2,172 research outputs found
Communication over Finite-Chain-Ring Matrix Channels
Though network coding is traditionally performed over finite fields, recent
work on nested-lattice-based network coding suggests that, by allowing network
coding over certain finite rings, more efficient physical-layer network coding
schemes can be constructed. This paper considers the problem of communication
over a finite-ring matrix channel , where is the channel
input, is the channel output, is random error, and and are
random transfer matrices. Tight capacity results are obtained and simple
polynomial-complexity capacity-achieving coding schemes are provided under the
assumption that is uniform over all full-rank matrices and is uniform
over all rank- matrices, extending the work of Silva, Kschischang and
K\"{o}tter (2010), who handled the case of finite fields. This extension is
based on several new results, which may be of independent interest, that
generalize concepts and methods from matrices over finite fields to matrices
over finite chain rings.Comment: Submitted to IEEE Transactions on Information Theory, April 2013.
Revised version submitted in Feb. 2014. Final version submitted in June 201
A uniform definition of stochastic process calculi
We introduce a unifying framework to provide the semantics of process algebras, including their quantitative variants useful for modeling quantitative aspects of behaviors. The unifying framework is then used to describe some of the most representative stochastic process algebras. This
provides a general and clear support for an understanding of their similarities and differences. The framework is based on State to Function Labeled Transition Systems, FuTSs for short, that are state-transition structures where each transition is a triple of the form (s; Ī±;P). The first andthe second components are the source state, s, and the label, Ī±, of the transition, while the third component is the continuation function, P, associating a value of a suitable type to each state s0. For example, in the case of stochastic process algebras the value of the continuation function on s0 represents the rate of the negative exponential distribution characterizing the duration/delay of the action performed to reach state s0 from s. We first provide the semantics of a simple formalism used to describe Continuous-Time Markov Chains, then we model a number of process algebras that permit parallel composition of models according to the two main interaction paradigms (multiparty and one-to-one synchronization). Finally, we deal with formalisms where actions and rates are kept separate and address the issues related to the coexistence of stochastic, probabilistic, and non-deterministic behaviors. For each formalism, we establish the formal correspondence between the FuTSs semantics and its original semantics
Agents, subsystems, and the conservation of information
Dividing the world into subsystems is an important component of the
scientific method. The choice of subsystems, however, is not defined a priori.
Typically, it is dictated by experimental capabilities, which may be different
for different agents. Here we propose a way to define subsystems in general
physical theories, including theories beyond quantum and classical mechanics.
Our construction associates every agent A with a subsystem SA, equipped with
its set of states and its set of transformations. In quantum theory, this
construction accommodates the notion of subsystems as factors of a tensor
product Hilbert space, as well as the notion of subsystems associated to a
subalgebra of operators. Classical systems can be interpreted as subsystems of
quantum systems in different ways, by applying our construction to agents who
have access to different sets of operations, including multiphase covariant
channels and certain sets of free operations arising in the resource theory of
quantum coherence. After illustrating the basic definitions, we restrict our
attention to closed systems, that is, systems where all physical
transformations act invertibly and where all states can be generated from a
fixed initial state. For closed systems, we propose a dynamical definition of
pure states, and show that all the states of all subsystems admit a canonical
purification. This result extends the purification principle to a broader
setting, in which coherent superpositions can be interpreted as purifications
of incoherent mixtures.Comment: 31+26 pages, updated version with new results, contribution to
Special Issue on Quantum Information and Foundations, Entropy, GM D'Ariano
and P Perinotti, ed
Observation of the Decay B^-āD_s^((*)+)K^-ā^-Ī½Ģ _ā
We report the observation of the decay B^- ā D_s^((*)+)K^-ā^-Ī½Ģ
_ā based on 342āāfb^(-1) of data collected at the Ī„(4S) resonance with the BABAR detector at the PEP-II e^+e^- storage rings at SLAC. A simultaneous fit to three D_s^+ decay chains is performed to extract the signal yield from measurements of the squared missing mass in the B meson decay. We observe the decay B^- ā D_s^((*)+)K^-ā^-Ī½Ģ
_ā with a significance greater than 5 standard deviations (including systematic uncertainties) and measure its branching fraction to be B(B^- ā D_s^((*)+)K^-ā^-Ī½Ģ
_ā)=[6.13_(-1.03)^(+1.04)(stat)Ā±0.43(syst)Ā±0.51(B(D_s))]Ć10^(-4), where the last error reflects the limited knowledge of the D_s branching fractions
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