N-body Study of Anisotropic Membrane Inclusions: Membrane Mediated Interactions and Ordered Aggregation

We study the collective behavior of inclusions inducing local anisotropic curvatures in a flexible fluid membrane. The N-body interaction energy for general anisotropic inclusions is calculated explicitly, including multi-body interactions. Long-range attractive interactions between inclusions are found to be sufficiently strong to induce aggregation. Monte Carlo simulations show a transition from compact clusters to aggregation on lines or circles. These results might be relevant to proteins in biological membranes or colloidal particles bound to surfactant membranes.Comment: 4 pages, 3 figs, LaTe

Dynamin recruitment by clathrin coats: a physical step?

Recent structural findings have shown that dynamin, a cytosol protein playing a key-role in clathrin-mediated endocytosis, inserts partly within the lipid bilayer and tends to self-assemble around lipid tubules. Taking into account these observations, we make the hypothesis that individual membrane inserted dynamins imprint a local cylindrical curvature to the membrane. This imprint may give rise to long-range mechanical forces mediated by the elasticity of the membrane. Calculating the resulting many-body interaction between a collection of inserted dynamins and a membrane bud, we find a regime in which the dynamins are elastically recruited by the bud to form a collar around its neck, which is reminiscent of the actual process preempting vesicle scission. This physical mechanism might therefore be implied in the recruitment of dynamins by clathrin coats.Comment: 11 pages, 6 figures, to appear in C.R.A.S. ser II

3D simulations of rising magnetic flux tubes in a compressible rotating interior: The effect of magnetic tension

Context: Long-term variability in solar cycles represents a challenging constraint for theoretical models. Mean-field Babcock-Leighton dynamos that consider non-instantaneous rising flux tubes have been shown to exhibit long-term variability in their magnetic cycle. However a relation that parameterizes the rise-time of non-axisymmetric magnetic flux tubes in terms of stellar parameters is still missing. Aims: We aim to find a general parameterization of the rise-time of magnetic flux tubes for solar-like stars. Methods: By considering the influence of magnetic tension on the rise of non-axisymmetric flux tubes, we predict the existence of a control parameter referred as $\Gamma_{\alpha_1}^{\alpha_2}$. This parameter is a measure of the balance between rotational effects and magnetic effects (buoyancy and tension) acting on the magnetic flux tube. We carry out two series of numerical experiments (one for axisymmetric rise and one for non-axisymmetric rise) and demonstrate that $\Gamma_{\alpha_1}^{\alpha_2}$ indeed controls the rise-time of magnetic flux tubes. Results: We find that the rise-time follows a power law of $\Gamma_{\alpha_1}^{\alpha_2}$ with an exponent that depends on the azimuthal wavenumber of the magnetic flux loop. Conclusions: Compressibility does not impact the rise of magnetic flux tubes, while non-axisymmetry does. In the case of non-axisymmetric rise, the tension force modifies the force balance acting on the magnetic flux tube. We identified the three independent parameters required to predict the rise-time of magnetic flux tubes, that is, the stellar rotation rate, the magnetic flux density of the flux tube, and its azimuthal wavenumber. We combined these into one single relation that is valid for any solar-like star. We suggest using this generalized relation to constrain the rise-time of magnetic flux tubes in Babcock-Leighton dynamo models.Comment: 18 pages, 15 figures, 6 tabula

Distributed upper-surface blowing concept

A low speed investigation was conducted in the Langley V/STOL tunnel to determine the powered lift aerodynamic performance of a distributed upper surface blown propulsive lift transport model. The model used blowing slots across the span of the wing to produce a thin jet efflux near the leading edge and at the knee of the trailing edge flap (internally blown jet flap). Results indicate that these concepts have both good propulsive related lift and low drag due to lift characteristics because of uniform spanwise propulsive thrust. The leading edge blowing concept provides low speed lift characteristics which are competitive with the flap-hinge-line blowing concept and does not require additional leading edge treatment for prevention of abrupt stall

Helicity and alpha-effect by current-driven instabilities of helical magnetic fields

Helical magnetic background fields with adjustable pitch angle are imposed on a conducting fluid in a differentially rotating cylindrical container. The small-scale kinetic and current helicities are calculated for various field geometries, and shown to have the opposite sign as the helicity of the large-scale field. These helicities and also the corresponding $\alpha$-effect scale with the current helicity of the background field. The $\alpha$-tensor is highly anisotropic as the components $\alpha_{\phi\phi}$ and $\alpha_{zz}$ have opposite signs. The amplitudes of the azimuthal $\alpha$-effect computed with the cylindrical 3D MHD code are so small that the operation of an $\alpha\Omega$ dynamo on the basis of the current-driven, kink-type instabilities of toroidal fields is highly questionable. In any case the low value of the $\alpha$-effect would lead to very long growth times of a dynamo in the radiation zone of the Sun and early-type stars of the order of mega-years.Comment: 6 pages, 7 figures, submitted to MNRA

Investigation of powered nacelles on a high aspect ratio NASA supercritical wing, phase 2

A modified wing with the long core separate flow nacelle and several E(3) nacelles was utilized. The effects of nacelle and pylon cant angles and nacelle longitudinal and vertical location were investigated over a Mach number range from 0.70 to 0.83. The results at the cruise condition 0.82 Mach number and 0.55 lift coefficient are presented

Measurement of thermal conductance of silicon nanowires at low temperature

We have performed thermal conductance measurements on individual single crystalline silicon suspended nanowires. The nanowires (130 nm thick and 200 nm wide) are fabricated by e-beam lithography and suspended between two separated pads on Silicon On Insulator (SOI) substrate. We measure the thermal conductance of the phonon wave guide by the 3 method. The cross-section of the nanowire approaches the dominant phonon wavelength in silicon which is of the order of 100 nm at 1K. Above 1.3K the conductance behaves as T3, but a deviation is measured at the lowest temperature which can be attributed to the reduced geometry

Design aspects of a solar array drive for spot, with a high platform stability objective

A solar array drive mechanism (MEGS) for the SPOT platform, which is a prototype of a multimission platform, is described. High-resolution cameras and other optical instruments are carried by the platform, requiring excellent platform stability in order to obtain high-quality pictures. Therefore, a severe requirement for the MEGS is the low level of disturbing torques it may generate considering the 0.6 times 10 to the minus 3 power deg/sec stability required. The mechanical design aspects aiming at reducing the mean friction torque, and therefore its fluctuations, are described as well as the method of compensation of the motor imperfections. It was concluded, however, that this is not sufficient to reach the stability requirement

Alien Registration- Fournier, Blanche G. (Lewiston, Androscoggin County)

https://digitalmaine.com/alien_docs/29754/thumbnail.jp