V型发动机两次判定可调气门法

指出在Ｖ型发动机两次判定可调气门的工作中易出现的错误，阐述采用简化工作循环图判定可调气门的方法，通过两个黄型例子，以加深对其理解和掌握。     

Corrosion resistance and antibacterial effects of hydroxyapatite coating induced by polyacrylic acid and gentamicin sulfate on magnesium alloy

Magnesium(Mg)alloys have attracted considerable research attention as potential biocompatible implant materials.However,the major barriers to the extended use of such medical devices are the possibility of high corrosion rate and implantassociated infections.To solve them,a novel polyacrylic acid(PAA)/gentamicin sulfate(GS)-hydroxyapatite(HAp)coating was synthesized by a one-step hydrothermal deposition method.Characteristics of functional coatings were investigated by SEM,FTIR and XRD.Corrosion properties of samples were evaluated by electrochemical and hydrogen evolution tests.Antibacterial activities of the coatings against Staphylococcus aureus(S.aureus)were measured by the plate-counting method.Results showed that the as-prepared HAp coating with dense and flawless morphologies could not only enhance the corrosion resistance of Mg alloys,but also improve the adhesion strength between the HAp coating and the substrate.In addition,the induction of the apatite coating during immersion confirmed the excellent mineralization ability of the HAp coating.Moreover,the obtained HAp coati ng possessed antibacterial properties and could prolong the release of GS.Thus,the PAA/GS-HAp coated Mg alloy could serve as a better candidate for biomedical applications with good anti-corrosion and antibacterial properties.     

In vitro corrosion of magnesium alloy AZ31 --- a synergetic influence of glucose and Tris

Biodegradable Mg alloys have generated great interest for biomedical applications. Accurate predictions of in vivo degradation of Mg alloys through cost-effective in vitro evaluations require the latter to be conducted in an environment close to that of physiological scenarios. However, the roles of glucose and buffering agents in regulating the in vitro degradation performance of Mg alloys has not been elucidated. Herein, degradation behavior of AZ31 alloy is investigated by hydrogen evolution measurements, pH monitoring and electrochemical tests. Results indicate that glucose plays a content-dependent role in degradation of AZ31 alloy in buffer-free saline solution. The presence of a low concentration of glucose, i.e. 1.0 g/L, decreases the corrosion rate of Mg alloy AZ31, whereas the presence of 2.0 and 3.0 g/L glucose accelerates the corrosion rate during long term immersion in saline solution. In terms of Tris-buffered saline solution, the addition of glucose increases pH value and promotes pitting corrosion or general corrosion of AZ31 alloy. This study provides a novel perspective to understand the bio-corrosion of Mg alloys in buffering agents and glucose containing solutions.     

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)₅/AZ31. Then, the (PAH/PSS)₅/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)₅/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)₅/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca₃(PO₄)₂ and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.     

黄土水工隧洞结构布置及其施工方法

根据黄土特性,讨论了黄土水工隧洞设计、布置和施工方法,通过工程实例阐明黄土水工隧洞设计中遇到的黄土不稳定性、湿陷及其接触带不均匀变形等问题,,也以工程实例进一步讨论了洞线布置、结构形式、衬砌材料、施工方法及工艺要求等。可供设计、施工人员参考。     

Supporting Product Family Design in a 3D CAD/PDM Integrated System

This paper addresses some key issues in supporting product family design in a 3 D CAD/ PDM integrated system and introduces the techniques developed or adopted in building the integrated system. The general architecture of a 3D CAD/PDM integrated system is organized as five tiers. Multi-agent technology is applied with a collaborative design environment. The rule-based product family architecture （ PFA ） and tabular layouts of article characteristics （TLAC） technique are applied to represent the knowledge for product families. They make the knowledge understandable, simplified and can be exchanged among heterogeneous information systems. A transparently concentric integrated mode is put forward to enable the heterogeneous processes to interact and communicate regardless of the language used to construct each process. With the mode, function calling and information exchanging among different processes are carried out via message translation/parse approach. Currently, the integrated system is implemented in the platform of Windows NT and 2000.     

Development of the zinc-air power battery on electric bicycles in China

Electric bikes powered by lead-acid batteries have developed very fast for several years in China. Because the inconvenience caused by the service performance and the inconsistency to the environmental protection policy of the lead-acid battery, the zinc-air power battery was proposed to solve the problem in this paper. The advantage and the feasibility of developing zinc-air power batteries in China have been illustrated in the paper. And, it is represented that development of electric bikes powered by the zinc-air power battery also can accelerate this kind of battery’s development in other electric vehicles, which is favorable to economic development and environmental protection.     

Fast valve power loss evaluation methodfor modular multi-level converter operatingat high-frequency

There is no common accepted way for calculating the valve power loss of modular multilevel converter (MMC). Valve power loss estimation based on analytical calculation is inaccurate to address the switching power loss and valve power loss estimation based on detailed electro-magnetic simulation is of low speed. To solve this problem, a method of valve power loss estimation based on the detailed equivalent simulation model of MMC is proposed. Results of valve power loss analysis of 201-level 500MW MMC operating at 50Hz~1000Hz are presented. It is seen that the valve power loss of a MMC increased by 12, 40 and 93 % under 200Hz, 500Hz and 1000Hz operating frequency. The article concludes that in a device with isolated inner AC system, MMC operating at higher frequency will be more competitive than typical 50Hz/60Hz MMC with moderate increase of operating power loss and significant reduction of the size of the AC components.     

桂林市环城水系水环境整治和通航工设计

桂林市抓住了山水名城的特征，从“水”字上做文章，对环城水系进行整治，兴建两江四湖工程，使漓江、桃花江的游船经船闸或升船机驶入中心城市的木龙湖、桂湖、榕湖和杉湖，更添山水城市独特景观。本文据作者1999－2001年在桂林参与该工程规划设计及工程实施，概要地阐述了两江四湖整治和通航设计中的主要问题，以有对环境景观的要求。这是水利工程服务城市环境的一项环境水利工程，也是新世纪水利工程的一项新课题。     

SnO-SnO2 modified two-dimensional MXene Ti3C2Tx for acetone gas sensor working at room temperature

Acetone,as widely used reagents in industry and laboratories,are extremely harmful to the human.So the detection of acetone gas concentrations and leaks in special environments at room temperature is essential.Herein,the nanocomposite combining SnO-SnO2 (p-n junction) and Ti3C2Tx MXene was successfully synthesized by a one-step hydrothermal method.Because of the existence of a small amount of oxygen during the hydrothermal conditions,part of the p-type SnO was oxidized to n-type SnO2,forming in-situ p-n junctions on the surface of SnO.The hamburger-like SnO-SnO2/Ti3C2Tx sensor exhibited improved acetone gas sensing response of 12.1 (Rg/Ra) at room temperature,which were nearly 11 and 4 times higher than those of pristine Ti3C2Tx and pristine SnO-SnO2,respectively.Moreover,it expressed a short recovery time (9 s) and outstanding reproducibility.Because of the different work functions,the Schottky barrier was formed between the SnO and the Ti3C2Tx nanosheets,acting as a hole accumulation layer (HALs) between Ti3C2Tx and tin oxides.Herein,the sensing mechanism based on the formation of hetero-junctions and high conductivity of the metallic phase of Ti3C2Tx MXene in SnO-SnO2/Ti3C2Tx sensors was discussed in detail.