4,340 research outputs found
Semiclassical Coherent States propagator
In this work, we derived a semiclassical approximation for the matrix
elements of a quantum propagator in coherent states (CS) basis that avoids
complex trajectories, it only involves real ones. For that propose, we used
the, symplectically invariant, semiclassical Weyl propagator obtained by
performing a stationary phase approximation (SPA) for the path integral in the
Weyl representation. After what, for the transformation to CS representation
SPA is avoided, instead a quadratic expansion of the complex exponent is used.
This procedure also allows to express the semiclassical CS propagator uniquely
in terms of the classical evolution of the initial point, without the need of
any root search typical of Van Vleck Gutzwiller based propagators. For the case
of chaotic Hamiltonian systems, the explicit time dependence of the CS
propagator has been obtained. The comparison with a
\textquotedbl{}realistic\textquotedbl{} chaotic system that derives from a
quadratic Hamiltonian, the cat map, reveals that the expression here derived is
exact up to quadratic Hamiltonian systems.Comment: 13 pages, 2 figure. Accepted for publication in PR
Role of dipolar interactions in a system of Ni nanoparticles studied by magnetic susceptibility measurements
The role of dipolar interactions among Ni nanoparticles (NP) embedded in an
amorphous SiO2/C matrix with different concentrations has been studied
performing ac magnetic susceptibility Chi_ac measurements. For very diluted
samples, with Ni concentrations < 4 wt % Ni or very weak dipolar interactions,
the data are well described by the Neel-Arrhenius law. Increasing Ni
concentration to values up to 12.8 wt % Ni results in changes in the
Neel-Arrhenius behavior, the dipolar interactions become important, and need to
be considered to describe the magnetic response of the NPs system. We have
found no evidence of a spin-glasslike behavior in our Ni NP systems even when
dipolar interactions are clearly present.Comment: 7 pages, 5 figures, 3 table
Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation
We present indications of thermalization and cooling of quasi-particles, a
precursor for quantum condensation, in a plasmonic nanoparticle array. We
investigate a periodic array of metallic nanorods covered by a polymer layer
doped with an organic dye at room temperature. Surface lattice resonances of
the array---hybridized plasmonic/photonic modes---couple strongly to excitons
in the dye, and bosonic quasi-particles which we call
plasmon-exciton-polaritons (PEPs) are formed. By increasing the PEP density
through optical pumping, we observe thermalization and cooling of the strongly
coupled PEP band in the light emission dispersion diagram. For increased
pumping, we observe saturation of the strong coupling and emission in a new
weakly coupled band, which again shows signatures of thermalization and
cooling.Comment: 8 pages, 5 figures including supplemental material. The newest
version includes new measurements and corrections to the interpretation of
the result
Evidence of Acute Mycoplasma Infection in a Patient with Incomplete and Atypical Kawasaki Disease: A Case Report
The etiology of
Kawasaki disease remains unknown despite
extensive studies. Some researchers suggest that
it is caused by an infectious agent. This is a
case report where a patient with incomplete
Kawasaki disease was found to have evidence
compatible with acute Mycoplasma pneumoniae
infection. This is one of the several case
reports linking Mycoplasma pneumoniae to
Kawasaki disease as a possible trigger. This is
perhaps due to a superantigen or is mediated by some other
mechanism. Accurate and timely testing for
Mycoplasma infections is difficult and has its
limitations. Despite this, Mycoplasma pneumoniae
should be considered in the differential and
workup for Kawasaki disease
From weak to strong coupling of localized surface plasmons to guided modes in a luminescent slab
We investigate a periodic array of aluminum nanoantennas embedded in a
light-emitting slab waveguide. By varying the waveguide thickness we
demonstrate the transition from weak to strong coupling between localized
surface plasmons in the nanoantennas and refractive index guided modes in the
waveguide. We experimentally observe a non-trivial relationship between
extinction and emission dispersion diagrams across the weak to strong coupling
transition. These results have implications for a broad class of photonic
structures where sources are embedded within coupled resonators. For
nanoantenna arrays, strong vs. weak coupling leads to drastic modifications of
radiation patterns without modifying the nanoantennas themselves, thereby
representing an unprecedented design strategy for nanoscale light sources
Increase in the magnitude of the energy barrier distribution in Ni nanoparticles due to dipolar interactions
The energy barrier distribution Eb of five samples with different
concentrations x of Ni nanoparticles using scaling plots from ac magnetic
susceptibility data has been determined. The scaling of the imaginary part of
the susceptibility Chi"(nu, T) vs. Tln(t/tau_0) remains valid for all samples,
which display Ni nanoparticles with similar shape and size. The mean value
increases appreciably with increasing x, or more appropriately with
increasing dipolar interactions between Ni nanoparticles. We argue that such an
increase in constitutes a powerful tool for quality control in magnetic
recording media technology where the dipolar interaction plays an important
role.Comment: 3 pages, 3 figures, 1 tabl
On Bargmann Representations of Wigner Function
By using the localized character of canonical coherent states, we give a
straightforward derivation of the Bargmann integral representation of Wigner
function (W). A non-integral representation is presented in terms of a
quadratic form V*FV, where F is a self-adjoint matrix whose entries are
tabulated functions and V is a vector depending in a simple recursive way on
the derivatives of the Bargmann function. Such a representation may be of use
in numerical computations. We discuss a relation involving the geometry of
Wigner function and the spacial uncertainty of the coherent state basis we use
to represent it.Comment: accepted for publication in J. Phys. A: Math. and Theo
Generalized Limits for Parameter Sensitivity via Quantum Ziv-Zakai Bound
We study the generalized limit for parameter sensitivity in quantum
estimation theory considering the effects of repeated and adaptive
measurements. Based on the quantum Ziv-Zakai bound, we derive some lower bounds
for parameter sensitivity when the Hamiltonian of system is unbounded and when
the adaptive measurements are implemented on the system. We also prove that the
parameter sensitivity is bounded by the limit of the minimum detectable
parameter. In particular, we examine several known states in quantum phase
estimation with non-interacting photons, and show that they can not perform
better than Heisenberg limit in a much simpler way with our result.Comment: 8pages, 5 figure
Pulmonary metastasectomy in colorectal cancer: a prospective study of demography and clinical characteristics of 543 patients in the Spanish colorectal metastasectomy registry (GECMP-CCR)
ObjectivesTo capture an accurate contemporary description of the practice of pulmonary metastasectomy for colorectal carcinoma in one national healthcare system.DesignA national registry set up in Spain by Grupo Español de Cirugía Metástasis Pulmonares de Carcinoma Colo-Rectal (GECMP-CCR).Setting32 Spanish thoracic units.ParticipantsAll patients with one or more histologically proven lung metastasis removed by surgery between March 2008 and February 2010.InterventionsPulmonary metastasectomy for one or more pulmonary nodules proven to be metastatic colorectal carcinoma.Primary and secondary outcome measuresThe age and sex of the patients having this surgery were recorded with the number of metastases removed, the interval between the primary colorectal cancer operation and the pulmonary metastasectomy, and the carcinoembryonic antigen level. Also recorded were the practices with respect to mediastinal lymphadenopathy and coexisting liver metastases.ResultsData were available on 543 patients from 32 units (6–43/unit). They were aged 32–88 (mean 65) years, and 65% were men. In 55% of patients, there was a solitary metastasis. The median interval between the primary cancer resection and metastasectomy was 28 months and the serum carcinoembryonic antigen was low/normal in the majority. Liver metastatic disease was present in 29% of patients at some point prior to pulmonary metastasectomy. Mediastinal lymphadenectomy varied from 9% to 100% of patients.ConclusionsThe data represent a prospective comprehensive national data collection on pulmonary metastasectomy. The practice is more conservative than the impression gained when members of the European Society of Thoracic Surgeons were surveyed in 2006/2007 but is more inclusive than would be recommended on the basis of recent outcome analyses. Further analyses on the morbidity associated with this surgery and the correlation between imaging studies and pathological findings are being published separately by GECMP-CCR
Coexistence of Paramagnetic-Charge-Ordered and Ferromagnetic-Metallic Phases in La0.5Ca0.5MnO3 evidenced by ESR
Throughout a complete Electron Spin Resonance (ESR) and magnetization study
of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated
state established in this compound below T~210 K. Between TN<T<TC, the ESR
spectra shows two lines characteristic of two different magnetic phases. From
the resonance field (Hr) derived for each line we argue that the
incommensurate-charge-ordering phase (ICO) which coexists with
ferromagnetic-metallic (FMM) clusters in this temperature interval, is mainly
paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a
relatively small field, which suggests that the internal energy associated with
those phases is very similar. Below TN, there is an appreciable FM contribution
to the magnetization and the ESR spectra indicates the presence of FM clusters
in an antiferromagnetic matrix (canted). Our results show that ESR could be a
very useful tool to investigate the nature of the phase-separated state now
believed to play a fundamental role in the physics of mixed valent manganites.Comment: 6 pages, 6 figure
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