戴煦《外切密率》“降位迟速”问题探赜

“杜氏三术”传入后,从明安图开始的中算家在证明和推广割圆捷术的同时,也关注其中的“降位迟速”问题。他们对这一问题的认识不尽相同,均考虑到了计算效率的问题,但在具体实施计算的过程中,戴煦对“降位迟速”问题的见解独到、处理方式极具价值。通过分析《外切密率》中的具体算例,从“降位迟速”问题的认识、弧度的分限、尾数的处理、误差的判断等方面,阐明戴煦所设计的“降位迟速”算法及所含的算理,为比较各算家所用“降位迟速”算法及廓清算法改进的路径提供借鉴。

收获机与运粮车纵向相对位置位速耦合协同控制方法与试验

针对主从导航收获协同卸粮作业过程中作业车辆纵向相对位置控制需求以及拖车驱动系统非线性度较高的问题,该研究设计了一种适用于主从导航协同收获卸粮作业的纵向相对位置协同控制方法。根据协同系统几何关系获得纵向相对位置偏差的平行协同模型,基于动力学原理和位速耦合控制方法设计了纵向相对位置控制器;通过面积辨识方法获取车速系统传递函数,基于传递函数构建仿真模型进行控制器参数全因子仿真优化试验,并与传统PD方法进行仿真对比试验,结果表明该研究方法的最优参数适应性优于传统PD。不同初始偏差的纵向协同田间空载试验结果表明,在主机速度为1 m/s时,3、7和10 m初始纵向偏差下,系统响应平均调节时间分别为7.73、17.2和23.2 s,9组试验的平均稳态绝对偏差为0.0918 m,平均相对速度稳态误差为0.0123 m/s,表明该方法具有较好的初始偏差适应性;田间协同收获作业表明,在主机速度为1 m/s时,平均稳态纵向相对位置偏差绝对值为0.0778 m,标准差为0.0913 m,协同精度能够满足收获协同卸粮的作业要求。研究结果可为自主收获作业系统研究提供支持。

转炉2^#方坯连铸机位速的探讨

本文通过分析钢水在结晶器内凝固的不均匀性及对钢水结晶的热量平衡计算,讨论了连铸中间包钢水温度、结晶器冷却水流量及进出水温差对工作拉坯速度的影响。

英汉语主、述位对比与翻译——以《荷塘月色》为例

系统功能语法中句子主、述位的划分对研究句子成分的功能具有重要意义。主、述位既是句子语法结构体,又是语言信息的承载体,它们的排列顺序不仅突出了不同信息的重要程度,而且还体现了不同语言的结构特征。在英、汉翻译过程中,只有了解了主、述位在不同语言里所具有的特征和所发挥的作用,才能成功地进行语言间的转换。本文从英、汉两种语言主、述位特点和主、述位推进模式出发,探讨其对句子结构、排列顺序及语篇衔接连贯的影响,并进一步阐释如何利用他们之间的异同进行翻译,真正做到准确、地道地传达原文的风采。

运行在信息高速公路上的网络银行——基于国际析数字理论下的中国银行

对个性化世界的探究将为中国网络银行提供坚实的发展动力。网络银行的兴起将使市场资金流动的速度加快并可能减少对现金的需求,因此中央银行货币政策的有效性正逐渐面对挑战。

Effects of sonic speed on location accuracy of acoustic emission source in rocks

To quantitatively study the location errors induced by deviation of sonic speed, the line and plane location tests were carried out. A broken pencil was simulated as acoustic emission source in the rocks. The line and plane location tests were carried out in the granite rod using two sensors and the cube of marble using four sensors, respectively. To compare the position accuracy between line and plane positions, the line poison test was also carried out on the marble surface. The results show that for line positioning, the maximum error of absolute distance is about 0.8 cm. With the speed difference of 200 m/s, the average value of absolute difference from the position error is about 0.4 cm. For the plane positioning, in the case of the sensor array of 30 cm, the absolute positioning distance is up to 8.7 cm. It can be seen that the sonic speed seriously impacts on the plane positioning accuracy. The plane positioning error is lager than the line positioning error, which means that when the line position can satisfy the need in practical engineering, it is better to use the line position instead of the plane location. The plane positioning error with the diagonal speed is the minimum one.

Effects of rolling parameters of snake hot rolling on strain distribution of aluminum alloy 7075

The realization way of snake rolling was introduced. Flow velocity, strain and stress distribution of 7075 aluminum alloy plate during snake rolling and symmetrical rolling were analyzed in Deform 3D. Effects of velocity ratio, offset distance between two rolls and pass reduction on the distribution of equivalent strain and shear strain were analyzed. The results show that flow velocity and equivalent strain on the lower layer of the plate are larger than those of the upper layer because of the larger velocity of the lower roll and the gap is increased with the increase of velocity ratio and pass reduction. The shear strain of roiling direction in the center point is almost zero during symmetrical rolling, while it is much larger during snake rolling because of the existence of rub zone. The shear strain is increased with the increase of velocity ratio, offset distance and pass reduction. This additional shear strain is beneficial to improve the in_homogeneous strain distribution.

Studies on phase and group velocities from acoustic logging

It is still argued whether we measure phase or group velocities using acoustic logging tools. In this paper, three kinds of models are used to investigate this problem by theoretical analyses and numerical simulations. First, we use the plane-wave superposition model containing two plane waves with different velocities and able to change the values of phase velocity and group velocity. The numerical results show that whether phase velocity is higher or lower than group velocity, using the slowness-time coherence （STC） method we can only get phase velocities. Second, according to the results of the dispersion analysis and branch-cut integration, in a rigid boundary borehole model the results of dispersion curves and the waveforms of the first-order mode show that the velocities obtained by the STC method are phase velocities while group velocities obtained by arrival time picking. Finally, dipole logging in a slow formation model is investigated using dispersion analysis and real-axis integration. The results of dispersion curves and full wave trains show similar conclusions as the borehole model with rigid boundary conditions.

主轴式滚磨光整加工接触力修正系数研究

高端装备关重件多采用主轴式滚磨光整加工提高零件表面完整性,传统的用反复实验摸索滚磨光整工艺的办法存在工件提供难或数量少的实际问题。基于EDEM仿真主轴式滚磨光整加工可以为工艺制定提供有效的帮助,但模拟仿真与实际工况的差异性尚未可知。将滚抛磨块尺寸、滚筒转速以及加工位置作为影响接触力大小的评价指标,考虑仿真模拟与实验验证的可比性,设计构建了与仿真模拟完全相同的实验装置和工艺参数环境,选用Hertz-Mindlin无滑移接触模型进行模拟仿真,探究模拟仿真与实验测试得到的工件与滚抛磨块之间的法向接触力的规律性。通过量化接触对象球径比、加工位置以及滚筒转速对于接触力的影响,推导出接触力相关修正系数的表达式,进而建立包含接触对象球径比和速位影响系数的滚抛磨块与工件之间的接触力计算公式,并验证了不同径向位置处接触力计算公式的适用性。结果表明:球径比系数在(2.6664~2.9601)之间,其值与滚抛磨块尺寸成负相关关系;速位修正系数在(0.9519~1.9097)之间;采用修正后接触力表达式进行分析计算,计算结果与实验测试结果相对误差值在(0.08~18.91)%之间,该方法可以为滚磨光整加工实际工艺磨块与工件之间接触力提供可信的计算方法。

Novel gravity passive navigation system

According to the characteristics of gravity passive navigation, this paper presents a novel gravity passive navigation system （GPNS）, which consists of the rate azimuth platform （RAP）, gravity sensor, digitally stored gravity maps, depth sensor and relative log. The algorithm of rate azimuth platform inertial navigation system, error state-space equations, measurement equations and GPNS optimal filter are described. In view of the measurements made by an onboard gravity sensor the Eotvos effect is introduced in the gravity measurement equation of a GPNS optimal filter. A GPNS is studied with the Matlab/Simulink tools; simulation results demonstrate that a GPNS has small errors in platform attitude and position. Because the inertial navigation platform is the rate azimuth platform in the GPNS and gravity sensor is mounted on the rate azimuth platform, the cost of the GPNS is lower than existing GPNS＇s and according to the above results the GPNS meets the need to maintain accuracy navigation for underwater vehicles over long intervals.

CONTROL OF ROBOT DRIVEN BY MULTIPLE ULTRASONIC MOTORS BASED ON ROBUST PARAMETER DESIGN

An ultrasonic motor （USM） is difficlt to be mathematically described because of its complex energy conversion and nonlinear parameters from increasing temperature and changing operating conditions. To achieve good performance of a three-joint robot directly driven by USM, according to the operating characteristics of USM, a new position-velocity feedback control strategy is proposed. In the control strategy, there are a total of 18 controller gains to he tuned. Through a series of ＂Design of Experiments＂ by the robust parameter design, an optimal and robust set of proportional integral derivative （PID） controller gains is obtained. Results show that the control strategy can achieve the best performance of the robot and the robust parameter design is effective and convenient to USMs.

Study on rate azimuth platform inertial navigation system

The cost of the gravity passive inertial navigation system will be lower witha rate azimuth platform and gravity sensor constituting a gravity measurement and navigationsystem. According to the system performance characteristics, we study the rate azimuth platforminertial navigation system (RAPINS), give the system navigation algorithm, error equations of theattitude, velocity and position of the rate azimuth platform, and random error models of theaccelerometer and gyro. Using the MATLAB/Simulink tools, we study the RAPINS and RAPINS withvelocity damping. Simulation results demonstrate that the RAPINS with velocity damping has smallerrors in platform attitude and position and satisfies gravity measurement and navigationrequirement.

Using a linear array to estimate the velocity of underwater moving targets

A new method uses a linear array that takes advantage of underwater physical sound fields to estimate the velocity of an underwater moving target. The mathematical model was established by considering the geometric relationship between the moving target installed with only two transducers to radiate sound of different frequencies and the linear array. In addition, deterministic maximum likelihood and signal phase matching algorithms were introduced to effectively find the directions of arrival （DOAs） of the sound sources of the two transducers installed on the target. Factors causing velocity measurement errors were considered. To track the target, a linear array with a compass, a pressure transducer, a signal conditioner and a digital recorder was configured. Relevant requirements for the array parameters were derived. The simulation showed that a 16-element array with an aperture of less than lm can measure velocity with relative error of no more＇, than 4% when including typical system errors. Anechoic pool and reservoir experiments confirmed these results.

PRECISION OF HSK TOOLING SYSTEM IN HIGH SPEED MACHINING

Based on the theory of elastic mechanics and material mechanics, the orientation precision of the hohl schaft kegel（HSK） tooling system in static and dynamic states is theoretically and experimentally studied. The relation between the clamping force and the shank taper is obtained. And a proper clamping force is found to be essential to assure the axial and radial orientation precisions of the HSK tooling system in high speed machining （HSM）. Analytical results show that the reason why the HSK tooling system can keep high precision at the high rotational speed is that the actual axial clamping force keeps the two surfaces of the shank and the spindle in contact all the time.

An intersection method for locating earthquakes in complex velocity models

The intersection method is one of the basic approaches for locating earthquakes and is not only robust but also efficient. However, its location accuracy is not high, especially for focal depth because the velocity model used for the conventional intersection method is based on homogeneous or laterally homogeneous media, which is too simple. In order to improve the accuracy, we have modified the existing intersection method. In the modified approach, the earthquake loci are not assumed to be circular or hyperbolic and calculation accuracy is improved using a minimum traveltime tree algorithm for tracing rays. The numerical model shows that the modified method can locate earthquakes in complex velocity models.

Design and Realization of a Monolithic GaAs 3Bit Phase Digitizing DAC

Design,realization,and test of a monolithic GaAs 3bit phase digitizing DAC for 3bit digital radio-frequency memory are detailedly described.The 0.5μm fully ion-implanted GaAs MESFET is used to fabricate the circuit in Nanjing Electronic Devices Institute’s (NEDI’s) 75mm standard process line.The high-speed DAC is designed with on-wafer 50Ω I/O impedance matching.Test results show that its work bandwidth is more than 1.5GHz,and phase accuracy is better than 4%.Its code conversion rate can be higher than 12Gbps.

AUTOMATIC CONTROL OF REGENERATIVE CUTTING CHATTER BASED ON OPTIMAL REGULATION OF SPINDLE SPEED

An applicable method to control regenerative cutting chatter automatically based on the optimal regulation of spindle speed is introduced. The optimal value of the phase shift angle of the regenerative chatter signal between the two successive cuts is 270°. The cutting process can be adjusted from the unstable region to stable one whenever regenerative chatter occurs if the phase shift angle is kept 270° by the optimal regulation of spindle speed. The theoretical analysis and the experimental results prove that the optimal regulation of spindle speed can effectively control regenerative cutting chatter. In addition, a reliablelly optimal control system of reliable spindle speed is presented. There is no need for system identification of the machine tool, and it is easy to put this regenerative chatter control method into practice, so the method has excellent application prospect.

主流数字音频的对比和研究

不同数字音频格式可以满足人们的不同需求。但是,不同格式对声音文件的大小、声音的波形、声音的音质等都有一定程度的影响。本文从主观和客观2个方面对Mp3和wav两种数字音频进行对比研究。在客观的实验数据中发现,位速和声压是影响Mp3音质的关键。WAV格式的兼容性很强。在主观评价中,就总体而言,WAV和MP3并未出现太大的音质差距。

Investigation on seismic response of a three-stage soil slope supported by anchor frame structure

Based on a typical prototype of a soil slope in engineering practice, a numerical model of a three-stage soil slope supported by the anchor frame structure was established by means of FLAC3D code. The dynamic responses of three-stage soil slope and frame structure were studied by performing a series of bidirectional Wenchuan motions in terms of the failure mode of three-stage structure, the acceleration of soil slope, the displacement of frame structure, and the anchor stress of frame structure. The response accelerations in both horizontal and vertical directions are the most largely amplified at the slope top of each stage subjected to different shaking cases. The platforms among the stages reduce the amplification effect of response acceleration. The residual displacement of frame structure increases significantly as the intensity of shaking case increases. The frame structure at each stage presents a combined displacement mode consisting of a translation and a rotation around the vertex. The anchor stress of frame structure is mainly increased by the first intense pulse of Wenchuan seismic wave, and it is sensitive to the intensity of shaking case. The anchor stress of frame structure at the first stage is the most considerably enlarged by earthquake loading.

Diagnosis and management of postural orthostatic tachycardia syndrome：A brief review

Postural orthostatic tachycardia syndrome （POTS） has been recognized since at least 1940.A review of the literature identifies differences in the definition for this condition and wide variations in treatment and outcomes.This syndrome appears to describe a group of conditions with differing pathophysiology,which requires treatment tailored to the true underlying disorder.Patients need to be fully evaluated to guide treatment.Further research is required to effectively classify the range of underlying pathophysioiogy that can produce this syndrome and to guide optimal management.