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This work numerically investigated the translational velocity of a negatively charged oil droplet in the water near a negatively charged solid surface under a DC electric field. The equilibrium separation distance between the charged oil droplet and the charged solid surface is calculated under different parameters and the translational motion of the droplet near the solid surface is simulated via a three-dimensional mathematical model. The results indicate that the velocity of the droplet is higher under a larger zeta potential of the solid surface and a smaller zeta potential of the droplet. When the absolute value of the negative zeta potential of the droplet is larger than that of the solid surface, the droplet will move in opposite direction of the electric field. It is also found that the droplet translational velocity increases with the decrease of the separation distance between the oil droplet and the solid surface.

Chlorophyll fluorescence-based method shows great potentials for on-site assessing the vitality of algae in treated ship's ballast water. However, there is very limited information on the mechanism of chlorophyll fluorescence in photosystem II (PSII) after the NaClO treatment. In this paper, the effects of NaClO treatments with five concentrations (0.01, 0.04, 0.08, 0.12 and 0.15 mg/L) and treating periods (6, 24 and 48 h) on the chlorophyll fluorescence kinetics and spectra of Chlorella vulgaris (C. vulgaris) and Platymonas helgolandica (P. helgolandica) were investigated. Experimental results showed that both exposure time and dose were important factors that affect the toxicity of NaClO to microalgae. Further analyses showed that the maximum photochemical quantum yield of PSII, photochemical quenching and yield decreased rapidly with the increase in NaClO concentrations in the range of 0.04 mg/L to 0.15 mg/L, suggesting that NaClO seriously inhibited PSII reaction centers of algae. In addition, the maxima value of fluorescence at excitation wavelength still appeared near 437 nm and 468 nm under NaClO stress, pointing to the pigments for fluorescence produced by algae were mainly chlorophyll a and chlorophyll b antenna. As compared to chlorophyll a, the relative fluorescence intensity of chlorophyll b decreased significantly in the all of NaClO treatments. According to the fluorescence emission spectra, treatment of NaClO resulted in a shift of the maximum peak of C. vulgaris and P. helgolandica from 685.2 nm to 681.9 nm and 685.2 nm to 680.5 within 6 h, respectively. This indicates that the structure of antenna light-absorbing pigments of PSII changed under NaClO stress. These results revealed that the chlorophyll fluorescence mechanism in PSII of damaged microalgae occurred variation, which was important for the reliable application of on-site analysis of ballast water indicator based on chlorophyll fluorescence detection.

Hypothesis The shape of the liquid film (SLF) between a glass slide and an oil droplet immersed in an aqueous solution is influenced by the direct current (DC) electric field. The liquid film, consisting of the central film region and the meniscus film region, is formed between a floating oil droplet and a glass slide overhead. Experiments The SLF was experimentally studied in aqueous solutions of different ionic concentrations and pH values. After the DC electric fields were applied along the glass slide in horizontal direction, the diameter of central film and the thickness of meniscus film were measured by the interference method with an optical microscope. Findings The diameter of the central film decreases with the increase in the applied electric fields and declines at higher pH values while increases when the ionic concentration increases. The meniscus film becomes thicker with the increase in applied electric fields and is thicker in pH = 11 solution and thinner in pH = 3 and 1 mM NaCl solution. This is the first study of dynamic thin liquid film under DC electric field, which may be attributed to the balance of dielectrophoretic (DEP) force, colloidal force and the deformable characteristic of the oil droplet.

A numerical study on the electrokinetic motion of a charged oil droplet near a charged air–water interface is presented in this paper. First, the separation distance between the oil droplet and the air–water interface is calculated, and then the electrokinetic velocity of the droplet is simulated utilizing a three-dimensional numerical model under different applied electric fields, droplet’s radii, ionic concentrations, zeta potentials of the oil–water interface, and zeta potentials of the air–water interface. The numerical results indicate that a negatively charged oil droplet near a negatively charged air–water interface moves in opposite direction of the direct current electric field and has larger velocity under higher electric field strength, droplet’s radius, ionic concentration, and absolute values of the two interface zeta potentials.

The 14-year trends of surface ozone were examined using observations from 12 urban sites and 4 regional sites over the Pearl River Delta (PRD) region in China over the 2006–2019 period. Surface ozone exhibits upward trends in the range of 0.28–1.02 ppb yr−1 at urban sites and mixed trends in the range of −0.29 – 0.21 ppb yr−1 at regional sites. Meanwhile, surface Ox (Ox = O3+NO2) mixing ratios exhibit downward trends at 9 urban sites and 3 regional sites in the range of −0.01 to −0.54 ppb yr−1, revealing that the ozone rise at urban sites is predominantly attributed to the reduced titration effect by nitric oxide (NO). The further decline of surface NO2 mixing ratios could drive the decreases in Ox mixing ratios and the increases in ozone mixing ratios at urban sites. In addition, surface Ox concentrations show a good correlation with aerosol concentrations, implying the dominant contributions of secondary production to aerosol and the consistent control strategies of ozone and aerosol pollution in PRD. For the abatement of ozone pollution, our results highlight the synergistic control of key precursors including nitrogen oxides and volatile organic compounds to counteract the reduced NO titration effect by inhibiting the photochemical production of ozone. At last, we also highlight the importance of establishing more regional sites in comprehensively assessing spatiotemporal changes in surface air pollutants in China.

A smartphone integrated microfluidic lab-on-chip device was developed for the real-time detection, counting and sizing of living algae in simulated ballast water samples. The device consists of a microfluidic chip, a customer-made fluorescence imaging platform and a smartphone. When living algae pass the laser illumination region of the microfluidic chip, chlorophyll fluorescence is emitted and shown in the smartphone. An algorithm in the smartphone detects, counts and sizes the detected living algae. As a proof of concept, two different sizes of algae were tested and a detection accuracy of larger than 92% was achieved. The sizing accuracy is 94%. The largest moving velocity allowed for detection is determined by the diameter of the algae and the frame per second (fps) of the smartphone. The device is simple in structure and operation and suitable for on-site evaluating the living status of algae in treated ship’s ballast water.

Flow-electrode capacitive deionization (FCDI) has gained lots of attention for the continuous operation, fast and scalable desalination process. However, the flow electrode slurry is poorly conductive and resulting in the high ions transport resistance, which restricts its desalination efficiency. In this work, a novel FCDI system was constructed by using the porous nickel foam (NFM) as the current collector, and its desalination performance was enhanced via the assistance of electro-catalytic water splitting. In detail, the functionalized current collectors (NFM-Co3O4 with enhanced oxygen evolution activity and NFM-Co(OH)2 with enhanced hydrogen evolution activity) were prepared through a two-step procedure of electrodeposition and subsequently anodic reaction/cathodic reaction. A desalination efficiency of 90.22% was obtained by the FCDI system adopted functionalized NFM (F-NFM-FCDI) after 100 min operation at applied voltage of 2.0 V, which was much higher than that of the FCDI system adopted bare NFM (NFM-FCDI, 65.37%). Moreover, F-NFM-FCDI system possessed higher charge efficiency (CE) of 81.24% and lower normalized energy consumption (NEC) of 237.54 J·mmol−1 under this condition. Mechanism analysis demonstrated that the enhancement on the desalination performance of F-NFM-FCDI system was attributed to the improved conductivity in flow-electrode chamber, which was due to the increase in the concentration of H+ and OH– caused by the enhanced electro-catalytic water splitting reaction during charging. In summary, this work provided a novel and facile strategy to improve the desalination performance of FCDI system by coupling with electro-catalytic water splitting.

Electrokinetic movement of spherical polystyrene particles at different liquid-fluid interfaces was experimentally investigated in this paper. A novel method was developed to place the particles rightly at the interfaces formed in a large plastic container. The velocity was measured by an optical microscope. The experimental results show that the particles (3, 5 and 10 μm in diameter) at the water-air interface, water-dodecane interface and NaCl solution-air interface move in the opposite direction of the applied electric field. The magnitude of the particles’ velocity increases linearly with the increase in the applied electric field. Moreover, for particles of the same size, the electrokinetic velocity at the liquid-fluid interfaces is larger than particles’ electrophoretic velocity in the bulk liquid phase. Under the same electric field, however, the electrokinetic velocity of smaller particles at the liquid-fluid interfaces is larger than that of larger particles. Such results are attributed to the surface charges at the liquid-fluid interface and the particle-liquid interface.

In this paper, a dynamic changing solid-liquid interfacial process was used for electrically detecting and counting underwater bubbles. The measurement system consists of a detection electrode, a reference electrode, an electric resistor connected in series with the two electrodes, a differential amplifier and a data acquisition system. Once a bubble touches the detection electrode submerged in a solution, the electrode-liquid interface is changed to the electrode-bubble interface. During this process, an electric pulse is generated and consequently be detected and counted by the measurement system. The generated electric signal is due to the dynamic change of the electric double layer (EDL) of the detection electrode. Experimental results show that the magnitude of the generated signals depends on bubble size, bubble rising height, exposed area of the detection electrode in solution and bubble-contacting position at the electrode. The magnitudes of the generated signals are larger in 3.5% NaCl solution than in pure water. Detection of air bubbles of 0.3 mm in diameter was achieved with a 3 mm × 3 mm detection electrode. The measurement system presented in this paper is simple and has a great potential on sensing and counting underwater bubbles, for applications such as underwater pipe leakage detection and bubble sensing in chemical engineering science.

This work reported that a novel omniphobic membrane distillation (MD) membrane was successfully fabricated by constructing a re-entrant microstructure via in-situ silica nanoparticle (SiNPs) growth on an electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)/3-aminopropyl-triethoxysilane (APTES) nanofibrous membrane, and subsequent hydrophobization. Introducing APTES provided the nucleation sites for in situ SiNPs growth on the hydrophobic nanofibers for re-entrant structure construction. After hydrophobization, the final membrane exhibited outstanding omniphobicity with high contact angle values of 151.49°, 140.64°, 119.59°, and 107.5° to water, mineral oil, 4 mM sodium dodecyl sulfate (SDS) and ethanol, respectively. More importantly, the prepared omniphobic membrane showed satisfactory wetting resistance in a feed solution containing a 3.5 wt% NaCl and 0.4 mM SDS, and the salt rejection was ~100%. In addition, the omniphobic membrane also demonstrated robust scaling resistance, which was in sharp contrast to the PVDF-HFP membrane. Meanwhile, during treating a mineral oil-in-saline (3.5 wt% NaCl) water emulsion, the omniphobic membrane displayed outstanding anti-wetting and anti-fouling properties, indicated by a steady state permeate flux and ~100% stable salt rejection during the continuously 72 h tests. These overall findings indicated that the prepared omniphobic membranes have great potential in MD for challenging industrial wastewaters.

A novel method for detecting and sizing airborne particles at single particle level is presented in this paper. When a particle hits a metal electrode which is grounded, electrostatic charges will be transferred between the particle and the electrode. As a result, an electrical current pulse will be generated in the measurement system. The number of the signal pulse represents the number of particles in the sample. To determine the effect of the particle size on the magnitude of the signal, the correlation between the magnitude of the signal and the size of particle was experimentally investigated. The results show that the magnitude of the measured signal is linearly proportional to the square of particle’s diameter. Such a correlation can be used to evaluate particle size from the measured signal. The airborne particle detection method presented in this paper can be used for counting and sizing airborne particles at single particle level.

Electrospun nanofibrous mats have been widely used as substrate to develop novel membranes for forward osmosis (FO) application due to its ultralow structure parameter (S). However, their large pore sizes usually hinder the formation of satisfied active layer. In this work, a novel composite FO membrane was designed and prepared with a carbon nanotubes (CNTs) interlayer between the dense polyamide (PA) layer and electrospun porous polyacrylonitrile (PAN) support layer. The presence of CNT interlayer minified the pore size of the substrate to provide a better platform for PA layer growth which inhibited the diffusion of the draw solute, thus keeping a stable osmosis pressure gradient on both side of the thin-film composite (TFC) membrane. The results revealed that the optimized FO membrane with CNTs interlayer exhibited water flux of 83.55% higher and reverse salt flux of 75.58% lower than the unmodified membrane in the active layer facing draw solution (AL-DS) mode. Such better overall FO performance suggested that the addition of CNTs interlayer would offer a promising avenue to prepare high-performance electrospinning-based FO membrane for practical application.

As worldwide forest fire frequently causes a serious threat to forest resources and global climate change, novel early forest fire monitoring and detection technologies are urgently required to explore. Herein, a self-powered forest fire alarm system (FFAS) is proposed by coupling thermosensitive effect and triboelectric effect as an aim of effective forest fire monitoring and detecting. The FFAS is fabricated as a self-powered early forest fire monitoring and detection system by connecting a spherical free-standingmode triboelectric nanogenerator (S-TENG) as power source with polydopamine-modified graphene oxide (P-GO) as thermosensitive sensor and commercial LEDs as alarm. When encountering an open fire or abnormal high temperature the thermosensitive sensor based on P-GO can be in-situ thermally reduced, inducing an obvious transition in electrical resistance. Thus, the output voltage of S-TENG can be tuned by the impedance matching effect between special output characteristics of TENG and working status of thermosensitive sensor, and then can directly light up the LEDs as alarm. Furthermore, the FFAS achieves a low temperature response (160 °C), rapid response time (~3 s), and especially no external power supply. Consequently, the FFAS based on impedance matching effect between TENG and thermosensitive sensor would provide a real-time, rapidly responsive, and self-powered monitoring strategy for the early forest fire warning and detection.

A novel system which can greatly improve the waving potential [1] of metal produced by a moving liquid–solid boundary is presented in this paper. By using a pair of copper electrodes immersed in an electrolyte solution, a significant electric potential is generated by changing the wetted surface area of only one electrode when a droplet falls into the electrolyte solution. Experiments show that the electric potential difference between the two electrodes is generated due to different wetted areas at the two electrodes. The magnitude of the generated electric current depends on the types of the electrolyte solution and the moving speed of the air-electrolyte solution interface. A droplet of 24 µL can generate a waving potential of three orders of high than that reported in the reference paper [1] . The approach of inserting a pair of asymmetrically insulated metal electrodes into an electrolyte solution makes it possible to utilize ordinary pure metal materials for harvesting waving potential energy from a dynamic moving liquid–air interface.

Size spectrum of biological particles directly affects nutrient cycling and energy flow distribution of marine ecosystems . Fast and accurate detection of the size and distribution of marine phytoplankton plays a very important role for in-depth study of physiological characteristics of marine phytoplankton community structure and function. In this paper, a novel detection method and system of size spectrum of microalgae cells on a microfluidic chip is presented. In this device, a microfluidic resistance pulse sensor (RPS) technology is adopted to determine the particle size of microalgae cells; chlorophyll fluorescence intensity is used to judge if a particle is a live microalgae cell or not. Inside a waterproof case, the system mainly comprises a microfluidic chip platform, a sample acquisition module, an optoelectronic detection unit, and a module performing data acquisition, data processing and system control. To demonstrate the performance of the developed system, experiments were conducted with three species of microalgae cells ( Isochrysis galbana , Dunaliella salina and Tetraselmis chui ), typical phytoplankton cells in marine environments, as samples. Comparison experiments between the developed detection system and a commercial flow cytometer were conducted. The results demonstrate that the developed system is reliable and accurate. The limit of detection of microalgae cell size is 3 μm for the current device and can be improved in the future. The presented microfluidic system provides a very promising method of size spectrum detection of microalgae cells with the advantages such as fast detection, small size and easy operation. It has a great potential for in-situ underwater detection of micro phytoplanktons pending further product development.

Capacitive detection of living microalgae from the sample suspension in a microfluidic chip is presented in this paper. A three-dimension capacitance sensor was designed by placing two cylindrical copper wires across the microfluidic channel. The frequency-dependent capacitive changes for both living and dead Dunaliella Salina were analyzed with Maxwell mixture theory and measured experimentally in this study. The results show that the amplitude of capacitive change is mainly influenced by algae's size, living status and the applied alternative current frequency. Specifically, capacitive change increases with the increase in algae size and decreases with the increase in frequency. For the same kind of algae, the capacitance change caused by the living algal, however, is larger than that of the dead one under the same frequency, which can be used to differentiate the living algae from the sample suspension. The method of frequency-dependent capacitive detection of live algae described in this paper is simple and sensitive. The experimentally determined frequency window can serve as a guideline to differentiate the living algal from the dead one.

Evaluation of radiation dose is very important for the detection of radiation damage. γ-H2AX is a popular biological dosimeter to evaluate the radiation effect. Typically, bulky and expensive commercial flow cytometers are used to detect γ-H2AX. This paper presents a miniaturized and high sensitive cytometer using a microfluidic chip for evaluating the radiation dose by detecting the mean immunofluorescence intensity of γ-H2AX. A compact optical focusing system and a shift-phase differential amplifier are designed to improve the detection sensitivity. Sample lymphocyte cells are stained by FITC fluorescent dye after being irradiated by UVC. Comparison experiments between the developed miniature cytometer and a commercial flow cytometer were conducted under different radiation doses. The developed microfluidic cytometer also demonstrates a good linear correlation between the measured fluorescence intensity and the irradiation dose with a detection limit similar to that of the commercial flow cytometer. The developed cytometer can evaluate quantitatively the radiation dose by the mean fluorescence intensity of γ-H2AX with a significantly smaller amount of blood samples than a commercial flow cytometer.

This paper reports a novel and very simple method for measuring the zeta potential of electrolyte solution–air interface. When a measuring electrode contacts the electrolyte solution–air interface, an electrical current will be generated due to the potential difference between the electrode–air surface and the electrolyte solution–air interface. The amplitude of the measured electric signal is linearly proportional to this potential difference; and depends only on the zeta potential at the electrolyte solution–air interface, regardless of the types and concentrations of the electrolyte. A correlation between the zeta potential and the measured voltage signal is obtained based on the experimental data. Using this equation, the zeta potential of any electrolyte solution–air interface can be evaluated quickly and easily by inserting an electrode through the electrolyte solution–air interface and measuring the electrical signal amplitude. This method was verified by comparing the obtained results of NaCl, MgCl2 and CaCl2 solutions of different pH values and concentrations with the zeta potential data reported in the published journal papers.

Sweat test based on chloride ion selective electrode is the common method for the diagnosis of Cystic Fibrosis (CF). In our previous study, the possibility of using chloride ion sensitive fluorescent dye to determine the chloride ion concentration with a small volume of sample has been explored. However, we found the conventional Stern–Volmer Equation is applicable only for large systems such as a fluorescent microscope with a large volume of sample and dye solution; and it is not valid for portable devices using a small photo detector and a small volume of sample and dye solution. Therefore, in this paper, extensive experiments were performed by using a miniature fluorescent detection system; the effects of the parameters including the concentration and the volume of fluorescent dye solution, the coefficient of Stern–Volmer plot, and the volume ratio of the fluorescent dye solution and the chloride solution were studied; and a modified Stern–Volmer Equation was obtained. Using the modified Stern–Volmer correlation, the miniature fluorescent detection device can detect the chloride ion concentration correctly and rapidly.

This paper reports a method of detecting nanoparticles using a microfluidic differential Resistive Pulse Sensor (RPS). Using a single microfluidic channel with two detecting arm channels placed at the two ends of the sensing section, the microfluidic differential RPS can achieve a high sensitivity allowing the detection of nanometer size particles. Two-stage differential amplification is used to further increase the signal-to-noise ratio. This method is able to detect nanoparticles of 490 nm and 220 nm on a microfluidic chip. The method described in this paper is simple and can be applied to develop a compact device without the need of bulky, sophisticated electronic instruments or complicated nano-fabrication processes.

By incorporating a viscous liquid force model into DEM simulations, the effect of liquid bridging between two tablets during a collision was studied. It was shown that when compared to the viscous force, the capillary force is several orders of magnitude smaller. In order to predict the capture of a falling tablet by the liquid bridge, it was necessary to adjust the limiting separation distance used in the viscous force model. Comparison of experimental results with the simulations, using oils with viscosities in the range of 100–1,000 cP, showed that there was a linear relationship between the limiting separation distance and the viscosity of the silicone oils. This viscosity-dependent separation distance varied in the range of 1–6 mm.

This paper presents a coating model to predict the mass coating uniformity in a Wurster fluid bed coater using a Monte Carlo method. The velocity and voidage data obtained using imaging techniques on the same Wurster coater are used as inputs to the model. The semi-circular Wurster fluid bed used in this work was 22.9 cm in diameter. A batch of 3.6 kg tablets was used to conduct coating experiments and the coating weight gain distribution results were compared to predictions from the simulation. The model rigorously considers the sheltering effect of particles as they move in the spray zone. Good agreement was obtained when comparing the results with an analytical model. Spray shape and orientation of discretization were found to play an important role in predicting the coating uniformity. A simple spray experiment in a particle-free bed showed that the direction of spray material, in general, was vertically upward. Simulation results confirmed that an upward cylindrical spray model gives better agreement with experimental results compared to a solid cone spray model. Finally, the model was used to predict the changes in coating uniformity with bed operating conditions such as gas velocity and gap height. A wider coating distribution was found for the case with the lower gas velocity and gap height.

A MATLAB™-based DEM (discrete element method) code was developed to study the particle motion in a pan coating device. The code was developed as a stand-alone program and provides simulation, visualization (GUI interface), and post-processing statistical analysis of particle movement. Results of DEM simulations are compared with those obtained from video-imaging experiments for 9 mm spherical polystyrene balls in a 58 cm diameter pan. The parameters compared are dynamic angle of repose and particle velocities in the x- (axial) and y- (parallel to cascading layer) directions within the spray zone in the cascading layer. The effects of pan loading and pan speed (6, 9, 12 rpm) on particle motion are compared and discussed. Good agreement was obtained between the DEM simulation and experimental results. The dynamic angle was found to increase with increasing pan speed and pan loading. The average cascading velocity was found to increase linearly with pan speed for both DEM and experiments. The velocity distributions both in the x- and y-direction were compared from simulation and experiments and found to be in good agreement. Velocity profiles along the entire top cascading layer of particles were also obtained using DEM. The particles in the cascading layer were found to reach their maximum velocity at positions close to the mid-point of the cascading surface. Comparison of simulated velocity profiles showed good agreement with published scaling laws for rotating drums, and a new correlation for scaling with respect to the pan loading is proposed.

The shape of standard round tablet was represented by using the intersection of three spherical surfaces. Using this model, the contact criteria for tablet–flat surface and tablet–tablet contact were developed and were applied for tablet–tablet contact using a DEM simulation implemented in Matlab™ code. In addition, a high-speed digital imaging system was used to capture the images of one tablet hitting another fixed tablet anchored to a flat surface. Comparison of angular velocity showed good agreement between simulation and experimental results. The simulations were compared with alternative multi-sphere representations for the shape of the tablet and the results showed that the simulation times for 66- and 178-sphere representations were much larger than that for the tablet simulations. In addition, the simulation results for all the multi-sphere representations were significantly different from those of the tablet simulation.

The successive analytical expressions up to fifth order for the Curie temperature, Tc(D,d), of the D-vector model on d-dimensional hypercubic lattices are evaluated by the Ginzburg-Landau theory based on cumulant expansion. The results by substituting d = 3 and D = 1, 2, 3 into the expressions approach order by order those of the Ising, XY, and Heisenberg models by Monte Carlo simulation (MC). The differences between ours and the other models are about 5.52, 6.86, and 7.94 percent, respectively.

Described is a scheme of successive approximations used to compute a critical point. An order parameter J is introduced automatically in the cumulant expansion. The critical temperature Tc is determined by the singular point of the curve of J versus temperature. This method is applied to (d + 1)-dimensional Ising layers. Tc as an analytical function of d is obtained for a system of uniform layers. A more realistic case, which lacks the layer to layer symmetry, is also investigated.