18,214 research outputs found
Construction of Many-Body Eigenstates with Displacement Transformations
Many-body eigenstates beyond the gaussian approximation can be constructed in
terms of local integrals of motion (IOM), although their actual computation has
been until now a daunting task. We present a new practical computation of IOMS
based on displacement transformations. It represents a general and systematic
way to extend Hartree-Fock and configuration interaction theories to higher
order. Our method combines minimization of energy and energy variance of a
reference state with exact diagonalization. We show that our implementation is
able to perform ground state calculations with high precision for relatively
large systems. Since it keeps track of the IMO's forming a reference state, our
method is particularly efficient dealing with excited states, both in accuracy
and the number of different states that can be constructed
On angled bounce-off impact of a drop impinging on a flowing soap film
Small drops impinging angularly on thin flowing soap films frequently
demonstrate the rare emergence of bulk elastic effects working in-tandem with
the more common-place hydrodynamic interactions. Three collision regimes are
observable: (a) drop piercing through the film, (b) it coalescing with the
flow, and (c) it bouncing off the film surface. During impact, the drop deforms
along with a bulk elastic deformation of the film. For impacts that are
close-to-tangential, the bounce-off regime predominates. We outline a reduced
order analytical framework assuming a deformable drop and a deformable
three-dimensional film, and the idealization invokes a phase-based parametric
study. Angular inclination of the film and the ratio of post and pre impact
drop sizes entail the phase parameters. We also perform experiments with
vertically descending droplets impacting against an inclined soap film, flowing
under constant pressure head. Model predicted phase domain for bounce-off
compares well to our experimental findings. Additionally, the experiments
exhibit momentum transfer to the film in the form of shed vortex dipole, along
with propagation of free surface waves. On consulting prior published work, we
note that for locomotion of water-walking insects using an impulsive action,
the momentum distribution to the shed vortices and waves are both significant,
taking up respectively 2/3-rd and 1/3-rd of the imparted streamwise momentum.
In view of the potentially similar impulse actions, this theory is applied to
the bounce-off examples in our experiments, and the resultant shed vortex
dipole momenta are compared to the momenta computed from particle imaging
velocimetry data. The magnitudes reveal identical order ( Ns),
suggesting that the bounce-off regime can be tapped as a simple analogue for
interfacial bio-locomotion relying on impulse reactions
Probabilistic Graphical Models on Multi-Core CPUs using Java 8
In this paper, we discuss software design issues related to the development
of parallel computational intelligence algorithms on multi-core CPUs, using the
new Java 8 functional programming features. In particular, we focus on
probabilistic graphical models (PGMs) and present the parallelisation of a
collection of algorithms that deal with inference and learning of PGMs from
data. Namely, maximum likelihood estimation, importance sampling, and greedy
search for solving combinatorial optimisation problems. Through these concrete
examples, we tackle the problem of defining efficient data structures for PGMs
and parallel processing of same-size batches of data sets using Java 8
features. We also provide straightforward techniques to code parallel
algorithms that seamlessly exploit multi-core processors. The experimental
analysis, carried out using our open source AMIDST (Analysis of MassIve Data
STreams) Java toolbox, shows the merits of the proposed solutions.Comment: Pre-print version of the paper presented in the special issue on
Computational Intelligence Software at IEEE Computational Intelligence
Magazine journa
Experimental study of laser dissimilar joining for Usibor 2000 and Al-T7075 with Tepex 102
Due to the needs of weight reduction in the automobile structures and of time reduction in the Body-In-White (BIW) manufacturing stage, effective and accurate dissimilar joining is demanded to take advantage of metal-polymer structures. Automotive industry is highly interested in the combination of metal alloys and composite materials; however, dissimilar joining of this type of materials without using mechanic or adhesive joining is a challenge. As an alternative to the classical joining techniques, laser technology can be used to join dissimilar materials. In laser direct joining, a laser beam is used to heat the metal and by conduction to heat the polymer up to melting temperature in the interface without reaching degradation temperature. In this work, an experimental procedure is proposed to set the basis of dissimilar joining between metal and composite parts for the automobile industry. To do that, laser texturing on metallic parts was studied and a wide battery of experimental test were performed to obtain the proper joining process parameters for dissimilar joining between Usibor 2000 and Al-T7075 with Tepex 102. Results show that is possible to reach over 17 MPa in lap shear adhesion test which is similar to the performance of typical adhesives used in automotive industry.Authors wish to thank Basque Country Government for financial support provided through MULTIMAT project Elkartek KK2017/00088 as well as the Spanish Industry ministry for support provided in INTEGRADDI project DPI 2016-79889
Chemical Oscillations out of Chemical Noise
The dynamics of one species chemical kinetics is studied. Chemical reactions
are modelled by means of continuous time Markov processes whose probability
distribution obeys a suitable master equation. A large deviation theory is
formally introduced, which allows developing a Hamiltonian dynamical system
able to describe the system dynamics. Using this technique we are able to show
that the intrinsic fluctuations, originated in the discrete character of the
reagents, may sustain oscillations and chaotic trajectories which are
impossible when these fluctuations are disregarded. An important point is that
oscillations and chaos appear in systems whose mean-field dynamics has too low
a dimensionality for showing such a behavior. In this sense these phenomena are
purely induced by noise, which does not limit itself to shifting a bifurcation
threshold. On the other hand, they are large deviations of a short transient
nature which typically only appear after long waiting times. We also discuss
the implications of our results in understanding extinction events in
population dynamics models expressed by means of stoichiometric relations
ON THE COMPARISON OF TIME SERIES USING SUBSAMPLING
In this paper we propose a procedure based on the subsampling techniques for the comparison of stationary time series that are not necessarily independent. We study a test based on the Euclidean distance between the autocorrelation functions of two series. Consistency of the proposed method is established. We present a Monte Carlo study with the size and the power of the proposed test.
Effects of fluid inertia and turbulence on force coefficients for squeeze film dampers
The effects of fluid inertia and turbulence on the force coefficients of squeeze film dampers are investigated analytically. Both the convective and the temporal terms are included in the analysis of inertia effects. The analysis of turbulence is based on friction coefficients currently found in the literature for Poiseuille flow. The effect of fluid inertia on the magnitude of the radial direct inertia coefficient (i.e., to produce an apparent added mass at small eccentricity ratios, due to the temporal terms) is found to be completely reversed at large eccentricity ratios. The reversal is due entirely to the inclusion of the convective inertia terms in the analysis. Turbulence is found to produce a large effect on the direct damping coefficient at high eccentricity ratios. For the long or sealed squeeze film damper at high eccentricity ratios, the damping prediction with turbulence included is an order of magnitude higher than the laminar solution
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