Synthesis,structural and optical properties of CdS nanoparticles with enhanced photocatalytic activities by photodegradation of organic dye molecules

CdS nanoparticles (NPs) were synthesized using co-precipitation method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to confirm the structures and morphologies of CdS NPs. X-ray diffraction data confirmed the crystal structure of the CdS NPs. Raman spectrum exhibited the Raman modes of LO and 2LO of CdS at 290 and 595 cm^?1 respectively. The evaluated band gap was 3.15 eV, this value was shifted compared with the bulk value and this could be a significance of a size quantization effect in the sample. The CdS nanoparticles showed higher photocatalytic activity for the discoloration of methyl orange (MO) under UV light irradiation for 90 min. The highest photocatalytic activity was obtained with the sample containing 0.3 wt % CdS nanoparticles, in which more than 98 % of the MO was discolored within 90 min.     

Information hiding in product development: the design churn effect

Execution of a complex product development project is facilitated through its decomposition into an interrelated set of localized development tasks. When a local task is completed, its output is integrated through an iterative cycle of system-wide integration activities. Integration is often accompanied by inadvertent information hiding due to the asynchronous information exchanges. We show that information hiding leads to persistent recurrence of problems (termed the design churn effect) such that progress oscillates between being on schedule and falling behind. The oscillatory nature of the PD process confounds progress measurement and makes it difficult to judge whether the project is on schedule or slipping. We develop a dynamic model of work transformation to derive conditions under which churn is observed as an unintended consequence of information hiding due to local and system task decomposition. We illustrate these conditions with a case example from an automotive development project and discuss strategies to mitigate design churn.

高能气体压裂技术在油田的应用

阐述高能气体压裂的作用机理和特点,并通过在油田的应用总结出现场施工工艺、应用效果和适用范围,为该技术的推广应用提供借鉴.     

Arc-evaporated CrN, CrN and CrCN coatings

The results of investigations of some tribological properties of chromium nitride, carbonitride and carbide films, prepared by cathodic arc-evaporation method (CAE) are presented in this article. The chemical composition of films was determined by the WDXs and EDXs. The different carbon content was obtained by using nitrogen and acetylene mixtures of various concentrations as the deposition atmosphere. The carbon content was ranging from 0 to 53 at.%. The adhesion of CrCN films was estimated from the analysis of scratch-test results comprising tangential (friction) force, acoustic emission and morphology of scratch surface. The films showed very good adhesion to steel substrates, expressed by L_c (critical load) value, as high as 90 N for carbon free films. The L_c decreased slightly as the carbon content increased. The hardness of films was investigated as a function of carbon content and was estimated by Jönsson-Hogmark method. The L_c value and hardness seem to be correlated in the same way with carbon content. The highest hardness (30 GPa) was obtained for CrN films, while carbon rich films (CrC) showed hardness at the level of 20 GPa. The tribological tests were performed in the ball-on-disk geometry in room air under the load of 1 N and 10 N. The wear rate of investigated films increased with carbon content above 20 at.%. The maximum value of the friction coefficient was 0.55, the same as for CrN films. It decreased to 0.33 as the carbon content increased.     

Hydroxyapatite-anatase-carbon nanotube nanocomposite coatings fabricated by electrophoretic codeposition for biomedical applications

In order to eliminate micro-cracks in the monolithic hydroxyapatite (HA) and composite hydroxyapatite/carbon nanotube (HA/CNT) coatings, novel HA/TiO₂/CNT nanocomposite coatings on Ti6Al4V were attempted to fabricate by a single-step electrophoretic codeposition process for biomedical applications. The electrophoretically deposited layers with difference contents of HA, TiO₂ (anatase) and CNT nanoparticles were sintered at 800°C for densification with thickness of about 7–10 μm. A dense and crack-free coating was achieved with constituents of 85 wt% HA, 10 wt% TiO₂ and 5 wt% CNT. Open-circuit potential measurements and cyclic potentiodynamic polarization tests were used to investigate the electrochemical corrosion behavior of the coatings in vitro conditions (Hanks’ solution at 37°C). The HA/TiO₂/CNT coatings possess higher corrosion resistance than that of the Ti6Al4V substrate as reflected by nobler open circuit potential and lower corrosion current density. In addition, the surface hardness and adhesion strength of the HA/TiO₂/CNT coatings are higher than that of the monolithic HA and HA/CNT coatings without compromising their apatite forming ability. The enhanced properties were attributed to the nanostructure of the coatings with the appropriate TiO₂ and CNT contents for eliminating micro-cracks and micro-pores.     

Effects of Reduced Gravity Conditions on Bubble Dispersion Characteristics in the Bubble Column

Bubble-liquid turbulent flow has an excellent heat and mass transfer behaviors than single gas or liquid flow. In order to analyze the effects of normal and reduced gravity on cold bubble-liquid two-phase turbulent flow in bubble column a second-order moment cold bubble-liquid two-phase turbulent model was developed to disclose the bubble dispersion characteristics. Under the reduced gravity condition, volume fraction caused by the decrease of buoyance force is larger than normal gravity level due to bigger bubble solid volume. In addition, bubble frequency is also decreased by in decrease of buoyance force. Normal and shear stresses have strongly anisotropic characteristics at every directions and have larger values under normal gravity than reduced gravity. The liquid turbulent kinetic energy has the two-peak bimodal distribution and weaker than bubble turbulent kinetic energy with one peak unimodal, which is caused by vigorous wake fluctuations. The correlation of fluctuation velocities between bubble and liquid has clearly anisotropic behaviors Under reduced gravity, the bubble motion has a little impact on liquid turbulent flow caused by slight buoyancy force, however, it will greatly reduce the liquid turbulent intensity due to energy cascade transport, which was transformed into bubbles or dissipated by interface friction. Bubble formation and detachment mechanisms affected by gravity conditions lead to the different levels of bubble dispersion distributions.     

多孔材料对轮胎空腔共振降噪机理的研究EI北大核心CSCD

轮胎空腔共振噪声对汽车NVH性能有决定性影响。为研究轮胎内部添加多孔材料的降噪机理,从轮胎力传递率出发,通过试验验证了轮胎力传递率与空腔噪声的一致性;建立了轮胎力传递率模型,并验证了模型的准确性;通过该模型研究了多孔材料对轮胎空腔共振噪声的降噪机理。结果表明:多孔材料对轮胎空腔共振降噪效果是耦合结构振动与声学降噪共同作用的结果,选择多孔材料时要综合考虑多孔材料的物理参数与声学参数,研究结果为改善汽车NVH性能和提高低噪声轮胎设计水平奠定理论基础和方法指导。     

Metallic Graphene Nanoribbons

Isolated graphene nanoribbons(GNRs)usually have energy gaps,which scale with their widths,owing to the lateral quantum confinement effect of GNRs.The absence of metallic GNRs limits their applications in device interconnects or being one-dimensional physics platform to research amazing properties based on metallicity.A recent study published in Science provided a novel method to produce metallic GNRs by inserting a symmetric superlattice into other semiconductive GNRs.This finding will broader the applications of GNRs both in nanoelectronics and fundamental science.     

An Indexing Method for Answering Queries on Moving Objects

We consider the problem of indexing a set of objects moving in d-dimensional spaces along linear trajectories. A simple external-memory indexing scheme is proposed to efficiently answer general range queries. The following are examples of the queries that can be answered by the proposed method: report all moving objects that will (i) pass between two given points within a specified time interval; (ii) become within a given distance from some or all of a given set of other moving objects. Our scheme is based on mapping the objects to a dual space, where queries about moving objects are transformed into polyhedral queries concerning their speeds and initial locations. We then present a simple method for answering such polyhedral queries, based on partitioning the space into disjoint regions and using a B+-tree to index the points in each region. By appropriately selecting the boundaries of each region, we guarantee an average search time that matches a known lower bound for the problem. Specifically, for a fixed d, if the coordinates of a given set of N points are statistically independent, the proposed technique answers polyhedral queries, on the average, in O((N/B)^1−1/d⋅(log _B N)^1/d+K/B) I/O's using O(N/B) space, where B is the block size, and K is the number of reported points. Our approach is novel in that, while it provides a theoretical upper bound on the average query time, it avoids the use of complicated data structures, making it an effective candidate for practical applications. The proposed index is also dynamic in the sense that it allows object insertion and deletion in an amortized update cost of log _B(N) I/O's. Experimental results are presented to show the superiority of the proposed index over other methods based on R-trees. recommend Ahmed Elmagarmid     

用于阵列流型快速测量的宽带方法

阵列流型是传声器阵列信号处理的重要参数,直接影响阵处理性能。阵列流型与传声器的一致性、阵列结构和使用环境等密切相关,已有方法按照频率和角度逐一完成测量,但耗时是密集频率宽带测量的突出问题。论文提出了一种传声器阵列流型宽带测量方法：通过分析宽带信号在离散傅里叶变换之后各频率数据的相关性,提出根据非相关性原则构造宽带测量源信号,并在数据处理中运用FFT算法,综合实现了阵列流型的快速测量。通过在半消声室内的实测证明了论文方法的高效性。方法具有重要的工程应用价值。