工程机械液压油缸的泄漏及防治

主要介绍液压系统的主要执行元件--液压油缸泄漏的方式以及应采用的防治对策.     

Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result. Project supported by the National Natural Science Foundation of China (No. 59835160) and Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (No. 50175097)     

成人教育应引入市场营销观念

目前我国的市场经济对人才的需求产生了多样化的特点 ,教育特别是成人教育为了适应市场需求 ,必须进行产业化调整。成人教育作为非义务教育应为发展经济服务 ,把成人教育办成像企业一样 ,按照市场营销规律去运行 ,这是一个值得探讨的问题。     

“管理经济学之父”拉泽尔谈人力资源

爱德华·拉泽尔是美国国家科学院院士,评估委员会成员;美国人文科学院院士;《劳动经济学杂志》创刊人和首任主编;美国劳动经济学会前会长(1998);美国政府雇员工资管理委员会咨询顾问。拉泽尔还担任过罗马尼亚、俄罗斯、乌克兰和格鲁吉亚等国家的经济改革顾问。拉泽尔在国际经济管理理论领域和经济政策领域都有着极大的影响力。他撰写的《人事管理经济学》一书,以10多种语言出版,畅销世界,影响深远,成为经典教材流行于一流商学院的核心课程之中,被公认为是人力资源管理学科的开山鼻祖,在西方学界被誉为"管理经济学之父"。     

清代康乾盛世以前滦河流域文明的五次高潮

滦河流域文明曾经有着比较深厚的文化积淀和丰富的内容,在历史上曾多次出现高潮,作者仅就清代康乾盛世以前的五次高潮做概述和简评。     

浅议利益相关者管理

利益相关者管理是现代企业管理和公司治理理论的核心内容之一，本文阐述了利益相关者的概念和分类。利益相关者管理产生的基础、发展进程和基本原则，并对企业如何开展利益相关者管理提出了建议。     

科学发展观的政治哲学解读

从政治哲学角度审视科学发展观的理论成因及其实践应用,可以切实地把握以人为本的政治意蕴、和谐社会的政治前提以及人与自然和谐发展的政治基础,继而确立人的自由与全面发展的政治根据。科学发展观在审视人类社会发展的经验与教训的基础上,深刻阐述了人、自然与社会的内在关联,其对人类生存境遇的深切关怀体现为对政治文明生成的有力支撑。在构建以人为本的和谐社会的当今时代,秉持科学发展观的政治哲学精神,对解决社会发展进程中出现的问题具有不可或缺的方法论意义。     

学生选择会计专业的影响因素研究综述

随着人工智能的发展以及财会软件的不断完善,会计专业学生就业形势日益严峻,但与此相对的却又是高层次会计专业人才紧缺数百万的困境.论文通过对国内外主要教育类期刊有关学生选择会计专业的文献进行整理分析,发现学生选择会计专业时受他人、个性特质、专业认知、就业情况等因素的影响,并据此提出了未来的研究方向.     

Tandem Biocatalysis by CotA-TJ102@UIO-66-NH2 and Novozym 435 for Highly Selective Transformation of HMF into FDCA

2,5-Furandicarboxylic acid(FDCA) is a potential biorenewable chemical for applications including plastics, polyamides, drugs, etc. The selective biosynthesis of FDCA from 5-hydroxymethylfurfural(HMF) by a specific enzyme poses a great challenge. In this study, we reported an efficient strategy to produce FDCA from HMF by the tandem biocatalysis of laccase(Cot A-TJ102@UIO-66-NH_2) and Novozym 435. For the first step, a nanoparticle metal–organic framework was synthesized as a carrier to immobilize Cot A-TJ102@UIO-66-NH_2, which was assigned for the production of 5-formyl-2-furancarboxylic acid(FFCA) and featured an enzyme loading of 255.54 mg/g, specific activity of 135.90 U/mg, and solid loading ratio of 99.65%. Under optimal conditions, an ideal FFCA yield of 98.5% was achieved, and the Cot A-TJ102@UIO-66-NH_2 presented a high recycling capacity after 10 cycles. For the second step, Novozym 435 was applied for the further conversion of FFCA into FDCA, presenting a high FDCA yield of 95.5% under the optimized conditions. Novozym 435 also exhibited a high recyclability after eight cycles. As a result, the tandem biocatalysis strategy provided a 94.2% FDCA yield from HMF, indicating its excellence as a method for FDCA production.     

职业教育发展的市场调节与政府干预

近来,有关政府与市场的关系问题一直是国家发展领域颇有争议的话题.本文通过分析市场经济条件下职业教育市场机制和政府干预各自的局限性,探讨新形势下我国职业教育发展的动力机制.