16,386 research outputs found
Structure of polydisperse inverse ferrofluids: Theory and computer simulation
By using theoretical analysis and molecular dynamics simulations, we
investigate the structure of colloidal crystals formed by nonmagnetic
microparticles (or magnetic holes) suspended in ferrofluids (called inverse
ferrofluids), by taking into account the effect of polydispersity in size of
the nonmagnetic microparticles. Such polydispersity often exists in real
situations. We obtain an analytical expression for the interaction energy of
monodisperse, bidisperse, and polydisperse inverse ferrofluids. Body-centered
tetragonal (bct) lattices are shown to possess the lowest energy when compared
with other sorts of lattices and thus serve as the ground state of the systems.
Also, the effect of microparticle size distributions (namely, polydispersity in
size) plays an important role in the formation of various kinds of structural
configurations. Thus, it seems possible to fabricate colloidal crystals by
choosing appropriate polydispersity in size.Comment: 22 pages, 8 figure
Magnetophoresis of nonmagnetic particles in ferrofluids
Ferrofluids containing nonmagnetic particles are called inverse ferrofluids.
On the basis of the Ewald-Kornfeld formulation and the Maxwell-Garnett theory,
we theoretically investigate the magnetophoretic force exerting on the
nonmagnetic particles in inverse ferrofluids due to the presence of a
nonuniform magnetic field, by taking into account the structural transition and
long-range interaction. We numerically demonstrate that the force can be
adjusted by choosing appropriate lattices, volume fractions, geometric shapes,
and conductivities of the nonmagnetic particles, as well as frequencies of
external magnetic fields.Comment: 24 pages, 7 figure
Level Set Dynamics and the Non-blowup of the 2D Quasi-geostrophic Equation
In this article we apply the technique proposed in Deng-Hou-Yu (Comm. PDE,
2005) to study the level set dynamics of the 2D quasi-geostrophic equation.
Under certain assumptions on the local geometric regularity of the level sets
of , we obtain global regularity results with improved growth estimate
on . We further perform numerical simulations to
study the local geometric properties of the level sets near the region of
maximum . The numerical results indicate that the
assumptions on the local geometric regularity of the level sets of in
our theorems are satisfied. Therefore these theorems provide a good explanation
of the double exponential growth of observed in this
and past numerical simulations.Comment: 25 pages, 10 figures. Corrected a few typo
A Simplified Scheme of Estimation and Cancellation of Companding Noise for Companded Multicarrier Transmission Systems
Nonlinear companding transform is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise greatly degrades the bit-error-rate (BER) performance of the companded multicarrier systems. In this paper, a simplified but effective scheme of estimation and cancellation of companding noise for the companded multicarrier transmission system is proposed. By expressing the companded signals as the summation of original signals added with a companding noise component, and subtracting this estimated companding noise from the received signals, the BER performance of the overall system can be significantly improved. Simulation results well confirm the great advantages of the proposed scheme over other conventional decompanding or no decompanding schemes under various situations
Hydrogen content in doped and undoped BaPrO3 and BaCeO3 by cold neutron prompt-gamma activation analysis
Proton uptake in undoped and Y-doped BaPrO3 has been measured by cold neutron prompt-gamma activation analysis, and compared to the proton uptake in Gd-doped BaCeO3, as determined by the same technique. The conventional proton incorporation model of perovskites in which oxygen ion vacancies, generated by the introduction of the trivalent dopant onto the tetravalent perovskite site, are filled with hydroxyl groups upon exposure of the sample to H2O containing atmospheres, predicts that the proton concentration in such materials should be no greater than the dopant concentration. In contradiction to this model, the proton concentration in BaPr1–xYxO3 after humidification is as much as three times greater than the dopant concentration, and even undoped samples contain a high concentration of protons. Moreover, x-ray photoemission spectra suggest that the Pr oxidation state is lowered upon hydration. In contrast, BaCe0.9Y0.1O3 shows a typical hydrogen concentration, of close to 90% of the yttrium concentration. The results are interpreted in terms of the variable valence of Pr, which can become reduced from the 4+ to the 3+ oxidation state upon exposure to water, and effectively behaves as a self-dopant within the structure
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