20,816 research outputs found
Theory of controlled quantum dynamics
We introduce a general formalism, based on the stochastic formulation of
quantum mechanics, to obtain localized quasi-classical wave packets as
dynamically controlled systems, for arbitrary anharmonic potentials. The
control is in general linear, and it amounts to introduce additional quadratic
and linear time-dependent terms to the given potential. In this way one can
construct for general systems either coherent packets moving with constant
dispersion, or dynamically squeezed packets whose spreading remains bounded for
all times. In the standard operatorial framework our scheme corresponds to a
suitable generalization of the displacement and scaling operators that generate
the coherent and squeezed states of the harmonic oscillator.Comment: LaTeX, A4wide, 28 pages, no figures. To appear in J. Phys. A: Math.
Gen., April 199
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Tricritical Ising Model with a Boundary
We study the integrable and supersymmetric massive deformation of the tricritical Ising model in the presence of a boundary. We use constraints from supersymmetry in order to compute the exact boundary -matrices, which turn out to depend explicitly on the topological charge of the supersymmetry algebra. We also solve the general boundary Yang-Baxter equation and show that in appropriate limits the general reflection matrices go over the supersymmetry preserving solutions. Finally, we briefly discuss the possible connection between our reflection matrices and boundary perturbations within the framework of perturbed boundary conformal field theory
Quantum Integrability of Certain Boundary Conditions
We study the quantum integrability of the O(N) nonlinear (nls) model
and the O(N) Gross-Neveu (GN) model on the half-line. We show that the \nls
model is integrable with Neumann, Dirichlet and a mixed boundary condition, and
that the GN model is integrable if \psi_+^a\x=\pm\psi_-^a\x. We also comment
on the boundary condition found by Corrigan and Sheng for the O(3) nls model.Comment: 11 pages, Latex file, minor changes, one reference adde
The differential diagnosis of Huntington's disease-like syndromes: 'red flags' for the clinician
A growing number of progressive heredodegenerative conditions mimic the presentation of Huntington's disease (HD). Differentiating among these HD-like syndromes is necessary when a patient with a combination of movement disorders, cognitive decline, behavioural abnormalities and progressive disease course proves negative to the genetic testing for HD causative mutations, that is, IT15 gene trinucleotide-repeat expansion. The differential diagnosis of HD-like syndromes is complex and may lead to unnecessary and costly investigations. We propose here a guide to this differential diagnosis focusing on a limited number of clinical features (‘red flags’) that can be identified through accurate clinical examination, collection of historical data and a few routine ancillary investigations. These features include the ethnic background of the patient, the involvement of the facio-bucco-lingual and cervical district by the movement disorder, the co-occurrence of cerebellar features and seizures, the presence of peculiar gait patterns and eye movement abnormalities, and an atypical progression of illness. Additional help may derive from the cognitive–behavioural presentation of the patient, as well as by a restricted number of ancillary investigations, mainly MRI and routine blood tests. These red flags should be constantly updated as the phenotypic characterisation and identification of more reliable diagnostic markers for HD-like syndromes progress over the following years
The X-ray emission of magnetic cataclysmic variables in the XMM-Newton era
We review the X-ray spectral properties of magnetic cataclysmic binaries
derived from observations obtained during the last decade with the large X-ray
observatories XMM-Newton, Chandra and Suzaku. We focus on the signatures of the
different accretion modes which are predicted according to the values of the
main physical parameters (magnetic field, local accretion rate and white dwarf
mass). The observed large diversity of spectral behaviors indicates a wide
range of parameter values in both intermediate polars and polars, in line with
a possible evolutionary link between both classes.Comment: To appear in the Proceedings of "The Golden Age of Cataclysmic
Variables (Palermo 2011)", in Mem. Soc. Astron. It. (7 pages, 3 figures
On the transition to efficiency in Minority Games
The existence of a phase transition with diverging susceptibility in batch
Minority Games (MGs) is the mark of informationally efficient regimes and is
linked to the specifics of the agents' learning rules. Here we study how the
standard scenario is affected in a mixed population game in which agents with
the `optimal' learning rule (i.e. the one leading to efficiency) coexist with
ones whose adaptive dynamics is sub-optimal. Our generic finding is that any
non-vanishing intensive fraction of optimal agents guarantees the existence of
an efficient phase. Specifically, we calculate the dependence of the critical
point on the fraction of `optimal' agents focusing our analysis on three
cases: MGs with market impact correction, grand-canonical MGs and MGs with
heterogeneous comfort levels.Comment: 12 pages, 3 figures; contribution to the special issue "Viewing the
World through Spin Glasses" in honour of David Sherrington on the occasion of
his 65th birthda
Nonlinear magnetotransport in interacting chiral nanotubes
Nonlinear transport through interacting single-wall nanotubes containing a
few impurities is studied theoretically. Extending the Luttinger liquid theory
to incorporate trigonal warping and chirality effects, we derive the current
contribution {\sl even} in the applied voltage and {\sl odd} in an
orbital magnetic field , which is non-zero only for chiral tubes and in the
presence of interactions.Comment: 4 pages, 1 figure, minor changes, to appear in PR
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