54,754 research outputs found
Correction to the geometric phase by structured environments: the onset of non-Markovian effects
We study the geometric phase of a two-level system under the presence of a
structured environment, particularly analysing its correction with the ohmicity
parameter and the onset of non-Markovianity. We firstly examine the system
coupled to a set of harmonic oscillators and studied the decoherence factor as
function of the environment's ohmicity parameter. Secondly, we propose the
two-level system coupled to a non-equilibrium environment, and show that these
environments display non-Markovian effects for all values of the ohmicity
parameter. The geometric phase of the two-level system is therefore computed
under the presence of both types of environment. The correction to the unitary
geometric phase is analysed in both, Markovian and non-Markovian regimes. Under
Markovian environments, the correction induced on the system's phase is mainly
ruled by the coupling constant between the system and the environment, while in
the non-Markovian regime, memory effects seem to trigger a significant
correction to the unitary geometric phase. The result is significant to the
quantum information processing based on the geometric phase in quantum open
systemsComment: 7 figures. Accepted for publication in Phys. Rev. A. arXiv admin
note: text overlap with arXiv:1303.493
Decoherence in composite quantum open systems: the effectiveness of unstable degrees of freedom
The effect induced by an environment on a composite quantum system is
studied. The model considers the composite system as comprised by a subsystem A
coupled to a subsystem B which is also coupled to an external environment. We
study all possible four combinations of subsystems A and B made up with a
harmonic oscillator and an upside down oscillator. We analyzed the decoherence
suffered by subsystem A due to an effective environment composed by subsystem B
and the external reservoir. In all the cases we found that subsystem A
decoheres even though it interacts with the environment only through its sole
coupling to B. However, the effectiveness of the diffusion depends on the
unstable nature of subsystem A and B. Therefore, the role of this degree of
freedom in the effective environment is analyzed in detailComment: 20 pages, 4 figures. Version to appear in Int. J. Mod. Phys.
Fluent Logic Workflow Analyser: A Tool for The Verification of Workflow Properties
In this paper we present the design and implementation, as well as a use
case, of a tool for workflow analysis. The tool provides an assistant for the
specification of properties of a workflow model. The specification language for
property description is Fluent Linear Time Temporal Logic. Fluents provide an
adequate flexibility for capturing properties of workflows. Both the model and
the properties are encoded, in an automated way, as Labelled Transition
Systems, and the analysis is reduced to model checking.Comment: In Proceedings LAFM 2013, arXiv:1401.056
Decoherence of a solid-state qubit by different noise correlation spectra
The interaction between solid-state qubits and their environmental degrees of
freedom produces non-unitary effects like decoherence and dissipation.
Uncontrolled decoherence is one of the main obstacles that must be overcome in
quantum information processing. We study the dynamically decay of coherences in
a solid-state qubit by means of the use of a master equation. We analyse the
effects induced by thermal Ohmic environments and low-frequency 1/f noise. We
focus on the effect of longitudinal and transversal noise on the
superconducting qubit's dynamics. Our results can be used to design
experimental future setups when manipulating superconducting qubits.Comment: 14 pages, 9 figures. Version to appear in Physics Letters A. arXiv
admin note: text overlap with arXiv:0809.4716 by other author
Mortalidad y morbilidad cardiovascular
En la actualidad se producen en España más de 120.000 muertes y más de 5 millones de estancias hospitalarias por enfermedades cardiovasculares al año. Por ello, las enfermedades cardiovasculares constituyen la primera causa de muerte y hospitalización en la población española. La enfermedad isquémica del corazón es la que ocasiona un mayor número de muertes cardiovasculares (31% en total, un 39% en varones y 24% en mujeres) en España. Este fenómeno se empezó a dar en el año 1996, y se debe al mayor descenso relativo de la mortalidad cerebrovascular respecto a la coronaria, invirtiéndose el llamado patrón mediterráneo en el que predominaba la enfermedad cerebrovascular. Cabe destacar que en los varones empieza a predominar la enfermedad isquémica del corazón sobre la cerebrovascular casi diez años antes, en 1987. En las mujeres el peso que tienen las enfermedades del aparato circulatorio en la mortalidad proporcional por todas las causas es mucho más importante que en los varones, ya que en las mujeres ocasionan cerca de la mitad de las muertes (40%) mientras que en los varones sólo representa un tercio de ellas (30%). A pesar de que la tasa bruta de mortalidad cardiovascular es mayor en las mujeres (328 por 100.000) que en los varones (284 por 100.000), las tasas especÃficas por grupo de edad son mayores en los varones excepto a partir de los 84 años de edad. Del mismo modo, la mortalidad ajustada por edad por las enfermedades cardiovasculares es más alta en los varones que en las mujeres. Esto se debe al mayor riesgo cardiovascular de los varones, reflejado en las tasas especÃficas de edad, y a que la enfermedad cardiovascular es mucho más frecuente en las edades avanzadas de la vida, donde el número de mujeres es muy superior al de varones. La tasa de mortalidad cardiovascular aumenta enormemente a medida que se incrementa la edad, siendo superior a mil por 100.000 habitantes en las personas mayores de 70 años (cuando la tasa bruta para todas las edades es de 306 por 100.000 habitantes en 2001). Hay importantes diferencias geográficas en la mortalidad cardiovascular en España, presentándose los valores más altos en Canarias, y las regiones peninsulares del sur y levante. Asumiendo que una parte importante de las mismas se deben a factores ambientales, estas diferencias geográficas sugieren un importante potencial de prevención de las enfermedades cardiovasculares en España. Comparando las tasas de mortalidad ajustadas por edad de España con las de otros paÃses occidentales se observa que para el total de las enfermedades del aparato circulatorio y para la enfermedad isquémica del corazón, España tiene unas tasas relativamente más bajas; en cuanto a la mortalidad por enfermedad cerebrovascular ocupa una posición intermedia-baja. Las tasas ajustadas de mortalidad por enfermedades del aparato circulatorio han disminuido en España desde 1975. En el perÃodo 1985-1995 descendieron un 26%, con un descenso medio anual del 2,4% (2,3% en varones y 2,5% en mujeres). La mayor parte del descenso de la mortalidad cardiovascular total se debe a una disminución media anual del 3,2% en la mortalidad cerebrovascular. Por tanto, el riesgo de morir por las enfermedades del aparato circulatorio está disminuyendo en España desde mediados de los años setenta, sobre todo debido al descenso de la mortalidad cerebrovascular. Sin embargo, y debido fundamentalmente al envejecimiento de la población, el número de muertes por coronariopatÃa ha aumentado. Por ello, el impacto demográfico, sanitario y social de estas enfermedades aumentará a lo largo de las próximas décadas. Se prevé un aumento en el número de hospitalizaciones por estas enfermedades en los próximos años, como consecuencia del desarrollo tecnológico que permitirá ofrecer a los pacientes nuevos instrumentos diagnósticos y terapéuticos, de la mayor supervivencia de los pacientes con estos problemas de salud y, en menor medida, del envejecimiento de la población española
Macroscopic tunneling, decoherence and noise-induced activation
We study the effects of the environment at zero temperature on tunneling in
an open system described by a static double-well potential. We show that the
evolution of the system in an initial Schrodinger cat state, can be summarized
in terms of three main physical phenomena, namely decoherence, quantum
tunneling and noise-induced activation. Using large-scale numerical
simulations, we obtain a detailed picture of the main stages of the evolution
and of the relevant dynamical processesComment: Contribution to the Proceedings of DICE'0
Interpretable models in machine learning
The research and development on machine learning has exploded in recent years due to the revolution
of neural networks, which have become the greatest hope in the field of artificial intelligence after
the improvements in hardware performance and the availability of high amounts of data. Nevertheless,
it appears that advancements have been slowed down recently, probably because neural networks are
reaching their precision limits. Moreover, neural networks have an imperfection that has not been remarked
frequently: they are a black box in which it is not possible to understand the precision procedure
of the network. In consequence, despite their precision, they do not provide us with strong arguments
to justify their predictions. Decision trees, on the other hand, are a really interpretable model, though
little precise. The objective of the study of this project is the creation of a mixed model between neural
networks and decision trees: the deciduous decision tree. This prediction model combines the structure
of a decision tree and the predictive capacities of the neural networks, aiming at reaching a custom intermediate
point in the dichotomy between precision and interpretability. The results obtained after the
analysis of several experiments conducted to the deciduous decision tree reveal that, even with a little
loss of precision, the gain of interpretability from the decisions that are made in the tree compensates
this loss. Therefore, this new model can be a starting point to make machine learning models be more
interpretable, which can be extremely useful in a huge variety of fields, such as medicine, sociology,
meteorology, law, etc
Nationalism in Spain: Is It a Danger to National Integrity?
In recent years there has been a worldwide resurgence of ethnic nationalism as ethnic minorities have seen in this ethnic differentiation a better way to increase their political power within the states where they reside. Spain is a complex country divided into a number of contrasting regions with widely varying economic and social structures as well as different historical, political, and cultural traditions that includes different languages. This extreme complexity is related to its national diversity and also to the political and social articulation of nationalist claims within the state. This study arrives at five conclusions. First, Basque and Catalan nationalism is an example to follow by other regions in order to get a higher level of self-government. Second, the possession of a different language is the most important factor of distinctiveness. Third, the economic situation is closely related to the resurgence of peripheral nationalism. Fourth, the present political configuration, although supported by the majority of population, could be easily transformed into a federal state. Finally, peripheral nationalism does not affect the national security because of the lack of internal and external support to the nationalist movements that employ violence as the means to reach their political goals
Visibility Fringe Reduction Due to Noise-Induced Effects: Microscopic Approach to Interference Experiments
Decoherence is the main process behind the quantum to classical transition.
It is a purely quantum mechanical effect by which the system looses its ability
to exhibit coherent behavior. The recent experimental observation of
diffraction and interference patterns for large molecules raises some
interesting questions. In this context, we identify possible agents of
decoherence to take into account when modeling these experiments and study
theirs visible (or not) effects on the interference pattern. Thereby, we
present an analysis of matter wave interferometry in the presence of a dynamic
quantum environment and study how much the visibility fringe is reduced and in
which timescale the decoherence effects destroy the interference of massive
objects. Finally, we apply our results to the experimental data reported on
fullerenes and cold neutrons.Comment: 14 pages, 5 figures. Version to appear in Mod. Phys.
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