17,166 research outputs found
The Extended Fock Basis of Clifford Algebra
We investigate the properties of the Extended Fock Basis (EFB) of Clifford
algebras introduced in [1]. We show that a Clifford algebra can be seen as a
direct sum of multiple spinor subspaces that are characterized as being left
eigenvectors of \Gamma. We also show that a simple spinor, expressed in Fock
basis, can have a maximum number of non zero coordinates that equals the size
of the maximal totally null plane (with the notable exception of vectorial
spaces with 6 dimensions).Comment: Minimal corrections to the published versio
Geometric realization and K-theoretic decomposition of C*-algebras
Suppose that A is a separable C*-algebra and that G_* is a (graded) subgroup
of K_*(A). Then there is a natural short exact sequence 0 \to G_* \to K_*(A)
\to K_*(A)/G_* \to 0.
In this note we demonstrate how to geometrically realize this sequence at the
level of C*-algebras. As a result, we KK-theoretically decompose A as 0 \to
A\otimes \Cal K \to A_f \to SA_t \to 0 where K_*(A_t) is the torsion subgroup
of K_*(A) and K_*(A_f) is its torsionfree quotient. Then we further decompose
A_t : it is KK-equivalent to \oplus_p A_p where K_*(A_p) is the p-primary
subgroup of the torsion subgroup of K_*(A). We then apply this realization to
study the Kasparov group K^*(A) and related objects.Comment: 9 pages.To appear in International J. Mat
On the consequences of the fact that atomic levels have a certain width
This note presents two ideas. The first one is that quantum theory has a
fundamentally perturbative basis but leads to nonperturbative states which it
would seem natural to take into account in the foundation of a theory of
quantum phenomena. The second one consists in questioning the validity of the
present notion of time. Both matters are related to the fact that atomic levels
have a certain width. This note is presented qualitatively so as to evidence
its main points, independently of the models on which these have been tested.Comment: 8 page
On the Commitment Capacity of Unfair Noisy Channels
Noisy channels are a valuable resource from a cryptographic point of view.
They can be used for exchanging secret-keys as well as realizing other
cryptographic primitives such as commitment and oblivious transfer. To be
really useful, noisy channels have to be consider in the scenario where a
cheating party has some degree of control over the channel characteristics.
Damg\r{a}rd et al. (EUROCRYPT 1999) proposed a more realistic model where such
level of control is permitted to an adversary, the so called unfair noisy
channels, and proved that they can be used to obtain commitment and oblivious
transfer protocols. Given that noisy channels are a precious resource for
cryptographic purposes, one important question is determining the optimal rate
in which they can be used. The commitment capacity has already been determined
for the cases of discrete memoryless channels and Gaussian channels. In this
work we address the problem of determining the commitment capacity of unfair
noisy channels. We compute a single-letter characterization of the commitment
capacity of unfair noisy channels. In the case where an adversary has no
control over the channel (the fair case) our capacity reduces to the well-known
capacity of a discrete memoryless binary symmetric channel
Document Retrieval on Repetitive Collections
Document retrieval aims at finding the most important documents where a
pattern appears in a collection of strings. Traditional pattern-matching
techniques yield brute-force document retrieval solutions, which has motivated
the research on tailored indexes that offer near-optimal performance. However,
an experimental study establishing which alternatives are actually better than
brute force, and which perform best depending on the collection
characteristics, has not been carried out. In this paper we address this
shortcoming by exploring the relationship between the nature of the underlying
collection and the performance of current methods. Via extensive experiments we
show that established solutions are often beaten in practice by brute-force
alternatives. We also design new methods that offer superior time/space
trade-offs, particularly on repetitive collections.Comment: Accepted to ESA 2014. Implementation and experiments at
http://www.cs.helsinki.fi/group/suds/rlcsa
The evolution of free wave packets
We discuss four general features of force-free evolution: (1) The spatial
spread of any packet changes with time in a very simple way. (2) Over
sufficiently short periods of time (whose duration is related to the spread in
momentum of the packet) the probability distribution moves but there is little
change in shape. (3) After a sufficiently long period (related to the initial
spatial spread) the packet settles into a simple form simply related to the
momentum distribution in the packet. In this asymptotic regime, the shape of
the probability distribution no longer changes except for its scale, which
increases linearly with the time. (4) There is an infinite denumerable set of
simple wave packets (the Hermite-Gauss packets) that do not change shape as
they evolve.Comment: 6 pages, 4 figures, didactic pape
Quantum coherence generated by interference-induced state selectiveness
The relations between quantum coherence and quantum interference are
discussed. A general method for generation of quantum coherence through
interference-induced state selection is introduced and then applied to `simple'
atomic systems under two-photon transitions, with applications in quantum
optics and laser cooling.Comment: 17 pages, 7 figures, to be published in Journal of Modern Optics'
special issue on quantum interferenc
Can thin-lipped mullet directly exploit the primary and detritic production of European macrotidal salt marshes?
Juveniles and adults (>100 mm) of Liza ramada colonize macrotidal salt marsh creeks of Mont Saint-Michel bay (France)between March and November, during spring tide floods (43% of the tides) and return to coastal waters during the ebb. This fish species actively feeds during its short stay in the creek (from 1 to 2 h). On average, each fish swallows sediment including living and inert organic matter, which amounts to 8% of its fresh body weight. Their diet is dominated by small benthic items (especially diatoms and salt marsh plant detritus), that correspond to the primary and detritic production of this macrotidal salt marsh creek. Despite very short submersion periods, mullets filter and ingest large quantities of sediment and concentrated organic matter (on average organic matter in stomach content is 31%) produced by these coastal wetlands. European salt marshes are thus shown to act as trophic areas for mullets, which are well adapted to this constraining habitat which is only flooded for short periods during spring tides
Education Through Camping
The purpose of this report was to provide a brief history of camping in the United States, an account of the Auburn, Washington School District’s elementary summer school pilot and first year camping program, the first in Washington State, and to present the education benefits of such a program
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