7,507 research outputs found
Flux limitation in ultrafiltration: Osmotic pressure model and gel layer model
The characteristic permeate flux behaviour in ultrafiltration, i.e., the existence of a limiting flux which is independent of applied pressure and membrane resistance and a linear plot of the limiting flux versus the logarithm of the feed concentration, is explained by the osmotic pressure model. In the mathematical description presented here, a quantity ΔΠn/(Rmk) is introduced which is the ratio of the resistance caused by the osmotic pressure and the resistance of the membrane itself. For high values of this quantity (19) the flux is practically limited by the osmotic pressure. p]Factors leading to high values of the quantityΔΠnn/(Rmk) are discussed and it is concluded that in the ultrafiltration of medium molecular weight solutes (10,000 to 100,000 daltons) osmotic pressure limitation is more likely than gel layer limitatio
Electrons doped in cubic perovskite SrMnO3: isotropic metal versus chainlike ordering of Jahn-Teller polarons
Single crystals of electron-doped SrMnO3 with a cubic perovskite structure
have been systematically investigated as the most canonical
(orbital-degenerate) double-exchange system, whose ground states have been
still theoretically controversial. With only 1-2% electron doping by Ce
substitution for Sr, a G-type antiferromagnetic metal with a tiny spin canting
in a cubic lattice shows up as the ground state, where the Jahn-Teller polarons
with heavy mass are likely to form. Further electron doping above 4%, however,
replaces this isotropic metal with an insulator with tetragonal lattice
distortion, accompanied by a quasi-one-dimensional 3z^2-r^2 orbital ordering
with the C-type antiferromagnetism. The self-organization of such dilute
polarons may reflect the critical role of the cooperative Jahn-Teller effect
that is most effective in the originally cubic system.Comment: 5 pages, 4 figure
Diffusion-induced instability and chaos in random oscillator networks
We demonstrate that diffusively coupled limit-cycle oscillators on random
networks can exhibit various complex dynamical patterns. Reducing the system to
a network analog of the complex Ginzburg-Landau equation, we argue that uniform
oscillations can be linearly unstable with respect to spontaneous phase
modulations due to diffusional coupling - the effect corresponding to the
Benjamin-Feir instability in continuous media. Numerical investigations under
this instability in random scale-free networks reveal a wealth of complex
dynamical regimes, including partial amplitude death, clustering, and chaos. A
dynamic mean-field theory explaining different kinds of nonlinear dynamics is
constructed.Comment: 6 pages, 3 figure
Effect of cation size variance on spin and orbital order in Eu(LaY)VO
We have investigated the -ion ( = rare earth or Y) size variance effect
on spin/orbital order in Eu(LaY)VO. The
size variance disturbs one-dimensional orbital correlation in -type
spin/-type orbital ordered states and suppresses this spin/orbital order. In
contrast, it stabilizes the other spin/orbital order. The results of neutron
and resonant X-ray scattering denote that in the other ordered phase, the
spin/orbital patterns are -type/-type, respectively.Comment: 4 pages, 4 figures, accepted to Rapid Communication in Physical
Review
Critical Collapse of Einstein Cluster
We observe critical phenomena in spherically symmetric gravitational collapse
of Einstein Cluster. We show analytically that the collapse evolution ends
either in formation of a black hole or in dispersal depending on the values of
initial parameters which characterize initial density and angular momentum of
the collapsing cloud. Near the threshold of black hole formation, we obtain
scaling relation for the mass of the black hole and find the critical exponent
value to be 3/2. We numerically confirm that there exist wide ranges of initial
parameter values around the critical configuration for which the model remains
shell-crossing free.Comment: Accepted for publication in Prog. Theor. Phy
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