294,311 research outputs found
Deformation-Driven Diffusion and Plastic Flow in Two-Dimensional Amorphous Granular Pillars
We report a combined experimental and simulation study of deformation-induced
diffusion in compacted two-dimensional amorphous granular pillars, in which
thermal fluctuations play negligible role. The pillars, consisting of
bidisperse cylindrical acetal plastic particles standing upright on a
substrate, are deformed uniaxially and quasistatically by a rigid bar moving at
a constant speed. The plastic flow and particle rearrangements in the pillars
are characterized by computing the best-fit affine transformation strain and
non-affine displacement associated with each particle between two stages of
deformation. The non-affine displacement exhibits exponential crossover from
ballistic to diffusive behavior with respect to the cumulative deviatoric
strain, indicating that in athermal granular packings, the cumulative
deviatoric strain plays the role of time in thermal systems and drives
effective particle diffusion. We further study the size-dependent deformation
of the granular pillars by simulation, and find that different-sized pillars
follow self-similar shape evolution during deformation. In addition, the yield
stress of the pillars increases linearly with pillar size. Formation of
transient shear lines in the pillars during deformation becomes more evident as
pillar size increases. The width of these elementary shear bands is about twice
the diameter of a particle, and does not vary with pillar size.Comment: 14 pages, 11 figure
Dual-scale roughness produces unusually water-repellent surfaces
Super-hydrophobicity can be achieved on relatively smooth surfaces. Short, wide pillars on slightly rough surfaces are shown to produce super-hydrophobic surfaces (see Figure) where neither the pillars nor the slight roughness suffice alone. This use of two length scales to create super-hydrophobic surfaces directly mimics the mechanism used by some plants including the lotus
The two pillars of design theory: Method of analysis and rhetoric
Since the 1960’s, there have been many initiatives for promoting theoretical understanding on design. However, in spite of definite progress, there are several puzzles and anomalies in the current theoretical landscape of design. We present an interpretation of the evolution of design theorizing that throws new light on these puzzles and anomalies. We contend that in the modern time, there have been two hidden inspirational sources for design theorizing, namely the method of analysis and rhetoric. As they concern different situations, their prescriptions in many ways differ. However, without explicit recourse to the sources, these mutually incompatible prescriptions, along with associated concepts and terms, have been mixed up in a confusing way. It is proposed that these two influences to design theory and practice have to be disentangled, to be able to act like two pillars supporting the phenomenon of designing. We hypothesize that actual design assignments require the mobilization of ideas and support from both pillar
Nanoscale Structure and Elasticity of Pillared DNA Nanotubes
We present an atomistic model of pillared DNA nanotubes (DNTs) and their
elastic properties which will facilitate further studies of these nanotubes in
several important nanotechnological and biological applications. In particular,
we introduce a computational design to create an atomistic model of a 6-helix
DNT (6HB) along with its two variants, 6HB flanked symmetrically by two double
helical DNA pillars (6HB+2) and 6HB flanked symmetrically by three double
helical DNA pillars (6HB+3). Analysis of 200 ns all-atom simulation
trajectories in the presence of explicit water and ions shows that these
structures are stable and well behaved in all three geometries. Hydrogen
bonding is well maintained for all variants of 6HB DNTs. We calculate the
persistence length of these nanotubes from their equilibrium bend angle
distributions. The values of persistence length are ~10 {\mu}m, which is 2
orders of magnitude larger than that of dsDNA. We also find a gradual increase
of persistence length with an increasing number of pillars, in quantitative
agreement with previous experimental findings. To have a quantitative
understanding of the stretch modulus of these tubes we carried out
nonequilibrium Steered Molecular Dynamics (SMD). The linear part of the force
extension plot gives stretch modulus in the range of 6500 pN for 6HB without
pillars which increases to 11,000 pN for tubes with three pillars. The values
of the stretch modulus calculated from contour length distributions obtained
from equilibrium MD simulations are similar to those obtained from
nonequilibrium SMD simulations. The addition of pillars makes these DNTs very
rigid.Comment: Published in ACS Nan
The two pillars of the European Central Bank
I interpret the European Central Bank's two-pillar strategy by proposing an empirical model for inflation that distinguishes between the short- and long-run components of inflation. The latter component depends on an exponentially weighted moving average of past monetary growth and the former on the output gap. Estimates for the 1971-2003 period suggest that money can be combined with other indicators to form the ‘broadly based assessment of the outlook for future price developments' that constitutes the ECB's second pillar. However, the analysis does not suggest that money should be treated differently from other indicators. While money is a useful policy indicator, all relevant indicators should be assessed in an integrated manner, and a separate pillar focused on monetary aggregates does not appear necessary. —Stefan Gerlac
Collapse of superhydrophobicity on nanopillared surfaces
The mechanism of the collapse of the superhydrophobic state is elucidated for
submerged nanoscale textures forming a three-dimensional interconnected vapor
domain. This key issue for the design of nanotextures poses significant
simulation challenges as it is characterized by diverse time and length scales.
State-of-the-art atomistic rare events simulations are applied for overcoming
the long time scales connected with the large free energy barriers. In such
interconnected surface cavities wetting starts with the formation of a liquid
finger between two pillars. This break of symmetry induces a more gentle bend
in the rest of the liquid-vapor interface, which triggers the wetting of the
neighboring pillars. This collective mechanism, involving the wetting of
several pillars at the same time, could not be captured by previous atomistic
simulations using surface models comprising a small number of pillars (often
just one). Atomistic results are interpreted in terms of a sharp-interface
continuum model which suggests that line tension, condensation, and other
nanoscale phenomena play a minor role in the simulated conditions
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