549 research outputs found
Tight embeddability of proper and stable metric spaces
We introduce the notions of almost Lipschitz embeddability and nearly
isometric embeddability. We prove that for , every proper
subset of is almost Lipschitzly embeddable into a Banach space if and
only if contains uniformly the 's. We also sharpen a result of N.
Kalton by showing that every stable metric space is nearly isometrically
embeddable in the class of reflexive Banach spaces.Comment: 19 page
Embeddings of locally finite metric spaces into Banach spaces
We show that if X is a Banach space without cotype, then every locally finite
metric space embeds metrically into X.Comment: 6 pages, to appear in Proceedings of the AM
Approximating quantum channels by completely positive maps with small Kraus rank
We study the problem of approximating a quantum channel by one with as few
Kraus operators as possible (in the sense that, for any input state, the output
states of the two channels should be close to one another). Our main result is
that any quantum channel mapping states on some input Hilbert space
to states on some output Hilbert space can be
compressed into one with order Kraus operators, where
, hence much less than
. In the case where the channel's outputs are all
very mixed, this can be improved to order . We discuss the optimality of
this result as well as some consequences.Comment: 13 page
Regulation of Arabidopsis 14-3-3 gene expression by GABA.
The function in plants of the non-protein amino acid, gamma-aminobutyric acid (GABA) is poorly understood. In this study, we show that GABA down-regulates the expression of a large sub-set of 14-3-3 gene family members in Arabidopsis thaliana seedlings in a calcium, ethylene and abscisic acid-dependent manner. Gene expression is not affected when seedlings are supplied with glutamate, a precursor of GABA. The repression of 14-3-3 gene expression by GABA is dependent on functional ethylene and abscisic acid signalling pathways, since the response is lost in the etr1-1, abi1-1 and abi2-1 mutants. Calcium measurements show that in contrast to glutamate, GABA does not elicit a cytoplasmic calcium elevation, suggesting that the GABA response is unlikely to be mediated by glutamate receptors, as has been suggested previously. We suggest that in addition to its role as a stress-related metabolite, GABA may regulate gene expression in Arabidopsis, including members of the 14-3-3 gene family
Approximation properties and Schauder decompositions in Lipschitz-free spaces
We prove that the Lipschitz-free space over a doubling metric space has the
bounded approximation property. We also show that the Lipschitz-free spaces
over or have monotone finite-dimensional Schauder
decompositions
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