2,984 research outputs found
Quantum Mechanics on SO(3) via Non-commutative Dual Variables
We formulate quantum mechanics on SO(3) using a non-commutative dual space
representation for the quantum states, inspired by recent work in quantum
gravity. The new non-commutative variables have a clear connection to the
corresponding classical variables, and our analysis confirms them as the
natural phase space variables, both mathematically and physically. In
particular, we derive the first order (Hamiltonian) path integral in terms of
the non-commutative variables, as a formulation of the transition amplitudes
alternative to that based on harmonic analysis. We find that the non-trivial
phase space structure gives naturally rise to quantum corrections to the action
for which we find a closed expression. We then study both the semi-classical
approximation of the first order path integral and the example of a free
particle on SO(3). On the basis of these results, we comment on the relevance
of similar structures and methods for more complicated theories with
group-based configuration spaces, such as Loop Quantum Gravity and Spin Foam
models.Comment: 29 pages; matches the published version plus footnote 7, a journal
reference include
Learning Incoherent Subspaces: Classification via Incoherent Dictionary Learning
In this article we present the supervised iterative projections and rotations (s-ipr) algorithm, a method for learning discriminative incoherent subspaces from data. We derive s-ipr as a supervised extension of our previously proposed iterative projections and rotations (ipr) algorithm for incoherent dictionary learning, and we employ it to learn incoherent sub-spaces that model signals belonging to different classes. We test our method as a feature transform for supervised classification, first by visualising transformed features from a synthetic dataset and from the âirisâ dataset, then by using the resulting features in a classification experiment
Muon and Tau Neutrinos Spectra from Solar Flares
Solar neutrino flares and mixing are considered. Most power-full solar flare
as the ones occurred on 23th February 1956, September 29th 1989, 28th October
and on 2nd-4th November 2003 are sources of cosmic rays, X, gamma and neutrino
bursts. These flares took place both on front or in the edge and in the hidden
solar disk. The observed and estimated total flare energy should be a source of
a prompt secondary neutrino burst originated, by proton-proton-pion production
on the sun itself; a more delayed and spread neutrino flux signal arise by the
solar charged flare particles reaching the terrestrial atmosphere. Our first
estimates of neutrino signals in largest underground detectors hint for few
events in correlation with, gamma,radio onser. Our approximated spectra for
muons and taus from these rare solar eruption are shown over the most common
background. The muon and tau signature is very peculiar and characteristic over
electron and anti-electron neutrino fluxes. The rise of muon neutrinos will be
detectable above the minimal muon threshold of 113 MeV. The rarest tau
appearence will be possible only for hardest solar neutrino energies above
3.471 GeVComment: 14 pages, 4 figures, Vulcano Conference 200
Raman scattering from phonons and magnons in RFe3)BO3)4
Inelastic light scattering spectra of several members of the RFe3(BO3)4
family reveal a cascade of phase transitions as a function of temperature,
starting with a structural, weakly first order, phase transition followed by
two magnetic phase transitions. Those consist of the ordering of the Fe-spin
sublattice revealed by all the compound, and a subsequent spin-reorientational
transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between
the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice
ordering leads to a strong suppression of the low energy magnetic scattering,
and a multiple peaked two-magnon scattering continuum is observed. Evidence for
short-range correlations is found in the `paramagnetic' phase by the
observation of a broad magnetic continuum in the Raman data, which persists up
to surprisingly high temperatures.Comment: 17 pages, 13 figure
Wave Mechanics of a Two Wire Atomic Beamsplitter
We consider the problem of an atomic beam propagating quantum mechanically
through an atom beam splitter. Casting the problem in an adiabatic
representation (in the spirit of the Born-Oppenheimer approximation in
molecular physics) sheds light on explicit effects due to non-adiabatic passage
of the atoms through the splitter region. We are thus able to probe the fully
three dimensional structure of the beam splitter, gathering quantitative
information about mode-mixing, splitting ratios,and reflection and transmission
probabilities
The Wiener-Hopf Formulation of the Penetrable Wedge Problem. Part III: The skew incidence case
Extrafloral-nectar based partner manipulation in plant-ant relationship
Plantâant interactions are generally considered as mutualisms, with both parties gaining benefits from
the association. It has recently emerged that some of these mutualistic associations have, however, evolved towards
other forms of relationships and, in particular, that plants may manipulate their partner ants to make reciprocation
more beneficial, thereby stabilizing the mutualism. Focusing on plants bearing extrafloral nectaries, we review recent
studies and address three key questions: (i) how can plants attract potential partners and maintain their services;
(ii) are there compounds in extrafloral nectar that could mediate partner manipulation; and (iii) are ants susceptible
to such compounds? After reviewing the current knowledge on plantâant associations, we propose a possible scenario
where plant-derived chemicals, such as secondary metabolites, known to have an impact on animal brain, could
have evolved in plants to attract and manipulate ant behaviour. This new viewpoint would place plantâanimal interaction
in a different ecological context, opening new ecological and neurobiological perspectives of drug seeking
and use
Pinch Technique for Schwinger-Dyson equations
In the context of scalar QED we derive the pinch technique self-energies and
vertices directly from the Schwinger-Dyson equations. After reviewing the
perturbative construction, we discuss in detail the general methodology and the
basic field-theoretic ingredients necessary for the completion of this task.
The construction requires the simultaneous treatment of the equations governing
the scalar self-energy and the fundamental interaction vertices. The resulting
non-trivial rearrangement of terms generates dynamically the Schwinger-Dyson
equations for the corresponding Green's functions of the background field
method. The proof relies on the extensive use of the all-order Ward-identities
satisfied by the full vertices of the theory and by the
one-particle-irreducible kernels appearing in the usual skeleton expansion. The
Ward identities for these latter quantities are derived formally, and several
subtleties related to the structure of the multiparticle kernels are addressed.
The general strategy for the generalization of the method in a non-Abelian
context is briefly outlined, and some of the technical difficulties are
discussed.Comment: 43 pages, 11 figures; title and abstract slightly modified, several
clarifying discussions added; final version to match the one accpted for
publication in JHE
Model-based monitoring and control of industrial freeze-drying processes: Effect of batch nonuniformity
Beyond the plane-parallel and Newtonian approach: Wide-angle redshift distortions and convergence in general relativity
We extend previous analyses of wide-angle correlations in the galaxy power
spectrum in redshift space to include all general relativistic effects. These
general relativistic corrections to the standard approach become important on
large scales and at high redshifts, and they lead to new terms in the
wide-angle correlations. We show that in principle the new terms can produce
corrections of nearly 10 % on Gpc scales over the usual Newtonian
approximation. General relativistic corrections will be important for future
large-volume surveys such as SKA and Euclid, although the problem of cosmic
variance will present a challenge in observing this.Comment: 14 pages, 5 figures; Typo in equation 5 corrected; results unaffecte
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