18,063 research outputs found
Lattice Boltzmann Method Simulation of 3-D Melting Using Double MRT Model with Interfacial Tracking Method
Three-dimensional melting problems are investigated numerically with Lattice
Boltzmann method (LBM). Regarding algorithm's accuracy and stability,
Multiple-Relaxation-Time (MRT) models are employed to simplify the collision
term in LBM. Temperature and velocity fields are solved with double
distribution functions, respectively. 3-D melting problems are solved with
double MRT models for the first time in this article. The key point for the
numerical simulation of a melting problem is the methods to obtain the location
of the melting front and this article uses interfacial tracking method. The
interfacial tracking method combines advantages of both deforming and fixed
grid approaches. The location of the melting front was obtained by calculating
the energy balance at the solid-liquid interface. Various 3-D conduction
controlled melting problems are solved firstly to verify the numerical method.
Liquid fraction tendency and temperature distribution obtained from numerical
methods agree with the analytical results well. The proposed double MRT model
with interfacial tracking method is valid to solve 3-D melting problems.
Different 3-D convection controlled melting problems are then solved with the
proposed numerical method. Various locations of the heat surface have different
melting front moving velocities, due to the natural convection effects.
Rayleigh number's effects to the 3-D melting process is discussed
Dynamical Model of Binary Asteroid Systems Using Binary Octahedrons
We used binary octahedrons to investigate the dynamical behaviors of binary
asteroid systems. The mutual potential of the binary polyhedron method is
derived from the fourth order to the sixth order. The irregular shapes,
relative orbits, attitude angles, as well as the angular velocities of the
binary asteroid system are included in the model. We investigated the relative
trajectory of the secondary relative to the primary, the total angular momentum
and total energy of the system, the three-axis attitude angular velocity of the
binary system, as well as the angular momentum of the two components. The
relative errors of total angular momentum and total energy indicate the
calculation has a high precision. It is found that the influence of the orbital
and attitude motion of the primary from the gravitational force of the
secondary is obvious. This study is useful for understanding the complicated
dynamical behaviors of the binary asteroid systems discovered in our Solar
system.Comment: 22 pages, 12 figure
Structural, Dynamic, and Vibrational Properties during Heat Transfer in Si/Ge Superlattices: A Car-Parrinello Molecular Dynamics Study
The structural, dynamic, and vibrational properties during the heat transfer
process in Si/Ge superlattices, are studied by analyzing the trajectories
generated by the ab initio Car-Parrinello molecular dynamics simulation. The
radial distribution functions and mean square displacements are calculated and
further discussions are made to explain and probe the structural changes
relating to the heat transfer phenomenon. Furthermore, the vibrational density
of states of the two layers (Si/Ge) are computed and plotted to analyze the
contributions of phonons with different frequencies to the heat conduction.
Coherent heat conduction of the low frequency phonons is found and their
contributions to facilitate heat transfer are confirmed. The Car-Parrinello
molecular dynamics simulation outputs in the work show reasonable
thermophysical results of the thermal energy transport process and shed light
on the potential applications of treating the heat transfer in the
superlattices of semiconductor materials from a quantum mechanical molecular
dynamics simulation perspective
Cross-domain Dialogue Policy Transfer via Simultaneous Speech-act and Slot Alignment
Dialogue policy transfer enables us to build dialogue policies in a target
domain with little data by leveraging knowledge from a source domain with
plenty of data. Dialogue sentences are usually represented by speech-acts and
domain slots, and the dialogue policy transfer is usually achieved by assigning
a slot mapping matrix based on human heuristics. However, existing dialogue
policy transfer methods cannot transfer across dialogue domains with different
speech-acts, for example, between systems built by different companies. Also,
they depend on either common slots or slot entropy, which are not available
when the source and target slots are totally disjoint and no database is
available to calculate the slot entropy. To solve this problem, we propose a
Policy tRansfer across dOMaIns and SpEech-acts (PROMISE) model, which is able
to transfer dialogue policies across domains with different speech-acts and
disjoint slots. The PROMISE model can learn to align different speech-acts and
slots simultaneously, and it does not require common slots or the calculation
of the slot entropy. Experiments on both real-world dialogue data and
simulations demonstrate that PROMISE model can effectively transfer dialogue
policies across domains with different speech-acts and disjoint slots.Comment: v
Achieving acoustic cloak by using compressible background flow
We propose a scheme of acoustic spherical cloaking by means of background
irrotational flow in compressible fluid. The background flow forms a virtual
curved spacetime and guides the sound waves bypass the cloaked objects. To
satisfy the laws of real fluid, we show that spatially distributed mass source
and momentum source are necessary to supply. The propagation of sound waves in
this system is studied via both geometric acoustics approximation and full wave
approach. The analytic solution of sound fields is obtained for plane wave
incidence. The results reveal the effect of phase retardation (or lead) in
comparison with the ordinary transformation-acoustic cloak. In addition, the
ability of cloaking is also evaluated for unideal background flows by analyzing
the scattering cross section.Comment: 15 pages, 6 figure
Effects of Slotted Structures on Nonlinear Characteristics of Natural Convection in a Cylinder with an Internal Concentric Slotted Annulus
Natural convection in a cylinder with an internally slotted annulus was
solved by SIMPLE algorithm, and the effects of different slotted structures on
nonlinear characteristics of natural convection were investigated. The results
show that the equivalent thermal conductivity Keq increases with Rayleigh
number, and reaches the maximum in the vertical orientation. Nonlinear results
were obtained by simulating the fluid flow at different conditions. With
increasing Rayleigh number, heat transfer is intensified and the state of heat
transfer changes from the steady to unsteady. We investigated different slotted
structures effects on natural convection, and analyze the corresponding
nonlinear characteristics
An observational proxy of halo assembly time and its correlation with galaxy properties
We show that the ratio between the stellar mass of central galaxy and the
mass of its host halo, , can be used as an
observable proxy of halo assembly time, in that galaxy groups with higher
assembled their masses earlier. Using SDSS groups of Yang et al., we study how
correlates with galaxy properties such as color, star formation rate,
metallicity, bulge to disk ratio, and size. Central galaxies of a given stellar
mass in groups with tend to be redder in color, more quenched in
star formation, smaller in size, and more bulge dominated, as increases.
The trends in color and star formation appear to reverse at ,
reflecting a down-sizing effect that galaxies in massive halos formed their
stars earlier although the host halos themselves assembled later (lower ).
No such reversal is seen in the size of elliptical galaxies, suggesting that
their assembly follows halo growth more closely than their star formation.
Satellite galaxies of a given stellar mass in groups of a given halo mass tend
to be redder in color, more quenched in star formation and smaller in size as
increases. For a given stellar mass, satellites also tend to be smaller
than centrals. The trends are stronger for lower mass groups. For groups more
massive than , a weak reversed trend is seen in
color and star formation. The observed trends in star formation are
qualitatively reproduced by an empirical model based on halo age abundance
matching, but not by a semi-analytical model tested here.Comment: 13 pages, 13 figures, accepted for publication in MNRA
Fine Grained Knowledge Transfer for Personalized Task-oriented Dialogue Systems
Training a personalized dialogue system requires a lot of data, and the data
collected for a single user is usually insufficient. One common practice for
this problem is to share training dialogues between different users and train
multiple sequence-to-sequence dialogue models together with transfer learning.
However, current sequence-to-sequence transfer learning models operate on the
entire sentence, which might cause negative transfer if different personal
information from different users is mixed up. We propose a personalized decoder
model to transfer finer granularity phrase-level knowledge between different
users while keeping personal preferences of each user intact. A novel personal
control gate is introduced, enabling the personalized decoder to switch between
generating personalized phrases and shared phrases. The proposed personalized
decoder model can be easily combined with various deep models and can be
trained with reinforcement learning. Real-world experimental results
demonstrate that the phrase-level personalized decoder improves the BLEU over
multiple sentence-level transfer baseline models by as much as 7.5%
Exploring the thermal energy contents of the intergalactic medium with the Sunyaev-Zel'dovich effect
We examine the thermal energy contents of the intergalactic medium (IGM) over
three orders of magnitude in both mass density and gas temperature using
thermal Sunyaev-Zel'dovich effect (tSZE). The analysis is based on {\it Planck}
tSZE map and the cosmic density field, reconstructed for the SDSS DR7 volume
and sampled on a grid of cubic cells of , together with a
matched filter technique employed to maximize the signal-to-noise. Our results
show that the pressure - density relation of the IGM is roughly a power law
given by an adiabatic equation of state, with an indication of steepening at
densities higher than about times the mean density of the universe. The
implied average gas temperature is in regions of mean
density, , increasing to about
for , and to
for . At a
given density, the thermal energy content of the IGM is also found to be higher
in regions of stronger tidal fields, likely due to shock heating by the
formation of large scale structure and/or feedback from galaxies and AGNs. A
comparison of the results with hydrodynamic simulations suggests that the
current data can already provide interesting constraints on galaxy formation.Comment: 9 pages, 5 figures, submitted to MNRAS, comments are welcom
Detection of missing baryons in galaxy groups with kinetic Sunyaev-Zel'dovich effect
We present the detection of the kinetic Sunyaev-Zel'dovich effect (kSZE)
signals from groups of galaxies as a function of halo mass down to , using the {\it Planck} CMB maps and
stacking about galaxy systems with known positions, halo masses, and
peculiar velocities. The signals from groups of different mass are constrained
simultaneously to take care of projection effects of nearby halos. The total
kSZE flux within halos estimated implies that the gas fraction in halos is
about the universal baryon fraction, even in low-mass halos, indicating that
the `missing baryons' are found. Various tests performed show that our results
are robust against systematic effects, such as contamination by infrared/radio
sources and background variations, beam-size effects and contributions from
halo exteriors. Combined with the thermal Sunyaev-Zel'dovich effect, our
results indicate that the `missing baryons' associated with galaxy groups are
contained in warm-hot media with temperatures between and .Comment: Significantly revised from the previous version. Accepted for
publication in Ap
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