Browsing by Author "Liu, Lu"

Now showing 1 - 3 of 3
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    A novel and efficient engine for P-/S-wave-mode vector decomposition for vertical transverse isotropic elastic reverse time migration
    (Society of Exploration Geophysicists, 2022) Zhang, Lele; Liu, Lu; Niu, Fenglin; Zuo, Jiahui; Shuai, Da; Jia, Wanli; Zhao, Yang
    Wave-mode decomposition plays a very important role in elastic reverse time migration (ERTM). Improved imaging quality can be achieved due to reduced wave-mode crosstalk artifacts. The current state-of-the-art methods for anisotropic wavefield separation are based on either splitting model strategy, low-rank approximation, or lower-upper (LU) factorization. Most of these involve expensive matrix computation and Fourier transforms with strong model assumptions. Based on the anisotropic-Helmholtz (ani-Helmholtz) decomposition operator and decoupled formulations, we develop a novel and efficient P-/S-wave-mode vector decomposition method in vertical transverse isotropic (VTI) media with application in ERTM. We first review the basics of classical Helmholtz decomposition and isotropic decoupled formulations. In addition, the ani-Helmholtz decomposition operator is built from the P- and S-wave polarizations of the Christoffel equation in VTI media. We then derive novel decoupled formulations of anisotropic P-/S-waves based on the obtained ani-Helmholtz operator. Moreover, we use the first-order Taylor expansion to approximate the normalization term from the derived decoupled formulations and obtain an efficient ani-Helmholtz decomposition approach, which produces vector P- and S-wavefields with correct units, phases, and amplitudes. Compared with the previous studies, our approach mitigates model assumptions, avoids intricate calculations, such as LU factorization or low-rank approximation, and only needs three fast Fourier transforms at each time step. In addition, the graphic processing unit technique is used to dramatically accelerate various functions of ERTM, such as wavefields extrapolation, decomposition, and imaging. Three synthetic examples demonstrate the effectiveness and feasibility of our proposed approach.
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    Genotoxicity and Cytotoxicity of Cadmium Sulfide Nanomaterials to Mice: Comparison Between Nanorods and Nanodots
    (Mary Ann Liebert, Inc., 2014) Liu, Lu; Sun, Meiqing; Li, Qingzhao; Zhang, Hongmei; Alvarez, Pedro J.J.; Liu, Huajie; Chen, Wei
    Cadmium sulfide (CdS) nanomaterials (such as CdS nanodots or nanorods) are widely used in optical, electronic, and biological applications. Large-scale production and use of these materials will likely result in accidental and incidental releases, which raise concerns about their potential environmental and human-health impacts. Most studies on toxicity of Cd-containing nanomaterials have focused on nanodots, and the relative toxicity of Cd containing nanorods is not well understood. Here, we compared genotoxicity and cytotoxicity of CdS nanorods (30-50nm diameter, 500-1100 nm length) and cubic CdS nanodots (3-5 nm) in mice by examining total cadmium accumulation in organs, acute toxicity, DNA damage, spermatozoon viability and abnormality, kidney and liver damage, and oxidative stress. Compared with (smaller) nanodots, nanorods resulted in relatively low bioaccumulation, acute toxicity, and damage to spermatozoa and the tested organs. Differences in toxicity between CdS nanodots and nanorods could not be fully explained by differences in their metal ion (Cd2 + ) release patterns, based on control tests with mice gavaged with dissolved CdCl2 at equivalent concentrations. This underscores that toxicity of metallic nanomaterials could not be solely predicted based either on their elemental composition or on the amount of ions released before receptor intake. Particle morphology (including size) may also need to be considered.
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    Mesoscale Modeling of Distributed Water Systems Enables Policy Search
    (Wiley, 2023) Zhou, Xiangnan; Duenas-Osorio, Leonardo; Doss-Gollin, James; Liu, Lu; Stadler, Lauren; Li, Qilin; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    It is widely acknowledged that distributed water systems (DWSs), which integrate distributed water supply and treatment with existing centralized infrastructure, can mitigate challenges to water security from extreme events, climate change, and aged infrastructure. However, it is unclear which are beneficial DWS configurations, i.e., where and at what scale to implement distributed water supply. We develop a mesoscale representation model that approximates DWSs with reduced backbone networks to enable efficient system emulation while preserving key physical realism. Moreover, system emulation allows us to build a multiobjective optimization model for computational policy search that addresses energy utilization and economic impacts. We demonstrate our models on a hypothetical DWS with distributed direct potable reuse (DPR) based on the City of Houston's water and wastewater infrastructure. The backbone DWS with greater than 92% link and node reductions achieves satisfactory approximation of global flows and water pressures, to enable configuration optimization analysis. Results from the optimization model reveal case-specific as well as general opportunities, constraints, and their interactions for DPR allocation. Implementing DPR can be beneficial in areas with high energy intensities of water distribution, considerable local water demands, and commensurate wastewater reuse capacities. The mesoscale modeling approach and the multiobjective optimization model developed in this study can serve as practical decision-support tools for stakeholders to search for alternative DWS options in urban settings.