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Search Results: 1 - 10 of 134375 matches for " Li Q "
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Fuzzy approach to analysis of flood risk based on variable fuzzy sets and improved information diffusion methods
Q. Li
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2013,
Abstract: The predictive analysis of natural disasters and their consequences is challenging because of uncertainties and incomplete data. The present article studies the use of variable fuzzy sets (VFS) and improved information diffusion method (IIDM) to construct a composite method. The proposed method aims to integrate multiple factors and quantification of uncertainties within a consistent system for catastrophic risk assessment. The fuzzy methodology is proposed in the area of flood disaster risk assessment to improve probability estimation. The purpose of the current study is to establish a fuzzy model to evaluate flood risk with incomplete data sets. The results of the example indicate that the methodology is effective and practical; thus, it has the potential to forecast the flood risk in flood risk management.
Longwave indirect effect of mineral dusts on ice clouds
Q. Min,R. Li
Atmospheric Chemistry and Physics Discussions , 2010,
Abstract: In addition to microphysical changes in clouds, changes in nucleation processes of ice cloud due to aerosols would result in substantial changes in cloud top distribution as mildly supercooled clouds are glaciated through heterogonous nucleation processes. Measurements from multiple sensors on multiple observing platforms over the Atlantic Ocean show that the cloud effective temperature increases with mineral dust loading with a slope of +3.06 °C per unit AOD. The macrophysical changes in ice cloud top distributions as a consequence of mineral dust-cloud interaction exert a strong cooling effect (up to 16 w m 2) of thermal infrared radiation on cloud systems. Induced changes of ice particle size by mineral dusts influence cloud emissivity and play a minor role in modulating the outgoing longwave radiation for optically thin ice clouds. Such a strong cooling forcing of thermal infrared radiation would have significant impacts on cloud systems and subsequently on climate.
Longwave indirect effect of mineral dusts on ice clouds
Q. Min,R. Li
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010, DOI: 10.5194/acp-10-7753-2010
Abstract: In addition to microphysical changes in clouds, changes in nucleation processes of ice cloud due to aerosols would result in substantial changes in cloud top temperature as mildly supercooled clouds are glaciated through heterogenous nucleation processes. Measurements from multiple sensors on multiple observing platforms over the Atlantic Ocean show that the cloud effective temperature increases with mineral dust loading with a slope of +3.06 °C per unit aerosol optical depth. The macrophysical changes in ice cloud top distributions as a consequence of mineral dust-cloud interaction exert a strong cooling effect (up to 16 Wm 2) of thermal infrared radiation on cloud systems. Induced changes of ice particle size by mineral dusts influence cloud emissivity and play a minor role in modulating the outgoing longwave radiation for optically thin ice clouds. Such a strong cooling forcing of thermal infrared radiation would have significant impacts on cloud systems and subsequently on climate.
Hadrons in Dense Matter and Medium Effects in Relativistic Heavy-Ion Collisions
G. Q. Li
Physics , 1997,
Abstract: Theoretical and experimental studies of hot and/or dense matter, such as is created in high-energy heavy-ion collisions, and encountered in compact objects in astrophysics, constitute one of the most active frontiers in nuclear physics. In these Lectures, we discuss various approaches to the description of hot and/or dense matter, including the simple Skyrme-type parameterization and relativistic Walecka-type models, as well as microscopic Dirac-Brueckner and QCD sum rule approaches. As density and/or temperature of the hadronic system increases, chiral symmetry is gradually restored, as indicated by the decrease of quark condensate. This has profound effects on the properties of hadrons, especially their masses. We review various theoretical predictions for hadron properties in dense matter. Experimentally, possible medium modifications of hadron properties can be studied through the measurements of particle spectra, flow, and particularly, electromagnetic observables. Particle production, especially the production of rare particles such as kaons, vector mesons, and antiparticles, provides useful insight into heavy-ion collision dynamics, and hadron properties in dense matter. Collective flows of various kinds are important observables in heavy-ion collisions. They probe essentially the entire reaction process, and thus are very useful for the determination of the reaction dynamics. They also reflect the properties of hadrons in dense matter. Electromagnetic signals are considered penetrating probes that may carry undistorted information about the early stage of high-energy heavy-ion collisions. We discuss various theoretical calculations of dilepton and photon production in heavy-ion collisions at SPS energies and various medium effects that have been proposed to explain the observed low-mass dilepton enhancement.
A theoretical study of the hydrogen-storage potential of (H_2)_4CH_4 in metal organic framework materials and carbon nanotubes
Q. Li,T. Thonhauser
Physics , 2012, DOI: 10.1088/0953-8984/24/42/424204
Abstract: The hydrogen-methane compound (H_2)_4CH_4---or for short H4M---is one of the most promising hydrogen-storage materials. This van der Waals compound is extremely rich in molecular hydrogen: 33.3 mass%, not including the hydrogen bound in CH_4; including it, we reach even 50.2 mass%. Unfortunately, H4M is not stable under ambient pressure and temperature, requiring either low temperature or high pressure. In this paper, we investigate the properties and structure of the molecular and crystalline forms of H4M, using ab initio methods based on van der Waals DFT (vdW-DF). We further investigate the possibility of creating the pressures required to stabilize H4M through external agents such as metal organic framework (MOF) materials and carbon nanotubes, with very encouraging results. In particular, we find that certain MOFs can create considerable pressure for H4M in their cavities, but not enough to stabilize it at room temperature, and moderate cooling is still necessary. On the other hand, we find that all investigated carbon nanotubes can create the high pressures required for H4M to be stable at room temperature, with direct implications for new and exciting hydrogen-storage applications.
Multi-GPU Distributed Parallel Bayesian Differential Topic Modelling
Aaron Q Li
Computer Science , 2015,
Abstract: There is an explosion of data, documents, and other content, and people require tools to analyze and interpret these, tools to turn the content into information and knowledge. Topic modeling have been developed to solve these problems. Topic models such as LDA [Blei et. al. 2003] allow salient patterns in data to be extracted automatically. When analyzing texts, these patterns are called topics. Among numerous extensions of LDA, few of them can reliably analyze multiple groups of documents and extract topic similarities. Recently, the introduction of differential topic modeling (SPDP) [Chen et. al. 2012] performs uniformly better than many topic models in a discriminative setting. There is also a need to improve the sampling speed for topic models. While some effort has been made for distributed algorithms, there is no work currently done using graphical processing units (GPU). Note the GPU framework has already become the most cost-efficient platform for many problems. In this thesis, I propose and implement a scalable multi-GPU distributed parallel framework which approximates SPDP. Through experiments, I have shown my algorithms have a gain in speed of about 50 times while being almost as accurate, with only one single cheap laptop GPU. Furthermore, I have shown the speed improvement is sublinearly scalable when multiple GPUs are used, while fairly maintaining the accuracy. Therefore on a medium-sized GPU cluster, the speed improvement could potentially reach a factor of a thousand. Note SPDP is just a representative of other extensions of LDA. Although my algorithm is implemented to work with SPDP, it is designed to be a general enough to work with other topic models. The speed-up on smaller collections (i.e., 1000s of documents), means that these more complex LDA extensions could now be done in real-time, thus opening up a new way of using these LDA models in industry.
Independent domains of disoriented chiral condensate
Q. H. Zhang,and X. Q. Li
Physics , 1997, DOI: 10.1103/PhysRevD.55.7302
Abstract: The probability distribution of a neutral pion fraction from independent domains of disoriented chiral condensate is characterized. The signal for the condensate is still clear for a large number of independent domains if one of them is predominant.
Coherent source radius in ppbar collisions
Q. H. Zhang,X. Q. Li
Physics , 1997, DOI: 10.1103/PhysRevC.57.1562
Abstract: We use a recently derived result to extract from two-pion interferometry data from $p\bar{p}$ collisions the radius of the coherent component in the source. We find a coherent source radius of about $2 fm$.
Cerenkov Emission by Neutral Particles in Gravitoelectro-magnetic Fields
X. Q. Li,S. Q. Liu
Physics , 2005,
Abstract: It is shown that under the post-Newtonian approximation the Einstein equations can be reduced to the standard Maxwell-type field equations in a medium; in such a context the Cerenkov emission by a neutralparticle gives large energy loss while the particle moves at faster than the phase speed of waves in the medium.
Contact angles in the pseudopotential lattice Boltzmann modeling of wetting
Q. Li,K. H. Luo,Q. J. Kang,Q. Chen
Physics , 2014, DOI: 10.1103/PhysRevE.90.053301
Abstract: In this paper, we aim to investigate the implementation of contact angles in the pseudopotential lattice Boltzmann modeling of wetting at a large density ratio. The pseudopotential lattice Boltzmann model [X. Shan and H. Chen, Phys. Rev. E 49, 2941 (1994)] is a popular mesoscopic model for simulating multiphase flows and interfacial dynamics. In this model, the contact angle is usually realized by a fluid-solid interaction. Two widely used fluid-solid interactions: the density-based interaction and the pseudopotential-based interaction, as well as a modified pseudopotential-based interaction formulated in the present paper, are numerically investigated and compared in terms of the achievable contact angles, the maximum and the minimum densities, and the spurious currents. It is found that the pseudopotential-based interaction works well for simulating small static (liquid) contact angles, however, is unable to reproduce static contact angles close to 180 degrees. Meanwhile, it is found that the proposed modified pseudopotential-based interaction performs better in light of the maximum and the minimum densities and is overall more suitable for simulating large contact angles as compared with the other two types of fluid-solid interactions. Furthermore, the spurious currents are found to be enlarged when the fluid-solid interaction force is introduced. Increasing the kinematic viscosity ratio between the vapor and liquid phases is shown to be capable of reducing the spurious currents caused by the fluid-solid interactions.
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