423 research outputs found
An application of recent developments of Data Envelopment Analysis to the evaluation of secondary schools in Portugal
This paper highlights the potentialities of Data Envelopment Analysis to evaluate the performance of organisations, using
the concept of super-efficiency - an extension of DEA which increases its performance - and presents an example from
the public sector to illustrate the method. The example selected is that of a school network where a place in a school can
be seen as a perishable good, as places which are not occupied during an academic year are wasted. Results for the
Portuguese Secondary school network show that the average efficiency of overcrowded schools, that is, those exceeding
their capacity, is lower than that of schools which are less crowded. This shows clearly that overcrowded schools, on
average, are less efficient in transforming their inputs into academic performance. It is this conviction, seldom proved
scientifically, which leads governments and international organisations to recommend planning criteria for public
facilities
Global Contamination Trends of Persistent Organic Chemicals
Environmental pollution by man-made persistent organic chemicals (POCs) has been a serious global issue for over half a century. Exposure to certain POCs may result in environmental and health effects including skin disorders, liver damage, birth defects, brain development, and certain types of cancers. Global Contamination Trends of Persistent Organic Chemicals provides comprehensive coverage of spatial and temporal trends of classical and emerging contaminants in aquatic, terrestrial, and marine ecosystems, including the Arctic and Antarctic ecosystems
Class D amplifier power stage with PWM feedback loop
This paper presents a Second-Order Pulse Width Modulation (PWM) feedback loop to improve Power Supply Rejection (PSR) of any open-loop PWM Class-D amplifiers (CDAs). PSR of the audio amplifier has always been a key parameter in mobile phone applications. In contrast to Class AB amplifiers, the poor PSR performance has always been the major drawback for CDAs with half-bridge connected power stage. The proposed PWM feedback loop is fabricated using GLOBALFOUNDRIES' (GF’s) 0.18 µm CMOS process technology. The measured PSR is more than 80 dB and the measured Total Harmonic Distortion (THD) is less than 0.04% with a 1 kHz input sinusoidal test tone
Modeling mitigation effects of watershield on shock waves
Shock and Vibration54225-234SHVI
Metal-insulator transition in disordered 2DEG including temperature effects
We calculate self-consistently the mutual dependence of electron correlations
and electron-defect scattering for a two dimensional electron gas at finite
temperature. We employ an STLS approach to calculate the electron correlations
while the electron scattering rate off Coulombic impurities and surface
roughness is calculated using self-consistent current-relaxation theory. The
methods are combined and self-consistently solved. We discuss a metal-insulator
transition for a range of disorder levels and electron densities. Our results
are in good agreement with recent experimental observations.Comment: 4 pages, RevTeX + epsf, 5 figure
Aetiology of allergic rhinitis in Hong Kong
ABSTRACTIn a 1993 survey, allergic rhinitis was identified as the most common allergic disease in Hong Kong, affecting 29.1% of schoolchildren. Recently (1995), the International Study of Asthma and Allergies in Childhood (ISAAC) also reported 44.5% current rhinitis among Hong Kong teenagers. Our objective was to study the aetiology of allergic rhinitis in Hong Kong using serological tests of allergen sensitization. In 57 allergic rhinitis patients and in the same number of age- and sex-matched controls the following were measured: serum total IgE, mixed aeroallergen IgE (Phadiatop™) and specific IgE versus house dust mite (HDM), cockroach, cat and dog dander, mould mixture (Penicillium, Cladosporium, Aspergillus and Alternaria species) and four local pollens (Bermuda grass, Timothy, ragweed and mugwort). Compared with controls, allergic rhinitis patients (26 males, 31 females; mean (± SD) age 25 ±11 years) had a significantly elevated serum total IgE concentration (mean ± SEM: 496 ± 88 vs 179 ± 38 kU/L) and an increased proportion of positive Phadiatop (95 vs 33%) and specific IgE tests versus HDM (90 vs 44%) and cockroach (42 vs 9%; Mann-Whitney U-test and χ2 tests all P < 0.005). There was no significant difference in sensitization to other allergens tested. House dust mite and cockroach are ubiquitous in Hong Kong with a warm, humid climate and crowded living conditions. Their identification as aetiological agents of allergic rhinitis should help in the development of environmental strategies for reducing the inhalant allergen load to prevent and control this prevalent and costly health problem in our community
Genotype Distribution and Sequence Variation of Hepatitis E Virus, Hong Kong
Most acute cases of infection with hepatitis E virus (HEV) in Hong Kong were autochthonous, sporadic, and occurred in older adults. All except 1 isolate belonged to genotype 4; most were phylogenetically related to swine isolates. The epidemiology is similar to that in industrialized countries, where zoonosis is the major source of HEV infection in humans
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