5,412 research outputs found
A verification library for multibody simulation software
A multibody dynamics verification library, that maintains and manages test and validation data is proposed, based on RRC Robot arm and CASE backhoe validation and a comparitive study of DADS, DISCOS, and CONTOPS that are existing public domain and commercial multibody dynamic simulation programs. Using simple representative problems, simulation results from each program are cross checked, and the validation results are presented. Functionalities of the verification library are defined, in order to automate validation procedure
Особенности интернет-маркетинга в России
This article is devoted to the study of Internet marketing in Russia. The article describes the main features of the Internet - marketing in Russia, elements of e-business. Ebusiness is a part of the contemporary information world and it helps all spheres of business from b2b, to c2c. The article reviews basic elements of internet-marketing as part of informational phenomenon. Данная статья посвящена интернет маркетингу в России. В статье рассмотрены основные особенности интернет - маркетинга в России, элементы электронного бизнеса. Электронный бизнес как часть современного информационного мира становится востребованным во всех сферах бизнеса от b2b, до с2с. В статье рассматриваются основные черты интернет маркетинга как информационного феномена
Set-Theoretic Types for Polymorphic Variants
Polymorphic variants are a useful feature of the OCaml language whose current
definition and implementation rely on kinding constraints to simulate a
subtyping relation via unification. This yields an awkward formalization and
results in a type system whose behaviour is in some cases unintuitive and/or
unduly restrictive. In this work, we present an alternative formalization of
poly-morphic variants, based on set-theoretic types and subtyping, that yields
a cleaner and more streamlined system. Our formalization is more expressive
than the current one (it types more programs while preserving type safety), it
can internalize some meta-theoretic properties, and it removes some
pathological cases of the current implementation resulting in a more intuitive
and, thus, predictable type system. More generally, this work shows how to add
full-fledged union types to functional languages of the ML family that usually
rely on the Hindley-Milner type system. As an aside, our system also improves
the theory of semantic subtyping, notably by proving completeness for the type
reconstruction algorithm.Comment: ACM SIGPLAN International Conference on Functional Programming, Sep
2016, Nara, Japan. ICFP 16, 21st ACM SIGPLAN International Conference on
Functional Programming, 201
Control spiral wave dynamics using feedback signals from line detectors
We numerically study trajectories of spiral-wave-cores in excitable systems
modulated proportionally to the integral of the activity on the straight line,
several or dozens of equi-spaced measuring points on the straight line, the
double-line and the contour-line. We show the single-line feedback results in
the drift of core center along a straight line being parallel to the detector.
An interesting finding is that the drift location in is a piecewise
linear-increasing function of both the feedback line location and time delay.
Similar trajectory occurs when replacing the feedback line with several or
dozens of equi-spaced measuring points on the straight line. This allows to
move the spiral core to the desired location along a chosen direction by
measuring several or dozens of points. Under the double-line feedback, the
shape of the tip trajectory representing the competition between the first and
second feedback lines is determined by the distance of two lines. Various drift
attractors in spiral wave controlled by square-shaped contour-line feedback are
also investigated. A brief explanation is presented.Comment: 6 pages and 7 figures; Accepted for publication in EPL; Figs.5 and 6
are in JPG forma
Statistical Self-Similarity of One-Dimensional Growth Processes
For one-dimensional growth processes we consider the distribution of the
height above a given point of the substrate and study its scale invariance in
the limit of large times. We argue that for self-similar growth from a single
seed the universal distribution is the Tracy-Widom distribution from the theory
of random matrices and that for growth from a flat substrate it is some other,
only numerically determined distribution. In particular, for the polynuclear
growth model in the droplet geometry the height maps onto the longest
increasing subsequence of a random permutation, from which the height
distribution is identified as the Tracy-Widom distribution.Comment: 11 pages, iopart, epsf, 2 postscript figures, submitted to Physica A,
in an Addendum the distribution for the flat case is identified analyticall
Facile synthesis of metal-free organic dyes featuring a thienylethynyl spacer for dye sensitized solar cells
In this article, we report the facile synthesis of metal-free dyes 6 and 7, their solution-based optical and redox properties and their use as sensitizers in dye-sensitized solar cells (DSSCs). Our studies indicate that the addition of the second thiophene unit in dye 7, decreases the oxidation and reduction potential and consequently the band gap of the molecule compared to 6. Furthermore, increasing the length of the conjugated spacer also affects on the properties of the DSSCs, with dye 7 providing a higher power conversion efficiency compared to 6 (η = 4.49 versus 3.23%)
Analytical theory of forced rotating sheared turbulence: The parallel case
Forced turbulence combined with the effect of rotation and shear flow is studied. In a previous paper [N. Leprovost and E. J. Kim, Phys. Rev. E 78, 016301 (2008)], we considered the case where the shear and the rotation are perpendicular. Here, we consider the complementary case of parallel rotation and shear, elucidating how rotation and flow shear influence the generation of shear flow (e.g., the direction of energy cascade), turbulence level, transport of particles, and momentum. We show that turbulence amplitude and transport are always quenched due to strong shear (ξ=νky2∕A⪡1, where A is the shearing rate, ν is the molecular viscosity, and ky is a characteristic wave number of small-scale turbulence), with stronger reduction in the direction of the shear than those in the perpendicular directions. In contrast with the case where rotation and shear are perpendicular, we found that rotation affects turbulence amplitude only for very rapid rotation (Ω⪢A) where it reduces slightly the anisotropy due to shear flow. Also, concerning the transport properties of turbulence, we find that rotation affects only the transport of particle and only for rapid rotation, leading to an almost isotropic transport (whereas, in the case of perpendicular rotation and shear, rotation favors isotropic transport even for slow rotation). Furthermore, the interaction between the shear and the rotation is shown to give rise to nondiffusive flux of angular momentum (Λ effect), even in the absence of external sources of anisotropy, which can provide a mechanism for the creation of shearing structures in astrophysical and geophysical systems
Transport and instability in driven two-dimensional magnetohydrodynamic flows
This paper concerns the generation of large scale flows in forced two-dimensional systems. A Kolmogorov flow with a sinusoidal profile in one direction (driven by a body force) is known to become unstable to a large scale flow in the perpendicular direction at a critical Reynolds number. This can occur in the presence of a beta-effect and has important implications for flows observed in geophysical and astrophysical systems. It has recently been termed ‘zonostrophic instability’ and studied in a variety of settings, both numerically and analytically. The goal of the present paper is to determine the effect of magnetic field on such instabilities using the quasi-linear approximation, in which the full fluid system is decoupled into a mean flow and waves of one scale. The waves are driven externally by a given, random body force and move on a fast time scale, while their stress on the mean flow causes this to evolve on a slow time scale. Spatial scale separation between waves and mean flow is also assumed, to allow analytical progress. The paper first discusses purely hydrodynamic transport of vorticity including zonostrophic instability, the effect of uniform background shear, and calculation of equilibrium profiles in which the effective viscosity varies spatially, through the mean flow. After brief consideration of passive scalar transport or equivalently kinematic magnetic field evolution, the paper then proceeds to study the full MHD system and to determine effective diffusivities and other transport coefficients using a mixture of analytical and numerical methods. This leads to results on the effect of magnetic field, background shear and beta-effect on zonostrophic instability and magnetically driven instabilitiesWe are grateful to the EPSRC for funding SD via a DTG research studentship
Sum rules for strange form factors and flavor singlet axial charges
In chiral models with SU(3) group structure, strange form factors of baryon
octet are evaluated by constructing their sum rules to yield theoretical
predictions comparable to the recent experimental data of SAMPLE Collaboration.
We also study sum rules for the flavor singlet axial currents for the EMC
experiment in a modified quark model.Comment: 15 pages, revised with references adde
Log-Poisson Hierarchical Clustering of Cosmic Neutral Hydrogen and Ly-alpha Transmitted Flux of QSO Absorption Spectrum
we study, in this paper, the non-Gaussian features of the mass density field
of neutral hydrogen fluid and the Ly-alpha transmitted flux of QSO absorption
spectrum from the point-of-view of self-similar log-Poisson hierarchy. It has
been shown recently that, in the scale range from the onset of nonlinear
evolution to dissipation, the velocity and mass density fields of cosmic baryon
fluid are extremely well described by the She-Leveque's scaling formula, which
is due to the log-Poisson hierarchical cascade. Since the mass density ratio
between ionized hydrogen to total hydrogen is not uniform in space, the mass
density field of neutral hydrogen component is not given by a similar mapping
of total baryon fluid. Nevertheless, we show, with hydrodynamic simulation
samples of the concordance CDM universe, that the mass density field
of neutral hydrogen, is also well described by the log-Poisson hierarchy. We
then investigate the field of Ly transmitted flux of QSO absorption
spectrum. Due to redshift distortion, Ly transmitted flux fluctuations
are no longer to show all features of the log-Poisson hierarchy. However, some
non-Gaussian features predicted by the log-Poisson hierarchy are not affected
by the redshift distortion. We test these predictions with the high resolution
and high S/N data of quasars Ly absorption spectra. All results given
by real data, including -hierarchy, high order moments and scale-scale
correlation, are found to be well consistent with the log-Poisson hierarchy. We
compare the log-Poisson hierarchy with the popular log-normal model of the
Ly transmitted flux. The later is found to yield too strong
non-Gaussianity at high orders, while the log-Poisson hierarchy is in agreement
with observed data.Comment: 24 pages, 9 figures, accepted by Ap
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