M-estimator with asymmetric influence function for estimating the Burr type III parameters with outliers

The Burr type III distribution allows for a wider region for the skewness and kurtosis plane, which covers several distributions including the log-logistic, and the Weibull and Burr type XII distributions. However, outliers may occur in the data set. The robust regression method such as an M-estimator with symmetric influence function has been successfully used to diminish the effect of outliers on statistical inference. However, when the data distribution is asymmetric, these methods yield biased estimators. We present an M-estimator with asymmetric influence function (AM-estimator) based on the quantile function of the Burr type III distribution to estimate the parameters for complete data with outliers. The simulation results show that the M-estimator with asymmetric influence function generally outperforms the maximum likelihood and traditional M-estimator methods in terms of the bias and root mean square errors. One real example is used to demonstrate the performance of our proposed method.     

多层球形手征介质透镜的焦点

应用并矢格林函数方法，给出了点源激励和阻抗匹配时多层球形手征介质透镜（Ｃｈｉｒｏｌｅｎｓ）的远区场分布；应用几何光学近似条件，得到了它的焦点计算公式．以双层和１０层手征介质球镜为例，考虑了手往导纳对焦点位置的影响．     

双各向同性介质中并矢格林函数的本征展开法和应用

首先引入了柱坐标系中的广义矢量波函｛Ｖ（ｈ），Ｗ（ｈ）｝，分别导出了圆柱和椭圆柱坐标系中双各向同性介质的并矢格林函数本征展开式．应用散射叠加法，给出了含源双各向同性介质圆柱位于另一种双各向同性介质中的并矢格林函数．由于互易手征介质和一般介质均为双各向同性介质的特殊情形，因此，文中所给出的公式具有更广泛的适用性．国家自然科学基金     

HEMT millimetre wave monolithic amplifier on InP

A single-stage lossy match cascode amplifier was realised on InP substrate. The amplifier has a small-signal gain of 17+or-1 dB over the frequency range 24-40 GHz. The active device is a 0.25 mu m triangular gate GaInAs/AlInAs HEMT lattice matched to InP.<>     

Impact of surface layer on In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

The surface potential of FETs has shown a strong effect on the channel potential and charge control in the channel. A study of the role of undoped versus doped cap layers in In_0.52Al_0.48As-In_0.53Ga_0.47 As-InP high-electron-mobility transistors (HEMT) is discussed. As the result of surface potential effect, direct comparison of 0.3×150-μm² gate devices yielded improved gate breakdown characteristics and a DC output conductance of less than 15 mS/mm for the surface undoped structure compared to 50 mS/mm for the doped structure. The surface undoped MEMT achieved a very high maximum stable gain of 19.2 dB compared to 16.0 dB for the surface doped HEMT at 18 GHz, largely due to the improved g_m/g ₀ ratio. This study demonstrates that control of the surface potential in In_0.52Al_0.48As-In_0.53Ga _0.47As-InP HEMTs is consistent with the effect of a gate recess in MESFETs. This study also shows that, in achieving high-gain applications of HEMTs, the surface potential near the gate edge should be optimized through unconventional surface layer design     

Nonminimum phase adaptive inverse control for settle performance applications

Single-track hard disk drive (HDD) seek performance is measured by settle time, $t_s$, defined as the time from the arrival of a seek command until the measured position reaches and stays within an acceptable distance from the target track. Our previous work has shown feedforward dynamic inversion, coupled with an aggressive desired trajectory $y_d$, is capable of achieving high performance settle times when the closed-loop dynamics are time-invariant and accurately modeled. In contrast, we describe an adaptive inversion procedure in this paper which removes the requirement for accurate initial models and tracks the position-variant dynamics present in our Servo Track Writer (STW) experimental apparatus. The proposed indirect adaptive inversion algorithm relies on a recursive least squares (RLS) estimate of the closed-loop dynamics. Pre-filtering of the RLS input signals, covariance resetting, and relative NMP system partitioning are necessary additions to the baseline adaptive algorithm in order to achieve fast settle times. Compared to the nonadaptive solution with accurate system identification, we show the adaptive algorithm achieves a 22% reduction in average settle time and a 53% reduction in settle time standard deviation.     

A New Study on the Doped Mott–Hubbard Insulator

By introducing a rotationally invariant Stratonovich–Hubbard (S-H) field we studied the doped Mott insulator phase of the two-dimension Hubbard model for U/t4–8. The static spin is decoupled by the S–H field and the static charge interaction is then treated by Hartree–Fock approximation. We sample random spin configurations by Monte Carlo simulation with the Metropolis updating algorithm. The Mott–Hubbard gap and static susceptibilities are studied near the half-filling at low temperature.     

The ensemble approach to neural-network learning and generalization

A method is suggested for learning and generalization with a general one-hidden layer feedforward neural network. This scheme encompasses the use of a linear combination of heterogeneous nodes having randomly prescribed parameter values. The learning of the parameters is realized through adaptive stochastic optimization using a generalization data set. The learning of the linear coefficients in the linear combination of nodes is achieved with a linear regression method using data from the training set. One node is learned at a time. The method allows for choosing the proper number of net nodes, and is computationally efficient. The method was tested on mathematical examples and real problems from materials science and technology.     

Low-conductance drain (LCD) design of InAlAs/InGaAs/InP HEMT's

The concepts of the low-conductance drain (LCD) design approach for lattice-matched InAlAs/InGaAs/InP HEMTs are demonstrated for improved device performance. The tradeoff for LCD HEMT characteristics is a tapered current gain cutoff frequency f_t under high drain-to-source bias. This behavior is, in principle, due to the fact that the LCD approach increases the effective gate length of the HEMTs in exchange for reduced peak channel electric field. Two-dimensional PISCES simulation was used to optimize the improvements while simultaneously minimizing this undesirable effect for an LCD HEMT structure