New compound upper bound on MIMO channel capacity

MIMO channel capacity may be severely degraded due to correlation between individual sub-channels of the matrix channel. Several models, which are limited to some specific scenarios, have been developed to date to account for this effect. In this letter, we derive a new upper bound on the mean (ergodic) MIMO capacity, which is not limited to a particular scenario and accounts for both transmit (Tx) and receive (Rx) end correlations in such a way that their impact can be estimated separately and compared. Thus, a conclusion can be made as to which end contributes more to capacity reduction. In general, the higher correlated end has a dominant effect on the capacity     

A performance analysis of a four‐leg inverter in two AC motor drives with independent vector control

This paper presents a performance analysis of a four‐leg inverter (FLI) in driving two motors with vector control. We show that an expanded two‐arm modulation (ETAM) known as a modulation method of a five‐leg inverter is applicable for the four‐leg inverter and we theoretically analyze a performance analysis of the four‐leg inverter in driving two motors with vector control. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An accurate and compact large signal model for III–V HBT devices

An accurate and compact large signal model is proposed for modeling heterojunction bipolar transistors (HBTs) based on III–V materials. In DC mode, the model includes self-heating, Kirk and Early effects, as well as the temperature dependence of the model parameters. In small signal mode, the model captures the variation of various AC parameters with bias. The procedure of extracting the model parameters uses DC and multiple bias S-parameter measurements. The model is compiled in the HP–ADS circuit simulator as user-compiled model and is verified by comparing its simulations to measurements in all modes of operation for an AlGaAs/GaAs transistor with an emitter area of 2 × 25 μm².     

Effects of thyroid hormone replacement therapy on nocturnal apnea in elderly patients with hypothyroidism

BACKGROUND AND STUDY AIMS: Dieulafoy's disease is a rare cause of upper gastrointestinal tract hemorrhage. The aim of the study was to evaluate the efficacy of endoscopic hemostasis and to analyze the mortality of patients with hemorrhage due to Dieulafoy's disease. PATIENTS AND METHODS: The retrospective analysis included patients from our institution who had undergone urgent endoscopic examination of the upper digestive tract and hemostatic interventions in the period between January 1994 and December 1996. RESULTS: Twenty-five patients were examined (18 men and 7 women, average age 52.6, SD+/-15.3, range 25-78). In 20 patients endoscopic injection sclerotherapy was performed (diluted epinephrine 1:10,000 plus polidocanol 1%) and Nd:YAG laser photocoagulation in five patients. In all patients a total of 44 interventional endoscopies were carried out. Repeated endoscopic hemostasis did not prove successful in two patients (8%, 2 men), and they were treated operatively. During the postoperative period one patient died because of multiorgan failure. The total mortality rate of all patients in which endoscopic hemostasis was done was 16% (4/25). None of the 21 surviving patients had rebleeding on long-term follow-up (mean: 29.4 months). CONCLUSIONS: Endoscopic hemostasis is a major therapeutic advance in the management of Dieulafoy's disease hemorrhage. Interventional endoscopy has decreased the need for surgical management and significantly reduced mortality.     

Self-assembled monolayer effect on the characteristics of organic diodes

In this paper, we study the effect of self-assembled monolayers (SAMs) on the electric behavior of organic diodes based on sexithiophene (6T) sandwiched between indium tin oxide (ITO) and aluminum. We have used molecules of SAMs based on a thiol with functional groups of oligothiophene (3T(CH₂)₆SH). Wettability measurements have been performed to characterize ITO surface energy and its modification upon deposition of SAMs. The results of contact angle measurements and surface energies demonstrate the homogeneity and rigidity of grafting surface. The current vs. applied voltage characteristics of devices show that conduction in weak biasing follow Richardson–Schottky behavior. Beyond 1.5 V, J–V characteristics can be successfully modeled by space-charge limited current (SCLC) theory followed by a trap charge limited current (TCLC). The electrical as well as optical characteristics of 6T layer are clearly affected by the presence of the SAM. The differences between ITO/SAM and bare ITO samples are interpreted in terms of structural effect induced by the self-assembled monolayer of 3T(CH₂)₆SH.     

Double liquid crystalline side-chain type block copolymers for hierarchically ordered nanostructures: Synthesis and morphologies in the bulk and thin film

Well-defined double liquid crystalline side-chain type block copolymers (DLC-BCPs) were synthesized by nitroxide-mediated living free radical polymerization (NMP) of two different types of styrene monomers containing liquid crystalline moieties. The molecular weights and compositions were controlled by changing the polymerization time and/or the feed amount of the monomers. The bulk morphologies were studied using wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). DLC-BCPs were favored to form microphase-separated lamellar structures over a wide range of volume fractions. By controlling the annealing conditions, further higher-ordered hierarchical nanostructures were obtained with a long-range alignment, in which the semi-crystalline side-chains were oriented parallel to the interface of microphase-separated lamellar structure. Thin film morphology was investigated using atomic force micrography (AFM). The formation of lamellar nanostructure with a long-range alignment vertically oriented to the silicon wafer substrate was achieved by simple thermal annealing.     

Analysis of a thin slot discontinuity in the reference plane of amicrostrip structure

This paper presents a perturbational approach based upon the spectral domain technique for the analysis of the discontinuity effects introduced by a thin slot in the ground plane of a microstrip line. The discontinuity problem is formulated in terms of the unknown slot field by using the notion of equivalent half-space problems, using a new rigorous procedure for deriving the TE-TM decomposition of the fields and equivalent transmission line models. The perturbation current on the infinite microstrip is computed once the electric field in the slot has been derived, and an equivalent circuit for the discontinuity is obtained from this perturbation current for the low-frequency regime. Computed results are presented and compared to the measured data