Exact Cosmological Solutions of Gravitational Theories

A global picture is drawn tying together most exact cosmological solutions of gravitational theories in four or more spacetime dimensions.Comment: 11 latex article style page

Limits on Lorentz invariance violation at the Planck energy scale from H.E.S.S. spectral analysis of the blazar Mrk 501

Some extensions to the Standard Model lead to the introduction of Lorentz symmetry breaking terms, expected to induce deviations from Lorentz symmetry around the Planck scale. A parameterization of effects due to Lorentz invariance violation (LIV) can be introduced by adding an effective term to the photon dispersion relation. This affects the kinematics of electron-positron pair creation by TeV $\gamma$ rays on the extragalactic background light (EBL) and translates into modifications of the standard EBL opacity for the TeV photon spectra of extragalactic sources. Exclusion limits are presented, obtained with the spectral analysis of H.E.S.S. observations taken on the blazar Mrk 501 during the exceptional 2014 flare. The energy spectrum, extending very significantly above 10 TeV, allows to place strong limits on LIV in the photon sector at the level of the Planck energy scale for linear perturbations in the photon dispersion relation, and provides the strongest constraints presently for the case of quadratic perturbations.Comment: To appear in proceedings of the 6th Roma International Conference on Astro-Particle Physics (RICAP 16

Cognitive and Social Help Giving in Online Teaching: An Exploratory Study

While literature suggests that college students may be less reluctant to seek help in online rather than traditional courses, little is known about how online instructors give help in ways that lead to increased student help seeking and academic success. In this study, we used theories and research on learning assistance and scaffolding, teacher immediacy, social presence, and academic help seeking to explore through a cross-case study design how three online instructors differed in their use of cognitive and social supports and how those differences related to student perceptions of support, help seeking, and performance. Primary data sources included all course postings by the instructors, interviews with the instructors, observational field notes on course discussions, student interviews, and final student grades. Archived course documents and student discussion postings were secondary data sources. Data analysis revealed that while all instructors provided cognitive and social support, they varied in their level of questioning, use of direct instruction, support for task structuring, and attention to group dynamics. This variation in teaching presence related to differences across the courses in student perceptions of support, student help seeking in course discussions, and final course grades. Implications for online teaching and suggestions for further research are offered

Deterministic Walks in Quenched Random Environments of Chaotic Maps

This paper concerns the propagation of particles through a quenched random medium. In the one- and two-dimensional models considered, the local dynamics is given by expanding circle maps and hyperbolic toral automorphisms, respectively. The particle motion in both models is chaotic and found to fluctuate about a linear drift. In the proper scaling limit, the cumulative distribution function of the fluctuations converges to a Gaussian one with system dependent variance while the density function shows no convergence to any function. We have verified our analytical results using extreme precision numerical computations.Comment: 18 pages, 9 figure

Alternative Theories on Economic Growth and the Co-evolution of Macro-Dynamics and Technological Change: A survey.

This paper aims to propose an approach to endogeneous growth considering the relationship between macro-dynamics and technical change. We draw upon two stream of literature: Cumulative causation and its macroscopic view of economic dynamics, and Evo-lutionary economics and its focus on micro-determinants of technical change. This paper presents a survey of the formal representation of the growth process and identifies the possible bridges between these two approaches. Our claim is that merging these two distinct theories might offer a framework to consider the co-evolution of macro-dynamics and technical change.Economic Growth, Technical Change, Cumulative Causation, Evolutionary Theory.

Demand and Technology Determinants of Structural Change and Tertiarisation: An Input-Output Structural Decomposition Analysis for four OECD Countries.

The paper provides fresh empirical evidence on the relative role of changes in final and intermediate demand as affecting the changes in the sectoral structure of advanced economies. These latter have led, over the last three decades, to the massive growth of service sectors. The paper draws upon the recently released OECD Input- Output (I-O) tables. The empirical analysis is based on an I-O Structural Decomposition Analysis carried out on 13 manufacturing and service sectors, from the end of 1960s to the end of 1990s. Although heterogeneous sectoral patterns emerge, we find that the structural changes leading to the growth of services, particularly KIBS (Knowledge Intensive Business Services), are mainly (domestic) demand-led, whereas the role of foreign trade remains marginal even in the last decade. We infer that, even in the case of the most technologically advanced service sectors, (domestic) demand constraints affect the degree of exploitation of technological opportunities and the patterns of growth.Structural change, Growth of Services, Input–Output.

Cumulative Causation and Evolutionary Micro-Founded Technical Change : A Growth Model with Integrated Economies

We propose to develop in this paper an alternative approach to the New Growth Theory to analyse growth rate divergence among integrated economies. The model presented here considers economic growth as a disequilibrium process. It introduces in a cumulative causation framework, micro-founded process of technical change taking into account elements rooted in evolutionary and Neo-Austrian literature. We then attempt to open the ‘Kaldor-Verdoorn law black-box’ using a micro-level modelling of industrial dynamics. We use this framework to study the nature and sources of growth rate divergence, focusing on the effect of some macro-economic parameters (income elasticities) and of some technological parameters (technological opportunities and absorptive capacities). If the results remain broadly in Kaldorian lines, this framework allows for more subtle considerations of growth rate divergence.

Cumulative Causation and Evolutionary Micro-Founded Technical Change: A Growth Model with Integrated Economies

We propose to develop in this paper an alternative approach to the New Growth Theory to analyse growth rate divergence among integrated economies. The model presented here considers economic growth as a disequilibrium process. It introduces in a cumulative causation framework, micro-founded process of technical change taking into account elements rooted in evolutionary and Neo-Austrian literature. We then attempt to open the "Kaldor-Verdoorn law black-box" using a micro-level modelling of industrial dynamics. We use this framework to study the nature and sources of growth rate divergence, focusing on the eect of some macro-economic parameters (income elasticities) and of some technological parameters (technological opportunities and absorptive capacities). If the results remain broadly in Kaldorian lines, this framework allows for more subtle considerations of growth rate divergence.Cumulative Growth, Technical Change, International Trade