1,652 research outputs found

    Position dependent energy level shifts of an accelerated atom in the presence of a boundary

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    We consider a uniformly accelerated atom interacting with a vacuum electromagnetic field in the presence of an infinite conducting plane boundary and calculate separately the contributions of vacuum fluctuations and radiation reaction to the atomic energy level shift. We analyze in detail the behavior of the total energy shift in three different regimes of the distance in both the low acceleration and high acceleration limits. Our results show that, in general, an accelerated atom does not behave as if immersed in a thermal bath at the Unruh temperature in terms of the atomic energy level shifts, and the effect of the acceleration on the atomic energy level shifts may in principle become appreciable in certain circumstances, although it may not be realistic for actual experimental measurements. We also examine the effects of the acceleration on the level shifts when the acceleration is of the order of the transition frequency of the atom and we find some features differ from what was obtained in the existing literature.Comment: 26 pages, 6 figures, version published in PR

    Applied type system

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    We present a type system that can effectively facilitate the use of types in capturing invariants in stateful programs that may involve (sophisticated) pointer manipulation. With its root in a recently developed framework Applied Type System (ATS), the type system imposes a level of abstraction on program states by introducing a novel notion of recursive stateful views and then relies on a form of linear logic to reason about such views. We consider the design and then the formalization of the type system to constitute the primary contribution of the paper. In addition, we mention a prototype implementation of the type system and then give a variety of examples that attests to the practicality of programming with recursive stateful views.National Science Foundation (CCR-0224244, CCR-0229480

    A technology and policy analysis for global E-business

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    Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2002.Includes bibliographical references (p. 49-51).We introduce an e-business analytical framework that focuses on transaction flows, including information, physical goods, and services. Within this framework, global e-business involves transaction flows that cross both organizational and national boundaries. Many challenging technology and policy issues arise from this trans-boundary characteristic of global e-business. These issues are analyzed using web aggregation as an example global e-business application. We start the analysis by introducing web aggregation services and their enabling technologies. Our survey of current status of web aggregation indicates that most services are still operated regionally despite their global presence. Although benefits of web aggregation have been realized in regions with extensive use of information aggregation, little is done at the global level. Our case study on worldwide price distribution of a nearly homogeneous consumer electronics product indicates great potential for global aggregation to bring information and efficiency to the global market. In addition to lack of global integration, we identified other deficiencies of web aggregation. Technological challenges and possible solutions to overcoming these deficiencies are discussed. However, having technological capability for trans-boundary information flow does not solve all problems in global aggregation. National policies often prohibit such flow into nations that have different policies, especially in database and privacy protection areas. We analyze these policy issues and propose future research on international policy harmonization.by Hongwei Zhu.S.M


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    Despite the importance of data quality in business analytics, most degree programs do not offer a course on the topic. It is usually left to the discretion of individual instructors to decide where and how much to cover the topic. In this case study, we describe a course on data quality in a Master of Science in Business Analytics program. Organized in eight modules, the first part of the course covers data preparation and preprocessing. This prepares students with the ability to tackle real datasets in other analytics courses. The second part covers analytics for data quality where algorithms for detecting and resolving data quality issues are covered. The third part addresses large scale and engineering issues of analytics practice where data collection needs to be managed and data quality tasks must be part of the pipeline

    Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

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    This is an open access article distributed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International license (CC BY-NC-ND 4.0) https://creativecommons.org/licenses/by-nc-nd/4.0/Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional (2D) numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.Peer reviewe