8,602 research outputs found
Shape mode analysis exposes movement patterns in biology: flagella and flatworms as case studies
We illustrate shape mode analysis as a simple, yet powerful technique to
concisely describe complex biological shapes and their dynamics. We
characterize undulatory bending waves of beating flagella and reconstruct a
limit cycle of flagellar oscillations, paying particular attention to the
periodicity of angular data. As a second example, we analyze non-convex
boundary outlines of gliding flatworms, which allows us to expose stereotypic
body postures that can be related to two different locomotion mechanisms.
Further, shape mode analysis based on principal component analysis allows to
discriminate different flatworm species, despite large motion-associated shape
variability. Thus, complex shape dynamics is characterized by a small number of
shape scores that change in time. We present this method using descriptive
examples, explaining abstract mathematics in a graphic way.Comment: 20 pages, 6 figures, accepted for publication in PLoS On
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Investigation of ducts as a “radar pinhole” for detecting objects through a wall
There is a continuing interest in the through-the-wall capabilities of radar. It has been found that walls behave as a low-pass medium, and therefore through-the-wall radar has been restricted to frequencies in the low GHz range. Unfortunately at these lower frequencies the resolution of the radar system is sacrificed. This thesis investigates the possibility of using a duct as a means of detecting objects through a wall. Ducts have been extensively studied in the past; however there has been limited research of ducts with two open ends. In this thesis the difference between an open-ended duct and a duct with two open ends is investigated through measurement and simulation. For simulation an approximate method is used that treats the duct as a waveguide. It is found that a significant amount of power is transmitted through a duct with two open ends. It is then shown that an object can be detected through a wall by using a duct that has been inserted into the wall. Then the two-way insertion loss of a duct with two open ends is determined through measurement and simulation. It is shown that a duct behaves as a high-pass medium and can be used as a propagation channel through a wall. The insertion loss due to the duct and the insertion loss through a concrete wall are comparedElectrical and Computer Engineerin
Three dimensional evolution of SN 1987A in a self-gravitating disk
The introduction of a exponential or power law gradient in the interstellar
medium (ISM) allows to produce an asymmetric evolution of the supernova remnant
(SNR) when the framework of the thin layer approximation is adopted.
Unfortunately both the exponential and power law gradients for the ISM do not
have a well defined physical meaning. The physics conversely is well
represented by an isothermal self-gravitating disk of particles whose velocity
is everywhere Maxwellian. . We derived a law of motion in the framework of the
thin layer approximation with a control parameter of the swept mass. The
photon's losses ,that are often neglected in the thin layer approximation, are
modeled trough a velocity dependence. The developed framework is applied to SNR
1987A and the three observed rings are simulated.Comment: 11 pages and 9 figures. arXiv admin note: text overlap with
arXiv:1109.401
2D wind clumping in hot, massive stars from hydrodynamical line-driven instability simulations using a pseudo-planar approach
Context: Clumping in the radiation-driven winds of hot, massive stars arises
naturally due to the strong, intrinsic instability of line-driving (the `LDI').
But LDI wind models have so far mostly been limited to 1D, mainly because of
severe computational challenges regarding calculation of the multi-dimensional
radiation force. Aims: To simulate and examine the dynamics and
multi-dimensional nature of wind structure resulting from the LDI. Methods: We
introduce a `pseudo-planar', `box-in-a-wind' method that allows us to
efficiently compute the line-force in the radial and lateral directions, and
then use this approach to carry out 2D radiation-hydrodynamical simulations of
the time-dependent wind. Results: Our 2D simulations show that the LDI first
manifests itself by mimicking the typical shell-structure seen in 1D models,
but how these shells then quickly break up into complex 2D density and velocity
structures, characterized by small-scale density `clumps' embedded in larger
regions of fast and rarefied gas. Key results of the simulations are that
density-variations in the well-developed wind statistically are quite isotropic
and that characteristic length-scales are small; a typical clump size is ~0.01R
at 2R, thus resulting also in rather low typical clump-masses ~10^17 g.
Overall, our results agree well with the theoretical expectation that the
characteristic scale for LDI-generated wind-structure is of order the Sobolev
length. We further confirm some earlier results that lateral `filling-in' of
radially compressed gas leads to somewhat lower clumping factors in 2D
simulations than in comparable 1D models. We conclude by discussing an
extension of our method toward rotating LDI wind models that exhibit an
intriguing combination of large- and small-scale structure extending down to
the wind base.Comment: 9 pages, 7 figures + 1 Appendix with 1 figure. Recommended for
publication in A&
Rectangular Layouts and Contact Graphs
Contact graphs of isothetic rectangles unify many concepts from applications
including VLSI and architectural design, computational geometry, and GIS.
Minimizing the area of their corresponding {\em rectangular layouts} is a key
problem. We study the area-optimization problem and show that it is NP-hard to
find a minimum-area rectangular layout of a given contact graph. We present
O(n)-time algorithms that construct -area rectangular layouts for
general contact graphs and -area rectangular layouts for trees.
(For trees, this is an -approximation algorithm.) We also present an
infinite family of graphs (rsp., trees) that require (rsp.,
) area.
We derive these results by presenting a new characterization of graphs that
admit rectangular layouts using the related concept of {\em rectangular duals}.
A corollary to our results relates the class of graphs that admit rectangular
layouts to {\em rectangle of influence drawings}.Comment: 28 pages, 13 figures, 55 references, 1 appendi
A surface electrode point Paul trap
We present a model as well as experimental results for a surface electrode
radio-frequency Paul trap that has a circular electrode geometry well-suited
for trapping of single ions and two-dimensional planar ion crystals. The trap
design is compatible with microfabrication and offers a simple method by which
the height of the trapped ions above the surface may be changed \emph{in situ}.
We demonstrate trapping of single and few Sr+ ions over an ion height range of
200-1000 microns for several hours under Doppler laser cooling, and use these
to characterize the trap, finding good agreement with our model.Comment: 10 pages, 11 figures, 1 tabl
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