Green's Relations in Finite Transformation Semigroups

We consider the complexity of Green's relations when the semigroup is given by transformations on a finite set. Green's relations can be defined by reachability in the (right/left/two-sided) Cayley graph. The equivalence classes then correspond to the strongly connected components. It is not difficult to show that, in the worst case, the number of equivalence classes is in the same order of magnitude as the number of elements. Another important parameter is the maximal length of a chain of components. Our main contribution is an exponential lower bound for this parameter. There is a simple construction for an arbitrary set of generators. However, the proof for constant alphabet is rather involved. Our results also apply to automata and their syntactic semigroups.Comment: Full version of a paper submitted to CSR 2017 on 2016-12-1

Composite mirror facets for ground based gamma ray astronomy

Composite mirrors for gamma-ray astronomy have been developed to fulfill the specifications required for the next generation of Cherenkov telescopes represented by CTA (Cherenkov Telescope Array). In addition to the basic requirements on focus and reflection efficiency, the mirrors have to be stiff, lightweight, durable and cost efficient. In this paper, the technology developed to produce such mirrors is described, as well as some tests that have been performed to validate them. It is shown that these mirrors comply with the needs of CTA, making them good candidates for use on a significant part of the array.Comment: 16 pages, 13 figures, accepted to be published on NIM

Francis Johnson: Music Master of Early Philadelphia

Guthrie P. Ramsey, Jr., Associate Professor of Music, University of Pennsylvania, delivers a lecture on Francis Johnson (1792-1844), Philadelphia band leader and composer. Johnson holds a special place in the history of American music. Although a free African American, he lived in an age when racial segregation and prejudice were commonplace. Despite these obstacles, he was able to achieve extraordinary renown and respect among the elite of Philadelphia through performances of his band at balls, parades, and promenade concerts. Following a series of concert tours late in his life, Johnson\u27s fame eventually extended through the Midwest and across the Atlantic to London. His music survives today in piano arrangements published during his lifetime. The lecture marked the opening of an exhibition in the Otto E. Albrecht Music Library. The exhibition included a selection from the over forty pieces of Johnson sheet music in the collection of the late Kurt Stein. Also part of the exhibition were prints, period newspaper articles, and a Kent bugle like that favored by Johnson. To download a podcast of the lecture, select one of the additional files below. Welcome, H. Carton Rogers, 00-04:52 Introduction, Richard Griscom, 04:52-13:06 Lecture, Guthrie P. Ramsay, Jr., 13:15-37:27 The event announcement is also available for download, by selecting the download button, at upper right. The exhibition is available in an online version, at: https://web.archive.org/web/20160422121347/https://www.library.upenn.edu/exhibits/music/fjohnson

Smart Emission - Building a Spatial Data Infrastructure for an Environmental Citizen Sensor Network

Item does not contain fulltextSmart Emission is a citizen sensor network using low-cost sensors that enables citizens to gather data about environmental quality, like air quality, noise load, vibrations, light intensities and heat stress. This paper introduces the design and development of the data infrastructure for the Smart Emission initiative and discusses challenges for the future. The Spatial Data Infrastructure (SDI) is open and accessible on the Internet using open geospatial standards and (Web-) client applications. Smart Emission as a citizen sensor network offers several possibilities for heterogonous applications, from health determination to spatial planning purposes, environmental monitoring for sustainable traffic management, climate adaptation in cities and city planning.Geospatial Sensor Webs Conference 2016 (GSW 2016), 29 augustus 201

Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean

The eastern equatorial Atlantic Ocean is subject to interannual fluctuations of sea surface temperatures, with climatic impacts on the surrounding continents. The dynamic mechanism underlying Atlantic temperature variability is thought to be similar to that of the El Nino/Southern Oscillation (ENSO) in the equatorial Pacific, where air-sea coupling leads to a positive feedback between surface winds in the western basin, sea surface temperature in the eastern basin, and equatorial oceanic heat content. Here we use a suite of observational data, climate reanalysis products, and general circulation model simulations to reassess the factors driving the interannual variability. We show that some of the warm events can not be explained by previously identified equatorial wind stress forcing and ENSO-like dynamics. Instead, these events are driven by a mechanism in which surface wind forcing just north of the equator induces warm ocean temperature anomalies that are subsequently advected toward the equator. We find the surface wind patterns are associated with long-lived subtropical sea surface temperature anomalies and suggest they therefore reflect a link between equatorial and subtropical Atlantic variability

Developments in fuel cell technologies in the transport sector

The demand for clean power source which can be used to run the various types of vehicles on the road is increasing on a daily basis due to the fact that high emissions released from internal combustion engine play a significant role in air pollution and climate change. Fuel cell devices, particularly Proton Exchange Membrane (PEM) type, are strong candidates to replace the internal combustion engines in the transport industry. The PEMFC technology still has many challenges including high cost, low durability and hydrogen storage problems which limit the wide-world commercialization of this technology. In this paper, the fuel cell cost, durability and performances challenges which are associated with using of fuel cell technology for transport applications are detailed and reviewed. Recent developments that deal with the proposed challenges are reported. Furthermore, problems of hydrogen infrastructure and hydrogen storage in the fuel cell vehicle are discussed

Nitrogen Response of Spring and Winter Wheat to Biosolids Compared to Chemical Fertiliser

Irish sewage sludge production was over 30,000 t/year in the 1990s (EPA, Ireland, 2003). Application to agricultural land is a management option for this organic material as it results in the recycling of the nutrients they contain for crop production. The EU Directive (91/271/EEC) encourages the recycling of sewage sludge as biosolids to agriculture. However, up to 1999, only about 5 % of biosolids produced was applied to agricultural land. In this study, several biosolids and a chemical fertiliser were used to assess N availability for spring and winter wheat (Triticum aestivum,) production in a pot experiment

Equus Unbound: Fairman Rogers and the Age of the Horse (Panel Discussion)

Podcast introduction, Kristin Winch, 00:00-01:17 Welcome and introduction, H. Carton Rogers, 01:17-05:06:30 Remarks by panel moderator Ann N. Greene, 06:35-20:15 Remarks by Herbert Moelis, 20:33-28:58 Remarks by Ellen Moelis, 28:58-39:45 Remarks by Dean Richardson, 39:45-46:45 Remarks by Douglas Kemmerer, 46:45-1:07:45 Questions and answers, 1:07:45-1:10:18 Concluding remarks, Lynne Farrington, 1:10:18-1:11:19 To download a podcast of this event, choose either the standard quality mp3 file (shorter download) or the high quality m4a file (longer download), below. To view the exhibition poster, select Download button at upper right