3,672 research outputs found
Lateral transport of thermal capillary waves
We demonstrate that collective motion of interfacial fluctuations can occur
at the interface between two coexisting thermodynamic phases. Based on computer
simulation results for driven diffusive Ising and Blume-Capel models, we
conjecture that the thermal capillary waves at a planar interface travel along
the interface if the lateral order parameter current j_op(y) is an odd function
of the distance y from the interface and hence possesses opposite directions in
the two phases. Such motion does not occur if j_op(y) is an even function of y.
A discrete Gaussian interface model with effective dynamics exhibits similiar
transport phenomena but with a simpler dispersion relation. These findings open
up avenues for controlled interfacial transport on the nanoscale.Comment: 4 pages, 6 figure
Oblique Gravity Wave Propagation During Sudden Stratospheric Warmings
Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors
Interfaces in driven Ising models: shear enhances confinement
We use a phase-separated driven two-dimensional Ising lattice gas to study
fluid interfaces exposed to shear flow parallel to the interface. The interface
is stabilized by two parallel walls with opposing surface fields and a driving
field parallel to the walls is applied which (i) either acts locally at the
walls or (ii) varies linearly with distance across the strip. Using computer
simulations with Kawasaki dynamics, we find that the system reaches a steady
state in which the magnetisation profile is the same as that in equilibrium,
but with a rescaled length implying a reduction of the interfacial width. An
analogous effect was recently observed in sheared phase-separated colloidal
dispersions. Pair correlation functions along the interface decay more rapidly
with distance under drive than in equilibrium and for cases of weak drive can
be rescaled to the equilibrium result.Comment: 4 pages, 3 figures Text modified, added Fig. 3b. To appear in Phys.
Rev. Letter
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The dynamic switch mechanism that leads to activation of LRRK2 is embedded in the DFGψ motif in the kinase domain.
Leucine-rich repeat kinase 2 (LRRK2) is a large multidomain protein, and LRRK2 mutants are recognized risk factors for Parkinson's disease (PD). Although the precise mechanisms that control LRRK2 regulation and function are unclear, the importance of the kinase domain is strongly implicated, since 2 of the 5 most common familial LRRK2 mutations (G2019S and I2020T) are localized to the conserved DFGψ motif in the kinase core, and kinase inhibitors are under development. Combining the concept of regulatory (R) and catalytic (C) spines with kinetic and cell-based assays, we discovered a major regulatory mechanism embedded within the kinase domain and show that the DFG motif serves as a conformational switch that drives LRRK2 activation. LRRK2 is quite unusual in that the highly conserved Phe in the DFGψ motif, which is 1 of the 4 R-spine residues, is replaced with tyrosine (DY2018GI). A Y2018F mutation creates a hyperactive phenotype similar to the familial mutation G2019S. The hydroxyl moiety of Y2018 thus serves as a "brake" that stabilizes an inactive conformation; simply removing it destroys a key hydrogen-bonding node. Y2018F, like the pathogenic mutant I2020T, spontaneously forms LRRK2-decorated microtubules in cells, while the wild type and G2019S require kinase inhibitors to form filaments. We also explored 3 different mechanisms that create kinase-dead pseudokinases, including D2017A, which further emphasizes the highly synergistic role of key hydrophobic and hydrophilic/charged residues in the assembly of active LRRK2. We thus hypothesize that LRRK2 harbors a classical protein kinase switch mechanism that drives the dynamic activation of full-length LRRK2
Phase behaviour of binary mixtures of diamagnetic colloidal platelets in an external magnetic field
Using fundamental measure density functional theory we investigate
paranematic-nematic and nematic-nematic phase coexistence in binary mixtures of
circular platelets with vanishing thicknesses. An external magnetic field
induces uniaxial alignment and acts on the platelets with a strength that is
taken to scale with the platelet area. At particle diameter ratio lambda=1.5
the system displays paranematic-nematic coexistence. For lambda=2, demixing
into two nematic states with different compositions also occurs, between an
upper critical point and a paranematic-nematic-nematic triple point. Increasing
the field strength leads to shrinking of the coexistence regions. At high
enough field strength a closed loop of immiscibility is induced and phase
coexistence vanishes at a double critical point above which the system is
homogeneously nematic. For lambda=2.5, besides paranematic-nematic coexistence,
there is nematic-nematic coexistence which persists and hence does not end in a
critical point. The partial orientational order parameters along the binodals
vary strongly with composition and connect smoothly for each species when
closed loops of immiscibility are present in the corresponding phase diagram.Comment: 9 pages, to appear in J.Phys:Condensed Matte
Bulk phase behaviour of binary hard platelet mixtures from density functional theory
We investigate isotropic-isotropic, isotropic-nematic and nematic-nematic
phase coexistence in binary mixtures of circular platelets with vanishing
thickness, continuous rotational degrees of freedom and radial size ratios
up to 5. A fundamental measure density functional theory, previously
used for the one-component model, is proposed and results are compared against
those from Onsager theory as a benchmark. For the system
displays isotropic-nematic phase coexistence with a widening of the biphasic
region for increasing values of . For size ratios , we
find demixing into two nematic states becomes stable and an
isotropic-nematic-nematic triple point can occur. Fundamental measure theory
gives a smaller isotropic-nematic biphasic region than Onsager theory and
locates the transition at lower densities. Furthermore, nematic-nematic
demixing occurs over a larger range of compositions at a given value of
than found in Onsager theory. Both theories predict the same
topologies of the phase diagrams. The partial nematic order parameters vary
strongly with composition and indicate that the larger particles are more
strongly ordered than the smaller particles
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