Fluid Flow and Heat Transfer in Serpentine Channels at Low Reynolds Numbers

Fluid flow and heat transfer in a two-dimensional serpentine channel was investigated numerically for Reynolds numbers between 175 and 725. A fifth-order finite differencing scheme was employed to carry out the computations. Three different geometries were studied. All three geometries consisted of the same wave length and the same shape of top and bottom walls, but different channel heights. In addition, two different inlet/outlet boundary conditions were investigated. It was found that the heat transfer as well as the pressure drop increase with decreasing channel height. For a given channel height, the results show that the time-averaged mean Nusselt number as well as the time averaged mean friction factor scale linearly with the Reynolds number.Air Conditioning and Refrigeration Project 6

Have Pentaquark States Been seen?

The status of the search for pentaquark baryons is reviewed in light of new results from the first two dedicated experiments from CLAS at Jefferson Lab and of new analyses from several laboratories on the $Theta^+(1540)$. Evidence for and against two heavier pentaquark states is also discussed.Comment: Added some references, corrected typo

Conjugacy in Garside groups I: Cyclings, powers, and rigidity

In this paper a relation between iterated cyclings and iterated powers of elements in a Garside group is shown. This yields a characterization of elements in a Garside group having a rigid power, where 'rigid' means that the left normal form changes only in the obvious way under cycling and decycling. It is also shown that, given X in a Garside group, if some power X^m is conjugate to a rigid element, then m can be bounded above by ||\Delta||^3. In the particular case of braid groups, this implies that a pseudo-Anosov braid has a small power whose ultra summit set consists of rigid elements. This solves one of the problems in the way of a polynomial solution to the conjugacy decision problem (CDP) and the conjugacy search problem (CSP) in braid groups. In addition to proving the rigidity theorem, it will be shown how this paper fits into the authors' program for finding a polynomial algorithm to the CDP/CSP, and what remains to be done.Comment: 41 page

Conjugacy in Garside Groups III: Periodic braids

An element in Artin's braid group B_n is said to be periodic if some power of it lies in the center of B_n. In this paper we prove that all previously known algorithms for solving the conjugacy search problem in B_n are exponential in the braid index n for the special case of periodic braids. We overcome this difficulty by putting to work several known isomorphisms between Garside structures in the braid group B_n and other Garside groups. This allows us to obtain a polynomial solution to the original problem in the spirit of the previously known algorithms. This paper is the third in a series of papers by the same authors about the conjugacy problem in Garside groups. They have a unified goal: the development of a polynomial algorithm for the conjugacy decision and search problems in B_n, which generalizes to other Garside groups whenever possible. It is our hope that the methods introduced here will allow the generalization of the results in this paper to all Artin-Tits groups of spherical type.Comment: 33 pages, 13 figures. Classical references implying Corollaries 12 and 15 have been added. To appear in Journal of Algebr

The impact of the EU ETS on the sectoral innovation system for power generation technologies: findings for Germany

This paper provides an overview of early changes in the sectoral innovation system for power generation technologies which have been triggered by the European Emission Trading Scheme (EU ETS). Based on a broad definition of the sector, our research analyses the impact of the EU ETS on the four building blocks knowledge and technologies, actors and networks, institutions and demand by combining two streams of literature, namely systems of innovation and environmental economics. Our analysis is based on 42 exploratory inter-views with German and European experts in the field of the EU ETS, the power sector and technological innovation. We find that the EU ETS mainly affects the rate and direction of the technological change of power generation technologies within the large-scale, coal-based power generation technological regime to which carbon capture technologies are added as a new technological trajectory. While this impact can be interpreted as defensive behaviour of incumbents, the observed changes should not be underestimated. We argue that the EU ETS' impact on corporate CO2 culture and routines may prepare the ground for the transition to a low carbon sectoral innovation system for power generation tech-nologies. --EU emission trading scheme (EU ETS),innovation system,power sector

The Lyman-alpha forest opacity and the metagalactic hydrogen ionization rate at z~2-4

Estimates of the metagalactic hydrogen ionization rate from the Lyman-alpha forest opacity in QSO absorption spectra depend on the complex density distribution of neutral hydrogen along the line-of-sight. We use a large suite of high resolution hydrodynamical simulations to investigate in detail the dependence of such estimates on physical and numerical parameters in the context of Lambda-CDM models. Adopting fiducial values for cosmological parameters together with published values of the temperature of the IGM and the effective optical depth, the metagalactic ionization rates which reproduce the Lyman-alpha effective optical depth at z=[2,3,4] are Gamma_HI=[1.3\pm^0.8_0.5, 0.9\pm0.3, 1.0\pm^0.5_0.3] \times 10^-12 s^-1, respectively. The errors include estimates of uncertainties in the relevant physical parameters and the numerical accuracy of the simulations. We find the errors are dominated by the uncertainty in the temperature of the low-density IGM. The estimated metagalactic hydrogen ionization rate for the neutral hydrogen distribution in the current concordance Lambda-CDM model is more than four times the value inferred for that in an Einstein-de Sitter model of the same r.m.s. density fluctuation amplitude sigma_8. The estimated ionization rate is also more than double that expected from updated estimates of the emissivity of observed QSOs alone. A substantial contribution from galaxies appears to be required at all redshifts.Comment: 13 pages, 7 figures, accepted to MNRAS, minor changes to submitted versio

The innovation impact of EU emission trading: findings of company case studies in the German power sector

This paper provides a comprehensive analysis of how the European Emission Trading System (EU ETS) as the core climate policy instrument of the European Union has impacted innovation. Towards this end, we investigate the impact of the EU ETS on research, development, and demonstration (RD&D), adoption, and organizational change. In doing so, we pay particular attention to the rela-tive influences of context factors (policy mix, market factors, public acceptance) as well as firm characteristics (value chain position, technology portfolio, size, vision). Empirically, our analysis is based on multiple case studies with 19 power generators, technology providers, and project developers in the German power sector which we conducted from June 2008 until June 2009. We find that the innovation impact of the EU ETS has remained limited so far because of the scheme’s initial lack in stringency and predictability and the relatively greater importance of context factors. Additionally, the impact varies tremendously across technologies, firms, and innovation dimensions, and is most pronounced for RD&D on carbon capture technologies and corporate procedural change. Our analysis suggests that the EU ETS by itself may not provide sufficient incentives for fundamental changes in corporate climate innovation activities at a level adequate for reaching political long-term targets. Based on the study’s findings, we derive a set of policy and research recommendations. --EU ETS,emission trading,innovation,technological change,adoption,diffusion,organizational change,power sector