孔隙尺度流动结晶过程机理研究

孔隙尺度渗流中的结晶及晶体生长过程常见于矿物质沉积、生物矿化等自然现象中,且在医药、食品、精细化工品、新材料等领域有着广泛应用。在实际应用中,理解并控制结晶及晶体生长过程具有极其重要的意义,例如:油气生产中的渗流孔隙结垢导致产量下降、稀土提取过程中的杂质浸出、医药产业中的提纯过程等。因此,研究水溶液中晶体结晶生长过程和其潜在机理就显得尤为重要。当前,微观尺度结晶现象由于其复杂性导致晶体形成机理尚不明确,过往研究试图通过分子动力学(Molecular dynamics)及密度泛函理论(Classical density function theory)对结晶过程进行研究。然而,受限于这些方法庞大的计算成本,较大尺度流动结晶现象无法被有效模拟及分析,这就导致在连续介质尺度结晶现象往往被忽视,与实际不符。此外,微纳尺度下现存晶体的生长对未来结晶过程的影响及相关机理仍待进一步研究。针对这些问题,报告人在橡树岭国家实验室工作期间将经典成核理论与流动、传质、相变反应耦合,开发了基于Darcy-Brinkman-Stokes (DBS)架构的数值求解器mpFoam。该求解器通过与在布鲁克海文国家实验室NSLS2光源进行的fast X-ray nanotomography (XnT)微通道流动结晶实验结果进行对比,验证了其准确性。利用该新型求解器,报告人针对不同无量纲数下孔隙流动内的表面结晶率进行了研究,结果发现有效表面结晶率受Damkohler数、Peclet数及结晶参数影响。晶体表面的沉积反应会通过消耗溶液中的反应物浓度产生排空效应影响附近新晶体的形成,进而降低表面结晶率。为了有效控制表面结晶现象,申报人提出了一个新的无量纲数α来描述表面反应率与结晶率的比值。通过同时维持相同的Damkohler数、Peclet数和α,尽管反应率及结晶率改变,表面结晶现象却能够基本保持不变。该研究成果的普适性能够为理解微纳尺度流动结晶过程机理提供理论基础,同时帮助指导未来类似渗流实验设计,有效控制微纳尺度孔隙流动过程中的表面结晶现象

Numerical Study of Mineral Nucleation and Growth on a Substrate

Nucleation and growth processes of minerals and other crystals can significantly affect one another due to the transport limitations and local depletion of reactive ions in the solution. Most numerical models and experimental measurements have typically focused on either growth or nucleation, but not both. In this work, we incorporate a heterogeneous nucleation process based on classical nucleation theory into a microcontinuum model that implements the Darcy-Brinkman-Stokes approach to study the interplay between nucleation and crystal growth on a substrate in diffusive systems. We demonstrate how the Damko??hler number (reaction rate) and nucleation rate prefactor change the effective nucleation rate on a substrate. Higher surface growth rates deplete the solute concentration around the nuclei that appear initially on the substrate, creating islands that screen against further nucleation. The model predicts that measured nucleation rates may be affected by the history of crystal nucleation on the substrate. In the extreme case of high growth rates relative to diffusion, it predicts that the rate of subsequent nucleation is limited by reactant depletion. We introduce a nondimensional number alpha to represent the relation between surface propagation rate during growth and the heterogeneous nucleation rate. We show that it is important to control Damko??hler number and alpha to achieve similar precipitation regimes at different reaction and nucleation rates. We suggest that the observed universality can guide the interpretation of experimental results on nucleation rates, since matching experiment can be achieved by tuning transport, reaction, and nucleation parameters simultaneously. In addition, we show how the bulk solution concentration affects the structure and topology of precipitation on a substrate

基于微流控技术调控生物大分子相分离

液-液相分离作为蛋白质等生物大分子组装成具有功能性的微液滴及无膜细胞器的基础,是生命体功能调控的一种极为普遍的方式,也是近年来新兴的前沿交叉领域。蛋白质相分离蕴含着微纳尺度流体在生物界面上复杂的力学机理,但是我们对相分离液滴成核生长的动力学及其精准调控的了解仍然有限。针对其中相分离微液滴形成的机制与调控的关键科学问题,本研究基于微流控技术,系统地研究了在不同实验条件下PGL-3蛋白质相分离的成核和生长动力学过程,实现了通过盐浓度以及蛋白质与固体表面之间的相互作用来控制相分离的生长过程和标度率。本研究提供了一个定量表征生物大分子相分离动态过程的体外系统,为深入理解生物大分子微液滴在复杂环境中的形成机制提供了研究基础

微观地质过程的瞬态表征和升尺度方法

页岩油气作为自然资源,对国家能源安全有重要的意义。酸化压裂在增加储层渗透率和提高产量方面表现突出,被广泛用于页岩油气田。现存的针对真实页岩样本的实验方法缺少对溶蚀过程的瞬态观测,无法量化溶蚀作用下孔隙结构随时间的变化,另一方面,微流实验在瞬态表征上优势明显,但缺少对真实岩样理化性质的研究。针对以上问题及应用需求,本工作研发了嵌入真实岩样的微流实验平台,在孔隙尺度实时记录溶蚀反应对页岩样本结构和流体流场的影响。同时,本工作运用理论和数值升尺度方法对孔隙、裂缝和复杂介质中的运移过程开展研究,为工程实践提供理论依据

Effect of Nucleation Heterogeneity on Mineral Precipitation in Confined Environments

The formation of new mineral phases in confined environments, especially in porous media, is crucial for various geological processes like mineralization and diagenesis. The nucleation and precipitation of minerals are initiated at the microscale through fluid-rock interaction, where dissolution of primary phases leads to supersaturated conditions and nucleation and growth of secondary ones. Previous research has focused primarily on either precipitation or nucleation, without fully exploring their combined impact. Our study introduces a computational framework that integrates classical nucleation theory with the micro-continuum method. We validated our model by comparing with experiments, and discovered that different surface nucleation rate changes the mode of precipitation from a preferential to uniform precipitate textures. Furthermore, our study uncovered that the conventional deterministic precipitation method tends to underestimate the permeability of the porous matrix. In contrast, the new framework significantly improves model accuracy by incorporating preferential precipitation and heterogeneous nucleation. The formation of minerals in confined environments, especially in porous media, is important for both natural processes and industrial applications. The resulting solid phases can greatly affect the porosity and permeability of the porous structure. Many previous studies have focused on either nucleation or precipitation, we still have a limited understanding of how both processes interact at different scales. In this study, we integrated the Darcy-Brinkman-Stokes method and classical nucleation theory to investigate the interplay between nucleation, precipitation, species transport, and their impact on permeability. Our findings show that adjusting the surface nucleation rates can change the mode of mineral precipitation from preferential to uniform. We also found that the traditional deterministic precipitation method underestimates permeability in certain scenario. Therefore, considering probabilistic nucleation is crucial when there is preferential precipitation and heterogeneous nucleation on the interfaces between the minerals and surrounding liquid under reactive flow conditions. The proposed computational framework focuses on investigating the heterogeneity of nucleation and its effects on mineral precipitation The new model is validated by comparing with experimental data, demonstrating an agreement in both nucleation morphology and rate The new model integrates probabilistic nucleation, resulting in a notable enhancement in the accuracy of permeability prediction

Sub-Nanogram Resolution Measurement of Inertial Mass and Density Using Magnetic-Field-Guided Bubble Microthruster

Artificial micro/nanomotors using active particles hold vast potential in applications such as drug delivery and microfabrication. However, upgrading them to micro/nanorobots capable of performing precise tasks with sophisticated functions remains challenging. Bubble microthruster (BMT) is introduced, a variation of the bubble-driven microrobot, which focuses the energy from a collapsing microbubble to create an inertial impact on nearby target microparticles. Utilizing ultra-high-speed imaging, the microparticle mass and density is determined with sub-nanogram resolution based on the relaxation time characterizing the microparticle's transient response. Master curves of the BMT method are shown to be dependent on the viscosity of the solution. The BMT, controlled by a gamepad with magnetic-field guidance, precisely manipulates target microparticles, including bioparticles. Validation involves measuring the polystyrene microparticle mass and hollow glass microsphere density, and assessing the mouse embryo mass densities. The BMT technique presents a promising chip-free, real-time, highly maneuverable strategy that integrates bubble microrobot-based manipulation with precise bioparticle mass and density detection, which can facilitate microscale bioparticle characterizations such as embryo growth monitoring. This work demonstrates a substantial progress of using swimming microrobots to perform precise tasks with sophisticated functions. This magnetic-field-guided bubble microthruster technique presents a promising chip-free, real-time, highly maneuverable strategy that integrates bubble microrobot-based manipulation with precise bioparticle mass and density detection with sub-nanogram resolution. This technique can facilitate microscale bioparticle characterizations such as embryo growth monitoring. imag

Prediction of Energy Resolution in the JUNO Experiment

International audienceThis paper presents the energy resolution study in the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The study reveals an energy resolution of 2.95% at 1 MeV. Furthermore, the study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data taking. Moreover, it provides a guideline in comprehending the energy resolution characteristics of liquid scintillator-based detectors

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^