2,693 research outputs found

    Free convection boundary layers driven by exothermic surface reactions: critical ambient temperatures

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    A model for the free convection boundary-layer flow near a forward stagnation point driven by heating from a surface on which there is a catalytic reaction is discussed. The governing equations are mude dimensionless so as to highlight the ambient temperature with themain emphasis being to determine critical ambient temperatures. The basic model is then reduced to a standard free convection problem by a transformation of variables from which bifurcation diagrams (plots of a dimensionless surface temperature against a dimensionless ambient temperature) can be constructed. These show a hysteresis bifurcation, the position of which can be readily deduced. A feature of the present formulation is the occurrence of disjoint bifurcation diagrams whereby the upper solution branch becomes separated from the lower solution branches. This aspect is also discussed in detail

    The effect of the order of the autocatalysis on the transverse stability of reaction fronts

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    A linear stability analysis of planar reaction fronts to transverse perturbations is considered for a system based on an autocatalytic reaction of general order p. Dispersion curves, plots of the growth rate σ against a transverse wavenumber k, are obtained for a range of values of p and D, where D is the ratio of the diffusion coefficients of autocatalyst and substrate. A value D0 of D, dependent on p, is found at which σmax, the maximum value of σ in the unstable regime, is largest, with D0 increasing as p is increased. An asymptotic analysis for small wavenumbers is derived, which enables the region in the (p,D) parameter space for instability to be determined. An analysis for D small is undertaken, which leads to upper bounds on the wavenumber for a possible instability

    The Impact of Sexual Harassment on Turnover Intentions, Absenteeism, and Job Satisfaction: Findings from Argentina, Brazil and Chile

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    This study, which tested the effects of sexual harassment on consequences previously indicated in US studies, (i.e., overall turnover intentions, overall absenteeism and job dissatisfaction), was conducted with 8108 employees chosen by the International Labour Organization (ILO) in three Latin American countries – Argentina, Brazil, and Chile. Multivariate and logistic regression were employed while controlling for age, education, gender, marital status, and race to analyze ILO’s database. Significant results revealed that Latin American employees who were sexually harassed were likely to have more turnover intentions and to engage in more absenteeism; yet they did not experience a significant decrease in job satisfaction. These results differ from US findings indicating that there are cross cultural differences in the consequences of sexual harassment. However, the more costly outcomes of sexual harassment (i.e., turnover intentions and absenteeism) are consistent with US findings, indicating the need for multinational companies to establish sexual harassment policies in Latin America as well despite their different legal systems

    Machine Learning in Minecraft: Proof of Concept for Object Detection Oriented Autonomous Bots in Minecraft

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    Machine learning provides new methods of problem solving through applied pattern recognition. An interesting challenge is to utilize machine learning in the automation of tasks and behaviors in virtual environments. Minecraft is an open-world, sandbox style game giving players nearly limitless freedom to alter a procedurally generated world. In the survival game mode, the player must collect resources to craft tools and build structures. The collection of resources can be tedious, so this project seeks to automate the standard initial task of collecting wood. By combining a convolutional neural network with API, a bot can collect resources while remaining scalable to procedural environments. This project utilizes the API Mineflayer for movement, and the Yolov8 neural network architecture from the Ultralytics package in Python for object detection. Data was initially collected in the form of 512x288 pixel images, uniformly sampled from the student researchers’ Minecraft gameplay. The data were then scaled and manually labeled into 7 distinct classes for each type of tree. After training the neural network for 15 epochs, the network could detect trees with an average precision of 88.5% at a recall threshold of 50%. This project has several limitations. Currently, the project is designed only to work on locally hosted servers. Furthermore, the bot’s point of view is generated by a simplified render of the Minecraft environment without dynamic lighting. Lastly, the difficulty is restricted so that the bot only encounters environmental threats. Future researchers may take interest in addressing any of these limitations or may create new datasets and scripts for collecting different resources. This project can also be expanded to include a state machine that switches between neural networks and scripts to carry out more complex behaviors as a sequence of discrete tasks

    An Overview of the Prospects for Sectoral Integration: The View from the United States

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    sectoral integration and United State

    Anomalous electron heating effects on the E region ionosphere in TIEGCM

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    We have recently implemented a new module that includes both the anomalous electron heating and the electron‐neutral cooling rate correction associated with the Farley‐Buneman Instability (FBI) in the thermosphere‐ionosphere electrodynamics global circulation model (TIEGCM). This implementation provides, for the first time, a modeling capability to describe macroscopic effects of the FBI on the ionosphere and thermosphere in the context of a first‐principle, self‐consistent model. The added heating sources primarily operate between 100 and 130 km altitude, and their magnitudes often exceed auroral precipitation heating in the TIEGCM. The induced changes in E region electron temperature in the auroral oval and polar cap by the FBI are remarkable with a maximum Te approaching 2200 K. This is about 4 times larger than the TIEGCM run without FBI heating. This investigation demonstrates how researchers can add the important effects of the FBI to magnetosphere‐ionosphere‐thermosphere models and simulators.NNX14Al13G - NASA GCR; NASA LWS; NNX14AE06G; NNX15AB83G; NNX12AJ54G - NASA HGI; ACI-1053575 - National Science Foundatio

    The Challenge of the F.T.A--Chapter 19

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    The theatre of the organised working class 1830-1930

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    This study of the theatre of the British Labour Movement had its roots in 1985 when History Workshop published a collection of documents relating to the Workers' Theatre Movements in Britain and America between 1880 and 1935. In his introductory essay in Theatres of the Left, Raphael Samuel concludes that there are no traditions in British Labour Theatre except those which have been broken or lost, that There is no continuous history of socialist or alternative history to be discovered, rather a succession of moments separated from one another by a rupture (1). Since this conclusion was reached, others have repeated Samuel's assertion in varying forms. So, Andrew Davies talks of "scanty Chartist theatrical activity" and of the mainstream lab6ur movement in the 1920s remaining "uninterested in cultural matters" and Ian Saville asserts that the conception of a partisan, organised theatre devoted to spreading the socialist message throughout the working classes only began to take shape in Britain in the mid-1920s (2). Yet a cursory glance at the theatre which preceded the Workers' Theatre Movement, a glance which Raphael Samuel provides in his introductory essay on theatre and socialism in Britain, reveals I a plethora of activity in the labour movement. From the Chartists and the Owlenites in the nineteenth century, through the Socialist Sunday Schools and the Socialist League to the Clarion movement, the Independent Labour Party and the Labour Party, the theatrical activity pointed to by Samuel is startling in comparison to anything we can see today. What follows is an attempt to look at some of those moments, to look at the plays they produced and at both how and why working class political organisations looked to the theatre, to try to ascertain if they were indeed no more than broken threads and if so to try to account for why this may be the case. It is also an attempt to re-examine some of our notions of what is political theatre, for since the discovery of the work of the Workers' Theatre Movement and subsequently of the Actresses Franchise League much has been made of these as the starting point of political theatre in Britain. Yet, for a country with one of the longest traditions of organised working class movements, such assertions seem at best strange, at worst dishonest. One clue as to the reason for such claims can be found in the characterisation of the theatre of the organised working class prior to the Workers' Theatre Movement which has become common currency. It was, in the words of Colin Chambers, primarily of ethical and anti-militarist rather than directly political", or in the words of Raphael Samuel: First, the belief that it is their mission to bring the working class into contact with "great" art (ie capitalist art) and second, the tendency to produce plays which may deal with the misery of the workerss may even deal with the class struggleg but which show no way out, and which therefore spread a feeling of defeat and despair (3). Such definitions of what is (or rather what is not) political theatre rest very heavily on a notion that political is most importantly propaganda. If the theatre that existed in connection with political organisations prior to 1926 was not propagandist then it follows for some that it was not political. What follows is therefore also an attempt to uncover a different approach, by looking at the groups own justifications for their involvement in theatrical ventures as part of the struggle for socialism

    Coronal disturbances and their effects on the dynamics of the heliosphere

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    The Sun blows out the solar wind which propagates into the interplanetary medium and forms the heliosphere about 100 AU across. The solar activity causes various types of time-dependent phenomena in the solar wind from long-lived corotating interaction regions to shorter on duration but more extreme events like coronal mass ejections. As these structures propagate outward from the Sun, they evolve and interact with each other and the ambient solar wind. Voyager 1 and 2 provided first unique in-situ measurements of these structures in the outer heliosphere. In particular, Voyager observations in the heliosheath, the outermost region of the heliosphere, showed highly variable plasma flows indicating effects of solar variations extending from the Sun to the heliosphere boundaries. Most surprisingly, Voyager 1 data shows shocks and pressure waves beyond the heliosphere in the interstellar medium. Important questions for the future Interstellar Probe mission are (1) how do the heliosphere boundaries respond to solar variations? (2) how do disturbances evolve in the heliosheath? and (3) how far does the Sun influence extend into the interstellar medium? This talk will review observations and recent modeling efforts demonstrating highly variable and dynamic nature of the global heliosphere in response to disturbances originated in the Sun's atmosphere.https://ui.adsabs.harvard.edu/abs/2019EPSC...13.1229P/abstractPublished versio
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