117 research outputs found
An efficient topology optimization method for steady gas flows in all flow regimes
An efficient topology optimization method applicable to both continuum and
rarefied gas flows is proposed in the framework of gas-kinetic theory. The
areas of gas and solid are marked by the material density, based on which a
fictitious porosity model is used to reflect the effect of the solid on the gas
and mimic the diffuse boundary condition on the gas-solid interface. The
formula of this fictitious porosity model is modified to make the model work
well in all flow regimes, i.e., from the continuum to free-molecular flow
regimes. To find the optimized material density, a gradient-based optimizer is
adopted and the design sensitivity is obtained by the continuous adjoint
method. To solve the primal kinetic equation and the corresponding adjoint
equation, the numerical schemes efficient and accurate in all flow regimes are
constructed. Several airfoil optimization problems are solved to demonstrate
the good performance and high efficiency of the present topology optimization
method, covering the flow conditions from continuum to rarefied, and from
subsonic to supersonic
Quantum-trajectory analysis for charge transfer in solid materials induced by strong laser fields
We investigate the dependence of charge transfer on the intensity of driving
laser field when SiO2 crystal is irradiated by an 800 nm laser. It is
surprising that the direction of charge transfer undergoes a sudden reversal
when the driving laser intensity exceeds critical values with different carrier
envelope phases. By applying quantum-trajectory analysis, we find that the
Bloch oscillation plays an important role in charge transfer in solid. Also, we
study the interaction of strong laser with gallium nitride (GaN) that is widely
used in optoelectronics. A pump-probe scheme is applied to control the quantum
trajectories of the electrons in the conduction band. The signal of charge
transfer is controlled successfully by means of theoretically proposed
approach
Transition-based directed graph construction for emotion-cause pair extraction
Emotion-cause pair extraction aims to extract all potential pairs of emotions and corresponding causes from unannotated emotion text. Most existing methods are pipelined framework, which identifies emotions and extracts causes separately, leading to a drawback of error propagation. Towards this issue, we propose a transition-based model to transform the task into a procedure of parsing-like directed graph construction. The proposed model incrementally generates the directed graph with labeled edges based on a sequence of actions, from which we can recognize emotions with the corresponding causes simultaneously, thereby optimizing separate subtasks jointly and maximizing mutual benefits of tasks interdependently. Experimental results show that our approach achieves the best performance, outperforming the state-of-the-art methods by 6.71% (p<0.01) in F1 measure
Efficient parallel solver for high-speed rarefied gas flow using GSIS
Recently, the general synthetic iterative scheme (GSIS) has been proposed to
find the steady-state solution of the Boltzmann equation in the whole range of
gas rarefaction, where its fast-converging and asymptotic-preserving properties
lead to the significant reduction of iteration numbers and spatial cells in the
near-continuum flow regime. However, the efficiency and accuracy of GSIS has
only been demonstrated in two-dimensional problems with small numbers of
spatial cell and discrete velocities. Here, a large-scale parallel computing
strategy is designed to extend the GSIS to three-dimensional high-speed flow
problems. Since the GSIS involves the calculation of the mesoscopic kinetic
equation which is defined in six-dimensional phase-space, and the macroscopic
high-temperature Navier-Stokes-Fourier equations in three-dimensional physical
space, the proper partition of the spatial and velocity spaces, and the
allocation of CPU cores to the mesoscopic and macroscopic solvers, are the keys
to improving the overall computational efficiency. These factors are
systematically tested to achieve optimal performance, up to 100 billion spatial
and velocity grids. For hypersonic flows around the Apollo reentry capsule, the
X38-like vehicle, and the space station, our parallel solver can get the
converged solution within one hour
RefGPT: Reference -> Truthful & Customized Dialogues Generation by GPTs and for GPTs
General chat models, like ChatGPT, have attained impressive capability to
resolve a wide range of NLP tasks by tuning Large Language Models (LLMs) with
high-quality instruction data. However, collecting human-written high-quality
data, especially multi-turn dialogues, is expensive and unattainable for most
people. Though previous studies have used powerful LLMs to generate the
dialogues automatically, but they all suffer from generating untruthful
dialogues because of the LLMs hallucination. Therefore, we propose a method
called RefGPT to generate enormous truthful and customized dialogues without
worrying about factual errors caused by the model hallucination. RefGPT solves
the model hallucination in dialogue generation by restricting the LLMs to
leverage the given reference instead of reciting their own knowledge to
generate dialogues. Additionally, RefGPT adds detailed controls on every
utterances to enable highly customization capability, which previous studies
have ignored. On the basis of RefGPT, we also propose two high-quality dialogue
datasets generated by GPT-4, namely RefGPT-Fact and RefGPT-Code. RefGPT-Fact is
100k multi-turn dialogue datasets based on factual knowledge and RefGPT-Code is
76k multi-turn dialogue dataset covering a wide range of coding scenarios. Our
code and datasets are released in https://github.com/ziliwangnlp/RefGP
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