Direction of arrival estimation using array model in time-frequency domain

Time-frequency analysis is combined with array processing to develop a direction of arrival (DOA) estimation method. The array data model is constructed in time-frequency domain by cross time-frequency distribution between the output of a reference sensor and those of two symmetric sub-arrays. Accordingly a subspace method is presented based on the average of two sub-arrays‘ time-frequency data vector model instead of the conventional array model, to estimate DOAs of multiple signals. Because the array data is processed both in spatial domain and 2-D time-frequency domain, the proposed method has an ability to select the signal of interesting, and is suitable for non-stationary signal. Additionally, the method is robust to noise and holds an advantage of low computational load. Simulations are conducted to verify the efficiency of the method and comparision is made with other methods.     

Robust algorithm of direction of arrival estimation for coherent wideband sources in unknown correlated noise fields

A robust algorithm of direction of arrival (DOA) estimation for coherent wideband sources in unknown correlated noise fields was investigated. The noise is usually unknown and correlated among sensors in practical applications, especially for arrays with comparatively small apertures. The spatially correlated noise incurs an increase in focusing error and a severe degradation in the DOA estimation, and therefore a method of focusing transformation based on differentiating covariance matrix was proposed to eliminate noise, hence reduce the focusing error. The simulation and experimental results demonstrate the effectiveness of the proposed method.     

Experimental studies on the impact of ASE noise of single-channel optical amplifiers in central office applications

We identified the amplified spontaneous emission-amplified spontaneous emission (ASE-ASE) beat noise from the semiconductor optical amplifier, which has been overlooked in previous studies, as a cause of severe system penalties when it was used to provide single-channel amplification in a dynamic central office environment through experimental studies. Our results pointed out that the ASE-ASE beat noise of the optical amplifier, other than its gain and noise figure, has to be considered to correctly predict its performance in these new applications.     

Early detection of diseases in plant tissue using spectroscopy – applications and limitations

Plant diseases can greatly affect the total production of food and agricultural materials, which may lead to high amount of losses in terms of quality, quantity and also in economic sense. To reduce the losses due to plant diseases, early diseases detection either based on a visual inspection or laboratory tests are widely employed. However, these techniques are labor-intensive and time consuming. In a view to overcome the shortcoming of these conventional approaches, several researchers have developed non-invasive techniques. Recently, spectroscopy technique has become one of the most available non-invasive methods utilized in detecting plant diseases. However, most of the studies on the application of this novel technology are still in the experimental stages, and are carried out in isolation with no comprehensive information on the most suitable approach. This problem could affect the advancement and commercialization of spectroscopy technology in early plant disease detection. Here, we review the applications and limitations of spectroscopy techniques (visible/infrared, electrical impedance and fluorescence spectroscopy) in early detection of plant disease. Particular emphasis was given to different spectral level, challenges and future outlook.     

Lie symmetries and conserved quantities of non—holonomic mechanical systems with unilateral Vacco constraints

In this paper,we study the Lie symmetries and the conserved quantities of non-holonomic mechanical systems with unilateral Vacco constraints.we give the conditions and the form of conserved quantities due to the Lie symmetries of the systems,and present the inverse problem of the above proble,i.e.finding the corresponding Lie symmetry transformation according to a given integral of the system.Finally,we give an example to illustrate the application of the results.     

Application of adaptive filter in time delay estimation——generalized quadratic interpolation method

The time delay estimation(TDE)of two different received sig-nals from the same source has attracted many interests of researchers inthe field of signal processing.A method described for precisely estimatingtime delay in this paper is based on the assumption that little prioriknowledge on statistical characteristics is available for the received signals.The variance of the estimate is derived.The basic architecture of thismethod is to use the adaptive noise canceller,in the steady state,andto interpolate the weight coefficients by using a generalized quadratic inter-polation matrix.The formula of the time delay estimation is presented.The method proposed by F.A.Reed is a special case of this method.The hardware implementation is much easier than that of theconventional time delay estimation method.The results of the systemsimulation and the experimental results at sea show a good agreementwith the theoretical analysis.     

Experimental Studies of Liquid Viscosity in Immiscible Al—In Alloys

The liquid viscosity o[ immiscible Al-In alloys was measured using an oscillating-cup viscometer. It has been found that the viscosity of Al-In melts changes abruptly at the critical temperature of liquid-liquid phase separation during the cooling process. The experimental data above the temperature of phase separation are fitted to the Arrhenius equation. The fitted results show that the temperature dependence o[the viscosity obeys the Arrhenius relationship.     

Robust H_∞ control of piecewise-linear chaotic systems with random data loss

<正>This paper studies the problem of robust H_∞control of piecewise-linear chaotic systems with random data loss. The communication links between the plant and the controller are assumed to be imperfect(that is,data loss occurs intermittently,which appears typically in a network environment).The data loss is modelled as a random process which obeys a Bernoulli distribution.In the face of random data loss,a piecewise controller is designed to robustly stabilize the networked system in the sense of mean square and also achieve a prescribed H_∞disturbance attenuation performance based on a piecewise-quadratic Lyapunov function.The required H_∞controllers can be designed by solving a set of linear matrix inequalities(LMIs).Chua's system is provided to illustrate the usefulness and applicability of the developed theoretical results.     

Experimental Test of the Non—reproducibility of Cross Sections in Dissipative Reactions

Two independent measurements of cross sections for the ^19F ^93Nb dissipative heavy ion collisions have been performed at incident energies from 100 to 108MeV in steps of 250keV.In the two measurements,two independently prepared targets were used.All other experimental conditions were identical in both experiments.The data indicate that non-reproducibility of the non-self-averaging oscillation is yielded in the two measurements.This supports the recent theoretical predictions of spontaneous coherence,slow phase randomization and extreme sensitivity in highly excited complex quantum systems.     

Robust networked H∞ synchronization of nonidentical chaotic Lur＇e systems

We mainly investigate the robust networked H∞synchronization problem of nonidentical chaotic Lur’e systems. In the design of the synchronization scheme, some network characteristics, such as nonuniform sampling, transmissioninduced delays, and data packet dropouts, are considered. The parameters of master–slave chaotic Lur’e systems often allow differences. The sufficient condition in terms of linear matrix inequality(LMI) is obtained to guarantee the dissipative synchronization of nonidentical chaotic Lur’e systems in network environments. A numerical example is given to illustrate the validity of the proposed method.     

Robust H_∞ control of uncertain systems with two additive time-varying delays

This paper is concerned with the problem of delay-dependent robust H∞control for a class of uncertain systems with two additive time-varying delays. A new suitable Lyapunov–Krasovskii functional(LKF) with triple integral terms is constructed and a tighter upper bound of the derivative of the LKF is derived. By applying a convex optimization technique, new delay-dependent robust H∞stability criteria are derived in terms of linear matrix inequalities(LMI). Based on the stability criteria, a state feedback controller is designed such that the closed-loop system is asymptotically stable.Finally, numerical examples are given to illustrate the effectiveness of the proposed method. Comparison results show that our results are less conservative than the existing methods.     

Noether——Lie symmetry and conserved quantities of mechanical system in phase space

In this paper, a new kind of symmetry and its conserved quantities of a mechanical system in phase space are studied. The definition of this new symmetry, i.e. a Noether--Lie symmetry, is presented, and the criterion of this symmetry is also given. The Noether conserved quantity and the generalized Hojman conserved quantity of the Noether--Lie symmetry of the system are obtained. The Noether--Lie symmetry contains the Noether symmetry and the Lie symmetry, and has more generalized significance.     

Elasto-dipolar magnons—a new class of nonexchange spin-wave excitations

Interference of phonon and magnetic dipolar spin-spin interaction mechanisms in a finite magnet can result in a previously unexplored class of nonexchange spin waves.     

The breakdown of Navier—Stokes hydrodynamics in small periodic systems

The results of direct particle simulations of 2-dimensional, convective flow are compared with truncated solutions of the Navier—Stokes equation, and show that the Navier—Stokes predictions are quite accurate throughout the transient development of the flow, if the correct value of the viscosity is used. The viscosity determines the steady values of the flow velocities, and the Navier—Stokes predictions are accurate for systems with multiple k vector forcing. At higher values of the fields, there is a limiting value of the forcing for which the character of the response matches the character of the forcing. Beyond this point there is a breakdown in hydrodynamic behaviour where the particle nature of the fluid dominates. Both multiphase solid and fluid regions are observed, plus cavitation, depending upon the forcing and the system geometry.     

Experimental research for direction of arrival estimation based on signal phase matching principle

In order to test the validity of signal phase matching principle (SPMP) applied to direction of arrival (DOA) estimation, experiments are carried out at a reservoir using 16 sensors array. Two kinds of method, Least Square Method for Signal Matching principle (LSMSPM) and singular value decomposition method for signal matching principle (SVDSPM), are used for DOA estimation. Their performances were analyzed and compared with MUSIC and conventional beam-forming (CBF) method. The results show that the 3 dB beam width obtained by SPMP is 1/4 to 1/7 as much as that obtained by CBF and 1/2 to 1/3 by MUSIC method. In addition, LSMSPM and SVDSPM are available for multi-sources DOA estimation and high resolution DOA estimation, which demonstrates that DOA estimation by SPMP method is better than that by MUSIC and CBF method.     

Experimental studies on the multistage constant modulus array for the estimation of directions-of-arrival

The performance of the multistage Constant Modulus (CM) array, one of the most striking blind beamforming algorithms, for the source Directions-of-Arrival (DOA) estimation was analyzed via computer simulations and water tank experiments, and was compared to that of other DOA estimation algorithms including the ‘non-blind‘ and the ‘blind‘. Firstly, a nominal array model and an array model with gain and phase perturbations were established,respectively. Secondly, the multistage CM array algorithm was described and computer simulations were conducted. Simulation results showed that the multistage CM array could correctly estimate the DOA at the same time when the sources were blindly recovered, and the angle separating ability of the algorithm was beyond the Rayleigh resolution limit. By changing the variance of the array model errors, it was also verified that the multistage CM array was more robust to the errors than some other algorithms mentioned in this paper. Finally, water tank experiments and data processing results were provided. Situations with different array sizes and source angular separations were considered. It was shown that the results were in good agreement with computer simulations. Results of computer simulations and water tank experiments verified that the DOAs of the multiple independent sources could be blindly and robustly estimated with the multistage CM array.     

Amplitude-difference method in the estimation of ultrasonic attenuation

In this paper a new method of ultrasonic quantitative diagnosis isdiscribed.This method can elminate the effect of system deviation and lessenthe the effect of beam radiation diffraction.In can be spp1ied together withmany kinks of B-scanners.To verify the method,this paper has shown a newmethod to make a tissue phantom and a special apparatus.The results showthat the method is useful in the diagnosis of diffuse liver diseases,tumors andcanccrs.It is also useful in the appraisal of the health and the stages of fetus.     

Evaluation of the mechanical properties of PMC interface using slice compression test — Analysis of transfer mechanism of interfacial shear stress

Properties of the fiber/matrix interface in SiO₂/epoxy and SiC/epoxy composite are investigated using the slice compression test (SCT) for the single fiber, where the specimen is loaded and unloaded between a plate which has different mechanical properties. It is found that the interfacial debonding proceeds from the polished surface at a soft plate side and that the fiber protrusion occurs after unloading. The fiber-protrusion length is directly measured at each applied stress level using a scanning electron microscope. Interfacial shear-sliding stress is obtained based on the constant shear-sliding stress analysis employing the obtained protrusion length. It is demonstrated that the value of interfacial shear-sliding stress shows good agreement with that obtained from another technique, the push-out test, on the same system. The relation between the fiber-protrusion length and applied stress is proportional to a certain extent. From this result, it is analytically pointed out that the applied stress has a limiting value in this SCT because of Poisson's effect. Also, two interfacial debonding criteria, which are determined analytically for the PMC, are discussed.