3,267 research outputs found
Deterministic constant-temperature dynamics for dissipative quantum systems
A novel method is introduced in order to treat the dissipative dynamics of
quantum systems interacting with a bath of classical degrees of freedom. The
method is based upon an extension of the Nos\`e-Hoover chain (constant
temperature) dynamics to quantum-classical systems. Both adiabatic and
nonadiabatic numerical calculations on the relaxation dynamics of the
spin-boson model show that the quantum-classical Nos\`e-Hoover chain dynamics
represents the thermal noise of the bath in an accurate and simple way.
Numerical comparisons, both with the constant energy calculation and with the
quantum-classical Brownian motion treatment of the bath, show that the
quantum-classical Nos\`e-Hoover Chain dynamics can be used to introduce
dissipation in the evolution of a quantum subsystem even with just one degree
of freedom for the bath. The algorithm can be computationally advantageous in
modeling, within computer simulation, the dynamics of a quantum subsystem
interacting with complex molecular environments.Comment: Revised versio
Selection and characterization of indigenous hydrocarbon-degrading bacteria from tourist ports in the Mediterranean Sea Basin
Quantifying cognitive-motor interference in virtual reality training after stroke: the role of interfaces
Globally, stroke is the second leading cause of death above the age of 60 years, with the actual
number of strokes to increase because of the ageing population. Stroke results into chronic
conditions, loss of independence, affecting both the families of stroke survivors but also public
health systems. Virtual Reality (VR) for rehabilitation is considered a novel and effective low-cost
approach to re-train motor and cognitive function through strictly defined training tasks in a safe
simulated environment. However, little is known about how the choice of VR interfacing
technology affects motor and cognitive performance, or what the most cost-effective rehabilitation
approach for patients with different prognostics is. In this paper we assessed the effect of four
different interfaces in the training of the motor and cognitive domains within a VR
neurorehabilitation task. In this study we have evaluated the effect of training using 2-dimensional
and 3-dimensional as well as traditional and natural user interfaces with both stroke survivors and
healthy participants. Results indicate that 3-dimensional interfaces contribute towards better
results in the motor domain at the cost of lower performance in the cognitive domain, suggesting
the use 2-dimensional natural user interfaces as a trade-off. Our results provide useful pointers for
future directions towards a cost-effective and meaningful interaction in virtual rehabilitation tasks
in both motor and cognitive domains.info:eu-repo/semantics/publishedVersio
Molecular Structures in T=1 states of 10B
Multi-center (molecular) structures can play an important role in light
nuclei. The highly deformed rotational band in 10Be with band head at 6.179 MeV
has been observed recently and suggested to have an exotic alpha:2n:alpha
configuration. A search for states with alpha:pn:alpha two-center molecular
configurations in 10B that are analogous to the states with alpha:2n:alpha
structure in 10Be has been performed. The T=1 isobaric analog states in 10B
were studied in the excitation energy range of E=8.7-12.1 MeV using the
reaction 1H(9Be,alpha)6Li*(T=1, 0+, 3.56 MeV). An R-matrix analysis was used to
extract parameters for the states observed in the (p,alpha) excitation
function. Five T=1 states in 10B have been identified. The known 2+ and 3-
states at 8.9 MeV have been observed and their partial widths have been
measured. The spin-parities and partial widths for three higher lying states
were determined. Our data support theoretical predictions that the 2+ state at
8.9 MeV (isobaric analog of the 7.54 MeV state in 10Be) is a highly clustered
state and can be identified as a member of the alpha:np:alpha rotational band.
The next member of this band, the 4+ state, has not been found. A very broad 0+
state at 11 MeV that corresponds to pure alpha+6Li(0+,T=1) configuration is
suggested and it might be related to similar structures found in 12C, 18O and
20Ne.Comment: 10 pages, 10 figures, accepted in Physical Review
Secrecy extraction from no-signalling correlations
Quantum cryptography shows that one can guarantee the secrecy of correlation
on the sole basis of the laws of physics, that is without limiting the
computational power of the eavesdropper. The usual security proofs suppose that
the authorized partners, Alice and Bob, have a perfect knowledge and control of
their quantum systems and devices; for instance, they must be sure that the
logical bits have been encoded in true qubits, and not in higher-dimensional
systems. In this paper, we present an approach that circumvents this strong
assumption. We define protocols, both for the case of bits and for generic
-dimensional outcomes, in which the security is guaranteed by the very
structure of the Alice-Bob correlations, under the no-signalling condition. The
idea is that, if the correlations cannot be produced by shared randomness, then
Eve has poor knowledge of Alice's and Bob's symbols. The present study assumes,
on the one hand that the eavesdropper Eve performs only individual attacks
(this is a limitation to be removed in further work), on the other hand that
Eve can distribute any correlation compatible with the no-signalling condition
(in this sense her power is greater than what quantum physics allows). Under
these assumptions, we prove that the protocols defined here allow extracting
secrecy from noisy correlations, when these correlations violate a Bell-type
inequality by a sufficiently large amount. The region, in which secrecy
extraction is possible, extends within the region of correlations achievable by
measurements on entangled quantum states.Comment: 23 pages, 4 figure
Robustness of the European power grids under intentional attack
The power grid defines one of the most important technological networks of
our times and sustains our complex society. It has evolved for more than a
century into an extremely huge and seemingly robust and well understood system.
But it becomes extremely fragile as well, when unexpected, usually minimal,
failures turn into unknown dynamical behaviours leading, for example, to sudden
and massive blackouts. Here we explore the fragility of the European power grid
under the effect of selective node removal. A mean field analysis of fragility
against attacks is presented together with the observed patterns. Deviations
from the theoretical conditions for network percolation (and fragmentation)
under attacks are analysed and correlated with non topological reliability
measures.Comment: 7 pages, 4 figure
An integrative virtual reality cognitive-motor intervention approach in stroke rehabilitation: a pilot study
Stroke is one of the most common causes of acquired disability, leaving numerous adults with
cognitive and motor impairments, and affecting patient’s capability to live independently. In
post-stroke it is imperative to initiate a process of intensive rehabilitation and personalized
objectives to maximize functional cognitive and motor recovery. Virtual Reality (VR)
technology is being widely applied to rehabilitation of stroke, however, not in an integrative
manner. Like traditional rehabilitation, these new tools mostly focus either in the cognitive or
in the motor domain, which can take to a reduced impact in the performance of activities of
daily living, most of them dual-task. Assuming the existence of cognitive and motor recovery
interdependence, RehabNet proposes a holistic approach. Here we present a one-month long
pilot study with three stroke patients whose training was a game-like VR version of the
Toulouse-Piéron cancellation test, adapted to be performed by repetitive arm reaching
movements. A standardized motor and cognitive assessment was performed pre and post
intervention. The first results on this intervention support a holistic model for rehabilitation of
stroke patients, sustaining interdependence on cognitive and motor recovery. Furthermore, we
observed that the impact of the integrative VR approach generalizes to the performance of the
activities of daily living.info:eu-repo/semantics/publishedVersio
Measurement of the 20 and 90 keV resonances in the N reaction via THM
The reaction is of primary importance in
several astrophysical scenarios, including fluorine nucleosynthesis inside AGB
stars as well as oxygen and nitrogen isotopic ratios in meteorite grains. Thus
the indirect measurement of the low energy region of the reaction has been performed to reduce the nuclear
uncertainty on theoretical predictions. In particular the strength of the 20
and 90 keV resonances have been deduced and the change in the reaction rate
evaluated.Comment: 4 pages, 4 figures, submitted to PR
Cliques and duplication-divergence network growth
A population of complete subgraphs or cliques in a network evolving via
duplication-divergence is considered. We find that a number of cliques of each
size scales linearly with the size of the network. We also derive a clique
population distribution that is in perfect agreement with both the simulation
results and the clique statistic of the protein-protein binding network of the
fruit fly. In addition, we show that such features as fat-tail degree
distribution, various rates of average degree growth and non-averaging,
revealed recently for only the particular case of a completely asymmetric
divergence, are present in a general case of arbitrary divergence.Comment: 7 pages, 6 figure
The Trojan Horse Method application on the 10B(p,α0)7Be reaction cross section measurements
The 10 B(p,α 0 ) 7 Be reaction cross section has been measured in an wide energy range from 2.2 MeV down to 3 keV in a single experiment applying THM. Optimized experimental set-up ensured good energy resolution leading to a good separation of α 0 and α 1 contributions to the cross section coming from the 7 Be ground and first excited state, respectively
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