An augmented moment method for stochastic ensembles with delayed couplings: II. FitzHugh-Nagumo model

Dynamics of FitzHugh-Nagumo (FN) neuron ensembles with time-delayed couplings subject to white noises, has been studied by using both direct simulations and a semi-analytical augmented moment method (AMM) which has been proposed in a recent paper [H. Hasegawa, E-print: cond-mat/0311021]. For $N$-unit FN neuron ensembles, AMM transforms original $2N$-dimensional {\it stochastic} delay differential equations (SDDEs) to infinite-dimensional {\it deterministic} DEs for means and correlation functions of local and global variables. Infinite-order recursive DEs are terminated at the finite level $m$ in the level-$m$ AMM (AMM$m$), yielding $8(m+1)$-dimensional deterministic DEs. When a single spike is applied, the oscillation may be induced if parameters of coupling strength, delay, noise intensity and/or ensemble size are appropriate. Effects of these parameters on the emergence of the oscillation and on the synchronization in FN neuron ensembles have been studied. The synchronization shows the {\it fluctuation-induced} enhancement at the transition between non-oscillating and oscillating states. Results calculated by AMM5 are in fairly good agreement with those obtained by direct simulations.Comment: 15 pages, 3 figures; changed the title with correcting typos, accepted in Phys. Rev. E with some change

An augmented moment method for stochastic ensembles with delayed couplings: I. Langevin model

By employing a semi-analytical dynamical mean-field approximation theory previously proposed by the author [H. Hasegawa, Phys. Rev. E {\bf 67}, 041903 (2003)], we have developed an augmented moment method (AMM) in order to discuss dynamics of an $N$-unit ensemble described by linear and nonlinear Langevin equations with delays. In AMM, original $N$-dimensional {\it stochastic} delay differential equations (SDDEs) are transformed to infinite-dimensional {\it deterministic} DEs for means and correlations of local as well as global variables. Infinite-order DEs arising from the non-Markovian property of SDDE, are terminated at the finite level $m$ in the level-$m$ AMM (AMM$m$), which yields $(3+m)$-dimensional deterministic DEs. Model calculations have been made for linear and nonlinear Langevin models. The stationary solution of AMM for the linear Langevin model with N=1 is nicely compared to the exact result. The synchronization induced by an applied single spike is shown to be enhanced in the nonlinear Langevin ensemble with model parameters locating at the transition between oscillating and non-oscillating states. Results calculated by AMM6 are in good agreement with those obtained by direct simulations.Comment: 18 pages, 3 figures, changed the title with re-arranged figures, accepted in Phys. Rev. E with some change

ANAEROBIC POWER AND DEVELOPMENT OF FATIGUE IN FREESTYLE SPRINT SWIMMING

INTRODUCTION -In literature there are conflicting views on the relationship between anaerobic swimming and dry-land power (CostiI1/1983; Höltke! 1992; Johnson!1993; Tanaka/1993). In 100 m -freestyle swimming the highest speed are reached at the beginning. The values vary between 95 and 100 % of individual maximum in the first and between 85 and 90 % in the last quarter. Differences in the final time are results of lower speed at beginning and! or of higher decrease in swim velocity during the race (Küehler!1993). This decrease of velocity is an expression of muscle fatigue. The results of competition analyses of top athletes correspond to results of dry-land power tests on' the biokinetic swim bench. METHODS -Members of the German national swim team were tested on the biokinetic swim bench. 22 athletes performed a test lasting one minute on level 5. The work per repetition was represented in percent of the personal maximum. Additionally for some athletes the 5 m -and 100 m freestyle sprint speed were analysed. The swimming speed in 100 m -sprint was expressed in percent from the maximum in 50 m -sprint. RESULTS -Summary shows table 1. Athletes a, c and E show similar intensities in swim race and dry-land test. Athlete 9 performed only low intensities at the beginning in both tests. This is not typical for sprinters. Decrease in intensity in dry-land power test characterises the level of anaerobic glycol tie metabolism. In this respect individual differences between top athletes were found. We observed variations in intensity at tests on the biokinetic swim bench during the year too. This is an expression of variations of metabolic muscle properties. Dryland testing on a swim bench can help the athlete to know more about metabolic properties of his "swim" muscles in the whole season. For a comparison of swimming and dry-land power it is necessary to use relative values in form of intensity of the maximum. REFERENCES -Costill, D. L, Douglas, S. K., Holdren, A. & Hargreaves, M. (1983). Sprint speed vs. swimming power. Swimming Technique, Val 20, 20-22. Höltke. V. (1992). Zur Effektivität von dynamischem Maximalkraft• und dynamischem Kraftausdauertraining bei Leistungsschwimmem der nationalen Spitzenklasse: ein Trainings experiment im Hochleistungssport. Erlen ee: SFT-Ver1ag. Johnson, R. E., Sharp, R. L. & Hedrick, C. E. (1993). Relatlonship of swimming power and dryland power to sprint freestyle performance: a multiple regression approach. J. Swimming Research, Val 0, 10-14 KOchler, J., L opold, H. & Leopold, W. (1993) Vergleichende Betrachtungen der Gestallun der Wettkämpfe der 50 m-und 100 mSchwimmdisziplinen der Besten der Olympischen Spiele 1992 und deutscher Spitzenschwimmer. IAT Leipzig. 28 S. Tanaka, H., Costill, D. L., Thomas, R., Fink, W. J. & Widrick, J J. (1993). Dry-land re• sistance training for competitive swimming. Med. Sei. Exer ., Vol. 25. No. 8, 952-959

New beam for the CERN fixed target heavy ion programme

The physicists of the CERN heavy ion community (SPS fixed target physics) have requested lighter ions than the traditional lead ions, to scale their results and to check their theories. Studies have been carried out to investigate the behaviour of the ECR4 for the production of an indium beam. Stability problems and the low melting point of indium required some modifications to the oven power control system which will also benefit normal lead ion production. Present results of the source behaviour and the ion beam characteristics will be presented

Ion-stimulated gas desorption yields and their dependence on the surface preparation of stainless steel

Ion-induced gas desorption yields were investigated for 4.2 MeV/u lead ions incident on 316 LN stainless steel surfaces. Focussed on a possible application for the Low Energy Ion Ring (LEIR) vacuum system, the influence of surface treatments like chemical etching, electropolishing and gold-coating on the desorption yields was studied with accelerator-type vacuum chambers. The surface composition of similar prepared samples was investigated with X-ray Photoemission Spectroscopy (XPS). Desorption yields for H2, CH4, CO, Ar and CO2, which are of fundamental interest for LEIR and future accelerator applications, are reported as a function of impact angle, ion dose and charge state (+27, +53) of the lead ion beam

Towards Digital Social Infrastructure? Digital Neighborly Connectedness as a Social Resource

Social infrastructure is made up of various material as well as non-material goods, ranging from venues for leisure such as movie theaters to indispensable everyday commodities, like sidewalks and streets. This is true both for urban and rural areas. However, the increasing emergence of digital aspects of social infrastructure has seemed to go unnoticed to some extent, with research specifically focusing on these digital aspects of social infrastructure being scarce at best—even though digitalization is currently a major emerging meta-development worldwide. The goal of our contribution is therefore to investigate the digital sphere and integrate it into the concept of social infrastructure. Drawing on descriptive findings from a multi-sited, community-based survey of residents in four rural areas in Germany (N = 413) as well as from 40 qualitative interviews, we present an integrative and expanded conceptualization of what we term a tangible digital social infrastructure. To do so, we examine digital neighborly connectedness as a social resource during the Covid-19 pandemic as a case study. We argue that digital neighborly connectedness served as both an integral part of on-site social infrastructure and as a social resource, especially during pandemic times. We discuss our results in light of current research on social infrastructure, with a specific focus on the scope of what counts as social infrastructure, as well as current discourse on social infrastructure in rural areas

Sequential localization of a complex electron fluid

Complex and correlated quantum systems with promise for new functionality often involve entwined electronic degrees of freedom. In such materials, highly unusual properties emerge and could be the result of electron localization. Here, a cubic heavy fermion metal governed by spins and orbitals is chosen as a model system for this physics. Its properties are found to originate from surprisingly simple low-energy behavior, with two distinct localization transitions driven by a single degree of freedom at a time. This result is unexpected, but we are able to understand it by advancing the notion of sequential destruction of an SU(4) spin-orbital-coupled Kondo entanglement. Our results implicate electron localization as a unified framework for strongly correlated materials and suggest ways to exploit multiple degrees of freedom for quantum engineering.Comment: 21 pages, 4 figures (preprint format