Search

The wettability mechanism of soil–water interfaces is of significant importance in geotechnical engineering. However, the effect of different contact angles on unsaturated sand soil behavior has been less understood. In this study, the wetting behavior of nano water droplets on various silica substrates is investigated using molecular dynamics. Seventeen groups of simulation systems with different interaction potential energies ($\varepsilon _{\mathrm{Si}} = 0.008$, 0.04, 0.2, 0.4, 0.6, 0.8, 1, 2 kcal/mol) and temperatures ($T = 273$, 298, 323, 353 K) are conducted. The results show that the contact angles varies intensively with interaction potential energies from 108.5° to 18.1°, which indicates a transition from hydrophobic to hydrophilic and wettability enhancement along with the increase of interaction potential energy. Simulation results also show that contact angles increase with the increase of temperature, whatever the hydrophobic or hydrophilic of the silica surface. Such phenomena are interpreted from the perspective of microstructure, along with the performance of macrostructure. In addition, results show that the contact angles are independent of the thickness and width (length) of silica substrate.

Quantum dynamics simulation and computational spectroscopy serve as indispensable tools for the theoretical understanding of various fundamental physical and chemical processes, ranging from charge transfer to photochemical reactions. When simulating realistic systems, the primary challenge stems from the overwhelming number of degrees of freedom and the pronounced many-body correlations. Here, we present Kylin-V, an innovative quantum dynamics package designed for accurate and efficient simulations of dynamics and spectroscopic properties of vibronic Hamiltonians for molecular systems and their aggregates. Kylin-V supports various quantum dynamics and computational spectroscopy methods, such as time-dependent density matrix renormalization group and our recently proposed single-site and hierarchical mapping approaches, as well as vibrational heat-bath configuration interaction. In this paper, we introduce the methodologies implemented in Kylin-V and illustrate their performances through a diverse collection of numerical examples. [ABSTRACT FROM AUTHOR]

An exciton–phonon (ex–ph) model based on our recently developed block interaction product basis framework is introduced to simulate the distal charge separation (CS) process in aggregated perylenediimide (PDI) trimer incorporating the quantum dynamic method, i.e., the time-dependent density matrix renormalization group. The electronic Hamiltonian in the ex–ph model is represented by nine constructed diabatic states, which include three local excited (LE) states and six charge transfer (CT) states from both the neighboring and distal chromophores. These diabatic states are automatically generated from the direct products of the leading localized neutral or ionic states of each chromophore's reduced density matrix, which are obtained from ab initio quantum chemical calculation of the subsystem consisting of the targeted chromophore and its nearest neighbors, thus considering the interaction of the adjacent environment. In order to quantum-dynamically simulate the distal CS process with massive coupled vibrational modes in molecular aggregates, we used our recently proposed hierarchical mapping approach to renormalize these modes and truncate those vibrational modes that are not effectively coupled with electronic states accordingly. The simulation result demonstrates that the formation of the distal CS process undergoes an intermediate state of adjacent CT, i.e., starts from the LE states, passes through an adjacent CT state to generate the intermediates (∼ 200 fs), and then formalizes the targeted distal CS via further charge transference (∼ 1 ps). This finding agrees well with the results observed in the experiment, indicating that our scheme is capable of quantitatively investigating the CS process in a realistic aggregated PDI trimer and can also be potentially applied to exploring CS and other photoinduced processes in larger systems. [ABSTRACT FROM AUTHOR]

Ambient noise autocorrelations can be used to reconstruct the seismic reflection response of the Earth structure beneath single stations using continuous recordings without the need for either active sources or earthquakes. In the last decade, this technique has emerged as an inexpensive approach with the potential to provide similar information to that from the classical receiver function (RF) analysis. Previous studies have located and mapped discontinuities at different crustal depths with ambient noise autocorrelations by applying different processing techniques. An ambient noise autocorrelation function (ACF) provides the body-wave reflectivity of the local structure, assuming a homogeneous distribution of noise sources. However, an effective method design is required in order to determine a reliable reflection response. Here, we review the theory behind the ambient noise ACF method and design a workflow to obtain the P -wave reflectivity with a special focus on the Moho depth. In particular, we calculate a smooth function to fit and subtract the zero-lag component in the time domain, that is, the large-amplitude signal near 0 lag time in the ACF. The zero-lag component can interfere with the reflection component, so its removal allows us to increase the frequency band to use. We bandpass filter the ACFs between 1 and 6 s. We also derive and apply a phase shift correction in the ACFs due to the integration of a homogeneously distributed noise field dominated by distant sources from deep below, such as teleseismic sources. Both linear and nonlinear, phase-weighted stacks are used. Linear stacking is used to identify the main interfaces since it ensures the linearity of the processing steps; nevertheless, nonlinear, phase-weighted stacking help validate the coherent signals. We test and apply our method to continuous vertical recordings from three stations in Ireland and five stations in different cratons and obtain clear P -wave reflection from the Moho and other crustal and upper-mantle discontinuities in most cases. However, noise coming from local heterogeneities, non-homogeneous distribution of the ambient noise sources or instrumental noise is also expected. Therefore, additional, a priori information is desirable to help identify key phases in single ACFs. We compute synthetic ACFs using P -wave velocity (V P) models from controlled-source profiles in Ireland. The relatively complex ACF traces obtained at the stations in Ireland show a close data-synthetic match for the Moho and mid-crustal discontinuities. The ACF traces from the stations in different cratons are directly compared with receiver functions showing overall agreement and offering complementary information on the origin of the signal. [ABSTRACT FROM AUTHOR]

Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater. Mg isotopes are significantly (up to 5‰) fractionated during carbonate precipitation by preferential incorporation of Mg, while hydrothermal reactions are associated with negligible Mg isotope fractionation by preferential sequestration of Mg. Thus, the marine Mg cycle could be reflected by seawater Mg isotopic composition (δMg), which might be recorded in marine carbonate. However, carbonates are both texturally and compositionally heterogeneous, and it is unclear which carbonate component is the most reliable for reconstructing δMg. In this study, we measured Mg isotopic compositions of limestone samples collected from the early Carboniferous Huangjin Formation in South China. Based on petrographic studies, four carbonate components were recognized: micrite, marine cement, brachiopod shell, and mixture. The four components had distinct δMg: (1) micrite samples ranged from −2.86‰ to −2.97‰; (2) pure marine cements varied from −3.40‰ to −3.54‰, while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range (−3.27‰ to −3.75‰); (3) values for the mixture component were −3.17‰ and −3.49‰; and (4) brachiopod shells ranged from −2.20‰ to −3.07‰, with the thickened hinge area enriched in Mg. Due to having multiple carbonate sources, neither the micrite nor the mixture component could be used to reconstruct δMg. In addition, the marine cement was homogenous in Mg isotopes, but lacking the fractionation by inorganic carbonate precipitation that is prerequisite for the accurate determination of δMg. Furthermore, brachiopod shells had heterogeneous C and Mg isotopes, suggesting a significant vital effect during growth. Overall, the heterogeneous δMg of the Huangjin limestone makes it difficult to reconstruct δMg using bulk carbonate/calcareous sediments. Finally, δMg was only slightly affected by the faunal composition of carbonate-secreting organisms, even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range (0.2‰-4.8‰) of fractionation during biogenic carbonate formation. [ABSTRACT FROM AUTHOR]