Hydrodynamic slip can align thin nanoplatelets in shear flow

The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. Here we show, by combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows. Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. This surprising effect is due to hydrodynamic slip at the liquid-solid interface and occurs when the slip length is larger than the platelet thickness; a slip length of a few nanometers may be sufficient to observe alignment. The predictions we developed by examining pure and surface-modified graphene is applicable to different solvent/2D material combinations. The emergence of a fixed orientation in a direction nearly parallel to the flow implies a slip-dependent change in several macroscopic transport properties, with potential impact on applications ranging from functional inks to nanocomposites.Energy Technolog

Insulin Resistance in Non-Obese Subjects Is Associated with Activation of the JNK Pathway and Impaired Insulin Signaling in Skeletal Muscle

BACKGROUND: The pathogenesis of insulin resistance in the absence of obesity is unknown. In obesity, multiple stress kinases have been identified that impair the insulin signaling pathway via serine phosphorylation of key second messenger proteins. These stress kinases are activated through various mechanisms related to lipid oversupply locally in insulin target tissues and in various adipose depots. METHODOLOGY/PRINCIPAL FINDINGS: To explore whether specific stress kinases that have been implicated in the insulin resistance of obesity are potentially contributing to insulin resistance in non-obese individuals, twenty healthy, non-obese, normoglycemic subjects identified as insulin sensitive or resistant were studied. Vastus lateralis muscle biopsies obtained during euglycemic, hyperinsulinemic clamp were evaluated for insulin signaling and for activation of stress kinase pathways. Total and regional adipose stores and intramyocellular lipids (IMCL) were assessed by DXA, MRI and (1)H-MRS. In muscle of resistant subjects, phosphorylation of JNK was increased (1.36±0.23 vs. 0.78±0.10 OD units, P<0.05), while there was no evidence for activation of p38 MAPK or IKKβ. IRS-1 serine phosphorylation was increased (1.30±0.09 vs. 0.22±0.03 OD units, P<0.005) while insulin-stimulated tyrosine phosphorylation decreased (10.97±0.95 vs. 0.89±0.50 OD units, P<0.005). IMCL levels were twice as high in insulin resistant subjects (3.26±0.48 vs. 1.58±0.35% H(2)O peak, P<0.05), who also displayed increased total fat and abdominal fat when compared to insulin sensitive controls. CONCLUSIONS: This is the first report demonstrating that insulin resistance in non-obese, normoglycemic subjects is associated with activation of the JNK pathway related to increased IMCL and higher total body and abdominal adipose stores. While JNK activation is consistent with a primary impact of muscle lipid accumulation on metabolic stress, further work is necessary to determine the relative contributions of the various mediators of impaired insulin signaling in this population

Earth curvature effects on subduction morphology: Modeling subduction in a spherical setting with the fast multipole boundary element method

We present the first application in geodynamics of a (Fast Multipole) Accelerated Boundary Element Method (Accelerated-BEM) for Stokes flow. The approach offers the advantages of a reduced number of computational elements and linear scaling with the problem size. We show that this numerical method can be fruitfully applied for the simulation of several geodynamic systems at the planetary scale in spherical coordinates, and we suggest a general approach for modeling combined mantle convection and plate tectonics. The first part of the paper is devoted to the technical exposition of the new approach, while the second part focuses on the effect played by Earth curvature on the subduction of a very wide oceanic lithosphere (W = 6,000 km and W = 9,000 km), comparing the effects of two different planetary radii (ER = 6,371 km, 2ER = 2 9 6,371 km), corresponding to an ‘‘Earth-like’’ model (ER) and to a ‘‘flat Earth’’ one (2ER). The results show a distinct difference between the two models: while the slab on a ‘‘flat Earth’’ shows a slight undulation, the same subducting plate on the ‘‘Earth-like’’ setting presents a dual behavior characterized by concave curvature at the edges and by a folding with wavelength of the order of magnitude of 1,000 km at the center of the slab