54,853 research outputs found
Bering's proposal for boundary contribution to the Poisson bracket
It is shown that the Poisson bracket with boundary terms recently proposed by
Bering (hep-th/9806249) can be deduced from the Poisson bracket proposed by the
present author (hep-th/9305133) if one omits terms free of Euler-Lagrange
derivatives ("annihilation principle"). This corresponds to another definition
of the formal product of distributions (or, saying it in other words, to
another definition of the pairing between 1-forms and 1-vectors in the formal
variational calculus). We extend the formula (initially suggested by Bering
only for the ultralocal case with constant coefficients) onto the general
non-ultralocal brackets with coefficients depending on fields and their spatial
derivatives. The lack of invariance under changes of dependent variables (field
redefinitions) seems a drawback of this proposal.Comment: 18 pages, LaTeX, amssym
On a Order Reduction Theorem in the Lagrangian Formalism
We provide a new proof of a important theorem in the Lagrangian formalism
about necessary and sufficient conditions for a second-order variational system
of equations to follow from a first-order Lagrangian.Comment: 9 pages, LATEX, no figures; appear in Il Nuovo Cimento
Letter from O.M. Anderson to Eugene Burdick Regarding Arrowheads, August 31, 1934
This letter dated August 31, 1934, from O.M. Anderson of Upham, North Dakota to Eugene Burdick, inquires about fixing flint arrowheads that Anderson has found. Anderson was referred to Eugene Burdick by Usher Burdick. The letterhead states that Anderson is a collector of antique firearms.https://commons.und.edu/burdick-papers/1063/thumbnail.jp
Molecular ferroelectric contributions to anomalous hysteresis in hybrid perovskite solar cells
We report a model describing the molecular orientation disorder in
CH3NH3PbI3, solving a classical Hamiltonian parametrised with electronic
structure calculations, with the nature of the motions informed by ab-initio
molecular dynamics. We investigate the temperature and static electric field
dependence of the equilibrium ferroelectric (molecular) domain structure and
resulting polarisability. A rich domain structure of twinned molecular dipoles
is observed, strongly varying as a function of temperature and applied electric
field. We propose that the internal electrical fields associated with
microscopic polarisation domains contribute to hysteretic anomalies in the
current--voltage response of hybrid organic-inorganic perovskite solar cells
due to variations in electron-hole recombination in the bulk.Comment: 10 pages; 4 figures, 2 SI figure
Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6752
We have searched for optical identifications for 39 Chandra X-ray sources
that lie within the 1.9 arcmin half-mass radius of the nearby (d = 4.0 kpc),
core-collapsed globular cluster, NGC 6752, using deep Hubble Space Telescope
ACS/WFC imaging in B435, R625, and H alpha. Photometry of these images allows
us to classify candidate counterparts based primarily on color-magnitude and
color-color diagram location. The color-color diagram is particularly useful
for quantifying the H alpha line equivalent width. In addition to recovering 11
previously detected optical counterparts, we propose 20 new optical IDs. In
total, there are 16 likely or less certain cataclysmic variables (CVs), nine
likely or less certain chromospherically active binaries, three galaxies, and
three active galactic nuclei (AGNs). The latter three sources, which had been
identified as likely CVs by previous investigations, now appear to be
extragalactic objects based on their proper motions. As we previously found for
NGC 6397, the CV candidates in NGC 6752 fall into a bright group that is
centrally concentrated relative to the turnoff-mass stars and a faint group
that has a spatial distribution that is more similar to that of the
turnoff-mass stars. This is consistent with an evolutionary scenario in which
CVs are produced by dynamical interactions near the cluster center and diffuse
to larger radius orbits as they age.Comment: 26 pages, 18 figure
Klein-Gordon Equation for Quark Pairs in Color Superconductor
The wave equation is derived for quark pairs in color superconductor in the
regime of low density / strong coupling.Comment: 4 pages, no figure
Probing Pair-Correlated Fermionic Atoms through Correlations in Atom Shot Noise
Pair-correlated fermionic atoms are created through dissociation of weakly
bound molecules near a magnetic-field Feshbach resonance. We show that
correlations between atoms in different spin states can be detected using the
atom shot noise in absorption images. Furthermore, using time-of-Flight imaging
we have observed atom pair correlations in momentum space
Using Early Data to Illuminate the Pioneer Anomaly
Analysis of the radio tracking data from the Pioneer 10/11 spacecraft at
distances between about 20 - 70 AU from the Sun has consistently indicated the
presence of an unmodeled, small, constant, Doppler blue shift drift of order 6
\times 10^{-9} Hz/s. After accounting for systematics, this drift can be
interpreted as a constant acceleration of a_P= (8.74 \pm 1.33) \times 10^{-8}
cm/s^2 directed towards the Sun, or perhaps as a time acceleration of a_t =
(2.92 \pm 0.44)\times 10^{-18} s/s^2. Although it is suspected that there is a
systematic origin to this anomaly, none has been unambiguously demonstrated. We
review the current status of the anomaly, and then point out how the analysis
of early data, which was never analyzed in detail, could allow a more clear
understanding of the origin of the anomaly, be it a systematic or a
manifestation of unsuspected physics.Comment: 19 pages, 6 figures, 2 tables, additional materia
Rigidity of compact Riemannian spin Manifolds with Boundary
In this article, we prove new rigidity results for compact Riemannian spin
manifolds with boundary whose scalar curvature is bounded from below by a
non-positive constant. In particular, we obtain generalizations of a result of
Hang-Wang \cite{hangwang1} based on a conjecture of Schroeder and Strake
\cite{schroeder}.Comment: English version of "G\'eom\'etrie spinorielle extrins\`eque et
rigidit\'es", Corollary 6 in Section 3 added, to appear in Letters Math. Phy
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