On the periodicity of irreducible elements in arithmetical congruence monoids

Arithmetical congruence monoids, which arise in non-unique factorization theory, are multiplicative monoids $M_{a,b}$ consisting of all positive integers $n$ satsfying $n \equiv a \bmod b$. In this paper, we examine the asymptotic behavior of the set of irreducible elements of $M_{a,b}$, and characterize in terms of $a$ and $b$ when this set forms an eventually periodic sequence

High temperature epsilon-near-zero and epsilon-near-pole metamaterial emitters for thermophotovoltaics

We propose a method for engineering thermally excited far field electromagnetic radiation using epsilon-near-zero metamaterials and introduce a new class of artificial media: epsilon-near-pole metamaterials. We also introduce the concept of high temperature plasmonics as conventional metamaterial building blocks have relatively poor thermal stability. Using our approach, the angular nature, spectral position, and width of the thermal emission and optical absorption can be finely tuned for a variety of applications. In particular, we show that these metamaterial emitters near 1500 K can be used as part of thermophotovoltaic devices to surpass the full concentration Shockley-Queisser limit of 41%. Our work paves the way for high temperature thermal engineering applications of metamaterials.Comment: 15 pages, 8 figure

Energetic Extremes in Aquatic Locomotion by Coral Reef Fishes

Underwater locomotion is challenging due to the high friction and resistance imposed on a body moving through water and energy lost in the wake during undulatory propulsion. While aquatic organisms have evolved streamlined shapes to overcome such resistance, underwater locomotion has long been considered a costly exercise. Recent evidence for a range of swimming vertebrates, however, has suggested that flapping paired appendages around a rigid body may be an extremely efficient means of aquatic locomotion. Using intermittent flow-through respirometry, we found exceptional energetic performance in the Bluelined wrasse Stethojulis bandanensis, which maintains tuna-like optimum cruising speeds (up to 1 metre s(-1)) while using 40% less energy than expected for their body size. Displaying an exceptional aerobic scope (22-fold above resting), streamlined rigid-body posture, and wing-like fins that generate lift-based thrust, S. bandanensis literally flies underwater to efficiently maintain high optimum swimming speeds. Extreme energetic performance may be key to the colonization of highly variable environments, such as the wave-swept habitats where S. bandanensis and other wing-finned species tend to occur. Challenging preconceived notions of how best to power aquatic locomotion, biomimicry of such lift-based fin movements could yield dramatic reductions in the power needed to propel underwater vehicles at high speed.Funding was provided by the Australian Research Council (to CJF) and the Danish Agency for Science, Technology and Innovation (to JFS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Evaluating the impact of active labor programs : results of cross country studies in Europe and Central Asia

The objective of this cross country study was to determine if there was any significant difference those individuals who participated in active labor programs (ALP) and similar individuals who did not participate in the programs (the comparison group), with regard to agreed outcome measures of program success (e.g., employment, wage levels) in four countries: the Czech Republic, Poland, Hungary, and Turkey. The study evaluated five different ALPs across the four countries for several categories of program participants, grouped by demographic characteristics and geographic location. The active labor programs studies comprised: retraining, public works or temporary community employment, wage subsidy, self-employment initiatives, and general employment services. All five ALPs evaluated were found to have a significant positive net impact for some population subgroups, a general finding supported by the 1996 OECD review that concluded that there are ALPs that work for most groups of individuals. However, the study found the impact was not significant for some sub-groups, and for some ALPs the impact was negative. The final chapter summarizesthe general trends in findings on the various outcome measures across demographic and regional subgroups.Environmental Economics&Policies,Poverty Impact Evaluation,ICT Policy and Strategies,Health Monitoring&Evaluation,Poverty Monitoring&Analysis