13,891 research outputs found
Hamiltonian systems with symmetry, coadjoint orbits and plasma physics
The symplectic and Poisson structures on reduced phase spaces are reviewed, including the symplectic structure on coadjoint orbits of a Lie group and the Lie-Poisson structure on the dual of a Lie algebra. These results are
applied to plasma physics. We show in three steps how the Maxwell-Vlasov equations for a collisionless plasma can be written in Hamiltonian form relative to a certain Poisson bracket. First, the Poisson-Vlasov equations are shown
to be in Hamiltonian form relative to the Lie-Poisson bracket on the dual of the (nite dimensional) Lie algebra of innitesimal canonical transformations. Then we write Maxwell's equations in Hamiltonian form using the canonical
symplectic structure on the phase space of the electromagnetic elds, regarded as a gauge theory. In the last step we couple these two systems via the reduction
procedure for interacting systems. We also show that two other standard models in plasma physics, ideal MHD and two-
uid electrodynamics, can be written in Hamiltonian form using similar group theoretic techniques
Explanation of the computer listings of Faraday factors for INTASAT users
Using a simplified form of the Appleton-Hartree formula for the phase refractive index, a relationship was obtained between the Faraday rotation angle along the angular path and the total electron content along the vertical path, intersecting the angular at the height of maximum electron density. Using the second mean value theorem of integration, the function B cosine theta second chi was removed from under the integral sign and replaced by a 'mean' value. The mean value factors were printed on the computer listing for 39 stations receiving signals from the INTASAT satellite during the specified time period. The data is presented by station and date. Graphs are included to demonstrate the variation of the Faraday factor with local time and season, with magnetic latitude, elevation and azimuth angles. Other topics discussed include a description of the bent ionospheric model, the earth's magnetic field model, and the sample computer listing
Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the delta Scuti stars rho Pup and DX Cet
High-resolution spectroscopy is a powerful tool to study the dynamical
structure of pulsating stars atmosphere. We aim at comparing the line asymmetry
and velocity of the two delta Sct stars rho Pup and DX Cet with previous
spectroscopic data obtained on classical Cepheids and beta Cep stars. We
obtained, analysed and discuss HARPS high-resolution spectra of rho Pup and DX
Cet. We derived the same physical quantities as used in previous studies, which
are the first-moment radial velocities and the bi-Gaussian spectral line
asymmetries. The identification of f=7.098 (1/d) as a fundamental radial mode
and the very accurate Hipparcos parallax promote rho Pup as the best standard
candle to test the period-luminosity relations of delta Sct stars. The action
of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle
variations in the radial velocity measurements of rho Pup. Using the
spectral-line asymmetry method, we also found the centre-of-mass velocities of
rho Pup and DX Cet, V_gamma = 47.49 +/- 0.07 km/s and V_gamma = 25.75 +/- 0.06
km/s, respectively. By comparing our results with previous HARPS observations
of classical Cepheids and beta Cep stars, we confirm the linear relation
between the atmospheric velocity gradient and the amplitude of the radial
velocity curve, but only for amplitudes larger than 22.5 km/s. For lower values
of the velocity amplitude (i.e., < 22.5 km/s), our data on rho Pup seem to
indicate that the velocity gradient is null, but this result needs to be
confirmed with additional data. We derived the Baade-Wesselink projection
factor p = 1.36 +/- 0.02 for rho Pup and p = 1.39 +/- 0.02 for DX Cet. We
successfully extended the period-projection factor relation from classical
Cepheids to delta Scuti stars.Comment: Accepted for publication in A&A (in press
Non-linear optomechanical measurement of mechanical motion
Precision measurement of non-linear observables is an important goal in all
facets of quantum optics. This allows measurement-based non-classical state
preparation, which has been applied to great success in various physical
systems, and provides a route for quantum information processing with otherwise
linear interactions. In cavity optomechanics much progress has been made using
linear interactions and measurement, but observation of non-linear mechanical
degrees-of-freedom remains outstanding. Here we report the observation of
displacement-squared thermal motion of a micro-mechanical resonator by
exploiting the intrinsic non-linearity of the radiation pressure interaction.
Using this measurement we generate bimodal mechanical states of motion with
separations and feature sizes well below 100~pm. Future improvements to this
approach will allow the preparation of quantum superposition states, which can
be used to experimentally explore collapse models of the wavefunction and the
potential for mechanical-resonator-based quantum information and metrology
applications.Comment: 8 pages, 4 figures, extensive supplementary material available with
published versio
Predicting narrow states in the spectrum of a nucleus beyond the proton drip line
Properties of particle-unstable nuclei lying beyond the proton drip line can
be ascertained by considering those (usually known) properties of its mirror
neutron-rich system. We have used a multi-channel algebraic scattering theory
to map the known properties of the neutron-C system to those of the
proton-O one from which we deduce that the particle-unstable
F will have a spectrum of two low lying broad resonances of positive
parity and, at higher excitation, three narrow negative parity ones. A key
feature is to use coupling to Pauli-hindered states in the target.Comment: 5 pages, 3 figure
Continuum coupled cluster expansion
We review the basics of the coupled-cluster expansion formalism for numerical
solutions of the many-body problem, and we outline the principles of an
approach directed towards an adequate inclusion of continuum effects in the
associated single-energy spectrum. We illustrate our findings by considering
the simple case of a single-particle quantum mechanics problem.Comment: 16 pages, 1 figur
A construction of Frobenius manifolds with logarithmic poles and applications
A construction theorem for Frobenius manifolds with logarithmic poles is
established. This is a generalization of a theorem of Hertling and Manin. As an
application we prove a generalization of the reconstruction theorem of
Kontsevich and Manin for projective smooth varieties with convergent
Gromov-Witten potential. A second application is a construction of Frobenius
manifolds out of a variation of polarized Hodge structures which degenerates
along a normal crossing divisor when certain generation conditions are
fulfilled.Comment: 46 page
Electromagnon excitations in modulated multiferroics
The phenomenological theory of ferroelectricity in spiral magnets presented
in [M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006)] is generalized to describe
consistently states with both uniform and modulated-in-space ferroelectric
polarizations. A key point in this description is the symmetric part of the
magnetoelectric coupling since, although being irrelevant for the uniform
component, it plays an essential role for the non-uniform part of the
polarization. We illustrate this importance in generic examples of modulated
magnetic systems: longitudinal and transverse spin-density wave states and
planar cycloidal phase. We show that even in the cases with no uniform
ferroelectricity induced, polarization correlation functions follow to the soft
magnetic behavior of the system due to the magnetoelectric effect. Our results
can be easily generalized for more complicated types of magnetic ordering, and
the applications may concern various natural and artificial systems in
condensed matter physics (e.g., magnon properties could be extracted from
dynamic dielectric response measurements).Comment: 5 page
Towards a microscopic theory of toroidal moments in bulk periodic crystals
We present a theoretical analysis of magnetic toroidal moments in periodic
systems, in the limit in which the toroidal moments are caused by a time and
space reversal symmetry breaking arrangement of localized magnetic dipole
moments. We summarize the basic definitions for finite systems and address the
question of how to generalize these definitions to the bulk periodic case. We
define the toroidization as the toroidal moment per unit cell volume, and we
show that periodic boundary conditions lead to a multivaluedness of the
toroidization, which suggests that only differences in toroidization are
meaningful observable quantities. Our analysis bears strong analogy to the
modern theory of electric polarization in bulk periodic systems, but we also
point out some important differences between the two cases. We then discuss the
instructive example of a one-dimensional chain of magnetic moments, and we show
how to properly calculate changes of the toroidization for this system.
Finally, we evaluate and discuss the toroidization (in the local dipole limit)
of four important example materials: BaNiF_4, LiCoPO_4, GaFeO_3, and BiFeO_3.Comment: replaced with final (published) version, which includes some changes
in the text to improve the clarity of presentatio
- …