Isothermal diffusion of water vapor in unsaturated soils based on Fick’s second law

In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.

Ethylene Stimulation of Rubberwood （Hevea brasiliensis） Increases the Water Permeability of Lumber

Hevea brasiliensis Muell. Arg. is an important industrial crop for natural rubber production. Latex biosynthesis occurs in the cytoplasm of highly specialized latex cells and latex bleeds out when the bark is tapped. Ethylene stimulation acts by increasing latex flow to the cells of inner bark from the latex cells, increasing yield and may affect the physical properties of rubberwood. The aim of this work was to assess the permeability properties of ethylene treated rubberwood （TRW） relative to untreated rubberwood （URW）, because in wood industrial technology, permeability relates to bondability and wood preservative treatments. The Hevea samples were of PRIM 600 strain, from 20-25 years old rubber trees. The TRW rubber trees had been stimulated by ethylene gas for six years. The rubberwood specimens were collected at a single plot of plantation to minimize variations in soil fertility, environmental exposures and silvicultural treatments at Tumbon Chaibury, Amphor Chaibury, Suratthani Province, Thailand. The moisture contents （MC） of fresh rubberwood were significantly different （P 〈 0.05） at 75% for TRW and 64% for URW. The permeability experiment followed Darcy＇s law, and the hydrostatic pressure was controlled. The average 0.005 Darcy water permeability of TRW was significantly higher than the 0.001 Darcy for URW. Water absorptions during 4 h water immersion of rubberwood blocks differed significantly, and TRW had higher absorption than URW also across 6 d of immersion. Scanning electron microscope （SEM） imaging showed anatomical effects that contribute to the fivefold permeability increase.

Analysis of the relationship between water level fluctuation and seismicity in the Three Gorges Reservoir(China)

The Three Gorges Reservoir is a good site for the further researches on reservoir induced seismicity due to decades＇ seismic monitoring. After the first water impounding in 2003, seismic activity becomes more frequent than that before water impoundment. In order to quantitatively study, the relationship between the water level fluctuation and earthquakes in TGR, we introduced statistical methods to attain the goal. First of all, we relocated the earthquakes in TGR region with double difference method and divided the earthquakes into 5 clusters with clustering analysis method. Secondly, to examine the impacts of water level fluctuation in different water filling stages on the seismic activity in the 5 clusters, a series of statistical analyses are applied. Pearson correlation results show that only the 175 m water level fluc- tuation has significantly positive impacts on the seismic activity in clusters I, II, III and V with correlation coefficients of 0.44, 0.38, 0.66 and 0.63. Cross-correlation analysis demonstrates that 0, ], 0 and 0 month time delay separately for the clusters I, II, III and V exists. It illustrated the influences of the water loading and pore pressure diffusion on induced earthquakes. Cointegration tests and impulse response analysis denoted that the 175 m water level only had long term and significant effects just on the seismic events in the intersection region of the Fairy Mount Fault and Nine-brook Fault. One standard deviation shock to 175 m water level increased the seismic activity in cluster V for the first 3 months, and then the negative influence was shown. After 7 months, the negative impulse response becomes stable. The long-term effect of the 175 m water impoundment also proved the important role of pore pressure diffusion in RIS with time.

Density Functional Theory Study of Water Diffusion and Clustering on Pd(111)

The internal structures as well as adsorption and hopping energies of monomers, dimers, trimers, tetramers, pentamers and hexamers of water on Pd（111） have been studied by density functional theory （DFT） plane-wave pseudopotential method which performs the firstprinciples quantum-mechanical calculations to explore the properties of crystals and surfaces in materials. Based on the calculations, we suppose that their absorption is via one water molecule for monomers, dimmers and trimers, but three water molecules for pentamers and hexamers. Moreover, there is one water molecule bonding with Pd atom by O atom in pentamers and hexamers, which explains why pentamers and hexamers are stable. The binding energies of polymers may be used to explain why the trimer comes close to two nearby monomers to form a stable pentamer instead of tetramer. And the difference of mobility of small water clusters is due to their different hopping energies.

Real-time flood forecasting of Huai River with flood diversion and retarding areas

A combination of the rainfall-runoff module of the Xin’anjiang model, the Muskingum routing method, the water stage simulating hydrologic method, the diffusion wave nonlinear water stage method, and the real-time error correction method is applied to the real-time flood forecasting and regulation of the Huai River with flood diversion and retarding areas. The Xin’anjiang model is used to forecast the flood discharge hydrograph of the upstream and tributary. The flood routing of the main channel and flood diversion areas is based on the Muskingum method. The water stage of the downstream boundary condition is calculated with the water stage simulating hydrologic method and the water stages of each cross section are calculated from downstream to upstream with the diffusion wave nonlinear water stage method. The input flood discharge hydrograph from the main channel to the flood diversion area is estimated with the fixed split ratio of the main channel discharge. The flood flow inside the flood retarding area is calculated as a reservoir with the water balance method. The faded-memory forgetting factor least square of error series is used as the real-time error correction method for forecasting discharge and water stage. As an example, the combined models were applied to flood forecasting and regulation of the upper reaches of the Huai River above Lutaizi during the 2007 flood season. The forecast achieves a high accuracy and the results show that the combined models provide a scientific way of flood forecasting and regulation for a complex watershed with flood diversion and retarding areas.

Molecular dynamics study of water diffusion in an amphiphilic block copolymer with large difference in the blocks＇ glass transition temperatures

Isothermal-isobaric molecular dynamics simu- lation was used to study the diffusion mechanism of water in polyurethane-block-poly（N-isopropyl acrylamide） （PU- block-PNIPAm） with a hydrophobic PU/hydrophilic PNIPAm mass ratio of 1.4 to 1 at 298 K and 450 K. Here, the experimental glass transition temperature （Tg） of PU is 243 K while that of PNIPAm is 383 K. Different amounts of water up to 15 wt-% were added to PU-block- PNIPAm. We were able to reproduce the specific volumes and glass transition temperatures （250 K and 390 K） of PU- block-PNIPAm. The computed self-diffusion coefficient of water increased exponentially with increasing water concentration at both temperatures （i.e., following the free volume model of Fujita）. It suggested that water diffusion in PU-block-PNIPAm depends only on its fractional free volume despite the free volume inhomo- geneity. It is noted that at 298 K, PU is rubbery while PNIPAm is glassy. Regardless of temperature, radial distribution functions showed that water formed clusters with sizes in the range of 0.2-0.4 nm in PU-block- PNIPAm. At low water concentrations, more clusters were found in the PU domain but at high water concentrations, more in the PNIPAm domain. It is believed that water molecules diffuse as clusters rather than as individual molecules.

Water’s motions in x–y and z directions of 2D nanochannels:Entirely different but tightly coupled

Two-dimensional(2D)material-based membrane separation has attracted increasing attention due to its promising performance compared with traditional membranes.However,in-depth understanding of water transportation behavior in such confined nanochannels is still lacking,which hinders the development of 2D nanosheets membranes.Herein,we investigated water confined in graphene or MoS_(2)nanochannels by molecular dynamics(MD)simulations and found water’s diffusivity always varied linearly with their mean square displacement along z direction(Δz^(2))when system variables(e.g.,water molecules’number,channel height,nonbonded interaction parameter,harmonic potential constraining water’s z-coordinate)changed.Such linear correlation applies to different water models and different force fields(FFs)of channel walls(e.g.,different Lennard–Jones parameters or even flexible FF),no matter whether water molecules form 3-,2-,or quasi-2-layer structure in the nanochannel.This indicates,though water molecules’motion along z direction(z-fluctuation,confined within 1 nm)and that in xy plane(xydiffusion)are entirely different,they are tightly coupled:Violent z-fluctuation would produce more transient void to facilitate xydiffusion,which is to the sharp contrary of bulk water,where motions in x,y,z directions are symmetric,but independent.Our work could help design high performance 2D nanochannels and discover more novel principles in nano-fluidics and membrane separation fields.

Chemomechanical Properties of Electrospun Polyvinyl Acetate(PVAc)Fiber Mat and its Application in Water-Triggered Self-folding

Environmental-stimulus-triggered self-folding mechanisms have found promising applications in many engineering fields.Recently,a water-activated self-folding procedure has been designed by using the electrospun polyvinyl acetate(PVAc)fiber mat which contains high tensile residual stresses in the vitrified fibers during the spinning processes.The water permeation initiates plasticization of PVAc fiber mat and leads to a material shrinkage.When water diffusion starts at the top surface of a PVAc sheet,a shrinkage variation along the diffusion pathway forms a bending hinge on the sheet,which has been demonstrated in 3D origami design.To capture the water-triggered plasticization mechanism and chemomechanical coupling deformation compatibility,a consistent finite deformation viscoplastic model is developed for the PVAc fiber mat under coupled chemomechanical loading conditions.The residual stress and‘fixed’strain are modeled through the unrecoverable plastic strain in the PVAc fiber mat.As water permeates into the PVAc fiber mat,the induced increase in mixing entropy lowers the glass transition temperature of the material,and results in a gradual relaxation of the fixed viscoplastic strain.A non-Fickian diffusion model suitable for glassy material is adopted to capture the water permeation in the PVAc fiber mat.After calibrated and validated by a series of experiments,the proposed model is implemented in ABAQUS software to simulate the water-activated self-folding of PVAc sheet.The numerical example for a typical origami design suggests a promising engineering application prospect.

Molecular surface functionalization of In_(2)O_(3) to tune interfacial microenvironment for enhanced catalytic performance of CO_(2) electroreduction

Indium-based materials(e.g.,In_(2)O_(3))are a class of promising non-noble metal-based catalysts for electroreduction of carbon dioxide(CO_(2)).However,competitive hydrogen reduction reaction(HER)on indium-based catalysts hampers CO_(2) reduction reaction(CO_(2)RR)process.We herein tune the interfacial microenvironment of In_(2)O_(3) through chemical graft of alkyl phosphoric acid molecules using a facile solution-processed strategy for the first time,which is distinguished from other researches that tailor intrinsic activity of In_(2)O_(3) themselves.The surface functionalization of alkyl phosphoric acids over In_(2)O_(3) is demonstrated to remarkably boost CO_(2) conversion.For example,octadecylphosphonic acid modified In_(2)O_(3) exhibits Faraday efficiency for H_(2) H_(2) H_(2)(FE)of as low as 6.6%and FEHCOOH of 86.5%at-0.67 V vs.RHE,which are far superior to parent In_(2)O_(3) counterparts(FE of 24.0%and FEHCOOH of 63.1%).Moreover,the enhancing effect of alkyl phosphoric acid functionalization is found to be closely related to the length of alkyl chains.By virtue of comprehensive experimental characterizations and molecular dynamics simulations,it is revealed that the modification of alkyl phosphoric acids significantly alters the interface microenvironment of the electrocatalyst,which changes the electrocatalyst surface from hydrophilic and aerophobic to hydrophobic and aerophilic.In this case,the water molecules are pushed away and more CO_(2) molecules are trapped,increasing local CO_(2) concentration at In_(2)O_(3) active sites,thus leading to the significantly enhanced CO_(2)RR and suppressed HER.This work highlights the importance of regulating the interfacial microenvironment of inorganic catalysts by molecular surface functionalization as a means for promoting the electrochemical performance in electrosynthesis and beyond.

Study on hydrodynamic diffusion law of the swelling particle slurry in karst pipeline

The swelling particle grouting material has demonstrated remarkable plugging effectiveness in high-pressure and large-flow burst water within karst pipelines.Currently,current research on the rheolog-ical model,flow computation theory,and plugging mechanism of this material is lacking.The conven-tional grouting slurry diffusion process,using the liquid-liquid two-phase flow method,fails to accurately simulate high solubility slurry and particle swelling.To address these limitations,this study established a precise constitutive model to describe the swelling particle slurry diffusion process in dynamic water.Additionally,a coupling calculation method was proposed to analyze the spatiotemporal heterogeneity of viscosity during slurry diffusion by considering the migration of slurry and the changes in viscosity.To investigate the interaction between particle swelling and flow field changes,a Compu-tational Fluid Dynamics-Discrete Element Method(CFD-DEM)coupling model was developed for the diffusion of swelling particle slurry.It is demonstrated that slurry viscosity increases exponentially within the diffusion front as the particle swelling rate rises,and the drag force exhibits an intriguing behavior of initially increasing and then decreasing as the slurry flows through the pipeline.Further-more,the CFD-DEM coupling model proved to be more accurate in describing viscosity distribution and diffusion distance compared to the finite element solution.The primary objective of this paper is to reveal the plugging mechanism and provide theoretical support for the engineering application of the swelling particle grouting material.

A comparison of chemical MSW compositional data between China and Denmark

Chemical waste compositions are important for municipal solid waste management, as they determine the pollution potentials from different waste strategies. A representative dataset for chemical characteristics of individual waste fractions is frequently required to assess chemical waste composition, but it is usually reported in developed countries and not in developing countries. In this study, a dataset for Chinese waste was established through careful data screening and assessment, named as CN dataset. Meanwhile, a dataset for Danish waste（DK dataset） was also summarized based on previous studies. In order to quantitatively evaluate the reliabilities of CN and DK datasets, the chemical waste compositions in four Chinese cities were estimated by utilizing both of them, respectively. It is indicated that the usage of CN datasets led to significantly lower discrepancies from the actual values based on laboratory analysis in most cases. Within the datasets, the moisture contents of food waste, paper, textiles, and plastics, the carbon content of food waste, as well as the oxygen content of plastics would induce significant divergences, which should be paid special attention when gathering the information. In addition, the fractional waste compositions in China showed similar features with other developing countries but differ significantly with developed countries. Thus the above-mentioned conclusions could also be true in other developing countries.