1,053 research outputs found
Dynamical and Stationary Properties of On-line Learning from Finite Training Sets
The dynamical and stationary properties of on-line learning from finite
training sets are analysed using the cavity method. For large input dimensions,
we derive equations for the macroscopic parameters, namely, the student-teacher
correlation, the student-student autocorrelation and the learning force
uctuation. This enables us to provide analytical solutions to Adaline learning
as a benchmark. Theoretical predictions of training errors in transient and
stationary states are obtained by a Monte Carlo sampling procedure.
Generalization and training errors are found to agree with simulations. The
physical origin of the critical learning rate is presented. Comparison with
batch learning is discussed throughout the paper.Comment: 30 pages, 4 figure
Optimized random phase approximations for arbitrary reference systems: extremum conditions and thermodynamic consistence
The optimized random phase approximation (ORPA) for classical liquids is
re-examined in the framework of the generating functional approach to the
integral equations. We show that the two main variants of the approximation
correspond to the addition of the same correction to two different first order
approximations of the homogeneous liquid free energy. Furthermore, we show that
it is possible to consistently use the ORPA with arbitrary reference systems
described by continuous potentials and that the same approximation is
equivalent to a particular extremum condition for the corresponding generating
functional. Finally, it is possible to enforce the thermodynamic consistence
between the thermal and the virial route to the equation of state by requiring
the global extremum condition on the generating functional.Comment: 8 pages, RevTe
Renormalized kinetic theory of classical fluids in and out of equilibrium
We present a theory for the construction of renormalized kinetic equations to
describe the dynamics of classical systems of particles in or out of
equilibrium. A closed, self-consistent set of evolution equations is derived
for the single-particle phase-space distribution function , the correlation
function , the retarded and advanced density response
functions to an external potential , and
the associated memory functions . The basis of the theory is an
effective action functional of external potentials that
contains all information about the dynamical properties of the system. In
particular, its functional derivatives generate successively the
single-particle phase-space density and all the correlation and density
response functions, which are coupled through an infinite hierarchy of
evolution equations. Traditional renormalization techniques are then used to
perform the closure of the hierarchy through memory functions. The latter
satisfy functional equations that can be used to devise systematic
approximations. The present formulation can be equally regarded as (i) a
generalization to dynamical problems of the density functional theory of fluids
in equilibrium and (ii) as the classical mechanical counterpart of the theory
of non-equilibrium Green's functions in quantum field theory. It unifies and
encompasses previous results for classical Hamiltonian systems with any initial
conditions. For equilibrium states, the theory reduces to the equilibrium
memory function approach. For non-equilibrium fluids, popular closures (e.g.
Landau, Boltzmann, Lenard-Balescu) are simply recovered and we discuss the
correspondence with the seminal approaches of Martin-Siggia-Rose and of
Rose.and we discuss the correspondence with the seminal approaches of
Martin-Siggia-Rose and of Rose.Comment: 63 pages, 10 figure
Electromigration-Induced Flow of Islands and Voids on the Cu(001) Surface
Electromigration-induced flow of islands and voids on the Cu(001) surface is
studied at the atomic scale. The basic drift mechanisms are identified using a
complete set of energy barriers for adatom hopping on the Cu(001) surface,
combined with kinetic Monte Carlo simulations. The energy barriers are
calculated by the embedded atom method, and parameterized using a simple model.
The dependence of the flow on the temperature, the size of the clusters, and
the strength of the applied field is obtained. For both islands and voids it is
found that edge diffusion is the dominant mass-transport mechanism. The rate
limiting steps are identified. For both islands and voids they involve
detachment of atoms from corners into the adjacent edge. The energy barriers
for these moves are found to be in good agreement with the activation energy
for island/void drift obtained from Arrhenius analysis of the simulation
results. The relevance of the results to other FCC(001) metal surfaces and
their experimental implications are discussed.Comment: 9 pages, 13 ps figure
Non-pharmacological interventions for adults with autism: a systematic review of randomised controlled trials
To determine the effects of non-pharmacological randomised controlled trials in adults with autism, a systematic review was conducted across five electronic databases. A total of 3865 abstracts were retrieved, of which 41 articles met all inclusion criteria: randomised controlled trial; non-pharmacological intervention; adults with autism; and English publication. Twenty included studies had strong methodological quality ratings. No meta-analysis could be performed due to heterogeneity between studies. Articles reported on interventions for (1) social functioning and language skills, (2) vocational rehabilitation outcomes, (3) cognitive skills training, and (4) independent living skills. Social functioning was the most studied intervention. PEERS for young adults and Project SEARCH plus ASD support interventions had the strongest evidence. Emerging evidence suggests non-pharmacological interventions could be effective.Otorhinolaryngolog
Multiobjective optimization of MPLS-IP networks with a variable neighborhood genetic algorithm
This paper presents a Genetic Algorithm for the optimization of multiple indices of Quality of Service of Multi Protocol Label Switching (MPLS) IP networks. The proposed algorithm, the Variable Neighborhood Multiobjective Genetic Algorithm (VN-MGA), is a Genetic Algorithm based on the NSGA-II, with the particular feature that solutions are encoded defining two different kinds of neighborhoods. The first neighborhood is defined by considering as decision variables the edges that form the routes to be followed by each request, whilst the second part of solution is kept constant. The second neighborhood is defined by considering the request sequence as decision variable, with the first part kept constant. Comparisons are performed with: (i) a VNS algorithm that performs a switch between the same two neighborhoods that are used in VN-MGA; and (ii) the results obtained with an integer linear programming solver, running a scalarized version of the multiobjective problem. The results indicate that the proposed VN-MGA outperforms the pure VNS algorithm, and provides a good approximation of the exact Pareto fronts obtained with Integer Linear Programming (ILP) approach, at a much smaller computational cost. Besides potential benefits of the application of the proposed approach to the optimization of packet routing in MPLS networks, this work raises the theoretical issue of the systematic application of variable encodings, which allow variable neighborhood searches, as generic operators inside general evolutionary computation algorithms. Codice rivista: E013138 Titolo rivista: APPLIED SOFT COMPUTING Issn: 1568-4946 Cordiali saluti CINECA - Servizio Gestione Rivist
Ab initio atomistic thermodynamics and statistical mechanics of surface properties and functions
Previous and present "academic" research aiming at atomic scale understanding
is mainly concerned with the study of individual molecular processes possibly
underlying materials science applications. Appealing properties of an
individual process are then frequently discussed in terms of their direct
importance for the envisioned material function, or reciprocally, the function
of materials is somehow believed to be understandable by essentially one
prominent elementary process only. What is often overlooked in this approach is
that in macroscopic systems of technological relevance typically a large number
of distinct atomic scale processes take place. Which of them are decisive for
observable system properties and functions is then not only determined by the
detailed individual properties of each process alone, but in many, if not most
cases also the interplay of all processes, i.e. how they act together, plays a
crucial role. For a "predictive materials science modeling with microscopic
understanding", a description that treats the statistical interplay of a large
number of microscopically well-described elementary processes must therefore be
applied. Modern electronic structure theory methods such as DFT have become a
standard tool for the accurate description of individual molecular processes.
Here, we discuss the present status of emerging methodologies which attempt to
achieve a (hopefully seamless) match of DFT with concepts from statistical
mechanics or thermodynamics, in order to also address the interplay of the
various molecular processes. The new quality of, and the novel insights that
can be gained by, such techniques is illustrated by how they allow the
description of crystal surfaces in contact with realistic gas-phase
environments.Comment: 24 pages including 17 figures, related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Low-lying quadrupole collective states of the light and medium Xenon isotopes
Collective low lying levels of light and medium Xenon isotopes are deduced
from the Generalized Bohr Hamiltonian (GBH). The microscopic seven functions
entering into the GBH are built from a deformed mean field of the Woods-Saxon
type. Theoretical spectra are found to be close to the ones of the experimental
data taking into account that the calculations are completely microscopic, that
is to say, without any fitting of parameters.Comment: 8 pages, 4 figures, 1 tabl
Theoretical description of phase coexistence in model C60
We have investigated the phase diagram of the Girifalco model of C60
fullerene in the framework provided by the MHNC and the SCOZA liquid state
theories, and by a Perturbation Theory (PT), for the free energy of the solid
phase. We present an extended assessment of such theories as set against a
recent Monte Carlo study of the same model [D. Costa et al, J. Chem. Phys.
118:304 (2003)]. We have compared the theoretical predictions with the
corresponding simulation results for several thermodynamic properties. Then we
have determined the phase diagram of the model, by using either the SCOZA, or
the MHNC, or the PT predictions for one of the coexisting phases, and the
simulation data for the other phase, in order to separately ascertain the
accuracy of each theory. It turns out that the overall appearance of the phase
portrait is reproduced fairly well by all theories, with remarkable accuracy as
for the melting line and the solid-vapor equilibrium. The MHNC and SCOZA
results for the liquid-vapor coexistence, as well as for the corresponding
critical points, are quite accurate. All results are discussed in terms of the
basic assumptions underlying each theory. We have selected the MHNC for the
fluid and the first-order PT for the solid phase, as the most accurate tools to
investigate the phase behavior of the model in terms of purely theoretical
approaches. The overall results appear as a robust benchmark for further
theoretical investigations on higher order C(n>60) fullerenes, as well as on
other fullerene-related materials, whose description can be based on a
modelization similar to that adopted in this work.Comment: RevTeX4, 15 pages, 7 figures; submitted to Phys. Rev.
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