1,235 research outputs found
Solid angle subtended by a cylindrical detector at a point source in terms of elliptic integrals
The solid angle subtended by a right circular cylinder at a point source
located at an arbitrary position generally consists of a sum of two terms: that
defined by the cylindrical surface () and the other by either of
the end circles (). We derive an expression for
in terms of elliptic integrals of the first and third kinds and give similar
expressions for using integrals of the first and second kinds.
These latter can be used alternatively to an expression also in terms of
elliptic integrals, due to Philip A. Macklin and included as a footnote in
Masket (Rev. Sci. Instr., 28 (3), 191-197, 1957). The solid angle subtended by
the whole cylinder when the source is located at an arbitrary location can then
be calculated using elliptic integrals.Comment: 10 pages, 3 figures, LaTex. Typos corrected. References added.
Accepted in Rad. Phys. Che
The functional integral with unconditional Wiener measure for anharmonic oscillator
In this article we propose the calculation of the unconditional Wiener
measure functional integral with a term of the fourth order in the exponent by
an alternative method as in the conventional perturbative approach. In contrast
to the conventional perturbation theory, we expand into power series the term
linear in the integration variable in the exponent. In such a case we can
profit from the representation of the integral in question by the parabolic
cylinder functions. We show that in such a case the series expansions are
uniformly convergent and we find recurrence relations for the Wiener functional
integral in the - dimensional approximation. In continuum limit we find
that the generalized Gelfand - Yaglom differential equation with solution
yields the desired functional integral (similarly as the standard Gelfand -
Yaglom differential equation yields the functional integral for linear harmonic
oscillator).Comment: Source file which we sent to journa
Detection of a Moving Rigid Solid in a Perfect Fluid
In this paper, we consider a moving rigid solid immersed in a potential
fluid. The fluid-solid system fills the whole two dimensional space and the
fluid is assumed to be at rest at infinity. Our aim is to study the inverse
problem, initially introduced in [3], that consists in recovering the position
and the velocity of the solid assuming that the potential function is known at
a given time. We show that this problem is in general ill-posed by providing
counterexamples for which the same potential corresponds to different positions
and velocities of a same solid. However, it is also possible to find solids
having a specific shape, like ellipses for instance, for which the problem of
detection admits a unique solution. Using complex analysis, we prove that the
well-posedness of the inverse problem is equivalent to the solvability of an
infinite set of nonlinear equations. This result allows us to show that when
the solid enjoys some symmetry properties, it can be partially detected.
Besides, for any solid, the velocity can always be recovered when both the
potential function and the position are supposed to be known. Finally, we prove
that by performing continuous measurements of the fluid potential over a time
interval, we can always track the position of the solid.Comment: 19 pages, 14 figure
Two-dimensional soliton cellular automaton of deautonomized Toda-type
A deautonomized version of the two-dimensional Toda lattice equation is
presented. Its ultra-discrete analogue and soliton solutions are also
discussed.Comment: 11 pages, LaTeX fil
Local law-of-the-wall in complex topography: a confirmation from wind tunnel experiments
It is well known that in a neutrally-stratified turbulent flow in a deep
constant-stress layer above a flat surface, the variation of the mean velocity
with respect to the distance from the surface obeys the logarithmic law (the
so-called ``law-of-the-wall''). More recently, the same logarithmic law has
been found also in the presence of non flat surfaces. It governs the dynamics
of the mean velocity (i.e. all the smaller scales are averaged out) and
involves renormalized effective parameters. Recent numerical simulations
analyzed by the authors of the present Letter show that a more intrinsic
logarithmic shape actually takes place also at smaller scales. Such a
generalized law-of-the-wall involves effective parameters smoothly depending on
the position along the underlying topography. Here, we present wind tunnel
experimental evidence confirming and corroborating this new-found property. New
results and their physical interpretation are also presented and discussed.Comment: 9 pages, (Latex), 4 figure
La mobilisation des connaissances en protection de l’enfance
La protection de l’enfance est l’un des secteurs de services qui se dĂ©veloppent le plus rapidement au Canada. Cependant, nous en savons Ă©tonnamment peu sur l’efficacitĂ© des services offerts aux enfants maltraitĂ©s et nĂ©gligĂ©s. Cet article examine de nouveaux modèles de mobilisation des connaissances conçus pour soutenir l’utilisation plus systĂ©matique de la recherche dans les services sociaux. Nous commençons par discuter des limites des modèles traditionnels de diffusion des connaissances. Ensuite, nous considĂ©rons certaines des recherches qui ont Ă©tĂ© faites sur les obstacles et les facteurs facilitant l’utilisation de la recherche en santĂ©, en Ă©ducation et dans les services sociaux. Enfin, nous prĂ©sentons un modèle de mobilisation des connaissances qui est mis Ă l’essai et Ă©valuĂ© dans un organisme de protection de l’enfance au QuĂ©bec, dĂ©crivons les processus locaux utilisĂ©s pour affiner les six indicateurs de rĂ©sultats (rĂ©currence de la maltraitance, retards scolaires, taux de placement, dĂ©placements d’une ressource Ă une autre, durĂ©e des soins et participation d’un tribunal) et concluons en prĂ©sentant un exemple d’un des indicateurs retenus.Child protection is one of the fastest growing services sectors in Canada, yet we know surprisingly little about the effectiveness of services for abused and neglected children. This article examines emerging knowledge mobilization models designed to support the more systematic use of research in social services. We start by discussing the limits of traditional knowledge dissemination models. We then consider some of the research that has been done on the barriers and facilitators of research utilization in health, education and social services. Finally, we present a knowledge mobilization model that is being pilot tested and evaluated in a child welfare agency in Quebec and describe the local processes used to refine six outcome indicators (recurrence of maltreatment ; school delay ; placement rate ; moves in care ; time in care ; and court involvement) and conclude by presenting an example of one of the selected indicators.La protecciĂłn de la infancia es uno de los sectores de servicios de más rápido desarrollo en Canadá. Sin embargo, es sorprendente lo poco que sabemos sobre la eficacia de los servicios que se ofrecen a los menores vĂctimas de maltrato o de negligencia. Este artĂculo examina nuevos modelos de movilizaciĂłn de conocimientos concebidos para apoyar un uso más sistemático de la investigaciĂłn en los servicios sociales. Discutimos, primero, los lĂmites de los modelos tradicionales de la difusiĂłn de conocimientos. A continuaciĂłn, consideramos algunas investigaciones sobre los obstáculos y estĂmulos al uso de la investigaciĂłn en los ámbitos de la salud, la educaciĂłn y los servicios sociales. Finalmente, presentamos un modelo de movilizaciĂłn de conocimientos en etapa de práctica piloto y evaluaciĂłn en una agencia de protecciĂłn de la infancia en Quebec ; describimos los procesos locales utilizados para afinar seis indicadores de resultados (recurrencia del maltrato, retrasos escolares, tasa de colocaciĂłn, desplazamiento de un recurso a otro, duraciĂłn de cuidados y participaciĂłn de un tribunal) y concluimos presentando un ejemplo de uno de los indicadores seleccionados
Steady Motion of a Rigid Disk of Finite Thickness on a Horizontal Plane
The article discusses the steady motion of a rigid disk of finite thickness
rolling on its edge on a horizontal plane under the influence of gravity. The
governing equations are presented and two cases allowing for a steady state
solution are considered: rolling on consistently rough ground and rolling on
perfectly smooth ground. The conditions of steady motion are derived for both
kinds of ground and it is shown that the possible steady motion of a disk is
either on a straight line in a circle. Also oscillations about steady state are
discussed and conditions for stable motion are established.Comment: 28 pages, 7 figure
Bernoulli type polynomials on Umbral Algebra
The aim of this paper is to investigate generating functions for modification
of the Milne-Thomson's polynomials, which are related to the Bernoulli
polynomials and the Hermite polynomials. By applying the Umbral algebra to
these generating functions, we provide to deriving identities for these
polynomials
Fluid Mechanical and Electrical Fluctuation Forces in Colloids
Fluctuations in fluid velocity and fluctuations in electric fields may both
give rise to forces acting on small particles in colloidal suspensions. Such
forces in part determine the thermodynamic stability of the colloid. At the
classical statistical thermodynamic level, the fluid velocity and electric
field contributions to the forces are comparable in magnitude. When quantum
fluctuation effects are taken into account, the electric fluctuation induced
van der Waals forces dominate those induced by purely fluid mechanical motions.
The physical principles are applied in detail for the case of colloidal
particle attraction to the walls of the suspension container and more briefly
for the case of forces between colloidal particles.Comment: ReVTeX format, one *.eps figur
Four-vortex motion around a circular cylinder
The motion of two pairs of counter-rotating point vortices placed in a
uniform flow past a circular cylinder is studied analytically and numerically.
When the dynamics is restricted to the symmetric subspace---a case that can be
realized experimentally by placing a splitter plate in the center plane---, it
is found that there is a family of linearly stable equilibria for same-signed
vortex pairs. The nonlinear dynamics in the symmetric subspace is investigated
and several types of orbits are presented. The analysis reported here provides
new insights and reveals novel features of this four-vortex system, such as the
fact that there is no equilibrium for two pairs of vortices of opposite signs
on the opposite sides of the cylinder. (It is argued that such equilibria might
exist for vortex flows past a cylinder confined in a channel.) In addition, a
new family of opposite-signed equilibria on the normal line is reported. The
stability analysis for antisymmetric perturbations is also carried out and it
shows that all equilibria are unstable in this case.Comment: 27 pages, 13 figures, to be published in Physics of Fluid
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