414 research outputs found
Effect of long range spatial correlations on the lifetime statistics of an emitter in a two-dimensional disordered lattice
The effect of spatial correlations on the Purcell effect in a bidimensional
dispersion of resonant nanoparticles is analyzed. We perform extensive
calculations on the fluorescence decay rate of a point emitter embedded in a
system of nanoparticles statistically distributed according to a simple 2D
lattice-gas model near the critical point. For short-range correlations (high
temperature thermalization) the Purcell factors present a long-tailed statistic
which evolves towards a bimodal distribution when approaching the critical
point where the spatial correlation length diverges. Our results suggest
long-range correlations as a possible origin of the large fluctuations of
experimental decay rates in disordered metal films.Comment: 6 pages, 5 figure
Poling effect on distribution of quenched random fields in a uniaxial relaxor ferroelectric
The frequency dependence of the dielectric permitivity's maximum has been
studied for poled and unpoled doped relaxor strontium barium niobate
(SBN-61:Cr). In both cases the maximum
found is broad and the frequency dispersion is strong. The present view of
random fields compensation in the unpoled sample is not suitable for explaining
this experimental result. We propose a new mechanism where the dispersion of
quenched random electric fields, affecting the nanodomains, is minimized after
poling. We test our proposal by numerical simulations on a random field Ising
model. Results obtained are in agreement with the polarization's measurements
presented by Granzow et al. [Phys. Rev. Lett {\bf 92}, 065701 (2004)].Comment: 7 pages, 4 figure
Accurate circuit analysis of resonant-type left handed transmission lines with inter-resonator coupling
In this paper, a circuit model for the description of left handed transmission lines based on
complementary split rings resonators CSRRs is proposed. As compared to previous models,
coupling between adjacent resonators is included in the present work. The conditions that make this
coupling significant are discussed. Specifically, it will be shown that it is barely present when
circular CSRRs are used to implement the left handed transmission line. However, if the line is
loaded with rectangular CSRRs separated by a small distance, inter-resonator coupling is important
and it significantly influences the electromagnetic behavior of the structures. It will be also shown
that under low or moderate coupling, it is possible to describe the structures by means of a simplified
model with modified parameters. Several prototype devices with different CSRR topologies and
coupling levels have been fabricated to illustrate the phenomenology associated with these
structures and the accuracy of their model descriptions. The results of this work can be of interest
for the design of planar microwave circuits based on CSRR left handed lines.Ministerio de EconomĂa y Ciencias de España-TEC2004-04249-C02-01 y TEC2004-04249-C02-02ComisiĂłn Europea (Red de Excelencia)-E 500252-2 METAMORPHOS
Dynamic Scaling in Diluted Systems Phase Transitions: Deactivation trough Thermal Dilution
Activated scaling is confirmed to hold in transverse field induced phase
transitions of randomly diluted Ising systems. Quantum Monte Carlo calculations
have been made not just at the percolation threshold but well bellow and above
it including the Griffiths-McCoy phase. A novel deactivation phenomena in the
Griffiths-McCoy phase is observed using a thermal (in contrast to random)
dilution of the system.Comment: 4 pages, 4 figures, RevTe
The detection of neutron clusters
A new approach to the production and detection of bound neutron clusters is
presented. The technique is based on the breakup of beams of very neutron-rich
nuclei and the subsequent detection of the recoiling proton in a liquid
scintillator. The method has been tested in the breakup of 11Li, 14Be and 15B
beams by a C target. Some 6 events were observed that exhibit the
characteristics of a multineutron cluster liberated in the breakup of 14Be,
most probably in the channel 10Be+4n. The various backgrounds that may mimic
such a signal are discussed in detail.Comment: 11 pages, 12 figures, LPCC 01-1
Universality Class of Thermally Diluted Ising Systems at Criticality
The universality class of thermally diluted Ising systems, in which the
realization of the disposition of magnetic atoms and vacancies is taken from
the local distribution of spins in the pure original Ising model at
criticality, is investigated by finite size scaling techniques using the Monte
Carlo method. We find that the critical temperature, the critical exponents and
therefore the universality class of these thermally diluted Ising systems
depart markedly from the ones of short range correlated disordered systems. Our
results agree fairly well with theoretical predictions previously made by
Weinrib and Halperin for systems with long range correlated disorder.Comment: 7 pages, 6 figures, RevTe
Weak quenched disorder and criticality: resummation of asymptotic(?) series
In these lectures, we discuss the influence of weak quenched disorder on the
critical behavior in condensed matter and give a brief review of available
experimental and theoretical results as well as results of MC simulations of
these phenomena. We concentrate on three cases: (i) uncorrelated random-site
disorder, (ii) long-range-correlated random-site disorder, and (iii) random
anisotropy.
Today, the standard analytical description of critical behavior is given by
renormalization group results refined by resummation of the perturbation theory
series. The convergence properties of the series are unknown for most
disordered models. The main object of these lectures is to discuss the
peculiarities of the application of resummation techniques to perturbation
theory series of disordered models.Comment: Lectures given at the Second International Pamporovo Workshop on
Cooperative Phenomena in Condensed Matter (28th July - 7th August 2001,
Pamporovo, Bulgaria). 51 pages, 12 figures, 1 style files include
Viability qPCR, a new tool for Legionella risk management
Background Viability quantitative Polymerase Chain Reaction (v-qPCR) is a recent analytical approach for only detecting live microorganisms by DNA amplification-based methods This approach is based on the use of a reagent that irreversibly fixes dead cells DNA. In this study, we evaluate the utility of v-qPCR versus culture method for Legionellosis risk management. Methods The present study was performed using 116 real samples. Water samples were simultaneously analysed by culture, v-qPCR and qPCR methods. Results were compared by means of a non-parametric test. Results In 11.6% of samples using both methods (culture method and v-qPCR) results were positive, in 50.0% of samples both methods gave rise to negative results. As expected, equivalence between methods was not observed in all cases, as in 32.1% of samples positive results were obtained by v-qPCR and all of them gave rise to negative results by culture. Only in 6.3% of samples, with very low Legionella levels, was culture positive and v-qPCR negative. In 3.5% of samples, overgrowth of other bacteria did not allow performing the culture. When comparing both methods, significant differences between culture and v-qPCR were in the samples belonging to the cooling towers-evaporative condensers group. The v-qPCR method detected greater presence and obtained higher concentrations of Legionella spp. (p < 0.001). Otherwise, no significant differences between methods were found in the rest of the groups. Conclusions The v-qPCR method can be used as a quick tool to evaluate Legionellosis risk, especially in cooling towers-evaporative condensers, where this technique can detect higher levels than culture. The combined interpretation of PCR results along with the ratio of live cells is proposed as a tool for understanding the sample context and estimating the Legionellosis risk potential according to 4 levels of hierarchy
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