11,161 research outputs found
Numerical modeling study of the momentum deposition of small amplitude gravity waves in the thermosphere
We study the momentum deposition in the thermosphere from the dissipation of
small amplitude gravity waves (GWs) within a wave packet using a fully
nonlinear two-dimensional compressible numerical model. The model solves the
nonlinear propagation and dissipation of a GW packet from the stratosphere
into the thermosphere with realistic molecular viscosity and thermal
diffusivity for various Prandtl numbers. The numerical simulations are
performed for GW packets with initial vertical wavelengths (λ<sub><i>z</i></sub>)
ranging from 5 to 50 km. We show that λ<sub><i>z</i></sub> decreases in
time as a GW packet dissipates in the thermosphere, in agreement with the
ray trace results of Vadas and Fritts (2005) (VF05). We also find good
agreement for the peak height of the momentum flux (<i>z</i><sub>diss</sub>) between our
simulations and VF05 for GWs with initial λ<sub><i>z</i></sub> ≤ 2π <i>H</i> in
an isothermal, windless background, where <i>H</i> is the density scale height. We
also confirm that <i>z</i><sub>diss</sub> increases with increasing Prandtl number. We
include eddy diffusion in the model, and find that the momentum deposition
occurs at lower altitudes and has two separate peaks for GW packets with
small initial λ<sub><i>z</i></sub>. We also simulate GW packets in a
non-isothermal atmosphere. The net λ<sub><i>z</i></sub> profile is a competition
between its decrease from viscosity and its increase from the increasing
background temperature. We find that the wave packet disperses more in the
non-isothermal atmosphere, and causes changes to the momentum flux and
λ<sub><i>z</i></sub> spectra at both early and late times for GW packets with
initial λ<sub><i>z</i></sub> ≥ 10 km. These effects are caused by the
increase in <i>T</i> in the thermosphere, and the decrease in <i>T</i> near the mesopause
Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.
International audienceUnderstanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.% Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope
BMP2 gene delivery to bone mesenchymal stem cell by chitosan-g-PEI nonviral vector
published_or_final_versio
A new metric for rotating charged Gauss-Bonnet black holes in AdS spaces
This paper presents a new metric for slowly rotating charged Gauss-Bonnet
black holes in higher dimensional anti-de Sitter spaces. Taking the angular
momentum parameter up to second order, the slowly rotating charged black
hole solutions are obtained by working directly in the action.Comment: 11 pages and accepted by Chin. Phys.
Modelling and control of the flame temperature distribution using probability density function shaping
This paper presents three control algorithms for the output probability density function (PDF) control of the 2D and 3D flame distribution systems. For the 2D flame distribution systems, control methods for both static and dynamic flame systems are presented, where at first the temperature distribution of the gas jet flames along the cross-section is approximated. Then the flame energy distribution (FED) is obtained as the output to be controlled by using a B-spline expansion technique. The general static output PDF control algorithm is used in the 2D static flame system, where the dynamic system consists of a static temperature model of gas jet flames and a second-order actuator. This leads to a second-order closed-loop system, where a singular state space model is used to describe the dynamics with the weights of the B-spline functions as the state variables. Finally, a predictive control algorithm is designed for such an output PDF system. For the 3D flame distribution systems, all the temperature values of the flames are firstly mapped into one temperature plane, and the shape of the temperature distribution on this plane can then be controlled by the 3D flame control method proposed in this paper. Three cases are studied for the proposed control methods and desired simulation results have been obtained
Probing neutral top-pion via a flavor-changing process
In the framework of topcolor-assisted-technicolor model(TC2), we study a
flavor-changing neutral top-pion production process . The study shows that there exists a resonance effect
which can enhance the cross section up to a few fb even tens fb. For a yearly
luminosity 100 at future linear colliders, there might be hundreds
even thousands events to be produced. On the other hand, the background of such
flavor-changing process is very clean due to the GIM mechanism in SM . With
such sufficient events and clean background, neutral toppion could be detected
at future linear colliders with high center of energy and luminosity. Our study
provides a possible way to test TC2 model.Comment: 10 pages, 4 figures,has been accepted by Phys.Rev.
The scalars from the topcolor scenario and the spin correlations of the top pair production at the LHC
The topcolor scenario predicts the existences of some new scalars. In this
paper, we consider the contributions of these new particles to the observables,
which are related to the top quark pair () production at the LHC. It
is found that these new particles can generate significant corrections to the
production cross section and the spin correlations.Comment: 23 pages, 4 figures; discussions and references added; agrees with
published versio
Topological quantum phase transition in an extended Kitaev spin model
We study the quantum phase transition between Abelian and non-Abelian phases
in an extended Kitaev spin model on the honeycomb lattice, where the periodic
boundary condition is applied by placing the lattice on a torus. Our analytical
results show that this spin model exhibits a continuous quantum phase
transition. Also, we reveal the relationship between bipartite entanglement and
the ground-state energy. Our approach directly shows that both the entanglement
and the ground-state energy can be used to characterize the topological quantum
phase transition in the extended Kitaev spin model.Comment: 9 Pages, 4 figure
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