18,255 research outputs found
Anticipating the response of excitable systems driven by random forcing
We study the regime of anticipated synchronization in unidirectionally
coupled model neurons subject to a common external aperiodic forcing that makes
their behavior unpredictable. We show numerically and by implementation in
analog hardware electronic circuits that, under appropriate coupling
conditions, the pulses fired by the slave neuron anticipate (i.e. predict) the
pulses fired by the master neuron. This anticipated synchronization occurs even
when the common external forcing is white noise.Comment: 12 pages (RevTex format
Mechanical, Electrical, and Magnetic Properties of Ni Nanocontacts
The dynamic deformation upon stretching of Ni nanowires as those formed with
mechanically controllable break junctions or with a scanning tunneling
microscope is studied both experimentally and theoretically. Molecular dynamics
simulations of the breaking process are performed. In addition, and in order to
compare with experiments, we also compute the transport properties in the last
stages before failure using the first-principles implementation of Landauer's
formalism included in our transport package ALACANT.Comment: 5 pages, 6 figure
Formation of a Metallic Contact: Jump to Contact Revisited
The transition from tunneling to metallic contact between two surfaces does
not always involve a jump, but can be smooth. We have observed that the
configuration and material composition of the electrodes before contact largely
determines the presence or absence of a jump. Moreover, when jumps are found
preferential values of conductance have been identified. Through combination of
experiments, molecular dynamics, and first-principles transport calculations
these conductance values are identified with atomic contacts of either
monomers, dimers or double-bond contacts.Comment: 4 pages, 5 figure
Theoretical study of finite temperature spectroscopy in van der Waals clusters. I. Probing phase changes in CaAr_n
The photoabsorption spectra of calcium-doped argon clusters CaAr_n are
investigated at thermal equilibrium using a variety of theoretical and
numerical tools. The influence of temperature on the absorption spectra is
estimated using the quantum superposition method for a variety of cluster sizes
in the range 6<=n<=146. At the harmonic level of approximation, the absorption
intensity is calculated through an extension of the Gaussian theory by Wadi and
Pollak [J. Chem. Phys. vol 110, 11890 (1999)]. This theory is tested on simple,
few-atom systems in both the classical and quantum regimes for which highly
accurate Monte Carlo data can be obtained. By incorporating quantum anharmonic
corrections to the partition functions and respective weights of the isomers,
we show that the superposition method can correctly describe the
finite-temperature spectroscopic properties of CaAr_n systems. The use of the
absorption spectrum as a possible probe of isomerization or phase changes in
the argon cluster is discussed at the light of finite-size effects.Comment: 17 pages, 9 figure
Anticipated synchronization: a metaphorical linear view
We study the regime of anticipated synchronization recently described on a
number of dynamical systems including chaotic and noisy ones. We use simple
linear caricatures to show the minimal setups able to reproduce the basic facts
described.Comment: 7 pages,5 figure
Multi-centre retrospective study of long-term outcomes following traumatic elbow luxation in 37 dogs
Numerical Implementation of Gradient Algorithms
A numerical method for computational implementation of gradient dynamical systems is presented. The method is based upon the development of geometric integration numerical methods, which aim at preserving the dynamical properties of the original ordinary differential
equation under discretization. In particular, the proposed method belongs to the class of discrete gradients methods, which substitute the gradient of the continuous equation with a discrete gradient, leading to a map that possesses the same Lyapunov function of the dynamical system,
thus preserving the qualitative properties regardless of the step size. In this work, we apply a discrete gradient method to the implementation of Hopfield neural networks. Contrary to most geometric integration
methods, the proposed algorithm can be rewritten in explicit form, which considerably improves its performance and stability. Simulation results show that the preservation of the Lyapunov function leads to an improved performance, compared to the conventional discretization.Spanish Government project no. TIN2010-16556 Junta de Andalucía project no. P08-TIC-04026 Agencia Española de Cooperación Internacional
para el Desarrollo project no. A2/038418/1
Influence of Zn excess on compositional, structural and vibrational properties of Cu2ZnSn0.5Ge0.5Se4 thin films and their effect on solar cell efficiency
This Accepted Manuscript will be available for reuse under a CC BY-NC-ND licence after 24 months of embargo periodThe effect of Zn content on compositional, structural and vibrational properties of Cu2ZnSn1-xGexSe4 (CZTGSe, x ~ 0.5) thin films is studied. Kesterite layer is deposited by co-evaporation onto 5 × 5 cm2 Mo/SLG substrate followed by a thermal treatment at maximum temperature of 480 °C, obtaining areas with different composition and morphology which are due to the sample position in the co-evaporation system and to the non-uniform temperature distribution across the substrate. Kesterite layers with higher Zn amounts are characterized by lower Cu and Ge contents; however, a uniform Ge distribution through the absorber layer is detected in all cases. The excess Zn concentration leads to the formation of ZnSe secondary phase on the surface and in the bulk of the absorber as determined by Raman spectroscopy. When higher Ge content and no ZnSe are present in the absorber layer, a compact structure is formed with larger grain size of kesterite. This effect could explain the higher Voc of the solar cell. The Zn content does not affect the bandgap energy significantly (Eg near 1.3 eV), although the observed effect of Zn excess in CZTGSe results in a decreased device performance from 6.4 to 4.2%. This investigation reveals the importance of the control of the off-stoichiometric CZTGSe composition during the deposition process to enhance solar cells propertiesThis work was supported by Spanish Ministry of Science, Innovation and Universities Project WINCOST (ENE2016-80788-C5-2-R) and European Project INFINITE CELL (H2020-MSCA-RISE-2017-777968). ARP also acknowledges financial support from Community of Madrid within Youth Employment Program (PEJD-2017-PRE/IND-4062). MG acknowledges the financial support from ACCIÓ-Generalitat de Catalunya within the TECNIOspring Plus fellowship (TECSPR18-1-0048
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