WC-(Fe,Ni,C) hardmetals with improved toughness through isothermal heat treatments

The influence of carbon additions on densification during liquid phase sintering of WC-(Fe,Ni,C) hardmetals, and of subsequent heat treatments on some mechanical properties, like hardness and fracture toughness, have been investigated. The relation between total carbon content in the mixtures and final density of the specimens has been determined, together with its effect on the structure of the resulting metallic binder phase. In addition, the relationship between hardness and toughness and WC grain size in these hardmetals has shown to be similar to that in the traditional WC-Co system. Nevertheless, the effect of isothermal heat treatments which bring about a modification of the microstructure of the metallic binder has proved to be beneficial for increasing toughness without an appreciable influence on hardness.     

A new high frequency wide band 180° differential power splitter

The analysis, design and performance of a wide band active GaAs IC 180° differential power splitter are presented. A two stage GaAs IC was developed composed of a microwave differential amplifier and a matched common-gate input. A large percentage of the GaAs chip contains active devices thereby providing a very large operating bandwidth and a reduced surface area.The use of power splitters is required to design mixers, balanced amplifiers, baluns, phase shifters and others circuits in the microwave and millimetric bands. The performance of power splitters is typically specified in terms of maximum magnitude and phase variation. This article presents the procedure to calculate the imbalance of the power splitter normalized outputs waves as a function of the microwave differential amplifier common mode rejection ratio CMRR, the coupling impedance Z _c ,and the transistors' electrical parameters. The comparison of the simulation results and the practical measurements shows the feasibility of this new structure.     

Off-line uninterruptible power supply with zero transfer time usingintegrated magnetics

An offline uninterruptible power supply (UPS) or emergency power system with zero transfer time is presented. The principal application is to personal computers and systems. The power transformer, a triport-like transformer, acts as an inverter and as a voltage stabilizer with no external loading coil. It is made with commercial EI scrapless laminations. The battery charging circuit is integrated into the transformer and improves the dynamic output response during line-mode operation. The result is robust, short-circuit-proof equipment with harmonic distortion of lower than 3%, a static output stability better than 1.5%, and a very high reliability     

New simplified method for the simulation of conducted EMI generated by switched power converters

A new simplified simulation method for the calculation of conducted electromagnetic interference (EMI) caused by switched power converters (SPCs) is presented. EMI simulation in real SPCs presents particular problems due to complex geometry and the wide range of time constants involved. This makes the computation of EMI a complex matter. The method presented here is based on a "source propagation path-derived disturbance" simulation process and is specially designed to simplify the mentioned computation problems. In the design of the proposed method, quick and robust simulations were preferred rather than very accurate results. The resulting models allow quite accurate predictions and sensitivity analysis when certain changes in components or layout are introduced. The paper presents two validation cases, where simulation and experimental results of conducted EMI generated by a general-purpose VSI, with different switching patterns and different layout, are compared.     

Method to interpolate induced current with low amount of sample points by means of Bezier surfaces

A new interpolation technique to represent the induced current with a very low amount of sample points and computational cost is presented. The amplitude and phase of the current are represented separately, each one being defined at any point of the scattering surface by an interpolating function, built using Bezier's surfaces.     

Operational aspects of bednet impregnation for community-based malaria control in Nicaragua, Ecuador, Peru and Colombia

OBJECTIVES: The authors tested the ability of International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes in discharge abstracts to identify medical inpatients who experienced an in-hospital complication, using complications identified through chart review as the gold standard. METHODS: Two sets of ICD-9-CM codes were used: an inclusive set including many medical diagnoses that may also be coexistent complicating conditions on admission rather than complications and an exclusive set consisting primarily of ICD-9-CM-specified complication and adverse drug event codes. RESULTS: Neither set performed well as a diagnostic test for complication occurrence according to receiver operating characteristic analysis (ROC areas were 0.61 for the inclusive set and 0.55 for the exclusive set). Sensitivities of the ICD-9-CM codes for complications were 0.34 for the inclusive set and 0.14 for the exclusive set. Corresponding positive predictive values were 0.32 and 0.37, respectively. Sensitivities of code definitions for individual complications were generally poor, less than 0.5 in most cases. CONCLUSIONS: The authors conclude that ICD-9-CM codes in discharge abstracts are poor measures of complication occurrence.