Influence diagnostics for generalized linear mixed models: applications to clustered data

The Cook's distance for generalized linear mixed models is investigated, with applications to clustered data. In particular, first-order approximations are derived for the best linear unbiased predictor of the parameters due to cluster deletion. A small-scale simulation study shows that the method provides an efficient way to identify influential clusters. The notion of joint and conditional influence is also considered to address the masking effects of cluster-wise deletion. A data set on maternity length of hospital stay illustrates the usefulness of the proposed diagnostics.     

Surface Modification in Polycrystalline Y2O3 Under High‐Pressure/High‐Temperature Processing Conditions

A pressure‐induced phase transformation is used to refine the grain size of polycrystalline Y₂O₃, by a factor of 3000. A surface modification effect accompanies the observed grain refinement, which becomes more apparent with increasing holding time under high pressure. The surface‐modified layer exhibits lower hardness and lower oxygen content relative to the underlying material. Moreover, it possesses columnar‐grained structure with cubic symmetry, whereas the interior has a monoclinic structure.     

Linear multiuser receivers in random environments

We study the signal-to-interference (SIR) performance of linear multiuser receivers in random environments, where signals from the users arrive in “random directions.” Such a random environment may arise in a DS-CDMA system with random signature sequences, or in a system with antenna diversity where the randomness is due to channel fading. Assuming that such random directions can be tracked by the receiver, the resulting SIR performance is a function of the directions and therefore also random. We study the asymptotic distribution of this random performance in the regime where both the number of users K and the number of degrees of freedom N in the system are large, but keeping their ratio fixed. Our results show that for both the decorrelator and the minimum mean-square error (MMSE) receiver, the variance of the SIR distribution decreases like 1/N, and the SIR distribution is asymptotically Gaussian. We compute closed-form expressions for the asymptotic means and variances for both receivers. Simulation results are presented to verify the accuracy of the asymptotic results for finite-sized systems     

Reduction of EMI emission from power converter using soft-switchingtechniques

Measured, conducted, and radiated electromagnetic interference (EMI) from a hard-switched flyback converter and a soft-switched converter of the same power are presented. Results indicate that the EMI emission can be substantially reduced by using the soft-switching technique in power converters     

Reduction of power converter EMI emission using soft-switchingtechnique

Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using a soft-switching technique in power converters. Thus, the soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested     

Optical temperature sensing based on the Goos-Hänchen effect

The possibility of constructing an optical sensor for temperature monitoring based on the Goos-H?nchen (GH) effect is explored using a theoretical model. This model considers the lateral shift of the incident beam upon reflection from a metal-dielectric interface, with the shift becoming a function of temperature due mainly to the temperature dependence of the optical properties of the metal. It is found that such a sensor can be most effective by using long wavelength p-polarized incident light at almost grazing incidence onto the metal, where significant variation of negative GH shifts can be observed as a function of the temperature.     

Semi-Structural Hot Melt Adhesives Based on Crosslinkable Functionalized Polyolefins

A structural or semi-structural adhesive is usually applied to the substrates as monomers, oligomers, or melts of polymers with reactive groups and is then polymerized or crosslinked in situ in the joint between the substrates. We have been studying a number of crosslinked functionalized polyolefins blended with tackifier used as semi-structural adhesives for bonding to oily galvanized steel surfaces. The functions of takifier, surface properties of adhesive and substrate, geometry effects of lap joints, adhesive T_β, chain end defects, network chain length, and cure kinetics of these systems will be discussed. Our experimental results indicate that lap shear strengths of galvanized steel joints depend on adhesive storage modulus to the power of roughly 1/2. A rough estimate of the fracture energy of the adhesive bond, G_a could be obtained from this relation. Although some estimated G_a values are too low while the others are too high, they seem to be in rough accord with the degree of interfacial bonding and the locus of failure of the lap shear bonds.     

Fast-scale instability of single-stage power-factor-correction power supplies

This paper describes the fast-scale bifurcation phenomena of a single-stage power-factor-correction (PFC) power supply which is a cost effective design for low-power applications. The circuit employs a cascade configuration of a boost converter and a forward converter, which share an active switch and operate in discontinuous conduction mode, to provide input PFC and tight output regulation. Main results are illustrated by "exact" circuit simulations as well as theoretical analysis based on the use of Jacobians. This work provides a convenient means of predicting stability boundaries which can facilitate the selection of practical parameter values for maintaining stable operation.