98,224 research outputs found
Onset of unsteady horizontal convection in rectangle tank at
The horizontal convection within a rectangle tank is numerically simulated.
The flow is found to be unsteady at high Rayleigh numbers. There is a Hopf
bifurcation of from steady solutions to periodic solutions, and the
critical Rayleigh number is obtained as for the
middle plume forcing at , which is much larger than the formerly obtained
value. Besides, the unstable perturbations are always generated from the
central jet, which implies that the onset of instability is due to velocity
shear (shear instability) other than thermally dynamics (thermal instability).
Finally, Paparella and Young's [J. Fluid Mech. 466 (2002) 205] first hypotheses
about the destabilization of the flow is numerically proved, i.e. the middle
plume forcing can lead to a destabilization of the flow.Comment: 4pages, 6 figures, extension of Chin. Phys. Lett. 2008, 25(6), in
pres
Phonon anomalies in pure and underdoped R{1-x}K{x}Fe{2}As{2} (R = Ba, Sr) investigated by Raman light scattering
We present a detailed temperature dependent Raman light scattering study of
optical phonons in Ba{1-x}K{x}Fe{2}As{2} (x ~ 0.28, superconducting Tc ~ 29 K),
Sr{1-x}K{x}Fe{2}As{2} (x ~ 0.15, Tc ~ 29 K) and non-superconducting
BaFe{2}As{2} single crystals. In all samples we observe a strong continuous
narrowing of the Raman-active Fe and As vibrations upon cooling below the
spin-density-wave transition Ts. We attribute this effect to the opening of the
spin-density-wave gap. The electron-phonon linewidths inferred from these data
greatly exceed the predictions of ab-initio density functional calculations
without spin polarization, which may imply that local magnetic moments survive
well above Ts. A first-order structural transition accompanying the
spin-density-wave transition induces discontinuous jumps in the phonon
frequencies. These anomalies are increasingly suppressed for higher potassium
concentrations. We also observe subtle phonon anomalies at the superconducting
transition temperature Tc, with a behavior qualitatively similar to that in the
cuprate superconductors.Comment: 5 pages, 6 figures, accepted versio
Effect of cadmium hyperaccumulation on antioxidative defense and proline accumulation of Solanum nigrum
Changes in cadmium (Cd) accumulation, the activity of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and the concentrations of malondialdehyde (MDA), chlorophyll and free proline in Solanum nigrum, Cd-hyperaccumulator were examined and compared with a non-hyperaccumulator, Solanum lycopersicum L. It was indicated that the root and leaf SOD, POD and CAT activities of S. nigrum were significantly higher than that of S. lycopersicum. In comparison with S. nigrum, there was a decrease in the growth and chlorophyll content, and an increase in MDA concentrations in the roots and leaves of S. lycopersicum. Although lipid peroxidation was promoted in both S. nigrum and S. lycopersicum by high Cd stress, higher increase occurred in the tissues of S. lycopersicum. The concentration of free proline in the leaves and roots of S. nigrum was higher than those in S. lycopersicum across all the Cd treatments. These results showed that the Cdhyperaccumulator, S. nigrum had a greater capacity than S. lycopersicum to adapt to oxidative stress caused by Cd.Key words: Solanum nigrum L., hyperaccumulator, antioxidative defense, proline, cadmium
Magnetization reversal through synchronization with a microwave
Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy.Comment: 4 pages, 5 figure
Zero-field magnetization reversal of two-body Stoner particles with dipolar interaction
Nanomagnetism has recently attracted explosive attention, in particular,
because of the enormous potential applications in information industry, e.g.
new harddisk technology, race-track memory[1], and logic devices[2]. Recent
technological advances[3] allow for the fabrication of single-domain magnetic
nanoparticles (Stoner particles), whose magnetization dynamics have been
extensively studied, both experimentally and theoretically, involving magnetic
fields[4-9] and/or by spin-polarized currents[10-20]. From an industrial point
of view, important issues include lowering the critical switching field ,
and achieving short reversal times. Here we predict a new technological
perspective: can be dramatically lowered (including ) by
appropriately engineering the dipole-dipole interaction (DDI) in a system of
two synchronized Stoner particles. Here, in a modified Stoner-Wohlfarth (SW)
limit, both of the above goals can be achieved. The experimental feasibility of
realizing our proposal is illustrated on the example of cobalt nanoparticles.Comment: 5 pages, 4 figure
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Determination of the Aspect-ratio Distribution of Gold Nanorods in a Colloidal Solution using UV-visible absorption spectroscopy
Knowledge of the distribution of the aspect ratios (ARs) in a chemically-synthesized colloidal solution of Gold Nano Rods (GNRs) is an important measure in determining the quality of synthesis, and consequently the performance of the GNRs generated for various applications. In this work, an algorithm has been developed based on the Bellman Principle of Optimality to readily determine the AR distribution of synthesized GNRs in colloidal solutions. This is achieved by theoretically fitting the longitudinal plasmon resonance of GNRs obtained by UV-visible spectroscopy. The AR distribution obtained from the use of the algorithm developed have shown good agreement with those theoretically generated one as well as with the previously reported results. After bench-marking, the algorithm has been applied to determine the mean and standard deviation of the AR distribution of two GNRs solutions synthesized and examined in this work. The comparison with experimentally derived results from the use of expensive Transmission Electron Microscopic images and Dynamic Light Scattering technique shows that the algorithm developed offers a fast and thus potentially cost-effective solution to determine the quality of the synthesized GNRs specifically needed for many potential applications for the advanced sensor systems
Exploring spin-orbital models with dipolar fermions in zig-zag optical lattices
Ultra-cold dipolar spinor fermions in zig-zag type optical lattices can mimic
spin-orbital models relevant in solid-state systems, as transition-metal oxides
with partially filled d-levels, with the interesting advantage of reviving the
quantum nature of orbital fluctuations. We discuss two different physical
systems in which these models may be simulated, showing that the interplay
between lattice geometry and spin-orbital quantum dynamics produces a wealth of
novel quantum phases.Comment: 4 pages + supplementary materia
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