structures of various macerals,the h

rinite needs high thermal energy to produce major gas hydrocarbons.The pyrolysis of exinite could effectively produce hydrocarbons.It is considered as a good hydrocarbon source.Although hydrocarbons could be limitedly generated through the pyrolysis of inertinite,they are relatively stable and poorly affected by the thermal degradation.Thus,th     

Contents and Abstracts of Journal of Mechanical Engineering,Vol.46,No.1～4,2010

<正>Structural Design and Hydrodynamics Analysis of a Self-reconfigurable Propeller1 DING Xilun1 WANG Zhengrong1, 2 ZHANG Wuxiang1 (1. Robotics Institute, Beihang University, Beijing 100083, China; 2. Navy Logistic Technology and Equipment Institute of PLA, Beijing 100072, China)     

Studies of the growth, evolution, and self-aggregation of β-amyloid fibrils using tapping-mode atomic force microscopy

Amyloid peptide (Aβ) is the major protein component of plaques found in Alzheimer's disease, and the aggregation of Aβ into oligomeric and fibrillic assemblies has been shown to be an early event of the disease pathway. Visualization of the progressive evolution of nanoscale changes in the morphology of Aβ oligomeric assemblies and amyloid fibrils has been accomplished ex situ using atomic force microscopy (AFM) in ambient conditions. In this report, the size and the shape of amyloid β(1-40) fibrils, as well as the secondary organization into aggregate structures were monitored at different intervals over a period of 5 months. Characterizations with tapping-mode AFM serve to minimize the strong adhesive forces between the probe and the sample to prevent damage or displacement of fragile fibrils. The early stages of Aβ growth showed a predominance of spherical seed structures, oligomeric assemblies, and protofibrils; however the size and density of fibrils progressively increased with time. Within a few days of incubation, linear assemblies and fibrils became apparent. Over extended time scales of up to 5 months, the fibrils formed dense ensembles spanning lengths of several microns, which exhibit interesting changes due to self-organization of the fibrils into bundles or tangles. Detailed characterization of the Aβ assembly process at the nanoscale will help elucidate the role of Aβ in the pathology of Alzheimer's disease.     

The biomechanics of plate fixation of periprosthetic femoral fractures near the tip of a total hip implant: cables, screws, or both?

Femoral shaft fractures after total hip arthroplasty (THA) remain a serious problem, since there is no optimal surgical repair method. Virtually all studies that examined surgical repair methods have done so clinically or experimentally. The present study assessed injury patterns computationally by developing three-dimensional (3D) finite element (FE) models that were validated experimentally. The investigation evaluated three different constructs for the fixation of Vancouver B1 periprosthetic femoral shaft fractures following THA. Experimentally, three bone plate repair methods were applied to a synthetic femur with a 5 mm fracture gap near the tip of a total hip implant. Repair methods were identical distal to the fracture gap, but used cables only (construct A), screws only (construct B), or cables plus screws (construct C) proximal to the fracture gap. Specimens were oriented in 15 degrees adduction to simulate the single-legged stance phase of walking, subjected to 1000 N of axial force, and instrumented with strain gauges. Computationally, a linearly elastic and isotropic 3D FE model was developed to mimic experiments. Results showed excellent agreement between experimental and FE strains, yielding a Pearson linearity coefficient, R2, of 0.92 and a slope for the line of best data fit of 1.06. FE-computed axial stiffnesses were 768 N/mm (construct A), 1023 N/mm (construct B), and 1102 N/mm (construct C). FE surfaces stress maps for cortical bone showed Von Mises stresses, excluding peaks, of 0-8 MPa (construct A), 0-15 MPa (construct B), and 0-20 MPa (construct C). Cables absorbed the majority of load, followed by the plates and then the screws. Construct A yielded peak stress at one of the empty holes in the plate. Constructs B and C had similar bone stress patterns, and can achieve optimal fixation.     

First-principles calculation of electronic properties of N-and X(X=S,Se,Te)-codoped anatase TiO2

本文运用密度泛函理论系统地研究了N和X(X=S,Se,Te)共掺杂锐钛矿TiO2时电子特性所受的影响。优化后的结构表明,在锐钛矿TiO2共掺杂时,由于掺杂原子有较大的原子半径而引起了大的晶格膨胀。从计算的替换能结果看,当X(X=S,Se,Te)掺杂到有N原子存在的TiO2时,若替换Ti原子,则不能很好地促进与N的协同作用,若替换O原子,则相反。从总态密度图和分态密度图来看,替换O原子后的N2p轨道和其他杂质带S 3p,Se 4p,Te 5p杂化在一起;同时替换Ti原子后,导带主要由Ti 3d轨道所占据,从而形成了S 3p(Se 4p or Te 5p)-N2p-Ti 3d杂化态。从Bader电荷的结果可知,替换O原子,电子转移是由N到X(X=S,Se,Te),而替换Ti原子后,电子转移是由X(X=S,Se,Te)到N。     

The Study of Arc Rate,Friction, and Wear Performance of C/C Composites in Pantograph–Catenary System

A series of tests on arc rate, friction coefficient, and wear rate of electrical current collectors sliding against overhead contact wires under different conditions was carried out on a high-speed friction and wear testing machine with a pin-on-disc configuration. The worn surface morphology and composition were examined using a scanning electron microscope and energy dispersion spectrum analyzer, respectively. The effects of current, velocity, and load on the arc rate, friction coefficient, and wear rate of C/C composites/QCr0.5 couples were investigated, and the influence mechanism of test parameters on C/C composites was explained. It is concluded that the wear rate increases with an increase in current and velocity and has a decreasing trend with the increase in load. The friction coefficient increases with an increase in velocity and load. The arc rate of C/C composites/QCr0.5 couples increases with an increase in current and velocity. Under the condition of the same current and velocity, when the load is 70 N, the arc rate is the lowest.     

Coordinate Control,Motion Optimization and Sea Experiment of a Fleet of Petrel-Ⅱ Gliders

The formation of hybrid underwater gliders has advantages in sustained ocean observation with high resolution and more adaptation for complicated ocean tasks. However, the current work mostly focused on the traditional gliders and AUVs.The research on control strategy and energy consumption minimization for the hybrid gliders is necessary both in methodology and experiment. A multi-layer coordinate control strategy is developed for the fleet of hybrid underwater gliders to control the gliders' motion and formation geometry with optimized energy consumption. The inner layer integrated in the onboard controller and the outer layer integrated in the ground control center or the deck controller are designed. A coordinate control model is proposed based on multibody theory through adoption of artificial potential fields. Considering the existence of ocean flow, a hybrid motion energy consumption model is constructed and an optimization method is designed to obtain the heading angle, net buoyancy, gliding angle and the rotate speed of screw propeller to minimize the motion energy with consideration of the ocean flow. The feasibility of the coordinate control system and motion optimization method has been verified both by simulation and sea trials. Simulation results show the regularity of energy consumption with the control variables. The fleet of three Petrel-Ⅱ gliders developed by Tianjin University is deployed in the South China Sea. The trajectory error of each glider is less than 2.5 km, the formation shape error between each glider is less than 2 km, and the difference between actual energy consumption and the simulated energy consumption is less than 24% actual energy. The results of simulation and the sea trial prove the feasibility of the proposed coordinate control strategy and energy optimization method. In conclusion, a coordinate control system and a motion optimization method is studied, which can be used for reference in theoretical research and practical fleet operation for both the traditional gliders and hybrid gliders.     

Chemical Assessment of Bottled Drinking Waters by IC,GC, and ICP‐MS

Abstract

Bottled water brands, consisting of both local and imported types, collected from Doha city, Qatar, were evaluated for their suitability for human consumption. Water quality constituents that were analyzed include trihalomethanes (THM) by GC‐ECD, turbidity, TDS, total hardness, total alkalinity, pH, EC, major anions by IC, and major cations and trace metals by ICP‐MS. The data obtained were compared with the WHO and the USEPA drinking water standards. As, Se, Ba, and Cu were undetected in all water samples. The levels of potential toxic metals in the studied brands were generally low, except for three brands that had Cd and Pb which exceeded the WHO limits. Fluoride was generally present in all bottled water brands at levels less than the lower optimum level. The reported data for pH, turbidity, TDS, EC, alkalinity, hardness, major anions, and major cations were generally in compliance with the WHO and the USEPA standards, with exception of five brands, where the levels of TDS, EC, F, and NO₃ exceeded the WHO recommended limits. Also, it was found that the concentrations of NO₃ F, Fe, Cr, Zn, and Pb were higher in the local brands. The levels of Cd, Mn, Ca, Mg, EC, alkalinity, SO₄, TDS, THM, and hardness were higher in the domestic brands, when compared to the imported ones. The levels of Cl, pH, turbidity, and Na in the domestic brands were comparable to imported ones. Three THM were found in 29% of water samples with three brands having CHCl₂Br and CHCl₃ levels exceeding the WHO standards.

Comparison of the results of this study with the reported label values of both domestic and imported bottled water showed good agreement with pH and K values, but significant variation for Ca, Mg, F, NO₃, and SO₄ in the imported brands and relatively low variation in the domestic brands. The results of chemical analysis of SRM 1460, trace elements in water, were generally in good agreement with NIST certified values.     

Reconfigurations of manufacturing systems—an empirical study on concepts, research, and applications

It is well known that the performance of a manufacturing system is susceptible to sudden changes in demand, either in terms of the quantity of products concerned or the product mix. Traditional manufacturing managers have been dealing with such situations by resorting to outsourcing of products; employing additional resources in terms of overtime, extra shifts, etc.; and adopting back logging policies using the goodwill of customers or making use of effective scheduling and inventory policies. However, in the recent times, they are also presented with the option of reconfiguring the manufacturing system (RMS), which offers a number of benefits. There are several keys enabling technologies to realize these benefits. The review of related literature helped in realizing that there are a number of alternative ways of resorting to reconfiguration. In this paper, the views and experiences of various researchers and practitioners as reported in literature are presented in an encapsulated manner bringing forth the multidimensional aspects of the subject area RMS. From various accounts reported in the international and Indian media, it is evident that the Indian manufacturing sector is performing well and is trying out various innovative practices; interestingly, many of which are related to RMS. A survey of Indian industries was carried out with the help of a survey using questionnaire as an instrument. The survey revealed various interesting facts about various RMS practices followed by the Indian manufacturing sector and the impact of reconfiguration on various performance measures of these organizations. The details of the survey and the findings of the same are also presented in this paper.     

Development of Image Reconstruction Algorithms for Few-View Computed Tomography at RFNC–VNIITF: History,State of the Art,and Prospects

Russian Journal of Nondestructive Testing - In the last 20 yr, RFNC–VNIITF has developed a linear-induction-accelerator-based radiography complex capable of reconstructing the 3D inner...     

Surface morphology of Diplodon expansus (Küster, 1856; Mollusca, Bivalvia, Hyriidae) gill filaments after exposure to environmentally relevant concentrations of atrazine herbicide

Brazilian endemic species Diplodon expansus (Küster, 1856) is found in freshwater bodies in the country's southeast, in large anthropogenic influence regions especially with an extensive agriculture emphasis. One of the main pesticides used in the species occurrence region is the atrazine herbicide, which has a great contamination potential in the aquatic environment. Therefore, several studies into its toxicity in aquatic systems have been developed. However, the tested concentrations are usually very high and rarely found in the environment and the short-term exposure responses in other aquatic organisms such as native bivalves are still scarce. Thus, this study sought to consider the potential effects of environmentally realistic concentrations of atrazine herbicide on the surface morphology of gill filaments of the bivalve D. expansus under laboratory-controlled conditions after short-term exposure. None of the animals died before the end of the experiment. The main alterations were observed on the frontal surface of filaments, which include mucus accumulation, cilia loss, and disruption. Mucus increased secretion and accumulation in the frontal filaments region preceded as a protective mechanism. Cilia loss and disruption on the frontal surface of the gill filament indicated that ciliated frontal cells were more sensitive to atrazine exposure and these alterations may cause gills functional damages, compromising the uptake of food particles and respiration. Therefore, higher sublethal concentrations of atrazine may compromise the survival and consequently the population of D. expansus in agriculture areas after a longer period of continuous exposure.     

On the Possibility of Experimental Study of Rare η-, ω-, and η"-Meson Decays with the U-70 Accelerator

We consider potential experiments at the U-70 accelerator (Institute for High Energy Physics, Protvino) on the search and study of rare neutral -, -, and "-meson decays that are critical for the modern theory, at a qualitatively new level of statistical accuracy. A special setup with the use of meson tagging and electromagnetic calorimetry on PbWO₄crystals is offered for this experiment. The neural net approach was invoked at the stage of data processing. The Monte Carlo simulation of the experiment demonstrated its high sensitivity to rare-decay detection, which far exceeds the existing world results.     

Optimization of thrust force, torque, and tool wear in drilling of coir fiber-reinforced composites using Nelder–Mead and genetic algorithm methods

Machining of composite materials is an important and current topic in modern researches on manufacturing processes. Determination of optimal cutting parameters is one of the most important elements in the machinability study of composites. Optimization has significant practical importance particularly for operating the machineries. In order to increase the accuracy of drill holes, the tool must be in good condition always as much as possible. To achieve good condition of tool, the optimization of machining parameters like drill bit diameter, spindle speed, and feed rate are mandatory. The objective of this paper is to study the effect of these process parameters on thrust force, torque, and tool wear in drilling of coir fiber-reinforced composites. The optimal settings of the parameters were determined through experiments planned, conducted, and analyzed using the Box–Behnken design, Nelder–Mead, and genetic algorithm methods. This paper also aimed to increase the cutting condition of tool, i.e., minimization of tool wear by applying the optimized input parameters using Nelder–Mead and genetic algorithm techniques.     

Dynamic performance of a cable with an inspection robot — analysis, simulation, and experiments

A special cable inspection robot is designed to inspect automatically the cables of a cable-stayed bridge. The free vibration equation of the cable-robot system is derived firstly to study the dynamic characteristics and safety performance of the system. Then, the effect of the robot on the cable natural frequency is discussed, and the dynamic response equation when a robot is climbing at a constant speed is deduced. Furthermore, the effect of the cable vibration on the robot’s climbing ability is studied. The natural frequency characteristics of the robot are analyzed and optimized to avoid the resonance between the cable and the robot, using a finite element model. Additionally, dynamic cable responses are simulated under different conditions wherein the robot mass are 10 and 200 kg, and the speeds are 0.2 and 0.3 m/s, respectively. At last, to demonstrate further the dynamic characteristics of the cable-robot system experimentally, cables are set up on the Junshan highway bridge over the Yangtze river. Similar experimental models of these cables are constructed, and vibration experiments are conducted to validate the theoretical calculation. The results show that a light robot has little effects on the cable vibration amplitude and vibration acceleration; this confirms the safety of the cable.