共查询到20条相似文献，搜索用时 187 毫秒
1.
Peng Guangzheng Chen Ping Zhao Tong 《北京理工大学学报》1999,19(3):71
Aim To present a new kind of
pneumatic position control system based on the analysis of the disadvantages of
conventional pneumatic position control systems. Methods The new kind of pneumatic
position control system used a new kind of actuator-cylinder with a built-in brake and a
displacement sensor. And PWM control method and fuzzy control algorithm were utilized in
the system to control the position of the cylinder, and the brake was used to fix the
cylinder to its target position after it reached the position.Results The stiffness of the system was
experimentally proved to be greatly improved and the position precision to be within
0.15mm. In addition, the system is free of great shock and wear. Conclusions The new kind of pneumatic
position control system is free of the disadvantages of conventional systems, and is of
practical value. 相似文献
2.
The isothermal oxidation behavior
of two kinds of alloying Ti-Al alloyTi-48Al-2Cr-2Nb and Ti-47Al-1Cr-1V-2.5Nb at 800℃ and 900℃
is investigated.Their high temperature
oxidation character and the influence of the alloying element upon the oxida－tion behavior are discussed.The
study shows that the oxidation resistance of two alloying Ti-Al alloy at 800℃ is poorer than that of
48Al.However,their oxidation properties at 900℃ are considerably improved,and the oxidation speed is much
lower than that of 48 Alalloy.At the two oxidation temperatures,Ti-48Al-2Cr-2Nb alloy
shows better oxidation resistance than that of Ti-47Al-1Cr-1V- 相似文献
3.
Based on the previous works of
the second author,a kind of finite difference scheme with third-order accuracy for the
homogeneous diffusion equation on non-uniform grid is presented.The proposed scheme is
unconditionally stable. 相似文献
4.
A generalized
formulation of dynamical real-space renormalization-group is suggested. The new version
replaces the single-spin flipping Glauber dynamics with the single-spin transition
dynamics so that it suits for arbitrary spin systems. 相似文献
5.
According to observed Gamma-ray
fit spectrum,Gamma-ray emission mechanism is analyzed.The upper limit of electron energy
that causes Gamma-ray emission is determined.The electrons obtain energy from synchrotron
absorption acceleration.Theconclusion is that high energy Gamma-ray is the result of
inverse-Compton scattering,and Gamma-rays with different energies radiate from different
regions in the crab nebula. 相似文献
6.
Aim To research the interpolation
algorithm of parallel connected machine tool based on stewart mechanism.Methods
The common idea of time-discrete interpolation algorithm and the inverse kinematics model
of parallel connected machine tool were used to evaluate the relation between tool motion
path and six telescopic legs and to derive one kind of interpolation algorithm.Object
oriented program design method was adopted to work out the simulation software and the
availability of the interpolation algorithm was testified by computer simulation.Results
and Conclusion Simulation results of machining process of sphere parts and
one-sheet-hyperboloid parts show that the interpolation algorithm proposed is correct and
practical, providing a new and feasible interpolation algorithm for parallel connected
machine tool. 相似文献
7.
Wang Guanglong 《北京理工大学学报》1999,19(3):12
Aim To study attitude measurement
method of flight body and attitude measurement principle of the earth magnetic field
sensor. To set up the attitude detecting maths model of the earth magnetic field sensor,
and propose the flight body attitude calculating method.Methods According
to Faraday electromagnetism induction law, i.e. when a wire loop incises the magnetic
force line of the earth magnetic field, it will bring about the induction electromotive
force, an attitude measurement system was designed based on the earth magnetic field
sensor. Results An earth magnetic field sensor and attitude measuring
system were designed, and experiment data were analyzed and processed. It was proved that
the rotating speed measurement error is 0.05r/s. Conclusion This earth
magnetic field sensor can be used to detect attitude of high-load rotating flight body. 相似文献
8.
Yang Shuchang Wei Ping 《北京理工大学学报》1999,19(3)
Aim To study a real-time traffic flow
measurement system providing necessary statistics of traffic flow parameters for traffic
departments through measuring vehicle number, velocity and other traffic parameters.Methods
The real-time traffic flow measurement was processed through image difference method.
Because of its capability for data processing at high speed, the RISC (reduced instruction
set computer) was used to carry out real-time and practical research on the whole system. Results
Experiment devices of real-time traffic flow measurement was developed and the practical
algorithm of image processing was designed and debugged. Conclusion In
practical traffic flow measurement, the precision of measuring vehicle number is over 95%.
The system work robustly under various conditions, it can automatically cope with the
gradual and sudden changes of the environment light. 相似文献
9.
Ma
Siyu 《北京师范大学学报(自然科学版)》2000,36(2):209-212
The optical
nonlinear coefficient of nonlinear glasses is studied by transmission coefficient in a
nonabsorption region or when absorption can be ignored. Numerical relations between
nonlinear coefficient and transmission coefficient are presented. As nonlinear coefficient
increases, the transmission coefficient decreases. The results can be used to analyze the
nonlinearity of glasses embedded with semiconductor quantum dots. 相似文献
10.
Two models of
molecular cloud in disk galaxies are proposed to investigate the formation of giant
molecular clouds (GMCs) under the gravitational instability and random collision using
PP(Particle-Particle) simulation. Some conclusions can be drawn: 1) The gravitational
instability can make small clouds form large clouds faster than random collision. 2) The
differential rotation in the gravitational instability model plays a positive role in the
agglomeration of molecular clouds. 相似文献
11.
邓德力 《贵州大学学报(自然科学版)》2010,27(2):23-25
利用黑洞的薄膜模型,研究了静态球对称Dilaton-Maxwell黑洞的热辐射规律。得到了黑洞的辐射能通量正比于黑洞视界温度四次方的结论,即黑洞的热辐射满足广义Stefan-Boltzmann定律。利用静态球对称黑洞的热质点模型,得到了当截断的固有距离η、黑洞的质量m及电荷Q取定后,距黑洞遥远的观察者所接受到的辐射能通量与观察者到黑洞之间的距离的平方成反比。 相似文献
12.
为研究在工程实际中经常遇到的无限大板含有椭圆孔及裂纹问题,采用改进的带裂尖单元位移不连续法,重点研究在内部压力作用下裂纹扩展规律.通过改变椭圆孔的几何参数,揭示出孔的几何参数对断裂参数应力强度因子(SIF)的影响.结果表明:椭圆孔对裂纹的应力强度因子(SIF)具有一定的屏蔽作用,这种屏蔽作用随着椭圆孔的几何参数而变化,该研究在工程上具有重要意义. 相似文献
13.
采用有限元数值模拟与实验研究方法,模拟分析了厚壁筒体翻孔工艺过程材料塑性变形规律及特点,研究了不同温度条件下工件预加工孔型、孔径等对厚壁接管成形尺寸的影响。研究结果表明,模拟与实验结果一致,当预加工孔型为反锥型且平均孔径为11?时,厚壁筒体翻孔后的接管尺寸符合要求。 相似文献
14.
考虑曲率的影响下计算获得了叶片前缘带扩张形孔的气膜冷却特性,分析了平均吹风比对气膜冷却效率的影响,并与传统的圆柱形孔气膜冷却特性进行了对比.结果表明:与圆柱形孔相比,扩张形孔射流的覆盖面更宽,冷却效率更高. 相似文献
15.
杨星宇 《北京师范大学学报(自然科学版)》2018,54(2):175-178
构造了一个简单的三维爱因斯坦-标量引力, 并找到了它在标量场?=2αφ(α为常数)这种情况下的黑洞解. 分析发现此黑洞与Reissner-Nordstrom黑洞存在相似之处, 但当标量场?满足α>2e时, 此黑洞的质量M可以取负值. 验证了此黑洞的温度和熵符合热力学定律,并 且定义了有良好零温极限的黑洞热力学能. 比较了此黑洞解度规与Reissner-Nordstrom度规,发 现了α2与1/l分别对应着Reissner-Nordstrom黑洞的质量与电荷. 相似文献
16.
姚毅 《四川理工学院学报(自然科学版)》1994,(4)
本文分析了腔体微波滤波器中侧面耦合小孔采用横截面上耦合孔等效电路模型的不合理性；建立了微波滤波器采用侧面耦合小孔的等效电路模型，并推导了其通带宽度的计算公式。 相似文献
17.
制动泵作为汽车制动系统的关键零部件,在工作过程中与活塞组成一对精密偶件,对其接触表面质量要求高．由于泵缸体结构复杂且为深盲孔,加工过程易出现孔径尺寸超差、有锥度、排屑困难等问题．所以根据制动泵缸体的结构特点制定了泵口成型加工、钻安装孔、铰内孔、油杯座加工、出油孔加工、加工内孔钩槽、补偿孔加工、珩磨内孔的加工工艺方案．生产实践表明该工艺方案可行,达到设计要求． 相似文献
18.
研究了9.6K低温下、本征GaAs高过超能量态电子自旋相干动力学的浓度依赖,发现当光子能量为1.57 eV,载流子浓度增大至2.65×1017 cm-3时电子自旋相干量子拍的相位翻转180°.理论计算表明量子拍的相位翻转为区分轻、重空穴系统提供了重要依据,当载流子浓度大于2.6×1017 cm-3时,量子拍的振幅主要起源于重空穴价带导带跃迁,当载流子浓度小于2.6×1017cm-1时,量子拍的振幅主要起源于轻空穴价带导带跃迁.因而,分别在轻空穴价带导带系统和重空穴价带导带系统实验测量电子自旋相干动力学成为可能,实验数据表明在轻空穴价带导带系统测得的电子自旋相干弛豫时间明显大于在重空穴价带导带系统测得的电子自旋相干弛豫时间. 相似文献
19.
邓昭镜 《西南师范大学学报(自然科学版)》2007,32(6):1-7
对稳态黑洞能谱的基本特征进行了研究．研究表明稳态黑洞是处于全无界能谱中的系统．在其外视界之外正、负能谱之间禁带能隙消失在外视界面上．在外视之外，黑体辐射系统或正能谱系统易于激发；反之，根据Landau的负能谱理论，在外视界之内负能谱系统易于激发．因此，黑洞的外视界是正、负能谱系统的交接面，在黑洞外视界以外黑洞显示为正能谱系统，而在黑洞外视界以内黑洞又显示为负能谱系统．有鉴于此，我们提出了一个判据，利用这个判据可以很容易地确定黑洞的热力学类型． 相似文献
20.
带有电荷、磁荷的一类任意加速黑洞的熵 总被引：1，自引：0，他引：1
对带有电荷、磁荷的任意加速黑洞,得到它的局部视界面方程. 由于这种黑洞是动态和非轴对称的,它的熵很难计算.引进一个新的坐标系,使得其中的00在视界面上正好是零.在此新坐标系下利用膜模型计算了该黑洞的熵. 计算结果表明:和稳态黑洞一样,动态黑洞的熵也是正比于它的视界面积. 相似文献