大负载超声振动磨削系统的设计

设计了一种大负载超声振动磨削系统,超声系统由换能器、圆柱圆锥形变幅杆和轮辐式砂轮组成.首先将轮辐式砂轮等效成轮毂为圆柱杆、辐板与轮缘为中厚板的复合模型,利用各接触面边界连续的条件推导系统的频率方程,完成了超声磨削系统的设计,制作了实验装置并分析验证了其声学振动特性.实验结果表明:利用轮辐式砂轮复合模型求解系统频率方程,...     

阵列式压电振子超声复合喷丸强化*

为了进一步改善超声喷丸强化质量,提升工件表面残余应力和显微硬度的均匀性,对压电振子阵列型超声喷丸强化加工系统进行了改进,提出了在强化加工过程中辅助工件往复运动的方法。对改进后的压电振子阵列型超声喷丸强化加工原理进行了阐述,分析了激振片的振动特性并进行了结构尺寸优化,应用Abaqus对工件往复运动下超声喷丸强化过程进行了仿真研究,分析了在不同的工件往复运动频率下,工件表面残余应力分布情况。实验测试了在不同喷丸强化时间及工件往复运动频率下超声喷丸强化加工质量,探究了喷丸时间和工件往复运动频率对工件表面显微硬度的影响。结果表明：在压电振子阵列型超声喷丸强化过程中辅助工件往返运动,可以有效提高工件表面残余应力和显微硬度分布的均匀性,工件表面强化质量得到提升。     

超声波雾化铝表面液滴的试验研究

介绍了一种超声波抑霜新方法。对频率20 kHz的超声波作用下铝表面液滴的雾化现象进行了可视化观测。对不同超声输入功率以及不同超声作用时间下,70 mm×70 mm×3 mm铝表面液滴群的雾化概率进行了分析。试验结果发现,超声波可以瞬间雾化铝板表面液滴;随着超声输入功率的增加,铝表面液滴雾化概率逐渐增加;功率越低,超声作用时间对液滴雾化概率的影响越显著。结果表明,超声波可以去除铝板表面作为结霜初始阶段的液滴,为冷表面有效抑霜提供了可能。     

液体推进剂模拟工质在离心喷嘴内流动特性研究

设计了一种双旋流槽离心式喷嘴,采用高速录像系统,研究了液体推进剂模拟工质在喷口处的雾化角特性。在实验基础上,建市r离心式喷嘴内流的VOF模型,基于FLUENT软件进行了数值模拟,获得了喷嘴内流场密度、速度分布特性。结果表明：喷雾初期喷嘴内存在一个空气核,随后很快消失,雾化角变小并趋于稳定。雾化角计算值与测量值吻合较好。     

双铂网雾化和超声雾化进样系统对ICP-AES分析性能的影响

从元素检出限、基体效应、ICP稳健性及记忆效应方面实验研究了双铂网雾化与超声雾化两种进样方式对ICP-AES分析性能的影响。结果表明,在超声雾化进样条件下,Cu,Pb,Zn,Cr,Cd,Ni的检出限较双铂网雾化的检出限降低了6～23倍;在基体效应方面,超声雾化进样时基体对元素原子及离子谱线强度的影响均较双铂网雾化系统明显,元素谱线增强/减弱的幅度受元素谱线、基体组成和浓度的影响;Ca和Mg基体对谱线强度的影响强于K和Na基体;离子谱线受基体的影响明显强于原子谱线。超声雾化系统进样时ICP的稳健性要劣于双铂网雾化系统,而且超声雾化系统的记忆效应较双铂网雾化器严重。     

弱酸试纸法测量功率超声珩磨空化声场的研究*

为了简便、直观地测量功率超声珩磨磨削区的空化声场强度及分布情况,提出了利用弱酸PH试纸测量磨削区空化声场的方法。利用超声空化效应产生的弱酸空化泡在PH试纸表面溃灭后,形成深浅和分布不同的变色区域,间接地表征油石表面空化声场的强弱和分布规律。通过对比不同超声频率、测试距离和时间,得出了最佳测试距离和时间。结果表明,当超声频率为18.6 kHz,距离为10 mm时,测得油石表面的空化声场强度和分布最佳。该方法可形象地评价功率超声珩磨磨削区空化声场的强度和分布情况,具有一定的实际应用价值。     

带有锥形孔的复合变幅杆设计及动态分析

在超声振动拉丝加工过程中,为了实现线材的顺利拉拔,需要应用带有锥形孔的复合变幅杆。为此,本文基于等效四端网络与传输矩阵法,建立了带锥形孔圆锥变幅杆的传输矩阵,推导出带锥形孔圆锥过渡复合变幅杆的频率方程的一般公式。根据推导出的频率方程,应用区间搜索法和牛顿迭代法获取了准确的数值解,实现了该复合变幅杆的纵向振动。之后,应用有限元软件Ansys对设计出的复合变幅杆分别进行模态分析和动力学特性分析,获得了各段不同长度下复合变幅杆谐振频率、放大系数以及最大应力值的变化规律。最后,对制造出的复合变幅杆进行阻抗与振动性能测试,结果表明其频率准确,且振幅比较稳定。     

脆性光学材料的超声磨削实验研究

分别采用超声磨削和普通磨削加工方法加工了几种脆性光学材料,研究了几种主要工艺参数对工件加工表面粗糙度的影响。结果表明,超声频率和振幅、金刚石磨料粒度、切深、工具的横向进给速度和旋转速度等工艺参数对表面粗糙度的影响较大。通过比较发现,超声磨削方法比普通磨削方法具有更好的加工表面粗糙度,更高的材料去除率,以及更低的工具磨损量。     

超声辅助磨削杯形砂轮变幅器设计与试验*

超声辅助磨削在硬脆材料的加工中应用广泛。为研制以杯形砂轮为加工工具的超声辅助磨削主轴附件式工具系统,建立了杯形砂轮变幅器的理论模型,推导了其频率方程,并通过Matlab开发了杯形砂轮变幅器设计软件。利用该软件结合有限元分析对杯形砂轮变幅器进行了设计。将研制的杯形砂轮变幅器与BT40刀柄一体化外套筒、导电滑环装配组成了杯形砂轮超声辅助磨削主轴附件式工具系统。对该超声振动系统进行了阻抗分析试验及超声谐振试验,结果表明,该超声振动系统阻抗性能较好,能够使杯形砂轮产生稳定的超声振动,验证了所提出的设计方法的正确性,为主轴附件式超声磨削装置的设计提供了理论参考。     

石灰浆液喷嘴雾化特性

石灰浆液雾化喷嘴是烟气喷雾干燥净化系统的关键设备.利用Win212-2型激光粒度分析仪,对外混及内-外混相结合双流体石灰浆液喷嘴的雾化特性进行了试验研究,分析了气液质量比、石灰浆液浓度等参数对雾化粒径分布和雾化角的影响规律.结果表明,气液质量比增大,浆液液滴平均直径减小,但当气液比增大到一定值后,粒径变化趋于平缓;浆液浓度增加,液滴平均直径增加;气液质量比增加,雾化角减小.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.