154,767 research outputs found
An Approximation Problem in Multiplicatively Invariant Spaces
Let be Hilbert space and a -finite
measure space. Multiplicatively invariant (MI) spaces are closed subspaces of that are invariant under point-wise multiplication by
functions in a fix subset of Given a finite set of data
in this paper we prove the
existence and construct an MI space that best fits , in the
least squares sense. MI spaces are related to shift invariant (SI) spaces via a
fiberization map, which allows us to solve an approximation problem for SI
spaces in the context of locally compact abelian groups. On the other hand, we
introduce the notion of decomposable MI spaces (MI spaces that can be
decomposed into an orthogonal sum of MI subspaces) and solve the approximation
problem for the class of these spaces. Since SI spaces having extra invariance
are in one-to-one relation to decomposable MI spaces, we also solve our
approximation problem for this class of SI spaces. Finally we prove that
translation invariant spaces are in correspondence with totally decomposable MI
spaces.Comment: 18 pages, To appear in Contemporary Mathematic
Luminance-dependent hue shift in protanopes
For normal trichromats, the hue of a light can change as its luminance varies. This Bezold-BrĂŒcke (B-B) hue shift is commonly attributed to nonlinearity in the blueâyellow opponent system. In the present study, we questioned whether protanopes experience analogous changes. Two protanopes (Ps) viewed spectral lights at six luminance levels across three log steps. Two normal trichromats (NTs) were tested for comparison. A variant of the color-naming method was used, with an additional âwhiteâ term. To overcome the difficulty of Psâ idiosyncratic
color naming, we converted color-naming functions into individual color spaces, by way of interstimulus similarities and multidimensional scaling (MDS). The color spaces describe each stimulus in terms of spatial coordinates, so that hue shifts are measured geometrically, as displacements along specific dimensions. For the NTs, a B-B shift derived through MDS agreed well with values obtained directly by matching color-naming functions. A change in color appearance was also observed for the Ps, distinct from that in perceived brightness. This change was about twice as large as the B-B shift for NTs and combined what the latter would distinguish as hue and saturation shifts. The protanopic analogue of the B-B shift indicates that the blueâyellow nonlinearity persists in the absence of a
redâgreen signal. In addition, at mesopic levels (# 38 td), the Psâ MDS solution was two dimensional at longer wavelengths, suggesting rod input. Conversely, at higher luminance levels (76 tdâ760 td) the MDS solution was essentially one dimensional, placing a lower limit on S-cone input at longer wavelengths
Algebra properties for Sobolev spaces- Applications to semilinear PDE's on manifolds
In this work, we aim to prove algebra properties for generalized Sobolev
spaces on a Riemannian manifold, where is of
Bessel-type with an operator generating a heat
semigroup satisfying off-diagonal decays. We don't require any assumption on
the gradient of the semigroup. To do that, we propose two different approaches
(one by a new kind of paraproducts and another one using functionals). We also
give a chain rule and study the action of nonlinearities on these spaces and
give applications to semi-linear PDEs. These results are new on Riemannian
manifolds (with a non bounded geometry) and even in the Euclidean space for
Sobolev spaces associated to second order uniformly elliptic operators in
divergence form.Comment: 29 page
Local tropical linear spaces
In this paper we study general tropical linear spaces locally: For any basis
B of the matroid underlying a tropical linear space L, we define the local
tropical linear space L_B to be the subcomplex of L consisting of all vectors v
that make B a basis of maximal v-weight. The tropical linear space L can then
be expressed as the union of all its local tropical linear spaces, which we
prove are homeomorphic to Euclidean space. Local tropical linear spaces have a
simple description in terms of polyhedral matroid subdivisions, and we prove
that they are dual to mixed subdivisions of Minkowski sums of simplices. Using
this duality we produce tight upper bounds for their f-vectors. We also study a
certain class of tropical linear spaces that we call conical tropical linear
spaces, and we give a simple proof that they satisfy Speyer's f-vector
conjecture.Comment: 13 pages, 1 figure. Some results are stated in a bit more generality.
Minor corrections were also mad
The Hodge bundle on Hurwitz spaces
In 2009 Kokotov, Korotkin and Zograf gave a formula for the class of the
Hodge bundle on the Hurwitz space of admissible covers of genus g and degree d
of the projective line. They gave an analytic proof of it. In this note we give
an algebraic proof and an extension of the result.Comment: 8 pages; misprints correcte
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