Thickness Of Water Layer Research Articles

Coefficient of restitution for silver nanoparticles colliding on a wet silver substrate

Air humidity can intervene in a particle–surface collision by forming a layer of water molecules on the surface. These water molecules act as a buffer layer that alters the collision condition. In this work, we study the effects of condensed water layer on the collision of 5-nm particles on a substrate by molecular dynamics simulations. The coefficient of restitution that is inversely proportional to the adhesion between the nanoparticle and the surface is used to characterize the collision. Results indicate that air humidity can either increase or decrease the coefficient of restitution in the studied nanoscale collisions, depending on the condensed water layer thickness and the surface energy of the substrate. The surface energy of the substrate varies with its Lennard-Jones potential. For a high surface energy substrate, the coefficient of restitution first increases then decreases by increasing the water layer thickness on the substrate when the impact velocity changes from 20 to 500 m/s. For a low surface energy substrate, the coefficient of restitution decreases because of a condensed water layer on the substrate at impact velocities less than 300 m/s. For higher impact velocities, the coefficient of restitution first increases, then decreases, with the condensed water layer thickness.

Editors’ Choice—Natural Convection Boundary Layer Thickness at Elevated Chloride Concentrations and Temperatures and the Effects on a Galvanic Couple

The natural convection boundary layer () and its influence on cathodic current in a galvanic couple under varying electrolytes as a function of concentration (1 − 5.3 M NaCl) and temperature (25 °C−45 °C) were understood. Polarization scans were obtained under quiescent conditions and at defined boundary layer thicknesses using a rotating disk electrode on platinum and stainless steel 304L (SS304L); these were combined to determine With increasing chloride concentration and temperature, decreased. Increased mass transport (Sherwood number) results in a decrease in providing a means to predict this important boundary. Using Finite Element Modeling, the cathodic current was calculated for an aluminum alloy/SS304L galvanic couple as a function of water layer (WL) thickness and cathode length. Electrolyte domains were delineated, describing (i) dominance of ohmic resistance over mass transport under thin WL, (ii) the transition from thin film to bulk conditions at and (iii) dominance of mass transport under thick WL. With increasing chloride concentration, cathodic current decreased due to decreases in mass transport. With increasing temperature, increased cathodic current was related to increases in mass transport and solution conductivity. This study has implications for sample sizing and corrosion prediction under changing environments.

Mapping barrier island soil moisture using a radiative transfer model of hyperspectral imagery from an unmanned aerial system

The advent of remote sensing from unmanned aerial systems (UAS) has opened the door to more affordable and effective methods of imaging and mapping of surface geophysical properties with many important applications in areas such as coastal zone management, ecology, agriculture, and defense. We describe a study to validate and improve soil moisture content retrieval and mapping from hyperspectral imagery collected by a UAS system. Our approach uses a recently developed model known as the multilayer radiative transfer model of soil reflectance (MARMIT). MARMIT partitions contributions due to water and the sediment surface into equivalent but separate layers and describes these layers using an equivalent slab model formalism. The model water layer thickness along with the fraction of wet surface become parameters that must be optimized in a calibration step, with extinction due to water absorption being applied in the model based on equivalent water layer thickness, while transmission and reflection coefficients follow the Fresnel formalism. In this work, we evaluate the model in both field settings, using UAS hyperspectral imagery, and laboratory settings, using hyperspectral spectra obtained with a goniometer. Sediment samples obtained from four different field sites representing disparate environmental settings comprised the laboratory analysis while field validation used hyperspectral UAS imagery and coordinated ground truth obtained on a barrier island shore during field campaigns in 2018 and 2019. Analysis of the most significant wavelengths for retrieval indicate a number of different wavelengths in the short-wave infra-red (SWIR) that provide accurate fits to measured soil moisture content in the laboratory with normalized root mean square error (NRMSE)< 0.145, while independent evaluation from sequestered test data from the hyperspectral UAS imagery obtained during the field campaign obtained an average NRMSE = 0.169 and median NRMSE = 0.152 in a bootstrap analysis.

Efficient and antifouling interfacial solar desalination guided by a transient salt capacitance model

Interfacial solar desalination has been considered as a promising strategy to address the challenge of freshwater scarcity because of its high solar-to-vapor efficiency. However, the high evaporation rate would be restrained if salt crystallization occurs on the evaporation interface. Herein, we propose a capacitance model to describe transient heat transfer and salt rejecting processes during interfacial evaporation. This model allows us to identify the water layer thickness as a new design parameter. With the new understanding, the downward water channel ratio can be minimized to reduce heat loss without salt fouling. Experimental demonstrations show the high efficiency and long-term stability of our design using extremely low-cost and easily accessible materials. The maximum daily freshwater yield is as high as 6.0 kg/m2 under natural sunlight. Our findings not only address the challenge of salt fouling but also provide insights into transient processes during interfacial evaporation.

Effect of Water Adsorption on the Frictional Properties of Hydrogenated Amorphous Carbon Films in Various Relative Humidities.

The tribological properties of hydrogenated amorphous carbon (a-C:H) films in ambient air were investigated from the microstructural point of view. a-C:H films with various microstructures (polymer-like, diamond-like, and graphite-like structures) were prepared, and the thickness of water adsorption layers on the films was measured. The adsorption behavior of water molecules on a-C:H films could be expressed with the Brunauer-Emmett-Teller (BET) isotherm, while the thicknesses of icelike and liquidlike water layers adsorbed on the films could be determined using the BET parameters C and nma. The polymer-like films exhibited the thickest icelike and liquidlike water adsorption layers, which decreased as the film structure changed to a diamond-like or a graphite-like structure. A strong relationship was observed between the thickness of water adsorption layers and the surface oxidation of the a-C:H films. The friction coefficient of the films in ambient air can be well explained by the surface oxidation and the thickness of water adsorption layers. Polymer-like films showed high friction coefficients due to the formation of a thick water layer on the films originated from the high surface oxidation of the film surface, whereas the graphite-like film exhibited a low friction coefficient due to low oxidation and a thin water adsorption layer. Furthermore, friction tests between the a-C:H films with different microstructures under ambient air were performed to determine the lowest friction pair in various relative humidities (RHs).

Liquid crystalline phases of linear alkylbenzene sulphonate in spray-dried detergent powders studied by small-angle X-ray scattering, TEM, and ATR-IR spectroscopy

Spray-dried detergent granules have a complex and multi-scale structure, in which submicron sized crystals of inorganic salts along with multi-lamellar stacks of surfactant molecules are dispersed within a matrix phase. In this study, two model formulations based on sodium linear alkylbenzene sulphonate (NaLAS) and sodium sulphate were used to investigate the molecular structure of stacked lamellae. The parameters of lamellar d-spacing, bilayer thickness (dHH) and water layer thickness (dW) were determined using small-angle X-ray scattering. Four sets of lamellae were detected in nil-silicate detergent powders conditioned at 33 % RH (relative humidity). The exposure of these samples to a higher RH level (75 %) resulted in a reduced number of coexisting lamellar phases by two. This was accompanied by an increase in lamellar d-spacings and a considerable reduction in bilayer thicknesses (dHH). The reduction in number of sets of lamellae was explained by an increase in the fluidity of the lamellar phases and disappearance of water-poor solid polymorphs. This was consistent with the results of FTIR for nil-silicate samples, indicating an increase in the conformational disorder of the alkyl chains at a higher RH value. Interestingly, in the presence of sodium silicate the lamellar phases display a greater degree of swelling at a relatively low RH value (33 % RH) as compared with those in the absence of sodium silicate. Nonetheless, the thickness of water layer was found to slightly decrease at a higher RH (75 %), which was attributed to the moisture-induced glass transition and kosmotropic effect of sodium silicates.

The Initiators of the Appearance of Organic Compounds on Earth, the Distribution of Natural Radionuclides in the Plant Mass

An experiment was performed on the synthesis of organic substances from a mixture of carbon monoxide and hydrogen on the surface of iron and cobalt, coated with carbide clusters, formed during processing at 573 K in an atmosphere of carbon monoxide. The obtained results indicate that the most likely direction of the formation of organic substances from mixtures of molecular hydrogen and carbon oxides is the thermal hydrogenation (radiation-thermal hydrogenation has a higher speed) at 300-573 K of carbide clusters covering the surface of metals. A significant fraction of organic matter on the Earth is formed during the solidification and cooling of the surface of a “hot” planet from 600 K to 300 K. Initiation by ionizing radiation creates the real condition for the highly endothermic processes of dissociation of water and carbon dioxide molecules, synthesis of new organic molecules and molecular oxygen. On a completely cooling up to 300 K planet this process continued by the vital activity of living organisms and during photosynthesis. The energy of quanta of visible light is much less than the energy of C=O bonds in the CO₂ molecule and the dissociation energy of the H-O bond in the H₂O molecules. The value of the energy of gamma quanta emitted by the K40 isotope is many times higher than the value of the dissociation energy of the H-O and C=O bonds. The analysis of numerous samples of water, soil, vegetation, livestock products showed the presence of K⁴⁰ radioisotopes in all samples. The role of gamma radiation of K⁴⁰ radioisotope should be taken into account at comprehensive analysis of initial stage of photosynthesis. This conclusion is consistent with the revealed facts of increased plant yields on soils with relatively high concentrations of natural radioisotopes, observation of photosynthesis under thick layers of water in the presence of only long-wave infrared rays or in the absence of chlorophyll and oxygen.

Updated Evaluation of Cholesterol's Influence on Membrane Oxygen Permeability.

There is a surprising gap in knowledge regarding the mechanism of oxygen (O2) diffusional delivery at the level of tissues and cells. Yet, the effectiveness of tumor radiotherapy, the success of tissue engineering, and healthy metabolism all require ample intracellular oxygen. Tissue-level diffusion takes place in a complex and crowded macromolecular environment. Cholesterol-rich cellular membranes have been thought to reduce oxygen flux. Here, we use atomistic molecular dynamics simulations to update prior estimates of bilayer permeability and related parameters for 1-palmitoyl,2-oleoylphosphatidylcholine (POPC) and POPC/cholesterol bilayers, using a modified O2 model with improved membrane-water partitioning behavior. This work estimates an oxygen permeability coefficient of 15±1cm/s for POPC and 11.5±0.4cm/s for POPC/cholesterol (1:1 molecular ratio) at 37°C. The permeability of POPC is found to be ~1/3 that of a water layer of similar thickness, and the permeability of POPC/cholesterol is estimated to be 20-30% below that of POPC. Void pathway visualization and free energy data support channeling of oxygen toward the center of cholesterol-incorporating membranes, while partition coefficient data suggest reduced membrane solubility of oxygen due to cholesterol. Further study is needed to understand whether diffusion pathway changes due to cholesterol and other molecular compositional factors influence oxygen availability within tissue.

Quantitative assessment of environmental phenomena on maximum pit size predictions in marine environments

Maximum pit sizes were predicted for dilute and concentrated NaCl and MgCl2 solutions as well as sea-salt brine solutions corresponding to 40% relative humidity (RH) (MgCl2-rich) and 76% RH (NaCl-rich) at 25 °C. A quantitative method was developed to capture the effects of various cathode evolution phenomena including precipitation and dehydration reactions. Additionally, the sensitivity of the model to input parameters was explored. Despite one's intuition, the highest chloride concentration (roughly 10.3 M Cl−) did not produce the largest predicted pit size as the ohmic drop was more severe in concentrated MgCl2 solutions. Therefore, the largest predicted pits were calculated for saturated NaCl (roughly 5 M Cl−). Next, it was determined that pit size predictions are most sensitive to model input parameters for concentrated brines. However, when the effects of cathodic reactions on brine chemistry are considered, the sensitivity to input parameters is decreased. Although there was not one main input parameter that influenced pit size predictions, two main categories were identified. Under similar chloride concentrations (similar RH), the water layer thickness (WL), and pit stability product, (i·x)sf, are the most influential factors. When varying chloride concentrations (RH), changes in WL, the brine specific cathodic kinetics on the external surface (captured in the equivalent current density (ieq)), and conductivity (κo) are the most influential parameters. Finally, it was noted that dehydration reactions coupled with precipitation in the cathode will have the largest effect on predicted pit size, and cause the most significant inhibition of corrosion damage.

The mechanism of micro-cracks formation in ultrasonic-assisted water confined laser micromachining silicon

In the ultrasonic-assisted water confined laser micromachining silicon, micro-cracks may generate. The effect of ultrasonic power and thickness of the water layer on the groove section’s micro-cracks is discussed systematically to control the micro-cracks formation and improve the processing quality. The experimental and simulational results indicate the maximum radius of the bubbles and the bubble interference coefficient have an important effect on the micro-cracks formation. The larger the maximum radius of the bubble, the shorter the micro-cracks formed, and the smaller the bubble interference coefficient, it is easier to produce micro-cracks. The bubble interference coefficient and the maximum radius of the bubble can be affected by the water layer thickness and ultrasonic power. Therefore the micro-cracks can be effectively controlled by selecting the appropriate water layer thickness of 1.5mm and ultrasonic power of 195W in this study. The study is obtained from this study provides a guide for micro-cracks under ultrasonic-assisted solution confined laser processing.

Multilayered salt water with high optical transparency for EMI shielding applications

Electromagnetic interference (EMI) shielding for visual observation applications, such as windows utilized in military or aerospace, is important but difficult to realize due to conventional materials having difficulty in achieving sufficient transparency and EMI shielding simultaneously. In this paper, we present multilayered structures based on salt water for simultaneous highly optical transparency (OT) and EM shielding effectiveness (SE) performance. In the proposed structures, planar acrylic and glass were used as two types of clear substrates to hold salt water. The measured OT of both acrylic/salt water/acrylic and glass/salt water/glass structures was higher than 90% with a nearly uniform light transmission, which introduced a negligible impact on optical observation. Furthermore, both simulations and experimental results demonstrated that the SE of the multilayer structure was higher than 20 dB in the X-band from 7.5 to 8.5 GHz. Moreover, the SE was significantly enhanced by increasing the thickness of the salt water layer. Especially, both OT and SE of the multilayered structures were improved simultaneously by increasing the salinity of the salt water. These proposed structures demonstrate great potential in EMI shielding observation applications.

(Keynote) Sensor Design, Construction and Validation for in-Situ Water Layer Thickness Determination during Accelerated Corrosion Testing

The design, construction, validation, and application of a sensor to determine water layer (WL) thickness in the range of 0 to 5 mm in salt spray testing using finite element modeling (FEM) and experimental methods is presented. The sensor determines WL thickness based on electrical resistivity, which is a function of the width of the sensor, distance between the electrodes, and solution conductivity. Sensor design, and validation under known WL thicknesses, was informed by FEM results. The utility of the sensor was shown by measuring WL thickness in a continuous salt spray test similar to ASTM B117 (3.5 wt % NaCl at 35 ˚C) and the range of specifications allowed within the standard were explored. Within the realms of accelerated corrosion testing, the angle of exposure played the largest role in WL thickness. Furthermore, it was found that above an angle of 20˚ from vertical the WL experiences semi-periodic run-off events causing a transient decrease in the WL by up to 80%. Finally, the angle of sample exposure in salt spray environments determines if thin film conditions are achieved, influencing the rate of corrosion. The large allowances for sample angle present in most standards for laboratory corrosion chamber testing pose a large source of test-to-test and chamber-to-chamber variability. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2020-5133 A

Molecular Dynamics Study of the Nanoscale Proton Density Distribution at the Ionomer-Catalyst Interface

The proton density in the cathode catalyst layer is a crucial variable to define the local reaction conditions in and thereby determine the performance and lifetime of polymer electrolyte fuel cells. We present a molecular modeling study to examine the proton density distribution in a water-filled, slab-like pore. The slab is confined by two distinct boundaries, the first consisting of a platinum single-crystalline surface and the second being a thin and dense skin layer of proton-conducting ionomer. Classical molecular dynamics simulations serve as a valuable tool to rationalize the impact of the molecular structure and properties of the ionomer film as well as the adsorption and charging state of the metal surface on structure and properties of interfacial water and the spatial distribution of protons. Boundary conditions at the metal surface are obtained from explicit quantum mechanical simulations at the DFT level. The oxide coverage at the metal surface and the water layer thickness are considered as crucial parameters. Results of detailed structural analyses elucidate the impact of a structured layer of near-surface water molecules at the platinum surface on accumulating protons at the interface.

Modeling of MRP Protection Considering Chemical Inhibition, Electrochemistry, and Mass Transport

Aluminum alloy AA2024-T3 is widely used in aerospace applications due to its high strength-to-weight ratio. However, because of its heterogeneous microstructure, it is susceptible to microgalvanic corrosion and pitting in chloride containing environments, requiring additional corrosion protection methods. Organic coatings are the primary corrosion protection method used in aluminum alloys and they are usually composed of pigments embedded in a polymeric matrix. The polymeric matrix promotes a high resistance to ionic movement and it provides barrier against the ingress of aggressive species onto the substrate. The pigments can provide corrosion protection by inhibiting corrosion reactions, providing cathodic protection to the substrate, and/or depositing a protective layer on the surface of the substrate. Recently, a coating system containing a Mg-rich primer (MgRP) has emerged as an effective alternative to the chromate-based coatings commonly used for this purpose. Due to the lower potential of Mg, MgRP can protect aluminum alloys via galvanic coupling, serving as a sacrificial anode and preventing the corrosion of the Al substrate. Additionally, recent studies showed that the electrolyte chemistry resulting from Mg dissolution is beneficial to localized corrosion inhibition of AA2024, providing corrosion protection even after pigment depletion.Localized corrosion of coated Al alloys can be affected by a large number of variables, such as water layer thickness, salt loading, pigment volume concentration of primer, chemistry of the primer, galvanic effects of pigment. and component geometry. The efficacy of the organic coating also depends on many variables. Exposure of the coating to UV radiation and aggressive solutions causes degradation of the polymeric matrix, which reduces the resistance to ionic movement and protection of the substrate against aggressive species. Thus, it is difficult to predict and quantify damage by localized corrosion, in addition to the efficacy and lifetime of a coating system.In this context, modeling can be used as a valuable assessment of parameter space to increase efficiency of experimental work. The objective of this work was to model the protection mechanisms offered by a MgRP coating system in AA2024, and investigate the influence of different variables on the effectiveness of the protection mechanism. The mechanisms of importance include protection via (a) the Mg pigment particles acting as sacrificial anodes, (b) the barrier to ion transport effected by the organic coating, and (c) changes in the electrolyte chemistry from dissolution of the Mg pigment particles. The modeling considers each of these protection mechanisms in isolation as well as in combination. Ultimately, this model will provide a better understanding and prediction of the protection mechanisms of the MgRP system and serve as a framework to study new coating systems.AcknowledgementsFinancial support from the SERDP program through the Office of Naval Research (C. Sanders) via Contract N00173-19-1-G011 as well as the DOD Corrosion Program Office through the US Air Force Academy via Contract FA7000-18-2-0006 is gratefully acknowledged.

Water-assisted femtosecond laser drilling of 4H-SiC to eliminate cracks and surface material shedding

This study adopted femtosecond laser with a wavelength of 515 nm to drill high-aspect-ratio micro through holes on a 500-μm thickness single-crystal SI-type 4H-SiC wafer. Firstly, through holes with a high aspect ratio of 20 were fabricated in air. However, the heat affect zone (HAZ), cracks, and surface material shedding around entrances and exits of the holes are inevitable in air even after chemical corrosion post-processing. In order to remove these defects, the water-assisted femtosecond laser drilling of 4H-SiC was investigated. The high-quality through holes free of cracks, surface material shedding, and HAZ were obtained under the action of internal scour and heat diffusion of water. Besides, the water layer thickness and the laser repetition frequency have a great influence on the processing quality and efficiency of the micro-holes. Finally, high-quality high-ratio-rate through micro-hole arrays on 4H-SiC were fabricated with the optimal process parameters, which is significant for the development of SiC electronic devices and the high-quality micro-fabrication of other hard and brittle materials.

Water adsorption on silica and calcium‐boroaluminosilicate glass surfaces—Thickness and hydrogen bonding of water layer

AbstractAdsorption isotherm of water on silica (modeled with fused quartz) and calcium‐boroaluminosilicate (Ca‐BAS) glass surfaces as a function of relative humidity (RH) was studied using Fourier transform infrared (FTIR) spectroscopy. The effective thickness of the adsorbed water layer and the distribution of hydrogen bonding interactions of water molecules in the adsorbed layer were determined by comparing the transmission FTIR spectra collected at the Brewster incidence angle with the theoretically calculated spectra. In the sub‐monolayer regime (&lt;30% RH), differences between the water spectra on fused quartz and Ca‐BAS glass could be related to the areal density of hydroxyl groups as well as the elemental composition of the surface determined with x‐ray photoelectron spectroscopy. In the transition regime (30%–60% RH), multilayers start growing and the difference between the fused quartz and Ca‐BAS surfaces diminishes as the humidity increases. In the multilayer regime (&gt;60% RH), the total amount as well as the hydrogen bonding interactions of adsorbed water layers become insensitive to the surface chemistry and are governed mostly by the phase transition (vapor condensation) behavior. Overall, this study reveals how the water layer thickness and structure on the multicomponent silicate glass surface in ambient conditions are different from those on the pure silica surface.

Picosecond pulsed underwater laser ablation of silicon and stainless steel: Comparing crater analysis methods and analysing dependence of crater characteristics on water layer thickness

Liquid layer thickness dependence of 515 nm, 7 picosecond pulsed laser ablation of stainless steel 304 and silicon is analyzed. Ablated crater volume and diameter are compared to ablated craters in ambient air by means of a novel, objective numerical procedure. While silicon ablation under a water layer is found to be more efficient in terms of removed material volume per pulse than ablation in ambient air, an opposite trend is found for stainless steel 304. For both materials, the ablation efficiently drops when the liquid layer thickness is decreased to 1 milimeter. A probable reason for the ablation efficiency drop is persistent bubble formation.

Non-Fickian Moisture Transport in Vegetable-Fiber-Reinforced Polymer Composites Using a Langmuir-Type Model.

The purpose of this article was to theoretically study the non-Fickian moisture absorption process in vegetable-fiber-reinforced polymer composites using a Langmuir-type model. Here, the focus was on evaluating the effect of the water layer thickness that surrounds the composite during the water migration process. The solutions of the governing equations were obtained using the finite volume method, considering constant thermophysical properties and non-deformable material. The results for the local and average moisture content and concentration, gradient values, and the transient rates of the free and bound (water) molecules in the process were presented and analyzed. It was observed that the water layer thickness strongly influenced the water absorption kinetics, the moisture content gradient values, and the equilibrium moisture content inside the material. It is envisaged that this new approach will contribute to better interpretation of experimental data and a better understanding of the physical phenomenon of water absorption, which directly affects the properties of composite materials.

Monitoring the extreme drought in the middle and lower reaches of the Yangtze River in 2019 from GRACE-FO satellites

In the summer and autumn of 2019, an extreme drought lasting 0.5 year in the middle and lower reaches of the Yangtze River had a major impact on local agricultural production and the ecological environment. Traditionally, drought severity assessment relies on drought-related parameters observed by in situ measurements, such as precipitation, evapotranspiration, runoff, and soil moisture. In the past two decades, GRACE/GRACE-FO gravity satellite data have been widely used to estimate global and regional terrestrial water storage anomalies (TWSA), but there are still limited studies on the quantitative assessment of the severity of drought using GRACE/GRACE-FO data. The objective of this study was to analyse the drought severity in the middle and lower reaches of the Yangtze River in the summer and autumn of 2019 using GRACE/GRACE-FO data and to compare our estimates with the traditional drought index. The GRACE-based drought severity index (GRACE-DSI) is a monthly global drought severity index based on the TWSA from the GRACE/GRACE-FO (GRACE-TWSA). In this study, we used spherical harmonic (SH) products from the GRACE/GRACE-FO to obtain the TWSA. GRACE data processing includes replacing the degree-1 and C 20 , removing the 2004–2009 mean SH, filtering to reduce correlated errors, Gaussian smoothing, calculating the equivalent water layer thickness on 1° ´ 1° grids, and correcting leakage errors with scale factors. We then calculated the GRACE-DSI based on the GRACE-TWSA with the trend and seasonal cycles removed. To ensure consistency, we processed the standardised precipitation evapotranspiration index (SPEI) similar to the GRACE data and standardised the new SPEI as the SPEI-Z. Our results indicated that the GRACE-DSI can successfully monitor the occurrence and development of drought in the middle and lower reaches of the Yangtze River in spatiotemporal domains. The GRACE/GRACE-FO successfully detected the extreme drought event that occurred in the east of Hubei, north of Jiangxi, and south of Anhui during the summer and autumn of 2019. In July, the arid region was located in the north of the Yangtze River basin, including Henan and Shandong provinces. In August, the drought intensified and moved south to the middle and lower reaches of the Yangtze River, reaching a maximum in September, especially in Hubei, Jiangxi, and Anhui provinces. The drought was weakened in October, but intensified again in November and December and expanded through the middle and lower reaches of the Yangtze River to the coastal regions, such as Fujian and Guangzhou provinces. The mean time series of the GRACE-DSI over Hubei, Jiangxi, Anhui, and Hunan provinces showed good agreement with the SPEI-Z in both amplitude and phase on the six month time scale (SPEI06-Z) with a correlation coefficient of 0.84. The time series of the GRACE-DSI and SPEI06-Z both clearly showed the extreme drought events that occurred in Hubei, Jiangxi, Anhui, and Hunan provinces during the spring and summer of 2011 and the summer and autumn of 2019. Our results also indicate that the GRACE-FO has the same drought monitoring capability as the GRACE.

Coarse-Grain Simulations of Solid Supported Lipid Bilayers with Varying Hydration Levels.

Supported lipid bilayers (SLBs) are a very popular system for the study of biomimetic membranes. Understanding of the interactions between the solid substrate and the lipid membrane opens pathways to the design of new materials with fine-tunable properties. While it is possible to study SLBs via molecular dynamics (MD) simulations, difficulties still remain for these strategies; in particular, the confined water layer thickness and structure are difficult to reproduce in simulations. We have explored different coarse-grained (CG) models for the membrane/support interaction, and their impact on the substrate hydration level. Our results highlight the relevance of including long-range interactions in CG-MD simulations of fluid SLBs. Modeled neutron reflectivity curves are deduced from the structures obtained by molecular simulations, and substrate parameters are optimized to match the experimental and modeled reflectivity curves. We expect our coarse-grained approach to open new perspectives for the simulations of SLBs of increasing complexity, including lipid layers of complex compositions, or adsorbed lipidic layers on patterned surfaces.