522 research outputs found
On the Equivalence Between Type I Liouville Dynamical Systems in the Plane and the Sphere
Producción CientíficaSeparable Hamiltonian systems either in sphero-conical coordinates on an S2 sphere or in elliptic coordinates on a R2 plane are described in a unified way. A back and forth route connecting these Liouville Type I separable systems is unveiled. It is shown how the gnomonic projection and its inverse map allow us to pass from a Liouville Type I separable system with a spherical configuration space
to its Liouville Type I partners where the configuration space is a plane and back. Several selected spherical separable systems and their planar cousins are discussed in a classical context
New solutions of Heun general equation
We show that in four particular cases the derivative of the solution of Heun
general equation can be expressed in terms of a solution to another Heun
equation. Starting from this property, we use the Gauss hypergeometric
functions to construct series solutions to Heun equation for the mentioned
cases. Each of the hypergeometric functions involved has correct singular
behavior at only one of the singular points of the equation; the sum, however,
has correct behavior
Geodesics around Weyl-Bach's Ring Solution
We explore some of the gravitational features of a uniform ring both in the
Newtonian potential theory and in General Relativity. We use a spacetime
associated to a Weyl static solution of the vacuum Einstein's equations with
ring like singularity. The Newtonian motion for a test particle in the
gravitational field of the ring is studied and compared with the corresponding
geodesic motion in the given spacetime. We have found a relativistic peculiar
attraction: free falling particle geodesics are lead to the inner rim but never
hit the ring.Comment: 8 figures, 14 pages. LaTeX w/ subfigure, graphic
On Virtual Displacement and Virtual Work in Lagrangian Dynamics
The confusion and ambiguity encountered by students, in understanding virtual
displacement and virtual work, is discussed in this article. A definition of
virtual displacement is presented that allows one to express them explicitly
for holonomic (velocity independent), non-holonomic (velocity dependent),
scleronomous (time independent) and rheonomous (time dependent) constraints. It
is observed that for holonomic, scleronomous constraints, the virtual
displacements are the displacements allowed by the constraints. However, this
is not so for a general class of constraints. For simple physical systems, it
is shown that, the work done by the constraint forces on virtual displacements
is zero. This motivates Lagrange's extension of d'Alembert's principle to
system of particles in constrained motion. However a similar zero work
principle does not hold for the allowed displacements. It is also demonstrated
that d'Alembert's principle of zero virtual work is necessary for the
solvability of a constrained mechanical problem. We identify this special class
of constraints, physically realized and solvable, as {\it the ideal
constraints}. The concept of virtual displacement and the principle of zero
virtual work by constraint forces are central to both Lagrange's method of
undetermined multipliers, and Lagrange's equations in generalized coordinates.Comment: 12 pages, 10 figures. This article is based on an earlier article
physics/0410123. It includes new figures, equations and logical conten
Projective dynamics and classical gravitation
Given a real vector space V of finite dimension, together with a particular
homogeneous field of bivectors that we call a "field of projective forces", we
define a law of dynamics such that the position of the particle is a "ray" i.e.
a half-line drawn from the origin of V. The impulsion is a bivector whose
support is a 2-plane containing the ray. Throwing the particle with a given
initial impulsion defines a projective trajectory. It is a curve in the space
of rays S(V), together with an impulsion attached to each ray. In the simplest
example where the force is identically zero, the curve is a straight line and
the impulsion a constant bivector. A striking feature of projective dynamics
appears: the trajectories are not parameterized.
Among the projective force fields corresponding to a central force, the one
defining the Kepler problem is simpler than those corresponding to other
homogeneities. Here the thrown ray describes a quadratic cone whose section by
a hyperplane corresponds to a Keplerian conic. An original point of view on the
hidden symmetries of the Kepler problem emerges, and clarifies some remarks due
to Halphen and Appell. We also get the unexpected conclusion that there exists
a notion of divergence-free field of projective forces if and only if dim V=4.
No metric is involved in the axioms of projective dynamics.Comment: 20 pages, 4 figure
Sleep Duration is Increased Following Muscle Damaging Exercise in Hot Environmental Conditions
Sleep and recovery measures are typically negatively affected by a muscle-damaging bout of exercise. However, it remains unknown if the additive effects of hot environmental conditions, resulting in increased core temperature and other thermoregulatory responses during the exercise bout, further progress changes in quantity and performance quality of sleep duration. PURPOSE: To investigate the effect of muscle-damaging exercise in the heat, compared to a thermoneutral condition, on sleep and recovery measures. METHODS: Ten healthy males (age: 23 ± 3yr; body mass: 78.7 ± 11.5kg; height: 176.9 ± 5cm; lactate threshold [LT]: 9.7 ± 1.0km.hr-1) performed two protocols in a randomized, counterbalanced order of downhill running (DHR) for 30-minutes at the LT in either a thermoneutral (ambient temperate [Tamb], 20°C; relative humidity [RH], 20%) or hot environmental condition (Tamb, 35°C; RH, 40%) at a -10% gradient. Sleep and recovery measures were collected from a wearable sleep device participants wore the night after the DHR. Differences in sleep and recovery measures following DHR in the heat compared to a thermoneutral condition were analyzed using paired samples T-tests. RESULTS: Sleep hours, restorative sleep hours, rapid eye movement (REM) sleep hours, and slow wave sleep (SWS) hours were all greater following the heat condition (mean ± SD; sleep hours: 6.70 ± 0.74hr, p = 0.040; restorative sleep hours: 3.31 ± 0.90hr, p = 0.012; REM sleep hours: 1.70 ± 0.64hr, p = 0.046; SWS hours: 1.61 ± 0.35hr, p = 0.015) compared to the thermoneutral condition (sleep hours: 5.24 ± 1.75hr; restorative sleep hours: 2.45 ± 1.11hr; REM sleep hours: 1.23 ± 0.68hr; SWS: 1.22 ± 0.53hr). Also, recovery was higher following the heat condition (recovery: 75.88 ± 15.31, p = 0.023) compared to the thermoneutral condition (recovery: 50.75 ± 21.46). Sleep efficiency, sleep disturbance, sleep deprivation, sleep score, %REM, %SWS, light sleep, resting heart rate, and heart rate variability were not different between conditions (ps \u3e 0.05). CONCLUSION: Following muscle-damaging exercise in the heat, sleep and recovery duration measures were increased compared to a thermoneutral condition. These findings suggest that performing muscle-damaging exercises in hot conditions may require a greater amount of sleep for optimal recovery
Spherical functions on the de Sitter group
Matrix elements and spherical functions of irreducible representations of the
de Sitter group are studied on the various homogeneous spaces of this group. It
is shown that a universal covering of the de Sitter group gives rise to
quaternion Euler angles. An explicit form of Casimir and Laplace-Beltrami
operators on the homogeneous spaces is given. Different expressions of the
matrix elements and spherical functions are given in terms of multiple
hypergeometric functions both for finite-dimensional and unitary
representations of the principal series of the de Sitter group.Comment: 40 page
Projective dynamics and first integrals
We present the theory of tensors with Young tableau symmetry as an efficient
computational tool in dealing with the polynomial first integrals of a natural
system in classical mechanics. We relate a special kind of such first
integrals, already studied by Lundmark, to Beltrami's theorem about
projectively flat Riemannian manifolds. We set the ground for a new and simple
theory of the integrable systems having only quadratic first integrals. This
theory begins with two centered quadrics related by central projection, each
quadric being a model of a space of constant curvature. Finally, we present an
extension of these models to the case of degenerate quadratic forms.Comment: 39 pages, 2 figure
On two-dimensional Bessel functions
The general properties of two-dimensional generalized Bessel functions are
discussed. Various asymptotic approximations are derived and applied to analyze
the basic structure of the two-dimensional Bessel functions as well as their
nodal lines.Comment: 25 pages, 17 figure
One pendulum to run them all
The analytical solution for the three-dimensional linear pendulum in a rotating frame of reference is obtained, including Coriolis and centrifugal accelerations, and expressed in terms of initial conditions. This result offers the possibility of treating Foucault and Bravais pendula as trajectories of the same system of equations, each of them with particular initial conditions. We compare them with the common two-dimensional approximations in textbooks. A previously unnoticed pattern in the three-dimensional Foucault pendulum attractor is presented
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