125 research outputs found
Quantitative ergodicity for the symmetric exclusion process with stationary initial data
We consider the symmetric exclusion process on the -dimensional lattice
with translational invariant and ergodic initial data. It is then known that as
diverges the distribution of the process at time converges to a
Bernoulli product measure. Assuming a summable decay of correlations of the
initial data, we prove a quantitative version of this convergence by obtaining
an explicit bound on the Ornstein -distance. The proof is based on the
analysis of a two species exclusion process with annihilation
A low-cost optical data acquisition system for vibration measurement
A low cost optical data acquisition system was designed to measure deflection of vibrating rotor blade tips. The basic principle of the new design is to record raw data, which is a set of blade arrival times, in memory and to perform all processing by software following a run. This approach yields a simple and inexpensive system with the least possible hardware. Functional elements of the system were breadboarded and operated satisfactorily during rotor simulations on the bench, and during a data collection run with a two-bladed rotor in the Lewis Research Center Spin Rig. Software was written to demonstrate the sorting and processing of data stored in the system control computer, after retrieval from the data acquisition system. The demonstration produced an accurate graphical display of deflection versus time
Large eddy simulations of a utility-scale horizontal axis wind turbine including unsteady aerodynamics and fluid-structure interaction modelling
Growing horizontal axis wind turbines are increasingly exposed to significant sources of unsteadiness, such as tower shadowing, yawed or waked conditions and environmental effects. Due to increased dimensions, the use of steady tabulated airfoil coefficients to determine the airloads along long blades can be questioned in those numerical fluid models that do not have the sufficient resolution to solve explicitly and dynamically the flow close to the blade. Various models exist to describe unsteady aerodynamics (UA). However, they have been mainly implemented in engineering models, which lack the complete capability of describing the unsteady and multiscale nature of wind energy. To improve the description of the blades' aerodynamic response, a 2D unsteady aerodynamics model is used in this work to estimate the airloads of the actuator line model in our fluidâstructure interaction (FSI) solver, based on 3D large eddy simulation. At each section along the actuator lines, a semi-empirical Beddoes-Leishman model includes the effects of noncirculatory terms, unsteady trailing edge separation, and dynamic stall in the dynamic evaluation of the airfoils' aerodynamic coefficients. The aeroelastic response of a utility-scale wind turbine under uniform, laminar and turbulent, sheared inflows is examined with one- and two-way FSI coupling between the blades' structural dynamics and local airloads, with and without the enhanced aerodynamics' description. The results show that the external half of the blade is dominated by aeroelastic effects, whereas the internal one is dominated by significant UA phenomena, which was possible to represent only thanks to the additional model implemented
Lewis Research Center spin rig and its use in vibration analysis of rotating systems
The Lewis Research Center spin rig was constructed to provide experimental evaluation of analysis methods developed under the NASA Engine Structural Dynamics Program. Rotors up to 51 cm (20 in.) in diameter can be spun to 16,000 rpm in vacuum by an air motor. Vibration forcing functions are provided by shakers that apply oscillatory axial forces or transverse moments to the shaft, by a natural whirling of the shaft, and by an air jet. Blade vibration is detected by strain gages and optical blade-tip motion sensors. A variety of analogy and digital processing equipment is used to display and analyze the signals. Results obtained from two rotors are discussed. A 56-blade compressor disk was used to check proper operation of the entire spin rig system. A special two-blade rotor was designed and used to hold flat and twisted plates at various setting and sweep angles. Accurate Southwell coefficients have been obtained for several modes of a flat plate oriented parallel to the plane of rotation
Hot ion plasma heating experiments in SUMMA
Initial results are presented for the hot-ion plasma heating experiments conducted in the new SUMMA (superconducting magnetic mirror apparatus) at NASA Lewis Research Center. A discharge is formed by applying a radially inward dc electric field between cylindrical anodes and hallow cathodes located at the peak of the mirrors. Data were obtained at midplane magnetic field strengths from 1.0 to 3.5 tesla. Charge-exchange neutral particle energy analyzer data were reduced to ion temperatures using a plasma model that included a Maxwellian energy distribution superimposed on an azimuthal drift, finite ion orbits, and radial variations in density and electric field. The best ion temperatures in a helium plasma were 5 keV and in hydrogen the H2(+) and H(+) ions were 1.2 keV and 1 keV respectively. Optical spectroscopy line broadening measurements yielded ion temperatures about 50 percent higher than the charge-exchange neutral particle analyzer results. Spectroscopically obtained electron temperature ranged from 3 to 30 eV. Ion temperature was found to scale roughly linearly with the ratio of power input-to-magnetic field strength, P/B
Representations of the q-deformed algebra
An algebra homomorphism from the q-deformed algebra
with generating elements , , and defining relations
, , (where
) to the extension of the
Hopf algebra is constructed. The algebra at
leads to the Lie algebra of the group ISO(2)
of motions of the Euclidean plane. The Hopf algebra is treated
as a Hopf -deformation of the universal enveloping algebra of
and is well-known in the literature. Not all irreducible representations of
can be extended to representations of the extension . Composing the homomorphism with irreducible
representations of we obtain representations of
. Not all of these representations of are
irreducible. The reducible representations of are decomposed
into irreducible components. In this way we obtain all irreducible
representations of when is not a root of unity. A part
of these representations turns into irreducible representations of the Lie
algebra iso when . Representations of the other part have no
classical analogue.Comment: 12 pages, LaTe
The First Passage Probability of Intracellular Particle Trafficking
The first passage probability (FPP), of trafficked intracellular particles
reaching a displacement L, in a given time t or inverse velocity S = t/L, can
be calculated robustly from measured particle tracks, and gives a measure of
particle movement in which different types of motion, e.g. diffusion, ballistic
motion, and transient run-rest motion, can readily be distinguished in a single
graph, and compared with mathematical models. The FPP is attractive in that it
offers a means of reducing the data in the measured tracks, without making
assumptions about the mechanism of motion: for example, it does not employ
smoothing, segementation or arbitrary thresholds to discriminate between
different types of motion in a particle track. Taking experimental data from
tracked endocytic vesicles, and calculating the FPP, we see how three molecular
treatments affect the trafficking. We show the FPP can quantify complicated
movement which is neither completely random nor completely deterministic,
making it highly applicable to trafficked particles in cell biology.Comment: Article: 13 pages, 8 figure
On the dynamical behavior of the ABC model
We consider the ABC dynamics, with equal density of the three species, on the
discrete ring with sites. In this case, the process is reversible with
respect to a Gibbs measure with a mean field interaction that undergoes a
second order phase transition. We analyze the relaxation time of the dynamics
and show that at high temperature it grows at most as while it grows at
least as at low temperature
Search for Periodic Gravitational Wave Sources with the Explorer Detector
We have developped a procedure for the search of periodic signals in the data
of gravitational wave detectors. We report here the analysis of one year of
data from the resonant detector Explorer, searching for pulsars located in the
Galactic Center (GC). No signals with amplitude greater than , in the range 921.32-921.38 Hz, were observed using data
collected over a time period of 95.7 days, for a source located at
hours and degrees. Our
procedure can be extended for any assumed position in the sky and for a more
general all-sky search, even with a frequency correction at the source due to
the spin-down and Doppler effects.Comment: One zipped file (Latex+eps figures). 33 pages, 14 figures. This and
related material also at http://grwav3.roma1.infn.it
Microservice Transition and its Granularity Problem: A Systematic Mapping Study
Microservices have gained wide recognition and acceptance in software
industries as an emerging architectural style for autonomic, scalable, and more
reliable computing. The transition to microservices has been highly motivated
by the need for better alignment of technical design decisions with improving
value potentials of architectures. Despite microservices' popularity, research
still lacks disciplined understanding of transition and consensus on the
principles and activities underlying "micro-ing" architectures. In this paper,
we report on a systematic mapping study that consolidates various views,
approaches and activities that commonly assist in the transition to
microservices. The study aims to provide a better understanding of the
transition; it also contributes a working definition of the transition and
technical activities underlying it. We term the transition and technical
activities leading to microservice architectures as microservitization. We then
shed light on a fundamental problem of microservitization: microservice
granularity and reasoning about its adaptation as first-class entities. This
study reviews state-of-the-art and -practice related to reasoning about
microservice granularity; it reviews modelling approaches, aspects considered,
guidelines and processes used to reason about microservice granularity. This
study identifies opportunities for future research and development related to
reasoning about microservice granularity.Comment: 36 pages including references, 6 figures, and 3 table
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