Symmetry Analysis in Linear Hydrodynamic Stability Theory: Classical and New Modes in Linear Shear

We present a symmetry classification of the linearised Navier-Stokes equations for a two-dimensional unbounded linear shear flow of an incompressible fluid. The full set of symmetries is employed to systematically derive invariant ansatz functions. The symmetry analysis grasps three approaches. Two of them are existing ones, representing the classical normal modes and the Kelvin modes, while the third is a novel approach and leads to a new closed-form solution of traveling modes, showing qualitatively different behaviour in energetics, shape and kinematics when compared to the classical approaches. The last modes are energy conserving in the inviscid case. They are localized in the cross-stream direction and periodic in the streamwise direction. As for the kinematics, they travel at constant velocity in the cross-stream direction, whilst in the streamwise direction they are accelerated by the base flow. In the viscous case, the modes break down due to damping of high wavenumber contributions

Trends and tradition: Negotiating different cultural models in relation to sustainable craft and artisan production

If the identity of ‘design’ as a practice is contested then the relationship of design and designers to craft and craft practices can be hugely confused. This lack of clarity can encourage non-design based organisations to promote the use of ‘trend forecasting’ as a panacea to the design dilemma associated with craft production for non-traditional markets. Consequently fashion sensitive trends become perceived as the driving force of design-led consumption. In this context how do we understand what ‘trend forecasting’ is and becomes when used in this manner? How does it contribute or not to the sustainability of local design cultures? This paper examines how these challenges have been interrogated and experienced through practice at Masters Level at Central Saint Martins College of Art and Design. It seeks sustainable strategies for design and craft drawing on a diverse range of examples to illustrate contemporary artefacts realised from a diverse range of projects, sources and geographical locations

A Study of the LXeGRIT Detection Efficiency for MeV Gamma-Rays during the 2000 Balloon Flight Campaign

LXeGRIT - Liquid Xenon Gamma-Ray Imaging Telescope - is the first prototype of a Compton telescope for \MeV \g-ray astrophysics based on a LXe time projection chamber. One of the most relevant figures of merit for a Compton telescope is the detection efficiency for \g-rays, which depends on diverse contributions such as detector geometry and passive materials, trigger efficiency, dead time, etc. A detailed study of the efficiency of the LXeGRIT instrument, based both on laboratory measurements and Monte Carlo simulations, is presented in this paper.Comment: 20 pages, 15 figures; submitted to NIM

Analysis of the two-point velocity correlations in turbulent boundary layer flows

The general objective of the present work is to explore the use of Rapid Distortion Theory (RDT) in analysis of the two-point statistics of the log-layer. RDT is applicable only to unsteady flows where the non-linear turbulence-turbulence interaction can be neglected in comparison to linear turbulence-mean interactions. Here we propose to use RDT to examine the structure of the large energy-containing scales and their interaction with the mean flow in the log-region. The contents of the work are twofold: First, two-point analysis methods will be used to derive the law-of-the-wall for the special case of zero mean pressure gradient. The basic assumptions needed are one-dimensionality in the mean flow and homogeneity of the fluctuations. It will be shown that a formal solution of the two-point correlation equation can be obtained as a power series in the von Karman constant, known to be on the order of 0.4. In the second part, a detailed analysis of the two-point correlation function in the log-layer will be given. The fundamental set of equations and a functional relation for the two-point correlation function will be derived. An asymptotic expansion procedure will be used in the log-layer to match Kolmogorov's universal range and the one-point correlations to the inviscid outer region valid for large correlation distances

Determinants of the capacity to adapt to climate change in multi-level governance systems - a meta-analysis of case study evidence

Determinants of the capacity to adapt to climate change in multi-level governance systems Determinants of the capacity to adapt to climate change in multi-level governance systems - a meta-analysis of case study evidenceBackground: Current literature about climate change adaptation provides a broad range of factors influencing the adaptive capacity. Furthermore, a frequent tenor is that “scale matters”. However, the effects of institutional interplay across governance levels on adaptive capacity and the effects of the interaction of institutions with other variables such as technology and information remain largely subject of debate. Therefore synthesizing the diverse findings of empirical studies in a methodologically coherent and integrative manner may provide theoretical foundations for answers on how to organize enhanced adaptive capacity within and across governance levels. Method: 1\. Against this background we develop a comprehensive multi-tier framework of variables that systematically influence adaptive capacity. This is done by adopting the conceptual groundwork of the Institutional Analysis and Development framework (Ostrom 1990; Ostrom/Gardner/Walker 1994; Ostrom 2005) and with special focus on cross-level variable interactions. 2\. We apply this framework of variables to the case of urban areas and conduct a model-centered meta-analysis of empirical studies in order to identify patterns in which urban adaptive capacity is determined by institutional interplay and variable interactions within and across governance levels. Results: The main results are: 1\. The study provides a comprehensive and coherent multi-tier framework of variables determining adaptive capacity. 2\. The analysis of urban adaptive capacity indicates that the level of urban adaptive capacity is attributable to the congruence of multiple variables. 3\. Specific patterns of conjoint causation are identified for financial, informational, and institutional multi-level-interactions of determinants of urban adaptive capacity. Conclusions: This multi-tier framework seems to be very promising for a better understanding of adaptive capacity and thereby for influencing vulnerability to climate change. It provides a meaningful background for future studies and may foster cumulative research on adaptive capacity. Moreover, it offers a tool for further investigations of level- and cross-level-dynamics