The underexpanded microjet emerging from a rectangular convergent nozzle with a high aspect ratio at the nozzle exit is investigated numerically using the Reynolds-averaged Navier-Stokes (RANS) simulation with the Men...The underexpanded microjet emerging from a rectangular convergent nozzle with a high aspect ratio at the nozzle exit is investigated numerically using the Reynolds-averaged Navier-Stokes (RANS) simulation with the Menter’s shear stress transport (SST) k-ω turbulence model. The simulation is performed at the nozzle pressure ratio of 5.0 to produce a strong shock and it is validated by a comparison with a rainbow schlieren picture of the microjet. The three-dimensional structure of the shock-containing rectangular microjet is demonstrated using the isopycnic surface and bright-field schlieren representations.展开更多
Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of su...Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers <em>M</em><em><sub>j</sub></em> ranging from 1.47 - 1.71, where the design Mach number is <em>M<sub>d</sub></em> = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45<span style="white-space:nowrap;">°</span> within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.展开更多
We systematically investigate the power distribution characteristics of microjets generated by prismatic scatterers with different shapes at sub-THz region(λ = 8.57 mm). Among these prismatic scatterers, the hexagona...We systematically investigate the power distribution characteristics of microjets generated by prismatic scatterers with different shapes at sub-THz region(λ = 8.57 mm). Among these prismatic scatterers, the hexagonal-type one shows better focusing feature than the others. Aiming at the hexagonal-type one, we propose a double-layer scatterer composed of a Teflon hexagonal prism as an outer layer and a semiconductor cuboid as an inner layer. Aiming at the double-layer scatterer, we further study the effects of refractive index, size, and shape of the inner cuboid on microjet’s features. The study allows us to present an optimized double-layer scatterer, which has a side length λ/2(λ) and a refractive index 2.0(1.4) for the inner(outer) layer. We show that the optimized scatterer can produce an ultra-strong, ultra-narrow microjet with a power enhancement of;0 and a full width at half maximum(FWHM) of;0.26λ, and the microjet is just located at the output face. The microjet keeps compact within the distance range of λ from the output face. These features and effects are explained from the viewpoint of ray optics theory. According to the optimized double-layer scatterer, we further study the multi-frequency focusing features of the microjets, and find that the microjet remains good features at harmonic frequencies 2f_(0) and 3f_(0). In addition, we investigate the effect of an Au sphere presence in the center of the microjet on the power distribution. The results show that a spherical dark spot with a size similar to that of the Au sphere emerges in the area where the Au sphere is placed. The feature can be used to measure the size of a metallic particle.展开更多
Swirl combustion serves as a helpful flame stabilization method,which also affects the combustion and emission characteristics.This article experimentally investigated the effects of CO_(2)microjets on combustion inst...Swirl combustion serves as a helpful flame stabilization method,which also affects the combustion and emission characteristics.This article experimentally investigated the effects of CO_(2)microjets on combustion instability and NO_(x)emissions in lean premixed flames with different swirl numbers.The microjets’control feasibility was examined from three variables of CO_(2)jet flow rate,thermal power,and swirl angles.Results indicate that microjets can mitigate the combustion instability and NO_(x)emissions in lean premixed burners with different swirl numbers and thermal power.Still,the damping effect of microjets in low swirl intensity is better than that in high swirl intensity.The damping ratio of pressure amplitude can reach the maximum of 98%,and NO_(x)emissions can realize the maximum reduction of 10.1×10^(−6)at the swirl angle of 30°.Besides,the flame macrostructure switches from an inverted cone shape to a petal shape,and the flame length reduction at low swirl intensity is higher than that of high swirl intensity.This research clarified the control differences of mitigation of combustion instability and NO_(x)emissions by microjets in lean premixed flames with different swirl numbers,contributing to the optimization of microjets control and the construction of high-performance burners.展开更多
High-intensity laser–plasma interactions produce a wide array of energetic particles and beams with promising applications.Unfortunately,the high repetition rate and high average power requirements for many applicati...High-intensity laser–plasma interactions produce a wide array of energetic particles and beams with promising applications.Unfortunately,the high repetition rate and high average power requirements for many applications are not satisfied by the lasers,optics,targets,and diagnostics currently employed.Here,we aim to address the need for high-repetition-rate targets and optics through the use of liquids.A novel nozzle assembly is used to generate highvelocity,laminar-flowing liquid microjets which are compatible with a low-vacuum environment,generate little to no debris,and exhibit precise positional and dimensional tolerances.Jets,droplets,submicron-thick sheets,and other exotic configurations are characterized with pump–probe shadowgraphy to evaluate their use as targets.To demonstrate a highrepetition-rate,consumable,liquid optical element,we present a plasma mirror created by a submicron-thick liquid sheet.This plasma mirror provides etalon-like anti-reflection properties in the low field of 0.1%and high reflectivity as a plasma,69%,at a repetition rate of 1 k Hz.Practical considerations of fluid compatibility,in-vacuum operation,and estimates of maximum repetition rate are addressed.The targets and optics presented here demonstrate a potential technique for enabling the operation of laser–plasma interactions at high repetition rates.展开更多
Pterostilbene(PT),a lipid-soluble polyphenol known for its antioxidant,anticancer,and various other biological properties,holds potential as an active ingredient in cosmetics for its anti-wrinkle and skin-whitening ef...Pterostilbene(PT),a lipid-soluble polyphenol known for its antioxidant,anticancer,and various other biological properties,holds potential as an active ingredient in cosmetics for its anti-wrinkle and skin-whitening effects.However,its application is limited by its low water solubility and poor penetration through the stratum corneum.To address these limitations,this study initially prepared Pterostilbene nanoliposomes(PT-NLPs)using a high shear-microjet homogenization treatment method,because of the distinctive hydrophilic and hydrophilic properties of the liposomes.The stability under different storage conditions of the PT-NLPs was evaluated by investigating the alterations of the particle size,PDI,Zeta potential and surface morphology,combined with the test results of Lumisizer stability analyzer.Finally,the comprehensive performance of PT-NLPs was evaluated through in vitro dermal and transdermal testing,human testing,and instrument testing.The results showed that the PT-NLPs treated by the high shear-microjet homogenisation method proposed in this paper possessed a 1.7-fold increase in the retention performance compared with the free PT solution,and no penetration occurred on the blood-brain barrier,indicating that PT-NLPs would not cause toxicity to the organism.The human efficacy evaluation found that the PT-NLPs whitening serum could improve skin dullness,brighten skin tone,and improve skin sensitivity after 14 days of use.The high shear-microjet homogenisation method proposed in this paper for the treatment of PT-NLPs improved the transdermal delivery properties of PT.The process has a broad application prospect in the fields of medicine and cosmetics.展开更多
This work focuses on the effect of the interval between two shocks on the ejecta formation from the grooved aluminum(Al_(1100))surface by using smoothed particle hydrodynamics numerical simulation.Two unsupported shoc...This work focuses on the effect of the interval between two shocks on the ejecta formation from the grooved aluminum(Al_(1100))surface by using smoothed particle hydrodynamics numerical simulation.Two unsupported shocks are obtained by the plate-impact between sample and two flyers at interval,with a peak pressure of approximately 30 GPa for each shock.When the shock interval varies from 2.11 to 7.67 times the groove depth,the bubble velocity reduces to a constant,and the micro jetting factor R_(J) from spike to bubble exhibits a non-monotonic change that decreases initially and then increases.At a shock interval of 3.6 times the groove depth,micro jetting factor R_(J) from spike to bubble reaches its minimum value of approximately 0.6.While,the micro jetting factor R_(F) from spike to free surface decreases linearly at first,and stabilizes around 0.25 once the shock interval surpasses 4.18 times the groove depth.When the shock interval is less than 4.18 times the groove depth,the unloading wave generated by the breakout of the first shock wave is superimpose with the unloading part of the second shock wave to form a large tensile area.展开更多
Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings ...Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.展开更多
A liquid-microjet(LJ)linear time-of-flight(TOF)mass spectrometer,coupled with a femtosecond laser ionization source,has been designed for direct measurements of mass spectra of liquid aqueous solutions.Two main featur...A liquid-microjet(LJ)linear time-of-flight(TOF)mass spectrometer,coupled with a femtosecond laser ionization source,has been designed for direct measurements of mass spectra of liquid aqueous solutions.Two main features of our designed spectrometer involve the coupling of a liquid microjet nozzle to a conventional ion optics and the application of femtosecond pulses for mass spectral ionization.The detailed design,construction,and simulation of this new spectrometer are presented.More importantly,we combined the experimental tests with the simulated electric fields and ion trajectories to investigate the performance of the designed spectrometer,especially the kind of disturbances of the nozzle electric field on the conventional ion optics.In our current design,the optimal E/R(E:extractor,R:repeller)electrode voltage ratio was found to be∼0.71 when the voltages on the R,E and G(ground)electrodes were set to be 1500,1060 and 0 V,respectively,whilst the voltage on the N nozzle electrode was required to be around 1250 V.The capability of the designed spectrometer has been demonstrated by recording the simulated mass spectra of the water,benzene and cytidine with their mass/charge ratios of 18,76 and 243,respectively.This work shall be helpful for the development of new all-liquid-phase mass spectral technology to be employed in the diagnosis of diseases by the mass analysis of human body fluids.展开更多
The objective of the present study is an experimental investigation of diffusion combustion of round microjets,i.e.,mixtures of hydrogen with methane,helium,and nitrogen.It is found that the evolution of burning micro...The objective of the present study is an experimental investigation of diffusion combustion of round microjets,i.e.,mixtures of hydrogen with methane,helium,and nitrogen.It is found that the evolution of burning microjets is associated with generation of a“bottleneck flame region”close to the nozzle exit,as it was observed earlier during hydrogen combustion.Combustion of a mixture of hydrogen and methane with increasing flow velocity occurs with the transformation of the torch.At first,a torch stabilized on the nozzle is observed,then it is divided into a stabilized part in contact with the nozzle and into a raised part of the torch.The combustion process occurs in two areas.A further increase in velocity promotes the breakdown of the raised torch,but maintains combustion in the nozzle area.The results on hydrogen/methane combustion are obtained in a smaller range of the microjet velocity than those of a hydrogen microjet.Somewhat similar data are derived for other gas additives.To make combustion of gas mixtures more stable with increasing microjet velocity,one has to increase the portion of hydrogen in the gas mixture or reduce the fractions of other gas additives.展开更多
Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debri...Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debris, and turbulent liquid flow generally deteriorate laser beam transmission stability, leading to low energy efficiency and poor surface quality. Here, we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer. The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region, and thus a very stable material removal process can be obtained. The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m sin its initial 500 μm displacement. The coupling effect of laser ablation, mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality. We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation(LIMJAA) based on its unique characteristics. High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMJAA with a single-pass laser scanning process in our experiments. LIMJAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels, square and circle microscale through-holes. The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.展开更多
A novel ultrasonic-assisted low-temperature soldering was developed to join AZ31B Mg alloy and 6061 Al alloy with a series of Sn–x Zn solders. The average maximum shear strength of the joints reaches up to 87.5 MPa a...A novel ultrasonic-assisted low-temperature soldering was developed to join AZ31B Mg alloy and 6061 Al alloy with a series of Sn–x Zn solders. The average maximum shear strength of the joints reaches up to 87.5 MPa at soldering temperature of 300 °C under ultrasonic assistance for only 5 s using Sn–20 Zn solder. The fracture path propagates completely in the soldering seam. The results indicate that the microjet generated by ultrasonic pressure in liquid solder could strike and splinter the Mg_2Sn intermetallic compounds into small pieces, which contributes to the enhancement of the joint strength. In addition, the primary Al(Zn) solid solution phase formed during cooling stage could also strengthen the joint due to the prevention of microcracks propagation.展开更多
With considering the scattering effect of grain boundary and the grain orientation,the molecular dynamics is used for the first time to comparatively investigate microjetting generated by monocrystalline tin surface a...With considering the scattering effect of grain boundary and the grain orientation,the molecular dynamics is used for the first time to comparatively investigate microjetting generated by monocrystalline tin surface and polycrystalline tin surface under plane impact loading in this work.The research results show that when the impact velocity is low,the scattering effect of grain boundary and different grain orientations in a polycrystalline tin will cause the sample to melt inhomogeneously,leading the shock wave front to attenuate,meanwhile,the inhomogeneous melting can result in jet deviating.Comparing with monocrystalline tin,the jet head velocity,jet velocity coefficient,and jet mass coefficient of polycrystalline tin at low impact velocity are all low.Moreover,as the impact velocity increases,this influence decreases and the microjetting results of polycrystalline tin and monocrystalline tin tend to be consistent with each other.展开更多
A method based on microjets is implemented to control the flow properties in a convergent-divergent nozzle undergoing a sudden expansion.Three different variants of this active control technique are explored numerical...A method based on microjets is implemented to control the flow properties in a convergent-divergent nozzle undergoing a sudden expansion.Three different variants of this active control technique are explored numerically by means of a finite-volume method for compressible fluid flow:with the first one,the control is implemented at the base,with the second at the wall,while the third one may be regarded as a combination of these.When jets are over-expanded,the control is not very effective.However,when a favourable pressure gradient is established in the nozzle,the control becomes effective,leading to an increase in the base pressure.展开更多
Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology...Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated that the components of different materials exhibited various fatigue lives under the same external conditions. When the groove depth was extended, the initiation crack life decreased rapidly, while the true stress amplitude was increased simultaneously. This gave an important explanation to the accelerating material loss rate during cavitation erosion. However, when the groove depth was fixed and the length varied, the fatigue life became complex, more fluctuant than that happened in depth. The results also indicate that the fatigue effect of cavitation plays an important role in contributing to the formation and propagation of characteristic pits.展开更多
Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion.In this paper,a high-spatiotemporal-resolution double-exposure photographic method is used to inv...Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion.In this paper,a high-spatiotemporal-resolution double-exposure photographic method is used to investigate the collapse of laser-induced cavitation bubbles at two values of the dimensionless distance from the bubble to the wall,γ=d/R_(max)=0.9 and 1.25(where d is the vertical distance between the bubble center and the wall and R_(max)is the maximum radius of the bubble).Complete high-resolution evolution sequences of bubbles near a rigid wall are captured from optical breakdown to second collapse.The generation and development of microjets and shock waves during cavitation bubble collapse are described in detail.The oscillations of the bubble near the rigid wall and the microjets and shock waves generated by the collapse are analyzed.It is shown that the presence of the rigid wall affects the development of the bubble and microjets.The microjet velocity can reach up to 64 m/s.Multiple shock waves are found to be generated by bubble collapse.展开更多
Due to the continuous enhancement of wafer processing precision requirements in the semiconductor industry,ultrasonic cleaning technology has garnered significant attention for its distinctive advantages in wafer clea...Due to the continuous enhancement of wafer processing precision requirements in the semiconductor industry,ultrasonic cleaning technology has garnered significant attention for its distinctive advantages in wafer cleaning processes.This study aims to investigate the mechanism of ultrasonic cavitation during wafer processing,with a specific focus on the dynamic behavior of transient and steady-state cavitation at varying ultrasonic frequencies,as well as the distribution characteristics of the flow field during acoustic cavitation.In this paper,we comprehensively analyze the mechanism by which microjet impact generates a robust shear force for efficient particle removal from solid surfaces,while quantitatively evaluating the effects of different microjet velocities on wall deformation and potential damage.This research not only enhances our understanding of acoustic cavitation cleaning principles but also provides substantial scientific support for enhancing precision device cleaning efficiency and reducing potential damage.展开更多
A fluid jet ejected from micron size nozzle is a commonly occurring phenomenon in biomedical engineering,printing technology and micro-fluidic applications.Disintegration of a jet into drops occurs due to disturbances...A fluid jet ejected from micron size nozzle is a commonly occurring phenomenon in biomedical engineering,printing technology and micro-fluidic applications.Disintegration of a jet into drops occurs due to disturbances induced by external sources.This work explores the various sources of perturbation and their effect on jet disintegration through numerical simulation of a two-dimensional non-isothermal model.The mathematical approach uses a novel technique to combine analytical solutions for the energy balance equation in the radial direction to solve the complete two dimensional problem.The two dimensional energy balance equation is simultaneously solved together with the axi-symmetric Navier–Stokes equations using the slender-jet approximation to predict jet velocity.The energy balance takes into account of peripheral heat transfer to the environment through analytical expressions derived from radial approximations.The model helps in understanding the factors in dynamic temperature variations that eventually render the jet unstable.The distinguishing aspect of this work is the analysis of the effect of a periodic thermal perturbation applied at any point in the domain of a progressive jet,a situation typically encountered in thermal inkjet printers and not considered previously.Results presented for non-isothermal jets which are both stationary and moving illustrate the effect of jet velocity in propagation of perturbation and subsequent drop formation.The major contribution of this numerical study is that it provides an insight on novel ways of controlling droplet formation in bubble jet printers.This study demonstrates that thermal disturbance propagating from periodic heating can be manipulated to shape the droplets and control their breakage point along the jet.展开更多
High-throughput quantitative approaches to study axon growth behaviors have remained a challenge.We have developed a 1024-chamber microfluidic gradient generator array that enables large-scale investigations of axon g...High-throughput quantitative approaches to study axon growth behaviors have remained a challenge.We have developed a 1024-chamber microfluidic gradient generator array that enables large-scale investigations of axon guidance and growth dynamics from individual primary mammalian neurons,which are exposed to gradients of diffusible molecules.Our microfluidic method(a)generates statistically rich data sets,(b)produces a stable,reproducible gradient with negligible shear stresses on the culture surface,(c)is amenable to the long-term culture of primary neurons without any unconventional protocol,and(d)eliminates the confounding influence of cell-secreted factors.Using this platform,we demonstrate that hippocampal axon guidance in response to a netrin-1 gradient is concentration-dependent—attractive at higher concentrations and repulsive at lower concentrations.We also show that the turning of the growth cone depends on the angle of incidence of the gradient.Our study highlights the potential of microfluidic devices in producing large amounts of data from morphogen and chemokine gradients that play essential roles not only in axonal navigation but also in stem cell differentiation,cell migration,and immune response.展开更多
文摘The underexpanded microjet emerging from a rectangular convergent nozzle with a high aspect ratio at the nozzle exit is investigated numerically using the Reynolds-averaged Navier-Stokes (RANS) simulation with the Menter’s shear stress transport (SST) k-ω turbulence model. The simulation is performed at the nozzle pressure ratio of 5.0 to produce a strong shock and it is validated by a comparison with a rainbow schlieren picture of the microjet. The three-dimensional structure of the shock-containing rectangular microjet is demonstrated using the isopycnic surface and bright-field schlieren representations.
文摘Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers <em>M</em><em><sub>j</sub></em> ranging from 1.47 - 1.71, where the design Mach number is <em>M<sub>d</sub></em> = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45<span style="white-space:nowrap;">°</span> within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61875148)。
文摘We systematically investigate the power distribution characteristics of microjets generated by prismatic scatterers with different shapes at sub-THz region(λ = 8.57 mm). Among these prismatic scatterers, the hexagonal-type one shows better focusing feature than the others. Aiming at the hexagonal-type one, we propose a double-layer scatterer composed of a Teflon hexagonal prism as an outer layer and a semiconductor cuboid as an inner layer. Aiming at the double-layer scatterer, we further study the effects of refractive index, size, and shape of the inner cuboid on microjet’s features. The study allows us to present an optimized double-layer scatterer, which has a side length λ/2(λ) and a refractive index 2.0(1.4) for the inner(outer) layer. We show that the optimized scatterer can produce an ultra-strong, ultra-narrow microjet with a power enhancement of;0 and a full width at half maximum(FWHM) of;0.26λ, and the microjet is just located at the output face. The microjet keeps compact within the distance range of λ from the output face. These features and effects are explained from the viewpoint of ray optics theory. According to the optimized double-layer scatterer, we further study the multi-frequency focusing features of the microjets, and find that the microjet remains good features at harmonic frequencies 2f_(0) and 3f_(0). In addition, we investigate the effect of an Au sphere presence in the center of the microjet on the power distribution. The results show that a spherical dark spot with a size similar to that of the Au sphere emerges in the area where the Au sphere is placed. The feature can be used to measure the size of a metallic particle.
基金This work was supported by the National Science Fund for Distinguished Young Scholars(Grant 51825605).
文摘Swirl combustion serves as a helpful flame stabilization method,which also affects the combustion and emission characteristics.This article experimentally investigated the effects of CO_(2)microjets on combustion instability and NO_(x)emissions in lean premixed flames with different swirl numbers.The microjets’control feasibility was examined from three variables of CO_(2)jet flow rate,thermal power,and swirl angles.Results indicate that microjets can mitigate the combustion instability and NO_(x)emissions in lean premixed burners with different swirl numbers and thermal power.Still,the damping effect of microjets in low swirl intensity is better than that in high swirl intensity.The damping ratio of pressure amplitude can reach the maximum of 98%,and NO_(x)emissions can realize the maximum reduction of 10.1×10^(−6)at the swirl angle of 30°.Besides,the flame macrostructure switches from an inverted cone shape to a petal shape,and the flame length reduction at low swirl intensity is higher than that of high swirl intensity.This research clarified the control differences of mitigation of combustion instability and NO_(x)emissions by microjets in lean premixed flames with different swirl numbers,contributing to the optimization of microjets control and the construction of high-performance burners.
基金supported by the Air Force Office of Scientific Research under LRIR Project 17RQCOR504 under the management of Dr. Riq Parraprovided by the AFOSR summer faculty program
文摘High-intensity laser–plasma interactions produce a wide array of energetic particles and beams with promising applications.Unfortunately,the high repetition rate and high average power requirements for many applications are not satisfied by the lasers,optics,targets,and diagnostics currently employed.Here,we aim to address the need for high-repetition-rate targets and optics through the use of liquids.A novel nozzle assembly is used to generate highvelocity,laminar-flowing liquid microjets which are compatible with a low-vacuum environment,generate little to no debris,and exhibit precise positional and dimensional tolerances.Jets,droplets,submicron-thick sheets,and other exotic configurations are characterized with pump–probe shadowgraphy to evaluate their use as targets.To demonstrate a highrepetition-rate,consumable,liquid optical element,we present a plasma mirror created by a submicron-thick liquid sheet.This plasma mirror provides etalon-like anti-reflection properties in the low field of 0.1%and high reflectivity as a plasma,69%,at a repetition rate of 1 k Hz.Practical considerations of fluid compatibility,in-vacuum operation,and estimates of maximum repetition rate are addressed.The targets and optics presented here demonstrate a potential technique for enabling the operation of laser–plasma interactions at high repetition rates.
基金supported by the Guangdong Provincial University Key Area Project[grant numbers 2023ZDZX4136]the Guangdong Provincial University Innovation Team Project[grant numbers 2023KCXTD085]+1 种基金the Guangdong Provincial Science and Technology Innovation Strategy Special Fund[grant numbers pdjh2022b1046]the Student Scientific Research Project of Jiangmen Polytechnic[grant numbers jzxsky20230102]。
文摘Pterostilbene(PT),a lipid-soluble polyphenol known for its antioxidant,anticancer,and various other biological properties,holds potential as an active ingredient in cosmetics for its anti-wrinkle and skin-whitening effects.However,its application is limited by its low water solubility and poor penetration through the stratum corneum.To address these limitations,this study initially prepared Pterostilbene nanoliposomes(PT-NLPs)using a high shear-microjet homogenization treatment method,because of the distinctive hydrophilic and hydrophilic properties of the liposomes.The stability under different storage conditions of the PT-NLPs was evaluated by investigating the alterations of the particle size,PDI,Zeta potential and surface morphology,combined with the test results of Lumisizer stability analyzer.Finally,the comprehensive performance of PT-NLPs was evaluated through in vitro dermal and transdermal testing,human testing,and instrument testing.The results showed that the PT-NLPs treated by the high shear-microjet homogenisation method proposed in this paper possessed a 1.7-fold increase in the retention performance compared with the free PT solution,and no penetration occurred on the blood-brain barrier,indicating that PT-NLPs would not cause toxicity to the organism.The human efficacy evaluation found that the PT-NLPs whitening serum could improve skin dullness,brighten skin tone,and improve skin sensitivity after 14 days of use.The high shear-microjet homogenisation method proposed in this paper for the treatment of PT-NLPs improved the transdermal delivery properties of PT.The process has a broad application prospect in the fields of medicine and cosmetics.
基金supported by the Doctoral Research Launch Foundation of Liaoning Province(Grant No.2022-BS-185),Chinathe Science Challenge Project(Grant No.TZ2016001),China+2 种基金the National Natural Science Foundation of China(Grant Nos.11972092,12172056,12002049),Chinathe key Laboratory of Computational Physics(Gant No.HX02021-24)720-24)Shenyang Ligong University Talent Introduction Support Fund,China。
文摘This work focuses on the effect of the interval between two shocks on the ejecta formation from the grooved aluminum(Al_(1100))surface by using smoothed particle hydrodynamics numerical simulation.Two unsupported shocks are obtained by the plate-impact between sample and two flyers at interval,with a peak pressure of approximately 30 GPa for each shock.When the shock interval varies from 2.11 to 7.67 times the groove depth,the bubble velocity reduces to a constant,and the micro jetting factor R_(J) from spike to bubble exhibits a non-monotonic change that decreases initially and then increases.At a shock interval of 3.6 times the groove depth,micro jetting factor R_(J) from spike to bubble reaches its minimum value of approximately 0.6.While,the micro jetting factor R_(F) from spike to free surface decreases linearly at first,and stabilizes around 0.25 once the shock interval surpasses 4.18 times the groove depth.When the shock interval is less than 4.18 times the groove depth,the unloading wave generated by the breakout of the first shock wave is superimpose with the unloading part of the second shock wave to form a large tensile area.
基金Supported by the National Natural Science Foundation of China(Nos.11972064,92052104)the Key Laboratory of Computational Aerodynamics,AVIC Aerodynamics Research Institute,China(No.YL2022XFX0405)the Fundamental Research Funds for the Central Universities,China.
文摘Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.
基金supported by the Knowledge Innovation Program of Wuhan-Basic Research(Nos.2023020201010084,2022010801010134)the National Key Research and Development Program of China(No.2019YFA0307700)the National Natural Science Foundation of China(Nos.12274418,22273116,12074389,11974381,22363011).
文摘A liquid-microjet(LJ)linear time-of-flight(TOF)mass spectrometer,coupled with a femtosecond laser ionization source,has been designed for direct measurements of mass spectra of liquid aqueous solutions.Two main features of our designed spectrometer involve the coupling of a liquid microjet nozzle to a conventional ion optics and the application of femtosecond pulses for mass spectral ionization.The detailed design,construction,and simulation of this new spectrometer are presented.More importantly,we combined the experimental tests with the simulated electric fields and ion trajectories to investigate the performance of the designed spectrometer,especially the kind of disturbances of the nozzle electric field on the conventional ion optics.In our current design,the optimal E/R(E:extractor,R:repeller)electrode voltage ratio was found to be∼0.71 when the voltages on the R,E and G(ground)electrodes were set to be 1500,1060 and 0 V,respectively,whilst the voltage on the N nozzle electrode was required to be around 1250 V.The capability of the designed spectrometer has been demonstrated by recording the simulated mass spectra of the water,benzene and cytidine with their mass/charge ratios of 18,76 and 243,respectively.This work shall be helpful for the development of new all-liquid-phase mass spectral technology to be employed in the diagnosis of diseases by the mass analysis of human body fluids.
基金carried out with the financial support of the Ministry of Science and Higher Education of the Russian Federation,Agreement dated 24.04.2024,No.075-15-2024-543.
文摘The objective of the present study is an experimental investigation of diffusion combustion of round microjets,i.e.,mixtures of hydrogen with methane,helium,and nitrogen.It is found that the evolution of burning microjets is associated with generation of a“bottleneck flame region”close to the nozzle exit,as it was observed earlier during hydrogen combustion.Combustion of a mixture of hydrogen and methane with increasing flow velocity occurs with the transformation of the torch.At first,a torch stabilized on the nozzle is observed,then it is divided into a stabilized part in contact with the nozzle and into a raised part of the torch.The combustion process occurs in two areas.A further increase in velocity promotes the breakdown of the raised torch,but maintains combustion in the nozzle area.The results on hydrogen/methane combustion are obtained in a smaller range of the microjet velocity than those of a hydrogen microjet.Somewhat similar data are derived for other gas additives.To make combustion of gas mixtures more stable with increasing microjet velocity,one has to increase the portion of hydrogen in the gas mixture or reduce the fractions of other gas additives.
基金financially supported by the Guangdong Provincial University Science and Technology Program(Grant No.2020KTSCX119)the Shenzhen Science and Technology Programs(Grant Nos.20200925155508001,GJHZ20190820151801786,JCYJ20210324115608024 and KQTD20170810110250357)。
文摘Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debris, and turbulent liquid flow generally deteriorate laser beam transmission stability, leading to low energy efficiency and poor surface quality. Here, we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer. The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region, and thus a very stable material removal process can be obtained. The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m sin its initial 500 μm displacement. The coupling effect of laser ablation, mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality. We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation(LIMJAA) based on its unique characteristics. High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMJAA with a single-pass laser scanning process in our experiments. LIMJAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels, square and circle microscale through-holes. The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.
基金supported financially by the State Key Laboratory of Advanced Brazing Filler Metals & Technology (No. SKLABFMT-2016-02)the CAST Innovation Fund Key Project and the National Natural Science Foundation of China (Nos. 51775299 and 51520105007)
文摘A novel ultrasonic-assisted low-temperature soldering was developed to join AZ31B Mg alloy and 6061 Al alloy with a series of Sn–x Zn solders. The average maximum shear strength of the joints reaches up to 87.5 MPa at soldering temperature of 300 °C under ultrasonic assistance for only 5 s using Sn–20 Zn solder. The fracture path propagates completely in the soldering seam. The results indicate that the microjet generated by ultrasonic pressure in liquid solder could strike and splinter the Mg_2Sn intermetallic compounds into small pieces, which contributes to the enhancement of the joint strength. In addition, the primary Al(Zn) solid solution phase formed during cooling stage could also strengthen the joint due to the prevention of microcracks propagation.
文摘With considering the scattering effect of grain boundary and the grain orientation,the molecular dynamics is used for the first time to comparatively investigate microjetting generated by monocrystalline tin surface and polycrystalline tin surface under plane impact loading in this work.The research results show that when the impact velocity is low,the scattering effect of grain boundary and different grain orientations in a polycrystalline tin will cause the sample to melt inhomogeneously,leading the shock wave front to attenuate,meanwhile,the inhomogeneous melting can result in jet deviating.Comparing with monocrystalline tin,the jet head velocity,jet velocity coefficient,and jet mass coefficient of polycrystalline tin at low impact velocity are all low.Moreover,as the impact velocity increases,this influence decreases and the microjetting results of polycrystalline tin and monocrystalline tin tend to be consistent with each other.
基金supported by the Structures and Materials(S&M)Research Lab of Prince Sultan University.
文摘A method based on microjets is implemented to control the flow properties in a convergent-divergent nozzle undergoing a sudden expansion.Three different variants of this active control technique are explored numerically by means of a finite-volume method for compressible fluid flow:with the first one,the control is implemented at the base,with the second at the wall,while the third one may be regarded as a combination of these.When jets are over-expanded,the control is not very effective.However,when a favourable pressure gradient is established in the nozzle,the control becomes effective,leading to an increase in the base pressure.
基金the National High-Tech Research and Development Program of China(No.2002AA331080)the Beijing Important Science Technology Projects(No.H024200050021).
文摘Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated that the components of different materials exhibited various fatigue lives under the same external conditions. When the groove depth was extended, the initiation crack life decreased rapidly, while the true stress amplitude was increased simultaneously. This gave an important explanation to the accelerating material loss rate during cavitation erosion. However, when the groove depth was fixed and the length varied, the fatigue life became complex, more fluctuant than that happened in depth. The results also indicate that the fatigue effect of cavitation plays an important role in contributing to the formation and propagation of characteristic pits.
基金support given by the National Natural Science Foundation of China(Grant Nos.52179092 and 52222904).
文摘Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion.In this paper,a high-spatiotemporal-resolution double-exposure photographic method is used to investigate the collapse of laser-induced cavitation bubbles at two values of the dimensionless distance from the bubble to the wall,γ=d/R_(max)=0.9 and 1.25(where d is the vertical distance between the bubble center and the wall and R_(max)is the maximum radius of the bubble).Complete high-resolution evolution sequences of bubbles near a rigid wall are captured from optical breakdown to second collapse.The generation and development of microjets and shock waves during cavitation bubble collapse are described in detail.The oscillations of the bubble near the rigid wall and the microjets and shock waves generated by the collapse are analyzed.It is shown that the presence of the rigid wall affects the development of the bubble and microjets.The microjet velocity can reach up to 64 m/s.Multiple shock waves are found to be generated by bubble collapse.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFB3207100)supported by the Hubei Provincial Strategic Scientist Training Plan(Grant No.2022EJD009).
文摘Due to the continuous enhancement of wafer processing precision requirements in the semiconductor industry,ultrasonic cleaning technology has garnered significant attention for its distinctive advantages in wafer cleaning processes.This study aims to investigate the mechanism of ultrasonic cavitation during wafer processing,with a specific focus on the dynamic behavior of transient and steady-state cavitation at varying ultrasonic frequencies,as well as the distribution characteristics of the flow field during acoustic cavitation.In this paper,we comprehensively analyze the mechanism by which microjet impact generates a robust shear force for efficient particle removal from solid surfaces,while quantitatively evaluating the effects of different microjet velocities on wall deformation and potential damage.This research not only enhances our understanding of acoustic cavitation cleaning principles but also provides substantial scientific support for enhancing precision device cleaning efficiency and reducing potential damage.
基金carried out as a part of a research project at Heritage Institute of Technology,Kolkata.
文摘A fluid jet ejected from micron size nozzle is a commonly occurring phenomenon in biomedical engineering,printing technology and micro-fluidic applications.Disintegration of a jet into drops occurs due to disturbances induced by external sources.This work explores the various sources of perturbation and their effect on jet disintegration through numerical simulation of a two-dimensional non-isothermal model.The mathematical approach uses a novel technique to combine analytical solutions for the energy balance equation in the radial direction to solve the complete two dimensional problem.The two dimensional energy balance equation is simultaneously solved together with the axi-symmetric Navier–Stokes equations using the slender-jet approximation to predict jet velocity.The energy balance takes into account of peripheral heat transfer to the environment through analytical expressions derived from radial approximations.The model helps in understanding the factors in dynamic temperature variations that eventually render the jet unstable.The distinguishing aspect of this work is the analysis of the effect of a periodic thermal perturbation applied at any point in the domain of a progressive jet,a situation typically encountered in thermal inkjet printers and not considered previously.Results presented for non-isothermal jets which are both stationary and moving illustrate the effect of jet velocity in propagation of perturbation and subsequent drop formation.The major contribution of this numerical study is that it provides an insight on novel ways of controlling droplet formation in bubble jet printers.This study demonstrates that thermal disturbance propagating from periodic heating can be manipulated to shape the droplets and control their breakage point along the jet.
基金This work was supported by a grant from the National Institutes of Health(1R01NS064387).
文摘High-throughput quantitative approaches to study axon growth behaviors have remained a challenge.We have developed a 1024-chamber microfluidic gradient generator array that enables large-scale investigations of axon guidance and growth dynamics from individual primary mammalian neurons,which are exposed to gradients of diffusible molecules.Our microfluidic method(a)generates statistically rich data sets,(b)produces a stable,reproducible gradient with negligible shear stresses on the culture surface,(c)is amenable to the long-term culture of primary neurons without any unconventional protocol,and(d)eliminates the confounding influence of cell-secreted factors.Using this platform,we demonstrate that hippocampal axon guidance in response to a netrin-1 gradient is concentration-dependent—attractive at higher concentrations and repulsive at lower concentrations.We also show that the turning of the growth cone depends on the angle of incidence of the gradient.Our study highlights the potential of microfluidic devices in producing large amounts of data from morphogen and chemokine gradients that play essential roles not only in axonal navigation but also in stem cell differentiation,cell migration,and immune response.
