Frequency Windows of Absolute Negative Conductance in Josephson Junctions

We report on anomalous conductance in a resistively and capacitively shunted Josephson junction which is simultaneously driven by ac and dc currents. The dependence of the voltage across the junction on the frequency of the ac current shows windows of absolute negative conductance regimes, i.e. for a positive (negative) dc current, the voltage is negative (positive).Comment: 4 pages, 1 figur

Negative conductances of Josephson junctions: Voltage fluctuations and energetics

We study a resistively and capacitively shunted Josephson junction, which is driven by a combination of time-periodic and constant currents. Our investigations concern three main problems: (A) The voltage fluctuations across the junction; (B) The quality of transport expressed in terms of the P\'eclet number; (C) The efficiency of energy transduction from external currents. These issues are discussed in different parameter regimes that lead to: (i) absolute negative conductance; (ii) negative differential conductance, and (iii) normal, Ohmic-like conductance. Conditions for optimal operation of the system are studied.Comment: 7 pages, 4 figures, Presented at the "Frontiers of Quantum and Mesoscopic Thermodynamics", 28 July - 2 August 2008, Prague, Czech Republi

Absolute negative mobility induced by thermal equilibrium fluctuations

A novel transport phenomenon is identified that is induced by inertial Brownian particles which move in simple one-dimensional, symmetric periodic potentials under the influence of both a time periodic and a constant, biasing driving force. Within tailored parameter regimes, thermal equilibrium fluctuations induce the phenomenon of absolute negative mobility (ANM), which means that the particle noisily moves {\it backwards} against a small constant bias. When no thermal fluctuations act, the transport vanishes identically in these tailored regimes. There also exist parameter regimes, where ANM can occur in absence of fluctuations on grounds which are rooted solely in the complex, inertial deterministic dynamics. The experimental verification of this new transport scheme is elucidated for the archetype symmetric physical system: a convenient setup consisting of a resistively and capacitively shunted Josephson junction device.Comment: 4 pages, 3 figures. Phys. Rev. Lett. (in press

Anomalous transport in biased ac-driven Josephson junctions: Negative conductances

We investigate classical anomalous electrical transport in a driven, resistively and capacitively shunted Josephson junction device. Novel transport phenomena are identified in chaotic regimes when the junction is subjected to both, a time periodic (ac) and a constant, biasing (dc) current. The dependence of the voltage across the junction on the dc-current exhibits a rich diversity of anomalous transport characteristics: In particular, depending on the chosen parameter regime we can identify so termed absolute negative conductance around zero dc-bias, the occurrence of negative differential conductance and, after crossing a zero conductance, the emergence of a negative nonlinear conductance in the non-equilibrium response regime remote from zero dc-bias.Comment: 7 pages, 5 figure

Demon-free quantum Brownian motors

A quantum Smoluchowski equation is put forward that consistently describes thermal quantum states. In particular, it notably does not induce a violation of the second law of thermodynamics. This so modified kinetic equation is applied to study {\it analytically} directed quantum transport at strong friction in arbitrarily shaped ratchet potentials that are driven by nonthermal two-state noise. Depending on the mutual interplay of quantum tunneling and quantum reflection these quantum corrections can induce both, either a sizable enhancement or a suppression of transport. Moreover, the threshold for current reversals becomes markedly shifted due to such quantum fluctuations.Comment: 4 pages 3 figure

Brownian motors: current fluctuations and rectification efficiency

With this work we investigate an often neglected aspect of Brownian motor transport: The r\^{o}le of fluctuations of the noise-induced current and its consequences for the efficiency of rectifying noise. In doing so, we consider a Brownian inertial motor that is driven by an unbiased monochromatic, time-periodic force and thermal noise. Typically, we find that the asymptotic, time- and noise-averaged transport velocities are small, possessing rather broad velocity fluctuations. This implies a corresponding poor performance for the rectification power. However, for tailored profiles of the ratchet potential and appropriate drive parameters, we can identify a drastic enhancement of the rectification efficiency. This regime is marked by persistent, uni-directional motion of the Brownian motor with few back-turns, only. The corresponding asymmetric velocity distribution is then rather narrow, with a support that predominantly favors only one sign for the velocity.Comment: 9 pages, 4 figure

Magnetic flux in mesoscopic rings: Quantum Smoluchowski regime

Magnetic flux in mesoscopic rings under the quantum Smoluchowski regime is investigated. Quantum corrections to the dissipative current are shown to form multistable steady states and can result in statistical enhancement of the magnetic flux. The relevance of quantum correction effects is supported v ia the entropic criterion. A possible application for a qutrit architecture of quantum information is proposed.Comment: 7 pages, 2 figure

Statistics of transition times, phase diffusion and synchronization in periodically driven bistable systems

The statistics of transitions between the metastable states of a periodically driven bistable Brownian oscillator are investigated on the basis of a two-state description by means of a master equation with time-dependent rates. The results are compared with extensive numerical simulations of the Langevin equation for a sinusoidal driving force. Very good agreement is achieved both for the counting statistics of the number of transitions and the residence time distribution of the process in either state. The counting statistics corroborate in a consistent way the interpretation of stochastic resonance as a synchronisation phenomenon for a properly defined generalized Rice phase.Comment: 15 pages, 9 figure

Reliability of fluctuation-induced transport in a Maxwell-demon-type engine

We study the transport properties of an overdamped Brownian particle which is simultaneously in contact with two thermal baths. The first bath is modeled by an additive thermal noise at temperature $T_A$. The second bath is associated with a multiplicative thermal noise at temperature $T_B$. The analytical expressions for the particle velocity and diffusion constant are derived for this system, and the reliability or coherence of transport is analyzed by means of their ratio in terms of a dimensionless P\'{e}clet number. We find that the transport is not very coherent, though one can get significantly higher currents.Comment: 14 pages, 5 figure

Heart Rate Variability in Children and Adolescents with Cerebral Palsy-A Systematic Literature Review.

This is the final version. Available from MDPI via the DOI in this record. Cardiac autonomic dysfunction has been reported in patients with cerebral palsy (CP). The aim of this study was to assess the existing literature on heart rate variability (HRV) in pediatric patients with CP and a special attention was paid to the compliance of the studies with the current HRV assessment and interpretation guidelines. A systematic review was performed in PubMed, Web of Science, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases searched for English language publications from 1996 to 2019 using Medical Subject Headings (MeSH) terms "heart rate variability" and "cerebral palsy" in conjunction with additional inclusion criteria: studies limited to humans in the age range of 0-18 years and empirical investigations. Out of 47 studies, 12 were included in the review. Pediatric patients with CP presented a significantly higher resting heart rate and reduced HRV, different autonomic responses to movement stimuli compared to children with normal development, but also reduced HRV parameters in the children dependent on adult assistance for mobility compared to those generally independent. None of the included studies contained the necessary details concerning RR intervals acquisition and HRV measurements as recommended by the guidelines. Authors of HRV studies should follow the methodological guidelines and recommendations on HRV measurement, because such an approach may allow a direct comparison of their results