A Temperature Compensation Approach for Micro-Electro-Mechanical Systems Accelerometer Based on Gated Recurrent Unit-Attention and Robust Local Mean Decomposition-Sample Entropy-Time-Frequency Peak Filtering.

MEMS accelerometers are significantly impacted by temperature and noise, leading to a considerable compromise in their accuracy. In response to this challenge, we propose a parallel denoising and temperature compensation fusion algorithm for MEMS accelerometers based on RLMD-SE-TFPF and GRU-attention. Firstly, we utilize robust local mean decomposition (RLMD) to decompose the output signal of the accelerometer into a series of product function (PF) signals and a residual signal. Secondly, we employ sample entropy (SE) to classify the decomposed signals, categorizing them into noise segments, mixed segments, and temperature drift segments. Next, we utilize the time-frequency peak filtering (TFPF) algorithm with varying window lengths to separately denoise the noise and mixed signal segments, enabling subsequent signal reconstruction and training. Considering the strong inertia of the temperature signal, we innovatively introduce the accelerometer's output time series as the model input when training the temperature compensation model. We incorporate gated recurrent unit (GRU) and attention modules, proposing a novel GRU-MLP-attention model (GMAN) architecture. Simulation experiments demonstrate the effectiveness of our proposed fusion algorithm. After processing the accelerometer output signal through the RLMD-SE-TFPF denoising algorithm and the GMAN temperature drift compensation model, the acceleration random walk is reduced by 96.11%, with values of 0.23032 g/h/Hz for the original accelerometer output signal and 0.00895695 g/h/Hz for the processed signal.

Evaluating disinfection performance of ultraviolet light-emitting diodes against the microalga Tetraselmis sp.: Assay methods, inactivation efficiencies, and action spectrum.

Ultraviolet light-emitting diodes (UV-LEDs) are among the most compact devices and safest technologies in water disinfection systems. However, the validation of different assay methods to evaluate the disinfection performance of different wavelengths (265, 280, 285, and 300 nm) of UV-LEDs toward marine microalgae remains poorly characterized. In this study, several detection assays, namely the culture-based most probable number (MPN) assay, membrane integrity-based vital stain (VS) assay, chlorophyll fluorescence assay, and photochemical efficiency assay, were compared to assess the viability of the marine microalga Tetraselmis sp., with results indicating the MPN assay to be the most sensitive. In addition, this study compared the inactivation kinetics, inactivation efficiency, and energy efficiency of Tetraselmis sp. under different UV wavelengths, as assessed by the VS and MPN assays. The fluence-response curves of Tetraselmis sp. varied with assay and wavelength, with Geeraerd's model fitting all fluence-response microalgal inactivation curves. The results showed a non-significant difference in inactivation efficiency among different wavelengths of UV-LEDs (except for 300 nm) when using the VS assay. On the contrary, significant differences among all wavelengths were observed with respect to inactivation efficiency when using the MPN assay. The wavelength of 265 nm exhibited maximum inactivation efficiency, whereas 285 nm achieved optimal energy efficiency. The UV action spectrum of Tetraselmis sp. exhibited the peak at 265 nm, a finding which matched well with the absorbance spectrum of DNA. The observations from this study provide a theoretical basis and technical support for the application of the emerging UV-LED light sources in the algicidal treatment of marine water.

The effect of variable stiffness of tuna-like fish body and fin on swimming performance.

The work in this paper focuses on the examination of the effect of variable stiffness distributions on the kinematics and propulsion performance of a tuna-like swimmer. This is performed with the use of a recently developed fully coupled fluid-structure interaction solver. The two different scenarios considered in the present study are the stiffness varied along the fish body and the caudal fin, respectively. Our results show that it is feasible to replicate the similar kinematics and propulsive capability to that of the real fish via purely passive structural deformations. In addition, propulsion performance improvement is mainly dependent on the better orientation of the force near the posterior part of swimmers towards the thrust direction. Specifically, when a variable body stiffness scenario is considered, the bionic body stiffness profile results in better performance in most cases studied herein compared with a uniform stiffness commonly investigated in previous studies. Given the second scenario, where the stiffness is varied only in the spanwise direction of the tail, similar tail kinematics to that of the live scombrid fish only occurs in association with the heterocercal flexural rigidity profile. The resulting asymmetric tail conformation also yields performance improvement at intermediate stiffness in comparison to the cupping and uniform stiffness.

Adsorption of Asphaltenes at Oil-Water and Oil-Clay Interfaces in the Presence of Humic Acids.

Humic substances in the soil and underground water are important media for the environmental fate and transport of oil pollutants, but direct experimental evidence is lacking on the effects of humic acids on the interfacial activity and adsorption properties of oil asphaltenes in the soil. In this study, the oil-water interfacial tension (IFT) was measured by optical contact angle instruments, while the isothermal adsorption of asphaltenes on two montmorillonites and one kaolinite was fitted using four classical models. Results demonstrated that the oil-water IFT decreased by 37.5% when the asphaltenes (500 mg L-1) were present in the oil, which further decreased by 62.7% when the humic acids (25 mg L-1) were added in the water. The best-fitted form of isotherm equation (Langmuir model) and the adsorption capacity were not changed by coating humic acids on the clay surface prior to asphaltene adsorption, but the presence of humic acids on the clay surface doubled the adsorption rate. Results also revealed that the asphaltenes could coaggregate with the humic acids at the oil-water interface or in the bulk water, but they were unlikely to coaggregate with the humic acids binding on the clay surface.

Recovery of Alexandrium tamarense under chronic exposure of TiO2 nanoparticles and possible mechanisms.

Harmful algal blooms (HAB), heavily influenced by human activities, pose serious hazard to aquatic ecology and human health. In this study, we monitored the physiological responses and paralytic shellfish poisoning toxins (PSTs) of the toxin-producing HAB species Alexandrium tamarense under titanium dioxide nanoparticles (nTiO2) exposure in the concentration range of 2-320 mg L-1 over a period of 13 days. The results showed the acute inhibition of nTiO2 on the algal growth, photosynthetic efficiency and esterase activity at all concentrations except 2 mg L-1. Nonetheless, they recovered after 13 days nTiO2 exposure from 20 to 80 mg L-1. The EC50 value increased from 85.1 mg L-1 in Day 4 to 140.9 mg L-1 in Day 13. The physiological recovery after prolonged exposure may result from the elimination of excess reactive oxygen species (ROS), a combined outcome of increased nTiO2 aggregation and algal antioxidant defense mechanisms. This observation is supported by the immediately increased antioxidant enzyme activities, including the superoxide dismutase (SOD) and catalase (CAT) activities upon nTiO2 exposure. Moreover, the production of PSTs in A. tamarense significantly increased by 1.41-1.76 folds after chronic nTiO2 exposure at all tested concentrations (p < 0.05), which might also be an adaptive response for the microalgae to overcome the stresses. In particular, the proportions of highly-toxic PSTs analogues GTX2/3, STX and dcSTX were significantly increased upon nTiO2 exposure (p < 0.05). Hence, the chronic nTiO2 exposure might aggravate the ecological impact of HABs. Furthermore investigations on different HAB species, especially those toxin-producing ones, and detail physiological responses are obviously needed.

Use of coupled wavelength ultraviolet light-emitting diodes for inactivation of bacteria in subsea oil-field injection water.

The development of subsea injection water disinfection systems will enable the novel exploration of offshore oilfields. Ultraviolet light emitting diodes (UV-LEDs) with peak wavelengths at 255 nm, 280 nm, 350 nm, and combinations of 255 nm and 350 nm, and 280 nm and 350 nm were investigated in this study to determine their efficiency at disinfecting saprophytic bacteria, iron bacteria, and sulfate reducing bacteria. Results show that UV-LEDs with peak wavelengths at 280 nm were the most practical in this domain because of their high performance in both energy-efficiency and reactivation suppression, although 255 nm UV-LEDs achieved an optimal germicidal effect in dose-based experiments. The use of combined 280 nm and 350 nm wavelengths also induced synergistic bactericidal effects on saprophytic bacteria.

Exposure of engineered nanoparticles to Alexandrium tamarense (Dinophyceae): Healthy impacts of nanoparticles via toxin-producing dinoflagellate.

Human activities can enhance the frequency, intensity and occurrence of harmful algal blooms (HABs). Engineered nanoparticles (ENPs), contained in many materials, will inevitably enter coastal waters and thus cause unpredictable impacts on aquatic organisms. However, knowledge of the influence of ENPs on HAB species is still lacking. In this study, we examined the effects of titanium dioxide nanoparticles (nTiO2), zinc oxide nanoparticles (nZnO) and aluminum oxide nanoparticles (nAl2O3) on physiological changes and paralytic shellfish poisoning toxins (PSTs) production of Alexandrium tamarense. We found a dose-dependent decrease in photosynthetic activity of A. tamarense under all three ENPs and a significant growth inhibition induced by nZnO. The largest reactive oxygen species (ROS) production was induced by nTiO2, followed by nZnO and nAl2O3. Moreover, the PSTs production rate increased by 3.9-fold for nTiO2 (p<0.01) and 4.5-fold for nAl2O3 (p<0.01) at a concentration of 200mgL-1. The major component, C2 was transformed to its epimer C1 and the proportion of decarbamoyl toxins increased under 200mgL-1 of nZnO and nAl2O3. In addition, the proportion of carbamate toxins increased upon exposure to 2mgL-1 ENPs, while decreased upon exposure to 200mgL-1 ENPs. The changes in PSTs production and composition might be an adaptive response for A. tamarense to overcome the stress of ENPs exposure. This work brings the first evidence that ENP would affect PSTs production and profiles.

A pivotal role of vacuolar H(+)-ATPase in regulation of lipid production in Phaeodactylum tricornutum.

Microalgal lipids have been considered as a promising source for biodiesel production. Alkaline pH can induce neutral lipid accumulation in microalgae cells. However, whether and how proton pumps, especially vacuolar H(+)-ATPase (V-ATPase), function in these processes is not well known. In this study, we treated Phaeodactylum tricornutum with V-ATPase specific inhibitor bafilomycin A1 (BFA1) to determine its role in lipid production. Firstly, V-ATPase activity was increased in the latter phase of microalgae growth. BFA1 treatment decreased the cell density and lipid contents. Further analysis showed that BFA1 treatment reduced the number and size of oil bodies. GC-MS analysis showed that lipid components were not affected by BFA1 treatment. Intracellular pH was decreased and nitrogen depletion was delayed after BFA1 treatment. RNA-Seq analysis showed that expression of genes involved in calcium signaling, sulfur metabolism, cell cycle, glycolysis, pentose phosphate pathway, porphyrin, chlorophyll metabolism and lipid catabolic metabolism were upregulated, while expression of genes involved in ion transmembrane transport, ubiquitin mediated proteolysis, SNARE interactions in vesicular transport, fatty acid biosynthesis were downregulated under BFA1 treatment. Our findings provided insights into the molecular mechanisms underlying lipid accumulation and the key genes involved in lipid metabolism in Phaeodactylum tricornutum in response to BFA1.

Molecular dynamics simulation of cyclodextrin aggregation and extraction of Anthracene from non-aqueous liquid phase.

Cyclodextrin (CD) extraction is widely used for the remediation of polycyclic aromatic hydrocarbons (PAH) pollution, but it remains unclear about the influence of CD aggregation on the PAH transport from non-aqueous liquid phase to water. The atomistic adsorption and complexation of PAHs (32 anthracenes) by CD aggregates (48 ß-cyclodextrins) were studied by molecular dynamics simulations at hundreds of nanoseconds time scale. Results indicated that high temperature promoted the ßCD aggregation in bulk oil, which was not found in bulk water. Nevertheless, the fractions of anthracenes entrapped inside the ßCDs cavity in both scenarios were significantly increased when temperature increased from 298 to 328K. Free energy calculation for the sub-steps of CD extraction demonstrated that the anthracenes could be extracted when the ßCDs arrived at the water-oil interface or after the ßCDs entered the bulk oil. The former was kinetic-controlled while the latter was thermodynamic-limited process. Results also highlighted the formation of porous structures by CD aggregates in water, which was able to sequestrate PAH clusters with the size obviously larger than the cavity diameter of individual CD. This provided an opportunity for the extraction of recalcitrant PAHs with molecular size larger than anthracenes by cyclodextrins.

Insights into asphaltene aggregation in the Na-montmorillonite interlayer.

This study aimed to provide insights into the diffusion and aggregation of asphaltenes in the Na-montmorillonite (MMT) interlayer with different water saturation, salinity, interlayer space and humic substances. The molecular configuration, density profile, diffusion coefficient and aggregation intensity were determined by molecular dynamic simulation, while the 3D topography and particle size of the aggregates were characterized by atomic force microscopy. Results indicated that the diffusivity of asphaltenes was up to 5-fold higher in the MMT interlayer filled with fresh water than with saline water (salinity: 35‰). However, salinity had little impact on the asphaltene aggregation. This study also showed a marked decrease in the mobility of asphaltenes with decrease in the pore water content and the interlayer space of MMT. This was more pronounced in the organo-MMT where the humic substances were present. The co-aggregation process resulted in the sequestration of asphaltenes in the hollow cone-shaped cavity of humic substances in the MMT interlayer, which decreased the asphaltene diffusion by up to one-order of magnitude and increased the asphaltene aggregation by about 33%. These findings have important ramifications for evaluating the fate and transport of heavy fractions of the residual oil in the contaminated soils.

Modeling the adsorption of PAH mixture in silica nanopores by molecular dynamic simulation combined with machine learning.

The persistence of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils is largely controlled by their molecular fate in soil pores. The adsorption and diffusion of 16 PAHs mixture in silica nanopore with diameter of 2.0, 2.5, 3.0 and 3.5 nm, respectively, were characterized by adsorption energy, mean square displacement, free surface area and free volume fraction using molecular dynamic (MD) simulation. Results suggested that PAHs adsorption in silica nanopores was associated with diffusion process while competitive sorption was not the dominant mechanism in context of this study. The partial least squares (PLS) regression and machine learning (ML) methods (i.e. support vector regression, M5 decision tree and multilayer perceptrons) were used to correlate the adsorption energy with the pore diameter and PAH properties (number of carbon atoms, aromatic ring number, boiling point, molecular weight, octanol-water partition coefficient, octanol-organic carbon partition coefficient, solvent accessible area, solvent accessible volume and polarization). Results indicated that the PAH adsorption could not be predicted by linear regression as the R(2)Y and Q(2)Y coefficients of PLS analysis was 0.375 and 0.199, respectively. The nonlinearity was well recognized by ML with correlation coefficient up to 0.9. Overall, the combination of MD simulation and ML approaches can assist in interpreting the sequestration of organic contaminants in the soil nanopores.

Molecular dynamic simulation of asphaltene co-aggregation with humic acid during oil spill.

Humic acid in water and sediment plays a key role in the fate and transport of the spilled oil, but little is known about its influence on the aggregation of heavy oil asphaltenes which is adverse for remediation. Molecular dynamic simulation was performed to characterize the co-aggregation of asphaltenes (continental model and Violanthrone-79 model) with Leonardite humic acid (LHA) at the toluene-water interface and in bulk water, respectively, to simulate the transport of asphaltenes from oil to water. At the toluene-water interface, a LHA layer tended to form and bind to the water by hydrogen bonding which provided a surface for the accumulation of asphaltenes by parallel or T-shape stacking. After entering the bulk water, asphaltene aggregates stacked in parallel were tightly sequestrated inside the inner cavity of LHA aggregates following surface adsorption and structure deformation. Asphaltene aggregation in water was 2-fold higher than at the toluene-water interface. The presence of LHA increased the intensity of asphaltene aggregation by up to 83% in bulk water while relatively less influence was observed at the toluene-water interface. Overall results suggested that the co-aggregation of asphaltene with humic acid should be incorporated to the current oil spill models for better interpreting the overall environmental risks of oil spill.

Mobility of phosphorus induced by sediment resuspension in the Three Gorges Reservoir by flume experiment.

The mobility of phosphorus (P) induced by sediment resuspension have been examined in a circulated flume. During the flume run, the water level and velocity were monitored, and water samples were taken for measurement of sediment and P concentrations. Peak values of both the P and sediment concentrations existed at x=4m, and then decreased slightly along the flume due to deposition. A faster P release was observed for coarser sediment, while a more sustained P release for finer sediment. Combining with the measured data from Yangtze River and sorption experiment, the relation between the load of total P (LTP) and sediment load (Qs) was estimated, and the expressions of distribution coefficient Kd and the concentration of particulate P (PP) were obtained. This study established a bridge between the small-scale sorption experiment and the field observation of natural scale, providing references for the management of contaminated sediment in natural rivers.

Polypyrrole shell@3D-Ni metal core structured electrodes for high-performance supercapacitors.

Three-dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high-performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D-Ni-core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as-prepared material exhibits a high specific capacitance (726 F g(-1) at a charge/discharge rate of 1 A g(-1)), good rate capability (a decay of 33% in Csp with charge/discharge rates increasing from 1 to 20 A g(-1)), and high cycle stability (only a small decrease of 4.2% in Csp after 1000 cycles at a scan rate of 100 mV s(-1)). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as-prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg(-1)) and superior long-term cycle ability (only 4.4% and 18.6% loss in Csp after 2000 and 5000 cycles, respectively).

[Mass Transport in Porous Sediments During a Turbulent Disturbance].

To examine mass transport in porous sediments during a turbulent flow, we established a simple sediment re-suspension device, made use of different sizes of sands as homogeneous sediments, and we injected 500 µg x cm(-3) soluble Rhodamine B into different parts of the sediment as the mass tracer, to observe mass transport during the turbulent condition. The research showed that in porous sediments, pore-water pressure difference would be generated because of the sediments' distinctive porosity and permeability, and further led to the convective flow and mass transport in porous media. Moreover, such mass transport was directly influenced by its burial depth and particle size of the sediment. While in homogeneous sediments, mass transport was strongly influenced in vertical direction under 200 r x min(-1) disturbance, and when moderately increased the size of porous particles under the same turbulent condition, such convection of pore-water would relatively enhance.

Molecular modeling of interactions between heavy crude oil and the soil organic matter coated quartz surface.

Molecular dynamic (MD) simulation was applied to evaluate the mobility, diffusivity and partitioning of SARA (saturates, aromatics, resins, asphaltenes) fractions of heavy crude oil on soil organic matter (SOM) coated quartz surface. Four types of SOM were investigated including Leonardite humic acid, Temple-Northeastern-Birmingham humic acid, Chelsea soil humic acid and Suwannee river fulvic acid. The SOM aggregation at oil-quartz interface decreased the adsorption of SARA on the quartz surface by 13-83%. Although the SOM tended to promote asphaltenes aggregation, the overall mobility of SARA was significantly greater on SOM-quartz complex than on pure quartz. Particularly, the diffusion coefficient of asphaltenes and resins increased by up to one-order of magnitude after SOM addition. The SOM increased the overall oil adsorption capacity but also mobilized SARA by driving them from the viscous oil phase and rigid quartz to the elastic SOM. This highlighted the potential of SOM addition for increasing the bioavailability of heavy crude oil without necessarily increasing the environmental risks. The MD simulation was demonstrated to be helpful for interpreting the role of SOM and the host oil phase for the adsorption and partitioning of SARA molecules, which is the key for developing more realistic remediation appraisal for heavy crude oil in soils.

Sorption and distribution of asphaltene, resin, aromatic and saturate fractions of heavy crude oil on quartz surface: molecular dynamic simulation.

The molecular scale sorption, diffusion and distribution of asphaltene, resin, aromatic and saturate fractions of heavy crude oil on quartz surface were studied using molecular dynamic simulation. Sorption of saturates on quartz decreased by 31% when temperature increased from 298 to 398K while opposite trend was observed for resins, but insignificant changes were found in asphaltenes and aromatics. Despite of this variety, the main contribution of interactions was van der Waals energy (>90%) irrespective of molecular components and temperatures. The diffusion coefficient of saturates was predicted as 10.8×10(-10)m(2)s(-1) while that of the remaining fractions was about 4×10(-10)m(2)s(-1) at 298K. The most likely oil distribution on quartz surface was that aromatics and saturates transported randomly into and out of the complex consisting of asphaltenes surrounded by resins, which was influenced by temperature. Overall, the knowledge on quartz-oil and oil-oil interactions gained in this study is essential for future risk assessment and remediation activities as previous studies on soil remediation either limited to light oil fractions with <40 carbons or treated the heavy crude oil as a single pseudo entity ignoring the interactions between oil fractions.

A lysimeter experimental study and numerical characterisation of the leaching of incinerator bottom ash waste.

Incinerator bottom ash (IBA) is a residual produced from incinerating municipal solid waste. In the past, IBA presented a big waste disposal problem; however, various recycling approaches have been adopted in recent years to mitigate this problem, as well as to provide a useful alternative to using primary aggregate resources. The use of IBA as an alternative to conventional aggregates in different civil engineering construction applications helps to conserve premium grade aggregate supplies; however, when IBA is in contact with water in the field, as a consequence of precipitation events or changes in water table, elements, such as salts and heavy metals, may be released to the soil and ground water. In this work, IBA waste was mixed with limestone aggregate to produce a blend with acceptable mechanical properties and minimum environmental risks for use as road foundation. The study focused on evaluating potential environmental impacts of some constituents, including sulphate, chloride, sodium, copper, zinc and lead in IBA blends using a lysimeter as a large scale leaching tool. Moreover, a specific scenario simulating field conditions was adopted in the lysimeter to assess the potential impact of changing conditions, such as IBA content in the blend, liquid to solid ratio (L/S) and pH value, on long-term release of heavy metals and salts. Then, numerical modelling was used to predict the release of the aforementioned constituents from IBA based on initial measurement of intrinsic material properties and the kinetic desorption process concept. Experimental results showed that zinc and lead were released in very low concentrations but sodium and sulphate were in high concentrations. The control limestone only blend also demonstrated low release concentrations of constituents in comparison to IBA blends, where constituent concentrations increased with increase in IBA content. Experimental results were compared with numerical results obtained using a non-equilibrium desorption model. Good agreement was found between the two sets of data.

Field scale DNAPLs transport under nonequilibrium sorption conditions.

The purpose of this work is to study the desorption of dense nonaqueous phase liquids (DNAPLs), TCE in particular, from solid particles in field scale heterogeneous aquifers upon their remediation. A computer program, capable of simulating the fate and transport of NAPLs in porous media, has been developed to work under nonequilibrium sorption conditions. The model has been applied to a field scale site at Hill Air Force Base, Utah, which has been contaminated by DNAPLs. The simulated domain was 155 ft (47.25 m) long, 60 ft (18.29 m) wide, and 15.5 ft (4.72 m) thick. This thickness represents only the saturated zone of the aquifer. Changes in permeability, grain size distribution, and sorptive properties throughout the site have been incorporated into the model. Immediately after the aquifer cleanup, the DNAPL concentration in the aqueous phase was assumed to be zero, and this was considered the start-off time for the simulation. Results show that, with an increase in time, the TCE diffused out of the solid particles, forming a plume. The rate of contaminant diffusion was observed to be very fast at the start, followed by a very slow stage, with a number of years required for substantial desorption of the contaminant from the solid particles. There were local variations in contaminant concentration in the fluid phase across the site due to aquifer heterogeneity. A comparison between numerical results and water samples taken from the site after the end of the cleanup operation is also presented.