Transport in a Levy ratchet: Group velocity and distribution spread

We consider the motion of an overdamped particle in a periodic potential lacking spatial symmetry under the influence of symmetric L\'evy noise, being a minimal setup for a ``L\'evy ratchet.'' Due to the non-thermal character of the L\'evy noise, the particle exhibits a motion with a preferred direction even in the absence of whatever additional time-dependent forces. The examination of the L\'evy ratchet has to be based on the characteristics of directionality which are different from typically used measures like mean current and the dispersion of particles' positions, since these get inappropriate when the moments of the noise diverge. To overcome this problem, we discuss robust measures of directionality of transport like the position of the median of the particles displacements' distribution characterizing the group velocity, and the interquantile distance giving the measure of the distributions' width. Moreover, we analyze the behavior of splitting probabilities for leaving an interval of a given length unveiling qualitative differences between the noises with L\'evy indices below and above unity. Finally, we inspect the problem of the first escape from an interval of given length revealing independence of exit times on the structure of the potential.Comment: 9 pages, 12 figure

Stationary states in Langevin dynamics under asymmetric L\'evy noises

Properties of systems driven by white non-Gaussian noises can be very different from these systems driven by the white Gaussian noise. We investigate stationary probability densities for systems driven by $\alpha$-stable L\'evy type noises, which provide natural extension to the Gaussian noise having however a new property mainly a possibility of being asymmetric. Stationary probability densities are examined for a particle moving in parabolic, quartic and in generic double well potential models subjected to the action of $\alpha$-stable noises. Relevant solutions are constructed by methods of stochastic dynamics. In situations where analytical results are known they are compared with numerical results. Furthermore, the problem of estimation of the parameters of stationary densities is investigated.Comment: 9 pages, 9 figures, 3 table

Bimodality and hysteresis in systems driven by confined L\'evy flights

We demonstrate occurrence of bimodality and dynamical hysteresis in a system describing an overdamped quartic oscillator perturbed by additive white and asymmetric L\'evy noise. Investigated estimators of the stationary probability density profiles display not only a turnover from unimodal to bimodal character but also a change in a relative stability of stationary states that depends on the asymmetry parameter of the underlying noise term. When varying the asymmetry parameter cyclically, the system exhibits a hysteresis in the occupation of a chosen stationary state.Comment: 4 pages, 5 figures, 30 reference

Stationary states for underdamped anharmonic oscillators driven by Cauchy noise

Using methods of stochastic dynamics, we have studied stationary states in the underdamped anharmonic stochastic oscillators driven by Cauchy noise. Shape of stationary states depend both on the potential type and the damping. If the damping is strong enough, for potential wells which in the overdamped regime produce multimodal stationary states, stationary states in the underdamped regime can be multimodal with the same number of modes like in the overdamped regime. For the parabolic potential, the stationary density is always unimodal and it is given by the two dimensional $\alpha$-stable density. For the mixture of quartic and parabolic single-well potentials the stationary density can be bimodal. Nevertheless, the parabolic addition, which is strong enough, can destroy bimodlity of the stationary state.Comment: 9 page

Paradoxical diffusion: Discriminating between normal and anomalous random walks

Commonly, normal diffusive behavior is characterized by a linear dependence of the second central moment on time, $\propto t$, while anomalous behavior is expected to show a different time dependence, $\propto t^{\delta}$ with $\delta 1$ for superdiffusive motions. Here we demonstrate that this kind of qualification, if applied straightforwardly, may be misleading: There are anomalous transport motions revealing perfectly "normal" diffusive character ($\propto t$), yet being non-Markov and non-Gaussian in nature. We use recently developed framework \cite[Phys. Rev. E \textbf{75}, 056702 (2007)]{magdziarz2007b} of Monte Carlo simulations which incorporates anomalous diffusion statistics in time and space and creates trajectories of such an extended random walk. For special choice of stability indices describing statistics of waiting times and jump lengths, the ensemble analysis of paradoxical diffusion is shown to hide temporal memory effects which can be properly detected only by examination of formal criteria of Markovianity (fulfillment of the Chapman-Kolmogorov equation).Comment: 8 pages, 7 figure

Dynamic Thermal Analysis of a Power Amplifier

This paper presents dynamic thermal analyses of a power amplifier. All the investigations are based on the transient junction temperature measurements performed during the circuit cooling process. The presented results include the cooling curves, the structure functions, the thermal time constant distribution and the Nyquist plot of the thermal impedance. The experiments carried out demonstrated the influence of the contact resistance and the position of the entire cooling assembly on the obtained results.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Romańskie napisy haftowane na jedwabnych pasmach z grobu nr 24 w kolegiacie w Kruszwicy

The article is a philological analysis and an initial epigraphic analysis of inscriptions embroidered on silk fabric found in 1960 in tomb no. 24 in the Romanesque collegiate church in Kruszwica. The preserved three pieces of silk (two are of identical length and one is a fragment) originally constituted probably a single object with the inscriptions arranged most likely into a sequence with a cohesive meaning (on the function of this object cf. articles by E. Dąbrowska and M. Cybulska and E. Orlińska-Mianowska in this volume). A philological analysis of the inscriptions preserved on the longer pieces of fabric makes it possible to ascertain that they comprise rhythmic-versification units. Inscription no.1 is in so-called rich hexameter, while inscription no. 2 is an incipit of a hymn to The Holy Spirit, attributed to Notker the Stammerer (Balbulus) from St. Gallen. The fragmentary inscription no. 3., barely several letters long, poses the greatest interpretation problem owing to the state of its preservation, which (according to B. Kürbis, who witnessed its discovery) could have been quite different than its present-day version. For this reason it seems possible to decipher the fragment in question in two ways, and the place which inscription no. 3. could have originally held in the sequence of inscriptions remains of a closely connected question. An epigraphic analysis of the inscriptions written in Romanesque capitals with elements of the uncial indicates their imitative execution (i.a. an error in the word: spiritus in inscription no. 2), albeit with the use of rather sophisticated lettering (the letter P). The shapes of the signs permit a restricted establishment of the time of the origin of the inscriptions, since some occur in codex writing and epigraphic much earlier than could be the date of the strips of fabric from Kruszwica (A in: gracia from inscription no. 2). By referring to a typology of Romanesque epigraphic writing presented by Rudolf M. Kloos, codex and epigraphic comparative material (which should be considerably expanded) allows us to propose an approximate time of the origin of the inscriptions as not later than the second half or the end of the twelfth century, especially if the object to which the discussed inscriptions belong had been imported from the West.Zarys treści: Artykuł stanowi analizę filologiczną i wstępną analizę epigraficzną wymienionych w tytule inskrypcji celem określenia możliwego czasu ich powstania na podstawie kryteriów epigraficznych.Abstract: This article is a philological and initial epigraphic analysis of the titular inscriptions aimed at defining the possible time of their origin upon the basis of epigraphic criteria

EFFECT OF MODE OF LOAD CARRIAGE ON POSTURAL SWAY

People commonly carry external loads for sport and recreational purposes; recently the safety of such practice has come into question. The purpose of this study was to evaluate balance under different load carriage conditions. Fifteen college-age individuals completed three blocks of quiet standing trials: unloaded, wearing a backpack, and wearing a shoulder bag. A-P sway amplitude was greater under the backpack condition than the unloaded condition (P = 0.013); however, A-P sway amplitude did not differ between the backpack and shoulder bag condition, nor did it differ between the unloaded and shoulder bag condition. M-L sway amplitude, sway area, peak sway velocity, and stance width were not dependent on load condition. This evidence suggests a backpack and shoulder bag are equally safe means of load carriage in college-age individuals