Continuous control of ionization wave chaos by spatially derived feedback signals

In the positive column of a neon glow discharge, two different types of ionization waves occur simultaneously. The low-dimensional chaos arising from the nonlinear interaction between the two waves is controlled by a continuous feedback technique. The control strategy is derived from the time-delayed autosynchronization method. Two spatially displaced points of observation are used to obtain the control information, using the propagation characteristics of the chaotic wave.Comment: Elsevier-Tex-File, 8 pages, 6 figures, submitted to PL

Magnetic anisotropy in hole-doped superconducting Ba 0.67K 0.33Fe 2As2 probed by polarized inelastic neutron scattering

We use polarized inelastic neutron scattering (INS) to study spin excitations of optimally hole-doped superconductor Ba$_{0.67}$K$_{0.33}$Fe$_2$As$_{2}$ ($T_c=38$ K). In the normal state, the imaginary part of the dynamic susceptibility, $\chi^{\prime\prime}(Q,\omega)$, shows magnetic anisotropy for energies below $\sim$7 meV with c-axis polarized spin excitations larger than that of the in-plane component. Upon entering into the superconducting state, previous unpolarized INS experiments have shown that spin gaps at $\sim$5 and 0.75 meV open at wave vectors $Q=(0.5,0.5,0)$ and $(0.5,0.5,1)$, respectively, with a broad neutron spin resonance at $E_r=15$ meV. Our neutron polarization analysis reveals that the large difference in spin gaps is purely due to different spin gaps in the c-axis and in-plane polarized spin excitations, resulting resonance with different energy widths for the c-axis and in-plane spin excitations. The observation of spin anisotropy in both opitmally electron and hole-doped BaFe$_2$As$_2$ is due to their proximity to the AF ordered BaFe$_2$As$_2$ where spin anisotropy exists below $T_N$.Comment: 5 pages, 4 figure

Evaluation of hybrid poplar clones under intensive cultivation for biomass production in Qu�bec

Paper presented at the 13th North American Agroforesty Conference, which was held June 19-21, 2013 in Charlottetown, Prince Edward Island, Canada.In Poppy, L., Kort, J., Schroeder, B., Pollock, T., and Soolanayakanahally, R., eds. Agroforestry: Innovations in Agriculture. Proceedings, 13th North American Agroforestry Conference, Charlottetown, Prince Edward Island, Canada, June 19-21, 2013.Three experimental plantations were established in 2012 at three sites in the Bas-Saint-Laurent and Lac-Saint-Jean regions to promote and demonstrate the short-rotation-intensive-culture (SRIC) hybrid poplar crop concept for biomass production. The general objective of this study was to evaluate already-available material for poplar plantations and new hybrid poplar clones, obtained from breeding at the Direction de la recherche forestire, for SRIC. Many performing clones from different hybrids with Populus maximowiczii, P. nigra, P. trichocarpa, P. deltoides (MxN, MxT, MxD, etc.) are already available for evaluation of their characteristics under various coppicing regimes. The plantations were established in collaboration with regional organizations involved in energy crops like Osons l'Osier and Nutrinor to compare coppicing ability and biomass yield among poplar clones. Preliminary growth results obtained after the first growing season are presented for several clones. Significant clone differences are expected in vigour, yield, and coppice regrowth after repeated rotations. Mechanical harvesting of the crop may also have a strong influence on resprouting and sustainability of the stools over repeated growth cycles.Pierre Perinet (1), Ursule Th�riault (2) and Fran�ois Tremblay (3) ; 1. Minist�re des Ressources naturelles, Direction de la recherche foresti�re, 2700, rue Einstein, Qu�bec, Canada G1P 3W8. 2. Osons l'Osier, 380, Rang 4, L'Isle-Verte, Qu�., Canada G0L 1K0. 3. Agrinova, 640, rue C�t� O., Alma (Qu�.) Canada G8B 7S8.Includes bibliographical references

Computational Complexity of Iterated Maps on the Interval (Extended Abstract)

The exact computation of orbits of discrete dynamical systems on the interval is considered. Therefore, a multiple-precision floating point approach based on error analysis is chosen and a general algorithm is presented. The correctness of the algorithm is shown and the computational complexity is analyzed. As a main result, the computational complexity measure considered here is related to the Ljapunow exponent of the dynamical system under consideration

Direct Observation of a Cross-Field Current-Carrying Plasma Rotating Around an Unstable Magnetized Plasma Column

The low-frequency instability of a magnetized plasma column and the anomalous radial plasma convection are shown to be linked with the existence of a radial cross-field current along a plasma channel rotating around the central magnetized plasma. The direct observation of the rotating plasma is obtained using an ultra-fast intensified camera. The ionizing electrons injected along the axis of the plasma column contribute to the accumulation of negative charges when the axial collector is at floating potential. The required neutrality leads to the continuous radial expulsion of energetic electrons and to the formation of a rotating plasma channel (m=1 unstable wave). This situation has previously been interpreted erroneously as a diamagnetic drift wave

Observation of a controllable PI-junction in a 3-terminal Josephson device

Recently Baselmans et al. [Nature, 397, 43 (1999)] showed that the direction of the supercurrent in a superconductor/normal/superconductor Josephson junction can be reversed by applying, perpendicularly to the supercurrent, a sufficiently large control current between two normal reservoirs. The novel behavior of their 4-terminal device (called a controllable PI-junction) arises from the nonequilibrium electron energy distribution established in the normal wire between the two superconductors. We have observed a similar supercurrent reversal in a 3-terminal device, where the control current passes from a single normal reservoir into the two superconductors. We show theoretically that this behavior, although intuitively less obvious, arises from the same nonequilibrium physics present in the 4-terminal device. Moreover, we argue that the amplitude of the PI-state critical current should be at least as large in the 3-terminal device as in a comparable 4-terminal device.Comment: 4 pages, 4 figures, to appear in Physical Review B Rapid Communication

Statistical analysis of correlations and intermittency of a turbulent rotating column in a magnetoplasma device

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)A detailed statistical analysis of density fluctuations in the cylindrical non-fusion device "Mistral" is performed. The experimental set-up is implemented in order to reach turbulent behavior in the rotating plasma column. Two different turbulent regimes are obtained corresponding to two selected sets of values for the anode potential and the biasing of the collecting plate. The first regime displays a slowly-rotating column characterized by the presence of a shear layer separating the plasma bulk from the scrape-off layer (SOL), the latter showing a strong intermittent behavior. The second regime corresponds to a weakly-rotating column in which coherence is lost in the plasma bulk and a standard diffusive process takes place in the SOL. These findings are supported by the calculation of the Hurst exponent of the turbulent signals using Wavelet-analysis techniques

PILOT: ProbabilistIc Lightweight grOup communication sysTem for Mobile Ad Hoc Networks

Providing reliable group communication is an ever recurring issue in distributed settings. In mobile ad hoc networks, this issue becomes more significant since all nodes act as peers, while the issue gets even more challenging due to highly dynamic and unpredictable topology changes. In order to overcome these difficulties, we deviate from the conventional point of view, i.e., we "fight fire with fire", by exploiting the nondeterministic nature of ad hoc networks. Inspired by the principles of gossip mechanisms and probabilistic quorum systems, we present in this paper a ProbabilistIc Lightweight grOup communication sysTem (PILOT) for ad hoc networks, a two layer system consisting of a set of protocols for reliable multicasting and data sharing in mobile ad hoc networks. The system performance, in terms of both reliability (fault tolerance) and efficiency (overhead), is predictable and controllable. We present an analysis of PILOT performance, which is used to fine tune protocol parameters to obtain the desired tradeoff between reliability and efficiency. We confirm the predictability and tunability of PILOT through simulations with ns-2

A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique

AIMS: We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg^2 of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources. METHODS: The KX method identifies quasars on the basis of their optical (R and z') to near-infrared (Ks) photometry and point-like morphology. We combine these data with optical (u*,g'r',i',z') and mid-infrared (3.6-24 micron) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars. RESULTS: Of 93 sources selected as candidate quasars by the KX method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 < z < 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies.Comment: 13 pages, 9 figures, A&A 494, p. 579-589. Replaced with published version. Fig. 9 in first astro-ph submission has been update