Experimental comparison of integer/fractional-order electrical models of plant

In this paper, different integer and fractional-order models are studied from electrical point of view, these models are used to fit the measured impedance data for different types of fruits and vegetables. Experimental work is done on eight different models for six types of fruits to verify the best fitting model. Electric impedance is measured in the range of frequencies (200 mHz–200 Khz) using a non-destructive method, where the tissues are not damaged by electrode insertion. Moreover, two integer order models have been extended to the fractional order domain where data analysis and fitting are applied. The extra degrees of freedom of the fractional order models have enhanced the fitting parameters showing better accuracy. The double Cole Model has been found to be the best fit among different integer and fractional models based on root mean square error (RMSE).     

多自由度无人船系统建模

本文通过对多自由度下无人船的运行情况分析,提出了多自由度的无人船建模方法,主要是通过分析建立无人船的六自由度的MMG分离型模型,并依次减少一个自由度,推导出了其五自由度、四自由度与三自由度下的数学运动模型,解决了无人船在各个自由度下的建模问题。在建模时依次讨论了各个自由度下无人船舵、螺旋桨、粘性流体动力的力与力矩模型,以及其受到的风、浪、流的干扰模型,得出了比较完整统一的各个自由度船体数学运动模型。     

A Comparison of Tonographic-Trace Simulations Achieved by Two Systems: Nonlinear Elastic and Linear Viscoelastic

Twenty normal clinical tonographic traces were averaged and compared at 10-s intervals by means of two systems: 1) the decay curves of a linear viscoelastic mathematical model having a single degree of freedom, and 2) nonlinear elastic models, including the classical (or current) Grant model. The linear viscoelastic model provided a considerably better match than the other models. So far as degree of match and facility of outflow values were concerned, the study showed the effect on the models of various investigators' formulations of ocular rigidity, corneal indentation, and tonometer calibration. In precise work facility of outflow values should be reported only if a measure of the degree of fit to the tonogram is given.     

ANALYSIS OF CELL-AVERAGING BASED DETECTORS FOR χ2 FLUCTUATING TARGETS IN MULTITARGET ENVIRONMENTS

The χ2 family of signal fluctuation distributions represents the main fluctuation models which most radar targets follow it in their reflections. This family can be categorized as fluctuation distribution with two degrees of freedom and those with four degrees of freedom. The first category represents an important class of fluctuation models which when illuminated by a coherent pulse train, return a train of fully correlated pulses (Swerling Ⅰ model) or fully decorrelated pulses (Swerling Ⅱ model). The detection of this type of fluctuating targets is therefore of great importance. This paper is devoted to the analysis of Cell-Averaging (CA) based detectors for the case where the radar receiver noncoherently integrates M square-law detected pulses and the signal fluctuation obeys χ2 statistics with two degrees of freedom. These detectors include the Mean-Of (MO), the Greatest-Of (GO) and the Smallest-Of (SO) schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the χ2 fluctuation model with two degrees of freedom (SWⅠ & SWⅡ). The numerical results show that the MO version has the best homogeneous performance, the SO scheme has the best multiple-target performance, while the GO procedure does not offer any merits, neither in the absence nor in the presence of outlying targets.     

光纤对接波导阵列的自对准技术

自对准技术是一种新的光纤与波导的对准技术,它更适宜光纤、波导阵列的对接。这种方法是利用V型槽的硅片与波导表面重叠调整而实现。它消除了角调整,化6维调节为2维调节。自对准V型槽的参数设计及腐蚀必须十分精细,它也是自对准技术的关键。     

Statistical modeling of W-CDMA signals for use over frequency-selective multipath channels

This letter presents a mathematical model for the statistics of wideband code-division multiple-access signals which experience multipath fading. The statistics are obtained from numerically generated signals, and are then modeled with an offset noncentral chi distribution with three degrees of freedom. The mathematical model is tested against the numerically generated data by the use of a chi-square goodness-of-fit test.     

Analysis of Cell-averaging Based Detectors for χ2 Fluctuating Targets in Multitarget Environments

The χ^2 family of signal fluctuation distributions represents the main fluctuation models which most radar targets follow it in their reflections. This family can be categorized as fluctuation distribution with two degrees of freedom and those with four degrees of freedom. The first category represents all important class of fluctuation models which when illuminated by a coherent pulse train, return a train of fully correlated pulses （Swerling Ⅰ model） or fully decorrelated pulses （Swerling Ⅱ model）. The detection of this type of fluctuating targets is therefore of great importance. This paper is devoted to the analysis of Cell-Averaging （CA） based detectors for the case where the radar receiver noncoherently integrates M square-law detected pulses and the signal fluctuation obeys 2 statistics with two degrees of freedom. These detectors include the Mean-Of （MO）, the Greatest-Of （GO） and the Smallest-Of（SO） schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the χ^2 fluctuation model with two degrees of freedom （SWI ＆ SWII）. The numerical results show that the MO version has the best homogeneous performance, the SO scheme has the best multiple-target performance, while the GO procedure does not offer any merits, neither in the absence nor in the presence of outlying targets.     

Statistical model for a mode-stirred chamber

The probability density functions for one- and three-dimensional fields in a mode-stirred chamber are derived and verified with chi-square goodness-of-fit tests on experimental data. Each of the three components of the field in the chamber is Rayleigh distributed, which is the same as chi distributed with six degrees of freedom. Each component of the power density is then exponentially distributed. Experimental data confirm these distributions, though unexpected high values, or outliers, were consistently found. Maximum-likelihood estimators of the functions' parameters are derived, and their accuracy is determined as a function of the amount of data. These results are applied to estimating chamber Q. The amount of data required for a given accuracy is determined     

Design,fabrication, modeling and control of a fabric-based spherical robotic arm

In this paper we present a spherical soft robotic arm made from fabric. The inflatable arm has a small mass and is pneumatically actuated. A configuration is employed with only three actuators controlling the two rotational degrees of freedom of a spherical joint. This differs from the commonly employed antagonistic pairs, including four actuators for two degrees of freedom. The fabrication procedure of the lightweight and compliant system is discussed in detail and uses commonly available materials and tools. The capability of the robotic arm to adjust the joint stiffness as a function of the actuator pressures is investigated and characterized for different deflection directions. The static mapping from the actuator pressures to the orientation of the robotic arm is identified from data and the inverse mapping is employed in a position controller. The modeling and controller derivation are performed for three different stiffness levels demonstrating the ability of the spherical robotic arm to change the joint stiffness independently of controlling the position. The position tracking performance is experimentally evaluated by tracking a square trajectory. A comparison of the tracking performance for the different stiffness levels shows that accurate tracking is more challenging for the smallest joint stiffness. A gray-box model capturing the interactions of the two degrees of freedom is used in a learning scheme that is applied for the smallest stiffness level. The learning approach reduces interactions between the two degrees of freedom and demonstrates the control performance achievable with the system developed.     

ATM network traffic characterization using two types of on–off sources

An approximate model for characterizing aggregated cell arrivals from heterogeneous sources to an ATM multiplexer is proposed. The model consists of two types of on–off sources and provides enough degrees of freedom to match a number of moments of cell arrival rates as well as the time correlation of the aggregated cell arrivals. Numerical results indicate that the queue length distributions obtained using the model closely approximate the exact results.     

VBR video traffic modeling and synthetic data generation using GA‐optimized Volterra filters

Variable bit rate (VBR) video traffic models, which accurately represent the traffic characteristics and statistical properties of real videos, can provide significant information about expected traffic behavior. This knowledge can be used in the development of effective control schemes and improved network quality of service. An interesting class of models based on the idea of generating a number of chi‐square sequences, by passing a Gaussian autoregressive (AR) process through a simple nonlinearity, was recently introduced. The gamma process in this class of models is obtained by a linear combination of the chi‐square sequences. This model is simple and allows for arbitrary selection of both the AR model and the shape parameter of the gamma probability density function. However, the AR filter order is chosen mainly on a trial‐and‐error basis. In addition, while the approach uses a linear combination of K chi‐square sequences, it fixes (K ? 2) coefficients and solves for only the remaining two because it has more equations than unknowns. Occasionally, the resulting solution is not feasible and additional trials for different solutions are required. It is therefore the objective of this paper to use genetic algorithms to provide a more systematic approach to find the various model parameters. The paper also presents a thorough statistical analysis of the generated synthetic data in order to assess its suitability for representing MPEG video traffic. A comparison with published results is carried out in terms of how close are the means, standard deviations, and the autocorrelation functions to those of the real data. A comparison of over 10000 replications and a number of different video traces reveals that a significant improvement can be achieved in almost all measures and for almost all the movies tested. Copyright © 2006 John Wiley & sons, Ltd.     

Degrees of Freedom Region of the MIMO X Channel

We provide achievability as well as converse results for the degrees of freedom region of a multiple-input multiple-output (MIMO) X channel, i.e., a system with two transmitters, two receivers, each equipped with multiple antennas, where independent messages need to be conveyed over fixed channels from each transmitter to each receiver. The inner and outer bounds on the degrees of freedom region are tight whenever integer degrees of freedom are optimal for each message. With M = 1 antennas at each node, we find that the total (sum rate) degrees of freedom are bounded above and below as 1 les eta*x les 4/3. If M > 1 and channel matrices are nondegenerate then the precise degrees of freedom eta*x = (4/3)M. Thus, the MIMO X channel has noninteger degrees of freedom when M is not a multiple of 3. Simple zero forcing without dirty paper encoding or successive decoding, suffices to achieve the (4/3)M degrees of freedom. If the channels vary with time/frequency then the channel with single antennas (M = 1) at all nodes has exactly 4/3 degrees of freedom. The key idea for the achievability of the degrees of freedom is interference alignment-i.e., signal spaces are aligned at receivers where they constitute interference while they are separable at receivers where they are desired. We also explore the increase in degrees of freedom when some of the messages are made available to a transmitter or receiver in the manner of cognitive radio.     

Sparse LCMV beamformer design for suppression of ground clutter inairborne radar

Cancellation of the ground clutter received at an airborne phased array radar is an inherently two dimensional problem. Clutter returns are Doppler shifted due to platform motion forcing the use of processors that can resolve targets in both velocity (Doppler) and azimuth. Fully adaptive processors that operate in both dimensions require prohibitively large computation so that reduced adaptive dimension, or partially adaptive processors must be considered. In conventional partially adaptive linearly constrained minimum variance (LCMV) beamformer design the approach taken has been to represent the interference subspace with some reduced set of vectors, typically the eigenvectors associated with the largest eigenvalues of the interference covariance matrix. This technique does yield good performance but will not give the optimum performance for a given partially adaptive dimension. In this paper, an off-line method for selecting the “best” degrees of freedom to be retained in a partially adaptive design is presented. The sequential algorithm described selects those degrees of freedom that best minimize the beamformer output mean square error. This approach leads to a sparse structure for the transformation matrix, which when implemented in a generalized sidelobe canceller (GSC) structure results in a reduction in the computational load. This approach also allows a reduction in the required adaptive dimension as compared to the eigenvector based approach. Illustrative examples demonstrate the effectiveness of this method     

Multidimensional Two-channel Linear Phase FIR Filter Banks and Wavelet Bases with Vanishing Moments

In the paper new design methods for multidimensional two-channel perfect reconstruction (PR) FIR filter banks are described. The filters have linear phase, achieve an arbitrarily high number of vanishing moments and can be used to obtain biorthogonal wavelet bases. Two-dimensional wavelet bases with square, rectangular, and hexagonal support are constructed. A design method that trades off vanishing moments and frequency selectivity is described. These two properties are both important in subband coding, but they each require a share of the degrees of freedom available from the total number of filter coefficients. Novel analytic formulae are derived and are applied to provide illustrative examples.     

Real frequency wide-band impedance matching with nonminimum reactance equalizers

This paper describes two modifications to the real frequency technique of broadband impedance matching. A fundamental limitation of all broadband matching techniques is that the real and imaginary parts of the equalizer impedance must be related by the Hilbert transform. It is shown that additional degrees of freedom in the Hilbert transform, and thus a better match, can be obtained by employing equalizer impedances with nonminimum reactance and by optimizing the equalizer resistance outside the stated bandwidth. Examples will be presented for a thin wire dipole antenna.     

Simply supported, ‘Joint less’ parallel mechanism based force–torque sensor

The platform of a hexapod is constrained to be a part of the structure whose six degrees of freedom are constrained by six linearly independent line constraints. The six line constraints are utilized for developing simply supported, ‘joint less’ six component parallel mechanism based force–torque sensor. The idea, model analysis, mechanical design and instrumentation are presented. The validity of the design is proved with prototype arrangements, two practical numerical examples and experimental results.     

On differential group-delay statistics for polarization-modedispersion emulators

We present a theoretical study on differential group-delay (DGD) statistics for common models of polarization-mode dispersion (PMD) emulators. Our study will show, for the first time to our knowledge, that the statistics for the length of the PMD vector will not necessarily behave as a system with three degrees of freedom when the number of sections in the PMD emulator is low. However, when the number of sections is large, i.e., 10 sections or more, the length of the PMD vector is well described with a system with three degrees of freedom     

Multitaper estimation of the innovation variance of a stationarytime series

Accurate computation of the innovation variance of a stationary time series by a nonparametric method provides useful information to judge the quality of fit of parametric models for the time series. Previous estimators of the innovation variance have made use of raw periodogram ordinates, smoothed periodogram ordinates, or periodogram ordinates following tapering. Smoothing provides more degrees of freedom at each frequency but fewer independent estimates, whereas tapering reduces side-lobe leakage if the dynamic range of the spectrum is high but produces only two degrees of freedom at each frequency. Here, we investigate estimation of innovation variance from finite sample sizes by the use of multiple tapering. The tapers are designed to reduce side-lobe leakage and produce increased degrees of freedom at each frequency. It is demonstrated that the multiple tapering approach produces much better estimates of the innovations variance than the other methods when the spectrum has a high dynamic range and/or is rapidly varying. The multitaper bandwidth parameter W may be selected using an obvious heuristic approach or by an automatic method. The multitaper method is hence an attractive alternative to conventional techniques     

Development of a parallel wire mechanism for measuring position and orientation of a robot end-effector

This paper presents a parallel wire mechanism developed for measuring six degrees of freedom of a robot end-effector. The mechanism consists of six parallel wire links. The position and orientation of a robot are obtained from the wire lengths measured in the parallel wire mechanism. The complex nonlinear equations of the forward kinematics are solved by using a Newton–Raphson method, and a unique solution is determined from the geometric configuration of the developed mechanism. The wire length error caused by longitudinal deformation of the wires is compensated by a wire compensation factor. Through the experiment, it is verified that the developed mechanism has an accuracy of ±0.05 mm, ±0.1° in the position and the orientation, respectively. The developed parallel wire mechanism can be used effectively for measuring the position and orientation of a six degree of freedom (DOF) of robot end-effector with low cost and effort.     

Adaptive alignment packaging for 2-D arrays of free-spaceoptical-interconnected optoelectronic systems

An adaptive alignment scheme for packaging two-dimensional (2D) arrays of optoelectronic systems interconnected by free-space optics is presented. A method of using three quadrant detectors to detect alignment errors in six degrees of freedom is described. However, the complexity of this system increases due to the interactions among the detected error signals. A novel control algorithm is presented to eliminate the interaction and simplify the design of the closed-loop feedback control. A computer simulation compares different algorithms and shows the effectiveness of the proposed algorithm. An experimental closed-loop feedback system demonstrated the principle of the error detection and correction of the proposed system with initial errors in multiple degrees of freedom