54 research outputs found
Level Set Jet Schemes for Stiff Advection Equations: The SemiJet Method
Many interfacial phenomena in physical and biological systems are dominated
by high order geometric quantities such as curvature.
Here a semi-implicit method is combined with a level set jet scheme to handle
stiff nonlinear advection problems.
The new method offers an improvement over the semi-implicit gradient
augmented level set method previously introduced by requiring only one
smoothing step when updating the level set jet function while still preserving
the underlying methods higher accuracy. Sample results demonstrate that
accuracy is not sacrificed while strict time step restrictions can be avoided
The Semi Implicit Gradient Augmented Level Set Method
Here a semi-implicit formulation of the gradient augmented level set method
is presented. By tracking both the level set and it's gradient accurate subgrid
information is provided,leading to highly accurate descriptions of a moving
interface. The result is a hybrid Lagrangian-Eulerian method that may be easily
applied in two or three dimensions. The new approach allows for the
investigation of interfaces evolving by mean curvature and by the intrinsic
Laplacian of the curvature. In this work the algorithm, convergence and
accuracy results are presented. Several numerical experiments in both two and
three dimensions demonstrate the stability of the scheme.Comment: 19 Pages, 14 Figure
Through-membrane electron-beam lithography for ultrathin membrane applications
We present a technique to fabricate ultrathin (down to 20 nm) uniform
electron transparent windows at dedicated locations in a SiN membrane for in
situ transmission electron microscopy experiments. An electron-beam (e-beam)
resist is spray-coated on the backside of the membrane in a KOH- etched cavity
in silicon which is patterned using through-membrane electron-beam lithography.
This is a controlled way to make transparent windows in membranes, whilst the
topside of the membrane remains undamaged and retains its flatness. Our
approach was optimized for MEMS-based heating chips but can be applied to any
chip design. We show two different applications of this technique for (1)
fabrication of a nanogap electrode by means of electromigration in thin
free-standing metal films and (2) making low-noise graphene nanopore devices
Comparison of knowledge, attitude and practice of Urban and rural households toward iron deficiency anemia in three provinces of Iran
Background: Lack of nutritional knowledge is one of the most important reasons of nutritional problems and consequently improper practice, which can lead to several complications. This study has been designed in order to compare knowledge, attitude and practices of the urban and rural households regarding iron deficiency anemia (IDA) in Boushehr, Golestan and Sistan & Balouchestan provinces in 2004. Methods: The sampling method at household's level in each province was the single-stage cluster sampling with equal size clusters. The necessary data were gathered with a structured questionnaire and via the interviews between the questioners and the eligible people in each household. Comparison of frequency of variables between urban and rural areas were tested by chi square test. Results: A total of 2306 households were selected as overall sample size. In urban areas, people recognized iron food sources better than rural areas. Knowledge level of respondents about vulnerable group for IDA and the favorite attitude of households toward IDA were better in urban areas of Sistan & Blouchestan and Golestan provinces. In Sistan & Balouchestan and Golestan, rural households who drank tea immediately before or after meal was more than urban ones. The majority of pregnant and lactating mothers (except for rural areas of Bushehr) did not take iron supplement regularly. Less than 60 percent of children used iron drop regularly. Conclusion: Knowledge, attitude, and practice levels of households toward IDA were not acceptable. One of the best ways of improving nutritional practice is nutritional education with focus on applying available food resources
An Immersed Interface Method for Discrete Surfaces
Fluid-structure systems occur in a range of scientific and engineering
applications. The immersed boundary(IB) method is a widely recognized and
effective modeling paradigm for simulating fluid-structure interaction(FSI) in
such systems, but a difficulty of the IB formulation is that the pressure and
viscous stress are generally discontinuous at the interface. The conventional
IB method regularizes these discontinuities, which typically yields low-order
accuracy at these interfaces. The immersed interface method(IIM) is an IB-like
approach to FSI that sharply imposes stress jump conditions, enabling
higher-order accuracy, but prior applications of the IIM have been largely
restricted to methods that rely on smooth representations of the interface
geometry. This paper introduces an IIM that uses only a C0 representation of
the interface,such as those provided by standard nodal Lagrangian FE methods.
Verification examples for models with prescribed motion demonstrate that the
method sharply resolves stress discontinuities along the IB while avoiding the
need for analytic information of the interface geometry. We demonstrate that
only the lowest-order jump conditions for the pressure and velocity gradient
are required to realize global 2nd-order accuracy. Specifically,we show
2nd-order global convergence rate along with nearly 2nd-order local convergence
in the Eulerian velocity, and between 1st-and 2nd-order global convergence
rates along with 1st-order local convergence for the Eulerian pressure. We also
show 2nd-order local convergence in the interfacial displacement and velocity
along with 1st-order local convergence in the fluid traction. As a
demonstration of the method's ability to tackle complex geometries,this
approach is also used to simulate flow in an anatomical model of the inferior
vena cava.Comment: - Added a non-axisymmetric example (flow within eccentric rotating
cylinder in Sec. 4.3) - Added a more in-depth analysis and comparison with a
body-fitted approach for the application in Sec. 4.
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