5,515 research outputs found
Service composition in stochastic settings
With the growth of the Internet-of-Things and online Web services, more services with more capabilities are available to us. The ability to generate new, more useful services from existing ones has been the focus of much research for over a decade. The goal is, given a specification of the behavior of the target service, to build a controller, known as an orchestrator, that uses existing services to satisfy the requirements of the target service. The model of services and requirements used in most work is that of a finite state machine. This implies that the specification can either be satisfied or not, with no middle ground. This is a major drawback, since often an exact solution cannot be obtained. In this paper we study a simple stochastic model for service composition: we annotate the tar- get service with probabilities describing the likelihood of requesting each action in a state, and rewards for being able to execute actions. We show how to solve the resulting problem by solving a certain Markov Decision Process (MDP) derived from the service and requirement specifications. The solution to this MDP induces an orchestrator that coincides with the exact solution if a composition exists. Otherwise it provides an approximate solution that maximizes the expected sum of values of user requests that can be serviced. The model studied although simple shades light on composition in stochastic settings and indeed we discuss several possible extensions
Gauge-invariant quark-antiquark nonlocal condensates in lattice QCD
We study, by numerical simulations on a lattice, the behaviour of the
gauge-invariant quark-antiquark nonlocal condensates in the QCD vacuum with
dynamical fermions. A determination is also done in the quenched approximation
and the results are compared with the full-QCD case. The fermionic correlation
length is extracted and compared with the analogous gluonic quantity.Comment: 14 pages, LaTeX file, + 6 PS figure
Topological susceptibility in Yang-Mills theory in the vacuum correlator method
We calculate the topological susceptibility of the Yang-Mills vacuum using
the field correlator method. Our estimate for the SU(3) gauge group, \chi^{1/4}
= 196(7) MeV, is in a very good agreement with the results of recent numerical
simulations of the Yang-Mills theory on the lattice.Comment: 5 pages (JETP Letters style
Improved lattice operators: the case of the topological charge density
We analyze the properties of a class of improved lattice topological charge
density operators, constructed by a smearing-like procedure. By optimizing the
choice of the parameters introduced in their definition, we find operators
having (i) a better statistical behavior as estimators of the topological
charge density on the lattice, i.e. less noisy; (ii) a multiplicative
renormalization much closer to one; (iii) a large suppression of the
perturbative tail (and other unphysical mixings) in the corresponding lattice
topological susceptibility.Comment: 11 pages (REVTEX) + 4 (uuencoded) figure
On Explicit Point Multi-Monopoles in SU(2) Gauge Theory
It is well known that the Dirac monopole solution with the U(1) gauge group
embedded into the group SU(2) is equivalent to the SU(2) Wu-Yang point monopole
solution having no Dirac string singularity. We consider a multi-center
configuration of m Dirac monopoles and n anti-monopoles and its embedding into
SU(2) gauge theory. Using geometric methods, we construct an explicit solution
of the SU(2) Yang-Mills equations which generalizes the Wu-Yang solution to the
case of m monopoles and n anti-monopoles located at arbitrary points in R^3.Comment: 1+7 pages, LaTe
Operational distance and fidelity for quantum channels
We define and study a fidelity criterion for quantum channels, which we term
the minimax fidelity, through a noncommutative generalization of maximal
Hellinger distance between two positive kernels in classical probability
theory. Like other known fidelities for quantum channels, the minimax fidelity
is well-defined for channels between finite-dimensional algebras, but it also
applies to a certain class of channels between infinite-dimensional algebras
(explicitly, those channels that possess an operator-valued Radon--Nikodym
density with respect to the trace in the sense of Belavkin--Staszewski) and
induces a metric on the set of quantum channels which is topologically
equivalent to the CB-norm distance between channels, precisely in the same way
as the Bures metric on the density operators associated with statistical states
of quantum-mechanical systems, derived from the well-known fidelity
(`generalized transition probability') of Uhlmann, is topologically equivalent
to the trace-norm distance.Comment: 26 pages, amsart.cls; improved intro, fixed typos, added a reference;
accepted by J. Math. Phy
Toward a well defined monopole creation operator
The lattice implementation of monopole creation operator proves to have problems related to bulk transitions that can possibly affect the interpretation of its mean value as an order parameter for monopole condensation. Preliminary evidence is presented that these unexpected behaviours are in fact only due to lattice artefacts and do not spoil the physical interpretation of the monopole operator
Performance of a deterministic source of entangled photonic qubits
We study the possible limitations and sources of decoherence in the scheme
for the deterministic generation of polarization-entangled photons, recently
proposed by Gheri et al. [K. M. Gheri et al., Phys. Rev. A 58, R2627 (1998)],
based on an appropriately driven single atom trapped within an optical cavity.
We consider in particular the effects of laser intensity fluctuations, photon
losses, and atomic motion.Comment: 10 pages, 6 figure
Superbroadcasting of continuous variables mixed states
We consider the problem of broadcasting quantum information encoded in the
average value of the field from N to M>N copies of mixed states of radiation
modes. We derive the broadcasting map that preserves the complex amplitude,
while optimally reducing the noise in conjugate quadratures. We find that from
two input copies broadcasting is feasible, with the possibility of simultaneous
purification (superbroadcasting). We prove similar results for purification
(M<=N) and for phase-conjugate broadcasting.Comment: 11 pages, 1 figure, revtex4 style, revised versio
Rhythmic inhibition allows neural networks to search for maximally consistent states
Gamma-band rhythmic inhibition is a ubiquitous phenomenon in neural circuits
yet its computational role still remains elusive. We show that a model of
Gamma-band rhythmic inhibition allows networks of coupled cortical circuit
motifs to search for network configurations that best reconcile external inputs
with an internal consistency model encoded in the network connectivity. We show
that Hebbian plasticity allows the networks to learn the consistency model by
example. The search dynamics driven by rhythmic inhibition enable the described
networks to solve difficult constraint satisfaction problems without making
assumptions about the form of stochastic fluctuations in the network. We show
that the search dynamics are well approximated by a stochastic sampling
process. We use the described networks to reproduce perceptual multi-stability
phenomena with switching times that are a good match to experimental data and
show that they provide a general neural framework which can be used to model
other 'perceptual inference' phenomena
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