Safety and CO2 emissions: Implications of using organic fluids in a ship’s waste heat recovery system

Current Marine Policies and regulations greatly favour the use of efficiency enhancing technologies such as the Organic Rankine Cycle (ORC) waste heat recovery systems (WHRS), through the entry into force of International Maritime Organisation (IMO) Energy Efficiency Design Index (EEDI). However, safety regulations such as IMO Safety Of Life At Sea (SOLAS), International Gas Code and Classification Societies still consider the use of highly flammable organic fluids on board ships as hazardous and undesirable, requiring special Administration approval. The benefits of organic fluids in emerging technologies will likely increase their usefulness on board in the near future. Furthermore, current ship safety systems and integrated platform management systems greatly reduce the risks associated with their low flash point making them acceptable for marine use given specific design considerations. This paper studies the case of an Aframax tanker navigating the route North Sea – Naantali, Finland using a slow speed diesel engine. A code with a multi-objective optimization approach generated explicitly for this purpose produces different optimal WHRS designs for the vessel’s operating profile. The WHRS is installed after the turbo compressors in the exhaust gas system, where it absorbs part of the available waste heat and converts it to electricity using a generator. This results in a reduction in fuel consumption, hence decreasing the emission of greenhouse gases. The different optimal designs are compared with a steam WHRS to show the strengths and weaknesses of using an ORC WHRS on board. The ORC technology is at its early stages of development in the marine field, it is important that safety policies follow the evolution of the technology and its associated safety equipment. This paper will serve to recognize the specific safety considerations associated with the ORC and highlight the advantages of carrying organic fluids on board as a solution to increasing CO2 emission restrictions and other environmental concerns

Lower Limits on Aperture Size for an ExoEarth-Detecting Coronagraphic Mission

The yield of Earth-like planets will likely be a primary science metric for future space-based missions that will drive telescope aperture size. Maximizing the exoEarth candidate yield is therefore critical to minimizing the required aperture. Here we describe a method for exoEarth candidate yield maximization that simultaneously optimizes, for the first time, the targets chosen for observation, the number of visits to each target, the delay time between visits, and the exposure time of every observation. This code calculates both the detection time and multi-wavelength spectral characterization time required for planets. We also refine the astrophysical assumptions used as inputs to these calculations, relying on published estimates of planetary occurrence rates as well as theoretical and observational constraints on terrestrial planet sizes and classical habitable zones. Given these astrophysical assumptions, optimistic telescope and instrument assumptions, and our new completeness code that produces the highest yields to date, we suggest lower limits on the aperture size required to detect and characterize a statistically-motivated sample of exoEarths.Comment: Accepted for publication in ApJ; 38 pages, 16 Figures, 3 Table

Interstellar Polarization in the Taurus Dark Clouds, Wavelength Dependent Position Angles and Cloud Structure Near TMC-1

We use polarimetric observations of two stars (HD29647, HD283809) in the general direction of TMC-1 in the Taurus Dark Cloud to investigate grain properties and cloud structure in this region. We show the data to be consistent with a simple two-component model, in which general interstellar polarization in the Taurus Cloud is produced by a widely distributed cloud component with relatively uniform magnetic field orientation; the light from stars close to TMC-1 suffers additional polarization arising in one (or more) subcloud(s) with larger average grain size and different magnetic field directions compared with the general trend. Towards HD29647, in particular, we show that the unusually low degree of visual polarization relative to extinction is due to the presence of distinct cloud components in the line of sight with markedly different magnetic field orientations. Stokes parameter calculations allow us to separate out the polarization characteristics of the individual components. Results are fit with the Serkowski empirical formula to determine the degree and wavelength of maximum polarization. Whereas lambda_max values in the widely distributed material are similar to the average (0.55um) for the diffuse interstellar medium, the subcloud in line of sight to HD~283809, the most heavily reddened star in our study, has lambda_max approx. 0.73um, indicating the presence of grains about 30% larger than this average. Our model also predicts detectable levels of circular polarization toward both HD~29647 and HD~283809.Comment: 17 pages including 6 figures, LaTeX, to appear in the Astrophysical Journal, vol 48

Une co-construction de la réussite. Le cas des expériences de formation en groupe de futurs enseignants

Cette étude est une analyse thématique des témoignages écrits de 67 étudiants en enseignement sur la qualité de leurs expériences de formation en groupe. L’analyse permet d’extraire des témoignages une série de thèmes importants pour assurer à la gestion du travail de groupe un déroulement propice au développement d’habiletés collaboratives et coopératives chez les futurs enseignants. Les résultats présentent les avantages et les défis du travail de groupe identifiés par les participants. Le but de cette recherche est de proposer des pistes pour orienter les pratiques collaboratives et coopératives dans les instituts de formation à l’enseignement pour intégration éventuelle au milieu de travail des futurs enseignants.This study is a thematic analysis of the written accounts of 67 pre-service teachers in regards to the quality of their training through group work experiences. The analysis has permitted the extraction of a series of themes from the accounts, which have been identified as being worthy of consideration in the administration of group work to ensure that the process is conducive to the development of cooperative and collaborative skills for pre-service teachers. The results present a critical analysis of the advantages and challenges of group work identified by the participants.  The objective is to propose orientations for collaborative and cooperative practices in teacher training institutions for eventual integration to pre-service teachers’ future workplaces.Este estudio es un análisis temático de los testimonios escritos de 67 estudiantes en enseñanza sobre la calidad de sus experiencias de formación en grupo. El análisis permite extraer de testimonios una serie de temas importantes para asegurar a la gestión del trabajo de grupo un desarrollo propicio al desarrollo de habilidades colaborativas y cooperativas entre los futuros profesores. Los resultados presentan las ventajas y los desafíos del trabajo de grupo identificados por los participantes. El fin de esta investigación es proponer pistas para orientar las prácticas colaborativas y cooperativas en los institutos de formación a la enseñanza para integración eventual en medio de trabajo de los futuros profesores

Origin of the anomalous Hall Effect in overdoped n-type cuprates: current vertex corrections due to antiferromagnetic fluctuations

The anomalous magneto-transport properties in electron doped (n-type) cuprates were investigated using Hall measurements at THz frequencies. The complex Hall angle was measured in overdoped Pr$_{\rm 2-x}$Ce$_{\rm x}$CuO$_{\rm 4}$ samples (x=0.17 and 0.18) as a continuous function of temperature above $T_c$ at excitation energies 5.24 and 10.5 meV. The results, extrapolated to low temperatures, show that inelastic scattering introduces electron-like contributions to the Hall response. First principle calculations of the Hall angle that include current vertex corrections (CVC) induced by electron interactions mediated by magnetic fluctuations in the Hall conductivity reproduce the temperature, frequency, and doping dependence of the experimental data. These results show that CVC effects are the source of the anomalous Hall transport properties in overdoped n$\text{-}$type cuprates.Comment: 5 pages, 3 figure

Sphaleron Transition Rate in Presence of Dynamical Fermions

We investigate the effect of dynamical fermions on the sphaleron transition rate at finite temperature for the Abelian Higgs model in one spatial dimension. The fermion degrees of freedom are included through bosonization. Using a numerical simulation, we find that massless fermions do not change the rate within the measurement accuracy. Surprisingly, the exponential dependence of the sphaleron energy on the Yukawa coupling is not borne out by the transition rate, which shows a very weak dependence on the fermion mass.Comment: 20 pages, 7 figures, LaTeX, psfi

The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk

The edge-on disk surrounding the nearby young star Beta Pictoris is the archetype of the "debris disks", which are composed of dust and gas produced by collisions and evaporation of planetesimals, analogues of Solar System comets and asteroids. These disks provide a window on the formation and early evolution of terrestrial planets. Previous observations of Beta Pic concluded that the disk gas has roughly solar abundances of elements [1], but this poses a problem because such gas should be rapidly blown away from the star, contrary to observations of a stable gas disk in Keplerian rotation [1, 2]. Here we report the detection of singly and doubly ionized carbon (CII, CIII) and neutral atomic oxygen (OI) gas in the Beta Pic disk; measurement of these abundant volatile species permits a much more complete gas inventory. Carbon is extremely overabundant relative to every other measured element. This appears to solve the problem of the stable gas disk, since the carbon overabundance should keep the gas disk in Keplerian rotation [3]. New questions arise, however, since the overabundance may indicate the gas is produced from material more carbon-rich than the expected Solar System analogues.Comment: Accepted for publication in Nature. PDF document, 12 pages. Supplementary information may be found at http://www.dtm.ciw.edu/akir/Documents/roberge_supp.pdf *** Version 2 : Removed extraneous publication information, per instructions from the Nature editor. No other changes mad

Rapid Dissipation of Primordial Gas from the AU Microscopii Debris Disk

The disk around AU Microscopii, an M1 star in the Beta Pictoris Moving Group, is extraordinarily well-suited for comparison to the Beta Pic debris disk (type A5V). We use far-UV absorption spectroscopy of AU Mic to probe its edge-on disk for small amounts of molecular hydrogen, the primary constituent of gas giant planets. Our conservative upper limit on the line-of-sight H_2 column density is 1.7 x 10^{19} cm^{-2}, which is 18.5 times lower than the limit obtained from non-detection of sub-mm CO emission (Liu et al. 2004). In addition, there is a hint of H_2 absorption at a column density an order of magnitude or more below our upper limit. The H_2-to-dust ratio in the AU Mic disk is < 6:1, similar to that in the Beta Pic disk. This shows that the primordial gas has largely been dissipated in less than about 12 Myr for both disks, despite their very different stellar masses and luminosities. It is extremely difficult to form a giant planet around AU Mic with current core-accretion scenarios in such a short time.Comment: 5 pages, 3 color figures. Accepted for publication in ApJ Letter

Tensor interaction constraints from beta decay recoil spin asymmetry of trapped atoms

We have measured the angular distribution of recoiling daughter nuclei emitted from the Gamow-Teller $\beta$ decay of spin-polarized $^{80}$Rb. The asymmetry of this distribution vanishes to lowest order in the Standard Model (SM) in pure Gamow-Teller decays, producing an observable very sensitive to new interactions. We measure the non-SM contribution to the asymmetry to be $A_{T}$= 0.015 $\pm$ 0.029 (stat) $\pm$ 0.019 (syst), consistent with the SM prediction. We constrain higher-order SM corrections using the measured momentum dependence of the asymmetry, and their remaining uncertainty dominates the systematic error. Future progress in determining the weak magnetism term theoretically or experimentally would reduce the final errors. We describe the resulting constraints on fundamental 4-Fermi tensor interactions.Comment: 11 pages, 13 figures; v2 published in Phys. Rev. C, with referee clarifications and figures improved for black-and-whit

Multifluid, Magnetohydrodynamic Shock Waves with Grain Dynamics II. Dust and the Critical Speed for C Shocks

This is the second in a series of papers on the effects of dust on multifluid, MHD shock waves in weakly ionized molecular gas. We investigate the influence of dust on the critical shock speed, v_crit, above which C shocks cease to exist. Chernoff showed that v_crit cannot exceed the grain magnetosound speed, v_gms, if dust grains are dynamically well coupled to the magnetic field. We present numerical simulations of steady shocks where the grains may be well- or poorly coupled to the field. We use a time-dependent, multifluid MHD code that models the plasma as a system of interacting fluids: neutral particles, ions, electrons, and various ``dust fluids'' comprised of grains with different sizes and charges. Our simulations include grain inertia and grain charge fluctuations but to highlight the essential physics we assume adiabatic flow, single-size grains, and neglect the effects of chemistry. We show that the existence of a phase speed v_phi does not necessarily mean that C shocks will form for all shock speeds v_s less than v_phi. When the grains are weakly coupled to the field, steady, adiabatic shocks resemble shocks with no dust: the transition to J type flow occurs at v_crit = 2.76 v_nA, where v_nA is the neutral Alfven speed, and steady shocks with v_s > 2.76 v_nA are J shocks with magnetic precursors in the ion-electron fluid. When the grains are strongly coupled to the field, v_crit = min(2.76 v_nA, v_gms). Shocks with v_crit < v_s < v_gms have magnetic precursors in the ion-electron-dust fluid. Shocks with v_s > v_gms have no magnetic precursor in any fluid. We present time-dependent calculations to study the formation of steady multifluid shocks. The dynamics differ qualitatively depending on whether or not the grains and field are well coupled.Comment: 43 pages with 17 figures, aastex, accepted by The Astrophysical Journa