9,431 research outputs found
Integral homology of real isotropic and odd orthogonal Grassmannians
We obtain a combinatorial expression for the coefficients of the boundary map
of real isotropic and odd orthogonal Grassmannians providing a natural
generalization of the formulas already obtained for Lagrangian and maximal
isotropic Grassmannians. The results are given in terms of the classification
into four types of covering pairs among the Schubert cells when identified with
signed -Grassmannian permutations. It turns out that these coefficients only
depend on the positions changed over each pair of permutations. As an
application, we give an orientability criterion, exhibit a symmetry of these
coefficients and, compute low-dimensional homology groups.Comment: 24 pages, 8 figures. We have improved the main result
Local Isometric immersions of pseudo-spherical surfaces and evolution equations
The class of differential equations describing pseudo-spherical surfaces,
first introduced by Chern and Tenenblat [3], is characterized by the property
that to each solution of a differential equation, within the class, there
corresponds a 2-dimensional Riemannian metric of curvature equal to . The
class of differential equations describing pseudo-spherical surfaces carries
close ties to the property of complete integrability, as manifested by the
existence of infinite hierarchies of conservation laws and associated linear
problems. As such, it contains many important known examples of integrable
equations, like the sine-Gordon, Liouville and KdV equations. It also gives
rise to many new families of integrable equations. The question we address in
this paper concerns the local isometric immersion of pseudo-spherical surfaces
in from the perspective of the differential equations that give
rise to the metrics. Indeed, a classical theorem in the differential geometry
of surfaces states that any pseudo-spherical surface can be locally
isometrically immersed in . In the case of the sine-Gordon
equation, one can derive an expression for the second fundamental form of the
immersion that depends only on a jet of finite order of the solution of the
pde. A natural question is to know if this remarkable property extends to
equations other than the sine-Gordon equation within the class of differential
equations describing pseudo-spherical surfaces. In an earlier paper [11], we
have shown that this property fails to hold for all other second order
equations, except for those belonging to a very special class of evolution
equations. In the present paper, we consider a class of evolution equations for
of order describing pseudo-spherical surfaces. We show that
whenever an isometric immersion in exists, depending on a jet of
finite order of , then the coefficients of the second fundamental forms are
functions of the independent variables and only.Comment: Fields Institute Communications, 2015, Hamiltonian PDEs and
Applications, pp.N
General method for constructing local-hidden-variable models for entangled quantum states
Entanglement allows for the nonlocality of quantum theory, which is the
resource behind device-independent quantum information protocols. However, not
all entangled quantum states display nonlocality, and a central question is to
determine the precise relation between entanglement and nonlocality. Here we
present the first general test to decide whether a quantum state is local, and
that can be implemented by semidefinite programming. This method can be applied
to any given state and for the construction of new examples of states with
local hidden-variable models for both projective and general measurements. As
applications we provide a lower bound estimate of the fraction of two-qubit
local entangled states and present new explicit examples of such states,
including those which arise from physical noise models, Bell-diagonal states,
and noisy GHZ and W states.Comment: Published version with new title and abstract, improved presentation
and new examples of LHV states. Codes are available at
https://github.com/paulskrzypczyk/localhiddenstatemodels (please cite this
paper if you use them). See also the related work by F. Hirsch et al
arXiv:1512.0026
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Public Systems for Public Employees in Brazil: Options for Reform
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Porous glass-ceramics from alkali activation and sinter-crystallization of mixtures of waste glass and residues from plasma processing of municipal solid waste
Alkali-activated aqueous slurries of fine glass powders, mostly deriving from the plasma processing of municipal solid waste ('Plasmastone'), were found to undergo progressive hardening at low temperature (75 degrees C) owing to the formation of C-S-H (calcium silicate hydrate) gels. Before complete setting, slurries could be easily foamed by vigorous mechanical stirring, with the help of a surfactant; finally, the resulting open-celled structure could be 'frozen' by a subsequent sintering treatment, with crystallization of Ca-Fe silicates. The densification of the struts upon firing was enhanced by mixing Plasmastone with up to 30 wt% recycled glasses and increasing the firing temperature from 800 to 1000 degrees C. A total porosity exceeding 75 vol%, comprising both well-interconnected macro- and micro-sized pores on cell walls, was accompanied by good compressive strength, well above 1 MPa. The stabilization of pollutants generally increased with increasing firing temperature and glass content, with some exceptions; no practical leaching was observed from samples deriving from Plasmastone combined with 30 wt% boro-aluminosilicate glass from the recycling of pharmaceutical vials
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