76,400 research outputs found

    The BCS Critical Temperature in a Weak External Electric Field via a Linear Two-Body Operator

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    We study the critical temperature of a superconductive material in a weak external electric potential via a linear approximation of the BCS functional. We reproduce a similar result as in Frank et al. (Commun Math Phys 342(1):189–216, 2016, [5]) using the strategy introduced in Frank et al. (The BCS critical temperature in a weak homogeneous magnetic field, [2]), where we considered the case of an external constant magnetic field

    The BCS critical temperature in a weak external electric field via a linear two-body operator

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    We study the critical temperature of a superconductive material in a weak external electric potential via a linear approximation of the BCS functional. We reproduce a similar result as in [Frank, Hainzl, Seiringer, Solovej, 2016] using the strategy introduced in [Frank, Hainzl, Langmann, 2018], where we considered the case of an external constant magnetic field.Comment: Dedicated to Herbert Spohn on the occasion of his seventieth birthday; 29 page

    Constructing compact 8-manifolds with holonomy Spin(7) from Calabi-Yau orbifolds

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    Compact Riemannian 7- and 8-manifolds with holonomy G(2) arid Spin(7) were first constructed by the author in 1994-5, by resolving orbifolds T-7/Gamma and T-8/Gamma. This paper describes a new construction of compact 8-manifolds with holonomy Spin(7). We start with a Calabi-Yau 4-orbifold Y with isolated singularities of a special kind. We divide by an antiholomorphic involution a of Y to get a real 8-orbifold Z = Y/. Then we resolve tire singularities of Z to get a compact 8-manifold M, which has metrics with holonomy Spin(7). Manifolds constructed in this way typically have large fourth Betti number b(4)(M).</sigma

    Steroid estrogen determination in sediment and sewage sludge: A critique of chromatographic / mass spectrometry methods incorporating a case study in method development

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    Current analytical methods for determining steroids in sewage sludge and sediment are reviewed and experimental data comparing LC/MS ESI and GC/MS quantification of extracts from these matrices is presented. The effect of matrix influence on method analysis and steroid recoveries was investigated and a comparison of GC and LC determination with mass spectrometry performed. Consequently upon this, an environmental analytically robust methodology is presented and using this technique analysis of sediments determined E1 to be the main steroid (<18 ng/g), EE2 and E3 were determined at far lower concentrations with minimal detection of E

    Overview of building information modelling in healthcare projects

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    In this paper, we explore how BIM functionalities together with novel management concepts and methods have been utilized in thirteen hospital projects in the United States and the United Kingdom. Secondary data collection and analysis were used as the method. Initial findings indicate that the utilization of BIM enables a holistic view of project delivery and helps to integrate project parties into a collaborative process. The initiative to implement BIM must come from the top down to enable early involvement of all key stakeholders. It seems that it is rather resistance from people to adapt to the new way of working and thinking than immaturity of technology that hinders the utilization of BIM

    Mediating boundaries between knowledge and knowing: ICT and R4D praxis

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    Research for development (R4D) praxis (theory-informed practical action) can be underpinned by the use of Information and Communication Technologies (ICTs) which, it is claimed, provide opportunities for knowledge working and sharing. Such a framing implicitly or explicitly constructs a boundary around knowledge as reified, or commodified – or at least able to be stabilized for a period of time (first order knowledge). In contrast ‘third-generation knowledge’ emphasizes the social nature of learning and knowledge-making; this reframes knowledge as a negotiated social practice, thus constructing a different system boundary. This paper offers critical reflections on the use of a wiki as a data repository and mediating technical platform as part of innovating in R4D praxis. A sustainable social learning process was sought that fostered an emergent community of practice among biophysical and social researchers acting for the first time as R4D co-researchers. Over time the technologically mediated element of the learning system was judged to have failed. This inquiry asks: How can learning system design cultivate learning opportunities and respond to learning challenges in an online environment to support R4D practice? Confining critical reflection to the online learning experience alone ignores the wider context in which knowledge work took place; therefore the institutional setting is also considered

    Optimizing egalitarian performance in the side-effects model of colocation for data center resource management

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    In data centers, up to dozens of tasks are colocated on a single physical machine. Machines are used more efficiently, but tasks' performance deteriorates, as colocated tasks compete for shared resources. As tasks are heterogeneous, the resulting performance dependencies are complex. In our previous work [18] we proposed a new combinatorial optimization model that uses two parameters of a task - its size and its type - to characterize how a task influences the performance of other tasks allocated to the same machine. In this paper, we study the egalitarian optimization goal: maximizing the worst-off performance. This problem generalizes the classic makespan minimization on multiple processors (P||Cmax). We prove that polynomially-solvable variants of multiprocessor scheduling are NP-hard and hard to approximate when the number of types is not constant. For a constant number of types, we propose a PTAS, a fast approximation algorithm, and a series of heuristics. We simulate the algorithms on instances derived from a trace of one of Google clusters. Algorithms aware of jobs' types lead to better performance compared with algorithms solving P||Cmax. The notion of type enables us to model degeneration of performance caused by using standard combinatorial optimization methods. Types add a layer of additional complexity. However, our results - approximation algorithms and good average-case performance - show that types can be handled efficiently.Comment: Author's version of a paper published in Euro-Par 2017 Proceedings, extends the published paper with addtional results and proof

    Chaotic root-finding for a small class of polynomials

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    In this paper we present a new closed-form solution to a chaotic difference equation, yn+1=a2yn2+a1yn+a0y_{n+1} = a_2 y_{n}^2 + a_1 y_{n} + a_0 with coefficient a0=(a14)(a1+2)/(4a2)a_0 = (a_1 - 4)(a_1 + 2) / (4 a_2), and using this solution, show how corresponding exact roots to a special set of related polynomials of order 2p,pN2^p, p \in \mathbb{N} with two independent parameters can be generated, for any pp
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