Effect of rGO Coating on Interconnected Co_3O_4 Nanosheets and Improved Supercapacitive Behavior of Co_3O_4/rGO/NF Architecture

In this study, the effect of reduced graphene oxide(rGO) on interconnected Co_3O_4 nanosheets and the improved supercapacitive behaviors is reported. By optimizing the experimental parameters, we achieved a specific capacitance of ~1016.4 F g^(-1) for the Co_3O_4/rGO/NF(nickel foam) system at a current density of 1 A g^(-1). However, the Co_3O_4/NF structure without rGO only delivers a specific capacitance of ~520.0 F g^(-1)at the same current density. The stability test demonstrates that Co_3O_4/rGO/NF retains ~95.5% of the initial capacitance value even after 3000 charge–discharge cycles at a high current density of 7 A g^(-1). Further investigation reveals that capacitance improvement for the Co_3O_4/rGO/NF structure is mainly because of a higher specific surface area(~87.8 m^2g^(-1))and a more optimal mesoporous size(4–15 nm) compared to the corresponding values of 67.1 m^2g^(-1) and 6–25 nm,respectively, for the Co_3O_4/NF structure. rGO and the thinner Co_3O_4 nanosheets benefit from the strain relaxation during the charge and discharge processes, improving the cycling stability of Co_3O_4/rGO/NF.

Impact of microsecond-pulsed plasma-activated water on papaya seed germination and seedling growth

The seed of Carica papaya consists of a hard shell-like testa with inhibitors in vivo causing slow,erratic and asynchronous germination.In this work,plasma-activated water prepared by microsecond-pulsed plasma jets(μPAW)was applied to treat papaya seeds.TheμPAW after plasma activation of 30 min was about 40℃.The reactive species such as NO_(2),NO_(3),and H_(2)O_(2)in theμPAW activated from deionized water were measured and correlated to the seed germination rate and the seedling growth performance.TheμPAW-treated papaya seed achieved a higher germination rate of 90%,which is 26%higher than the control group using deionized water.Comparing the results with a hot water(40℃)reference group showed that the reactive species inμPAW played primary roles in germination improvement,with little effect caused by the heat shock.TheμPAW also sterilized the treated seeds,reducing the germination stress.The morphological change in the seeds was observed by SEM,showing an effect of physical etching after treatment promoting seed imbibition.The biochemical mechanism of the seed germination was deduced with reference to the evolution of surface chemistry,functional groups,and ABA content.The accelerated seed metabolism observed was corresponded to the chemical modification pathway.Besides,early seedlings developed from treated seeds were observed to be healthy,grow more leaves,and have better root structures.The content of MDA in the treated papaya seedlings decreased along with increased SOD and higher ion concentration.TheμPAW that can be prepared at atmospheric pressure for bulk production offers a low-risk and cost-effective seed priming technology that may significantly increase the production of agricultural crops.

Rock physics model for velocity–pressure relations and its application to shale pore pressure estimation

Acoustic wave velocity has been commonly utilized to predict subsurface geopressure using empirical relations.Acoustic wave velocity is, however, affected by many factors. To estimate pore pressure accurately, we here propose to use elastic rock physics models to understand and analyze quantitatively the various contributions from these different factors affecting wave velocity. We report a closed-form relationship between the frame flexibility factor(γ) in a rock physics model and differential pressure, which presents the major control of pressure on elastic properties such as bulk modulus and compressional wave velocity. For a gas-bearing shale with abundant micro-cracks and fractures, its bulk modulus is much lower at abnormally high pore pressure(high γ values) where thin cracks and flat pores are open than that at normal hydrostatic pressure(low γ values) where pores are more rounded on average. The developed relations between bulk modulus and differential pressure have been successfully applied to the Upper Ordovician Wufeng and Lower Silurian Longmaxi formations in the Dingshan area of the Sichuan Basin to map the three-dimensional spatial distribution of pore pressure in the shale, integrating core, log and seismic data. The estimated results agree well with field measurements. Pressure coefficient is positively correlated to gas content. The relations and methods reported here could be useful for hydrocarbon exploration, production, and drilling safety in both unconventional and conventional fields.

Improving resolution of superlens based on solid immersion mechanism

Super-resolution imaging with superlens has been one of the fundamental research topics. Unfortunately, the resolution of superlens is inevitably restrained by material loss. To address the problem, we introduce the solid immersion mechanism into the slab superlens and the cylindrical superlens. The proposed solid immersion slab superlens(SISSL) and the solid immersion cylindrical superlens(SICSL) can improve the resolution by converting evanescent wave to propagating wave using high refractive index materials. From the perspective of applications, the cylindrical superlens with finite cross section and the ability of magnification or demagnification has more advantages than the slab superlens. Therefore,we focus on demonstrating analytically the super-resolution imaging of SICSL. Due to the impedance mismatching caused by solid immersion mechanism, the whispering gallery modes(WGMs) are excited between SICSL and the air interface.We clarify the excitation conditions of WGMs and analyze their influence on the imaging quality of SICSL. The SISSL and SICSL may pave a way to apply in lithography technique and real-time biomolecular imaging in future.

Broadband and wide-angle plane focal surface Luneburg lens

The energy crisis has aroused widespread concern, and the reform of energy structure is imminent. In the future,the energy structure will be dominated by the solar energy and other renewable energy sources. The solar concentrating technology as a promising method has been widely studied for collecting solar energy. However, the previous solar concentrating technologies suffer from some drawbacks, such as low focusing efficiency and large concentrating size. The Luneburg lens with highly efficient aberration-free focusing provides a new route for solar/energy concentrator. In this work, we designed a plane focal surface Luneburg lens(PFSLL) by transformation optics(TO). The PFSLL provides a relatively high focusing efficiency and concentration ratio of collection of energy. At the same time, it circumvents the disadvantage of curve surface of the classical Luneburg lens in device integration. Based on the reciprocity of electromagnetic waves, the PFSLL can also be applied to the antenna field to achieve broadband wide-angle scanning and highly directional radiation.

Young's double slit interference with vortex source

The fast and convenient demultiplex of optical vortex(OV) mode is crucial for its further application. We propose a novel approach that combines classic Young's doublet with an OV source to effectively identify the OV mode through the analysis of interference patterns. The interference patterns of the OV source incident on the double slits can be perfectly illustrated by using both the classical double-slit interference method and the Huygens–Fresnel principle. The interference fringes will twist along the negative or positive direction of x axis when topological charge(TC)l>0 or l<0, and the degree of the movement varies with the TC, allowing for a quantitative display of the OV characteristics through the interference patterns. Additionally, we deduce analytically that the zeroth-order interference fringe has a linear relationship with the TC and the vertical position. These findings highlight the ability to identify the OV mode by analyzing the interference patterns produced by Young's doublet.

Preliminary study of an open-air water-contacting discharge for direct nitrogen fixation

Efficient nitrogen fixation through a reactive plasma process attracts intense interest due to the environmental issues induced by the conventional Haber–Bosch method. In this work, we present a direct and simple fixation routine without any catalysts for nitrogen in open air using an atmospheric-pressure pin-to-solution plasma electrolytic system. Nitrate, nitrite, and ammonia as the nitrogen-derived chemicals in solution were analyzed as indicators under various discharge conditions to estimate the energy efficiency of this process. The results show that the nitrogen fixation process was much more efficient by the pin-positive discharge compared to the negative one. N chemicals preferred to be formed when the solution was of negative polarity. It was also found that, with the help of solution circulation, the energy efficiency was enhanced compared to that of static liquid. However, an inverse trend was observed with the increase of the discharge current. Further study by optical emission spectroscopy indicates the important roles of active N2* and water vapour and their derived species near the plasma–water interface in the fixation process.

Visualization of gold nanoparticles formation in DC plasma-liquid systems

Dual argon plasmas ignited by one direct current power source are used to treat an aqueous solution of hydrogen tetrachloroaurate-(Ⅲ)trihydrate(HAuCl_(4)·3H_(2)O)which is contained in an H-type electrochemical cell.The solution contained in one cell acts as a cathode,and in the other as an anode.Experiments are carried out to directly visualize the formation process of gold nanoparticles(Au NPs)in separated cells of the H-type electrochemical reactor.The results and analyzes suggest that hydrogen peroxide and hydrated electrons generated from the plasma-liquid interactions play the roles of reductants in the solutions,respectively.Hydrogen peroxide can be generated in the case of the liquid being a cathode or an anode,while most of hydrated electrons are formed in the case of the liquid being an anode.Therefore,the reduction of the AuCl_(4)−ions is mostly attributed to the hydrogen peroxide as the liquid acts as a cathode,while to the hydrogen peroxide and hydrated electrons as the liquid acts as an anode.Moreover,the p H value of the solution can be used to tune the formation processes and final form of the Au NPs due to its mediation of reductants.

Super-hydrophobic film deposition by an atmospheric-pressure plasma process and its anti-icing characteristics

In this work,the super-hydrophobic(SH)surface was prepared through chemical vapor deposition process by an argon atmospheric pressure plasma jet source with HMDSN(hexamethyldisilazane)as the polymerization precursor.Plasma synthesized organosilicon(SiOxCyHz)thin films with water contact angle over 160°and sliding angle below 5°,were able to be achieved.FTIR and XPS analysis indicates a large number of hydrocarbon compositions were polymerized in the thin films enduing the latter very-low surface free energy.SEM shows the SH films display micro-nanostructure and with high degree of averaged surface roughness 190 nm evaluated by AFM analysis.From experiments under controlled low-temperature and moisture conditions,the prepared SH surface exhibits good anti-icing effects.Significantly prolonging freezing time was achievable on the SH thin films for both static and sliding water droplets.This investigation demonstrates the anti-icing potentials of SH surface prepared through low-cost simple atmospheric-pressure plasma polymerization process.

Plasma electrolytic liquefaction of cellulosic biomass

In this paper, the rapid liquefaction of a corncob was achieved by plasma electrolysis, providing a new method for cellulosic biomass liquefaction. The liquefaction rate of the corncob was 95% after 5 min with polyethylene glycol and glycerol as the liquefying agent. The experiments not only showed that H^+ ions catalyzed the liquefaction of the corncob, but also that using accelerated H^+ ions, which were accelerated by an electric field, could effectively improve the liquefaction efficiency. There was an obvious discharge phenomenon, in which the generated radicals efficiently heated the solution and liquefied the biomass, in the process of plasma electrolytic liquefaction. Finally, the optimum parameters of the corncob liquefaction were obtained by experimentation, and the liquefaction products were analyzed.

A simple derivative spectrophotometric method for simultaneously detecting nitrate and nitrite in plasma treated water

A spectrophotometric technique is developed to simultaneously quantify nitrate and nitrite in plasma treated water.The measurement is based on examining the inflection points(wavelengths)in the derivative absorbance of the nitrate or nitrite solution.At the inflection points of the pure nitrate solution,the derivative absorbance is zero and independent of the nitrate’s concentration,and thus the nitrite’s concentration in a mixed nitrate and nitrite solution can be obtained by using the Beer’s law at these points.The nitrate’s concentration can also be achieved from the inflection points of nitrite in the same manner.The relation between the tested substance’s(nitrate or nitrite)concentration and the second-or the third-order absorbances is obtained at these inflection points.Test measurements for mixed aqueous solutions of nitrate and nitrite with or without hydrogen peroxide confirm the reliability of this technique.We applied this technique to quantify the nitrate and nitrite generated in air plasma treated aqueous solutions.The results indicate that both nitrate and nitrite concentrations increase with the plasma treatment time,and the nitrite species is found to be generated prior to the nitrate species in the air plasma treated aqueous solution.Moreover,the production rate of total nitrogen species is independent of the solutions’p H value.These results are relevant to diverse applications of plasma activated solutions in materials processing,biotechnology,medicine and other fields.

Plasma electrolytic liquefaction of sawdust

As a renewable carbon resource, biomass can be converted into polyols, aromatic hydrocarbons, alkanes, and other products by traditional catalytic liquefaction method, which has been widely used in production and life. The efficient development and utilization of biomass energy will play a very positive role in solving the problems of energy and ecological environment. A way of combining the plasma electrolysis with traditional catalytic liquefaction realizes the efficient liquefaction of sawdust, which provides a new liquefaction way for traditional biomass conversion. In this experiment, the effects of solution composition, catalyst content and power supply on solution resistance and liquefaction rate are analyzed.It is found that solution composition and catalyst content have a great influence on solution resistance. The results show that the liquefaction rate is highest and the resistance is smallest when the solution resistance is 500 ?. The liquefaction rate is greatly affected by the solution temperature, and the solution temperature is determined by the output power between the two electrodes. The output power includes the heating power of the electric field and the discharge power of the plasma.We measure the electric potential field distribution in the solution and the plasma power. It is found that the output power between the two poles increases nonlinearly(from 0 to 270 W) with time. In two minutes, the electric field heating power increases from 0 to 105 W and then decreases to 70 W, while the plasma power increases from 0 to 200 W. It is well known that in the first 70 seconds of the experiment the electric field heating is dominant, and then the plasma heating turns into a main thermal source. In this paper, plasma electrolysis and traditional catalytic liquefaction are combined to achieve the efficient liquefaction of sawdust, which provides a new way for biomass liquefaction.

Three-Dimensional Broadband Acoustic Waveguide Cloak

The propagation of acoustic waves is a fundamental topic in shallow ocean acoustics.We numerically demonstrate a three-dimensional zone of silence consisting of a circular tube with gradient index metamaterials attached to its rigid wall.The cloaking effect is verified by fine agreement with analytical calculations.

Increasing the·OH radical concentration synergistically with plasma electrolysis and ultrasound in aqueous DMSO solution

In recent years,significant increases in waste processing and material engineering have been seen by using advanced oxidation processes.The treatment results and energy yields of these processes are largely determined by the generation and retention of reactive oxygen species(ROS).However,increasing the amount of ROS remains a key challenge because of the unavailability of performance-and energy-efficient techniques.In this study,plasma electrolysis,ultrasound,and plasma electrolysis combined with ultrasound were used to treat dimethyl sulfoxide(DMSO)solutions,and the results showed that the two methods can synergistically convert filament discharge into spark discharge,and the conversion of the discharge mode can significantly increase the concentration of OH radicals and effectively improve the efficiency of DMSO degradation.We verified the rationality of the results by analyzing the mass transfer path of ROS based on the reaction coefficients and found that the OH radicals in aqueous solution were mainly derived from the decomposition of hydrogen peroxide.These findings indicated that the synergistic action of plasma electrolysis and ultrasound can enhance the production of chemically reactive species,and provide new insights and guiding principles for the future translation of this combined strategy into real-life applications.Our results demonstrated that the synergistic strategy of ultrasound and plasma electrolysis is feasible in the switching mode and increasing the ROS,and may open new routes for materials engineering and pollutant degradation.

Colorimetric quantification of aqueous hydrogen peroxide in the DC plasma-liquid system

The quantification of hydrogen peroxide(H_(2)O_(2))generated in the plasma-liquid interactions is of great importance,since the H_(2)O_(2)species is vital for the applications of the plasma-liquid system.Herein,we report on in situ quantification of the aqueous H_(2)O_(2)(H_(2)O_(2)aq)using a colorimetric method for the DC plasma-liquid systems with liquid as either a cathode or an anode.The results show that the H_(2)O_(2)aqyield is 8-12 times larger when the liquid acts as a cathode than when the liquid acts as an anode.The conversion rate of the gaseous OH radicals to H_(2)O_(2)aqis 4-6 times greater in the former case.However,the concentrations of dissolved OH radicals for both liquid as cathode and anode are of the same order of tens of n M.

Dielectric metasurface evolution from bulk to monolayer by strong coupling of quasi-BICs for second harmonic boosting

2D materials are promising candidates as nonlinear optical components for on-chip devices due to their ultrathin structure. In general, their nonlinear optical responses are inherently weak due to the short interaction thickness with light. Recently, there has been great interest in using quasi-bound states in the continuum (q-BICs) of dielectric metasurfaces, which are able to achieve remarkable optical near-field enhancement for elevating the second harmonic generation (SHG) emission from 2D materials. However, most studies focus on the design of combining bulk dielectric metasurfaces with unpatterned 2D materials, which suffer considerable radiation loss and limit near-field enhancement by high-quality q-BIC resonances. Here, we investigate the dielectric metasurface evolution from bulk silicon to monolayer molybdenum disulfide (MoS2), and discover the critical role of meta-atom thickness design on enhancing near-field effects of two q-BIC modes. We further introduce the strongcoupling of the two q-BIC modes by oblique incidence manipulation, and enhance the localized optical field on monolayer MoS2dramatically. In the ultraviolet and visible regions, the MoS2SHG enhancement factor of our design is 105times higher than that of conventional bulk metasurfaces, leading to an extremely high nonlinear conversion efficiency of 5.8%. Our research will provide an important theoretical guide for the design of high-performance nonlinear devices based on 2D materials.

Operando monitoring transition dynamics of responsive polymer using optofluidic microcavities

Optical microcavities have become an attractive platform for precision measurement with merits of ultrahigh sensitivity,miniature footprint and fast response.Despite the achievements of ultrasensitive detection,optical microcavities still face significant challenges in the measurement of biochemical and physical processes with complex dynamics,especially when multiple effects are present.Here we demonstrate operando monitoring of the transition dynamics of a phase-change material via a self-referencing optofluidic microcavity.We use a pair of cavity modes to precisely decouple the refractive index and temperature information of the analyte during the phase-transition process.Through real-time measurements,we reveal the detailed hysteresis behaviors of refractive index during the irreversible phase transitions between hydrophilic and hydrophobic states.We further extract the phase-transition threshold by analyzing the steady-state refractive index change at various power levels.Our technology could be further extended to other materials and provide great opportunities for exploring on-demand dynamic biochemical processes.

Multiple resonant excitations of surface plasmons in a graphene stratified slab by Otto configuration and their independent tuning

Multiple resonant excitations of surface plasmons in a graphene stratified slab are realized by Otto configuration at terahertz frequencies. The proposed graphene stratified slab consists of alternating dielectric layers and graphene sheets, and is sandwiched between a prism and another semi-infinite medium. Optical response and field distribution are determined by the transfer matrix method with the surface current density boundary condition.Multiple resonant excitations appear on the angular reflection spectrum, and are analyzed theoretically via the phase-matching condition. Furthermore, the effects of the system parameters are investigated. Among them, the Fermi levels can tune the corresponding resonances independently. The proposed concept can be engineered for promising applications, including angular selective or multiplex filters, multiple channel sensors, and directional delivery of energy.

Hybrid functional calculations on the band gap bowing parameters of In_xGa_(1-x)N

The electronic band structures and band gap bowing parameters of In_xGa_(1-x)N are studied by the firstprinciples method based on the density functional theory. Calculations by employing both the Heyd-ScuseriaErnzerh of hybrid functional(HSE06) and the Perdew-Burke-Ernzerhof(PBE) one are performed. We found that the theoretical band gap bowing parameter is dependent significantly on the calculation method, especially on the exchange-correlation functional employed in the DFT calculations. The band gap of In_xGa_(1-x)N alloy decreases considerably when the In constituent x increases. It is the interactions of s–s and p–p orbitals between anions and cations that play significant roles in formatting the band gaps bowing. In general, the HSE06 hybrid functional could provide a good alternative to the PBE functional in calculating the band gap bowing parameters.

Reactive oxygen species in plasma against E.coli cells survival rate

In this paper, we report on the contrastive analysis of inactivation efficiency of E. coli cells in solution with different disinfection methods. Compared with the hydrogen peroxide solution and the ozone gas, the atmospheric-pressure He plasma can completely kill the E. coli cells in the shortest time. The inactivation efficiency of E. coli cells in solution can be well described by using the chemical reaction rate model. X-ray photoelectron spectroscopy(XPS) analysis shows that the C–O or C=O content of the inactivated E. coli cell surface by plasma is predominantly increased, indicating the quantity of oxygen-containing species in plasma is more than those of two other methods, and then the C–C or C–H bonds can be broken, leading to the etching of organic compounds. Analysis also indicates that plasma-generated species can play a crucial role in the inactivation process by their direct reactions or the decompositions of reactive species, such as ozone into OH radicals in water, then reacting with E. coli cells.