单晶钽裂纹尖端的位错原位观察

本文利用原创双金属片技术,在透射电子显微镜中实现了对小尺寸单晶钽(Ta)拉伸变形的原位实验观察.由于裂纹尖端的塑性区具有与材料整体塑性变形类似的特征,因此本实验针对裂纹尖端处的位错行为进行了研究.实验发现随着裂纹的扩展,有大量呈弯曲或钩状的位错不断形核,并朝着位错弯曲的部分滑移.在进一步的拉伸应力作用下,位错的长直部分不断长大并使这些位错在裂纹尖端堆积.对裂纹尖端的原位高分辨图像观察,发现在单晶钽中有大量伯氏矢量b=1/2〈111〉型位错的形核和逃逸现象.因此,证明这些混合位错对BCC单晶钽的塑性变形有一定贡献,并首次给出了纳米尺度材料中位错堆积的实验证据.     

Modification of nano-eutectic structure and the relation on hydrogen storage properties: A novel Ti–V–Zr medium entropy alloy

TiV-based alloys present desirable hydrogen storage properties owing to the formation of Body-centered cubic (BCC) solid solutions. However, the nanostructure that helps hydrogen absorption and desorption is hard to be designed and prepared in these alloys. In this study, Ti₄₀Zr_60-xV_x (x = 20, 25, 30) alloys with hyperfine nano-eutectic structures of 50–500 nm in lamellar space are prepared, and the nano-eutectic structures can be refined by increasing Zr content. Ti₄₀Zr_60-xV_x alloy powder exhibits excellent activation and hydrogenation properties. The phase separation and nano-eutectic structure are formed due to the differences of atomic size in Ti₄₀Zr_60-xV_x alloys. The highest total hydrogenation capacity of 2.4 wt% is obtained within 10 min at 200 °C under 1 MPa H₂ by Ti₄₀V₃₅Zr₂₅ alloy, surpassing that of Ti₄₀Zr₄₀V₂₀ and Ti₄₀Zr₃₀V₃₀ alloys of 2.2 wt% in 20min. Based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, lower energy is required for the hydrogenation of Ti₄₀V₃₅Zr₂₅ alloy. Due to the formation of some stable hydrides, the Ti₄₀Zr_60-xV_x alloys show lower reversible hydrogenation capacities. The spinodal decomposition in Ti₄₀V₃₅Zr₂₅ alloy facilitates the formation of reticular eutectics, which provide high-density phase interfaces and produce “synergistic effect”. As a result, the hydrogenation kinetic and capacity are enhanced significantly.     

On inverse DEA model: The case of variable returns to scale

Lertworasirikul et al. (2011) proposed an inverse BCC model for the case of VRS. They used an MOLP model to assist them in the process of finding inputs. The proof of the main theorem contains considerable mistakes which invalidate the proof. Moreover, there are some ambiguities about the use of MOLP. The current article points out the drawbacks of Lertworasirikul et al. (2011) and then corrects the use of MOLP in a proposed inverse BCC model. This commentary continues with a revision of the aforementioned theorem with a valid proof. The proposed proof is entirely different from and simpler than Lertworasirikul et al’s. (2011). A numerical example illustrates the proposed models.     

基于测量不确定度的日电量估计方法

随着智能电网的发展,电力企业对关口日电量及基于关口日电量的各种统计数据的准确性要求不断提高,为保证电能计量系统日电量的正确性,快速定位错误数据,提出一种基于测量不确定度理论,使用优化算法来对日电量进行估计的方法。首先,介绍了测量不确定度理论及其在电力系统中的应用,分析其用于电力系统的估计辨识的优势;其次,在给出的直流电量潮流计算模型和测量不确定度理论基础上确定了日电量的估计思路;最后,给出基于测量不确定度的日电量的评价函数,从而建立了基于测量不确定度的电量优化估计模型,给出了使用细菌群体趋药性(bacterial colony chemotaxis,BCC)优化算法对日电量进行估计的步骤。通过IEEE39和IEEE118节点系统仿真算例验证了所提方法的有效性和可行性。     

Ba4(Nd0.85Bi0.15)28/3Ti18O54陶瓷低温化研究

采用复合添加BaCuO2-CuO和BaO-B2O3-SiO2助剂的方法,研究了Ba4(Nd0.85Bi0.15)28/3 Ti18O54陶瓷的低温烧结特性和微波介电性能.添加2.5wt?CuO2-CuO和5wt?O-B2O3-SiO2后Ba4(Nd0.85 Bi0.15)28/3 Ti18O54陶瓷在950℃烧结成瓷,气孔率为5.29%,介电常数ε为60.25,Q·f值为2577GHz(5.6GHz),频率温度系数τf为 25.1ppm/℃,可与Cu电极浆料低温共烧.     

Study of cyclic performance of V-Ti-Cr alloys employed for hydrogen compressor

The development of a suitable hydrogen compressor plays one of the key roles to realize the fuel cell vehicle as well as for many other stationary and mobile applications of hydrogen. V-Ti-Cr BCC alloys are considered as promising candidates for effective hydrogen storage. The cyclic durability of hydrogen absorption and desorption is very important for these alloys to be realized as practical options. In connection to this, two alloys of V-Ti-Cr, (1) V₄₀Ti_21.5Cr_38.5 and (2) V₂₀Ti₃₂Cr₄₈, were selected and their cyclic hydrogen absorption-desorption performance was evaluated up to 100 cycles for temperature and pressure ranges of 20–300 °C and 5–20 MPa, respectively. It has been found that the cyclic hydrogen storage capacity continuously decreased for one composition while it was stable after 10 cycles for another composition. This performance difference of the alloys was studied in terms of their structural and microscopic properties and the results are presented in this paper.     

The effect of a Ti-V-based BCC alloy as a catalyst on the hydrogen storage properties of MgH2

The effect of Ti_0.4Cr_0.15Mn_0.15V_0.3 (termed BCC due to the body centered cubic structure) alloy on the hydrogen storage properties of MgH₂ was investigated. It was found that the hydrogenated BCC alloy showed superior catalysis properties compared to the quenched and ingot samples. As an example, the 1 h milled MgH₂ + 20 wt.% hydrogenated BCC shows a peak temperature of dehydrogenation of about 294 °C. This is 16, 27 and 74 °C lower than those of MgH₂ ball milled with quenched BCC, ingot BCC and an uncatalysed MgH₂ sample, respectively. The hydrogenated BCC alloy is much easier to crush into small particles, and embed in MgH₂ aggregates as revealed by X-ray diffraction and scanning electron microscope results. The BCC not only increases the hydrogen atomic diffusivity in the bulk Mg but also promotes the dissociation and recombination of hydrogen. The activation energy, E_a, for the dehydrogenation of the MgH₂/hydrogenated BCC mixture was found to be 71.2 ± 5 kJ mol H₂⁻¹ using the Kissinger method. This represents a significant decrease compared to the pure MgH₂ (179.7 ± 5 kJ mol H₂⁻¹), suggesting that the catalytic effect of the BCC alloy significantly decreases the activation energy of MgH₂ for dehydrogenation by surface activation.     

基于大规模语料库的现代汉语动宾搭配知识库构建

汉语缺乏词形变化,语法信息需通过词语搭配关系获得,且在生活中词语通常在搭配中发挥交际作用。因此无论是在语言学本体,还是在自然语言处理的各项任务中,词语搭配知识都尤为重要。各种搭配中,动宾搭配能够反映句子轮廓,并在数量和多样性方面具有优势地位,故该文聚焦于构建现代汉语动宾搭配知识库,以期为自然语言处理提供基础知识,同时也为语言本体研究、语言教学等提供大量实例。该文首先从语言本体的角度出发,总结了动宾搭配的知识体系,并根据该体系制定相应形式化检索式140个,从BCC语料库中抽取动宾搭配知识,并对抽取结果进行了初步消歧,最终获得动宾搭配300万对,形成动宾搭配知识库。     

生物质复合型煤在热分析仪中的燃烧行为研究

通过热分析技术对以农作物秸杆、城市生活垃圾、林业加工废弃物等生物质和云南先锋褐煤为原料制得的生物质复合型煤的燃烧行为进行了实验研究 .结果表明 ,生物质复合型煤的燃烧过程大致可以分为四个阶段 ,即脱水干燥、挥发分的析出和燃烧、挥发分燃烧和焦炭表面燃烧并存的过渡阶段、焦炭的表面燃烧 ;且生物质复合型煤 ( BCC)具有着火温度低、燃尽率高等特点 .此外通过对热重 ( TG)、差示扫描量热 ( DSC)曲线的深入分析 ,对 BCC的有关燃烧动力学参数进行了研究     

Phytoplankton community succession shaping bacterioplankton community composition in Lake Taihu, China

PCR-denaturing gradient gel electrophoresis (DGGE) and canonical correspondence analysis (CCA) were used to explore the relationship between succession of phytoplankton community and temporal variation of bacterioplankton community composition (BCC) in the eutrophic Lake Taihu. Serious Microcystis bloom was observed in July-December 2008 and Bacillariophyta and Cryptophyta dominated in January-June 2009. BCC was characterized by DGGE of 16S rRNA gene with subsequent sequencing. The DGGE banding patterns revealed a remarkable seasonality which was closely related to phytoplankton community succession. Variation trend of Shannon-Wiener diversity index in bacterioplankton community was similar to that of phytoplankton community. CCA revealed that temperature and phytoplankton played key roles in structuring BCC. Sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in freshwater: Alphaproteobacteria, Betaproteobacteria, Bacteroidetes and Actinobacteria. The cluster STA2-30 (affiliated with Actinobacteria) was found almost across the sampling time at the two study sites. We observed that the family Flavobacteriaceae (affiliated with Bacteroidetes) tightly coupled to diatom bloom and the cluster ML-5-51.2 (affiliated with Actinobacteria) dominated the bacterioplankton communities during Microcystis bloom. These results were quite similar at the two sampling sites, indicating that BCC changes were not random but with fixed pattern. Our study showed insights into relationships between phytoplankton and bacterioplankton communities at species level, facilitating a better understanding of microbial loop and ecosystem functioning in the lake.