Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. II. Stability of operation.

In this paper, the second of a series of two presenting a detailed description of thermal diffusion cloud chamber operation, we address the operational stability of the vapor–gas mixture in a diffusion cloud chamber with respect to density profile extrema and the accompanying possibility of buoyancy-driven convective flow disturbances. We examine conditions for stable operation (no convective flow disturbances) in the central portion of the cloud chamber, as well as conditions necessary for stable operation in the vicinity of the cloud chamber wall. We find that the total density profile in the central portion of the cloud chamber can pass through a density minimum even though the density at the upper plate surface is less than the density at the lower plate surface. This local density profile inversion can result in unstable (convective) behavior that propagates through the cloud chamber. Furthermore, we find that local extrema in the total density profile near the chamber wall can lead to subtle, convective flows that are difficult to detect yet can exert a profound influence on nucleation in the central portion of the cloud chamber. We have developed a simple method to estimate the limiting total pressure in a cloud chamber that will support stable operation. From results of our investigations based upon this method, it appears that the thermal diffusion cloud chamber is best suited for experiments at higher temperatures where the accessible total pressure range is largest. Finally, we find that results of our investigation into the effects of total pressure and kind of background gas on nucleation in diffusion cloud chambers involving the low molecular weight alcohols and hydrogen and helium background gases cannot be explained on the basis of these kind of density disturbances occurring within the diffusion cloud chamber. Also, for (relatively) low vapor pressure materials, such as 1-pentanol or other high molecular weight alcohols and alkanes stability limitations may preclude nucleation measurements at low temperatures using a diffusion cloud chamber altogether

Two-dimensional transport and wall effects in the thermal diffusion cloud chamber. I. Analysis and operations criteria.

In this paper we present results of a two-dimensional (z,r) treatment of the mass and energy transfer processes that occur during the operation of a thermal diffusion cloud chamber. The location of the wall is considered in solving the mass and energy transport equations, in addition to the vertical distance, z, between the upper and lower plate surfaces. We examine the effect of aspect (diameter to height) ratio on chamber operation; the effects of operation with either a dry or a wet interior chamber wall on temperature, supersaturation, nucleation rate, and total density profiles in the chamber; the effect of overheating the interior of the chamber wall on these conditions within the cloud chamber; and the effects associated with using different density background gases on the operation of the chamber. In a second paper, immediately following, we apply the formalism and the solutions developed in this paper to address the important problem of buoyancy-driven convection that can accompany (seemingly normal) operation of thermal diffusion cloud chambers in nearly all ranges of total pressure and temperature

Sustainable Development Report 2019 : transformations to achieve the Sustainable Development Goals: includes the SDG Index and Dashboards

Resumen: Esta es la cuarta edición del informe anual de los logros por país en relación a los 17 Objetivos de Desarrollo Sostenible, preparado conjuntamente por Bertelsmann Stiftung y la Red de Soluciones para el Desarrollo Sostenible (SDSN). El informe incluye los 193 Estados miembros de las Naciones Unidas y presenta datos sobre los cambios a lo largo del tiempo en los indicadores de los ODS, así como los cálculos de las trayectorias hasta 2030

Nucleation of sulfur hexafluoride

We measured the homogeneous nucleation of sulfur hexafluoride using a diffusion cloud chamber under conditions that avoid the possibility of non-diffusive modes of transport within the cloud chamber thus ensuring reliable data from our measurements. We extended the critical supersaturation measurements into the critical region for SF6 using helium as background gas

Durchsetzung der EU-Gleichbehandlungsrichtlinien: das Vorabentscheidungsverfahren zum EuGH

Die europäische und die innerstaatliche Rechtsetzungsebene verschränken sich immer mehr, insbesondere im Diskriminierungsschutz wurden zentrale Rechtsgrundlagen im Rahmen der EU geschaffen. Vor diesem Hintergrund sind Kenntnisse zum Vorabentscheidungsverfahren vor dem Gerichtshof der Europäischen Union (EuGH) für Anwältinnen und Anwälte zunehmend wichtig. Die Handreichung stellt das EuGH-Vorabentscheidungsverfahren vor und erläutert mit praktischen Handlungsanleitungen, was Anwältinnen und Anwälte alles beachten müssen, wenn sie eine erfolgreiche EuGH-Vorlage zur Durchsetzung der EU-Gleichbehandlungsrichtlinien anstreben

PHA Guidance for Correlating H2S Concentrations in Process Streams to Severity of Adverse Health Outcomes in the Event of a Leak

PresentationProcess hazard analysis (PHA) teams are responsible for determining and categorizing the potential impact of a loss of containment. For streams containing hydrogen sulfide (H2S), the health and safety consequences of a worker being exposed to H2S are a function of airborne concentration in the breathing zone and duration of exposure. PHA teams often do not have the technical knowledge to link the known concentration of H2S in the process stream to an adverse health outcome. This paper describes the methodology and the assumptions made in developing such guidance. H2S concentration in the stream was correlated to concentration of H2S in the breathing zone. Vapor releases used dispersion modeling, while liquid releases required additional modeling to determine the amount of H2S liberated from the released liquid. Modeling was done on different process streams under a variety of conditions. Concentration in the breathing zone was linked to the most probable health and safety outcome by surveying relevant literature published by private and government sources. This correlated the stream concentration of H2S directly to the consequence categorization used in the PHA. Results were summarized, providing simplified guidance that is valid over a wide range of process conditions and release scenarios

Die rol van en beperkings op die regbank om sosiale vrede in Suid-Afrika te bevorder

Judge Eberhard Bertelsmann of the North Gauteng High Court delivered the address published here as he delivered it in Afrikaans in the series of FW de Klerk lectures in Potchefstroom on 20 February 2012.  He dealt with the role of and limitations on the judiciary to promote social peace in South Africa, pointing out the achievements of the courts in the establishment of the constitutional dispensation over the past decades.  He however also showed that the courts are over-burdened and that court administration leaves much to be desired.  Litigants and practitioners do not hesitate to abuse the system and ugly incidents of unethical conduct have marred the professions.  Judges however do not take these trends lying down and measures to rectify the situation are well underway.  Fair, understandable, predictable and speedy adjudication without fear, favour or prejudice continues to be the contribution of judges to the protection of the South African democracy.   &nbsp