1,173 research outputs found
Recursive quantum convolutional encoders are catastrophic: A simple proof
Poulin, Tillich, and Ollivier discovered an important separation between the
classical and quantum theories of convolutional coding, by proving that a
quantum convolutional encoder cannot be both non-catastrophic and recursive.
Non-catastrophicity is desirable so that an iterative decoding algorithm
converges when decoding a quantum turbo code whose constituents are quantum
convolutional codes, and recursiveness is as well so that a quantum turbo code
has a minimum distance growing nearly linearly with the length of the code,
respectively. Their proof of the aforementioned theorem was admittedly "rather
involved," and as such, it has been desirable since their result to find a
simpler proof. In this paper, we furnish a proof that is arguably simpler. Our
approach is group-theoretic---we show that the subgroup of memory states that
are part of a zero physical-weight cycle of a quantum convolutional encoder is
equivalent to the centralizer of its "finite-memory" subgroup (the subgroup of
memory states which eventually reach the identity memory state by identity
operator inputs for the information qubits and identity or Pauli-Z operator
inputs for the ancilla qubits). After proving that this symmetry holds for any
quantum convolutional encoder, it easily follows that an encoder is
non-recursive if it is non-catastrophic. Our proof also illuminates why this
no-go theorem does not apply to entanglement-assisted quantum convolutional
encoders---the introduction of shared entanglement as a resource allows the
above symmetry to be broken.Comment: 15 pages, 1 figure. v2: accepted into IEEE Transactions on
Information Theory with minor modifications. arXiv admin note: text overlap
with arXiv:1105.064
Multi-Agent Coverage Control with Energy Depletion and Repletion
We develop a hybrid system model to describe the behavior of multiple agents
cooperatively solving an optimal coverage problem under energy depletion and
repletion constraints. The model captures the controlled switching of agents
between coverage (when energy is depleted) and battery charging (when energy is
replenished) modes. It guarantees the feasibility of the coverage problem by
defining a guard function on each agent's battery level to prevent it from
dying on its way to a charging station. The charging station plays the role of
a centralized scheduler to solve the contention problem of agents competing for
the only charging resource in the mission space. The optimal coverage problem
is transformed into a parametric optimization problem to determine an optimal
recharging policy. This problem is solved through the use of Infinitesimal
Perturbation Analysis (IPA), with simulation results showing that a full
recharging policy is optimal
The role of BK potassium channels in analgesia produced by alpha-2 adrenergic receptors
BACKGROUND AND OBJECTIVE: Millions of people suffer from pain worldwide, and annually, great economic costs are imposed on societies for pain relief. Analgesics such as alpha-2 adrenergic receptor agonists, which have low risk of complications, can be effective in assuaging pain and reducing costs. According to former studies, potassium channels play an important role in the analgesic mechanism of these receptors. This study aimed to determine the role of BK potassium channels in analgesia induced by alpha-2 adrenergic receptors. METHODS: This study was performed on 56 male Wistar rats weighing 250-300 g that were divided into seven groups of eight rats. We administered 0. 7 mg/kg intraperitoneal (IP) injection of clonidine, 1 mg/kg IP injection of yohimbine, and 5 mg/kg intracerebroventricular (ICV) injection of yohimbine. Iberiotoxin at a dose of 100 nm was also injected ICV. Normal saline and DMSO were applied as solvents. Pain severity was evaluated using formalin test at a concentration of 2%. FINDINGS: The chronic pain induced by formalin injection was relieved by IP injection of 0. 7 mg/kg clonidine. Moreover, 5 μg/kg and 1 μg/kg ICV administration of yohimbine with mean chronic pain scores of 2. 29±0. 13 and 2. 09±0. 07, respectively, could significantly inhibit analgesic effect of clonidine with mean chronic pain score of 1. 55±0. 14 (p<0. 001). ICV injection of iberiotoxin with mean chronic pain score of 2. 33±0. 16 at a dose of 100 nm significantly diminished analgesic effects of clonidine. CONCLUSION: Alpha-2 adrenergic receptor agonists could induce analgesia in the animals, and the antagonist of this receptor inhibited the analgesic effect of agonists of these receptors. BK channel inhibition prevented analgesic effect of adrenergic receptor agonists, as well. © 2016, Babol University of Medical Sciences. All rights reserved
Examples of minimal-memory, non-catastrophic quantum convolutional encoders
One of the most important open questions in the theory of quantum
convolutional coding is to determine a minimal-memory, non-catastrophic,
polynomial-depth convolutional encoder for an arbitrary quantum convolutional
code. Here, we present a technique that finds quantum convolutional encoders
with such desirable properties for several example quantum convolutional codes
(an exposition of our technique in full generality will appear elsewhere). We
first show how to encode the well-studied Forney-Grassl-Guha (FGG) code with an
encoder that exploits just one memory qubit (the former Grassl-Roetteler
encoder requires 15 memory qubits). We then show how our technique can find an
online decoder corresponding to this encoder, and we also detail the operation
of our technique on a different example of a quantum convolutional code.
Finally, the reduction in memory for the FGG encoder makes it feasible to
simulate the performance of a quantum turbo code employing it, and we present
the results of such simulations.Comment: 5 pages, 2 figures, Accepted for the International Symposium on
Information Theory 2011 (ISIT 2011), St. Petersburg, Russia; v2 has minor
change
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