Influence of degeneracy on behaviour of homojunction GaAs bipolar transistor

In the letter the beneficial influence of degeneracy mechanisms on the electrical properties of a homojunction bipolar transistor has been highlighted.     

Prognostic factors for survival in patients with brain metastases from renal cell carcinoma

BACKGROUND: Patients presenting with brain metastases from renal cell carcinoma portend a poor prognosis, with a reported median survival of 4-6 months. Given their short life expectancy, these patients generally have been excluded from clinical trials that assess the efficacy of medical treatments. However, clinical impression suggests that some patients may achieve long term palliation. METHODS: The clinical features of 68 patients who were treated at the Institut Gustave Roussy for brain metastases from renal cell carcinoma were collected retrospectively. Using univariate and multivariate analyses, a prognostic model based on independent prognostic factors was established. An external data set of 57 patients was used to validate the model. RESULTS: The median survival was 7 months. On univariate analysis survival was related significantly to the following adverse prognostic factors: no initial nephrectomy, left side and temporal location of brain metastases, presence of fever or weight loss, erythrocyte sedimentation rate > 50 mm/h, and time from initial diagnosis to brain metastases < or = 18 months. Multivariate analyses identified the previous variable as well as the presence of other visceral metastases as independent prognostic factors. Forty-four patients (65%) with no or 1 adverse prognostic factor (average risk group) had a median survival of 8 months and a 26% 1-year survival rate. Twenty-four patients (35%) with 2 adverse prognostic factors (poor risk group) had a median survival of 3 months and a 1-year survival rate of 9%. This model proved to be discriminant in an external data set; the median survival of patients assigned to the average risk group was 11 months (46% 1-year survival rate) compared with 4 months (9% 1-year survival rate) for patients assigned to the poor risk group. CONCLUSIONS: Patients presenting with brain metastases from renal cell carcinoma and poor risk prognostic factors are highly unlikely to benefit from medical treatments except symptomatic procedures. Conversely, the enrollment of patients with average risk prognostic factors into clinical trials dealing with chemotherapy or immunotherapy may be considered.     

Secretion of growth hormone in hyperthyroidism

The authors studied growth hormone (GH) secretion in a group of adult controls and another group of hyperthyroid patients after stimulation with intravenous insulin-induced (0,1 IU/kg) hypoglycemia, aiming to clear out the problem of discrepancies in literature concerning GH secretion in hyperthyroidism. They concluded that in this syndrome, GH levels are significantly higher than those of controls. The GH releasing response is normal, though it could be expected to be decreased due to decreased pituitary GH contents as a result of permanent somatotrophic cell stimulation.     

Description and experimental results of a semi-indirect ceramic evaporative cooler

Evaporative cooling is used in industrial and air conditioning processes to reduce temperature in different fluids. Direct evaporation systems can lead to environmental problems such as Legionnaire's disease, and indirect systems reduce system efficiency.This work presents the manufacture, test bed set up and trials carried out on a ceramic evaporative cooling system which acts as a semi-indirect cooler. Depending on air characteristics, it may act as a sensible or enthalpic exchanger. The water cooled in a cooling tower, using the return air coming from the conditioned room (22 °C and 50% comfort conditions) goes through the ceramic pipes, exchanging sensible and latent heat with a current of outdoor air.The use of this recovery system is mainly in climates with a high temperature and humidity such as tropical environments where the system yields a decrease in supply air humidity, using the cooling power of return air.The tests presented show the system behaviour for various supply air conditions.     

Computational modelling of multiscale morphologies in polymer-liquid crystal blends

Simulations of material architectures in polymer-liquid crystal blends driven by phase separation-phase ordering-texturing processes are presented. The study shows that mixtures of polymers and liquid crystals result in blend morphologies that organize at several scales. For thermally driven instabilities, morphologies of polymer droplets embedded in a liquid crystal matrix show colloidal crystallinity. Large polymer drops strongly affect the orientation of the matrix, producing textures consisting of defect lattices. This work shows that thermally driven phase separation-phase ordering-texturing processes can result in multiscale materials, with length scales cascading down from droplets to interfaces, and finally to nanoscale defects.     

Study of the AlCl3 catalytic activity on aromatic hydrocarbons—II: Mesophase formation

When naphthalene is carbonized in the presence of AlCl₃, polymerization and disproportionation reactions mainly occur up to approximately 300°C. Then, when the temperature is further increased, the catalyst gives rise to additional processes which are accompanied by H₂ evolution. Mesophase formation is observed at relatively low temperatures. After the catalyst removal the obtained mesophase seems to be stable in a wide temperature interval. Unusually low $\text{C}\text{H}$ ratios and high aliphatic hydrogen contents were observed in the catalytically formed mesophase. These properties are probably responsible for the solubility behaviour in conventional solvents. It is thought that the polymerization and disproportionation processes referred to above lead to the formation of high molecular weight nearly planar molecules, which contain fully aromatic and tetralin-like rings in their structures. These molecules would then be able to enter into the stacking process leading to the mesophase formation.     

Epidemiology of chronic bronchitis

In this short paper, the definition of chronic bronchitis, as it is now widely accepted by epidemiologists, is given and a comparison is made with the disease as usually referred to by general practitioners. Risk factors which are related to the development of the disease are then briefly discussed and the importance of internal parameters is underlined. At last, the methodological difficulties which arise in the assessment of the relationship between air pollution and respiratory symptoms are emphasized.     

A New Robust Variable Step-Size NLMS Algorithm

A new framework for designing robust adaptive filters is introduced. It is based on the optimization of a certain cost function subject to a time-dependent constraint on the norm of the filter update. Particularly, we present a robust variable step-size NLMS algorithm which optimizes the square of the a posteriori error. We also show the link between the proposed algorithm and another one derived using a robust statistics approach. In addition, a theoretical model for predicting the transient and steady-state behavior and a proof of almost sure filter convergence are provided. The algorithm is then tested in different environments for system identification and acoustic echo cancelation applications.     

Photovoltaic module reliability model based on field degradation studies

Crystalline silicon photovoltaic (PV) modules are often stated as being the most reliable element in PV systems. This presumable high reliability is reflected by their long power warranty periods. In agreement with these long warranty times, PV modules have a very low total number of returns, the exceptions usually being the result of catastrophic failures. Up to now, failures resulting from degradation are not typically taken into consideration because of the difficulties in measuring the power of an individual module in a system. However, lasting recent years PV systems are changing from small isolated systems to large grid‐connected power stations. In this new scenario, customers will become more sensitive to power losses and the need for a reliability model based on degradation may become of utmost importance. In this paper, a PV module reliability model based on degradation studies is presented. The main analytical functions of reliability engineering are evaluated using this model and applied to a practical case, based on state‐of‐the‐art parameters of crystalline silicon PV technology. Relevant and defensible power warranties and other reliability data are obtained with this model based on measured degradation rates and time‐dependent power variability. In the derivation of the model some assumptions are made about the future behaviour of the products—i.e. linear degradation rates—although the approach can be used for other assumed functional profiles as well. The method documented in this paper explicitly shows manufacturers how to make reasonable and sensible warranty projections. Copyright © 2008 John Wiley & Sons, Ltd.