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Extended Gauss-Markov theorem for nonparametric mixed-effects models
(2001-02-01)
Huang, SY
;
Lu, HHS
;
交大名義發表
;
National Chiao Tung University
The Gauss-Markov theorem provides a golden standard for constructing the best linear unbiased estimation for linear models. The main purpose of this article is to extend the Gauss-Markov theorem to include nonparametric mixed-effects models. The extended Gauss-Markov estimation (or prediction) is shown to be equivalent to a regularization method and its minimaxity is addressed. The resulting Gauss-Markov estimation serves as an oracle to guide the exploration for effective nonlinear estimators adaptively. Various examples are discussed. Particularly, the wavelet nonparametric regression example and its connection with a Sobolev regularization is presented. (C) 2001 Academic Press.
Improvement of machining accuracy by fuzzy logic at corner parts for wire-EDM
(2001-09-16)
Lin, CT
;
Chung, IF
;
Huang, SY
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Wire electrical discharge machining (wire-EDM) has always occupied an important position in some production fields, due to its capability of machining hard materials and intricate shapes. However, the machining accuracy, especially at corner parts, may be destroyed because of some phenomena such as wire deflection and vibration, etc. The purpose of this paper is to develop a control strategy based on fuzzy logic so that the machining accuracy at corner parts for wire-EDM can be improved. The fuzzy rules based on the wire-EDM's physical characteristics, experimental data, and operator's experience are constructed, so that the reduced percentage of sparking force can be determined by a multi-variables fuzzy logic controller. The objective of the total control is to improve the machining accuracy at corner parts, but still keep the cutting feedrate at fair values. As a result of experiments, machining errors of corner parts, especially in rough-cutting, can be reduced to less than 50% of those in normal machining, while the machining process time increases not more than 10% of the normal value. (C) 2001 Elsevier Science B.V. All rights reserved.
Generalized cross-validation for wavelet shrinkage in nonparametric mixed effects models
(2003-09-01)
Lu, HHS
;
Huang, SY
;
Lin, FH
;
統計學研究所
;
Institute of Statistics
A nonlinear wavelet shrinkage estimator was proposed in an earlier article by Huang and Lu. Such an estimator combined the asymptotic equivalence to the best linear unbiased prediction and the Bayesian estimation in nonparametric mixed-effects models. In this article, a data-driven GCV method is proposed to select hyperparameters. The proposed GCV method has low computational cost and can be applied to one or higher dimensional data. It can be used for selecting hyperparameters for either level independent or level dependent shrinkage. It can also be used for selecting the primary resolution level and the number of vanishing moments in the wavelet basis. The strong consistency of the GCV method is proved.
Hot-carrier effects on power characteristics of SiGeHBTs
(2004-06-01)
Huang, SY
;
Chen, KM
;
Huang, GW
;
Tseng, HC
;
Hsu, TL
This letter investigates hot-carrier (HQ effects on the power characteristics of Si-SiGe HBTs using load-pull measurements. We found that the output power, power gain, and linearity of Si-SiGe HBTs are degraded after HC stress. Under constant base-current measurement, the HC-induced power performance degradation is found to be much worse than that under constant collector-current measurement. The HC effects on the cutoff frequency, nonlinearity terms of base-current and collector-current, and third-order intermodulation (IM3) cancellation effect have been analyzed to explain the experimental observations.
Interference analysis and resource allocation for TDD-CDMA systems to support asymmetric services by using directional antennas
(2005-05-01)
Wang, LC
;
Huang, SY
;
Tseng, YC
;
資訊工程學系
;
電信工程研究所
This paper explores the advantages of using directional antennas in time division duplex (TDD) code division multiple access (CDMA) systems to support asymmetric traffic services. In the TDD-CDMA system, the transmission for asymmetric traffic from neighboring cells may cause the cross-slot interference, which can seriously degrade system capacity. To avoid the cross-slot interference for TDD-CDMA systems, many current resource allocation algorithms typically require a global control on the transmission direction (either downlink or uplink) in each time slot. Apparently, this requirement substantially constrains the flexibility of TDD-CDMA systems to deliver asymmetric traffic services in a more practical situation where every cell may have different uplink and downlink bandwidth requirements. We analyze the interference of the TDD-CDMA system with a trisector cellular architecture, where three directional antennas are employed at each base station. We find that the directivity of directional antennas can provide an additional degree of freedom for allocating radio resource. Taking advantage of this property, we introduce the concept of virtual cell, defined as the same converge area of a cell but is composed of three sectors from the three adjacent base stations. Furthermore, we propose a new virtual cell-based distributed code/time slot allocation algorithm to enable a TDD-CDMA system to provide asymmetric services with different rates of asymmetry in every cell coverage area. We demonstrate that the proposed algorithm does not only offer more flexibility in handling nonuniform traffic patterns, but maintain good radio link performance and call blocking performance.
Perpendicular interface resistance in Co/NbxTi1-x multilayers for normal and superconducting NbTi alloy with x=0.4, 0.6
(2005-05-15)
Huang, SY
;
Lee, SF
;
Huang, JC
;
Hwang, GH
;
Yao, YD
We report here the resistance of Co/NbxTi1-x multilayers, for x=0.4 and 0.6, with current flowing perpendicular to the layer plane at 4.2 K. When NbTi films are sandwiched between Co, we found that there are critical thicknesses of 20 nm for x=0.4 and 27 nm for x=0.6, below which no superconducting transition could be found. Using a series resistor model, we extracted the unit area resistance of one pair of Co/NbTi interfaces and compared with the pure Nb case we have reported. The influence of mean free paths and superconducting coherence lengths is analyzed. (c) 2005 American Institute of Physics.
Hot-carrier induced degradations on RF power characteristics of SiGe heterojunction bipolar transistors
(2005-06-01)
Huang, SY
;
Chen, KM
;
Huang, GW
;
Liang, V
;
Tseng, HC
Hot-carrier (HC) effects on high-frequency and RF power characteristics of Si/SiGe HBTs are investigated in this paper. By using the two-tone load-pull measurement, we find that not only the cutoff frequency, but also the output power performances of Si/SiGe HBTs are suffered by the HC stress. In this work, S-parameters and intrinsic elements of an equivalent hybrid-pi model were used to validate the HC effects on high-frequency characteristics. With different bias conditions, the degradations of cutoff frequency, power gain, and linearity are found to be worse under constant base-current measurement than that under constant collector-current measurement. The HC-induced degradations on the current gain, transconductance, and ideality-factor of base and collector currents are analyzed to explain the experimental observations.
Linearity and power characteristics of SiGeHBTs at high temperatures for RF applications
(2005-07-01)
Chen, KM
;
Peng, AS
;
Huang, GW
;
Chen, HY
;
Huang, SY
In this paper, the power gain, power-added efficiency (PAE) and linearity of power SiGe heterojunction-bipolar transistors at various temperatures have been presented. The power characteristics were measured using a two-tone load-pull system. For transistors biased with fixed base voltage, the small-signal power gain and PAE of the devices increase with increasing temperature at low base voltages, while they decrease at high base voltages. Besides, the linearity is improved at high temperature for all voltage biases. However, for devices with fixed collector current, the small-signal power gain, PAE, and linearity are nearly unchanged with temperature. The temperature dependence of power and linearity characteristics can be understood by analyzing the cutoff frequency, the collector current, Kirk effect and nonlinearities of transconductance at different temperatures.

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