The bisolute sorption and thermodynamic behavior of organic pollutants on low temperature biochars (LTB) at 300 °C and high temperature biochars (HTB) at 700 °C were determined to elucidate sorptive properties of biochar changed with pyrolytic temperatures. The structural characteristics and isotherms shape of the biochar were more dependent on the pyrolytic temperature than on the biomass feedstocks, which included orange peel, pine needle, and sugar cane bagasse. For LTB, the thermally altered organic matter colocalized with the carbonized matter, and the visible fine pores of the fixed carbons were plugged by the remaining volatile carbon. For HTB, most of the volatile matter was gone and the fixed matter was composed of fully carbonized adsorptive sites. Monolayer adsorption of 1-naphthol to HTB was dominant but was suppressed by phenol. In comparison, LTB displayed exceptional sorption behavior where partition and adsorption were concurrently promoted by a cosolute and elevated temperature. In addition to monolayer surface coverage, pore-filling mechanisms may contribute to the increase of adsorption fraction. Moreover, the entropy gain was a dominant force driving the partition and adsorption processes in LTB. Thus, the colocalizing partition phase and adsorptive sites in LTB are proposed to be in interencased states rather than in physical separation.
Two-dimensional arrays are required to generate 3-D acoustic images in both near-field and far-field regions. However, almost all of the sparse methods, which decrease the number of elements, only synthesize the 2-D sparse arrays in far-field conditions. In this paper, a novel method is proposed for optimizing sparse array in both near-field and far-field conditions that improving the sparseness of the optimized array. First, a new energy function is proposed and successfully synthesizes sparse arrays in both near-field and far-field conditions. The simplified form of the new energy function is then presented for cutting down computational load during optimization process. Second, the nongrid sparse array technology, which connotes irregular element positioning, is introduced into the simulated annealing algorithm to extensively reduce the number of active elements. Finally, the optimized method is demonstrated through designing a cross array with 100 + 100 elements. The results show notable improvements on the array characteristics in random working distances over those reported in the literature.
Congruent coordinate transformations are used to convert second-order models to a form in which the mass, damping, and stiffness matrices can be interpreted as a passive mechanical system. For those systems which can be constructed from interconnected mass, stiffness, and damping elements, it is shown that the input–output preserving transformations can be parametrized by an orthogonal matrix whose dimension corresponds to the number of internal masses—those masses at which an input is not applied nor an output measured. Only a subset of these transformations results in mechanically realizable models. For models with a small number of internal masses, complete discrete mapping of the transformation space is possible, permitting enumeration of all mechanically realizable models sharing the original model’s input–output behavior. When the number of internal masses is large, a nonlinear search of transformation space can be employed to identify mechanically realizable models. Applications include scale model vibration testing of complicated structures and the design of electromechanical filters.
In this paper, we proposed a miniature quadrupedal piezoelectric robot with a mass of 1.8 g and a body length of 4.6 cm. The robot adopts a novel spatial parallel mechanism as its transmission. Each leg of the robot has two degrees of freedom (DOFs): swing and lift. The trajectory necessary for walking is achieved by the appropriate phasing of these two DOFs. A new manufacturing method for piezoelectric actuators was developed. During the stacking process, discrete patterned PZT pieces are used to avoid dielectric failure caused by laser cutting. Copper-clad FR-4 is used as the solder pad instead of copper foil, making the connection between the pad and the actuator more reliable. The lift powertrain of the robot was modeled and the link length of the powertrain was optimized based on the model. The maximum output force of each leg can reach 26 mN under optimized design parameters, which is 1.38 times the required force for successful walking. The frequency response of the powertrain was measured and fitted to the second-order system, which enabled increased leg amplitudes near the powertrain resonance of approximately 70 Hz with adjusted drive signals. The maximum speed of the robot without load reached 48.66 cm/s (10.58 body lengths per second) and the payload capacity can reach 5.5 g (3.05 times its mass) near the powertrain resonance.
Human observation of the ocean has gradually evolved from the sea surface to systematic monitoring and sampling through seafloor observation networks, and constant current power supply has become the main power supply method for seafloor observation networks due to its high reliability. There are some studies on current source to voltage source converters, but there are few studies on current source to current source (CS/CS) converters, which affects the expansion of power supply networks for seafloor observation networks. In this paper, by employing input current sharing and output voltage doubling circuits, an active clamp dual-inductor isolated CS/CS converter which uses a single-stage conversion circuit to realize constant current source conversion with a wide output voltage range is proposed. Active clamp technology at the primary side of the proposed circuit is employed to recover energy stored in leakage inductance, suppress voltage spikes of the primary side switches, and achieve zero-voltage switching of the primary side switches. The secondary side’s output voltage doubling circuit resonates with transformer leakage inductance to achieve zero-current switching of the secondary side diodes, which can reduce losses and enhance efficiency. The operating principles of the proposed circuit are analyzed in detail, and the characteristic and parameter design analysis, including current conversion ratio, transformer turn ratio, power inductors, and resonant capacitors and inductor, are presented. Finally, the experimental results based on a 100 W experimental prototype validate the feasibility of the proposed converter.
When fluid stratification is induced by the vertical gradients of two scalars with different diffusivities, double-diffusive convection (DDC) may occur and play a crucial role in mixing. Such a process exists in many natural and engineering environments. Especially in the ocean, DDC is omnipresent since the seawater density is affected by temperature and salinity. The most intriguing phenomenon caused by DDC is the thermohaline staircase, i.e., a stack of alternating well-mixed convection layers and sharp interfaces with very large gradients in both temperature and salinity. Here we investigate DDC and thermohaline staircases in the salt finger regime, which happens when warm saltier water lies above cold fresher water and is commonly observed in the (sub)tropic regions. By conducting direct numerical simulations over a large range of parameters, we reveal that multiple equilibrium states exist in fingering DDC and staircases even for the same control parameters. Different states can be established from different initial scalar distributions or different evolution histories of the flow parameters. Hysteresis appears during the transition from a staircase to a single salt finger interface. For the same local density ratio, salt finger interfaces in the single-layer state generate very different fluxes compared to those within staircases. However, the salinity flux for all salt finger interfaces follows the same dependence on the salinity Rayleigh number of the layer and can be described by an effective power law scaling. Our findings have direct applications to oceanic thermohaline staircases.
micro-gyroscope inertial devices have a wide range of development and application,with the rapid development of technology of micro electro mechanical systems,in which micro-fluid gyroscope with small size,light weight,low cost,high impact resistance and other unique advantages.According to the different principles,several typical micro-fluid gyroscope are introduced,including gas convection micro-gyroscope,jet micro-gyroscope,ECF micro-fluid and super-fluid gyroscope,in which gas convection micro-gyroscope and jet micro-gyroscope are common type fluid gyroscope and ECF micro-fluid and super-fluid gyroscope are new type fluid gyroscope.The theory,application and application prospect are analysed.Micro-fluid gyroscope will play a more and more important role in the areas of inertial navigation,automatic control and some others.
The errors of structural parameters are the important sources causing the errors in the construction control process of cable-stayed bridge.To analyze the sensitivity of influences of various structural design parameters on the completion status of the long span composite girder cable-stayed bridge,the Guanyinyan Changjiang River Bridge in Jiangjin was cited as an example,the finite element method was used to calculate the influence of each parameter on the geometric shape and stress of the main girder of the completion status of the bridge.The results of the calculation reveal that the weight of the main girder,fabricated length of the stay cables,weight of the deck plates and temperature differences have significant influences on the geometric shape and stress,however,the influence of elastic modulus of the deck plates and main girder on the completion status of the bridge is not great.
In order to design a high-performance piezoelectric bimorph actuator for flapping-wing micro aerial vehicle,this paper synthesized orthogonal experiment and finite element direct coupled-field analysis simulation to optimize the actuator's structure and geometric parameters.Different experimental schemes were achieved based on the orthogonal table.Through range analysis of the simulation results,the relative importance of factors influencing this actuator's bending angle index was determined.Subsequently,the optimal scheme which can enhance the actuator's performance was obtained.The simulation results show that the proposed method can increase the stroke angle significantly,which satisfies the design requirements of the flapping wing biomimetic MAV.
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