Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different in...Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.展开更多
Fluorescence imaging in the second near-infrared window(NIR-II,900-1880 nm)offers high signalto-background ratio(SBR),enhanced definition,and superior tissue penetration,making it ideal for real-time surgical navigati...Fluorescence imaging in the second near-infrared window(NIR-II,900-1880 nm)offers high signalto-background ratio(SBR),enhanced definition,and superior tissue penetration,making it ideal for real-time surgical navigation.However,with single-channel imaging,surgeons must frequently switch between the surgi⁃cal field and the NIR-II images on the monitor.To address this,a coaxial dual-channel imaging system that com⁃bines visible light and 1100 nm longpass(1100LP)fluorescence was developed.The system features a custom⁃ized coaxial dual-channel lens with optimized distortion,achieving precise alignment with an error of less than±0.15 mm.Additionally,the shared focusing mechanism simplifies operation.Using FDA-approved indocya⁃nine green(ICG),the system was successfully applied in dual-channel guided rat lymph node excision,and blood supply assessment of reconstructed human flap.This approach enhances surgical precision,improves opera⁃tional efficiency,and provides a valuable reference for further clinical translation of NIR-II fluorescence imaging.展开更多
To reduce the vibration of the Coaxial Helicopter Main Transmission System(CHMTS)considering both level and vertical flight conditions,a vibration evaluation and optimization model for the CHMTS was built.The vibratio...To reduce the vibration of the Coaxial Helicopter Main Transmission System(CHMTS)considering both level and vertical flight conditions,a vibration evaluation and optimization model for the CHMTS was built.The vibration simulation model of the CHMTS was set up by gear dynamics theory and loaded contact analysis.For better evaluation of the system vibration,a vibration evaluation method for the CHMTS was established by the G1 method-variation coefficient method.A hybrid Gravitational Search Algorithm-Simulated Annealing(GSA-SA)algorithm was combined to balance convergence speed and searching accuracy.The principle test was conducted to prove the accuracy of theoretical method,in which the maximum relative error is16.26%.The optional results show that the vibration of the optimized transmission system decreases significantly,in which the maximum reduction of key vibration indicators reaches more than 20%.The theoretical results have been compared to the experiment to verify the effectiveness of the vibration optimization method.The proposed method could be extended to other fields.展开更多
In this paper,we present a novel approach to study the electrical properties of intact rock by combining impedance and vector network analyzer measurements in the frequency range from 5 Hz to 3 GHz.For the firsttime,t...In this paper,we present a novel approach to study the electrical properties of intact rock by combining impedance and vector network analyzer measurements in the frequency range from 5 Hz to 3 GHz.For the firsttime,this study enables electrical characterization of the exact same rock sample over nine orders of magnitude in frequency range,utilizing a coaxial cell apparatus with specificallyprepared rock samples.Three types of rocks(basalt,sandstone and granite)with low to intermediate porosity(12.24%,16.9%and 7.49%,respectively)were characterized at varying saturation levels.The relaxation behavior of the samples was quantifiedusing an advanced phenomenological model incorporating both the dielectric constant and electrical conductivity in the form of Debye and Cole-Cole representations.Across the frequency range,three distinct relaxation processes were identified:a high-frequency water process and two interfacial processes related to interactions between the aqueous pore solution and mineral particles(membrane relaxation and Maxwell-Wagner effects).Additionally,an apparent direct current conductivity was observed.This comprehensive broadband analysis represents a further step toward the in situ characterization of rocks using electromagnetic fieldmeasurement methods and demonstrates advancements in both methodology and understanding of rock properties compared to existing studies.展开更多
The packaging quality of coaxial laser diodes(CLDs)plays a pivotal role in determining their optical performance and long-term reliability.As the core packaging process,high-precision laser welding requires precise co...The packaging quality of coaxial laser diodes(CLDs)plays a pivotal role in determining their optical performance and long-term reliability.As the core packaging process,high-precision laser welding requires precise control of process parameters to suppress optical power loss.However,the complex nonlinear relationship between welding parameters and optical power loss renders traditional trial-and-error methods inefficient and imprecise.To address this challenge,a physics-informed(PI)and data-driven collaboration approach for welding parameter optimization is proposed.First,thermal-fluid-solid coupling finite element method(FEM)was employed to quantify the sensitivity of welding parameters to physical characteristics,including residual stress.This analysis facilitated the identification of critical factors contributing to optical power loss.Subsequently,a Gaussian process regression(GPR)model incorporating finite element simulation prior knowledge was constructed based on the selected features.By introducing physics-informed kernel(PIK)functions,stress distribution patterns were embedded into the prediction model,achieving high-precision optical power loss prediction.Finally,a Bayesian optimization(BO)algorithm with an adaptive sampling strategy was implemented for efficient parameter space exploration.Experimental results demonstrate that the proposedmethod effectively establishes explicit physical correlations between welding parameters and optical power loss.The optimized welding parameters reduced optical power loss by 34.1%,providing theoretical guidance and technical support for reliable CLD packaging.展开更多
To optimize secondary air nozzle structure in purifying burner,this study focused on the comparison of purification,combustion and NO_(x)emission characteristics of pulverized coal preheated by a 30 kW purifying burne...To optimize secondary air nozzle structure in purifying burner,this study focused on the comparison of purification,combustion and NO_(x)emission characteristics of pulverized coal preheated by a 30 kW purifying burner with coaxial and centrosymmetric structures.Centrosymmetric structure shifted the position of main burning region down in high-temperature reduction unit(HTRU),and the number of branches differently influenced the temperature in different regions with this structure.For reductive gas components,CO concentration with centrosymmetric structure was higher compared to coaxial structure,while the differences in H_(2)and CH_(4)concentrations were smaller.Centrosymmetric structure was more disadvantageous to improve physicochemical properties of pulverized coal compared to coaxial structure,and this structure with four branches further deteriorated its properties compared to two branches.In mild combustion unit(MCU),the temperature at top was lower with centrosymmetric structure,while was higher in the rest.Centrosymmetric structure more effectively reduced NO_(x)emission compared to coaxial structure,but with slight sacrifice of combustion efficiency(η).Moreover,both two-branch and four-branch centrosymmetric structures realized ultra-low NO_(x)emission(<50 mg·m^(-3))with high η of over 98.50%,and the former was more advantageous.With this optimal structure,η and NO_(x)emission were 99.25%and 40.42 mg·m^(-3).展开更多
Tin dioxide(SnO_(2))with a high theoretical specific capacity of 1494 mAh g^(-1)is a promising candidate anode material for lithium storage.However,the shortcomings of serious volume expansion and low conductivity lim...Tin dioxide(SnO_(2))with a high theoretical specific capacity of 1494 mAh g^(-1)is a promising candidate anode material for lithium storage.However,the shortcomings of serious volume expansion and low conductivity limit its wide application.Herein,coaxial nano-multilayered C/SnO_(2)/TiO_(2)composites were fabricated via layerby-layer self-assembly of TiO_(2)and SnO_(2)-gel layers on the natural cellulose filter paper,followed by thermal treatment under a nitrogen atmosphere.Through engineering design of the assembly process,the optimal C/SinO_(2)/TiO_(2)composite features five alternating SnO_(2)and TiO_(2)nanolayers,with TiO_(2)as the outside shell(denoted as C/TSTST).This unique structure endows the C/TSTST with excellent structural stability and electrochemical kinetics,making it a high-performance anode for lithium-ion batteries(LIBs).The C/TSTST composite delivers a high reversible capacity of 676 mAh g^(-1)at 0.1 A g^(-1)after 200 cycles and retains a capacity of 504 mAh g^(-1)at 1.0 A g^(-1),which can be recovered to 781 mAh g^(-1)at 0.1 A g^(-1)The significantly enhanced electrochemical performance is attributed to the hierarchical hybrid structure,where the carbon core combined with coaxial TiO_(2)nanolayers serves as a structural scaffold,ameliorating volume change of SnO_(2)while creating abundant interfacial defects for enhanced lithium storage and rapid charge transport.These findings are further demonstrated by the density functional theory(DFT)calculations.This work provides an efficient strategy for designing coaxial nano-multilayered transition metal oxide-related electrode materials,offering new insights into high-performance LIBs anodes.展开更多
Focusing on aerodynamic characteristics of rigid coaxial rotor of a high-speed helicopter in hover and forward flight, a wind tunnel test is conducted in the 8 m ? 6 m low-speed straightflow wind tunnel of China Aerod...Focusing on aerodynamic characteristics of rigid coaxial rotor of a high-speed helicopter in hover and forward flight, a wind tunnel test is conducted in the 8 m ? 6 m low-speed straightflow wind tunnel of China Aerodynamics Research and Development Center. In the experiment,a 4 m diameter composite model rigid coaxial rotor is designed and manufactured, and firstorder flapping frequency ratio of the blade is 1.796 to ensure sufficient stiffness at the blade root.Rotor aerodynamic performance is measured under hovering and high advance ratio conditions.Also, the numerical method is used to calculate aerodynamic characteristics in typical states of the rigid coaxial rotor for analysis purpose. The rotor lift-drag ratio and lateral lift offset in the experiment are emphatically analyzed for the rigid coaxial rotor. The results indicate that in forward flight condition, the rotor lift-drag ratio first increases and then decreases with the increment of advance ratio and lift offset. When advance ratio remains constant, with the increment of lift offset, the lift-drag ratio of rigid coaxial rotor first increases and then decreases.展开更多
Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of th...Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.展开更多
The coaxial compound helicopter has two possible strategies for heading control: collective differential and rudder deflection. A flight dynamics model is developed to assess the effect of different heading control st...The coaxial compound helicopter has two possible strategies for heading control: collective differential and rudder deflection. A flight dynamics model is developed to assess the effect of different heading control strategies. This includes the trim characteristics, steady flight performance,controllability, and manoeuvrability. The trim study demonstrates that heading control strategies are less influential on trim results, and the steady flight performance is also not significantly affected by the heading control strategy adopted. The controllability analysis shows although heading bandwidth and phase delay results at various speeds with different heading control strategies are all satisfied, the control derivative of the collective differential decreases as speed increases, and its heading aggressive agility is degraded into Level 3 in high-speed flight. In addition, using collective differential would lead to severe heading-rolling coupling as forward speed increases. On the contrary, the control derivative and aggressive agility of the rudder deflection is improved with forward speed, and there is no evidence of heading-rolling coupling. Finally, the transient turn MissionTask-Element(MTE) is utilized to investigate the heading manoeuvre characteristics in different heading control strategies, which indicates that the collective differential would add the amplitude of control input and the power consumption during this MTE.展开更多
Polystyrene(PS) fibers with core-shell structures were fabricated by coaxial electrostatic spinning,[10_TD$IF]in which there are liquid epoxy or curing agent as the core and PS as the shell. Scanning electron microsco...Polystyrene(PS) fibers with core-shell structures were fabricated by coaxial electrostatic spinning,[10_TD$IF]in which there are liquid epoxy or curing agent as the core and PS as the shell. Scanning electron microscopy(SEM), Fourier transform infrared(FTIR) spectra and optical microscope were utilized for charactering the morphology and composition of the fibers. Composite coatings embedded with the healant-loaded coreshell fibers have been prepared and the self-healing of the scratch on the coatings has been revealed.展开更多
A coaxial dielectric barrier discharge（DBD） reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond（ns）pulse to generate atmospheric ...A coaxial dielectric barrier discharge（DBD） reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond（ns）pulse to generate atmospheric pressure plasma. The comparative study on the discharge characteristics of the discharge uniformity, power deposition, energy efficiency, and operation temperature between AC and ns pulsed coaxial DBD is carried out in terms of optical and electrical characteristics and operation temperature for optimizing the coaxial DBD reactor performance. The voltages across the air gap and dielectric layer and the conduction and displacement currents are extracted from the applied voltages and measured currents of AC and ns pulsed coaxial DBDs for the calculation of the power depositions and energy efficiencies through an equivalent electrical model. The discharge uniformity and operating temperature of the coaxial DBD reactor are monitored and analyzed by optical images and infrared camera. A heat conduction model is used to calculate the temperature of the internal quartz tube. It is found that the ns pulsed coaxial DBD has a much higher instantaneous power deposition in plasma, a lower total power consumption, and a higher energy efficiency compared with that excited by AC power and is more homogeneous and stable. The temperature of the outside wall of the AC and ns pulse excited coaxial DBD reaches 158 ℃ and 64.3 ℃ after 900 s operation, respectively.The experimental results on the comparison of the discharge characteristics of coaxial DBDs excited by different powers are significant for understanding of the mechanism of DBDs,reducing energy loss, and optimizing the performance of coaxial DBD in industrial applications.展开更多
Firefighting protective clothing is a crucial protective equipment for firefighters to minimize skin burn and ensure safety firefighting operation and rescue mission.A recent increasing concern is to develop self-powe...Firefighting protective clothing is a crucial protective equipment for firefighters to minimize skin burn and ensure safety firefighting operation and rescue mission.A recent increasing concern is to develop self-powered fire warning materials that can be incorporated into the firefighting clothing to achieve active fire protection for firefighters before the protective clothing catches fire on fireground.However,it is still a challenge to facilely design and manufacture thermoelectric(TE)textile(TET)-based fire warning electronics with dynamic surface conformability and breathability.Here,we develop an alternate coaxial wet-spinning strategy to continuously produce alternating p/n-type TE aerogel fibers involving n-type Ti_(3)C_(2)T_(x)MXene and p-type MXene/SWCNT-COOH as core materials,and tough aramid nanofiber as protective shell,which simultaneously ensure the flexibility and high-efficiency TE power generation.With such alternating p/n-type TE fibers,TET-based self-powered fire warning sensors with high mechanical stability and wearability are successfully fabricated through stitching the alternating p-n segment TE fibers into aramid fabric.The results indicate that TET-based fire warning electronics containing 50 p-n pairs produce the open-circuit voltage of 7.5 mV with a power density of 119.79 nW cm-2 at a temperature difference of 300℃.The output voltage signal is then calculated as corresponding surface temperature of firefighting clothing based on a linear relationship between TE voltage and temperature.The fire alarm response time and flame-retardant properties are further displayed.Such self-powered fire warning electronics are true textiles that offer breathability and compatibility with body movement,demonstrating their potential application in firefighting clothing.展开更多
AIM： To compare the changes in corneal biomechanics measured by ocular response analyzer （ORA） after 2.2-ram microincision cataract surgery and 3.0-mm standard coaxial phacoemulsification. METHODS： The prospectiv...AIM： To compare the changes in corneal biomechanics measured by ocular response analyzer （ORA） after 2.2-ram microincision cataract surgery and 3.0-mm standard coaxial phacoemulsification. METHODS： The prospective nonrandomized study comprised eyes with cataract that had 2.2-mm coaxial microincision or 3.0 -mm standard incision phacoemulsification. The corneal hysteresis （CH）, corneal resistance factor （CRF）, corneal-compensated intraocular pressure （IOPcc） and Goldmann-correlated intraocular pressure （IOPg） were measured by ORA preoperatively and at ld, 1-, 2-, 3- and 4-week postoperatively. Results were analyzed and compared between groups. RESULTS： In both groups, CH decreased in the immediate postoperative period （P〈0.05）, returned to the preoperative level at one week （P =0.249） in the 2.2-mm group, and at two weeks in the 3.0-mm group （P --0.264）; there was no significant change in CRF values. In 2.2-mm group, mean IOPcc and IOPg increased at ld postoperatively （both ,P〈0.05）, and returned to preoperative level at one week （,0 =0.491 and P =0.923, respectively）. In 3.0-mm group, mean IOPcc and IOPg increased at ld and lwk postoperatively （P =0.005 and ,P =0.029, respectively）, and returned to preoperative level at 2wk （P =0.347 and P =0.887, respectively）. CONCLUSION： Significant differences between preoperative and postoperative corneal biomechanical values were found for CH, IOPcc and IOPg. But the recovery time courses were different between the two groups. The 2.2-mm coaxial microincision cataract surgery group seemed recovery faster compared to the 3.0-mm standard coaxial phacoemulsification group.展开更多
We present a coaxial detection of the backscattered electrons in SEM. The lens-aperture has been used to filter in energy and focus the backscattered electrons. This particular geometry allows us to eliminate the low ...We present a coaxial detection of the backscattered electrons in SEM. The lens-aperture has been used to filter in energy and focus the backscattered electrons. This particular geometry allows us to eliminate the low energy backscattered electrons and collect the backscattered electrons, which are backscattered close to the incident beam orientation. The main advantage of this geometry is adapted to topographic contrast attenuation and atomic number contrast enhancement. Thus this new SEM is very suitable to analyze the material composition.展开更多
Compared with traditional mechanical seals,magnetic fluid seals have unique characters of high airtightness,minimal friction torque requirements,pollution-free and long life-span,widely used in vacuum robots.With the ...Compared with traditional mechanical seals,magnetic fluid seals have unique characters of high airtightness,minimal friction torque requirements,pollution-free and long life-span,widely used in vacuum robots.With the rapid development of Integrate Circuit（IC）,there is a stringent requirement for sealing wafer-handling robots when working in a vacuum environment.The parameters of magnetic fluid seals structure is very important in the vacuum robot design.This paper gives a magnetic fluid seal device for the robot.Firstly,the seal differential pressure formulas of magnetic fluid seal are deduced according to the theory of ferrohydrodynamics,which indicate that the magnetic field gradient in the sealing gap determines the seal capacity of magnetic fluid seal.Secondly,the magnetic analysis model of twin-shaft magnetic fluid seals structure is established.By analyzing the magnetic field distribution of dual magnetic fluid seal,the optimal value ranges of important parameters,including parameters of the permanent magnetic ring,the magnetic pole tooth,the outer shaft,the outer shaft sleeve and the axial relative position of two permanent magnetic rings,which affect the seal differential pressure,are obtained.A wafer-handling robot equipped with coaxial twin-shaft magnetic fluid rotary seals and bellows seal is devised and an optimized twin-shaft magnetic fluid seals experimental platform is built.Test result shows that when the speed of the two rotational shafts ranges from 0-500 r/min,the maximum burst pressure is about 0.24 MPa.Magnetic fluid rotary seals can provide satisfactory performance in the application of wafer-handling robot.The proposed coaxial twin-shaft magnetic fluid rotary seal provides the instruction to design high-speed vacuum robot.展开更多
Core-shell nanofibers were prepared by coaxial electrospinning technology,with poly（ethylene oxide）（PEO） as the core while poly（acrylic acid）（PAA） as the shell.PEO and PAA can form polymer complexes based on h...Core-shell nanofibers were prepared by coaxial electrospinning technology,with poly（ethylene oxide）（PEO） as the core while poly（acrylic acid）（PAA） as the shell.PEO and PAA can form polymer complexes based on hydrogen bonding.In order to avoid forming strong hydrogen bonding complexes at nozzle and blocking spinning process,a polar aprotic solvent,N,N-dimethylformamide（DMF）,was selected to dissolve PEO and PAA respectively.SEM,TEM and DSC were utilized to characterize the morphology and structure of PEO-PAA core-shell nanofibers.FTIR spectra demonstrated that hydrogen bonding was formed at the core-shell interface.In addition,the PAA shell of the nanofibers can be cross-linked by ethylene glycol（EG） under heat treatment,which increases the stability and extends the potential applications in aqueous environment.展开更多
Vascular networks inside organs provide the means for metabolic exchange and adequate nutrition.Similarly,vascular or nutrient networks are needed when building tissue constructs>500μm in vitro due to the hydrogel...Vascular networks inside organs provide the means for metabolic exchange and adequate nutrition.Similarly,vascular or nutrient networks are needed when building tissue constructs>500μm in vitro due to the hydrogel compact pore size of bioinks.As the hydrogel used in bioinks is rather soft,it is a great challenge to reconstruct effective vascular networks.Recently,coaxial 3 D bioprinting was developed to print tissue constructs directly using hollow hydrogel fibers,which can be treated as built-in microchannels for nutrient delivery.Furthermore,vascular networks could be printed directly through coaxial 3 D bioprinting.This review summarizes recent advances in coaxial bioprinting for the fabrication of complex vascularized tissue constructs including methods,the effectiveness of varying strategies,and the use of sacrificial bioink.The limitations and challenges of coaxial 3 D bioprinting are also summarized.展开更多
The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including...The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State(VRS)area was performed.The calculations were carried out under the condition of variable blade pitch angle values providing a fixed timeaverage thrust value.Visualization data of free vortex wake shapes,flow structures,and velocity fields were obtained and analyzed.The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed.The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations,growth of rotor power consumption relative to the hover,growth of rotor induced velocities relative to the hover,and growth of the required rotor blade pitch angles values.The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.展开更多
Aiming at the position and attitude tracking of coaxial rotor aircraft(CRA),this paper proposes a combinatorial control method of sliding mode control(SMC)coupled with proportional-integralderivative control(PIDC).Con...Aiming at the position and attitude tracking of coaxial rotor aircraft(CRA),this paper proposes a combinatorial control method of sliding mode control(SMC)coupled with proportional-integralderivative control(PIDC).Considering the complete description of flight dynamics,aerodynamics and airflow interference,the dynamical model of CRA is established.The dynamical model is simplified according to the actual flight,then the simplified dynamical model is divided into two subsystems:a fully-actuated subsystem and an under-actuated subsystem.The controller of the fully-actuated subsystem consists of a SMC controller coupled with a rate bounded PIDC controller,while the controller of the under-actuated subsystem is composed of a SMC controller.The sliding manifold is defined by combining the position and velocity tracking errors of the state variables for each subsystem.Lyapunov stability theory is used to verify the stability of the sliding mode controller,which ensures that all state trajectories of the system can reach and stay on the sliding mode surface,the uncertainty and external interference of the model are compensated.Simulation and experiment compared with the conventional PIDC are carried out,the results demonstrate the effectiveness and the robustness of the proposed control method of this paper.展开更多
基金support from the National Natural Science Foundation of China(No.12002386).
文摘Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.
基金Supported by the National Natural Science Foundation of China(U23A20487)the National Key R&D Program of China(2022YFB3206000)+1 种基金Dr.Li Dak Sum&Yip Yio Chin Development Fund for Regenerative Medicine,Zhejiang Universitythe National Natural Science Foundation of China(61975172).
文摘Fluorescence imaging in the second near-infrared window(NIR-II,900-1880 nm)offers high signalto-background ratio(SBR),enhanced definition,and superior tissue penetration,making it ideal for real-time surgical navigation.However,with single-channel imaging,surgeons must frequently switch between the surgi⁃cal field and the NIR-II images on the monitor.To address this,a coaxial dual-channel imaging system that com⁃bines visible light and 1100 nm longpass(1100LP)fluorescence was developed.The system features a custom⁃ized coaxial dual-channel lens with optimized distortion,achieving precise alignment with an error of less than±0.15 mm.Additionally,the shared focusing mechanism simplifies operation.Using FDA-approved indocya⁃nine green(ICG),the system was successfully applied in dual-channel guided rat lymph node excision,and blood supply assessment of reconstructed human flap.This approach enhances surgical precision,improves opera⁃tional efficiency,and provides a valuable reference for further clinical translation of NIR-II fluorescence imaging.
基金funded by the National Natural Science Foundation of China(No.52105060)the Special Transmission Project,China(No.KY-1044-2023-0458)。
文摘To reduce the vibration of the Coaxial Helicopter Main Transmission System(CHMTS)considering both level and vertical flight conditions,a vibration evaluation and optimization model for the CHMTS was built.The vibration simulation model of the CHMTS was set up by gear dynamics theory and loaded contact analysis.For better evaluation of the system vibration,a vibration evaluation method for the CHMTS was established by the G1 method-variation coefficient method.A hybrid Gravitational Search Algorithm-Simulated Annealing(GSA-SA)algorithm was combined to balance convergence speed and searching accuracy.The principle test was conducted to prove the accuracy of theoretical method,in which the maximum relative error is16.26%.The optional results show that the vibration of the optimized transmission system decreases significantly,in which the maximum reduction of key vibration indicators reaches more than 20%.The theoretical results have been compared to the experiment to verify the effectiveness of the vibration optimization method.The proposed method could be extended to other fields.
文摘In this paper,we present a novel approach to study the electrical properties of intact rock by combining impedance and vector network analyzer measurements in the frequency range from 5 Hz to 3 GHz.For the firsttime,this study enables electrical characterization of the exact same rock sample over nine orders of magnitude in frequency range,utilizing a coaxial cell apparatus with specificallyprepared rock samples.Three types of rocks(basalt,sandstone and granite)with low to intermediate porosity(12.24%,16.9%and 7.49%,respectively)were characterized at varying saturation levels.The relaxation behavior of the samples was quantifiedusing an advanced phenomenological model incorporating both the dielectric constant and electrical conductivity in the form of Debye and Cole-Cole representations.Across the frequency range,three distinct relaxation processes were identified:a high-frequency water process and two interfacial processes related to interactions between the aqueous pore solution and mineral particles(membrane relaxation and Maxwell-Wagner effects).Additionally,an apparent direct current conductivity was observed.This comprehensive broadband analysis represents a further step toward the in situ characterization of rocks using electromagnetic fieldmeasurement methods and demonstrates advancements in both methodology and understanding of rock properties compared to existing studies.
基金funded by the National Key R&D Program of China,Grant No.2024YFF0504904.
文摘The packaging quality of coaxial laser diodes(CLDs)plays a pivotal role in determining their optical performance and long-term reliability.As the core packaging process,high-precision laser welding requires precise control of process parameters to suppress optical power loss.However,the complex nonlinear relationship between welding parameters and optical power loss renders traditional trial-and-error methods inefficient and imprecise.To address this challenge,a physics-informed(PI)and data-driven collaboration approach for welding parameter optimization is proposed.First,thermal-fluid-solid coupling finite element method(FEM)was employed to quantify the sensitivity of welding parameters to physical characteristics,including residual stress.This analysis facilitated the identification of critical factors contributing to optical power loss.Subsequently,a Gaussian process regression(GPR)model incorporating finite element simulation prior knowledge was constructed based on the selected features.By introducing physics-informed kernel(PIK)functions,stress distribution patterns were embedded into the prediction model,achieving high-precision optical power loss prediction.Finally,a Bayesian optimization(BO)algorithm with an adaptive sampling strategy was implemented for efficient parameter space exploration.Experimental results demonstrate that the proposedmethod effectively establishes explicit physical correlations between welding parameters and optical power loss.The optimized welding parameters reduced optical power loss by 34.1%,providing theoretical guidance and technical support for reliable CLD packaging.
基金Postdoctoral Fellowship Program of CPSF(GZC20232672)CAS Project for Young Scientists in Basic Research(YSBR-028)the Strategic Priority Research Program(XDA29010200)are gratefully acknowledged.
文摘To optimize secondary air nozzle structure in purifying burner,this study focused on the comparison of purification,combustion and NO_(x)emission characteristics of pulverized coal preheated by a 30 kW purifying burner with coaxial and centrosymmetric structures.Centrosymmetric structure shifted the position of main burning region down in high-temperature reduction unit(HTRU),and the number of branches differently influenced the temperature in different regions with this structure.For reductive gas components,CO concentration with centrosymmetric structure was higher compared to coaxial structure,while the differences in H_(2)and CH_(4)concentrations were smaller.Centrosymmetric structure was more disadvantageous to improve physicochemical properties of pulverized coal compared to coaxial structure,and this structure with four branches further deteriorated its properties compared to two branches.In mild combustion unit(MCU),the temperature at top was lower with centrosymmetric structure,while was higher in the rest.Centrosymmetric structure more effectively reduced NO_(x)emission compared to coaxial structure,but with slight sacrifice of combustion efficiency(η).Moreover,both two-branch and four-branch centrosymmetric structures realized ultra-low NO_(x)emission(<50 mg·m^(-3))with high η of over 98.50%,and the former was more advantageous.With this optimal structure,η and NO_(x)emission were 99.25%and 40.42 mg·m^(-3).
基金financially supported by the National Natural Science Foundation of China(Nos.22302133 and 22405161)Central Guidance on Local Science and Technology Development Fund of Hebei Province,China(No.236Z4406G)+5 种基金the Natural Science Foundation of Hebei Education Department,China(No.BJ2025100)the Natural Science Foundation of Hebei Province,China(No.B2021210001)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2024D01A157)the Key R&D Plan of Karamay(No.2024zdyf0009)Karamay Innovation Environment Construction Plan(Innovative Talents)Project(No.2024hjcxrc0029)the Research Foundation of China University of Petroleum-Beijing at Karamay(No.XQZX20240023)
文摘Tin dioxide(SnO_(2))with a high theoretical specific capacity of 1494 mAh g^(-1)is a promising candidate anode material for lithium storage.However,the shortcomings of serious volume expansion and low conductivity limit its wide application.Herein,coaxial nano-multilayered C/SnO_(2)/TiO_(2)composites were fabricated via layerby-layer self-assembly of TiO_(2)and SnO_(2)-gel layers on the natural cellulose filter paper,followed by thermal treatment under a nitrogen atmosphere.Through engineering design of the assembly process,the optimal C/SinO_(2)/TiO_(2)composite features five alternating SnO_(2)and TiO_(2)nanolayers,with TiO_(2)as the outside shell(denoted as C/TSTST).This unique structure endows the C/TSTST with excellent structural stability and electrochemical kinetics,making it a high-performance anode for lithium-ion batteries(LIBs).The C/TSTST composite delivers a high reversible capacity of 676 mAh g^(-1)at 0.1 A g^(-1)after 200 cycles and retains a capacity of 504 mAh g^(-1)at 1.0 A g^(-1),which can be recovered to 781 mAh g^(-1)at 0.1 A g^(-1)The significantly enhanced electrochemical performance is attributed to the hierarchical hybrid structure,where the carbon core combined with coaxial TiO_(2)nanolayers serves as a structural scaffold,ameliorating volume change of SnO_(2)while creating abundant interfacial defects for enhanced lithium storage and rapid charge transport.These findings are further demonstrated by the density functional theory(DFT)calculations.This work provides an efficient strategy for designing coaxial nano-multilayered transition metal oxide-related electrode materials,offering new insights into high-performance LIBs anodes.
文摘Focusing on aerodynamic characteristics of rigid coaxial rotor of a high-speed helicopter in hover and forward flight, a wind tunnel test is conducted in the 8 m ? 6 m low-speed straightflow wind tunnel of China Aerodynamics Research and Development Center. In the experiment,a 4 m diameter composite model rigid coaxial rotor is designed and manufactured, and firstorder flapping frequency ratio of the blade is 1.796 to ensure sufficient stiffness at the blade root.Rotor aerodynamic performance is measured under hovering and high advance ratio conditions.Also, the numerical method is used to calculate aerodynamic characteristics in typical states of the rigid coaxial rotor for analysis purpose. The rotor lift-drag ratio and lateral lift offset in the experiment are emphatically analyzed for the rigid coaxial rotor. The results indicate that in forward flight condition, the rotor lift-drag ratio first increases and then decreases with the increment of advance ratio and lift offset. When advance ratio remains constant, with the increment of lift offset, the lift-drag ratio of rigid coaxial rotor first increases and then decreases.
基金China Postdoctoral Science Foundation (20100481368)National Key Laboratory Foundation of China
文摘Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions of China, the program of China Scholarships Council (No. 201706830016)the National Natural Science Foundation of China (No. 11672128)
文摘The coaxial compound helicopter has two possible strategies for heading control: collective differential and rudder deflection. A flight dynamics model is developed to assess the effect of different heading control strategies. This includes the trim characteristics, steady flight performance,controllability, and manoeuvrability. The trim study demonstrates that heading control strategies are less influential on trim results, and the steady flight performance is also not significantly affected by the heading control strategy adopted. The controllability analysis shows although heading bandwidth and phase delay results at various speeds with different heading control strategies are all satisfied, the control derivative of the collective differential decreases as speed increases, and its heading aggressive agility is degraded into Level 3 in high-speed flight. In addition, using collective differential would lead to severe heading-rolling coupling as forward speed increases. On the contrary, the control derivative and aggressive agility of the rudder deflection is improved with forward speed, and there is no evidence of heading-rolling coupling. Finally, the transient turn MissionTask-Element(MTE) is utilized to investigate the heading manoeuvre characteristics in different heading control strategies, which indicates that the collective differential would add the amplitude of control input and the power consumption during this MTE.
基金financially supported by the MOS of China (No. 2017YFB0703300)the National Natural Science Foundation ofChina (No. 51673117)the Science and Technology Innovation Commission of Shenzhen (Nos. JSGG20160226201833790, JCYJ20150625102750478)
文摘Polystyrene(PS) fibers with core-shell structures were fabricated by coaxial electrostatic spinning,[10_TD$IF]in which there are liquid epoxy or curing agent as the core and PS as the shell. Scanning electron microscopy(SEM), Fourier transform infrared(FTIR) spectra and optical microscope were utilized for charactering the morphology and composition of the fibers. Composite coatings embedded with the healant-loaded coreshell fibers have been prepared and the self-healing of the scratch on the coatings has been revealed.
基金supported by National Natural Science Foundation of China(Nos.51777091 and 51677083)
文摘A coaxial dielectric barrier discharge（DBD） reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond（ns）pulse to generate atmospheric pressure plasma. The comparative study on the discharge characteristics of the discharge uniformity, power deposition, energy efficiency, and operation temperature between AC and ns pulsed coaxial DBD is carried out in terms of optical and electrical characteristics and operation temperature for optimizing the coaxial DBD reactor performance. The voltages across the air gap and dielectric layer and the conduction and displacement currents are extracted from the applied voltages and measured currents of AC and ns pulsed coaxial DBDs for the calculation of the power depositions and energy efficiencies through an equivalent electrical model. The discharge uniformity and operating temperature of the coaxial DBD reactor are monitored and analyzed by optical images and infrared camera. A heat conduction model is used to calculate the temperature of the internal quartz tube. It is found that the ns pulsed coaxial DBD has a much higher instantaneous power deposition in plasma, a lower total power consumption, and a higher energy efficiency compared with that excited by AC power and is more homogeneous and stable. The temperature of the outside wall of the AC and ns pulse excited coaxial DBD reaches 158 ℃ and 64.3 ℃ after 900 s operation, respectively.The experimental results on the comparison of the discharge characteristics of coaxial DBDs excited by different powers are significant for understanding of the mechanism of DBDs,reducing energy loss, and optimizing the performance of coaxial DBD in industrial applications.
基金This work was financially supported by the Opening Project of National Local Joint Laboratory for Advanced Textile Processing and Clean Production(FX2022006)Guiding Project of Natural Science Foundation of Hubei province(2022CFC072)+2 种基金Guiding Project of Scientific Research Plan of Education Department of Hubei Province(B2022081)Shenghong Key Scientific Research Project of Emergency Support and Public Safety Fiber Materials and Products(2022-rw0101)Science and Technology Guidance Program of China National Textile and Apparel Council(2022002).
文摘Firefighting protective clothing is a crucial protective equipment for firefighters to minimize skin burn and ensure safety firefighting operation and rescue mission.A recent increasing concern is to develop self-powered fire warning materials that can be incorporated into the firefighting clothing to achieve active fire protection for firefighters before the protective clothing catches fire on fireground.However,it is still a challenge to facilely design and manufacture thermoelectric(TE)textile(TET)-based fire warning electronics with dynamic surface conformability and breathability.Here,we develop an alternate coaxial wet-spinning strategy to continuously produce alternating p/n-type TE aerogel fibers involving n-type Ti_(3)C_(2)T_(x)MXene and p-type MXene/SWCNT-COOH as core materials,and tough aramid nanofiber as protective shell,which simultaneously ensure the flexibility and high-efficiency TE power generation.With such alternating p/n-type TE fibers,TET-based self-powered fire warning sensors with high mechanical stability and wearability are successfully fabricated through stitching the alternating p-n segment TE fibers into aramid fabric.The results indicate that TET-based fire warning electronics containing 50 p-n pairs produce the open-circuit voltage of 7.5 mV with a power density of 119.79 nW cm-2 at a temperature difference of 300℃.The output voltage signal is then calculated as corresponding surface temperature of firefighting clothing based on a linear relationship between TE voltage and temperature.The fire alarm response time and flame-retardant properties are further displayed.Such self-powered fire warning electronics are true textiles that offer breathability and compatibility with body movement,demonstrating their potential application in firefighting clothing.
基金Supported by Shanxi Provincial Health Department of Science and Technology Research Projects (No.201201019)
文摘AIM： To compare the changes in corneal biomechanics measured by ocular response analyzer （ORA） after 2.2-ram microincision cataract surgery and 3.0-mm standard coaxial phacoemulsification. METHODS： The prospective nonrandomized study comprised eyes with cataract that had 2.2-mm coaxial microincision or 3.0 -mm standard incision phacoemulsification. The corneal hysteresis （CH）, corneal resistance factor （CRF）, corneal-compensated intraocular pressure （IOPcc） and Goldmann-correlated intraocular pressure （IOPg） were measured by ORA preoperatively and at ld, 1-, 2-, 3- and 4-week postoperatively. Results were analyzed and compared between groups. RESULTS： In both groups, CH decreased in the immediate postoperative period （P〈0.05）, returned to the preoperative level at one week （P =0.249） in the 2.2-mm group, and at two weeks in the 3.0-mm group （P --0.264）; there was no significant change in CRF values. In 2.2-mm group, mean IOPcc and IOPg increased at ld postoperatively （both ,P〈0.05）, and returned to preoperative level at one week （,0 =0.491 and P =0.923, respectively）. In 3.0-mm group, mean IOPcc and IOPg increased at ld and lwk postoperatively （P =0.005 and ,P =0.029, respectively）, and returned to preoperative level at 2wk （P =0.347 and P =0.887, respectively）. CONCLUSION： Significant differences between preoperative and postoperative corneal biomechanical values were found for CH, IOPcc and IOPg. But the recovery time courses were different between the two groups. The 2.2-mm coaxial microincision cataract surgery group seemed recovery faster compared to the 3.0-mm standard coaxial phacoemulsification group.
基金the National Natural Science Foundation of China!10045001
文摘We present a coaxial detection of the backscattered electrons in SEM. The lens-aperture has been used to filter in energy and focus the backscattered electrons. This particular geometry allows us to eliminate the low energy backscattered electrons and collect the backscattered electrons, which are backscattered close to the incident beam orientation. The main advantage of this geometry is adapted to topographic contrast attenuation and atomic number contrast enhancement. Thus this new SEM is very suitable to analyze the material composition.
基金supported by National Natural Science Foundation of China (Grant No. 50675027)
文摘Compared with traditional mechanical seals,magnetic fluid seals have unique characters of high airtightness,minimal friction torque requirements,pollution-free and long life-span,widely used in vacuum robots.With the rapid development of Integrate Circuit（IC）,there is a stringent requirement for sealing wafer-handling robots when working in a vacuum environment.The parameters of magnetic fluid seals structure is very important in the vacuum robot design.This paper gives a magnetic fluid seal device for the robot.Firstly,the seal differential pressure formulas of magnetic fluid seal are deduced according to the theory of ferrohydrodynamics,which indicate that the magnetic field gradient in the sealing gap determines the seal capacity of magnetic fluid seal.Secondly,the magnetic analysis model of twin-shaft magnetic fluid seals structure is established.By analyzing the magnetic field distribution of dual magnetic fluid seal,the optimal value ranges of important parameters,including parameters of the permanent magnetic ring,the magnetic pole tooth,the outer shaft,the outer shaft sleeve and the axial relative position of two permanent magnetic rings,which affect the seal differential pressure,are obtained.A wafer-handling robot equipped with coaxial twin-shaft magnetic fluid rotary seals and bellows seal is devised and an optimized twin-shaft magnetic fluid seals experimental platform is built.Test result shows that when the speed of the two rotational shafts ranges from 0-500 r/min,the maximum burst pressure is about 0.24 MPa.Magnetic fluid rotary seals can provide satisfactory performance in the application of wafer-handling robot.The proposed coaxial twin-shaft magnetic fluid rotary seal provides the instruction to design high-speed vacuum robot.
基金financially supported by the National Natural Science Foundation of China(No.51373032)Science and Technology Commission of Shanghai Municipality(STCSM,No.16JC1400700)
文摘Core-shell nanofibers were prepared by coaxial electrospinning technology,with poly（ethylene oxide）（PEO） as the core while poly（acrylic acid）（PAA） as the shell.PEO and PAA can form polymer complexes based on hydrogen bonding.In order to avoid forming strong hydrogen bonding complexes at nozzle and blocking spinning process,a polar aprotic solvent,N,N-dimethylformamide（DMF）,was selected to dissolve PEO and PAA respectively.SEM,TEM and DSC were utilized to characterize the morphology and structure of PEO-PAA core-shell nanofibers.FTIR spectra demonstrated that hydrogen bonding was formed at the core-shell interface.In addition,the PAA shell of the nanofibers can be cross-linked by ethylene glycol（EG） under heat treatment,which increases the stability and extends the potential applications in aqueous environment.
基金the National Key Research and Development Program of China(No.2018YFA0703000)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(No.51521064)。
文摘Vascular networks inside organs provide the means for metabolic exchange and adequate nutrition.Similarly,vascular or nutrient networks are needed when building tissue constructs>500μm in vitro due to the hydrogel compact pore size of bioinks.As the hydrogel used in bioinks is rather soft,it is a great challenge to reconstruct effective vascular networks.Recently,coaxial 3 D bioprinting was developed to print tissue constructs directly using hollow hydrogel fibers,which can be treated as built-in microchannels for nutrient delivery.Furthermore,vascular networks could be printed directly through coaxial 3 D bioprinting.This review summarizes recent advances in coaxial bioprinting for the fabrication of complex vascularized tissue constructs including methods,the effectiveness of varying strategies,and the use of sacrificial bioink.The limitations and challenges of coaxial 3 D bioprinting are also summarized.
文摘The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State(VRS)area was performed.The calculations were carried out under the condition of variable blade pitch angle values providing a fixed timeaverage thrust value.Visualization data of free vortex wake shapes,flow structures,and velocity fields were obtained and analyzed.The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed.The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations,growth of rotor power consumption relative to the hover,growth of rotor induced velocities relative to the hover,and growth of the required rotor blade pitch angles values.The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.
基金supported by National Natural Science Founda-tion of china(Grant No.51774042).
文摘Aiming at the position and attitude tracking of coaxial rotor aircraft(CRA),this paper proposes a combinatorial control method of sliding mode control(SMC)coupled with proportional-integralderivative control(PIDC).Considering the complete description of flight dynamics,aerodynamics and airflow interference,the dynamical model of CRA is established.The dynamical model is simplified according to the actual flight,then the simplified dynamical model is divided into two subsystems:a fully-actuated subsystem and an under-actuated subsystem.The controller of the fully-actuated subsystem consists of a SMC controller coupled with a rate bounded PIDC controller,while the controller of the under-actuated subsystem is composed of a SMC controller.The sliding manifold is defined by combining the position and velocity tracking errors of the state variables for each subsystem.Lyapunov stability theory is used to verify the stability of the sliding mode controller,which ensures that all state trajectories of the system can reach and stay on the sliding mode surface,the uncertainty and external interference of the model are compensated.Simulation and experiment compared with the conventional PIDC are carried out,the results demonstrate the effectiveness and the robustness of the proposed control method of this paper.
