17,447 research outputs found
Micellization in the presence of polyelectrolyte
We present a simple model to study micellization of amphiphiles condensed on
a rodlike polyion. Although the mean field theory leads to a first order
micellization transition for sufficiently strong hydrophobic interactions, the
simulations show that no such thermodynamic phase transition exists. Instead,
the correlations between the condensed amphiphiles can result in a structure
formation very similar to micelles.Comment: 8 pages, 7 figure
Calculation of compressible turbulent boundary layers with pressure gradients and heat transfer
Calculation of compressible turbulent boundary layers with pressure gradients and heat transfe
Computing in Additive Networks with Bounded-Information Codes
This paper studies the theory of the additive wireless network model, in
which the received signal is abstracted as an addition of the transmitted
signals. Our central observation is that the crucial challenge for computing in
this model is not high contention, as assumed previously, but rather
guaranteeing a bounded amount of \emph{information} in each neighborhood per
round, a property that we show is achievable using a new random coding
technique.
Technically, we provide efficient algorithms for fundamental distributed
tasks in additive networks, such as solving various symmetry breaking problems,
approximating network parameters, and solving an \emph{asymmetry revealing}
problem such as computing a maximal input.
The key method used is a novel random coding technique that allows a node to
successfully decode the received information, as long as it does not contain
too many distinct values. We then design our algorithms to produce a limited
amount of information in each neighborhood in order to leverage our enriched
toolbox for computing in additive networks
Dynamics of fast pattern formation in porous silicon by laser interference
Patterns are fabricated on 290 nm thick nanostructured porous silicon layers by phase-mask laser interference using single pulses of an excimer laser (193 nm, 20 ns pulse duration). The dynamics of pattern formation is studied by measuring in real time the intensity of the diffraction orders 0 and 1 at 633 nm. The results show that a transient pattern is formed upon melting at intensity maxima sites within a time 1-µs) upon melting induced by homogeneous beam exposure and related to the different scenario for releasing the heat from hot regions. The diffraction efficiency of the pattern is finally controlled by a combination of laser fluence and initial thickness of the nanostructured porous silicon layer and the present results open perspectives on heat release management upon laser exposure as well as have potential for alternative routes for switching applications.Postprint (published version
Imaging Polarimetric Observations of a New Circumstellar Disk System
Few circumstellar disks have been directly observed. Here we use sensitive
differential polarimetric techniques to overcome atmospheric speckle noise in
order to image the circumstellar material around HD 169142. The detected
envelope or disk is considerably smaller than expectations based on the
measured strength of the far-IR excess from this system
Tight local approximation results for max-min linear programs
In a bipartite max-min LP, we are given a bipartite graph \myG = (V \cup I
\cup K, E), where each agent is adjacent to exactly one constraint
and exactly one objective . Each agent controls a
variable . For each we have a nonnegative linear constraint on
the variables of adjacent agents. For each we have a nonnegative
linear objective function of the variables of adjacent agents. The task is to
maximise the minimum of the objective functions. We study local algorithms
where each agent must choose based on input within its
constant-radius neighbourhood in \myG. We show that for every
there exists a local algorithm achieving the approximation ratio . We also show that this result is the best possible
-- no local algorithm can achieve the approximation ratio . Here is the maximum degree of a vertex , and
is the maximum degree of a vertex . As a methodological
contribution, we introduce the technique of graph unfolding for the design of
local approximation algorithms.Comment: 16 page
Representations and -theory of Discrete Groups
Let be a discrete group of finite virtual cohomological dimension
with certain finiteness conditions of the type satisfied by arithmetic groups.
We define a representation ring for , determined on its elements of
finite order, which is of finite type. Then we determine the contribution of
this ring to the topological -theory , obtaining an exact
formula for the difference in terms of the cohomology of the centralizers of
elements of finite order in .Comment: 4 page
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