2,296 research outputs found
Black holes, parallelizable horizons and half-BPS states for the Einstein-Gauss-Bonnet theory in five dimensions
Exact vacuum solutions with a nontrivial torsion for the
Einstein-Gauss-Bonnet theory in five dimensions are constructed. We consider a
class of static metrics whose spacelike section is a warped product of the real
line with a nontrivial base manifold endowed with a fully antisymmetric
torsion. It is shown requiring solutions of this sort to exist, fixes the
Gauss-Bonnet coupling such that the Lagrangian can be written as a Chern-Simons
form. The metric describes black holes with an arbitrary, but fixed, base
manifold. It is shown that requiring its ground state to possess unbroken
supersymmetries, fixes the base manifold to be locally a parallelized
three-sphere. The ground state turns out to be half-BPS, which could not be
achieved in the absence of torsion in vacuum. The Killing spinors are
explicitly found.Comment: 11 pages, no figures, notation clarified; version accepted for
publication in Physical Review
The null divergence factor
Let be a vector field defined in a open subset . We call a null divergence factor a solution of the equation . In previous works it has been shown that this function plays a fundamental role in the problem of the center and in the determination of the limit cycles. In this paper we show how to construct systems with a given null divergence factor. The method presented in this paper is a generalization of the classical Darboux method to generate integrable systems
Large EU banks have remained undercapitalised for long stretches of time
Book-valued capital ratios and regulatory inertia are some of the causes, write Mark J. Flannery and Emanuela Giacomin
Inverse heat conduction to model and optimise a geothermal field
Geothermal heat exchanger fields are complex systems that exploit the soil as a heat reservoir for space heating and cooling. They consist of several heat exchangers conveniently arranged in a given soil portion. The design of heat exchanger fields is a key phase to ensure the long-term sustainability of such renewable energy systems. This task requires modelling the relevant processes in the system, i.e., the heat transfer within and outside the exchangers. We propose a mathematical model for the study of the heat conduction into the soil that considers the presence of the exchangers. This problem is formulated and solved with an analytical approach. Some numerical experiments are used to show the effectiveness of the proposed method through a comparison with a reference approximation procedure, based on a finite difference method. Moreover, the obtained analytical solution is used in an optimisation procedure to compute the best position of the exchangers by minimising the adverse effect of neighbouring devices. The obtained results are promising and show that the proposed procedure can be exploited as an effective tool in the design of geothermal systems
Hybrid Control Systems: a Design Case Study
This paper presents a modification to UML to improve the modelling and analysis of discrete-event dynamic system (DEDS) representations of manufacturing systems. It shows how Petri nets can be used to improve the representation and analysis of the dynamic model of a system specified using UML. Finally the technique is illustrated by its application to a simplified production line
Biocontrol Ability and Action Mechanism of Starmerella bacillaris (Synonym Candida zemplinina) Isolated from Wine Musts against Gray Mold Disease Agent Botrytis cinerea on Grape and Their Effects on Alcoholic Fermentation
Gray mold is one of the most important diseases of grapevine in temperate climates. This plant pathogen affects plant growth and reduces wine quality. The use of yeasts as biocontrol agents to apply in the vineyard have been investigated in recent years as an alternative to agrochemicals. In this work, fermenting musts obtained from overripe grape berries, therefore more susceptible to infection by fungal pathogens such as Botrytis cinerea, were considered for the selection of yeasts carrying antifungal activity. Thirty-six isolates were identified as Starmerella bacillaris, a species recently proven to be of enological interest. Among them 14 different strains were studied and antifungal activity against B. cinerea was demonstrated, for the first time, to be present in S. bacillaris species. The production of volatile organic compounds (VOCs), tested in vitro, was found to be the main responsible of S. bacillaris antifungal effects. All the strains were able to reduce B. cinerea decay on wounded grape berries artificially inoculated with gray mold. The colonization level of wound was very high reaching, after 5 days, a concentration of 10(6) cells per ml of grape juice obtained after berry crushing. At this cell concentration S. bacillaris strains were used to ferment synthetic and natural musts. The sequential yeast inoculation, performed by adding S. cerevisiae 48 h after S. bacillaris, was needed to complete sugar consumption and determined a significant increase in glicerol content and a reduction of ethanol and acetic acid concentrations. The high wound colonization ability, found in this work, together with the propensity to colonize grape berry and the interesting enological traits possessed by the selected S. bacillaris strains allow the use of this yeast as biocontrol agent on vine and grape berries with possible positive effects on must fermentation, although the presence of S. cerevisiae is needed to complete the fermentation process. This work introduces new possibilities in wine yeast selection programs in order to identify innovative wine yeasts that are simultaneously antifungal agents in vineyards and alternative wine starters for grape must fermentation and open new perspective to a more integrated strategy for increasing wine quality
An overlapping domain decomposition method for the solution of parametric elliptic problems via proper generalized decomposition
A non-intrusive proper generalized decomposition (PGD) strategy, coupled with
an overlapping domain decomposition (DD) method, is proposed to efficiently
construct surrogate models of parametric linear elliptic problems. A parametric
multi-domain formulation is presented, with local subproblems featuring
arbitrary Dirichlet interface conditions represented through the traces of the
finite element functions used for spatial discretization at the subdomain
level, with no need for additional auxiliary basis functions. The linearity of
the operator is exploited to devise low-dimensional problems with only few
active boundary parameters. An overlapping Schwarz method is used to glue the
local surrogate models, solving a linear system for the nodal values of the
parametric solution at the interfaces, without introducing Lagrange multipliers
to enforce the continuity in the overlapping region. The proposed DD-PGD
methodology relies on a fully algebraic formulation allowing for real-time
computation based on the efficient interpolation of the local surrogate models
in the parametric space, with no additional problems to be solved during the
execution of the Schwarz algorithm. Numerical results for parametric diffusion
and convection-diffusion problems are presented to showcase the accuracy of the
DD-PGD approach, its robustness in different regimes and its superior
performance with respect to standard high-fidelity DD methods
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