Quantum cosmological Friedman models with a Yang-Mills field and positive energy levels

We prove the existence of a spectral resolution of the Wheeler-DeWitt equation when the matter field is provided by a Yang-Mills field, with or without mass term, if the spatial geometry of the underlying spacetime is homothetic to $\R[3]$. The energy levels of the resulting quantum model, i.e., the eigenvalues of the corresponding self-adjoint Hamiltonian with a pure point spectrum, are strictly positive.Comment: 9 pages, v3: minor corrections to bring it in line with the published versio

Edge vulnerability in neural and metabolic networks

Biological networks, such as cellular metabolic pathways or networks of corticocortical connections in the brain, are intricately organized, yet remarkably robust toward structural damage. Whereas many studies have investigated specific aspects of robustness, such as molecular mechanisms of repair, this article focuses more generally on how local structural features in networks may give rise to their global stability. In many networks the failure of single connections may be more likely than the extinction of entire nodes, yet no analysis of edge importance (edge vulnerability) has been provided so far for biological networks. We tested several measures for identifying vulnerable edges and compared their prediction performance in biological and artificial networks. Among the tested measures, edge frequency in all shortest paths of a network yielded a particularly high correlation with vulnerability, and identified inter-cluster connections in biological but not in random and scale-free benchmark networks. We discuss different local and global network patterns and the edge vulnerability resulting from them.Comment: 8 pages, 4 figures, to appear in Biological Cybernetic

Crosslinked biopolymer bundles: crosslink reversibility leads to cooperative binding/unbinding phenomena

We consider a biopolymer bundle consisting of filaments that are crosslinked together. The crosslinks are reversible: they can dynamically bind and unbind adjacent filament pairs as controlled by a binding enthalpy. The bundle is subjected to a bending deformation and the corresponding distribution of crosslinks is measured. For a bundle consisting of two filaments, upon increasing the bending amplitude, a first-order transition is observed. The transition is from a state where the filaments are tightly coupled by many bound crosslinks, to a state of nearly independent filaments with only a few bound crosslinks. For a bundle consisting of more than two filaments, a series of first-order transitions is observed. The transitions are connected with the formation of an interface between regions of low and high crosslink densities. Combining umbrella sampling Monte Carlo simulations with analytical calculations, we present a detailed picture of how the competition between crosslink shearing and filament stretching drives the transitions. We also find that, when the crosslinks become soft, collective behavior is not observed: the crosslinks then unbind one after the other leading to a smooth decrease of the average crosslink density.Comment: 12 pages, 13 figure

Problems of operationalizing the concept of a cost-of-living index

The aim of our paper is to discuss the problems of operationalizing the concept of a .cost-of-living-index. (COLI). For this purpose we are first undertaking a theoretical analysis of Diewert’s theory of superlative index numbers as one possible approach to approximate a COLI. We show that Diewert.s superlative index approach is arguable in many points and that the approach requires restrictive assumptions which are not likely to be met in observed households behaviour. To get a better idea about the deviation of observed households behaviour from the neoclassical assumptions about utility maximizing behaviour, we are estimating an Almost Ideal Demand System and a Quadratic Almost Ideal Demand System with cross section micro data from the German income and expenditure survey. Using the results of the demand system estimations we calculate COLIs and compare them with superlative index numbers and the Laspeyres price index.cost-of-living index; superlative index numbers; Diewert; demand systems

Regional Indexes of Activity: Combining the Old with the New

This paper proposes a framework to construct indexes of activity which links two strands of the index literature – the traditional business cycle analysis and the latent variable approach. To illustrate the method, we apply the framework to Australian regional data, namely to two resource-rich and two service-based states. The results reveal differences in the evolution and drivers of economic activity across the four states. We also demonstrate the value of the Index in a broader context by using a structural vector autoregression (SVAR) approach to analyse the effects of shocks from the US and from China. This Index-SVAR approach facilitates a richer analysis because the unique feature of the index method proposed here allows impulse responses to be traced back to the components.Regional economic activity, coincident indicators, dynamic latent factor model

Automated tutoring for a database skills training environment

Universities are increasingly offering courses online. Feedback, assessment, and guidance are important features of this online courseware. Together, in the absence of a human tutor, they aid the student in the learning process. We present a programming training environment for a database course. It aims to offer a substitute for classroom based learning by providing synchronous automated feedback to the student, along with guidance based on a personalized assessment. The automated tutoring system should promote procedural knowledge acquisition and skills training. An automated tutoring feature is an integral part of this tutoring system

Floppy modes and non-affine deformations in random fiber networks

We study the elasticity of random fiber networks. Starting from a microscopic picture of the non-affine deformation fields we calculate the macroscopic elastic moduli both in a scaling theory and a self-consistent effective medium theory. By relating non-affinity to the low-energy excitations of the network (``floppy-modes'') we achieve a detailed characterization of the non-affine deformations present in fibrous networks.Comment: 4 pages, 2 figures, new figure

Ceramic coating effect on liner metal temperatures of film-cooled annular combustor

An experimental and analytical investigation was conducted to determine the effect of a ceramic coating on the average metal temperatures of full annular, film cooled combustion chamber liner. The investigation was conducted at pressures from 0.50 to 0.062. At all test conditions, experimental results indicate that application of a ceramic coating will result in significantly lower wall temperatures. In a simplified heat transfer analysis, agreement between experimental and calculated liner temperatures was achieved. Simulated spalling of a small portion of the ceramic coating resulted in only small increases in liner temperature because of the thermal conduction of heat from the hotter, uncoated liner metal