铝-钢脉冲DE-GMAW与CMT熔钎焊热循环曲线测试与对比

介绍一种新的铝-钢异种金属焊接方法脉冲旁路耦合电弧MIG焊(pulsed DE-GMAW),将该方法应用于铝和镀锌钢板的焊接,得到成型良好的焊缝.采用接触式测量法测量pulsed DE-GMAW法在不同焊接参数下的热循环曲线,并与CMT进行对比分析,结果表明:CMT法通过推拉丝及短路波形控制能减小焊接过程中的热输入;而pulsed DE-GMAW法通过增加旁路电流达到分流的目的,也可以降低输入母材的热量,2种方法的热输入控制效果相当,均能较好实现铝-钢异种金属的焊接.     

Research on CO2 welding inverter power source under fuzzy PI current waveform control

CO2气体保护焊中影响飞溅和焊缝成形的直接因素是焊接电流.文章通过电流波形发生器产生符合提高焊接质量的短路、燃弧阶段的电流波形,并设计了相应的模糊PI控制器,构成CO2焊接逆变电源的模糊PI电流波形控制系统,以减少飞溅,提高焊缝成形.仿真研究表明,所设计的控制器系统能使焊接电流快速、准确地跟踪给定的电流波形.文中讨论了回路电感对短路末期焊接电流大小的影响,为实际的CO2焊接逆变电源控制系统的设计提供理论依据和参考.     

并联双闭环控制方式对GMAW焊接过程的影响

在对短路过渡熔化极气体保护焊（GMAW）的飞溅及焊缝成形影响因素分析的基础上，基于数字信号处理器控制系统建立了一个全数字式并联双闭环控制系统，分别对短路阶段及燃弧阶段的焊接电参数进行调节，达到对短路、燃弧期间电流波形的分阶段适应性控制，以改善短路过渡GMAW工艺性能的目的．实验结果表明，采用该方式控制的波控数字式GMAW焊接电源，在焊接性能上与普通平特性逆变焊接电源相比有较大的提高，飞溅减小、焊接过程稳定、焊缝成形好，更加适合GMAW短路过渡焊．     

短路过渡的CO2焊波形控制探索

针对CO2焊短路过渡飞溅产生的机理,研究了减小飞溅、实现波形控制核心技术问题,设计了实现波控的软、硬件方案,对电压、电流进行了有效控制.实验结果表明,该设计方案能明显减小飞溅、改善焊缝成形.     

二氧化碳短路过渡焊电流波形控制模式的研究

针对二氧化碳弧焊熔滴短路过渡过程动特性差，飞溅大的特点，对一种关联式电流波形智能控制器的波控模式进行了研究，提出了实时控制熔滴过渡过程电流波形的波控基本模式。试验表明，该波控模式能对弧焊过程实施有效波控，尤其适宜于带有交流纹波成分的整流焊接电源的波控。采用该控制模式，通过波控器的快速分流作用，可抑制弧焊短路初期，短路未期的电流增长和燃弧初期的电弧冲击，能够优化熔滴过渡过程的电流波形，使液桥柔顺破断，熔滴无冲击地进入熔池，从而改善了二氧化碳在弧焊过程中的动特性，抑制了焊接飞溅。     

焊接电弧声与飞溅的相关性研究

建立了计算机检测分析系统，对ＣＯ２焊接电弧声与飞溅的关系及影响飞溅的因素作了深入研究．结果发现了焊接飞溅与短路结束时电弧声能量及短路平均声能量成线性关系，从而提出用电弧声能量来表征焊接飞溅的新型传感方法．     

协同式CO2焊电弧自身传感模糊控制系统

为了减小 CO2 焊接过程中的飞溅和改善焊缝成型 ,实现焊接参数的最佳匹配。介绍了一种在波形控制基础上 ,采用电弧自身传感的协同式模糊控制方法对焊接过程参数进行实时控制的逆变式 CO2 焊机控制系统。它通过电弧自身传感对 CO2 焊接过程有重要影响的短路过渡频率的检测 ,通过模糊处理和模糊判决之后 ,实时的对电弧电压进行控制 ,以保持焊接过程中规范参数的协同匹配关系。实验结果表明 ,采用该控制系统的焊机 ,实现了焊接规范参数的自动匹配和自动调节 ,同时明显改善了焊缝成型和降低了焊接过程中的飞溅。     

水蒸气保护下电弧堆焊工艺特点

通过分析不同焊接规范下的焊接电压和电流的波形 .研究了水蒸气保护下电弧及熔滴过渡的特点 ,发现其电弧过程行为有“燃弧—熄弧—短路”和“燃弧—短路”两种形式 .在焊丝直径和送丝速度一定的情况下 ,通过调节焊接回路中的电感量和电源电压 ,可以改变电弧的过程行为形式 .若电弧过程呈“燃弧—熄弧—短路”交替进行 ,并且熄弧时间最短时 ,短路过渡频率最高 ,在这种情况下 ,飞溅小 ,焊道成型好 ,焊接过程稳定 .     

基于虚拟仪器的CO2弧焊品质定量评价系统

采用虚拟仪器技术开发了CO2 弧焊品质定量评价和焊接参数优化系统 ,用多元线性回归和多元非线性回归模型作为核心算法预测飞溅量 ,对短路过渡CO2 弧焊品质进行定量化的评价 .系统采用数据拟合算法 ,以短路过渡频率为优化目标 ,在一定条件下对焊接参数进行优化 .     

微机控制可控硅弧焊电源的研究

本文介绍一种硬、软件十分简单、稳定可靠的微机控制弧焊电源应用系统。提出了PID算法是能够兼顾静动特性的微机——可控硅电源系统的控制算法,并讨论了PID算法中各参数的变化对短路过渡时电流波形的影响。试验结果表明,本文推出的系统完全能够满足MMA,TIG等焊接方法的工艺要求,且具有飞溅小、电弧稳定、调节范围宽和动特性可控等特点。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the