 噻虫嗪在芹菜上施用后的残留风险较低,但其代谢产物噻虫胺有残留风险。噻虫嗪与噻虫胺施用对土壤环境影响较小。     

From nanorings to nanodots by patterning with block copolymers

We demonstrate three different transfer patterns that can be achieved by use of a surface reconstructed block copolymer film where metal is evaporated onto the surface of the film, providing the contrast. Thin films of diblock copolymers having cylindrical microdomains oriented normal to the surface with long-range lateral order were used. Solvent reconstruction of the film, followed by a glancing angle metal evaporation and thermal annealing, led to three different decorations of the films with gold. These films were used as masks for pattern transfer of pores, columns, and rings to underlying substrate with high fidelity.     

机车车轮轮缘探伤方法及定量标准的探讨

针对机车车轮轮缘形状的特殊性,对机车车轮轮缘部位的探伤方法进行了探索,研制了轮缘周向缺陷及纵向缺陷探伤对比试块,研制了相应的WM2R型双晶纵波探头和双晶双向扫查横波斜探头;利用数字式超声波探伤仪制作波幅-当量曲线,提出了确定轮缘缺陷当量方法,在应用实践中得到了验证。     

Suppression of radiative decay of CdTe quantum dots in a photonic crystal with a pseudogap

Abstract

Observation-angle dependence of the spontaneous emission life-time of CdTe quantum dots (QDs) embedded in a pseudogap photonic crystal (PC) film has been demonstrated. Comparison of two PC films with different photonic band-gaps (PBGs) differentiates the PBG effect from the electronic and/or chemical interactions between CdTe QDs and the host medium. This lifetime modification of QDs by a PC with pseudogap can be very useful in applications for optoelectronic devices such as QD lasers and QD switches.     

Active-clamp ZVS converter with step-up voltage conversion ratio

This article presents the circuit implementation and design considerations of a zero voltage switching (ZVS) converter with voltage step-up for battery-based applications. An active-clamp circuit including one auxiliary switch and one clamp capacitor is connected in parallel with the main switch to allow resonant behaviour by the output capacitances of switches and transformer leakage inductance during the transition interval. Thus, the ZVS turn-on of switches can be achieved. The switching losses and thermal stresses of the semiconductors are reduced. The circuit configuration, operation principle and design considerations of the converter are discussed in detail. Finally, experiments conducted on a laboratory prototype rated at 200 W are provided to verify the theoretical analysis and the effectiveness of the proposed converter.     

Synthesis, Crystal Structure and Properties of a New 3D Supramolecular Metal–Organic Framework with Stable Tunnels

A flexible polycarboxyl ligand of tetrahydrofuran-2,3,4,5-tetracarboxylic acid (H₄THFTCA) and a common rigid aromatic ligand of 1,10-phenanthroline (phen) have been successfully co-assembled with Cu(NO₃)₂·3H₂O to give out a novel 3D supramolecular metal–organic framework (MOF) compound, [Cu₂(THFTCA)(phen)(H₂O)₂·CH₃CH₂OH·3H₂O] _n (1), by a solution self-assembly process. Compound 1 has been characterized as a 2D layered coordination polymer constructed by THFTCA^4? and Cu²⁺ ions, and the layer present a novel (3.5²)(3².5³.6⁴.7) topological network. Interestingly, the layers are fused each other via strong π–π stacking interactions among adjacent ligands of the terminal phen, so that a 3D supramolecular MOF with 1D rhomboidal tunnels array is formed. The thermogravimetric analysis and corresponding powder X-ray diffraction analysis have revealed that the tunnels structure of 1 could be retained after all guest molecules are removed, and the framework could resist the collapse even heating up to 210?°C. An opinion has also been proposed that the larger accessible volume of the guests means the larger stress on the backbone of the MOF after the guests are removed, and the stress is harmful to the stability of the supramolecular porous structure. Finally, the application properties based on the porous structure have also been primarily evaluated.     

正极材料LiFePO4/C掺杂改性的研究进展

LiFePO₄/C具有高温稳定性好、价格低廉、循环性能良好、环保等性能,是一种具有发展潜力的锂离子动力电池正极材料之一,因此在锂离子电池行业备受关注。但由于其电子电导率低以及锂离子扩散速率慢等缺点制约其发展。介绍了磷酸铁锂的结构、性能、充放电原理和掺杂机理,尤其对近年来LiFePO₄/C材料的掺杂改性研究进行了综述。