The Orientation of the Reconnection X-line

We propose a criterion for identifying the orientation of the X-line when two regions of plasma with arbitrary densities, temperatures, and magnetic fields undergo reconnection. The X-line points in the direction that maximizes the (suitably-defined) Alfv\'en speed characterizing the reconnection outflow. For many situations a good approximation is that the X-line bisects the angle formed by the magnetic fields

Heating of solar chromosphere by electromagnetic wave absorption in a plasma slab model

The heating of solar chromospheric inter-network regions by means of the absorption of electromagnetic (EM) waves that originate from the photospheric blackbody radiation is studied in the framework of a plasma slab model. The absorption is provided by the electron-neutral collisions in which electrons oscillate in the EM wave field and electron-neutral collisions damp the EM wave. Given the uncertain nature of the collision cross-section due to the plasma micro-turbulence, it is shown that for plausible physical parameters, the heating flux produced by the absorption of EM waves in the chromosphere is between $20 - 45$ % of the chromospheric radiative loss flux requirement. It is also established that there is an optimal value for the collision cross-section, $5 \times 10^{-18}$ m$^{2}$, that produces the maximal heating flux of 1990 W m$^{-2}$.Comment: Physics of Plasmas, in press, April 2011 issue (final printed version, typos in proofs corrected

Size and phase control of cobalt-carbide nanoparticles using OH- and Cl- anions in a polyol process

Exchange coupled cobalt–carbide nanocomposites and single-phase Co2C nanoparticles were synthesized using the polyol process. Hydroxide and chloride anions were used to controlcarbide phase and particle shape. Synthesized Co x C nanocomposites exhibited average diameters around 300 nm. Co x C nanocomposites synthesized at 0.25 M [OH−] and [Cl−] formed clusters of capped nanorods, whereas synthesis at 0.37 M [OH−] and [Cl−] produced clusters of long blade-like particles. For single-phase Co2C, an [OH−] and [Cl−] of 0.71 M was used and produced clusters of ellipsoidal grains. The Co x C nanocomposites comprised of capped nanorods possessed a BH max of 1.65 MGOe with a magnetic saturation and coercivity values of 38 emu/g and 2.4 kOe, respectively. Co2C possessed a saturation magnetization of 16 emu/g and coercivity of 1.3 kOe

Fast ignition of fusion targets by laser-driven electrons

We present hybrid PIC simulations of fast electron transport and energy deposition in pre-compressed fusion targets, taking full account of collective magnetic effects and the hydrodynamic response of the background plasma. Results on actual ignition of an imploded fast ignition configuration are shown accounting for the increased beam divergence found in recent experiments [J.S. Green et al., Phys. Rev. Lett. 100, 015003 (2008)] and the reduction of the electron kinetic energy due to profile steepening predicted by advanced PIC simulations [B. Chrisman et al. Phys. Plasmas 15, 056309 (2008)]. Target ignition is studied as a function of injected electron energy, distance of cone-tip to dense core, initial divergence and kinetic energy of the relativistic electron beam. We found that beam collimation reduces substantially the ignition energies of the cone-guided fuel configuration assumed here.Comment: 15 pages, 9 figures. accepted for publication in Plasma Physics and Controlled Fusio

Synthesis of high magnetization FeCo alloys prepared by a modified polyol process

High magnetization, soft ferromagnetic FeCo alloy nanoparticles were synthesized at various Fe to Co ratios using a modified polyol process. Transmission electron microscopy images revealed that Fe-rich particles had a cubic shape with a mean particle size of 100 nm, while Co-rich particles had a spherical shape. A maximum saturation magnetization of 212 emu/g was recorded for both Fe60Co40 and Fe75Co25 particles. X-ray diffraction scans at room temperatureof synthesized particles were characteristic of body-centered-cubic single-phase FeCo. Variabletemperature x-ray diffraction scans under N2 gas revealed an order–disorder transition at 600 °C and a transition to a face-centered-cubic crystal structure at 1000 °C

Enhancement of Solid Fuel Combustion in a Hybrid Rocket Motor Using Amorphous Ti–Al–B Nanopowder Additives

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Ageing as a price of cooperation and complexity: Self-organization of complex systems causes the ageing of constituent networks

The analysis of network topology and dynamics is increasingly used for the description of the structure, function and evolution of complex systems. Here we summarize key aspects of the evolvability and robustness of the hierarchical network-set of macromolecules, cells, organisms, and ecosystems. Listing the costs and benefits of cooperation as a necessary behaviour to build this network hierarchy, we outline the major hypothesis of the paper: the emergence of hierarchical complexity needs cooperation leading to the ageing of the constituent networks. Local cooperation in a stable environment may lead to over-optimization developing an ‘always-old’ network, which ages slowly, and dies in an apoptosis-like process. Global cooperation by exploring a rapidly changing environment may cause an occasional over-perturbation exhausting system-resources, causing rapid degradation, ageing and death of an otherwise ‘forever-young’ network in a necrosis-like process. Giving a number of examples we explain how local and global cooperation can both evoke and help successful ageing. Finally, we show how various forms of cooperation and consequent ageing emerge as key elements in all major steps of evolution from the formation of protocells to the establishment of the globalized, modern human society. Thus, ageing emerges as a price of complexity, which is going hand-in-hand with cooperation enhancing each other in a successful community

Resolution of the equatorial spread F problem: Revisited

An overview of recent advances made in understanding the phenomenon of equatorial spread F (ESF) is presented and a discussion of unresolved issues that need to be addressed. The focus is on research that has occurred in the last decade. The topics include satellite observations, theory, and modeling. The suggested areas that require further exploration are a unified theory of turbulence extending from 100 s m to 10 s cm, the impact of geomagnetic storms on the development of equatorial spread F, the need for accurate thermospheric wind measurements and models, and identifying the underlying physics of ESF in the post-midnight sector during solar minimum