输电线路激光除冰技术试验分析及工程应用设计

为防止覆冰对输电线路的危害,从理论分析、模拟试验、工程应用设计等方面系统研究了输电线路激光除冰技术,分别得出了CO2、Nd:YAG激光除冰特性:1.5kW CO2激光融冰体速度约为728.5mm3/s,单位能耗为2.08J/mm3;Nd:YAG固体激光融冰效果稍高于CO2激光,突出优点在于其热应力除冰;激光除冰时瓷绝缘子安全阈值约20.5～54.4J/mm2,复合绝缘子远小于该值,导线安全阈值很高,几乎不会损伤。结果表明激光可用于输电线路除冰,具有热融冰效应和热应力效应,如结合机械除冰可大大提高除冰效率和效果。根据研究结果提出了其工程应用设计方案:工程化车载式激光除冰系统选用固体激光器,输出功率1～1.5kW,光斑直径15～20mm,发散角3mrad,作用距离为100～1000m,激光电源采用车载发电机,总功耗≤50kW。预计未来3～5a激光除冰速度将可提高3～4倍,激光除冰系统可向小型化、便携式方法发展。     

钢芯铝绝缘导线融冰传热数值分析

为消除电网覆冰灾害,对一种嵌入绝缘层的钢芯铝绞线结构进行了融冰研究,简要介绍了其在不断电情况下,利用线路运行电流实现在线融冰技术的原理。针对该导线结构,文章从传热学角度对其融冰物理过程进行了分析,建立了无重力条件下该导线融冰时的简易数学模型,推导了该导线达到融冰稳态时,导线各部分温度分布解析式,设计定制了嵌入绝缘层的钢芯铝绞线来进行融冰实验,实验结果验证了该导线融冰的有效性和可行性。     

黄河万家寨河段河冰冰厚遥感提取及年内变化特征分析

冰凌观测是防凌的前提,是冰凌研究的基础,因此全面准确的冰凌观测可为科学防凌提供可靠的依据。为此,以黄河万家寨库区河段为例,通过冰厚反演算法对其冰厚数据进行遥感反演,利用Lebedev模型对反演结果进行验证,并对结果进行年内变化特征分析。结果表明,卫星遥感反演结果与实测及模型验证结果接近,相关系数为0.8;冰厚演变总体呈成冰、流凌、初封、稳封、融冰、开河的生消演变过程。反演冰厚结果可为黄河内蒙段防凌减灾等实际工作提供参考依据。     

Superconductivity in heavily boron-doped silicon carbide

Abstract

The discoveries of superconductivity in heavily boron-doped diamond in 2004 and silicon in 2006 have renewed the interest in the superconducting state of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a metallic phase from which upon further doping superconductivity can emerge. Recently, we discovered superconductivity in a closely related system: heavily boron-doped silicon carbide. The sample used for that study consisted of cubic and hexagonal SiC phase fractions and hence this led to the question which of them participated in the superconductivity. Here we studied a hexagonal SiC sample, free from cubic SiC phase by means of x-ray diffraction, resistivity, and ac susceptibility.     

高温矿井用蓄冰球受控循环风降温技术的研究

随着矿井开采深度的增加和采掘机械化水平的不断提高,矿井高温热害问题越来越严重。为保障采矿工业持续健康发展,必须采取相应措施进行治理。文章就近年来国内外高温矿井降温技术发展的现状和趋势及井下循环风的利用方面进行了研究,提出了高温矿井用蓄冰球受控循环风降温技术。     

Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3

Abstract

The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr_1.261CoO₃ has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr_1.261CoO₃ is a composite crystal that consists of the [CoO₃] and [2Sr] subsystems. The [CoO₃] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO₆ polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO₃] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co–O bonds than the Oh sites: d_av. =2.039(4) Å (TP) and 1.895(3) Å (Oh). The averaged Co bond valences are Co^3.56(3)+ in the Oh sites and Co^2.45(3)+ in the TP sites, suggesting that a considerable amount of Co³⁺ ions are mixed with Co⁴⁺ions in the Oh sites and with Co²⁺ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S=0 low-spin state for Co³⁺(dε⁶), S=1/2 low-spin state for Co⁴⁺(dε⁵) and S=3/2 high-spin state for Co²⁺(dε⁵dγ²). The Weiss temperature, approximately 0.8 K, implies that Sr_1.261CoO₃ naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co³⁺ ions. These results suggest that the nonmagnetic Co³⁺ ions play an essential role in the magnetism of Sr_2γCoO₃ systems.     

Biomechanics of fibrous proteins of the extracellular matrix studied by Brillouin scattering

Brillouin light scattering (BLS) spectroscopy is a technique that is able to detect thermally excited phonons within a material. The speed of propagation of these phonons can be determined from the magnitude of the Brillouin frequency shift between incident and scattered light, thereby providing a measure of the mechanical properties of the material in the gigahertz range. The mechanical properties of the extracellular matrices of biological tissues and their constituent biopolymers are important for normal tissue function and disturbances in these properties are widely implicated in disease. BLS offers the prospect of measuring mechanical properties on a microscopic scale in living tissues, thereby providing insights into structure–function relationships under normal and pathological conditions. In this study, we investigated BLS in collagen and elastin—the fibrous proteins of the extracellular matrix (ECM). Measurements were made on type I collagen in rat tail tendon, type II collagen in articular cartilage and nuchal ligament elastin. The dependence of the BLS spectrum on fibre orientation was investigated in a backscattering geometry using a reflective substrate. Two peaks, a bulk mode arising from phonon propagation along a quasi-radial direction to the fibre axis and a mode parallel to the surface, depending on sample orientation relative to the fibre axis, could be distinguished. The latter peak was fitted to a model of wave propagation through a hexagonally symmetric elastic solid, and the five components of the elasticity tensor were combined to give axial and transverse Young''s, shear and bulk moduli of the fibres. These were 10.2, 8.3, 3.2 and 10.9 GPa, and 6.1, 5.3, 1.9 and 8 GPa for dehydrated type I collagen and elastin, respectively. The former values are close to those previously reported. A microfocused BLS approach was also applied providing selection of single fibres. The moduli of collagen and elastin are much higher than those measured at lower frequency using macroscopic strains, and the difference between them is much less. We therefore believe, like previous investigators, that molecular-scale viscoelastic effects are responsible for the frequency dependence of the fibre biomechanics. Combining BLS with larger-scale mechanical testing methods therefore should, in the future, provide a means of following the evolution of mechanical properties in the formation of the complex structures found in the ECM.     

Genesis of enhanced photoactivity of CdS/Nix nanocomposites for visible-light-driven splitting of water

A series of CdS/Ni_x nanocomposite photocatalysts, containing ca. 0.6–15 wt% Ni, were synthesized using a one-step hydrothermal method and characterized for their crystallographic, morphological, interfacial, and optical properties. Rietveld refinement of powder XRD data revealed the coexistence of wurtzite (hexagonal) and zinc blende (cubic) phases of CdS in ratios dependent on Ni content. Only a fraction of Ni existed as a secondary phase of NiS while the majority occupied the lattice positions of hexagonal CdS. Whereas up to 10-fold enhancement in H₂ evolution compared with pure CdS was observed for samples containing ∼1.5–4.5 wt% Ni, samples with smaller or larger Ni content displayed poor activity for visible-light-induced splitting of water in presence of sulfide–sulphite ions as sacrificial electron donors. In contrary to recent findings, our study reveals that the enhanced CdS photoactivity is not a result of charge transfer between p-type NiS and n-type CdS, Ni-induced visible-region absorbance, or the coating of CdS particles by non-photoactive NiS. Instead, the preparation-dependent hexagonal/cubic CdS phase boundaries and particle morphology may play a crucial role. Additionally, certain Ni-doping-induced sub-bandgap shallow energy levels contribute to charge carrier separation.     

Nano Sized Copper Selenide Thin Film Pre-Cursor by A Liquid Phase Chemical Growth Process

The deposition of copper selenide(CuSe)thin films was carried out using liquid phase chemical bath deposition process at the optimized growth parameters as:60℃deposition temperature,90 minutes deposition time,pH equal to 10.5±0.1 and 72±2 r/min speed of mechanical rotation.The as-grown deposits exhibited excellent uniformity and physical adherency with the substrate surface and are smooth and diffusely reflecting with colour changing from yellowish orange to dark chocolate during deposition.The layer is of the order of 300 nm thick.The EDS analysis technique gave film composition to be nearly stoichiometric(Cu=47.89%,Se=52.11%).An X-ray diffraction analysis showed CuSe to be polycrystalline hexagonal with a good match of d-values and intensities of reflections.The crystallite size is in the nanorange(50-60 nm).The as-deposited CuSe exhibited a high coefficient of absorption(α=105cm-1)with a direct optical band gap of 1.81 eV.Compared to other chalcogenides,CuSe films exhibit low resistance;room temperature electrical resistivity being 1.55×103?cm.The electrical conductivity decreased with increase in temperature up to 473 K;showing totally unusual behaviour from that of the semiconducting property.The thermo probe measurements showed n-type conduction of the samples.