基于伪随机序列的多波束水声探测系统的信道估计技术

多波束水声探测系统不同方向回波信号的同时检测,可以理解为通信中的信道估计问题。在水下多径传播环境中,多径信道的时延参数和幅度衰减参数的估计是多波束探测系统实现目标探测、定位和识别的基础,而抑制来自其它波束的多址干扰(MAI)是信道估计算法的重要目标。将直接序列码分多址(Direct Sequence Code-Division Multiple Access,简称DS-CDMA)通信系统模型应用于水声多波束探测系统。建立了基于伪随机序列的水下多波束探测系统的信号模型,研究了基于子空间方法的超分辨率信道估计算法。并给出了数值仿真实现,分析了信噪比、多址干扰及发射波束数等对信道估计算法性能的影响。仿真结果表明,该算法具有抑制多址干扰的性能,信道参数的估计方差逼近Cramer-Rao下界。这种信道估计技术尤其适合应用于多波束参量阵探测系统。     

Least-squares channel estimation assisted by self-interference cancellation for mobile pseudo-random-postfix orthogonal-frequencydivision multiplexing applications

A least-squares (LS) channel estimation (CE) technique is investigated to apply pseudo-random-postfix orthogonal-frequency-division multiplexing (PRP-OFDM) communications onto mobile applications, which often operate on a rapidly time-varying frequency-selective fading channel. Since conventional techniques exploiting a moving averager cannot function on a rapidly time-varying channel, the proposed technique takes advantage of several self-interference cancellation (SIC) methods to effectively and timely reduce inter-path interference, inter-symbol interference (ISI) and inter-block interference (IBI). The proposed technique can therefore overcome frequency selectivity caused by multipath fading and time selectivity caused by mobility; in particular, OFDM communication is often anticipated to operate in environments where both wide Doppler spread and long delay spread exist. Meanwhile, lower mean-square estimation errors, lower error probabilities and lower error floors can also be achieved using the proposed technique. Since conventional techniques based on minimum-mean-square-error (MMSE) CE usually highly require a priori channel information or many training preambles, a generic estimator assisted from LS CE is exploited as it can be performed serially, block by block, to reduce computational complexity. Extensive computer simulations in conjunction with strict statistical analysis are carried out to verify the improvements provided by the proposed technique.     

A time-efficient and accurate strain estimation concept for ultrasonic elastography using iterative phase zero estimation

In ultrasonic elastography, the exact estimation of temporal displacements between two signals is the key to estimating strain. An algorithm was previously proposed that estimates these displacements using phase differences of the corresponding base-band signals. A major advantage of these algorithms compared with correlation techniques is the computational efficiency. In this paper, an extension of the algorithm is presented that iteratively takes into account the time shifts of the signals to overcome the problems of aliasing and accuracy in the estimation of the phase shift. Thus, it can be proven that the algorithm is equivalent to the search of the maximum of the correlation function. Furthermore, a robust logarithmic compression is proposed that only compresses the envelope of the signal. This compression does not introduce systematic errors and significantly reduces decorrelation noise. The resulting algorithm is a computationally simple and very fast alternative to conventional correlation techniques, and the accuracy of strain images is improved.     

Channel estimation for time-hopping pulse position modulation ultra-wideband communication systems

Ultra-wideband (UWB) communication systems are used in indoor environments with dense multi-path characteristics. Therefore channel estimation has an important role in the receiver of these systems. A new approach for data-aided (DA) and non-data-aided (NDA) channel estimation is proposed, which is called the pulse compression (PC) method. This method is useful for UWB systems employing time-hopping pulse position modulation. The PC method requires only some basic operations such as sampling, overlap-add and finite impulse response filtering. The PC method, in both DA and NDA scenarios, in spite of its low complexity, outperforms the maximum-likelihood (ML) method in channel parameters estimation. The bit error rate (BER) of the DA method, in single-user scenario, performs as well as the ML method, and in multi-user scenario, in the worst case, there is only 0.5 dB loss compared with the ML method. In the case of NDA scenario, the proposed method outperforms the NDA-ML method, that is, in the single-user scenario about 4 dB gain at the BER of 1023 is observed. In multi-user scenario, it outperforms significantly the NDA-ML method, and its performance loss in comparison with the perfect channel knowledge scenario is about 3 dB at the BER of 1023.     

Numerical method of thermal shock resistance estimation by quenching of samples in water

A temperature dependence of a transient heat transfer for cylindrical and ball samples (of different surface roughness) of 3–60 mm diameters heated up to the temperature range from 150 to 1200° C and quenched in a water bath of large volume was established. The measurement errors of the transient heat transfer defined by different methods with regard to hysteresis and statistical nature of boiling phenomena were evaluated. The study revealed, that the transition point from bubble to film boiling and vice versa differs essentially. The transient heat transfer in the field of bubble boiling did not depend on the size and the shape of the samples, their surface roughness and thermo-physical properties. But the magnitude of hysteresis in changing between the boiling regimes were substantially governed by the geometrical and thermo-physical characteristics of the samples. The examples of thermal stresses estimation which caused quenching damage to ZrC samples, heated up to a wide range of temperature from 150 to 1200 C, are given. The obtained data on the transient heat transfer and proposed recommendation on the temperature regimes of quenching for convenient sample sizes can form a basis of a standard for the numerical evaluation of the thermal shock resistance.     

Blind channel estimation for multiple input multiple output uplink guard-band assisted code division multiple access systems with layered space frequency equalisation

Single carrier (SC) code division multiple access (CDMA) with block transmission has been shown to be more effective while utilising a low-complexity equaliser to combat frequency-selective fading channels, when compared with conventional direct sequence CDMA technology. It also has lower peak-to-average power ratio and lower frequency sensitivity compared with multicarrier CDMA. The authors propose two blind channel estimation methods for uplink multiple input multiple output SC-CDMA systems with block transmisssion-one is the subspace-based method and the other is the so-called autocorrelation contribution method (ACM). Both the methods provide close performance to the case with perfect channel knowledge at high signal-to- noise ratio (SNR) without any training data required. It is shown that ACM yields a better performance than the subspace method at a lower SNR, and a similar performance at a high SNR, with the advantages of avoiding rank determination and noise power estimation as in the subspace method. In addition, the authors integrate layered space frequency equalisation with blind channel estimation, which provides improved performance over the conventional linear equalisation, by employing successive interference cancellation.     

充电器对移动电话比吸收率影响的研究

阐述电磁波对人体的影响可测试参数比吸收率的定义、测试方法和测试系统,分析影响移动电话比吸收率的主要因素,重点研究移动电话附件充电器对移动电话比吸收率的影响,提出充电器对移动电话的等效天线影响模型,并通过实际的测试数据来验证模型.基于模型提出降低充电器对移动电话比吸率影响的改进措施,为移动电话设计提供参考依据.     

Degassing of Al-Si-X powders assisted by flushing with argon or nitrogen

The results reported in this paper showing the effect of different degassing modes on the Al-20Si-3Cu-1 Mg powder are a complement of our previous papers concerning the continuous and non-continuous degassing sequences of the same powder. This research was mainly directed at an improvement in the technique to remove volatile and gaseous contaminants from the porous compact made from the Al-20Si-3Cu-1 Mg powder. This improvement has been possible by modifying the conventional degassing process of the powder as reported previously, namely degassing of the powder assisted by flushing with depurative gases such as argon or nitrogen. It is apparent that flushing with argon or nitrogen increases the efficiency of moisture and hydrogen evolution in comparison with the conventional degassing mode.     

Spectrum constructing with nonuniform samples using least-squares approximation by cosine polynomials

The least-squares approximation of cosine polynomials is used to construct the spectrum from the simulated nonuniform samples of the interferogram given by a step-mirror-based static Fourier transform spectrometer. Numerical and experimental results show the stability of the algorithm and a spectrum-constructing error of 0.03%.     

Sequential and parallel schemes for adaptive 2-D parameter estimation with application to image estimation

In this paper, the non-causal quarter plane 2-D Recursive Least Squares (2D-RLS) algorithm for adaptive processing is developed. The complexity of this algorithm turns out to beO(L ⁶) per iteration, for anL ×L window. With the aim of reducing this complexity, the matrix gains appearing in the algorithm are replaced by scalar gains. This approach yields the Approximate 2-D Recursive Least Squares (A2D-RLS) algorithm, which is shown to have a complexity ofO(L ²). With the objective of reducing the computation time even further, a parallel scheme is developed for the A2D-RLS algorithm. Since the algorithm is inherently sequential, its parallelization involves some more approximations. The desired accuracy of the estimated parameters is shown to place an upper bound on the number of processors. The parallel scheme is suitable for implementation on shared memory as well as distributed memory machines. The algorithm is applied to the problem of image estimation. Simulation results giving speed-up, efficiency, and the accuracy of the estimated image are presented.     

用环形试样测定软磁材料磁各向异性的研究

采用趋近饱和定律测定了纳米晶合金环形试样有效磁各向异性常数＜K＞.为了对比测量的准确度,同时测试了传统的晶态坡莫合金环形试样的磁晶各向异性.结果表明,用环形试样可以完成对低矫顽力的软磁材料进行磁各向异性的测定.     

Catalytic decolorization of azo-stuff with electro-coagulation method assisted by cobalt phosphomolybdate modified kaolin

The new catalytic decoloration of C.I. Acid Red 3R with electro-coagulation (EC) method assisted by cobalt phosphomolybdate modified kaolin has been studied. The result showed that this process could effectively remove the C.I. Acid Red 3R contained in wastewater and its color removal efficiency could reach up to 98.3% in 7 min. The kinetics of the catalytic decolorization of Acid Red 3R was also studied. The decolorization reaction order was dependent on the initial concentration [R](0) with respect to the concentration of C.I. Acid Red 3R. At lower [R](0) the order was first, which then decreases with increasing [R](0). The operating parameters such as initial pH, current density and temperature were also investigated. A possible reaction mechanism was proposed.     

Synthesis of nano-sized NaY zeolite composite from metakaolin by ionothermal method with microwave assisted

Nano-sized NaY zeolite had been synthesized from metakaolin by ionothermal method with microwave assisted. Its structure had been characterized by XRD, SEM, HREM, and its physicochemical properties and catalytic characteristics were studied. The results showed that the size of the product was 150–250 nm, relative crystallinity 69.16%, Si/Al ratio 5.02. Compared with conventional NaY zeolite, nano-sized zeolite composite had larger surface area and mesopore volume, better thermal stability, higher cracking activity, higher gasoline selectivity, lower coke and gas selectivity. So it has good industry application prospects.     

Fully automated 96-well liquid-liquid extraction for analysis of biological samples by liquid chromatography with tandem mass spectrometry

A fully automated high-throughput liquid-liquid extraction (LLE) methodology has been developed for preparation of biological samples using a 96-well LLE plate and a 96-channel robotic liquid handling workstation. The 96-well LLE plate is made of a 96-well filter plate filled with inert diatomaceous earth particles, allowing continuous and efficient extraction of analytes between the aqueous biological sample and the organic extraction solvent. Two carboxylic acid-based protease inhibitor compounds with high and low levels of plasma protein binding were chosen for the development and application of the automated methodology. The LLE extracts of the plasma samples of the two compounds were analyzed by high-performance liquid chromatography with electrospray (ESI) tandem mass spectrometry (LC-MS/MS). The LC-MS/MS method was developed using a rapid gradient LC separation, followed by sample introduction through an ionspray interface in the negative ion mode and tandem mass spectrometric detection with selected reaction monitoring. In the optimized LLE method, a formate buffer solution was first loaded into a 96-well filter plate packed with inert diatomaceous earth material. Then crude plasma samples and a water-immiscible organic solvent, methyl ethyl ketone, were sequentially added to the LLE plate so that LLE would occur in the interface between the two liquid phases on the surface of individual particles in each well. The organic eluate containing extracted analytes was evaporated and reconstituted for LC-MS/MS analysis. This fully automated LLE methodology avoids several disjointed steps involved in a manual or semiautomated LLE method, leading to significantly reduced sample preparation time, increased sample throughput, and clean sample extracts for improved ESI-MS/MS detection. The automated LLE methodology is universal and can be employed for sample preparation of other biological fluids. The complete bioanalytical method, based on the automated LLE and fast gradient LC-MS/MS, was validated and successfully applied to the quantitative analysis of protease inhibitors in rat plasma.     

Pose estimation for autonomous grasping with a robotic arm system

A robust and accurate method for estimating the 3-D pose of a planar rigid object is presented. This article demonstrates that 3-D pose estimation becomes feasible by using the 2-D tracking points on an object of scale-invariant feature transform (SIFT) and 3-D point cloud detected by stereo vision on an object, assuming that a 3-D geometric model of an object is known a priori. The roll and pitch angles of an object are estimated by the normal vector of approximate plane of 3-D point cloud on an object and the yaw angle is estimated by 2-D tracking point on an object of SIFT. Accurate object detection and localization in the camera coordinate system is crucial for grasping. In the motion planning, the bidirectional rapidly exploring random tree algorithm is used to search for a valid path for efficient grasping. Our robot arm can robustly and autonomously grasp a randomly rotative rigid object detected by SIFT in 3-D space. We have realized a grasping scenario with a dexterous arm (ADAM) such that an object in front of ADAM can be grasped. This demonstration shows how the proposed components build a dexterous and robust system integrating object detection, pose estimation, and motion planning.     

Strength estimation for silicon nitride specimens with a spherical void

Silicon nitride specimens embedded with a single spherical void were prepared for a flexural strength test. The measured flexural strengths of the specimens were compared with theoretically estimated strengths. Estimation of the strengths was done using a Gibbs free-energy criterion. The energy was calculated by Eshelby's equivalent inclusion method for a specimen with an embedded void. Good correspondence was obtained between the experimental and the estimated fracture loads. A deviation of the estimated strength from the experimental value was observed for voids whose diameters were comparable with intrinsic defects.     

Direction-of-arrival estimation for uncorrelated and coherent signals with fewer sensors

A novel direction-of-arrival (DOA) estimation method with fewer sensors is proposed when uncorrelated and coherent signals coexist, and two effective criteria to estimate the number of uncorrelated and coherent signals are also developed. First, the DOA matrix is constructed. Then, the DOAs of uncorrelated signals can be estimated by these proposed criteria and the related eigenvalues of the DOA matrix. Secondly, with the eigenvectors of the DOA matrix, which are related to coherent signals, the coherent signals that belong to the multipath of different far-field sources can be resolved separately using a spatial smoothing technique. Moreover, the DOA estimation accuracy of coherent signals can be further improved by an orthogonal projection technique. Simulation results demonstrate the effectiveness and efficiency of the proposed method.     

Vp×B electron linear accelerator with TE-wave assisted by plasma for beam stabilization

The V_p × B acceleration scheme with the use of a transverse electromagnetic wave is demonstrated experimentally, in which a pre-ionized plasma is supplemented for obtaining a stable electron beam. The slow wave structure employed here is a dielectric loaded waveguide, and an electron beam in the accelerator induces surfaces charges on the dielectric. The electron beam on account of acceleration also produces a dilute plasma to neutralize the surface charges. An initial energy gain of 2.5 keV for the electron beam is observed from an incident energy of 60 keV without any external vertical magnetic field. When an external vertical magnetic field of 1.5 G is applied under the same conditions for performing the V_p × B scheme, an additional 1.5 keV energy gain is observed.     

Dissimilar Al/Mg alloys friction stir lap welding with Zn foil assisted by ultrasonic

The Zn-added ultrasonic assisted friction stir lap welding (UaFSLW) was carried out to improve the quality of dissimilar Al/Mg alloys joint. The effects of ultrasonic power on the joint quality were also investigated. The results indicated that the larger effective lap width and mixing region between Mg and Al (Mg/Al MR) were attained by Zn foil addition and external ultrasonic assistance. Compared with the conventional joint, the finer and better-distributed Mg-Zn IMCs placing the continuous Al-Mg IMCs were formed in the Mg/Al MR of the Zn-added UaFSLW joint. The Zn foil addition and external ultrasonic assistance significantly improved the tensile shear load of the joint, and the load was increased with the increase of the ultrasonic power. The maximum tensile shear load of 7.95 kN was attained, which was 52.6% larger than that of the conventional joint.     

Wideband balanced folded dipole antenna with a dual-arm monopole structure for mobile handsets

In this study, a balanced antenna for mobile handset applications with enhanced bandwidth performance, covering the bands from 1.8 to 2.45 GHz, is investigated. The antenna is a slot planar dipole with folded structure and a dual-arm on each half. The antenna impedance was investigated using a two-port S-parameter method. For the purpose of antenna power gain measurement, a wide bandwidth planar balun was employed to support a balanced feed from an unbalanced source. For validation, a prototype of the proposed antenna was fabricated and tested. The performance of the antenna was then verified in terms of return loss, radiation patterns and power gain. The calculated and measured results show good agreement and the results also confirm good wideband characteristics with low induced current in the ground plane, thus minimising performance variations and SAR.