2,313 research outputs found

    Complex Zeros of the Partition Function in Lattice Quantum Chromodynamics

    Get PDF
    The theory of Lee and Yang, which relates the distribution of the zeros of the partition function to the phase structure of a system, is applied to lattice field theory with dynamical fermions. A method is described in which the partition function is evaluated as a finite polynomial in either the bare fermion mass or the 'fugacity'. The roots of this polynomial which are relevant to the physics, i. e. those close to the real axis, are then studied. The partition function zeros are first studied in the fermion mass plane for SU(3), SU(2) and U(1) gauge theories with four flavours of staggered fermions in the infinite coupling limit. Differences are observed in the distributions of zeros on finite lattices, but all are consistent with the expected critical point at ma = 0 on an infinite lattice. The SU(3) and U(1) calculations are then extended to weaker couplings and, in the SU(3) case, to larger systems. In Chapter 7 we perform the expansion in the fugacity plane. The Grand Canonical Partition Function is expanded in terms of Canonical Partition Functions for fixed fermion number. The distributions of zeros give strong evidence for the existence,or otherwise, of a phase transition at finite chemical potential

    “Teaching is a learning experience”:: Exploring Faculty Engagement with Low-Income Adult Learners in a College-Community Partnership Program

    Get PDF
    This article examines interview data with faculty teaching in a college-community partnership program for low-income adult students in an urban setting. The purpose of the study was to explore faculty understandings of the diverse learning needs of their students and the perceptions they have of the efficacy of their teaching practices regarding course design and delivery. Findings highlight the central dynamic of teaching as a negotiated relationship and process of mutual learning between faculty and students, and the means by which faculty work to create engaging and empowering classroom environments. Our research is relevant to educators interested in designing and delivering courses from a social justice perspective in order to encourage adults from low-income communities to pursue a post-secondary pathway. Keywords: post-secondary access, adult learners, low-income student engagement, socialjustice educationLe prĂ©sent article examine des donnĂ©es d’entrevues rĂ©alisĂ©es avec le corps professoral dans le cadre d’un programme de partenariat collĂšge-communautĂ© Ă  l’intention d’étudiants adultes Ă  faible revenu en milieu urbain. L’étude avait pour but d’explorer la façon dont le corps professoral comprend les divers besoins en apprentissage de ses Ă©tudiants et la façon dont il perçoit l’efficacitĂ© de ses pratiques d’enseignement en ce qui a trait Ă  la conception et Ă  l’offre des cours. Les rĂ©sultats font ressortir la dynamique centrale de l’enseignement en tant que relation nĂ©gociĂ©e et comme processus d’apprentissage mutuel entre le corps professoral et les Ă©tudiants, et les moyens par lesquels le corps professoral s’emploie Ă  crĂ©er des environnements de salle de classe captivants et stimulants. Notre recherche s’avĂšre pertinente pour les Ă©ducateurs qui souhaitent concevoir et offrir des cours dans une perspective de justice sociale afin d’encourager les adultes issus des communautĂ©s Ă  faible revenu Ă  poursuivre des Ă©tudes postsecondaires. Mots-clĂ©s : accĂšs aux Ă©tudes postsecondaires, apprenants adultes, faible revenu, engagementdes Ă©tudiants, Ă©ducation Ă  la justice social

    Oral fluorography: Detection of corneal vascularization

    Get PDF
    Corneal vascularization is a pathological process occurring in a cornea suffering physical and/or physiological insult. Its presentation could impair clear vision and thus its detection is important. Unfortunately current methods to detect and grade corneal vascularization are largely subjective and therefore a uniform system to identify and grade its presence does not exist. This study has explored a method using oral fluorescein angiography to examine corneal vessel growth. The results show that corneal vascularization fluoresces and leaks fluorescein during an oral fluorescein study. This information indicates that a method potentially exists to detect, grade and follow corneal vascularization through an objective means

    Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

    Get PDF
    The desaturation and elongation of [1-14C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level

    Concept of Operations for Management by Trajectory

    Get PDF
    This document describes Management by Trajectory (MBT), a concept for future air traffic management (ATM) in which every flight operates in accordance with a four-dimensional trajectory (4DT) that is negotiated between the airspace user and the Federal Aviation Administration (FAA) to respect the airspace user's goals while complying with National Airspace System (NAS) constraints. In the present-day NAS, the ATM system attempts to predict the trajectory for each flight based on the approved flight plan and scheduled or controlled departure time. However, once the aircraft starts to move, controllers tactically manage the aircraft to implement traffic management restrictions, separate otherwise conflicting aircraft, and address arising NAS constraints. Tactical controller actions are not directly communicated to the automation systems or other stakeholders. Furthermore, the initial trajectory prediction does not anticipate these disruptions or how they will impact the flight. Consequently, and compounded by gaps in required data and models, trajectory predictions are less accurate than possible, which affects Traffic Flow Management (TFM) performance. A cornerstone of the MBT concept is that all air vehicles have, at all times, an assigned 4DT from their current state to their destination. These assigned trajectories consist of trajectory constraints and descriptions. Pilots and air traffic controllers, with the aid of automation, operate the aircraft to comply with the assigned trajectory, unless first negotiating a revision. Equipped aircraft have substantial responsibility for complying with the assigned trajectory without controller intervention. To maximize the operational flexibility available to the airspace user, the assigned trajectory only imposes trajectory constraints as required to achieve the ATM goals of NAS constraint compliance and aircraft separation. Trajectory descriptions are added to the assigned trajectory to ensure sufficient predictability. To further improve trajectory prediction accuracy, airspace users supplement the assigned trajectory by broadcasting intent information and updating it as necessary. Air vehicle intent is a more detailed description of the airspace user's plan for how the flight will fly the assigned trajectory. Air vehicle intent can change freely, without negotiation, as long as it remains in compliance with the assigned trajectory. Aircraft assigned trajectories, air vehicle intent, and predicted trajectories are shared, creating a common view among stakeholders. A NAS Constraint Service gathers and publishes information about all known NAS constraints, enabling airspace users to be informed participants in trajectory negotiation. Trajectory constraints in the assigned trajectory are mapped to NAS constraints to facilitate identifying which aircraft are affected when NAS constraints change. To support efficient trajectory negotiation, all aircraft provide current information about air vehicle capabilities. Assigned trajectories are constructed to satisfy all known NAS constraints, improving trajectory stability and predictability. Uncertainty and disruptions are handled by modifying the assigned trajectory as far in advance as possible. By proactively negotiating changes to the assigned trajectory, rather than relying on controller-selected tactical actions such as vectors to resolve traffic conflicts or implement miles-in-trail restrictions, MBT keeps aircraft on closed trajectories that are fully known to all stakeholders. Since reactive air traffic control actions cannot be predicted in advance, the downstream trajectory cannot be accurately predicted until they happen. Reliable trajectory predictions allow the system to identify needed modifications to trajectories further in advance, where they can be negotiated and communicated as amendments (i.e., additional or altered trajectory constraints) to the assigned trajectory. Decision Support Tools (DSTs) aid controllers in rapidly defining and communicating closed trajectories to the aircraft and support all stakeholders in trajectory negotiation. Anticipated MBT benefit mechanisms include more accurate trajectory predictions, improved ATM performance and robustness to off-nominal conditions, increased flexibility and operational efficiency, reduced impediments to emerging classes of airspace users accessing NAS resources, reduced environmental impacts, and enhanced safety

    Moons Are Planets: Scientific Usefulness Versus Cultural Teleology in the Taxonomy of Planetary Science

    Full text link
    We argue that taxonomical concept development is vital for planetary science as in all branches of science, but its importance has been obscured by unique historical developments. The literature shows that the concept of planet developed by scientists during the Copernican Revolution was theory-laden and pragmatic for science. It included both primaries and satellites as planets due to their common intrinsic, geological characteristics. About two centuries later the non-scientific public had just adopted heliocentrism and was motivated to preserve elements of geocentrism including teleology and the assumptions of astrology. This motivated development of a folk concept of planet that contradicted the scientific view. The folk taxonomy was based on what an object orbits, making satellites out to be non-planets and ignoring most asteroids. Astronomers continued to keep primaries and moons classed together as planets and continued teaching that taxonomy until the 1920s. The astronomical community lost interest in planets ca. 1910 to 1955 and during that period complacently accepted the folk concept. Enough time has now elapsed so that modern astronomers forgot this history and rewrote it to claim that the folk taxonomy is the one that was created by the Copernican scientists. Starting ca. 1960 when spacecraft missions were developed to send back detailed new data, there was an explosion of publishing about planets including the satellites, leading to revival of the Copernican planet concept. We present evidence that taxonomical alignment with geological complexity is the most useful scientific taxonomy for planets. It is this complexity of both primary and secondary planets that is a key part of the chain of origins for life in the cosmos.Comment: 68 pages, 16 figures. For supplemental data files, see https://www.philipmetzger.com/moons_are_planets

    Venue Shift Following Devolution: When Reserved Meets Devolved in Scotland

    Get PDF
    This article examines the means used to address blurred or shifting boundaries between reserved UK and devolved Scottish policy. It outlines the main issues of multi-level governance and intergovernmental relations in Scotland and the initial problems faced in identifying responsibility for policy action. While it suggests that legislative ambiguities are now mainly resolved with the use of ‘Sewel motions', it highlights cases of Scottish action in reserved areas, including the example of smoking policy in which the Scottish Executive appears to ‘commandeer' a previously reserved issue. However, most examples of new Scottish influence suggest the need for UK support or minimal UK interest

    RPGR-associated retinal degeneration in human X-linked RP and a murine model

    Get PDF
    PURPOSE. We investigated the retinal disease due to mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene in human patients and in an Rpgr conditional knockout (cko) mouse model. METHODS. XLRP patients with RPGR-ORF15 mutations (n = 35, ages at first visit 5–72 years) had clinical examinations, and rod and cone perimetry. Rpgr-cko mice, in which the proximal promoter and first exon were deleted ubiquitously, were back-crossed onto a BALB/c background, and studied with optical coherence tomography and electroretinography (ERG). Retinal histopathology was performed on a subset. RESULTS. Different patterns of rod and cone dysfunction were present in patients. Frequently, there were midperipheral losses with residual rod and cone function in central and peripheral retina. Longitudinal data indicated that central rod loss preceded peripheral rod losses. Central cone-only vision with no peripheral function was a late stage. Less commonly, patients had central rod and cone dysfunction, but preserved, albeit abnormal, midperipheral rod and cone vision. Rpgr-cko mice had progressive retinal degeneration detectable in the first months of life. ERGs indicated relatively equal rod and cone disease. At late stages, there was greater inferior versus superior retinal degeneration. CONCLUSIONS. RPGR mutations lead to progressive loss of rod and cone vision, but show different patterns of residual photoreceptor disease expression. Knowledge of the patterns should guide treatment strategies. Rpgr-cko mice had onset of degeneration at relatively young ages and progressive photoreceptor disease. The natural history in this model will permit preclinical proof-of-concept studies to be designed and such studies should advance progress toward human therapy

    Water in cratonic lithosphere : calibrating laboratory-determined models of electrical conductivity of mantle minerals using geophysical and petrological observations

    Get PDF
    Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q06010, doi:10.1029/2012GC004055.Measurements of electrical conductivity of “slightly damp” mantle minerals from different laboratories are inconsistent, requiring geophysicists to make choices between them when interpreting their electrical observations. These choices lead to dramatically different conclusions about the amount of water in the mantle, resulting in conflicting conclusions regarding rheological conditions; this impacts on our understanding of mantle convection, among other processes. To attempt to reconcile these differences, we test the laboratory-derived proton conduction models by choosing the simplest petrological scenario possible – cratonic lithosphere – from two locations in southern Africa where we have the most complete knowledge. We compare and contrast the models with field observations of electrical conductivity and of the amount of water in olivine and show that none of the models for proton conduction in olivine proposed by three laboratories are consistent with the field observations. We derive statistically model parameters of the general proton conduction equation that satisfy the observations. The pre-exponent dry proton conduction term (σ0) and the activation enthalpy (ΔHwet) are derived with tight bounds, and are both within the broader 2σ errors of the different laboratory measurements. The two other terms used by the experimentalists, one to describe proton hopping (exponent r on pre-exponent water content Cw) and the other to describe H2O concentration-dependent activation enthalpy (term αCw1/3 added to the activation energy), are less well defined and further field geophysical and petrological observations are required, especially in regions of higher temperature and higher water content.The SAMTEX data were acquired through funding provided by the Continental Dynamics program of the U.S. National Science Foundation (grant EAR0455242 to RLE), the South African Department of Science and Technology (grant to South African Council for Geoscience), and Science Foundation Ireland (grant 05/RGP/GEO001 to AGJ) plus financial and/or logistical support provided by all members of the SAMTEX consortium. JF was initially supported by an IRCSET grant to AGJ for the TopoMed project (TopoMed: Plate reorganization in the western Mediterranean: Lithospheric causes and topographic consequences) within the European Science Foundation’s TOPOEUROPE EUROCORES (http://www.esf.org/activities/eurocores/ running-programmes/topo-europe.html), and subsequently by an SFI PI grant (10/IN.1/I3022) to AGJ for IRETHERM (www.iretherm.ie).2012-12-1