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Droplet-based microfluidic technology can be utilized as a microreactor to prepare novel functional monodisperse microcapsules. In this study, a droplet-based microfluidic chip with surface modification, which allowed the one-step preparation of double emulsion microcapsules. An O/W/O double emulsion using polyethylene (glycol) diacrylate (PEGDA) solution as the intermediate water phase was prepared by regulating the hydrophilicity and hydrophobicity of the chip surface, with PEGDA microcapsules prepared using UV polymerization. And then anti-tumor drug paclitaxel and neurotoxin 6-OHDA were encapsulated in microcapsules for drug and toxicology evaluation, respectively. Compared to controls, drug-loaded microcapsules caused a significant increase in the death rate of PC12 cells. This indicates that the obtained drug-loaded microcapsules could be used in drug evaluation and potentially in drug screening and delivery.

To solve the control problem of nonstrict feedback nonlinear systems, a backstepping technique based controller design method is developed by integrating a robust control law with the excellent parameter identification algorithm of indirect adaptive framework. Each of unknown system functions that contain whole states is approximated by adding together a bounded time-varying parameter and a fuzzy approximator related to the current step and previous states only in the backstepping design procedure, which solves the algebraic loop problem existing in nonstrict feedback systems. Then the command filter is combined with the adaptive backstepping to construct the robust control law by which the differentiation operation of the virtual control signal can be avoided. Subsequently the swapping scheme is used to convert the studied system into a linear time-varying form. Both the weight vector of the fuzzy logic system and the bounded time-varying parameter are estimated by a least-squares identification algorithm under relaxed excitation conditions, so that the accurate value of system functions can be obtained. All signals in the closed-loop system are proved to be bounded. A simulation example is put forward to verify effectiveness of the presented method.

Hypothesis Electrorheological fluid (ERF) is a kind of suspension or colloid composed of fine particles and insulating oil as continuous phase. The second miscible liquid phase with less affinity to the particles than the continuous phase is expected to influence particles aggregation, assembly and spanning mesostructures. Hence, it should be possible to tune the rheological and electrorheological properties and stability by the addition of second miscible liquid with different chain length and substituents. Experiments We developed a giant ERF (GERF) with a binary liquid phase (BLP) by the addition of alkane to the silicone oil continuous phase. We studied the shear stress and viscosity under different shear rates, thixotropy and particle size distributions of these suspensions and characterized the concentration variation of GERFs under quiescent conditions by measuring the backscattering light intensity variation through vertical scanning. Findings The dispersed particle size distribution is broadened, which produces higher static yield stress and lower zero-field viscosity than those of a single-liquid-phase GERF. The ER efficiency is much higher with the addition of alkane, reaching 10656, which is 1.8 times larger than that of single-liquid-phase suspensions. We performed 100-day stability testing and found that the GERF with 1-phenyldodecane showed excellent stability and performance.

Here, we analyzed the internal structure of ZnO varistors with X-ray micro-CT technology and showed that the porosity and pore volume at the radial edge is considerably higher than at other regions. Experimental results showed that the breakdown phenomenon usually occurs near the outer edge of circular varistors. The distribution of impulse currents applied to concentric ring electrodes indicated that the current ratio at the edge region increased as the total current increased. The pores are insulating under low electric fields and the current through the pores is almost zero. Hence, the voltage gradient at the edge region is higher than that elsewhere. Additionally, the simulation results were consistent with this assumption. The amounts of open pore defects, which showed a conductive state after break down, increased, and the proportion of the current flow through the pores increased accordingly, which lead to a local temperature rise and breakdown.

The aging performance of zinc oxide (ZnO) varistors doped with aluminum and indium was investigated. Alternating current (AC) accelerated aging voltages of 0.85U1mA, 0.90U1mA and 0.95U1mA were applied to the doped varistors at a temperature of 115 °C for more than 1000 h. The electrical properties of the varistors before and after the aging process were evaluated by measuring their current–voltage, capacitance–voltage, and dielectric characteristics. The results showed that the ZnO varistor samples exhibited stable electrical properties under the applied aging conditions. Degradation rate coefficients (Kt) of 0.03, 0.05 and 0.06 were obtained at AC accelerated aging voltages of 0.85U1mA, 0.90U1mA and 0.95U1mA, respectively. The results indicated that the varistor ceramics should be able to operate safely and continuously under the given conditions for more than 110 years, which meets the requirements of surge arresters in power systems. These findings are important for improving the aging performance of ZnO varistors and the general security and stability of power systems.

Zinc-oxide varistors doped with gallium, indium, and silver were studied. Samples showed excellent electrical properties with a voltage gradient of 467.9 V/mm, a nonlinear coefficient of 68.5, and a barrier height of 2.15 eV. Accelerated burn-in alternating voltages of 80%U1mA, 85%U1mA, and 90%U1mA were applied to the samples for more than 200∼h at a temperature of 115 °C. Doping with silver played an important role in reducing the donor density while also raising the barrier height, which helped restrain the aging process and enhanced the aging stability as a result. These varistors performed better in aging stability tests with degradation rate coefficients of 0.04, 0.06, and 0.07 obtained under the given burn-in voltage. They provide the basis for safe and stable operations of surge arresters.

This paper presents a novel approach for automatic, rapid and efficient micro-droplet mixing on ‘open-surface’ droplet-based microfluidics system via magnetic actuation. A two-step micro-fabrication process was employed to decorate the magnetically functionalized polydimethylsiloxane (PDMS) membrane with micro-pillar arrays (MPA) to reduce the adhesion on resident droplets. Droplet manipulation relies on the localized deformation of the elastic membrane under external magnetic fields, thus relieving the additives of magnetic components to the droplets that is commonly required in conventional magnetism-based actuation. Via integration with peripheral computer-based regulator, swift droplet mixing is realized via controlling the coalescent droplets back and forth to generate internal fluid circulations for enhanced mass transfer within the droplet. The comparison of mixing performance between the coalesce-and-stop and back-and-forth mode was systematically performed, which verifies that the back-and-forth actuation of the droplets can obviously improve the mixing efficiency, and typically a higher driving frequency on the droplet renders a shorter mixing duration. With driving frequency of 2.5 cycles/s, the mixing homogeneity can reach 80% within 0.6 s and reach 90% within 1.5 s. Also, it has been experimentally demonstrated that the proposed system can accelerate the dilution under various volume ratios, including 1:2, 1:5, and 1:10. Finally, we demonstrated that the platform can be used to dynamically manipulate the droplets, allowing the de-pinning effect for molecular concentrating and obvious detection sensitivity enhancement in terms of Surface-Enhanced Raman Scattering (SERS). Owing to the superiorities including programmable efficient mixing and parallel scalability, the study herein offers insights for exploiting cost-effective and versatile microfluidics platform for future application in biological analysis, chemical micro-reactions, and trace molecule detections.

SnO2 quantum dots (QDs) ended with chlorine ions are introduced at the interface of spin-coated TiO2 electron selective layer (ESL)/perovskite to fill the pinholes in the layer and passivate the trapping defects. As a result of the increased interface electron collection and reduced bulk recombination, the planar perovskite solar cell with the QDs modified ESL gives the large power conversion efficiency enhancement from 14.9% to 17.3% and greatly improved stability under the continuous light irradiation.

Recently, surface with desirable gradients has been proved to be a powerful tool for diverse applications from biological systems and chemical analysis to material science. In this work, we demonstrate a versatile and universal approach to realize controllable physicochemical properties in orthogonal gradients on polydimethylsiloxane (PDMS) surface. Based on a novel microfluidics network, we can easily establish the concentration gradients within the microfluidic channel for surface polymerization or chemical deposition to realize the stable characteristic gradient on the PDMS substrate. The method was introduced to prepare surface with two-dimensional physical (roughness) gradients, or combinational physicochemical gradients to study the synergistic effect on interested phenomenon. As a proof of concept, the experimental results show that the as-prepared substrate can effectively influence in various fields, such as protein adsorption and nano-particle immobilization, which can potentially be used for future systematical study in biological systems or practical applications in bio/chemical analysis/sensing.

Scanning electron microscopy, electric field-current density measurements, capacitance-voltage testing, X-ray diffraction analysis, and energy dispersive X-ray spectroscopy were performed to study the effects of rare earth-yttrium and gallium doping on the microstructure and electrical properties of ZnO varistors. Our results indicated that the introduction of gallium and yttrium strengthened the barrier height of grain boundaries and led to a decrease in the grain resistance. Both the voltage gradient and nonlinear coefficient of the samples increased and then decreased as the gallium doping level was increased at a given rare earth-yttrium. The residual voltage ratio and the leakage current varied with the opposite relationship. The findings of this study could help to improve the protective effects of surge protection devices assembled from ZnO ceramic varistors and enhance the stability of power systems.

During the water entry phase in heavy lift marine operations, the involved crane system must satisfy stringent safety requirements. A hydraulic crane driven by a secondary controlled unit that has the advantage of high dynamic behavior and energy efficiency is investigated in this paper. The detailed models of the crane system and the offshore operating conditions are established. To guarantee functionality of the crane system under harsh sea conditions, a cascade control structure is constructed. In the outer loop, an extended state observer is used to estimate the unmeasured payload states. Then, an impedance controller is designed to realize trajectory tracking and impedance regulation of the payload. In the inner loop, the reference trajectory is provided by the impedance controller. An indirect adaptive robust control approach is applied to maximize the achievable tracking performance and to obtain accurate parameter estimates of the secondary controlled unit in the presence of parametric uncertainties and unknown disturbances. The proposed controller can lower a payload to a desired position, and keep the values of the hydrodynamic forces and wire tension within acceptable bounds at the same time. Comparative simulation results verify the effectiveness of the proposed control method.

Summary In recent years, metal halide perovskite opens the new era of the photovoltaic field. The highest power conversion efficiency has exceeded 23%. Although most of reported perovskite solar cells (PSCs) were fabricated by solution methods, the vacuum thermal evaporation method has its unique advantages, such as easy controlling of film thickness, compatibility with tandem cell designs, flexibility to tune interfaces, free of solvent, etc. In this paper, we review the development and progress of the vacuum thermal evaporation method for fabricating PSCs.

We describe a controllable sliding method for fabricating millions of isolated femto- to nanoliter-sized droplets with defined volume, geometry and position and a speed of up to 375 kHz. In this work, without using a superhydrophobic or superoleophobic surface, arrays of droplets are instantly formed on the patterned substrate by sliding a strip of liquid, including water, low-surface-tension organic solvents and solution, along the substrate. To precisely control the volume of the droplets, we systemically investigate the effects of the size of the wettable pattern, the viscosity of the liquid and sliding speed, which were found to vary independently to tune the height and volume of the droplets. Through this method, we successfully fabricated an oriented single metal–organic framework crystal array with control over their XY positioning on the surface, as characterized by microscopy and X-ray diffraction (XRD) techniques.

Wide-bandgap perovskites (WBPs) are attractive candidates for constructing tandem photovoltaic devices, but they are often much more prone to defect formation and other interfacial problems. Fixing these problems can boost the performance of WBP solar cells and is thus crucial for achieving a high overall energy conversion efficiency. Toward this end, we performed a systematic study on the construction of a 2D/3D heterostructure on the WBP surface to passivate the defects and to regulate the interfacial properties by varying the chain length of alkylammonium bromides in the 2D part. Hexanelammonium bromide (HABr) was found to be the champion in multiple respects. The optimized interfacial energy band structure and the reduced defect density with HABr allowed to achieve a remarkable 19.8% photovoltaic efficiency with a prominent open-circuit voltage (VOC) of 1.31 V. HABr also reduced interfacial capacitance by improving hole transport, substantially alleviating the hysteresis of the corresponding devices. Last but not least, the HABr-induced hydrophobicity in the 2D layer can not only block moisture, but also retard migration of the alkali cations from the perovskites across the interface, eventually endowing the WBP based devices with a superior moisture stability.

Segregation is a phenomenon of inhomogeneous distribution of constituent elements during crystallization and could be found in alloy, polymers, colloid, etc. Some researchers have also found component segregation in perovskite crystals. Until now, the existing research reports are all about the halogen segregation of perovskite at the micro level, while the research about the component segregation of perovskite at the macro level is blank, leaving no relevant application developed. Therefore, we can broaden the PUFs-based application of perovskite crystals by employing the multi-wavelength emission property arising from component macrosegregation. We synthesized perovskite crystal arrays with macroscopic composition segregation in one step by surface-tension-confined evaporative self-assembly. The macrosegregation in perovskite crystals prepared with different halogen ratios and temperature was surveyed. The photoluminescence spectra of perovskite crystals were investigated. Perovskite crystals with composition segregation could generate physically unclonable cryptographic primitives, which were made by a simple and random process and difficult to replicate. According to the number of peaks in the spectrum, we converted the optical response into quaternary cryptographic keys, and demonstrated the randomness and stability of the system. This study excavated the application prospect of macroscopic component segregation perovskite in all-photonic cryptographic primitives.

To avoid collisions between guide ship and approach ship during the underway replenishment process, it is important to maintain a certain distance between them. Based on trajectory tracking requirements, a control strategy suitable for engineering applications is proposed for an approach ship without velocity measurements. First, considering the effects of wind, waves, currents, hydrodynamic interactions and the highline cable system, models are established for the two ships. Second, a leader-follower approach is used to maintain the expected longitudinal and transverse distances between the two ships. Third, an extended state observer is designed according to the position, heading, propeller speed and rudder angle of the approach ship. Two time-varying parameters in the observer are estimated in the controller design process. Therefore, the linear speeds, yaw rate, and total system uncertainties can be observed. Fourth, the propeller speed and rudder angle, other than the surge force and steering moment, are considered as the control inputs, which are constructed by the command filter backstepping method. The stability of the proposed control system is verified. Finally, a simulation is performed to demonstrate the effectiveness of the proposed method.

Magnetorheological gel (MRG) excels in the material properties in term of adjustability and sedimentation performance, which could upgrade the performances of the current magnetorheological fluid based adjustable devices for structural control and vibration mitigation. However, the characterization and modelling of the stress-strain hysteresis responses of MRG has not been reported in the past, which are fundamental steps towards engineering applications. In this study, the stress-strain hysteresis of polyurethane based MRG sample with 60% carbonyl iron particle weight fraction was characterized under sinusoidal shear excitations with broad ranges of strain amplitude (5%–100%), excitation frequency (0.1 Hz–2 Hz) and magnetic fields (0–0.91 T). Significant stress overshooting phenomenon were observed under the application of low magnetic fields (0.27 T). A structurally-simple and accurate phenomenological model has been established to capture this unique nonlinearity. By validating the experimental results, the proposed model accurately predicts the hysteretic behaviour and the overshoot of the MRG under the excitation scenarios and the magnetic fields considered. Finally, the support vector machine (SVM) was implemented to provide the solution to the model generalization. The SVM-assisted model showed good agreement with the experimental data and can benefit the efficiency and viability in developing controllable MRG-based devices and system.

In this paper, two kinds of isotropic giant electrorheological elastomers (GERE) were prepared with urea-coated barium titanyl oxalate nanoparticles as dielectric particles filler, poly (dimethyl siloxane) (PDMS) as an elastic matrix and silicone oil as a plasticizer. Such GEREs are far superior to other isotropic and even anisotropic electrorheological elastomers (EREs), showing excellent electrorheological (ER) performance. The theoretic mechanism in elastomers prepared by us should be explained by saturation surface polarization or orientational polarization model. More interestingly, the storage modulus increment (ΔG′) of GEREs displays curvilinear dependence on the electric field due to poor particle mobility and different mobility under different electric fields, rather than a predicted linear variation. After testing their viscoelastic and dielectric properties and microstructures, we found that too high of the powder content leads to the serious agglomeration of particles and the performance degradation of the elastomer. An incorporation of silicone oil improved the dispersion state and wettability between the particles and matrix. At the same time, silicone oil reduced the hardness of the matrix and made the particles align more easily in the PDMS matrix. Lower initial modulus and higher field-induced modulus make GEREs containing silicone oil have ultrahigh storage modulus sensitivity, in which the best-performing sample achieved a storage modulus change exceeding 400 kPa and attained a maximum relative ER effect of 3280% at 3 kV/mm. Finally, the GERE was used to reversibly control the amplitude of circular motion within seconds by varying electric fields, revealing broad potential application in vibration control.

High-quality single-wall carbon nanotube (SWCNT) films were lightly fluorinated by treatment with xenon difluoride at room temperature, which led to the formation of ionic C–F bonds on tube walls and controllable p-type doping of the nanotubes. The fluorinated SWCNT films showed improved electronic conductivity and a higher work function. In addition, the fluorination process increased the areal density of SWCNT films and decreased their surface roughness, leading to better interface contact between them and silicon. As a result, a heterojunction solar cell constructed using the lightly fluorinated SWCNT film has a high power conversion efficiency of 13.6% and excellent stability.

In this study, we successively and parallelly slide a solvent strip on a polydimethylsiloxane microwell array to dilute the solution within the microwells. A total of 60 concentration gradients were generated one by one along the sliding direction within minutes while simultaneously forming 60 microwells with the same concentration perpendicular to the sliding direction. Using theoretical calculations, simulated predictions and experimental verification, we could regulate the concentration gradient on the microwell array by tuning the parameters of the sliding head and sliding speed. Afterwards, we cultured human non-small cell lung cancer cells and produced an anticancer drug concentration gradient on the microwell array by this sliding method. The cell viability was examined to demonstrate the potential of this method for high-throughput cell-based drug testing and screening, and this open microwell array method may enable further analysis during a drug-screening process.

Electrochemical performance of the as-prepared silicon based composite electrode for lithium ion battery can be enhanced by modifying the surface morphology of the Cu foil used as the anode current collector. Increasing the roughness of the Cu foil, contributes to the strong interface adhesion between the anode current collector and the silicon based active composite material slurry layer. The electrode with surface morphology modified Cu current collector delivers higher specific capacity and exhibits better rate capability than that with unmodified Cu current collector. It is also found that the cycle-life of the silicon based composite electrode has been significantly improved by using a surface morphology modified anode current collector. The enhanced cyclability is attributed to the good electrical contact integrality between the active materials and the anode current collector. The improved electrochemical performance indicates that optimizing the anode current collector system can be a valuable alternative for improving electrochemical properties of lithium ion rechargeable batteries.

Conventional hydraulic actuators in which the output force is regulated through servo-valves or variable pumps usually suffer from great noise and low efficiency. To overcome this hurdle, a novel force tracking electro-hydraulic actuator based on Pascal's principle is developed. The novel device uses an electric cylinder to change the volume of enclosed fluid and generate the desired loading pressure. In order to further improve the performance of the novel actuator, an integrated design procedure in which the mechanisms and control structure are designed simultaneously is studied. Firstly, the complete mathematical model of the novel actuator is established. The nonlinear system is translated into a linear time-varying model by replacing the effective bulk modulus of hydraulic oil with a time-varying coefficient. The feasibility of the semi-closed control structure with pressure feedback is analyzed on frequency domain and a compound controller is given. Secondly, performance indexes such as stability criteria, bandwidth, control errors and continuous operation capability of the novel actuator are presented in detail. Interactions of the design variables are analyzed through numerical simulations. Afterwards, a nonlinear constrained multi-objective optimization problem including both mechanical and control parameters is formulated. To prevent the optimization progress from falling into local minimum point, a particle swarm algorithm is employed to carry out the optimization design. Experiment results demonstrate the effectiveness of the proposed integrated design method. And simulations are executed to verify the higher efficiency of the proposed novel electro-hydraulic actuator which is compared with the valve-controlled counterpart.

Interstitial La0.7Pr0.3Fe11.5Si1.5C0.2Hx hydrides with large magnetocaloric effect are prepared. It is found that the addition of carbon atoms can lower the rate of hydrogen absorption/release, which is beneficial to an accurate control of hydrogen content. The Curie temperature T-C can be adjusted to the room temperature by changing the carbon/hydrogen content. The introduction of carbon atoms leads to a remarkable reduction of thermal/magnetic hysteresis because the first-order magnetic transition is weakened. The maximal magnetic entropy change of La0.7Pr0.3Fe11.5Si1.5C0.2H1.2 is found to be 22.1 J/kg K at T-C = 321 K without hysteresis loss for a field change of 0-5 T. (C) 2012 Elsevier B.V. All rights reserved.

In this study, we established a simple method for evaluating the PCR compatibility of various common materials employed when fabricating microfluidic chips, including silicon, several kinds of silicon oxide, glasses, plastics, wax, and adhesives. Two-temperature PCR was performed with these materials to determine their PCR-inhibitory effect. In most cases, adding bovine serum albumin effectively improved the reaction yield. We also studied the individual PCR components from the standpoint of adsorption. Most of the materials did not inhibit the DNA, although they noticeably interacted with the polymerase. We provide a simple method of performing PCR-compatibility testing of materials using inexpensive instrumentation that is common in molecular biology laboratories. Furthermore, our method is direct, being performed under actual PCR conditions with high temperature. Our results provide an overview of materials that are PCR-friendly for fabricating microfluidic devices. The PCR reaction, without any additives, performed best with pyrex glass, and it performed worst with PMMA or acrylic glue materials.

The electrochemical properties of ferrocene (Fc) on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) in the presence and absence of surfactants have been investigated by progressively voltammetric sweeping. Dihexadecyl phosphate (DHP) and hexadecyl trismethyl ammonium chloride (HTAC) are found to impact the redox reactions of Fc adsorbed on MWNT surfaces. An excess amount of DHP dispatches Fc from MWNTs surfaces, leading to weakly adsorbed configuration of Fc. The formal potential of the adsorbed Fc in the presence of DHP shifts to a lower potential. Cationic surfactant HTAC on MWNT surfaces depresses the redox reactions corresponding to the weakly adsorbed configuration of Fc. It becomes evident that the configuration and hence redox reactions of Fc depend strongly on the presence and concentrations of surfactants on the electrode surfaces and in the buffer solutions.

It is found that nucleic acids can enhance the fluorescence intensity of yttrium(III) (Y(3+))-rutin in presence of cetyltrimethylammonium bromide (CTMAB) system. In hexamethylenetetramine (HMTA)-HCl buffer, the maximum enhanced fluorescence is produced, with maximum excitation and emission wavelengths at 452 and 520 nm, respectively. Based on this, a new fluorimetric method of determination of nucleic acids is proposed. Under optimum conditions, the enhanced fluorescence intensity is proportion to the concentration of nucleic acids in the range of 1.0 x 10(-7) to 1.0 x 10(-5)g/ml for fish sperm DNA (fsDNA), 1.0 x 10(-7) to 4.6 x 10(-6)g/ml for yeast RNA (yRNA), their detection limits (S/N=3) are 7.5 x 10(-8), 8.0 x 10(-8)g/ml, respectively. The interaction mechanism is also studied.