Monte Carlo Optimization,Simulation and Sensitivity of Queueing Networks

The degradation of a drug product over time must be studied carefully to determine the appropriate shelf-life of the product. It is desirable to use data from all batches of the drug product to estimate a common shelf-life. The current Food and Drug Administration Guideline for analyzing data from multiple batches in stability studies emphasizes hypothesis testing for assessing the equality of degradation rates among batches. We propose a definition for a meaningful difference in batch degradation rates. Furthermore, we use simultaneous confidence intervals for estimating differences in batch slopes and for making decisions about pooling data from separate batches. We believe that an estimation procedure based on simultaneous confidence intervals is philosophically and practically a better approach to this problem.     

Reflections of the outgoing editors

Abstract

In the past decades, culture has increasingly been accepted as a dimension to be planned and managed within public policy, alongside social, economic and ecological considerations. Techniques for impact assessment of interventions on our economy, ecology and society are becoming more sophisticated, but are not yet well established within the cultural domain. This paper presents the results of a systematic literature review on applications of cultural impact assessment (CIA) internationally. Findings indicate that CIA has largely been practiced since 2002 to understand the impact of development processes on indigenous communities. While interest in CIA was also apparent in areas of public policy, particularly local government, little evidence was found of the practice actually established. A divergent understanding of CIA was found in the ‘cultural’ (funded arts and heritage) sector where it was understood as both impact on culture, but also impact of cultural activities. Only two developed tools for measuring cultural impact were found, one each for indigenous contexts and cities. Recommendations for strengthening CIA practice include establishing agreed definitions of culture and cultural impact, and validated tools, including measurement frameworks and indicators.     

Take-or-pay contracts for renewables deployment

Renewables require support policies to deliver the European 20% target. We discuss the requirements for least-cost development and efficient operation and quantify how different schemes (i) allow for the development of a renewable energy technology portfolio; (ii) reduce rent transfers to infra-marginal technologies or better than marginal resource bases and (iii) minimise regulatory risk and thus capital costs for new projects.     

Formalisation: An Interview with Hernando de Soto

The Peruvian economist Hernando de Soto is internationally renowned for his writings on the informal economy. Through his work as the President of the Institute for Liberty and Democracy (ILD) in Lima, he has effectively advocated the creation of a legal system to help the poor access property rights. In his latest book, The Amazon is not Avatar, he makes a significant shift away from the problems caused by massive urban migrations to cities to focusing on the benefits of property and business rights for resource-rich indigenous communities in the Amazon. Angus Laurie interviews De Soto on his current thinking and highlights why he has had such an important influence on social housing in Latin America. Copyright © 2011 John Wiley & Sons, Ltd.     

Use of a dislocation-based boundary element model to extract crack growth rates from depth distributions of intergranular stress corrosion cracks

A dislocation-based boundary element model was used to simulate intergranular stress corrosion crack propagation in virtual microstructures. A Monte Carlo approach was used in which the propagation of approximately 100 cracks was calculated for different Voronoi generated microstructures. At every simulation step the model gave the position of the crack tip together with stress intensity factors K_I and K_II. Using a simple power-law-type crack growth rate $\mathit{da}/\mathit{dt}=D_p{K}^{m_p}$, the depth of each particular crack can be calculated knowing the time the samples were exposed to the stress and corrosive environment. Existing experimental data giving crack depth distributions for Alloy 600, and XM-19 and 304 stainless steel are investigated and the best-fit crack growth law established. Alloy 600 in a light water reactor environment and XM-19 in high-temperature water both lead to m_p = 3. While for 304 stainless steel in the more aggressive K₂S₄O₆/H₂SO₄ (pH 2) an exponent m_p = 0.8 was found.     

Three-dimensional observation of SiO2 hollow spheres with a double-shell structure using aberration-corrected scanning confocal electron microscopy

Optical sectioning using scanning confocal electron microscopy (SCEM) is a new three-dimensional (3D) imaging technique which promises improved depth resolution, particularly for laterally extended objects. Using a stage-scanning system to move the specimen in three dimensions, two-dimensional (2D) images sliced from any plane in XYZ space can be obtained in shorter acquisition times than those required for conventional electron tomography. In this paper, a double aberration-corrected SCEM used in annular dark-field mode was used to observe the 3D structure of SiO(2) hollow spheres fabricated by a carbon template method. The double-shell structure of the sample was clearly reflected in both XY- and XZ-sliced images. However, elongation along the optical axis was still evident in the XZ-sliced images even when double aberration correctors were used. Application of a deconvolution technique to the experimental XZ-sliced images reduced the elongated shell thicknesses of the SiO(2) sphere by 40-50% and the selectivity of information at a certain sample depth was also enhanced. Subsequently, 3D reconstruction by stacking the deconvoluted slice images restored the spherical surface of a SiO(2) sphere.     

Cardiovascular action of verapamil in the dog with particular reference to myocardial contractility and atrioventricular conduction

Verapamil (Isoptin) caused a dose-dependent peripheral vasodilation, increase in myocardial contractility, and tachycardia in the anaesthetized dog. Propranolol pretreatment blocked the cardiac stimulation following verapamil but the vasodilation was unaltered. Inflation of a thoracic aortic balloon prevented the fall in intravascular pressure and reduced the tachycardia and positive inotropic responses. These experiments suggest that clinical doses of verapamil cause peripheral vasodilation which leads to a sympathetic reflex induced increase in heart rate and myocardial contractility. Verapamil also had a direct myocardial depressant action which became evident at doses above the range used clinically. The drug increased the PR interval in conscious dogs for up to 60 minutes. This effect was partly mediated through cholinergic stimulation and partly through a direct depression on atrioventricular conduction.