803 research outputs found
Sudden transition between classical and quantum decoherence
We study the dynamics of quantum and classical correlations in the presence
of nondissipative decoherence. We discover a class of initial states for which
the quantum correlations, quantified by the quantum discord, are not destroyed
by decoherence for times t < \bar{t}. In this initial time interval classical
correlations decay. For t > \bar{t}, on the other hand, classical correlations
do not change in time and only quantum correlations are lost due to the
interaction with the environment. Therefore, at the transition time \bar{t} the
open system dynamics exhibits a sudden transition from classical to quantum
decoherence regime.Comment: version accepted for publication by Physical Review Letter
Inequality in Healthcare Utilization in Italy: How Important Are Barriers to Access?
With the ageing population, equitable access to medical care has proven to be paramount for the effective and efficient management of all diseases. Healthcare access can be hindered by cost barriers for drugs or exams, long waiting lists or difficult access to the place where the needed healthcare service is provided. The aim of this paper is to investigate whether the probability of facing one of these barriers varies among individuals with different socio-economic status and care needs, controlling for geographical variability. Methods. The sample for this study included 9629 interviews with Italian individuals, aged 15 and over, from the second wave (2015) of the European Health Interview Survey, which was conducted in all EU Member States. To model barriers to healthcare, two-level variance components of logistic regression models with a nested structure given by the four Italian macro-areas were considered. Results. Of the barriers considered in this study, only two were found to be significantly associated with healthcare utilization. Specifically, they are long waiting lists for specialist service accessibility (adjOR = 1.20, 95% CI (1.07; 1.35)) and very expensive exams for dental visit accessibility (adjOR = 0.84, 95% CI (0.73; 0.96)). Another important result was the evidence of an increasing north–south gradient for all of the considered bar-riers. Conclusion. In Italy, healthcare access is generally guaranteed for all of the services, except for specialist and dental visits that face a waiting time and financial barriers. However, barriers to healthcare were differentiated by income and sex. The north–south gradient for healthcare utilization could be explained through the existing differences in organizational characteristics of the several regional healthcare services throughout Italy
Protecting entanglement via the quantum Zeno effect
We study the exact entanglement dynamics of two atoms in a lossy resonator.
Besides discussing the steady-state entanglement, we show that in the strong
coupling regime the system-reservoir correlations induce entanglement revivals
and oscillations and propose a strategy to fight against the deterioration of
the entanglement using the quantum Zeno effect.Comment: 4 pages, 3 figure
Statistical advances in epidemiology and public health
The key role of statistical modeling in epidemiology and public health is unquestionable [...]
Entanglement Trapping in Structured Environments
The entanglement dynamics of two independent qubits each embedded in a
structured environment under conditions of inhibition of spontaneous emission
is analyzed, showing entanglement trapping. We demonstrate that entanglement
trapping can be used efficiently to prevent entanglement sudden death. For the
case of realistic photonic band-gap materials, we show that high values of
entanglement trapping can be achieved. This result is of both fundamental and
applicative interest since it provides a physical situation where the
entanglement can be preserved and manipulated, e.g. by Stark-shifting the qubit
transition frequency outside and inside the gap.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. on Friday 16 May
200
Tripartite entanglement dynamics in a system of strongly driven qubits
We study the dynamics of tripartite entanglement in a system of two strongly
driven qubits individually coupled to a dissipative cavity. We aim at
explanation of the previously noted entanglement revival between two qubits in
this system. We show that the periods of entanglement loss correspond to the
strong tripartite entanglement between the qubits and the cavity and the
recovery has to do with an inverse process. We demonstrate that the overall
process of qubit-qubit entanglement loss is due to the second order coupling to
the external continuum which explains the exp[-g^2 t/2+g^2 k t^3/6+\cdot] for
of the entanglement loss reported previously.Comment: 9 pages, 5 figure
Sudden death and sudden birth of entanglement in common structured reservoirs
We study the exact entanglement dynamics of two qubits in a common structured
reservoir. We demonstrate that, for certain classes of entangled states,
entanglement sudden death occurs, while for certain initially factorized
states, entanglement sudden birth takes place. The backaction of the
non-Markovian reservoir is responsible for revivals of entanglement after
sudden death has occurred, and also for periods of disentanglement following
entanglement sudden birth.Comment: 4 pages, 2 figure
Phenomenological memory-kernel master equations and time-dependent Markovian processes
Do phenomenological master equations with memory kernel always describe a
non-Markovian quantum dynamics characterized by reverse flow of information? Is
the integration over the past states of the system an unmistakable signature of
non-Markovianity? We show by a counterexample that this is not always the case.
We consider two commonly used phenomenological integro-differential master
equations describing the dynamics of a spin 1/2 in a thermal bath. By using a
recently introduced measure to quantify non-Markovianity [H.-P. Breuer, E.-M.
Laine, and J. Piilo, Phys. Rev. Lett. 103, 210401 (2009)] we demonstrate that
as far as the equations retain their physical sense, the key feature of
non-Markovian behavior does not appear in the considered memory kernel master
equations. Namely, there is no reverse flow of information from the environment
to the open system. Therefore, the assumption that the integration over a
memory kernel always leads to a non-Markovian dynamics turns out to be
vulnerable to phenomenological approximations. Instead, the considered
phenomenological equations are able to describe time-dependent and
uni-directional information flow from the system to the reservoir associated to
time-dependent Markovian processes.Comment: 5 pages, no figure
Slow pyrolysis as a method for biochar production from carob waste: Process investigation and products’ characterization
The zero-waste city challenge of the modern society is inevitably addressed to the development of model’s waste-to-energy. In this work, carob waste, largely used in the agro-industrial sector for sugar extraction or locust beangum (LBG) production, is considered as feedstock for the slow pyrolysis process. According to the Food and Agriculture Organization of the United Nations (FAO), in 2012, the world production of carobs was ca. 160,000 tons, mainly concentrated in the Mediterranean area (Spain, Italy, Morocco, Portugal, and Greece). To evaluate the biomass composition, at first, the carob waste was subjected to thermo-gravimetric analysis. The high content of fixed carbon suggests that carobs are a plausible candidate for pyrolysis conversion to biochar particles. The thermal degradation of the carob waste proceeds by four different steps related to the water and volatile substances’ removal, degradation of hemicellulose, lignin and cellulose degradation, and lignin decomposition. Considering this, the slow pyrolysis was carried out at three different temperatures, specifically, at 280, 340, and 400◦C, and the obtained products were characterized. Varying the processing temperature, the proportion of individual products’ changes with a reduction in the solid phase and an increase in liquid and gas phases, with an increase in the pyrolysis temperature. The obtained results suggest that carob waste can be considered a suitable feedstock for biochar production, rather than for fuels’ recovery
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