8,424 research outputs found

### The Inertia Coefficients of an Airship in a Frictionless Fluid

The apparent inertia of an airship hull is examined. The exact solution of the aerodynamical problem is studied for hulls of various shapes with special attention given to the case of an ellipsoidal hull. So that the results for the ellipsoidal hull may be readily adapted to other cases, they are expressed in terms of the area and perimeter of the largest cross section perpendicular to the direction of motion by means of a formula involving a coefficient kappa which varies only slowly when the shape of the hull is changed, being 0.637 for a circular or elliptic disk, 0.5 for a sphere, and about 0.25 for a spheroid of fineness ratio. The case of rotation of an airship hull is investigated and a coefficient is defined with the same advantages as the corresponding coefficient for rectilinear motion

### Feshbach resonance scattering under cylindrical harmonic confinement

A problem of collisions of atoms with two-channel zero-range interaction in
an atomic waveguide is solved by using of a renormalization procedure. A
matching of the solution to a solution of the related one-dimensional problem
leads to relation between the one-dimensional and three-dimensional scattering
parameters. The scattering amplitude and bound states for the confined system
demonstrate differences from the related free and one-dimensional systems.Comment: Completely rewritten version,8 pages with 5 figures, uses REVTe

### Some expansions associated with Bessel functions

An Expansion for the Product of Two Bessel Functions.-1.1. An expansion for the product of two Bessel functions obtained by one of us(1) led to the discovery of a different expansion for the said product multiplied by the leading terms in the power series for the Bessel functions. Two proofs of this second expansion are given here

### Clebsch Potentials in the Variational Principle for a Perfect Fluid

Equations for a perfect fluid can be obtained by means of the variational
principle both in the Lagrangian description and in the Eulerian one. It is
known that we need additional fields somehow to describe a rotational
isentropic flow in the latter description. We give a simple explanation for
these fields; they are introduced to fix both ends of a pathline in the
variational calculus. This restriction is imposed in the former description,
and should be imposed in the latter description. It is also shown that we can
derive a canonical Hamiltonian formulation for a perfect fluid by regarding the
velocity field as the input in the framework of control theory.Comment: 15 page

### A Variational Principle for Dissipative Fluid Dynamics

In the variational principle leading to the Euler equation for a perfect
fluid, we can use the method of undetermined multiplier for holonomic
constraints representing mass conservation and adiabatic condition. For a
dissipative fluid, the latter condition is replaced by the constraint
specifying how to dissipate. Noting that this constraint is nonholonomic, we
can derive the balance equation of momentum for viscous and viscoelastic fluids
by using a single variational principle. We can also derive the associated
Hamiltonian formulation by regarding the velocity field as the input in the
framework of control theory.Comment: 15 page

### The Inertial Coefficients of an Airship in a Frictionless Fluid

This report deals with the investigation of the apparent inertia of an airship hull. The exact solution of the aerodynamical problem has been studied for hulls of various shapes and special attention has been given to the case of an ellipsoidal hull. In order that the results for this last case may be readily adapted to other cases, they are expressed in terms of the area and perimeter of the largest cross section perpendicular to the direction motion by means of a formula involving a coefficient K which varies only slowly when the shape of the hull is changed, being 0.637 for a circular or elliptic disk, 0.5 for a sphere, and about 0.25 for a spheroid of fineness ratio 7. For rough purposes it is sufficient to employ the coefficients, originally found for ellipsoids, for hulls otherwise shaped. When more exact values of the inertia are needed, estimates may be based on a study of the way in which K varies with different characteristics and for such a study the new coefficient possesses some advantage over one which is defined with reference to the volume of fluid displaced. The case of rotation of an airship hull has been investigated also and a coefficient has been defined with the same advantages as the corresponding coefficient for rectilinear motion

### The decay of a simple eddy

The principal result obtained in this report is a generalization of Taylor's formula for a simple eddy. The discussion of the properties of the eddy indicates that there is a slight analogy between the theory of eddies in a viscous fluid and the quantum theory of radiation. Another exact solution of the equations of motion of viscous fluid yields a result which reminds one of the well-known condition for instability in the case of a horizontally stratified atmosphere

### Generation of atom-atom correlations inside and outside the mutual light cone

We analyze whether a pair of neutral two level atoms can become entangled in
a finite time while they remain causally disconnected. The interaction with the
e. m. field is treated perturbatively in the electric dipole approximation. We
start from an initial vacuum state and obtain the final atomic correlations for
the cases where n = 0, 1, or 2 photons are produced in a time t, and also when
the final field state is unknown. Our results show that correlations are
sizable inside and outside the mutual light cone for n= 1 and 2, and also that
quantum correlations become classical by tracing over the field state. For n =
0 we obtain entanglement generation by photon propagation between the atoms,
the correlations come from the indistinguishability of the source for n = 1,
and may give rise to entanglement swapping for n = 2.Comment: v2: Minor changes, references added. v3: full revision, appendix
added. v4: Minor changes. Accepted in Phys. Rev.

### Representations and Properties of Generalized $A_r$ Statistics

A generalization of $A_r$ statistics is proposed and developed. The
generalized $A_r$ quantum statistics is completely specified by a set of
Jacobson generators satisfying a set of triple algebraic relations.
Fock-Hilbert representations and Bargmann-Fock realizations are derived.Comment: 12 pages, to appear in IJMPA (2006

- â€¦