9,646 research outputs found
Increasing Distributed Generation Penetration using Soft Normally-Open Points
No full textThis paper considers the effects of various voltage control solutions on facilitating an increase in allowable levels of distributed generation installation before voltage violations occur. In particular, the voltage control solution that is focused on is the implementation of `soft' normally-open points (SNOPs), a term which refers to power electronic devices installed in place of a normally-open point in a medium-voltage distribution network which allows for control of real and reactive power flows between each end point of its installation sites. While other benefits of SNOP installation are discussed, the intent of this paper is to determine whether SNOPs are a viable alternative to other voltage control strategies for this particular application. As such, the SNOPs ability to affect the voltage profile along feeders within a distribution system is focused on with other voltage control options used for comparative purposes. Results from studies on multiple network models with varying topologies are presented and a case study which considers economic benefits of increasing feasible DG penetration is also given
The Enhanced Electrochemical Performance of Nanocrystalline Li[Li0.26Ni0.11Mn0.63]O-2 Synthesized by the Molten-Salt Method for Li-ion batteries
No full textNanocrystalline Li[Li0.26Ni0.11Mn0.63]O2 were easily prepared by using Ni0.15Mn0.85(OH)(2) and Li2CO3 as precursors and KCI as melt-salt for the high capacity materials of Li-ion storage. The obtained nanopartides showed same morphology of polygonal shape and the particle size distribution increased with increasing sinter temperature. The Li[Li[0.26Ni0.11Mn0.63]O2 electrode sintered at 800 degrees C for 12 h exhibits a reversible capacity of more than 300 mAh g(-1) at 0.1 C rate between 2 V and 4.8V and the capacity retention remains 86% and 90% after 90 cycles at the rate of 0.5 C and 1 C, respectively. These superior electrochemical performances are discussed in detail and ascribed to the low dimension and well-crystallized particles. The low dimension provides a short diffusion path and fast transport channels for the lithium ion insertion/extraction reactions and the well-crystallized structure restrains the elimination of oxide ion vacancies and metal ions rearrangement during charge-discharge cycling. (C) 2013 Elsevier Ltd. All rights reserved.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000332812300039&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701ElectrochemistrySCI(E)[email protected]
Discontinuous Galerkin Methods for Numerical Weather Prediction: DG in a large-eddy simulation
No full textThe coarse grid of numerical weather prediction and climate models requires parametrization models to resolve atmospheric processes that are smaller than the grid size. For parametrization development, these processes are simulated by a high resolution model. At the Royal Netherlands MeteorologicalInstitute, the Dutch Atmospheric Large-Eddy Simulation (DALES) is used. This three-dimensional high resolution model uses advection schemes that are too diffusive when steep gradients are present. In this thesis, an advection scheme based on the Discontinuous Galerkin (DG) method is implementedfor DALES.The DG method is known to be dispersive. To remove those non-physical oscillations, the moment limiter of Krivodonova is used. Krivodonova constructed the limiter for one- and two-dimensions. In this thesis the moment limiter and limiting order are derived for three-dimensions. DALES is a model based on the finite difference method and uses operational splitting. Therefore, the DG advection scheme needs a mapping from each cell average to all nodal values that are needed for one DG cell, and a mapping back, which we called mapping a and b respectively. Mappings a that are discussed are taking the cell average as value for all nodal points of the DG cell (cell average a), and taking the L -projection of the cell average to the continuous finite element space (L -projection). This thesis describes mappings b that calculate cell averages of nodal DG values (cell average b)and calculate the cell averages of the tendencies of DG values (cell average of tendency). Using cell average a combined with cell average of tendency, made the DG method as diffusive as the first order upwind scheme. Substituting the cell average a method with the L -projection, the DG method becamevery dispersive, meaning that there was not enough diffusion. At last, cell average b was tested with the L -projection. Its numerical results showed that the speed of the advection was slower than the theoretical velocity. Therefore, a method is suggested which does not need mappings. An option couldbe a supergrid that takes multiple DALES cells as a DG cell.Applied Mathematic
Optimal <i>L</i><sup>2</sup> Error Estimates for the Interior Penalty DG Method for Maxwell’s Equations in Cold Plasma
No full textAbstractIn this paper, we consider an interior penalty discontinuous Galerkin (DG) method for the time-dependent Maxwell’s equations in cold plasma. In Huang and Li (J. Sci. Comput., 42 (2009), 321-340), for both semi and fully discrete DG schemes, we proved error estimates which are optimal in the energy norm, but sub-optimal in the L2-norm. Here by filling this gap, we show that these schemes are optimally convergent in the L2-norm on quasi-uniform tetrahedral meshes if the solution is sufficiently smooth.</jats:p
On orbit categories with dg enhancement
No full textWe show that pretriangulated dg categories enjoy a universal property and
deduce that the passage to an orbit quotient commutes with the dg quotient. In
particular, for a triangulated category with dg enhancement and an endofunctor,
there exists a unique triangulated orbit category.
As an application, we prove that for any connective, smooth and proper dg
algebra , its perfect derived category is equivalent to the generalized
-cluster category of . This implies that the orbit
-cluster category of is equivalent to the generalized -cluster
category of , which implies a conjecture by Ikeda-Qiu for the case when
is a smooth proper graded gentle algebra
Electrochemical stability of glyme-based electrolytes for Li-O2 batteries studied by in situ infrared spectroscopy.
No full textIn situ subtractively normalized Fourier transform infrared spectroscopy (SNIFTIRS) experiments were performed simultaneously with electrochemical experiments relevant to Li-air battery operation on gold electrodes in two glyme-based electrolytes: diglyme (DG) and tetraglyme (TEGDME), tested under different operational conditions. The results show that TEGDME is intrinsically unstable and decomposes at potentials between 3.6 and 3.9 V vs. Li+/Li even in the absence of oxygen and lithium ions, while DG shows a better stability, and only decomposes at 4.0 V vs. Li+/Li in the presence of oxygen. The addition of water to the DG based electrolyte exacerbates its decomposition, probably due to the promotion of singlet oxygen formation
Dg algebras with enough idempotents, their dg modules and their derived categories
No full textWe develop the theory dg algebras with enough idempotents and their dg modules and show their equivalence with that of small dg categories and their dg modules. We introduce the concept of dg adjunction and show that the classical covariant tensor-Hom and contravariant Hom-Hom adjunctions of modules over associative unital algebras are extended as dg adjunctions between categories of dg bimodules. The corresponding adjunctions of the associated triangulated functors are studied, and we investigate when they are one-sided parts of bifunctors which are triangulated on both variables. We finally show that, for a dg algebra with enough idempotents, the perfect left and right derived categories are dual to each other.The author is highly indebted to Alexander Zimmermann for the careful reading of these notes, for his comments and for his help in improving the presentation. This work is backed by reseach projects from the Ministerio de Economía y Competitividad of Spain(MTM201346837-P and MTM201677445-P) and the Fundación ’Séneca’ of Murcia(19880/GERM/15), both with a part of FEDER funds. We thank these institutions for their support
Space-time FE-DG discretization of the anisotropic diffusion equation in any dimension: The spectral symbol
No full textThe multidimensional heat equation, along with its more general version known as the (linear) anisotropic diffusion equation, is discretized by a discontinuous Galerkin (DG) method in time and a finite element (FE) method of arbitrary regularity in space. We show that the resulting space-time discretization matrices enjoy an asymptotic spectral distribution as the mesh fineness increases, and we determine the associated spectral symbol, i.e., the function that carefully describes the spectral distribution. The analysis of this paper is carried out in a stepwise fashion, without omitting details, and it is supported by several numerical experiments. It is preparatory to the development of specialized solvers for linear systems arising from the FE-DG approximation of both the heat equation and the anisotropic diffusion equation
A comparison between different approaches for the numerical treatment of bottom discontinuities in a DG perspective
No full textThe use of Discontinuous Galerkin (DG) numerical schemes for the Shallow Water Equations (SWE) integration is greatly increased in the last decade. The efforts of many researchers were initially devoted to conceive techniques for the exact preservation of the motionless state over non-flat bottom. Recently, such efforts are mainly oriented to the proper treatment of the bottom discontinuities and to the exact preservation of the moving-water steady flows.
In this work, in the unified context consisting of third-order accurate DG-SWE schemes, a comparison between five numerical treatments of the bottom discontinuities is presented.
We consider three widespread approaches that perform well if the motionless state has to be preserved. First, a simple technique, which consists in a proper initialization of the bed elevation that imposes the continuity of the bottom profile is taken into account [Kesserwani and Liang, INT J NUMER METH ENG, 86, 47-69, 2011]. Then, we consider the hydrostatic reconstruction method [Audusse et al., SIAM J SCI COMPUT, 25, 2050-2065, 2004] and a path-conservative scheme based on a linear integration path [Parés, SIAM J NUMER ANAL, 44, 300-321, 2006].
We also consider two further approaches (both based on mechanical principles) which are promising for the preservation of a moving-water steady state. A model is obtained modifying the hydrostatic reconstruction as suggested in [Caleffi and Valiani, ASCE JEM, 135(7), 684-696, 2009]. This method is characterized by a correction of the numerical flux based on the local conservation of the total energy. The last model is obtained improving the path-conservative scheme using a non-linear path.
Several test cases are used to verify the accuracy, the well-balancing, the behavior in simulating a quiescent flow and the resolution in simulating unsteady flows of the models. A specific test case is also introduced to highlight the difference between the five schemes when a steady moving flow interacts with a bottom step
The amoebal MAP kinase response to Legionella pneumophila is regulated by DupA
No full textThe amoeba Dictyostelium discoideum can support replication of Legionella pneumophila. Here we identify the dupA gene, encoding a putative tyrosine kinase/dual-specificity phosphatase, in a screen for D. discoideum mutants altered in allowing L. pneumophila intracellular replication. Inactivation of dupA resulted in depressed L. pneumophila growth and sustained hyperphosphorylation of the amoebal MAP kinase ERK1, consistent with loss of a phosphatase activity. Bacterial challenge of wild-type amoebae induced dupA expression and resulted in transiently increased ERK1 phosphorylation, suggesting that dupA and ERK1 are part of a response to bacteria. Indeed, over 500 of the genes misregulated in the dupA(-) mutant were regulated in response to L. pneumophila infection, including some thought to have immune-like functions. MAP kinase phosphatases are known to be highly upregulated in macrophages challenged with L. pneumophila. Thus, DupA may regulate a MAP kinase response to bacteria that is conserved from amoebae to mammals
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