空化器参数对超空泡初生位置影响大涡模拟

为揭示空化器参数对超空泡初生位置的影响规律,离散求解了三维气液两相大涡模拟控制方程组,对三维不同空化器参数模型下超空泡流动进行了数值模拟。在不同空化数条件下,通过数值模拟获得超空泡无量纲几何参数并与实验数据对比,结果表明两者吻合良好。在此基础上,分析了不同空化器形状、直径对超空泡初生位置影响。分析结果为探索高速航行体空化器性能与水动力特性提供了数值参考。

位置度超差对轴流压气机流场性能影响的数值研究

以单级轴流压气机为研究对象,采用数值计算方法研究了叶片位置度超差对压气机流场性能的影响。计算结果表明,当叶片位置度发生变化时,压气机的等熵效率、总压比等气动参数都不同程度地呈现恶化趋势,并且轴向位置度的影响大于周向位置度;叶片周向及轴向位置度的变化对压气机叶片气动载荷和进口攻角的影响规律各不相同。

机器人位置稳定时间和超调量的算法研究

根据国标要求对位置稳定时间和位置超调量进行测试,按照标准中的定义对其算法进行研究,为后续开发性能测评软件提供算法支持。实到位置的确定标准并未详细给出,其取值的不同会对结果造成一定的影响,门限带的取值不同对结果的影响最明显,门限带越大,位置稳定时间越小,但对位置超调量的影响并不明显。门限带的取值大于位置超调量时,就会出现过阻尼状态,机器人在空载低速(50%和10%额定速度)和100%负载10%速度条件下运行时比较容易出现过阻尼状态。

首釜搅拌桨叶和B进料位置的改造对橡胶质量的影响

根据冷模优化实验结果 ,聚合首釜搅拌底桨由双螺带式改为四叶框式和催化剂B由微偏心位置改为偏心位置进料 ,在生产中应用后 ,聚合釜中单体、溶剂和催化剂的混合分散更均匀 ,最终降低了催化剂的用量 ,橡胶的内在质量也得到改善 ,在原料质量下降时 ,可稳定聚合反应。

量子思维应用于音位研究初探

量子思维与音位研究的历史可以追溯到20世纪初量子力学的发现。随着时间的推移,这两个领域的研究逐渐联系起来,形成了量子音位学理论。量子思维为音位研究提供了一种新的分析和解释方式。然而,国内外仍欠缺关注量子思维应用于音位的研究。通过引入连续性、不确定性、超位置、纠缠和相干等量子思维的概念,传统的二分法对音位的理解可以得到深化和扩展。量子力学的数学模型和工具可以更好地描述音位之间的连续性和交叉现象,更好揭示复杂语言中音位的组织方式,并探索语言中微观规律和特征,并为音位学研究提供新的视角。然而,量子思维在音位研究中的应用尚处于初级阶段,仍需进行更多的实证研究和理论探索来验证和完善这一方法。

基于激光跟踪仪的工业机器人性能测试与评价分析

本文首先围绕工业机器人性能测试相关要求、检测指标设置进行了分析。为做好针对工业机器人的性能测试与评价工作,本文围绕实验对象及测试设备的选择、工业机器人性能测量系统构建及工作原理等基于激光跟踪仪的工业机器人性能测试平台搭建要素展开分析。在此基础上,本文选择工业机器人位姿准确度及重复性、工业机器人位置稳定时间及位置超调量、工业机器人轨迹准确度和轨迹重复性三项重要项目进行测试与评价,仅供参考。

纳米定位技术的发展现状

超精密位置控制技术是超精密加工和测量的基础。通过对现有几种具有纳米分辨率的驱动系统进行比较,分析了各种定位系统的特点,展望了纳米定位技术的发展方向。

基于LED通信的定位技术

虽然传统无线电技术己经被广泛使用并且技术也相当成熟,但是工业界和科学界都认为下一代无线通信系统的接入技术将是基于多种接入技术的组合,其中也包括光无线(OW)通信接入技术。该文提出了一套可见光通信的定位技术,并对现有的定位技术进行了改进,通过仿真和实验验证了可见光用于室内定位的可行性以及优越性。该文在充分研究IEEE802.15.7标准的基础上,提出一种利用超帧的通信时隙进行室内定位的方法。其次建立室内信道光功率分布模型并仿真得出室内的直射和反射信道光功率分布,为位置指纹建库奠定基础。提出优化位置指纹的方案,减少位置指纹查找时间和计算过程。并且搭建可见光通信硬件平台,通过LED进行信号传输和接收,进一步验证可见光用于通信的可行性。

伺服驱动器“A-09”报警故障分析与处理

本文对电动缸伺服驱动器显示"A-09"报警故障进行了分析,完成了故障定位,通过改进连接电缆屏蔽层处理方式及驱动器本体封盖、窗口导电处理工艺的措施经试验验证有效,问题得到较好解决。

一种发动机油底壳加工工艺探讨

对发动机油底壳的加工工艺进行了详细的探讨,并详细阐述了试制和批量两种加工工艺的夹具设计方案与加工工艺的特点,对批量生产过程中遇到的热变形误差累计的技术难点,进行了深入的探讨,并给出了具体的解决方案。

Central venous port placement in advanced breast cancer patients:comparison of the anatomic- landmark and ultrasound-guided techniques

Objective： The aim of this study was to compare the anatomic-landmark and ultrasound-guided techniques in the placement of an internal jugular vein port in patients with advanced breast cancer. Methods： Between March 2010 and October 2010, 60 patients with advanced breast cancer underwent central venous port placement for the delivery of chemotherapy, preferably through the internal jugular vein. Patients were randomly assigned to either the anatomic-landmark or the ultrasound-guided group. Failure on first attempt, number of attempts until successful catheterization, time to successful placement, the accordance of the two placement approaches, and the demographics of each patient were recorded. Results： The consistency of the direction of two lines drawn using the anatomic-landmark and ultrasound-guided techniques or of the diameter of the internal jugular vein as determined by the two approaches was 85% （51/60）. The rate of successful place- ment at first attempt was higher in the ultrasound group than in the anatomic-landmark group （P 〈 0.05）. A greater number of attempts and longer time to successful port placement were needed in the latter （P 〈 0.05）. Conclusion： The findings of this study indicate that, in the placement of an internal jugular vein port, the ultrasound （US）-guJded technique has several advantages over the anatomic-landmark technique.

Defects detection in typical positions of bend pipes using low-frequency ultrasonic guided wave

In order to analyze the possibility of detecting defects in bend pipe using low-frequency ultrasonic guided wave, the propagation of T(0,1) mode and L(0,2) mode through straight-curved-straight pipe sections was studied. FE(finite element) models of bend pipe without defects and those with defects were introduced to analyze energy distribution, mode transition and defect detection of ultrasonic guided wave. FE simulation results were validated by experiments of four different bend pipes with circumferential defects in different positions. It is shown that most energy of T(0,1) mode or L(0,2) mode focuses on extrados of bend but little passes through intrados of bend, and T(0,1) mode or L(0,2) mode is converted to other possible non-axisymmetric modes when propagating through the bend and the defect after bend respectively. Furthermore, L(0,2) mode is more sensitive to circumferential notch than T(0,1) mode. The results of this work are beneficial for practical testing of pipes.

Doping Copper Ions in a Metal-Organic Framework(UiO-66-NH2):Location Effect Examined by Ultrafast Spectroscopy

We constructed two types of copper-doped metal-organic framework(MOF),i.e.,Cu@UiO-66-NH2 and Cu-UiO-66-NH2.In the former,Cu2+ions are impregnated in the pore space of the amine-functionalized,Zr-based UiO-66-NH2;while in the latter,Cu^2+ions are incorporated to form a bimetal-center MOF,with Zr^4+being partially replaced by Cu2+in the Zr-O oxo-clusters.Ultrafast spectroscopy revealed that the photoinduced relaxation kinetics associated with the ligand-to-cluster charge-transfer state is promoted for both Cudoped MOFs relative to undoped one,but in a sequence of Cu-UiO-66-NH2>Cu@UiO-66-NH2>UiO-66-NH2.Such a sequence turned to be in line with the trend observed in the visible-light photocatalytic hydrogen evolution activity tests on the three MOFs.These findings highlighted the subtle effect of copper-doping location in this Zr-based MOF system,further suggesting that rational engineering of the specific metal-doping location in alike MOF systems to promote the photoinduced charge separation and hence suppress the detrimental charge recombination therein is beneficial for achieving improved performances in MOF-based photocatalysis.

Quasispecies dynamics in main core epitopes of hepatitis B virus by ultra-deep-pyrosequencing

AIM:To investigate the variability of the main immunodominant motifs of hepatitis B virus(HBV) core gene by ultra-deep-pyrosequencing(UDPS).METHODS:Four samples(2 genotype A and 2 genotype D) from 4 treatment-na ve patients were assessed for baseline variability.Two additional samples from one patient(patient 4,genotype D) were selected for analysis:one sample corresponded to a 36-mo treatment-free period from baseline and the other to the time of viral breakthrough after 18 mo of lamivudine treatment.The HBV region analyzed covered amino acids 40 to 95 of the core gene,and included the two main epitopic regions,Th50-69 and B74-84.UDPS was carried out in the Genome Sequencer FLX system(454 Life Sciences,Roche).After computer filtering of UDPS data based on a Poisson statistical model,122 813 sequences were analyzed.The most conserved position detected by UDPS was analyzed by site-directed mutagenesis and evaluated in cell culture.RESULTS:Positions with highest variability rates were mainly located in the main core epitopes,confirming their role as immune-stimulating regions.In addition,the distribution of variability showed a relationship with HBV genotype.Patient 1(genotype A) presented the lowest variability rates and patient 2(genotype A) had 3 codons with variability higher than 1%.Patient 3 and 4(both genotype D) presented 5 and 8 codons with variability higher than 1%,respectively.The median baseline frequencies showed that genotype A samples had higher variability in epitopic positions than in the other positions analyzed,approaching significance(P = 0.07,sample 1 and P = 0.05,sample 2).In contrast,there were no significant differences in variability between the epitopic and other positions in genotype D cases.Interestingly,patient 1 presented a completely mutated motif from amino acid 64 to 67(E 64 LMT 67),which is commonly recognized by T helper cells.Additionally,the variability observed in all 4 patients was particularly associated with the E 64 LMT 67 motif.Codons 78 and 79 were highly conserved in all samples,in keeping with their involvement in the interaction between the HBV virion capsid and the surface antigens(HBsAg).Of note,codon 76 was even more conserved than codons 78 and 79,suggesting a possible role in HBsAg interactions or even in hepatitis B e antigen conformation.Sequential analysis of samples from patient 4(genotype D) illustrated the dynamism of the HBV quasispecies,with strong selection of one minor baseline variant coinciding with a decrease in core variability during the treatment-free and lamivudinetreated period.The drop in variability seemed to result from a "steady state" situation of the HBV quasispecies after selection of the variant with greatest fitness.CONCLUSION:Host immune pressure seems to be the main cause of HBV core evolution.UDPS analysis is a useful technique for studying viral quasispecies.

Chaotic pulse position modulation ultra-wideband system based on particle filtering

Traditional chaotic pulse position modulation(CPPM)system has many drawbacks.It introduces delay into the feedback loop,which will lead to divergence of chaotic map easily.The wrong decision of data will cause error propagation.Mismatch of parameters and synchronization error between the receiver and transmitter will arouse high bit error rate.To solve these problems,a demodulation algorithm of CPPM based on particle filtering is proposed.According to the mathematical model of the system,it tracks the real signal by online separation in demodulation.Simulation results show that the proposed method can track the true signal better than the traditional CPPM scheme.What's more,it has good synchronization robustness,reduced error propagation by wrong decision and low bit error rate.

Low-Density Parity-Check Codes for Noncoherent UWB Communication Systems

In order to guarantee reliable data transmission, powerful channel coding techniques are usually required in noncoherent ultra-wideband(UWB) communication systems. Accordingly, several forward error correction(FEC) codes, such as Reed-Solomon and convolutional codes have been used in noncoherent UWB systems to improve the bit error rate(BER) performance. In this paper, low-density parity-check(LDPC) codes are further studied as more powerful FEC candidates for noncoherent UWB systems. Two LDPC codes and the corresponding decoding procedures are presented for noncoherent UWB systems. Moreover, performance comparison between the LDPC codes and other FEC codes are provided for three major noncoherent UWB communication systems, namely, noncoherent pulse position modulation(NC-PPM), transmitted reference(TR) and transmitted reference pulse cluster(TRPC). Both theoretical analysis and simulation results show that the two investigated LDPC codes outperform other existing FEC codes with limited penalty in terms of complexity and therefore they are promising FEC candidates for noncoherent UWB systems with low-cost and low-power consumption.

Approximate Solution of D-Dimensional Klein-Gordon Equation with Hulthn-Type Potential via SUSYQM

Approximate analytical solutions of the D-dimensional Klein-Gordon equation are obtained for the scalarand vector general Hulthen-type potential and position-dependent mass with any l by using the concept of supersymmetricquantum mechanics (SUSYQM).The problem is numerically discussed for some cases of parameters.

Application of an Analytical Method to Locate a Mixing Plane in a Supersonic Compressor

In order to achieve greater pressure ratios, compressor designers have the opportunity to use transonic configurations. In the supersonic part of the incoming flow, shock waves appear in the front part of the blades and propagate in the upstream direction. In case of multiple blade rows, steady simulations have to impose an azimuthal averaging （mixing plane） which prevents these shock waves to extend upstream. In the present paper, several mixing plane locations are numerically tested and compared in a supersonic configuration. An analytical method is used to describe the shock pattern. It enables to take a critical look at the CFD （computational fluid dynamics） steady results. Based on this method, the shock losses are also evaluated. The good agreement between analytical and numerical values shows that this method can be useful to wisely forecast the mixing plane location and to evaluate the shift in performances due to the presence of the mixing plane.

Ignition, flame propagation and extinction in the supersonic mixing layer flow

The supersonic mixing layer flow,consisting of a relatively cold,slow diluted hydrogen stream and a hot,faster air stream,is numerically simulated with detailed transport properties and chemical reaction mechanisms.The evolution of the combustion process in the supersonic reacting mixing layer is observed and unsteady phenomena of ignition,flame propagation and extinction are successfully captured.The ignition usually takes place at the air stream side of braid regions between two vortexes due to much higher temperature of premixed gases.After ignition,the flame propagates towards two vortexes respectively located on the upstream and downstream of the ignition position.The apparent flame speed is 1569.97 m/s,which is much higher than the laminar flame speed,resulting from the effects of expansion,turbulence,vortex stretching and consecutive ignition.After the flame arrives at the former vortex,the flame propagates along the outer region of the vortex in two branches.Then the upper flame branch close to fuel streamside distinguishes gradually due to too fuel-riched premixed mixtures in the front of the flame and the strong cooling effect of the adjacent cool fuel flow,while the lower flame branch continues to propagate in the vortex.

Prediction of hypersonic boundary layer transition with variable specific heat on plane flow

When an aircraft flies at a hypersonic speed,the temperature of gas inner boundary layer near the wall is so high that the specific heat is no longer a constant but dependent upon the temperature.It is necessary to consider its effect on transition location.In this paper,the transition locations of hypersonic plane boundary layer are predicted with the improved e N method,and the results of the specific heat dependent upon temperature are compared with those of constant specific heat.The flow parameters are taken as those corresponding to the condition at a height of 40 km and the Mach numbers of oncoming flow are 6,7,and 8,respectively.It is found that the transition locations calculated by the variable specific heat are closer to the leading edge than those by the constant specific heat.The deviations in most cases are around 30 percent.All the results prove that the real gas effect should be taken into consideration when one predicts transition location for hypersonic flow.Whether the first or second mode wave determines the transition location relies on the oncoming flow Mach number and the wall condition.