212 research outputs found
Behavior of different numerical schemes for population genetic drift problems
In this paper, we focus on numerical methods for the genetic drift problems,
which is governed by a degenerated convection-dominated parabolic equation. Due
to the degeneration and convection, Dirac singularities will always be
developed at boundary points as time evolves. In order to find a \emph{complete
solution} which should keep the conservation of total probability and
expectation, three different schemes based on finite volume methods are used to
solve the equation numerically: one is a upwind scheme, the other two are
different central schemes. We observed that all the methods are stable and can
keep the total probability, but have totally different long-time behaviors
concerning with the conservation of expectation. We prove that any extra
infinitesimal diffusion leads to a same artificial steady state. So upwind
scheme does not work due to its intrinsic numerical viscosity. We find one of
the central schemes introduces a numerical viscosity term too, which is beyond
the common understanding in the convection-diffusion community. Careful
analysis is presented to prove that the other central scheme does work. Our
study shows that the numerical methods should be carefully chosen and any
method with intrinsic numerical viscosity must be avoided.Comment: 17 pages, 8 figure
Tacchi: A Pluggable and Low Computational Cost Elastomer Deformation Simulator for Optical Tactile Sensors
Simulation is widely applied in robotics research to save time and resources.
There have been several works to simulate optical tactile sensors that leverage
either a smoothing method or Finite Element Method (FEM). However, elastomer
deformation physics is not considered in the former method, whereas the latter
requires a massive amount of computational resources like a computer cluster.
In this work, we propose a pluggable and low computational cost simulator using
the Taichi programming language for simulating optical tactile sensors, named
as Tacchi . It reconstructs elastomer deformation using particles, which allows
deformed elastomer surfaces to be rendered into tactile images and reveals
contact information without suffering from high computational costs. Tacchi
facilitates creating realistic tactile images in simulation, e.g., ones that
capture wear-and-tear defects on object surfaces. In addition, the proposed
Tacchi can be integrated with robotics simulators for a robot system
simulation. Experiment results showed that Tacchi can produce images with
better similarity to real images and achieved higher Sim2Real accuracy compared
to the existing methods. Moreover, it can be connected with MuJoCo and Gazebo
with only the requirement of 1G memory space in GPU compared to a computer
cluster applied for FEM. With Tacchi, physical robot simulation with optical
tactile sensors becomes possible. All the materials in this paper are available
at https://github.com/zixichen007115/Tacchi .Comment: 8 pages, 6 figures, accepted by IEEE Robotics and Automation Letter
Multivariate analysis and optimal configuration of wind-photovoltaic complementary power generation system
Advantages of wind-solar complementary power generation system to utilize solar and wind energy in the aspect of resource and technical economy have been reviewed tersely. Convenience of entering and exiting generating equipment and load from DC as well as AC bus are interpreted briefly. The factors that affect the electrical power output of the system were analyzed and studied. Based on the law of energy conservation, the energetic matching algorithm was proposed which forms the foundation of optimal configuration of system. Finally, the intelligent control and on-line monitoring of wind-solar complementary power generation system were discussed
Prenatal diagnosis of fetal intracranial medulloepithelioma: a case report
Intracranial medulloepithelioma is a very rare and highly malignant tumor that is typically diagnosed in childhood and has an inferior prognosis. In the current report, we described a case of fetal intracranial medulloepithelioma that was detected during the third trimester by prenatal ultrasonography, which displayed homogenous echogenicity with well-circumscribed margins and abundant blood flow. On magnetic resonance imaging, it was hyperintense on both T1- and T2-weighted magnetic resonance imaging. The fetal intracranial tumor was progressive, with rapid expansion within 3 weeks. The report aimed to provide knowledge on the clinical characteristics of fetal intracranial medulloepithelioma in prenatal diagnosis, particularly the radiological features
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