10,270 research outputs found

    Preliminary design of a Primary Loop Pump Assembly (PLPA), using electromagnetic pumps

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    A preliminary design study of flight-type dc conduction-permanent magnetic, ac helical induction, and ac linear induction pumps for circulating 883 K (1130 F) NaK at 9.1 kg/sec (20 lb/sec) is described. Various electromagnetic pump geometrics are evaluated against hydraulic performance, and the effects of multiple windings and numbers of pumps per assembly on overall reliability were determined. The methods used in the electrical-hydraulic, stress, and thermal analysis are discussed, and the high temperature electrical materials selected for the application are listed

    An exactly solvable model of a superconducting to rotational phase transition

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    We consider a many-fermion model which exhibits a transition from a superconducting to a rotational phase with variation of a parameter in its Hamiltonian. The model has analytical solutions in its two limits due to the presence of dynamical symmetries. However, the symmetries are basically incompatible with one another; no simple solution exists in intermediate situations. Exact (numerical) solutions are possible and enable one to study the behavior of competing but incompatible symmetries and the phase transitions that result in a semirealistic situation. The results are remarkably simple and shed light on the nature of phase transitions.Comment: 11 pages including 1 figur

    A framework for understanding the factors influencing pair programming success

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    Pair programming is one of the more controversial aspects of several Agile system development methods, in particular eXtreme Programming (XP). Various studies have assessed factors that either drive the success or suggest advantages (and disadvantages) of pair programming. In this exploratory study the literature on pair programming is examined and factors distilled. These factors are then compared and contrasted with those discovered in our recent Delphi study of pair programming. Gallis et al. (2003) have proposed an initial framework aimed at providing a comprehensive identification of the major factors impacting team programming situations including pair programming. However, this study demonstrates that the framework should be extended to include an additional category of factors that relate to organizational matters. These factors will be further refined, and used to develop and empirically evaluate a conceptual model of pair programming (success)

    The contribution of organisational factors to vicarious trauma in mental health professionals: a systematic review and narrative synthesis

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    Background: The negative impact of trauma work has been well documented in mental health professionals. There are three main phenomena used to describe these effects: Secondary Traumatic Stress (STS), Vicarious Trauma (VT) and Compassion Fatigue (CF). To date, the majority of research has focused on the contribution of individual level factors. However, it is imperative to also understand the role of organizational factors. Objectives: This review examines the role of organizational factors in ameliorating or preventing STS, VT, and CF in mental health professionals. We further aimed to identify specific elements of these factors which are perceived to be beneficial and/or detrimental in mitigating against the effects of STS, VT, and CF. Method: Studies were identified by searching the electronic databases Medline, PsycINFO, Embase, Web of Science and SCOPUS with final searches taking place on 10 March 2021. Results: Twenty-three quantitative studies, eight qualitative studies, and five mixed methods studies were included in the final review. A narrative synthesis was conducted to analyse the findings. The results of the review highlight the importance of regular supervision within supportive supervisory relationships, strong peer support networks, and balanced and diverse caseloads. The value of having an organizational culture which acknowledges and validates the existence of STS was also imperative. Conclusions: Organizations have an ethical responsibility to support the mental health professionals they employ and provide a supportive environment which protects them against STS. This review provides preliminary evidence for the types of support that should be offered and highlights the gaps in the literature and where future research should be directed. Further research is needed to evaluate which strategies–and under what conditions–best ameliorate and prevent STS

    Geometrical dependence of decoherence by electronic interactions in a GaAs/GaAlAs square network

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    We investigate weak localization in metallic networks etched in a two dimensional electron gas between 2525\:mK and 750750\:mK when electron-electron (e-e) interaction is the dominant phase breaking mechanism. We show that, at the highest temperatures, the contributions arising from trajectories that wind around the rings and trajectories that do not are governed by two different length scales. This is achieved by analyzing separately the envelope and the oscillating part of the magnetoconductance. For T0.3T\gtrsim0.3\:K we find \Lphi^\mathrm{env}\propto{T}^{-1/3} for the envelope, and \Lphi^\mathrm{osc}\propto{T}^{-1/2} for the oscillations, in agreement with the prediction for a single ring \cite{LudMir04,TexMon05}. This is the first experimental confirmation of the geometry dependence of decoherence due to e-e interaction.Comment: LaTeX, 5 pages, 4 eps figure

    RPA approach to rotational symmetry restoration in a three-level Lipkin model

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    We study an extended Lipkin-Meshkov-Glick model that permits a transition to a deformed phase with a broken continuous symmetry. Unlike simpler models, one sees a persistent zero-frequency Goldstone mode past the transition point into the deformed phase. We found that the RPA formula for the correlation energy provides a useful correction to the Hartree-Fock energy when the number of particle N satisfies N > 3, and becomes accurate for large N. We conclude that the RPA correlation energy formula offers a promising way to improve the Hartree-Fock energy in a systematic theory of nuclear binding energies.Comment: RevTex, 11 pages, 3 postscript figure

    An algebraic approach to problems with polynomial Hamiltonians on Euclidean spaces

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    Explicit expressions are given for the actions and radial matrix elements of basic radial observables on multi-dimensional spaces in a continuous sequence of orthonormal bases for unitary SU(1,1) irreps. Explicit expressions are also given for SO(N)-reduced matrix elements of basic orbital observables. These developments make it possible to determine the matrix elements of polynomial and a other Hamiltonians analytically, to within SO(N) Clebsch-Gordan coefficients, and to select an optimal basis for a particular problem such that the expansion of eigenfunctions is most rapidly convergent.Comment: 19 pages, 8 figure

    Liver transplantation for arteriohepatic dysplasia (Alagille's syndrome)

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    Thirteen out of 268 children (<18 years old) underwent hepatic transplantation (OLT) for end-stage liver disease (ESLD) associated with arteriohepatic dysplasia (AHD). Seven children are alive and well with normal liver function. Six children died, four within 11 days of the operation and the other two at 4 and 10 months after the OLT. Vascular complications with associated septicemia were responsible for the deaths of three children. Two died of heart failure and circulatory collapse, secondary to pulmonary hypertension and congenital heart disease. The remaining patient died of overwhelming sepsis not associated with technical complications. Seven patients had a portoenterostomy or portocholecystostomy early in life; five of these died after the OLT. Severe cardiovascular abnormalities in some of our patients suggest that complete hemodynamic monitoring with invasive studies should be performed in all patients with AHD, especially in cases of documented hypertrophy of the right ventricle. The improved quality of life in our surviving patients confirms the validity of OLT as a treatment of choice in cases of ESLD due to AHD. © 1992 Springer-Verlag

    Direct measurement of the phase coherence length in a GaAs/GaAlAs square network

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    The low temperature magnetoconductance of a large array of quantum coherentloops exhibits Altshuler-Aronov-Spivak oscillations which periodicitycorresponds to 1/2 flux quantum per loop.We show that the measurement of the harmonics content in a square networkprovides an accurate way to determine the electron phase coherence lengthL_ϕL\_{\phi} in units of the lattice length without any adjustableparameters.We use this method to determine L_ϕL\_{\phi} in a network realised from a 2Delectron gas (2DEG) in a GaAS/GaAlAs heterojunction. The temperaturedependence follows a power law T1/3T^{-1/3} from 1.3 K to 25 mK with nosaturation, as expected for 1D diffusive electronic motion andelectron-electron scattering as the main decoherence mechanism.Comment: Additional experimental data in version
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