10,194 research outputs found
Phenomenological model for a novel melt-freeze phase of sliding bilayers
Simulations show that sliding bilayers of colloidal particles can exhibit a
new phase, the ``melt-freeze'' phase, where the layers stochastically alternate
between solidlike and liquidlike states. We introduce a mean field
phenomenological model with two order parameters to understand the interplay of
two adjacent layers while the system is in this remarkable phase. Predictions
from our numerical simulations of a system in the melt-freeze phase include the
tendency of two adjacent layers to be in opposite states (solid and liquid) and
the difference between the fluctuation of the order parameter in one layer
while the other layer is in the same phase compared to the fluctuation while
the other layer is in the opposite phase. We expect this behavior to be seen in
future simulations and experiments.Comment: 6 Pages, 6 figure
Properties of Dynamic Earthquake Ruptures With Heterogeneous Stress Drop
Earthquake rupture is a notoriously complex process, at all observable scales.
We introduce a simplified semi-dynamic crack model to investigate the connection
between the statistical properties of stress and those of macroscopic source
parameters such as rupture size, seismic moment, apparent stress drop and radiated
energy. Rupture initiation is treated consistently with nucleation on a linear slip-weakening
fault, whereas rupture propagation and arrest are treated according to
the Griffith criterion. The available stress drop is prescribed as a spatially correlated
random field and is shown to potentially sustain a broad range of magnitudes. By
decreasing the amplitude of the stress heterogeneities or increasing their correlation
length the distribution of earthquake sizes presents a transition from Gutenberg-
Richter to characteristic earthquake behavior. This transition is studied through a
mean-field analysis. The bifurcation to characteristic earthquake behavior is sharp,
reminiscent of a first-order phase transition. A lower roll-off magnitude observed
in the Gutenberg-Richter regime is shown to depend on the correlation length of the
available stress drop, rather than being a direct signature of the nucleation process.
More generally, we highlight the possible role of the stress correlation length scale
on deviations from earthquake source self-similarity. The present reduced model
is a building block towards understanding the effect of structural and dynamic
fault heterogeneities on the scaling of source parameters and on basic properties
of seismicity
Sheaf representations of MV-algebras and lattice-ordered abelian groups via duality
We study representations of MV-algebras -- equivalently, unital
lattice-ordered abelian groups -- through the lens of Stone-Priestley duality,
using canonical extensions as an essential tool. Specifically, the theory of
canonical extensions implies that the (Stone-Priestley) dual spaces of
MV-algebras carry the structure of topological partial commutative ordered
semigroups. We use this structure to obtain two different decompositions of
such spaces, one indexed over the prime MV-spectrum, the other over the maximal
MV-spectrum. These decompositions yield sheaf representations of MV-algebras,
using a new and purely duality-theoretic result that relates certain sheaf
representations of distributive lattices to decompositions of their dual
spaces. Importantly, the proofs of the MV-algebraic representation theorems
that we obtain in this way are distinguished from the existing work on this
topic by the following features: (1) we use only basic algebraic facts about
MV-algebras; (2) we show that the two aforementioned sheaf representations are
special cases of a common result, with potential for generalizations; and (3)
we show that these results are strongly related to the structure of the
Stone-Priestley duals of MV-algebras. In addition, using our analysis of these
decompositions, we prove that MV-algebras with isomorphic underlying lattices
have homeomorphic maximal MV-spectra. This result is an MV-algebraic
generalization of a classical theorem by Kaplansky stating that two compact
Hausdorff spaces are homeomorphic if, and only if, the lattices of continuous
[0, 1]-valued functions on the spaces are isomorphic.Comment: 36 pages, 1 tabl
Synthetic Engineering of Graphene Nanoribbons with Excellent Liquid-Phase Processability
Micro heat exchanger by using MEMS impinging jets
A micro impinging-jet heat exchanger is presented here. Heat transfer is studied for single jet, slot arrays and jet arrays. In order to facilitate micro heat transfer measurements with these devices, a MEMS sensor chip, which has an 8 x 8 temperature-sensor array on one side, and an integrated heater on the other side has been designed and fabricated. This sensor chip allows 2-D surface temperature
measurement with various jets impinging on it. It is
found that micro impinging jets can be highly efficient when compared to existing macro impinging-jet microelectronics packages such as IBM 4381. For example, using a single nozzle jet (500-μm diameter driven by 5 psig pressure), the sensor chip (2 x 2 cm^2) temperature can be cooled down from 70 to 33°C. The cooling becomes more efficient when
nozzle arrays (4x5 over 1 cm^2 area) are used under
the same driving pressure. Interestingly, although
higher driving pressure gives better cooling (lower
surface temperature), the cooling efficiency, defined
as h/0.5pv^2, is actually higher for lower driving
pressure
Comparing different accelerometer cut-points for sedentary time in children
Actigraph accelerometers are hypothesized to be valid measurements for assessing children\u27s sedentary time. However, there is considerable variation in accelerometer cut-points used. Therefore, we compared the most common accelerometer sedentary cut-points of children performing sedentary behaviors. Actigraph Actitrainer uniaxial accelerometers were used to measure children\u27s activity intensity (29 children, 5-11 years old) during different activities, namely playing computer games, nonelectronic sedentary games, watching television and playing outdoors. A structured protocol was the criterion for assessing the validity of four common cut-points (100, 300, 800, 1100 counts/minute). The median counts during all sedentary behaviors were below the lowest comparison cut-point of 100 cpm. The 75th percentile values for the sedentary behaviors were always below the cut-point of 300 cpm. Our results suggest that the cut-point of <100 cpm is the most appropriate
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