11,338 research outputs found
Uniqueness for weak solutions of parabolic equations with a fractional time derivative
We prove uniqueness for weak solutions to abstract parabolic equations with
the fractional Marchaud or Caputo time derivative. We consider weak solutions
in time for divergence form equations when the fractional derivative is
transferred to the test function.Comment: Accepted version to appear in Contemporary Mathematics. Corrected
inaccuracies regarding historical results in the introduction. Also changed
the initial condition for the equation and fixed typo
Separation of a Lower Dimensional Free Boundary in a Two Phase Problem
This paper studies local properties of a two phase free boundary problem for
the fractional Laplacian. The main result states that the two free boundaries
of the positive and negativity sets cannot touch
Writers' Bloc: reading into late Soviet experience through Latvian artists' books.
Previously in the University eprints HAIRST pilot service at http://eprints.st-andrews.ac.uk/archive/00000364/Article 1 of 6 in an issue devoted to Scandinavian and Baltic visual cultureThis article focuses on book works by Latvian artists during the late-Soviet period, and also offers an initial discussion of the peculiarities of the Soviet publishing environment, as it existed shortly before the USSR’s annexation of Latvia at the end of World War II, and the roughly concurrent publication experiences of progressive artists in inter-bellum Latvia, the so-called First Republic.
During its heyday in the 1960s and 70s the artist’s book was hailed by many practitioners in the West as the superlative democratic art form, due to the hypothetical possibility of the widespread ownership of the art object. An examination of how artist-authored books developed amid Latvian society's repeated, abrupt transitions between democracy and totalitarianism during the past century may further illuminate this concept of a democratic art medium.Postprin
Quantum Superpositions Cannot be Epistemic
Quantum superposition states are behind many of the curious phenomena
exhibited by quantum systems, including Bell non-locality, quantum
interference, quantum computational speed-up, and the measurement problem. At
the same time, many qualitative properties of quantum superpositions can also
be observed in classical probability distributions leading to a suspicion that
superpositions may be explicable as probability distributions over less
problematic states, that is, a suspicion that superpositions are
\emph{epistemic}. Here, it is proved that, for any quantum system of dimension
, this cannot be the case for almost all superpositions. Equivalently, any
underlying ontology must contain ontic superposition states. A related question
concerns the more general possibility that some pairs of non-orthogonal quantum
states could be ontologically indistinct (there are
ontological states which fail to distinguish between these quantum states). A
similar method proves that if
then must approach ontological distinctness as
. The robustness of these results to small experimental
error is also discussed.Comment: Updated to published version with slgihtly extended discussion and
corrected mistakes. 6 + 7 pages, Quantum Studies: Mathematics and
Foundations. Online First. (2015
Treating Time Travel Quantum Mechanically
The fact that closed timelike curves (CTCs) are permitted by general
relativity raises the question as to how quantum systems behave when time
travel to the past occurs. Research into answering this question by utilising
the quantum circuit formalism has given rise to two theories: Deutschian-CTCs
(D-CTCs) and "postselected" CTCs (P-CTCs). In this paper the quantum circuit
approach is thoroughly reviewed, and the strengths and shortcomings of D-CTCs
and P-CTCs are presented in view of their non-linearity and time travel
paradoxes. In particular, the "equivalent circuit model"---which aims to make
equivalent predictions to D-CTCs, while avoiding some of the difficulties of
the original theory---is shown to contain errors. The discussion of D-CTCs and
P-CTCs is used to motivate an analysis of the features one might require of a
theory of quantum time travel, following which two overlapping classes of new
theories are identified. One such theory, the theory of "transition
probability" CTCs (T-CTCs), is fully developed. The theory of T-CTCs is shown
not to have certain undesirable features---such as time travel paradoxes, the
ability to distinguish non-orthogonal states with certainty, and the ability to
clone or delete arbitrary pure states---that are present with D-CTCs and
P-CTCs. The problems with non-linear extensions to quantum mechanics are
discussed in relation to the interpretation of these theories, and the physical
motivations of all three theories are discussed and compared.Comment: 20 pages, 4 figures. Edited in response to peer revie
Preprojective representations of valued quivers and reduced words in the Weyl group of a Kac-Moody algebra
This paper studies connections between the preprojective representations of a
valued quiver, the (+)-admissible sequences of vertices, and the Weyl group by
associating to each preprojective representation a canonical (+)-admissible
sequence. A (+)-admissible sequence is the canonical sequence of some
preprojective representation if and only if the product of simple reflections
associated to the vertices of the sequence is a reduced word in the Weyl group.
As a consequence, for any Coxeter element of the Weyl group associated to an
indecomposable symmetrizable generalized Cartan matrix, the group is infinite
if and only if the powers of the element are reduced words. The latter
strengthens known results of Howlett, Fomin-Zelevinsky, and the authors
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