3D attitude measurement by means of spread spectrum modulated ultrasonic wave

Local position and attitude measurement methods are necessary for the navigation of autonomous robots and the other applications. In this paper, a 3D attitude measurement method is proposed. This method uses the spread spectrum modulated ultrasonic wave for the measurement of the pseudo-distance of each pathway between transmitter and receiver elements that are arranged in an array. The relative attitude between transmitter and receiver unit could be calculated from the relationship between these pseudo-distances. The use of spread spectrum modulation enables the high accuracy, noise tolerance, and coexistence of multiple transmitter devices by code division multiple access (CDMA) between transmitter and receiver elements. A pair of transmitter and receiver prototype for proposed method was manufactured, and the fundamental performance was examined in experiments. As a result, accuracy of σ=0.78 mm in the pseudo-distance measurement of each pathway between transmitter and receiver elements was confirmed, and about 0.01 rad resolution in the attitude measurement was also confirmed.     

超高压可控并联电抗器录波回放系统设计

随着大电网互联和大容量、远距离输电系统的发展,电网对电能质量提出了更高的要求。在超高压线路中可控并联电抗器已成为系统稳定必要的设备,因此对可控并联电抗器录波回放系统的研究也就显得更加重要。该文主要研究的是可控并联电抗器的录波回放系统所工作的硬件环境及软件编程的流程图。     

Estimates of the maximum likelihood of parameters of weak optical signals during photodetecting by means of recording photoelectron emission moments

A likelihood function is obtained for estimating parameters of weak optical signals during detecting by means of recording emission moments of each photoelectron. Likelihood equations are derived and solved by an example of optimal estimates of a Gaussian pulse. Expressions for compatible and incompatible estimates of all three unknown parameters of the pulse are obtained. Analytical expressions for the Kramer-Rao bounds determining the quality of the estimates obtained are also derived. The variances of compatible estimates of the signal amplitude are demonstrated to be three times those of incompatible estimates, while the variances of the estimates of all parameters are inversely proportional to the product of the signal amplitude and its duration.     

Holographic measurement of the wave aberration of an electron microscope by means of the phases in the Fourier spectrum

The resolution limit achievable by holographic correction of the aberrations of an electron microscope depends critically on the information available about the microscope parameters when the hologram was taken. The measuring technique based on symmetry relations of the phases in the Fourier spectrum of the reconstructed electron wave is outlined and experimentally tested.     

Inverse scattering problem for the wave equation in a one-dimensional inhomogeneous medium

A one-dimensional inverse scattering problem for the Helmholtz wave equation is considered. The problem consists in reconstruction of the refractive index of transparent inhomogeneous media from a specified complex reflection spectrum. A method previously proposed by the authors for reconstruction of the Bragg gratings in the coupled mode approximation is used. Numerical simulations of the inverse scattering problem for the classical Rayleigh layer and for an exponentially smooth transitional layer are performed. The solutions obtained demonstrate the high efficiency of the proposed approach. The accuracy of refractive index reconstruction turns out to be essentially dependent on the degree of layer smoothness. The proposed approach can be applied in problems of the development of coated and interference optics, in synthesis of the Bragg gratings and multilayer optical mirrors, and in radiophysics and acoustics.     

A pulsed two-channel Nd:YAG laser with an improved spatial structure of IR radiation for prompt recording and development of photothermoplastic holograms

A two-channel Nd:YAG laser for high-speed recording and development of photothermoplastic holograms has been created. In two independent channels, the laser generates monopulse radiation of nanosecond duration (30 ns) at the second harmonic frequency (λ ₂ = 0.532 μm) and IR radiation (λ ₁ = 1.064 μm) produced by quasi-stationary free-running lasing of millisecond duration (4 ms). The radiations with wavelengths λ ₂ and λ ₁ are used, respectively, for exposure and development of photothermoplastic holograms. A method based on the use of a passive resonator is proposed to improve the spatial structure of IR radiation during lasing.     

Soil moisture assessment by means of compressional and shear wave velocities: Theoretical analysis and experimental setup

In previous works, the authors presented the outline of a method for measuring the moisture content in agricultural soils via elastic waves, along with experimental results obtained on a specimen of sandy soil. This work illustrates other aspects and results of the research, regarding both the underlying theory and the design and realization of an improved measurement system. Firstly, the derivation of the simplified equations which are at the basis of the moisture measurement is thoroughly illustrated and discussed, starting from the more complex (and generally unmanageable) equations of elastic waves in unconsolidated porous media. The analysis suggests that by measuring the velocities of low-frequency compressional and shear waves in soils, it is possible not only to measure the water content, but also the uniformity in the water distribution. Secondly, the design and the practical realization of an experimental setup, which is able to measure the velocity of compressional and shear waves in soils, is illustrated in detail. The use of custom-built compressional and shear waves electromechanical actuators, together with geophones, low noise preamplifiers, and suitable signal processing techniques, brought to the realization of an effective and reasonably accurate measurement system.     

Analysis of elastic wave scattering problems using volume integral equation method

A volume integral equation method (VIEM) is applied for the effective analysis of elastic wave scattering problems in unbounded solids containing isotropic or anisotropic inclusions. It should be noted that this newly developed numerical method does not require Green’s function for anisotropic inclusions to solve this class of problems since only Green’s function for the unbounded isotropic matrix is involved in their formulation for the analysis. Through the analysis of plane wave scattering problems in unbounded isotropic matrix with isotropic or anisotropic inclusions, it will be established that this new method is very accurate and effective for solving plane wave scattering problems in unbounded solids containing isotropic or anisotropic inclusions.     

Flow measurement by the end-depth method in inverted semicircular channels

A free overfall at the end of an open channel provides a simple means for measuring flow discharge. The paper presents a simplified approach for the computation of end-depth of a free overfall in horizontal or mildly sloping inverted semicircular channels. Using a known end-depth the discharge can be estimated. The flow over a free overfall in an inverted semicircular channel is simulated by that over a sharp-crested weir to calculate the end-depth-ratio (EDR). The mathematical model is calibrated by the experimental data, making the coefficient of velocity a free parameter. The EDR, related to the critical depth, is around 0.705 for a critical depth–diameter ratio up to 0.42. The computed results agree satisfactorily with the experimental data.     

New reactor dedicated to in operando studies of model catalysts by means of surface x-ray diffraction and grazing incidence small angle x-ray scattering

A new experimental setup has been developed to enable in situ studies of catalyst surfaces during chemical reactions by means of surface x-ray diffraction (SXRD) and grazing incidence small angle x-ray scattering. The x-ray reactor chamber was designed for both ultrahigh-vacuum (UHV) and reactive gas environments. A laser beam heating of the sample was implemented; the sample temperature reaches 1100 K in UHV and 600 K in the presence of reactive gases. The reactor equipment allows dynamical observations of the surface with various, perfectly mixed gases at controlled partial pressures. It can run in two modes: as a bath reactor in the pressure range of 1-1000 mbars and as a continuous flow cell for pressure lower than 10(-3) mbar. The reactor is connected to an UHV preparation chamber also equipped with low energy electron diffraction and Auger spectroscopy. This setup is thus perfectly well suited to extend in situ studies to more complex surfaces, such as epitaxial films or supported nanoparticles. It offers the possibility to follow the chemically induced changes of the morphology, the structure, the composition, and growth processes of the model catalyst surface during exposure to reactive gases. As an example the Pd(8)Ni(92)(110) surface structure was followed by SXRD under a few millibars of hydrogen and during butadiene hydrogenation while the reaction was monitored by quadrupole mass spectrometry. This experiment evidenced the great sensitivity of the diffracted intensity to the subtle interaction between the surface atoms and the gas molecules.     

Stabilization of an inverted pendulum-cart system by fractional PI-state feedback

This paper deals with pole placement PI-state feedback controller design to control an integer order system. The fractional aspect of the control law is introduced by a dynamic state feedback as u(t)=_Kpx(t)+_KIIα(x(t))$u\left(t\right)=K_{p}x\left(t\right)+K_I{\mathfrak{I}}_{\alpha }\left(x\right(t\left)\right)$. The closed loop characteristic polynomial is thus fractional for which the roots are complex to calculate. The proposed method allows us to decompose this polynomial into a first order fractional polynomial and an integer order polynomial of order n−1$n-1$ (n being the order of the integer system). This new stabilization control algorithm is applied for an inverted pendulum-cart test-bed, and the effectiveness and robustness of the proposed control are examined by experiments.     

Investigation of droplet size distribution in two-phase flows using a combined method for recording droplet fluorescence and diffraction scattering of light

A prototype of a combined measurement system (MS) based on the fluorescent and small-angle methods of determining the parameters of a fuel-air spray using a pulsed laser as a light source and a color digital video camera to record spray sections was designed and tested. The tests of the MS showed that it has good performance and is suitable for determining the characteristics of advanced atomizers in a pressure chamber. Spatial concentration distributions of aerosols generated by a centrifugal atomizer were studied. Distributions of time-averaged Sauter diameters of droplets, their concentration, and the circumferential inhomogeneity of droplet concentration in the spray cross section were obtained. A study of fuel atomization from a plate was performed showing the possibility of using this device in power plants to improve the atomization performance compared to the atomization of a free jet in crossflow.     

应用梯度矢量流Snake和灰预测的人脸轮廓跟踪

为了提高动态图像序列中人脸轮廓跟踪时梯度矢量流(GVF) Snake算法的实时性,同时解决人脸跟踪中的遮挡问题,提出了GVF Snake和单变量一阶灰色模型GM(1,1)相结合的人脸轮廓提取方法.该方法首先利用人脸运动信息和肤色模型粗略地检测出运动人脸轮廓,然后采用GVF Snake算法将人脸轮廓精确地提取出来,从而有...     

EMA recording of ultrasound lamb waves excited by laser nanopulses

The process of recording ultrasound excited by short laser pulses in metal plates using a wideband EMA receiver was experimentally studied. The investigation results can be used for creating noncontact methods and facilities for ultrasound inspection of thin-sheet metalwares.     

散射法表面粗糙度测量

介绍了标量和矢量两种散射理论，并用软X射线反射率对超光滑表面进行散射测量，同时应用这两种理论计算了超光滑表面粗度均方根值，从计算结果来看，两种理论所得结果与WYKO测量结果吻合较好。     

Automatic recording of object motion by the speckle method in the terahertz range

Using a microbolometer detector array, we recorded real-time images of metallic and dielectric objects illuminated by monochromatic terahertz radiation, including those hidden behind an opaque barrier. It is shown that the characteristics of movement of rough objects dynamic can be retrieved from the dynamics of the speckle structure of their images in the terahertz range. An automatic processing algorithm for terahertz videos with recording of moving objects was developed and software implemented.