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

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 $d$-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 18O(p,α)15{}^{18}{\rm O}(p,\alpha){}^{15}N reaction via THM

The $^{18}{\rm O}(p,\alpha)^{15}{\rm N}$ 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 $^{18}{\rm O}(p,\alpha)^{15}{\rm N}$ 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