5,258 research outputs found
Polydispersity Effects in Colloid-Polymer Mixtures
We study phase separation and transient gelation in a mixture consisting of
polydisperse colloids and non-adsorbing polymers, where the ratio of the
average size of the polymer to that of the colloid is approximately 0.063.
Unlike what has been reported previously for mixtures with somewhat lower
colloid polydispersity, the addition of polymers does not expand the
fluid-solid coexistence region. Instead, we find a region of fluid-solid
coexistence which has an approximately constant width but an unexpected
re-entrant shape. We detect the presence of a metastable gas-liquid binodal,
which gives rise to two-stepped crystallization kinetics that can be
rationalized as the effect of fractionation. Finally, we find that the
separation into multiple coexisting solid phases at high colloid volume
fractions predicted by equilibrium statistical mechanics is kinetically
suppressed before the system reaches dynamical arrest.Comment: 11 pages, 5 figure
Diffusive Evolution of Stable and Metastable Phases II: Theory of Non-Equilibrium Behaviour in Colloid-Polymer Mixtures
By analytically solving some simple models of phase-ordering kinetics, we
suggest a mechanism for the onset of non-equilibrium behaviour in
colloid-polymer mixtures. These mixtures can function as models of atomic
systems; their physics therefore impinges on many areas of thermodynamics and
phase-ordering. An exact solution is found for the motion of a single, planar
interface separating a growing phase of uniform high density from a
supersaturated low density phase, whose diffusive depletion drives the
interfacial motion. In addition, an approximate solution is found for the
one-dimensional evolution of two interfaces, separated by a slab of a
metastable phase at intermediate density. The theory predicts a critical
supersaturation of the low-density phase, above which the two interfaces become
unbound and the metastable phase grows ad infinitum. The growth of the stable
phase is suppressed in this regime.Comment: 27 pages, Latex, eps
Relation Between First Arrival Time and Permeability in Self-Affine Fractures with Areas in Contact
We demonstrate that the first arrival time in dispersive processes in
self-affine fractures are governed by the same length scale characterizing the
fractures as that which controls their permeability. In one-dimensional channel
flow this length scale is the aperture of the bottle neck, i.e., the region
having the smallest aperture. In two dimensions, the concept of a bottle neck
is generalized to that of a minimal path normal to the flow. The length scale
is then the average aperture along this path. There is a linear relationship
between the first arrival time and this length scale, even when there is strong
overlap between the fracture surfaces creating areas with zero permeability. We
express the first arrival time directly in terms of the permeability.Comment: EPL (2012)
Variability in surface electromyogram during gait analysis of low back pain patients
This paper describes the analysis of the variance of the amplitude of surface electromyogram (SEMG) recorded from the L4/ L5 region of the erector spinae for healthy participants and people suffering with low back pain (LBP) when they were walking and running on a treadmill. The results indicate that there was no significant difference in the variance and in the change of variance over time of the exercise between the two groups when the participants were walking. However, when the participants were running, there was a significant difference between the two cohorts. While there was an increase in the variance over the duration of the exercise for both of the groups, the increase in variance of the LBP group was much greater (order of ten times) compared with that of the healthy participants. The difference between the two groups was also very significant when observing the change of variance over time. From these results, it is suggested that variance of SEMG of the muscles of the lower back, recorded when the participants are running, can be used to identify LBP patients
Proliferation of anomalous symmetries in colloidal monolayers subjected to quasiperiodic light fields
Quasicrystals provide a fascinating class of materials with intriguing
properties. Despite a strong potential for numerous technical applications, the
conditions under which quasicrystals form are still poorly understood.
Currently, it is not clear why most quasicrystals hold 5- or 10-fold symmetry
but no single example with 7 or 9-fold symmetry has ever been observed. Here we
report on geometrical constraints which impede the formation of quasicrystals
with certain symmetries in a colloidal model system. Experimentally, colloidal
quasicrystals are created by subjecting micron-sized particles to
two-dimensional quasiperiodic potential landscapes created by n=5 or seven
laser beams. Our results clearly demonstrate that quasicrystalline order is
much easier established for n = 5 compared to n = 7. With increasing laser
intensity we observe that the colloids first adopt quasiperiodic order at local
areas which then laterally grow until an extended quasicrystalline layer forms.
As nucleation sites where quasiperiodicity originates, we identify highly
symmetric motifs in the laser pattern. We find that their density strongly
varies with n and surprisingly is smallest exactly for those quasicrystalline
symmetries which have never been observed in atomic systems. Since such high
symmetry motifs also exist in atomic quasicrystals where they act as
preferential adsorption sites, this suggests that it is indeed the deficiency
of such motifs which accounts for the absence of materials with e.g. 7-fold
symmetry
Integrated hybrid VO<sub>2</sub>–silicon optical memory
Vanadium dioxide (VO2) is an interesting material for hybrid photonic integrated devices due to its insulator–metal phase transition. Utilizing the hysteresis of the phase transition in voltage-biased VO2, we demonstrate a compact hybrid VO2–silicon optical memory element integrated into a silicon waveguide. An optical pulse writes the VO2 memory, leading to an optical attenuation that can be read out by the optical transmission in a silicon waveguide. Our on-chip memory cell can be optically written with energy as low as 23.5 pJ per pulse and with a 10–90% rise time of ∼100 ns. This approach is promising for optical data storage in silicon photonic integrated circuits
The role of SQSTM1 (p62) in mitochondrial function and clearance in human cortical neurons.
Sequestosome-1 (SQSTM1/p62) is involved in cellular processes such as autophagy and metabolic reprogramming. Mutations resulting in the loss of function of SQSTM1 lead to neurodegenerative diseases including frontotemporal dementia. The pathogenic mechanism that contributes to SQSTM1-related neurodegeneration has been linked to its role as an autophagy adaptor, but this is poorly understood, and its precise role in mitochondrial function and clearance remains to be clarified. Here, we assessed the importance of SQSTM1 in human induced pluripotent stem cell (iPSC)-derived cortical neurons through the knockout of SQSTM1. We show that SQSTM1 depletion causes altered mitochondrial gene expression and functionality, as well as autophagy flux, in iPSC-derived neurons. However, SQSTM1 is not essential for mitophagy despite having a significant impact on early PINK1-dependent mitophagy processes including PINK1 recruitment and phosphorylation of ubiquitin on depolarized mitochondria. These findings suggest that SQSTM1 is important for mitochondrial function rather than clearance
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