15,366 research outputs found
Binding of Oppositely Charged Membranes and Membrane Reorganization
We consider the electrostatic interaction between two rigid membranes, with
different surface charge densities of opposite sign, across an aqueous solution
without added salt. Exact solutions to the nonlinear Poisson-Boltzmann equation
are obtained and their physical meaning discussed. We also calculate the
electrostatic contribution to the free energy and discuss the renormalization
of the area per head group of the charged lipids arising from the Coulomb
interaction.Comment: 13 pages, 6 figures, to be published in EJP
Phase Transitions in Lyotropic Nematic Gels
In this paper, we discuss the equilibrium phases and collapse transitions of
a lyotropic nematic gel immersed in an isotropic solvent. A nematic gel
consists of a cross-linked polymer network with rod-like molecules embedded in
it. Upon decreasing the quality of the solvent, we find that a lyotropic
nematic gel undergoes a discontinuous volume change accompanied by an
isotropic-nematic transition. We also present phase diagrams that these systems
may exhibit. In particular, we show that coexistence of two isotropic phases,
of two nematic phases, or of an isotropic and a nematic phase can occur.Comment: 13 pages Revtex, 10 figures, submitted to EPJ
Non-equilibrium fluctuations and mechanochemical couplings of a molecular motor
We investigate theoretically the violations of Einstein and Onsager
relations, and the efficiency for a single processive motor operating far from
equilibrium using an extension of the two-state model introduced by Kafri {\em
et al.} [Biophys. J. {\bf 86}, 3373 (2004)]. With the aid of the Fluctuation
Theorem, we analyze the general features of these violations and this
efficiency and link them to mechanochemical couplings of motors. In particular,
an analysis of the experimental data of kinesin using our framework leads to
interesting predictions that may serve as a guide for future experiments.Comment: 4 pages, 4 figures, accepted to Phys. Rev. Let
Mapping the Dirac point in gated bilayer graphene
We have performed low temperature scanning tunneling spectroscopy
measurements on exfoliated bilayer graphene on SiO2. By varying the back gate
voltage we observed a linear shift of the Dirac point and an opening of a band
gap due to the perpendicular electric field. In addition to observing a shift
in the Dirac point, we also measured its spatial dependence using spatially
resolved scanning tunneling spectroscopy. The spatial variation of the Dirac
point was not correlated with topographic features and therefore we attribute
its shift to random charged impurities.Comment: 3 pages, 3 figure
Spatially resolved spectroscopy of monolayer graphene on SiO2
We have carried out scanning tunneling spectroscopy measurements on
exfoliated monolayer graphene on SiO to probe the correlation between its
electronic and structural properties. Maps of the local density of states are
characterized by electron and hole puddles that arise due to long range
intravalley scattering from intrinsic ripples in graphene and random charged
impurities. At low energy, we observe short range intervalley scattering which
we attribute to lattice defects. Our results demonstrate that the electronic
properties of graphene are influenced by intrinsic ripples, defects and the
underlying SiO substrate.Comment: 6 pages, 7 figures, extended versio
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Direct Slicing of STEP Based NURBS Models for Solid Freeform Fabrication
Direct slicing of CAD models to generate process planning instructions for solid freeform
fabrication may overcome inherent disadvantages of using STL format in terms of the process
accuracy, ease of file management, and incorporation of multiple materials. This paper will
present the results of our development of a direct slicing algorithm for layered freeform
fabrication. The direct slicing algorithm was based on a neutral, international standard (ISO
10303) STEP-formatted NURBS geometric representation and is intended to be independent of
any commercial CAD software. The following aspects of the development effort will be
presented: 1) Determination of optimal build direction based upon STEP-based NURBS models;
2) Adaptive subdivision of NURBS data for geometric refinement; and 3) Ray-casting slice
generation into sets of raster patterns. Feasibility studies applying the direct slicing algorithm to
example models and the generation of fabrication planning instructions involving multi-material
structures will also be presented.Mechanical Engineerin
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