Ignition and combustion in a laminar mixing zone

The analytic investigation of laminar combustion processes which are essentially two- or three-dimensional present some mathematical difficulties. There are, however, several examples of two-dimensional flame propagation which involve transverse velocities that are small in comparison with that in the principal direction of flow. Such examples occur in thc problem of flame quenching by a cool surface, flame stabilization on a heated flat plate, combustion in laminar mixing zones, etc. In these cases the problem may be simplified by employing what is known in fluid mechanics as the boundary-layer approximation, since it was applied first by Prandtl in his treatment of the viscous flow over a flat plate. Physically it consists in recognizing that if the transverse velocity is small, the variations of flow properties along the direction of main flow are small in comparison with those in a direction normal to the main flow. The analytic description of the problem simplifies accordingly. The present analysis considers the ignition and combustion in the laminar mixing zone between two parallel moving gas streams. One stream consists of a cool combustible mixture, the second is hot combustion products. The two streams come into contact at a given point and a laminar mixing process follows in which the velocity distribution is modified by viscosity, and the temperature and composition distributions by conduction, diffusion, and chemical reaction. The decomposition of the combustible stream is assumed to follow first-order reaction kinetics with temperature dependence according to the Arrhenius law. For a given initial velocity, composition, and temperature distribution, the questions to be answered are: (1) Does the combustible material ignite; and (2) how far downstream of the initial contact point does the flame appear and what is the detailed process of development. Since the hot stream is of infinite extent, it is found that ignition always takes place at some point of the stream. However, when the temperature of the hot stream drops below a certain value, the distance required for ignition increases so enormously that it essentially does not occur in a physical apparatus of finite dimension. The complete development of the laminar flame front is computed using an approximation similar to the integral technique introduced by von Kármán into boundary layer theory

Privatização da educação nos Estados Unidos: Aumento da saturação e segregação

This article outlines different forms of education privatization operating globally, examines their prevalence within the United States, and analyzes whether student marginalization and segregation occurs at the local level. We analyze six U.S. districts with higher saturation levels of charter schools, the most predominant type of privatization (Camden, NJ, Washington DC, Flint, MI, Detroit, MI, Natomas, CA, and Oakland, CA). We find education privatization increasing in the US, but unevenly dispersed, with charter schools concentrated primarily in urban areas serving students of color. Furthermore, segregation in education remains a major issue for all types of schools, with students of color in urban contexts often attending intensely segregated schools (over 90% students of color). Instead of mitigating the segregation problem, student selection by charter school appears to exacerbate it, specifically for special education students.Este artículo describe diferentes formas de privatización de la educación que operan a nivel mundial, examina su prevalencia dentro de los Estados Unidos y analiza si la marginación y segregación de los estudiantes ocurre a nivel local. Analizamos seis distritos de EE. UU. Con mayores niveles de saturación de escuelas charter, el tipo de privatización más predominante (Camden, NJ, Washington DC, Flint, MI, Detroit, MI, Natomas, CA y Oakland, CA). Encontramos que la privatización de la educación aumenta en los Estados Unidos, pero está dispersa de manera desigual, con escuelas charter concentradas principalmente en áreas urbanas que atienden a estudiantes de color. Además, la segregación en la educación sigue siendo un problema importante para todo tipo de escuelas, ya que los estudiantes de color en contextos urbanos a menudo asisten a escuelas intensamente segregadas (más del 90% de estudiantes de color). En lugar de mitigar el problema de la segregación, la selección de estudiantes por la escuela charter parece exacerbarlo, específicamente para los estudiantes de educación especial.Este artigo descreve diferentes formas de privatização da educação operando globalmente, examina sua prevalência nos Estados Unidos e analisa se a marginalização e segregação de alunos ocorrem em nível local. Analisamos seis distritos dos EUA com níveis mais altos de saturação de escolas charter, o tipo mais predominante de privatização (Camden, NJ, Washington DC, Flint, MI, Detroit, MI, Natomas, CA e Oakland, CA). A privatização da educação está aumentando nos EUA, mas dispersa de maneira desigual, com escolas charter concentradas principalmente em áreas urbanas que atendem estudantes de cor. Além disso, a segregação na educação continua sendo uma questão importante para todos os tipos de escolas, com estudantes de cor em contextos urbanos freqüentando escolas intensamente segregadas (mais de 90% dos estudantes de cor). Em vez de atenuar o problema de segregação, a seleção de estudantes por escola charter parece exacerbá-lo, especificamente para estudantes de educação especial

CORPORATIONS--DIRECTORS--APPLICATION TO NEWLY CREATED DIRECTORSHIPS OF STATUTORY PROVISIONS FOR FILLING VACANCIES

Only thirteen states have statutes specifying who may fill directorships created by an increase in the board. However, twenty-eight others provide by statute that the board is or may be empowered to fill vacancies. The question whether such a provision permits the board to fill directorships arising on an increase in the board was before the Delaware court in the recent case of Johnston v. Automatic Steel Products, Inc. The by-laws specified that an increase in the board created vacancies which the board could fill. The board acted thereunder, and this action and the by-law were challenged. The court held that vacancies as used in the Delaware statute did not encompass newly created directorships, and that the shareholders could not empower the board to fill these positions without statutory authority. As the construction of the term vacancies is an open question in twenty-five of the states an examination of the question seems fitting

CORPORATIONS-PREEMPTIVE RIGHT TO SUBSCRIBE TO STOCK ISSUES- NECESSITY OF ACTION BY THE SHAREHOLDER

In Oppenheimer v. Win. F. Chiniquy Co., a stockholder sought to compel the corporation to issue to him his pro rata share of treasury stock which had been offered to the shareholders on August 6, 1945. The final date for application was September 6, but no time for payment was specified. The shareholder wrote to the company accepting the offer before the final date, but did not tender payment until October 16. The corporation had not disposed of the shares, and the court ordered the company to issue them to the shareholder, holding that the delay was of no importance

TAXATION-FEDERAL ESTATE TAX-CHARITABLE DEDUCTION-CERTAINITY OF AMOUNT OF GIFT IN REMAINDER TO CHARITY WHEN CORPUS MAY BE INVADED FOR LIFE TENANT

Testator left his estate in trust for the life of his mother, giving her a life income of $750 per month. The trustees were authorized to use the rest of the income and the principal for her pleasure, comfort and welfare and were instructed to care and provide for her as she might desire. A deduction for a gift to charity of a portion of the remainder was disallowed by the commissioner. The executor sued to recover the tax paid, alleging that the annual income from the estate exceeded the mother\u27s fixed share by$6000, that she had independent investments, earning $300 per month, that she was a woman of moderate needs, without dependents, living on substantially less than$750 per month, and that she was eighty-five years old at the death of the testator. The district court dismissed the complaint for failure to state a cause of action. The circuit court of appeals reversed, holding that despite the provisions of the power, there was an issue of fact whether the corpus was threatened with invasion. On certiorari to the United States Supreme Court, held, reversed. The amount of the charitable gift was not presently ascertainable,\u27\u27 as the trustees\u27 disbursements were not limited by any ready standard. Henslee v. Union Planters National Bank & Trust Co., (U.S. 1949) 69 S.Ct. 290

LABOR LAW-RAILWAY LABOR ACT-EFFECT OF CREATION OF NATIONAL RAILROAD ADJUSTMENT BOARD ON JURISDICTION OF COURTS

The 1934 amendments to the Railway Labor Act (R.L.A.) created the National Railroad Adjustment Board (N.R.A.B.) to hear and decide disputes involving employee grievances and controversies over application and interpretation of agreements, as distinguished from disputes concerning making of collective agreements

NEPC Review: Beyond the Mirage: How Pragmatic Stewardship Could Transform Learning Outcomes in International Education Systems

A report, Beyond the Mirage: How Pragmatic Stewardship Could Transform Learning Outcomes in International Education Systems, prescribes a shift in the leadership role of education ministers &ndash; from providers and guarantors of education to pragmatic stewards of education systems. Focusing on the organization of education sectors in the Global South, the report contends that this shift will address the need for higher quality education, rather than simply providing access to education. The &ldquo;pragmatic stewardship&rdquo; advocated in the report involves strategies that increasingly incorporate private actors. Accordingly, the report draws on four case studies of different types of private-sector involvement in education as examples of a broader shift by education ministers. However, each case contains limitations &ndash; some discussed, others not &ndash; that undermine their suitability as successful examples of divesting public education systems of their primary role as guarantors and providers of education. While the report claims to be &ldquo;non-ideological&rdquo; and &ldquo;beyond the mirage&rdquo; of the education privatization debate, the funders of the report (no publisher is listed) have a material stake in a main program cited as evidence, raising concerns about conflicts of interest. The use of questionable evidence and the conflicts of interest combine to render the report&rsquo;s recommendations unsubstantiated.</p

Les politiques éducatives aux États-Unis

Les décideurs politiques des États-Unis hésitent actuellement entre deux approches pour améliorer la qualité de l’école : des systèmes fondés sur le marché, qui privatisent la gestion des établissements, et des approches en termes de renforcement des capacités, qui intensifient les investissements publics. Cet article analyse les orientations, les mises en œuvre et les résultats de ces politiques à la Nouvelle-Orléans et dans le Massachusetts. À la Nouvelle-Orléans, la privatisation de l’éducation par le biais des charter schools a accru la concurrence entre établissements, mais également la stratification et la ségrégation des élèves, tandis que les résultats aux tests restent faibles. Avec une toute autre approche, basée sur l’investissement public, le Massachusetts a mis en œuvre la péréquation du financement entre établissements, accru le temps d’apprentissage et amélioré la préparation des enseignants ; il arrive en tête de l’évaluation nationale des progrès éducatifs dans toutes les matières.US education policymakers are currently deliberating between two approaches to improving school quality: market-based systems that privatize school management, and capacity-building approaches that deepen public investments. This article analyses policies, practices and outcomes of jurisdictions employing these two approaches: New Orleans and Massachusetts. In New Orleans, privatizing education through charter schools has increased competition between schools, but also increased stratification and segregation of students, while test scores remain low. Using a public investment approach, Massachusetts equitably funded schools, expanded learning time, and provided stronger preparation for teachers; it leads the nation on national assessment of education progress (NAEP) across subjects.Los responsables políticos de Estados Unidos vacilan actualmente entre dos aproximaciones para mejorar la calidad de la escuela : unos sistemas fundados en el mercado, que privatizan la gestión de los establecimientos, y unas aproximaciones en términos de reforzamiento de capacidades que intensifican las inversiones públicas. Este artículo analiza las orientaciones, las implementaciones y los resultados de estas políticas en dos Estados, Luisiana y Massachusetts. En la Nueva Orleans, la privatización de la educación mediante las Charter schools ha favorecido la competencia entre establecimientos y también la estratificación y segregación de los alumnos mientras que los resultados en las pruebas seguiron siendo muy bajos. Con una aproximación muy distinta, basada en la inversión pública, el Massachusetts ha desarrollado la perecuación de la financiación entre establecimientos, aumentado el tiempo de aprendizaje y mejorado la preparación de los docentes ; ya ha llegado al mejor nivel en la evaluación nacional de los progresos educativos en todas las asignaturas

Importation of Exotic Ticks and Tick-Borne Spotted Fever Group Rickettsiae into the United States by Migrating Songbirds

Birds are capable of carrying ticks and, consequently, tick-transmitted microorganisms over long distances and across geographical barriers such as oceans and deserts. Ticks are hosts for several species of spotted fever group rickettsiae (SFGR), which can be transmitted to vertebrates during blood meals. In this study, the prevalence of this group of rickettsiae was examined in ticks infesting migratory songbirds by using polymerase chain reaction (PCR). During the 2009 and 2010 spring migration season, 2064 northward-migrating passerine songbirds were examined for ticks at Johnson Bayou, Louisiana. A total of 91 ticks was removed from 35 individual songbirds for tick species identification and spotted fever group rickettsia detection. Ticks were identified as Haemaphysalis juxtakochi (n = 38, 42%), Amblyomma longirostre (n = 22, 24%), Amblyomma nodosum (n = 17, 19%), Amblyomma calcaratum (n = 11, 12%), Amblyomma maculatum (n = 2, 2%), and Haemaphysalis leporispalustris (n = 1, 1%) by comparing their 12S rDNAgene sequence to homologous sequences in GenBank. Most of the identified ticks were exotic species originating outside of the United States. The phylogenetic analysis of the 71 ompA gene sequences of the rickettsial strains detected in the ticks revealed the occurrence of 6 distinct rickettsial genotypes. Two genotypes (corresponding to a total of 28 samples) were included in the Candidatus Rickettsia amblyommii clade (less than 1% divergence), 2 of them (corresponding to a total of 14 samples) clustered with Rickettsia sp. “Argentina” with less than 0.2% sequence divergence, and 2 of them (corresponding to a total of 27 samples), although closely related to the R. parkeri–R. africae lineage (2.50–3.41% divergence), exhibited sufficient genetic divergence from its members to possibly constitute a new rickettsial genotype. Overall, there does not seem to be a specific relationship between exotic tick species, the rickettsiae they harbor, or the reservoir competence of the corresponding bird species

Forecasting resilience profiles of the run-up to regime shifts in nearly-one-dimensional systems

The forecasting of sudden, irreversible shifts in natural systems is a challenge of great importance, whose realization could allow pre-emptive action to be taken to avoid or mitigate catastrophic transitions, or to help systems adapt to them. In recent years, there have been many advances in the development of such early warning signals. However, much of the current toolbox is based around the tracking of statistical trends and therefore does not aim to estimate the future time scale of transitions or resilience loss. Metric-based indicators are also difficult to implement when systems have inherent oscillations which can dominate the indicator statistics. To resolve these gaps in the toolbox, we use additional system properties to fit parsimonious models to dynamics in order to predict transitions. Here, we consider nearly-one-dimensional systems-higher dimensional systems whose dynamics can be accurately captured by one-dimensional discrete time maps. We show how the nearly one-dimensional dynamics can be used to produce model-based indicators for critical transitions which produce forecasts of the resilience and the time of transitions in the system. A particularly promising feature of this approach is that it allows us to construct early warning signals even for critical transitions of chaotic systems. We demonstrate this approach on two model systems: of phosphorous recycling in a shallow lake, and of an overcompensatory fish population.</p