A theoretical study of the signal enhancement mechanism of coaxial DP-LIBS

In the field of dual-pulse laser-induced breakdown spectroscopy(DP-LIBS)research,the pursuit of methods for determining pulse intervals and other parameters quickly and conveniently in order to achieve optimal spectral signal enhancement is paramount.To aid researchers in identification of optimal signal enhancement conditions and more accurate interpretation of the underlying signal enhancement mechanisms,theoretical simulations of the spatiotemporal processes of coaxial DP-LIBS-induced plasma have been established in this work.Using a model based on laser ablation and two-dimensional axisymmetric fluid dynamics,plasma evolutions during aluminum–magnesium alloy laser ablation under single-pulse and coaxial dualpulse excitations have been simulated.The influences of factors,such as delay time,laser fluence,plasma temperature,and particle number density,on the DP-LIBS spectral signals are investigated.Under pulse intervals ranging from 50 to 1500 ns,the time evolutions of spectral line intensity,dual-pulse emission enhancement relative to the single-pulse results,laser irradiance,spatial distribution of plasma temperature and species number density,as well as laser irradiance shielded by plasma have been obtained.The study indicates that the main reason behind the radiation signal enhancement in coaxial DP-LIBS-induced plasma is attributed to the increased species number density and plasma temperature caused by the second laser,and it is inferred that the shielding effect of the plasma mainly occurs in the boundary layer of the stagnation point flow over the target surface.This research provides a theoretical basis for experimental research,parameter optimization,and signal enhancement tracing in DP-LIBS.

Identifying the enhancement mechanism of Al/MoO_(3) reactive multilayered films on the ignition ability of semiconductor bridge using a one-dimensional gas-solid two-phase flow model

Energetic Semiconductor bridge(ESCB)based on reactive multilayered films(RMFs)has a promising application in the miniature and intelligence of initiator and pyrotechnics device.Understanding the ignition enhancement mechanism of RMFs on semiconductor bridge(SCB)during the ignition process is crucial for the engineering and practical application of advanced initiator and pyrotechnics devices.In this study,a one-dimensional(1D)gas-solid two-phase flow ignition model was established to study the ignition process of ESCB to charge particles based on the reactivity of Al/MoO_(3) RMFs.In order to fully consider the coupled exothermic between the RMFs and the SCB plasma during the ignition process,the heat release of chemical reaction in RMFs was used as an internal heat source in this model.It is found that the exothermal reaction in RMFs improved the ignition performance of SCB.In the process of plasma rapid condensation with heat release,the product of RMFs enhanced the heat transfer process between the gas phase and the solid charge particle,which accelerated the expansion of hot plasma,and heated the solid charge particle as well as gas phase region with low temperature.In addition,it made up for pressure loss in the gas phase.During the plasma dissipation process,the exothermal chemical reaction in RMFs acted as the main heating source to heat the charge particle,making the surface temperature of the charge particle,gas pressure,and gas temperature rise continuously.This result may yield significant advantages in providing a universal ignition model for miniaturized ignition devices.

Contact Electrification Spectrum for Performance Enhancement Mechanism Investigation of Triboelectric Nanogenerators based on Silicone Elastomers with Different Surface Microstructures

Triboelectric nanogenerators(TENGs)based on conjunctive effects of contact electrification(CE)and electrostatic induction are emerging as a new mechanical energy harvesting and sensing technique for promising applications in smart wearables,Internet of Things(IoTs),etc.The surface microstructure of a flexible triboelectric material for the increase of surface area is a common strategy for performance enhancement of TENGs,but the real roles of surface microstructures on their output performance are still not explicit due to the lack of suitable analysis tool and rational experimental design.Taking advantages of the surface-sensitive characteristic of CE effect,this work exploited and developed the electric signal patterns generated by single impact of TENGs as a kind of CE spectrum to analyze and speculate the real roles of surface microstructures of flexible triboelectric materials on the output performance of TENGs.Firstly,four different kinds of surface microstructures,namely planar surface(PS)and three combinations of two basic surface microstructures,i.e.,micro lens arrays(MLAs),fabric textures(FTs),and hierarchical structures of MLAs on FTs(MLA/FTs),were elaborately designed and introduced for an identical triboelectric material(i.e.,silicone elastomer)by a(micro)molding synthesis route.Then they were used for assembly of TENGs based on vertical contact mode to conduct performance evaluation under the same triggering conditions.Through systematic analysis and comparison of their highly repeatable CE spectra by programmed machine,it was found that the surface microstructure for a flexible triboelectric material to maximally enhance the output performance of a TENG shall achieve a positive synergistic effect of increasing triboelectric charge density,effective contact area and contacting/separating velocity,rather than simple increase of its surface area.

Mechanical properties and enhancement mechanisms of titanium-graphene nanocomposites

Molecular dynamics(MD)simulations of the titanium-graphene nanocomposites(TiGNCs)under uniaxial tension are carried out to investigate the mechanical properties and reinforcement mechanism of graphene in composites.It is found that introduction of mechanically robust graphene limits the strain-induced dislocation and araorphization and thereby highly improves the mechanical properties of metallic titanium that are greatly affected by the crystal stacking orientation of graphene and titanium layers.The thickness of titanium layers,interface interaction and working temperature play an important role in the mechanical strength and elastic moduli of composites.The results show the mechanical properties of TiGNCs are monotonically enhanced with reduction of the titanium layer thickness and working temperature,and the Young5s modulus obtained by MD simulation are higher than that predicted by the rule of mixture(ROM)due to consideration of interfacial interaction in computational calculation.In addition,once the critical thickness of titanium layer is reached,graphene wrinkles are induced in composites because of Poisson's effect induced large lateral compression stress in the interface region.This study provides helpful insights into fundamental understanding reinforcing mechanism of graphene and ultimately contribute to the optimal design and performance of mechanically robust graphene-based metallic composites.

Coercivity enhancement mechanism of Tb-diffusion Nd-Fe-B sintered magnets studied by magneto-optical Kerr optical microscope

The coercivity,microstructure,and magnetic domain structure of Nd-Fe-B sintered magnets by grain boundary diffusion process(GBDP) with TbH3 nanoparticles were systematically investigated.Compared to the original magnet,the coercivity(Hci) of the GBDP magnets improved from 1702 to 2374 kA·m^(-1) with few remanence reduced from 1.338 to 1.281 T.Electron probe microanalysis(EPMA) analysis showed that Tb diffused along grain boundary,mainly concentrated in the boundary layer of the main phase,and formed a core-shell structure.Magneto-optical Kerr optical microscope(MOKE) analysis showed that there were two types of magnetic domain reversal in one grain:gradual reversal(GR) and abrupt reversal(AR).When the applied field decreased from saturated magnetic field,the reversal magnetic domain nucleated and then spread over the whole grain gradually,which was called GR.However,some grains kept the single domain state until Hh which was a value of reverse direction applied field in second quadrant in hysteresis loops.When the applied field increased above Hh,reversed magnetic domain would suddenly appear and occupy most of the area of the grain,which was called AR.That is because AR grains have higher reversed magnetic domain nucleation field(HRN2) than GR grains(HRN1).After GBDP,the area of AR region increased obviously and GR region decreased accordingly,indicating that the core-shell structure could change GR grain into AR grain.The coreshell structure could suppress flipping of the magnetization of the grains due to the large magnetic anisotropy of Tbrich shell.Therefore,large AR area led to high coercivity.

Manganese oxide and derivative-modified materials in advanced oxidation processes:A review of modification enhancement and activation mechanisms

Manganese oxides(MNO_(x)),as low-toxicity and high-abundance catalysts,have been demonstrated to hold great promise for application in advanced oxidation processes(AOPs).However,further application of this material is restricted due to its unsatisfactory oxidant activation efficiency.Fortunately,recently remarkable research on deep activation mechanisms and modification of MNO_(x)have been undertaken to improve its reactivity.Herein,modification enhancement mechanisms of MNO_(x)to efficiently degrade various organic contaminants were discussed and highlighted,including metal doping,coupling with other metal oxides,composite with carbonaceous material,and compounding with other support.The activation mechanisms of different MNO_(x)and derivative-modified material(such as doped MNO_(x),metal oxide-MNO_(x)hybrids,and MNO_(x)-carbonaceous material hybrids)were summarized in great details,which was specifically categorized into both radical and non-radical pathways.The effects of pH,inorganic ions,and natural organic matter on degradation reactions are also discussed.Finally,future research directions and perspectives are presented to provide a clear interpretation on the MNO_(x)initiated AOPs.

A Polyvinyl Alcohol/Acrylamide Hydrogel with Enhanced Mechanical Properties Promotes Full-Thickness Skin Defect Healing by Regulating Immunomodulation and Angiogenesis Through Paracrine Secretion

Hydrogel-based tissue-engineered skin has attracted increased attention due to its potential to restore the structural integrity and functionality of skin.However,the mechanical properties of hydrogel scaffolds and natural skin are substantially different.Here,we developed a polyvinyl alcohol(PVA)/acrylamide based interpenetrating network(IPN)hydrogel that was surface modified with polydopamine(PDA)and termed Dopa-gel.The Dopa-gel exhibited mechanical properties similar to native skin tissue and a superior ability to modulate paracrine functions.Furthermore,a tough scaffold with tensile resistance was fabricated using this hydrogel by three-dimensional printing.The results showed that the interpenetration of PVA,alginate,and polyacrylamide networks notably enhanced the mechanical properties of the hydrogel.Surface modification with PDA endowed the hydrogels with increased secretion of immunomodulatory and proangiogenic factors.In an in vivo model,Dopa-gel treatment accelerated wound closure,increased vascularization,and promoted a shift in macrophages from a proinflammatory M1 phenotype to a prohealing and anti-inflammatory M2 phenotype within the wound area.Mechanistically,the focal adhesion kinase(FAK)/extracellular signal-related kinase(ERK)signaling pathway may mediate the promotion of skin defect healing by increasing paracrine secretion via the Dopa-gel.Additionally,proangiogenic factors can be induced through Rho-associated kinase-2(ROCK-2)/vascular endothelial growth factor(VEGF)-mediated paracrine secretion under tensile stress conditions.Taken together,these findings suggest that the multifunctional Dopa-gel,which has good mechanical properties similar to those of native skin tissue and enhanced immunomodulatory and angiogenic properties,is a promising scaffold for skin tissue regeneration.

Performance-control-orientated hybrid metal additive manufacturing technologies:state of the art,challenges,and future trends

Metal additive manufacturing(AM)technologies have made significant progress in the basic theoretical field since their invention in the 1970s.However,performance instability during continuous processing,such as thermal history,residual stress accumulation,and columnar grain epitaxial growth,consistently hinders their broad application in standardized industrial production.To overcome these challenges,performance-control-oriented hybrid AM(HAM)technologies have been introduced.These technologies,by leveraging external auxiliary processes,aim to regulate microstructural evolution and mechanical properties during metal AM.This paper provides a systematic and detailed review of performance-control-oriented HAM technology,which is categorized into two main groups:energy field-assisted AM(EFed AM,e.g.ultrasonic,electromagnetic,and heat)technologies and interlayer plastic deformation-assisted AM(IPDed AM,e.g.laser shock peening,rolling,ultrasonic peening,and friction stir process)technologies.This review covers the influence of external energy fields on the melting,flow,and solidification behavior of materials,and the regulatory effects of interlayer plastic deformation on grain refinement,nucleation,and recrystallization.Furthermore,the role of performance-control-oriented HAM technologies in managing residual stress conversion,metallurgical defect closure,mechanical property improvement,and anisotropy regulation is thoroughly reviewed and discussed.The review concludes with an analysis of future development trends in EFed AM and IPDed AM technologies.

The enhancing effect and promoting mechanisms of the stereoisomeric monoterpene alcohol esters as enhancers for drugs with different physicochemical properties

To explore the structure-activity connections of amphiphilic permeation enhancers containing the length of the hydrophobic chains as well as the properties of the polar head,O-acylgeraniol and O-acylnerol derivatives were synthesized from geraniol/nerol(cis-isomer of geraniol) and pharmaceutical excipient acids in this research. Their promotion of the percutaneous absorption of three drugs as the model, flurbiprofen(FP), isosorbide dinitrate(ISDN) and donepezil(DNP), which were selected based on their physicochemical properties,was tested by in vitro skin penetration and in vivo. Molecular simulation, ATR-FTIR, CLSM and histological observation were implement to evaluate the mode of action of the enhancers.The results indicated that(E)-3,7-dimethyl-2,6-octadien-1-yl tetradecanoate(GER-C14, trans-)achieved the highest enhancement ability for the three drugs;additionally, the in vivo results obtained were in good correlation with the in vitro data. Molecular docking results suggested that enhancers loosen the hydrogen bonds between ceramides, and the results of molecular simulation indicated that GER-C14, NER-C14 could insert into the middle of the lipid bilayer to form an independent phase. According to ATR-FTIR and histological evaluation, the enhancers extracted lipids and influenced the protein region, thereby disturbing the skin array. In addition, CLSM described the dynamic effects of enhancers on lipids between stratum corneum(SC) cells. In conclusion, GER-C14 had a better penetration promotion effect, which broadened our understanding of stereoisomeric penetration enhancers.

A Facile Route for the Large Scale Fabrication of Graphene Oxide Papers and Their Mechanical Enhancement by Cross-linking with Glutaraldehyde

A facile route for the large scale production of graphene oxide(GO) papers and their mechanical enhancement has been presented in this work. The novel paper-like GO made from individual GO sheets in aqueous suspension can be achieved in large scale by a simple drop casting method on hydrophobic substrates.Significant enhancement in mechanical stiffness(341%) and fracture strength(234%) of GO paper have been achieved upon modification with a small amount(less than 10 wt%) of glutaraldehyde(GA). The cross-linking reaction takes place between hydroxyl groups on the surface of GO and aldehyde groups of GA, through forming hemiacetal structure, which can result in distinct mechanical enhancement of the GO papers.

Facial Expression Recognition Using Enhanced Convolution Neural Network with Attention Mechanism

Facial Expression Recognition(FER)has been an interesting area of research in places where there is human-computer interaction.Human psychol-ogy,emotions and behaviors can be analyzed in FER.Classifiers used in FER have been perfect on normal faces but have been found to be constrained in occluded faces.Recently,Deep Learning Techniques(DLT)have gained popular-ity in applications of real-world problems including recognition of human emo-tions.The human face reflects emotional states and human intentions.An expression is the most natural and powerful way of communicating non-verbally.Systems which form communications between the two are termed Human Machine Interaction(HMI)systems.FER can improve HMI systems as human expressions convey useful information to an observer.This paper proposes a FER scheme called EECNN(Enhanced Convolution Neural Network with Atten-tion mechanism)to recognize seven types of human emotions with satisfying results in its experiments.Proposed EECNN achieved 89.8%accuracy in classi-fying the images.

Conductive Polymer Composites Fabricated by Disposable Face Masks and Multi-Walled Carbon Nanotubes: Crystalline Structure and Enhancement Effect

Influenced by recent COVID-19,wearing face masks to block the spread of the epidemic has become the simplest and most effective way.However,after the people wear masks,thousands of tons of medical waste by used dis-posable masks will be generated every day in the world,causing great pressure on the environment.Herein,con-ductive polymer composites are fabricated by simple melt blending of mask fragments(mask polypropylene,short for mPP)and multi-walled carbon nanotubes(MWNTs).MWNTs were used as modifiers for composites because of their high strength and high conductivity.The crystalline structure,mechanical,electrical and thermal enhancement effect of the composites were investigated.MWNTs with high thermal stability acted the role of promoting the crystallisation of mPP by expediting the crystalline nucleation,leading to the improvement of amount for crystalline nucleus.MWNTs fibers interpenetrate with each other in mPP matrix to form conducting network.With 2.0 wt% MWNTs loading,the tensile strength and electrical conductivity of the composites were increased by 809% and 7 orders of magnitude.MWNTs fibers interpenetrate with each other in mPP matrix to form conducting network.Thus,more conducting paths were constructed to transport carriers.The findings may open a way for high value utilization of the disposable masks.

STUDIES ON FLUORESCENCE ENHANCING EFFECT AND ALKALINE DEGRADATION MECHANISM OF DOXYCYCLINE AND METHACYCLINE

Degradation reaction of doxycycline or methacycline was carried out in KOH solution and intense fluorescence was obtained.A degradation mechanism of doxycycline or methacycline was suggested.

Mechanism of Electromagnetic Flow Control Enhanced by Electro-Discharge in Water

Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is designed to generate the Lorentz force in the micro plasma channel. During the discharge process, the resistance in the channel decreases rapidly and a large current density appears between the discharge electrodes. After the actuator is applied in the leading edge of a flat plate, the separation region and downstream turbulent boundary layer on the plate disappear. Meanwhile, a skin-friction drag force reduction is achieved.

Enhancing CO_(2)capture of an aminoethylethanolamine-based non-aqueous absorbent by using tertiary amine as a proton-transfer mediator:From performance to mechanism

Non-aqueous absorbents(NAAs)have attracted increasing attention for CO_(2)capture because of their great energy-saving potential.Primary diamines which can provide high CO_(2)absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability.In this study,a promising strategy that using tertiary amines(TAs)as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine(AEEA,diamine)/dimethyl sulfoxide(DMSO)(A/D)NAA.Surprisingly,some employed TAs such as N,N-diethylaminoethanol(DEEA),N,N,N’,N’’,N’’-pentamethyldiethylenetriamine(PMDETA),3-dimethylamino-1-propanol(3DMA1P),and N,N-dimethylethanolamine(DMEA)enhanced not only the regenerability of the A/D NAA but also the CO_(2)absorption performance.Specifically,the CO_(2)absorption loading and cyclic loading were increased by about 12.7%and 15.5%-22.7%,respectively.The TA-enhanced CO_(2)capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations.During CO_(2)absorption,the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species(AEEACOO-)to store CO_(2),thus enhancing CO_(2)absorption.For CO_(2)desorption,the TA first provided protons directly to AEEACOO-as a proton donor;moreover,it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO-.Consequently,the presence of TA made it easier for AEEACOO-to obtain protons to decompose,resulting in enhanced CO_(2)desorption.In a word,introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO_(2)absorption performance and the regenerability,which was an efficient way to“kill two birds with one stone”.

Research Progress on Plant Source Herbicide Adjuvants

As the important components of pesticide adjuvants, vegetable oil and its derivative adjuvants will be the focus of future development of herbicide adjuvants due to their superiority in good affinity with plants, strong biological degradability, few risk of damage, environrnental safety and ability to improve the weed control efficient. The research progress and application status of the plant source herbicide adjuvants were summarized, as well as the weeding enhancement mechanism and the effects on the environment and non-target organisms, and the existing problems and development trends were reviewed.

Magnetic emission intensity enhancement for amorphous alloys by constructing a multi-phase structure withα-Fe nanocrystals

The perturbation in the magnetic field generated by the rotation or oscillation of magnetic domains in magnetic materials can emit low-frequency electromagnetic waves,which are expected to be used in low-frequency communications.However,the magnetic emission intensity,defined by the perturbation ability,of current commercially applied amorphous alloys,such as Metglas,cannot meet the application requirements for low-frequency antennas due to the domain motion energy loss.Herein,a multi-phase Metglas amorphous alloy was constructed by incorporatingα-Fe nanocrystals using rapid annealing to manipulate the domain movement.It was found that 3.89 times higher magnetic emission intensity is obtained compared to the pristine due to the synergism of the deformation and displacement mechanisms.Moreover,the low-frequency magnetic emission performance verification was carried out by preparing magnetoelectric composites as the antenna vibrator by assembling the alloy and macro piezoelectric fiber composites(MFC).Enhancements of magnetic emission intensity are found at 93.3%and 49.2%at the first and second harmonic frequencies compared with the unmodified alloy vibrator.Therefore,the approach leads to the development of high-performance communication with a novel standard for evaluation.

Progress of Microbial Enhanced Oil Recovery in Laboratory Investigation

This paper describes a simple, easy process for screening microorganisms, and introduces a laboratory simulation device and process of microbial enhanced oil recovery (MEOR) , which is a necessary research step for trial in oilfields. The MEOR mechanism and the influence of adsorption, diffusion, metabolism, nutrition, porosity, and permeability are analyzed. The research indicates that different microbes have different efficiencies in EOR and that different culture types play different roles in EOR. The effect of syrup is better than that of glucose, and larger porosity is favorable to the reproduction and growth of microbes, thereby improving the oil recovery. Using crude oil as a single carbon source is more appreciable because of the decrease in cost of oil recovery. At the end of this paper, the development of polymerase chain reaction (PCR) for the future is discussed.

Understanding the improved performance of sulfur-doped interconnected carbon microspheres for Na-ion storage

As one of the low-cost energy storage systems,Na-ion batteries(NIBs)have received tremendous attention.However,the performance of current anode materials still cannot meet the requirements of NIBs.In our work,we obtain sulfur-doped interconnected carbon microspheres(S-CSs)via a simple hydrothermal method and subsequent sulfurizing treatment.Our S-CSs exhibit an ultrahigh reversible capacity of 520 mAh g^(-1) at 100 mA g^(-1) after 50 cycles and an excellent rate capability of 257 mAh g^(-1),even at a high current density of 2 A g^(-1).The density functional theory calculations demonstrate that sulfur doping in carbon favors the adsorption of Na atom during the sodiation process,which is accountable for the performance enhancement.Furthermore,we also utilize operando Raman spectroscopy to analyze the electrochemical reaction of our S-CSs,which further highlights the sulfur doping in improving Na-ion storage performance.

A comprehensive review of miniatured wind energy harvesters

Following the current rapid development of the Internet of Things(IoT)and wireless condition monitoring systems,energy harvesters which use ambient energy have become a key part of achieving an energy-autonomous system.Miniature wind energy harvesters have attracted widespread attention because of their great potential of power density as well as the rich availability of wind energy in many possible areas of application.This article provides readers with a glimpse into the state-of-the-art of miniature wind energy harvesters.The crucial factors for them to achieve high working efficiency under lower operational wind speed excitation are analyzed.Various potential energy coupling mechanisms are discussed in detail.Design approaches for broadening operational wind-speed-range given a variety of energy coupling mechanisms are also presented,as observed in the literature.Performance enhancement mechanisms including hydrodynamic configuration optimization,and non-linear vibration pick-up structure are reviewed.Conclusions are drawn and the outlook for each coupling mechanisms is presented.