1,316 research outputs found
Lyapunov exponents from geodesic spread in configuration space
The exact form of the Jacobi -- Levi-Civita (JLC) equation for geodesic
spread is here explicitly worked out at arbitrary dimension for the
configuration space manifold M_E = {q in R^N | V(q) < E} of a standard
Hamiltonian system, equipped with the Jacobi (or kinetic energy) metric g_J. As
the Hamiltonian flow corresponds to a geodesic flow on (M_E,g_J), the JLC
equation can be used to study the degree of instability of the Hamiltonian
flow. It is found that the solutions of the JLC equation are closely resembling
the solutions of the standard tangent dynamics equation which is used to
compute Lyapunov exponents. Therefore the instability exponents obtained
through the JLC equation are in perfect quantitative agreement with usual
Lyapunov exponents. This work completes a previous investigation that was
limited only to two-degrees of freedom systems.Comment: REVTEX file, 10 pages, 2 figure
Analyzing intramolecular vibrational energy redistribution via the overlap intensity-level velocity correlator
Numerous experimental and theoretical studies have established that
intramolecular vibrational energy redistribution (IVR) in isolated molecules
has a heirarchical tier structure. The tier structure implies strong
correlations between the energy level motions of a quantum system and its
intensity-weighted spectrum. A measure, which explicitly accounts for this
correaltion, was first introduced by one of us as a sensitive probe of phase
space localization. It correlates eigenlevel velocities with the overlap
intensities between the eigenstates and some localized state of interest. A
semiclassical theory for the correlation is developed for systems that are
classically integrable and complements earlier work focusing exclusively on the
chaotic case. Application to a model two dimensional effective spectroscopic
Hamiltonian shows that the correlation measure can provide information about
the terms in the molecular Hamiltonian which play an important role in an
energy range of interest and the character of the dynamics. Moreover, the
correlation function is capable of highlighting relevant phase space structures
including the local resonance features associated with a specific bright state.
In addition to being ideally suited for multidimensional systems with a large
density of states, the measure can also be used to gain insights into the phase
space transport and localization. It is argued that the overlap intensity-level
velocity correlation function provides a novel way of studying vibrational
energy redistribution in isolated molecules. The correlation function is
ideally suited to analyzing the parametric spectra of molecules in external
fields.Comment: 16 pages, 13 figures (low resolution
New AGNs discovered by H.E.S.S
During the last year, six new Active Galactic Nuclei (AGN) have been
discovered and studied by H.E.S.S. at Very High Energies (VHE). Some of these
recent discoveries have been made thanks to new enhanced analysis methods and
are presented at this conference for the first time. The three blazars 1ES
0414+009, SHBL J001355.9-185406 and 1RXS J101015.9-311909 have been targeted
for observation due to their high levels of radio and X-ray fluxes, while the
Fermi/LAT catalogue of bright sources triggered the observation of PKS 0447-439
and AP Librae. Additionally, the BL Lac 1ES 1312-423 was discovered in the
field-of-view (FoV) of Centaurus A thanks to the large exposure dedicated by
H.E.S.S. to this particularly interesting source. The newly-discovered sources
are presented here and in three companion presentations at this conference.Comment: 8 pages, 3 figures, proceeding from the 25th Texas Symposium on
Relativistic Astrophysics (Heidelberg, Germany, 2010
Iron causes lipid oxidation and inhibits proteasome function in multiple myeloma cells: A proof of concept for novel combination therapies
Adaptation to import iron for proliferation makes cancer cells potentially sensitive to iron toxicity. Iron loading impairs multiple myeloma (MM) cell proliferation and increases the efficacy of the proteasome inhibitor bortezomib. Here, we defined the mechanisms of iron toxicity in MM.1S, U266, H929, and OPM-2 MM cell lines, and validated this strategy in preclinical studies using Vk*MYC mice as MM model. High-dose ferric ammonium citrate triggered cell death in all cell lines tested, increasing malondialdehyde levels, the by-product of lipid peroxidation and index of ferroptosis. In addition, iron exposure caused dose-dependent accumulation of polyubiquitinated proteins in highly iron-sensitive MM.1S and H929 cells, suggesting that proteasome workload contributes to iron sensitivity. Accordingly, high iron concentrations inhibited the proteasomal chymotrypsin-like activity of 26S particles and of MM cellular extracts in vitro. In all MM cells, bortezomib-iron combination induced persistent lipid damage, exacerbated bortezomib-induced polyubiquitinated proteins accumulation, and triggered cell death more efficiently than individual treatments. In Vk*MYC mice, addition of iron dextran or ferric carboxymaltose to the bortezomib-melphalan-prednisone (VMP) regimen increased the therapeutic response and prolonged remission without causing evident toxicity. We conclude that iron loading interferes both with redox and protein homeostasis, a property that can be exploited to design novel combination strategies including iron supplementation, to increase the efficacy of current MM therapies
Benefits of Urologic-Dermatologic Consultations for the Diagnosis of Cutaneous Penile Lesions: A Prospective Study
INTRODUCTION: We evaluated the benefits of a specialized consultation created in 2014 for cutaneous penile lesions.
MATERIALS AND METHODS: We performed a descriptive prospective study evaluating all patients sent for a monthly urologic-dermatologic consultation at a French university hospital from September 2014 to September 2015 for cutaneous penile lesions. All patients evaluated were included. We collected the demographic data, clinical examination findings, and the proposed diagnosis and treatment for every patient.
RESULTS: A total of 27 patients were included; 4 (14.8%) had been referred by a general physician and 23 (85.2%) by a specialist. Cutaneous penile lesions had evolved within 12 months in 15 patients (55.6%). Penile cancer was diagnosed in 5 patients (18.5%), of which 3 were squamous cell carcinoma (11.1%), 1 was metastasis of melanoma (3.7%), and 1 was extramammary Paget disease (3.7%). In addition, 1 patient (3.7%) had a premalignant lesion on a condyloma, 12 (44.4%) had balanitis, 2 (7.4%) had psoriasis lesions, 3 (11.1%) had condylomas, 1 (3.7%) had genital melanosis, and 3 (11.2%) had normal findings. Four patients (16.6%) underwent biopsy, 8 (33.3%) underwent surgery, and 12 (50%) received local treatment.
CONCLUSION: The use of urologic-dermatology specialized consultations resulted in encouraging findings. Patients can benefit from multidisciplinary expertise and rapid treatment of various disorders. Thus, it seems important to develop reference centers created specifically for cancerous disease
The highly polarized open cluster Trumpler 27
We have carried out multicolor linear polarimetry (UBVRI) of the brightest
stars in the area of the open cluster Trumpler 27. Our data show a high level
of polarization in the stellar light with a considerable dispersion, from to . The polarization vectors of the cluster members appear to be
aligned. Foreground polarization was estimated from the data of some non-member
objects, for which two different components were resolved: the first one
associated with a dust cloud close to the Sun producing
and degrees, and a second component, the main source of
polarization for the cluster members, originated in another dust cloud, which
polarizes the light in the direction of degrees. From a detailed
analysis, we found that the two components have associated values for the first one, and for the other. Due the
difference in the orientation of both polarization vectors, almost 90 degrees
(180 degrees at the Stokes representation), the first cloud (
degrees) depolarize the light strongly polarized by the second one ( degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in
A
Hamiltonian dynamics and geometry of phase transitions in classical XY models
The Hamiltonian dynamics associated to classical, planar, Heisenberg XY
models is investigated for two- and three-dimensional lattices. Besides the
conventional signatures of phase transitions, here obtained through time
averages of thermodynamical observables in place of ensemble averages,
qualitatively new information is derived from the temperature dependence of
Lyapunov exponents. A Riemannian geometrization of newtonian dynamics suggests
to consider other observables of geometric meaning tightly related with the
largest Lyapunov exponent. The numerical computation of these observables -
unusual in the study of phase transitions - sheds a new light on the
microscopic dynamical counterpart of thermodynamics also pointing to the
existence of some major change in the geometry of the mechanical manifolds at
the thermodynamical transition. Through the microcanonical definition of the
entropy, a relationship between thermodynamics and the extrinsic geometry of
the constant energy surfaces of phase space can be naturally
established. In this framework, an approximate formula is worked out,
determining a highly non-trivial relationship between temperature and topology
of the . Whence it can be understood that the appearance of a phase
transition must be tightly related to a suitable major topology change of the
. This contributes to the understanding of the origin of phase
transitions in the microcanonical ensemble.Comment: in press on Physical Review E, 43 pages, LaTeX (uses revtex), 22
PostScript figure
Chaos and Complexity of quantum motion
The problem of characterizing complexity of quantum dynamics - in particular
of locally interacting chains of quantum particles - will be reviewed and
discussed from several different perspectives: (i) stability of motion against
external perturbations and decoherence, (ii) efficiency of quantum simulation
in terms of classical computation and entanglement production in operator
spaces, (iii) quantum transport, relaxation to equilibrium and quantum mixing,
and (iv) computation of quantum dynamical entropies. Discussions of all these
criteria will be confronted with the established criteria of integrability or
quantum chaos, and sometimes quite surprising conclusions are found. Some
conjectures and interesting open problems in ergodic theory of the quantum many
problem are suggested.Comment: 45 pages, 22 figures, final version, at press in J. Phys. A, special
issue on Quantum Informatio
Collapses and explosions in self-gravitating systems
Collapse and reverse to collapse explosion transition in self-gravitating
systems are studied by molecular dynamics simulations. A microcanonical
ensemble of point particles confined to a spherical box is considered; the
particles interact via an attractive soft Coulomb potential. It is observed
that the collapse in the particle system indeed takes place when the energy of
the uniform state is put near or below the metastability-instability threshold
(collapse energy), predicted by the mean-field theory. Similarly, the explosion
in the particle system occurs when the energy of the core-halo state is
increased above the explosion energy, where according to the mean field
predictions the core-halo state becomes unstable. For a system consisting of
125 -- 500 particles, the collapse takes about single particle crossing
times to complete, while a typical explosion is by an order of magnitude
faster. A finite lifetime of metastable states is observed. It is also found
that the mean-field description of the uniform and the core-halo states is
exact within the statistical uncertainty of the molecular dynamics data.Comment: 9 pages, 14 figure
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