Showing papers in "Science China-technological Sciences in 2014"

Dynamics of electric activities in neuron and neurons of network induced by autapses

Abstract: The effect of autapse on adjusting the membrane of potentials of neuron is described by imposing a time-delayed feedback on the membrane of neuron in a close loop type, and the Hindmarsh-Rose (HR) neuron under autapse is investigated. Firstly, the electric activity of single HR neuron under electric autapse and chemical autapse is investigated. It is found that quiescent neuron is activated due to appropriate time delay and feedback gain in the autapse, and the autapse plays an important role in waking up neuron. The parameter region for periodic, chaotic activity of neuron under autapse is calculated in a numerical way, and transition from spiking to bursting is observed by increasing the feedback gain and time delay carefully. Furthermore, the collective electric activities of neurons in a ring network is investigated and abundant electric activities are observed due to the competition between the autapse and the time-delayed coupling between adjacent neurons in the network, and time delay in coupling between neurons also plays an important role in enhancing synchronization in the network.

A design method and numerical study for a new type parabolic trough solar collector with uniform solar flux distribution

Abstract: The non-uniform concentrated solar flux distribution on the outer surface of the absorber tube can lead to large circumferential temperature difference and high local temperature of the absorber tube wall, which is one of the primary causes of parabolic trough solar receiver (PTR) failures. In this paper, a secondary reflector used as a homogenizing reflector (HR) in a conventional parabolic trough solar collector (PTSC) was recommended to homogenize the solar flux distribution and thus increase the reliability of the PTR. The design method of this new type PTSC with a HR was also proposed. Meanwhile, the concentrated solar flux distribution was calculated by adopting the Monte Carlo ray-trace (MCRT) method. Then, the coupled heat transfer process within the PTR was simulated by treating the solar flux calculated by the MCRT method as the heat flux boundary condition for the finite volume method model. The solar flux distribution on the outer surface of the absorber tube, the temperature field of the absorber tube wall, and the collector efficiency were analyzed in detail. It was revealed that the absorber tube could almost be heated uniformly in the PTSC with a HR. As a result, the circumferential temperature difference and the maximum temperature could be reduced significantly, while the efficiency tended to decrease slightly due to the inevitably increased optical loss. Under the conditions studied in this paper, although the collector efficiency decreased by about 4%, the circumferential temperature difference was reduced from about 25 to 3 K and the maximum temperature was reduced from 667 to 661 K.

Liquid phase 3D printing for quickly manufacturing conductive metal objects with low melting point alloy ink

Abstract: Conventional 3D metal printings are generally time-consuming as well as lacking of high performance printable inks. From an alternative way, here we proposed the method of liquid phase 3D printing for quickly making conductive metal objects. Through introducing metal alloys whose melting point is slightly above room temperature as printing inks, several representative structures spanning from one, two and three dimension to more complex patterns were demonstrated to be quickly fabricated. Compared with the air-cooling in a conventional 3D printing, the liquid-phase-manufacturing offers a much higher cooling rate and thus significantly improves the speed in fabricating the target metal objects. This unique strategy also efficiently prevents the liquid metal inks from air oxidation, which is hard to avoid otherwise in an ordinary 3D printing. The key physical factors (such as properties of the cooling fluid, air pressure within the syringe barrel and needle diameter, types and properties of the printing ink) and several interesting intermediate fluids interaction phenomena between liquid metal and conventional cooling fluids such as water or ethanol, which evidently affecting the printing quality, were disclosed. In addition, a basic route to make future liquid phase 3D printer incorporated with both syringe pump and needle arrays was also suggested. The liquid phase 3D printing, which owns potential values not available in a conventional method, opens an efficient way for quickly making conductive metal objects in the coming time.

Effects of grain size on phase transition behavior of nanocrystalline shape memory alloys

Abstract: We report recent advances in the experimental and theoretical study of grain size (GS) effects on the thermal and mechanical properties of nanostructured NiTi polycrystalline shape memory alloy (SMA). It is shown that when GS < 60 nm, the superelastic stress-strain hysteresis loop area (H) of the polycrystal decreases rapidly with GS and tends to vanish as GS approaches 10 nanometers. At the same time, the temperature dependence of the transition stress also decreases with GS and eventually approaches zero, leading to a wide superelastic temperature window and breakdown of the Clausius-Claperyon relationship. Rate dependence of the stress-strain responses is significantly reduced and the cyclic stability of the material is improved by the nanocrystallization. It is proposed that the emergence of such significant changes in the behavior of the material with GS reduction originate from the large increase in the area-to-volume ratios of the nanometer-thick interfaces (grain boundary and Austenite-Martensite (A-M) interface) in the polycrystal. In particular, with GS reduction, interfacial energy terms will gradually become dominant over the bulk energy of the crystallite, eventually bring fundamental changes in the phase transition responses of the material. Modelling strategy leading to the establishment of quantitative relationships among GS, grain boundary, A-M interfaces and the macroscopic responses of the material are outlined. grain size effects, phase transition behavior, grain boundary and austenite-martensite (A-M) interface, nanocrystalline NiTi shape memory alloys

Meso-damage cracking characteristics analysis for rock and soil aggregate with CT test

Abstract: The aim of this paper is to investigate the damage cracking characteristics of rock and soil aggregate (RSA) by X-ray computed tomography (CT) under uniaxial compressive loading. The mean CT value for the region of interest (ROI) is used to analyze the cracking characteristics. Also, the mathematical morphology method based on the image threshold segmentation is used to obtain characteristic parameters of cracks to describe the cracking evolution of RSA. Results show that the elastic mismatch between rock blocks and soil matrix is the primary reason for RSA cracking. The mean CT value for the RSA specimen, rock block inclusions, and their adjacent soil regions decreases with the increasing stress level. However, it is more sensitive for block inclusions than soil regions. Using the image segmentation method, length, area and mean width of cracks obey to power function distribution. Crack statistical characteristics are closely related to the rock block’s distribution and morphology. These results may be useful to reveal the mesoscopic cracking mechanism, establish meso-damage evolution equation, and constitutive relation for RSA.

Progress in optimization of mass transfer processes based on mass entransy dissipation extremum principle

Abstract: The mass entransy and its dissipation extremum principle have opened up a new direction for the mass transfer optimization. Firstly, the emergence and development process of both the mass entransy and its dissipation extremum principle are reviewed. Secondly, the combination of the mass entransy dissipation extremum principle and the finite-time thermodynamics for optimizing the mass transfer processes of one-way isothermal mass transfer, two-way isothermal equimolar mass transfer, and isothermal throttling and isothermal crystallization are summarized. Thirdly, the combination of the mass entransy dissipation extremum principle and the constructal theory for optimizing the mass transfer processes of disc-to-point and volume-to-point problems are summarized. The scientific features of the mass entransy dissipation extremum principle are emphasized.

Bifurcation analysis for Hindmarsh-Rose neuronal model with time-delayed feedback control and application to chaos control

Abstract: This paper is concerned with bifurcations and chaos control of the Hindmarsh-Rose (HR) neuronal model with the time-delayed feedback control. By stability and bifurcation analysis, we find that the excitable neuron can emit spikes via the subcritical Hopf bifurcation, and exhibits periodic or chaotic spiking/bursting behaviors with the increase of external current. For the purpose of control of chaos, we adopt the time-delayed feedback control, and convert chaos control to the Hopf bifurcation of the delayed feedback system. Then the analytical conditions under which the Hopf bifurcation occurs are given with an explicit formula. Based on this, we show the Hopf bifurcation curves in the two-parameter plane. Finally, some numerical simulations are carried out to support the theoretical results. It is shown that by appropriate choice of feedback gain and time delay, the chaotic orbit can be controlled to be stable. The adopted method in this paper is general and can be applied to other neuronal models. It may help us better understand the bifurcation mechanisms of neural behaviors.

Compatible hybrid 3D printing of metal and nonmetal inks for direct manufacture of end functional devices

Abstract: The currently available 3D printing still cannot simultaneously deal with the metal and nonmetal inks together due to their huge difference in the melting points and poor compatible printability between each other. Here through introducing the low melting point alloy Bi35In48.6Sn16Zn0.4 and silicone rubber as functional inks, we proposed a compatible hybrid 3D printing method for manufacturing the desired device, the supporting substrate and the allied package structure together. The principle of pneumatic-typed 3D printing of multiple inks was described and typical physical properties of the ink Bi35In48.6Sn16Zn0.4 were measured. Several key factors dominating the printing quality such as the temperature of the printing head, the air pressure exerted upon the liquid metal ink in the syringe, the moving velocity and the height of the printing head etc. were clarified. A general way of directly printing out 3D structured electronic devices consisting of both metal and nonmetal materials was demonstrated. Such hybrid objects were patterned and formed up layer by layer with Bi35In48.6Sn16Zn0.4 alloy and silicone rubber which would become solidified after standing for a period of time under room temperature. To illustrate the compatible printability of these printing inks, a three-layer tricolor LED stereo circuit with controlled lighting capability was further manufactured and evaluated. The present study opens an important hybrid 3D printing way for directly manufacturing functional and structural end devices in an easy and low cost way.

Monthly discharge forecasting using wavelet neural networks with extreme learning machine

Abstract: Accurate and reliable hydrological forecasting is essential for water resource management. Feedforward neural networks can provide satisfactory forecast results in most cases, but traditional gradient-based training algorithms are usually time-consum- ing and may easily converge to local minimum. Hence, how to obtain more appropriate parameters for feedforward neural networks with more precise prediction within shorter time has been a challenging task. Extreme learning machine (ELM), a new training algorithm for single-hidden layer feedforward neural networks (SLFNs), has been proposed to avoid these disadvantages. In this study, a conjunction model of wavelet neural networks with ELM (WNN-ELM) is proposed for 1-month ahead discharge forecasting. The a trous wavelet transform is used to decompose the original discharge time series into several sub-series. The sub-series are then used as inputs for SLFNs coupled with ELM algorithm (SLFNs-ELM); the output is the next step observed discharge. For comparison, the SLFNs-ELM and support vector machine (SVM) are also employed. Monthly discharge time series data from two reservoirs in southwestern China are derived for validating the models. In addition, four quantitative standard statistical performance evaluation measures are utilized to evaluate the model performance. The results indicate that the SLFNs-ELM performs slightly better than the SVM for peak discharge estimation, and the proposed model WNN-ELM provides more accurate forecast precision than SLFNs-ELM and SVM.

Damage evolution and dynamic response of cement asphalt mortar layer of slab track under vehicle dynamic load

Abstract: The damage evolution and dynamic performance of a cement asphalt (CA) mortar layer of slab track subjected to vehicle dynamic load is investigated in this paper. Initially, a statistical damage constitutive model for the CA mortar layer is developed using continuous damage mechanics and probability theory. In this model, the strength of the CA mortar elements is treated as a random variable, which follows the Weibull distribution. The inclusion of strain rate dependence affords considering its influence on the damage development and the transition between viscosity and elasticity. Comparisons with experimental data support the reliability of the model. A three-dimensional finite element (FE) model of a slab track is then created with the commercial software ABAQUS, where the devised model for the CA mortar is implemented as a user-defined material subroutine. Finally, a vertical vehicle model is coupled with the FE model of the slab track, through the wheel-rail contact forces, based on the nonlinear Hertzian contact theory. The evolution of the damage and of the dynamic performance of the CA mortar layer with various initial damage is investigated under the train and track interaction. The analysis indicates that the proposed model is capable of predicting the damage evolution of the CA mortar layer exposed to vehicle dynamic load. The dynamic compressive strain, the strain rate, and the induced damage increase significantly with an increase in the initial damage, whereas the dynamic compressive stress exhibits a sharp decrease with the increasing initial damage. Also, it is found that the strain rate dependence significantly influences the damage evolution and the dynamic behavior of the CA mortar layer.

Equilibrium scour depth at offshore monopile foundation in combined waves and current

Abstract: Unlike the pier scour in bridge waterways, the local scour at offshore monopile foundations should take into account the effect of wave-current combination. Under the condition of wave-current coexistence, the water-soil interfacial scouring is usually coupled with the pore-pressure dynamics inside of the seabed. The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume. Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile. The concomitance of horseshoe vortex and local scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for scouring development under the combined waves and current. Based on similarity analyses, an average-velocity based Froude number ( Fr a) is proposed to correlate with the equilibrium scour depth ( S / D ) at offshore monopile foundation in the combined waves and current. An empirical expression for the correlation between S/D and Fr a is given for predicting equilibrium scour depth, which may provide a guide for offshore engineering practice.

Effects of channel blocks on the spiking regularity in clustered neuronal networks

Abstract: In this paper, we discuss the influences of channel blocks on the spiking regularity in a clustered neuronal network by applying stochastic Hodgkin-Huxley neuronal models as the building blocks. With the aid of simulation results, we reveal that the spiking regularity of the clustered neuronal network could be resonantly enhanced via fine-tuning of the non-blocked potassium channel fraction xK. While the non-blocked sodium channel fraction xNa can enhance the spiking regularity of the clustered neuronal network in most cases. These results indicate that not only sodium channel blocks but also potassium channel blocks could have great influences on the regularity of spike timings in the clustered neuronal networks. Considering the importance of spike timings in neuronal information transforming processes, our results may give some implications for understanding the nonnegligible role of randomness in ion channels in neuronal systems.

Application of DVA theory in vibration reduction of carbody with suspended equipment for high-speed EMU

Abstract: The theory of dynamic vibration absorber (DVA) was applied to restrain the vibration of carbody for high-speed electric multiple unit (EMU). The carbody was modeled as an Euler-Bernoulli beam with the equipment mounted on the chassis regarded as a DVA. Suspension parameters of the equipment were optimized based on the modal analysis of the beam and parameter optimization of the DVA. Vertical motion equations of the carbody and equipment were derived to study the effect of the suspension parameters on the vibration of carbody, which included the suspension frequency, damping ratio, mounting position and mass. Then a 3D rigid-flexible coupled vehicle system dynamics model was built to simulate the response of carbody and equipment to track excitation. The results show that the equipment mounted on the carbody chassis can be regarded as a DVA to reduce the flexible vibration of carbody, and the optimum suspension frequency can be calculated theoretically with the first-order vertical bending mode of carbody considered. Heavy equipment should be mounted to the carbody center as close as possible to obtain a significant vibration reduction, while light equipment has quite limited contribution to that. Also, a laboratory test was conducted on the full-scale test rig which shows a good agreement with the theoretical analysis and dynamic simulations. The faster the vehicle runs, the more significant are the advantages of the elastic suspension.

Pushover analysis of underground structures: Method and application

Abstract: Pushover analysis is common because of its conceptual simplicity and computational attractiveness in computing seismic demand. Considering that traditional pushover analysis is restricted in underground structures due to the stark differences in the seismic response characteristics of surface structures, this paper proposes a pushover analysis method for underground structures and its application in seismic damage assessment. First, three types of force distribution are presented based on ground response analysis. Next, the target displacements and analysis models are established according to force-based and performance-based design. Then, the pushover analysis procedure for underground structures is described. Next, the applicability of pushover analysis to underground structures is verified by comparing the responses of a Chongwenmen subway station determined by the proposed procedure and by nonlinear response history analysis. In addition, two other points are made: that the inverted triangular distribution of effective earthquake acceleration is more practical than the other two distributions, and that performance-based design is more effective than force-based design. Finally, a cyclic reversal loading pattern based on one cycle of reversal loads as an earthquake event is presented and applied to the seismic damage assessment of underground structures. The results show that the proposed pushover analysis can be effectively applied to the seismic design and damage assessment of underground structures.

Numerical study on flexural behaviors of steel reinforced engineered cementitious composite (ECC) and ECC/concrete composite beams

Abstract: Engineered cementitious composite (ECC) is a class of high performance cementitious composites with pseudo strain-hardening behavior and excellent crack control capacity. Substitution of concrete with ECC can largely reduce the cracking and durability problems associated with brittleness of concrete. In this paper, a simplified constitutive model of the ECC material was applied to simulate the flexural behaviors of the steel reinforced ECC and ECC/concrete composite beams with finite element method. The simulation results are found to be in good agreement with test results, indicating that the finite element model is reasonably accurate in simulating the flexural behaviors of the steel reinforced ECC flexural members. The effects of the ECC modulus, ECC tensile ductility, ECC thickness and ECC position on flexural behaviors in terms of ultimate moment, deflection and the maximum crack width of the steel reinforced ECC or ECC/concrete composite beam are hence evaluated.

A review of heavy-duty legged robots

Abstract: Heavy-duty legged robots have been regarded as one of the important developments in the field of legged robots because of their high payload-total mass ratio, terrain adaptability, and multitasking. The problems associated with the development and use of heavy-duty legged robots have motivated researchers to conduct many important studies, covering topics related to the mechanical structure, force distribution, control strategy, energy efficiency, etc. Overall, heavy-duty legged robots have three main characteristics: greater body masses, larger body sizes, and higher payload-total mass ratios. Thus, various heavy-duty legged robots and their performances are reviewed here. This review presents the current developments with regard to heavy-duty legged robots. Also, the main characteristics of high-performance heavy-duty legged robots are determined and conclusions are drawn. Furthermore, the current research of key techniques of heavy-duty legged robots, including the mechanical structure, force distribution, control method, and power source, is described. To assess the transportation capacity of heavy-duty legged robots, performance evaluation parameters are proposed. Finally, problems that need further research are addressed.

Design of single-axis flexure hinges using continuum topology optimization method

Abstract: The design of compliant hinges has been extensively studied in the size and shape level in the literature. This paper presents a method for designing the single-axis flexure hinges in the topology level. Two kinds of hinges, that is, the translational hinge and the revolute hinge, are studied. The basic optimization models are developed for topology optimization of the translational hinge and the revolute hinge, respectively. The objective for topology optimization of flexure hinges is to maximize the compliance in the desired direction meanwhile minimizing the compliances in the other directions. The constraints for accomplishing the translational and revolute requirements are developed. The popular Solid Isotropic Material with Penalization method is used to find the optimal flexure hinge topology within a given design domain. Numerical results are performed to illustrate the validity of the proposed method.

Stability switches and Bogdanov-Takens bifurcation in an inertial two-neuron coupling system with multiple delays

Abstract: In this paper, we investigate an inertial two-neural coupling system with multiple delays. We analyze the number of equilibrium points and demonstrate the corresponding pitchfork bifurcation. Results show that the system has a unique equilibrium as well as three equilibria for different values of coupling weights. The local asymptotic stability of the equilibrium point is studied using the corresponding characteristic equation. We find that multiple delays can induce the system to exhibit stable switching between the resting state and periodic motion. Stability regions with delay-dependence are exhibited in the parameter plane of the time delays employing the Hopf bifurcation curves. To obtain the global perspective of the system dynamics, stability and periodic activity involving multiple equilibria are investigated by analyzing the intersection points of the pitchfork and Hopf bifurcation curves, called the Bogdanov-Takens (BT) bifurcation. The homoclinic bifurcation and the fold bifurcation of limit cycle are obtained using the BT theoretical results of the third-order normal form. Finally, numerical simulations are provided to support the theoretical analyses.

A hybrid dynamic programming-rule based algorithm for real-time energy optimization of plug-in hybrid electric bus

Abstract: The optimization of the control strategy of a plug-in hybrid electric bus (PHEB) for the repeatedly driven bus route is a key technique to improve the fuel economy. The widely used rule-based (RB) control strategy is lacking in the global optimization property, while the global optimization algorithms have an unacceptable computation complexity for real-time application. Therefore, a novel hybrid dynamic programming-rule based (DPRB) algorithm is brought forward to solve the global energy optimization problem in a real-time controller of PHEB. Firstly, a control grid is built up for a given typical city bus route, according to the station locations and discrete levels of battery state of charge (SOC). Moreover, the decision variables for the energy optimization at each point of the control grid might be deduced from an off-line dynamic programming (DP) with the historical running information of the driving cycle. Meanwhile, the genetic algorithm (GA) is adopted to replace the quantization process of DP permissible control set to reduce the computation burden. Secondly, with the optimized decision variables as control parameters according to the position and battery SOC of a PHEB, a RB control is used as an implementable controller for the energy management. Simulation results demonstrate that the proposed DPRB might distribute electric energy more reasonably throughout the bus route, compared with the optimized RB. The proposed hybrid algorithm might give a practicable solution, which is a tradeoff between the applicability of RB and the global optimization property of DP.

Firing properties and synchronization rate in fractional-order Hindmarsh-Rose model neurons

Abstract: We find that the fractional-order Hindmarsh-Rose model neuron demonstrates various types of firing behavior as a function of the fractional order in this study. There exists a clear difference in the bifurcation diagram between the fractional-order Hindmarsh-Rose model and the corresponding integer-order model even though the neuron undergoes a Hopf bifurcation to oscillation and then starts a period-doubling cascade to chaos with the decrease of the externally applied current. Interestingly, the discharge frequency of the fractional-order Hindmarsh-Rose model neuron is greater than that of the integer-order counterpart irrespective of whether the neuron exhibits periodic or chaotic firing. Then we demonstrate that the firing behavior of the fractional-order Hindmarsh-Rose model neuron has a higher complexity than that of the integer-order counterpart. Also, the synchronization phenomenon is investigated in the network of two electrically coupled fractional-order model neurons. We show that the synchronization rate increases as the fractional order decreases.

Cold-temperature deformation of nano-sized tungsten and niobium as revealed by in-situ nano-mechanical experiments

Abstract: We constructed and developed an in-situ cryogenic nanomechanical system to study small-scale mechanical behavior of materials at low temperatures. Uniaxial compression of two body-centered-cubic (bcc) metals, Nb and W, with diameters between 400 and 1300 nm, was studied at room temperature and at 165 K. Experiments were conducted inside of a Scanning Electron Microscope (SEM) equipped with a nanomechanical module, with simultaneous cooling of sample and diamond tip. Stress-strain data at 165 K exhibited higher yield strengths and more extensive strain bursts on average, as compared to those at 298 K. We discuss these differences in the framework of nano-sized plasticity and intrinsic lattice resistance. Dislocation dynamics simulations with surface-controlled dislocation multiplication were used to gain insight into size and temperature effects on deformation of nano-sized bcc metals.

Low frequency wide bandwidth MEMS energy harvester based on spiral-shaped PVDF cantilever

Abstract: In this paper, a piezoelectric energy harvester based on spiral-shaped polyvinylidene fluoride (PVDF) cantilever is designed and fabricated for harvesting low frequency vibration energy in the environment. In this design, the spiral-shaped PVDF cantilever is major for lowering the resonant frequency by increasing the length of the cantilever; Copper and silicon proof masses on both sides are working on further decreasing the resonant frequency and widen its bandwidth. Due to the high flexibility of the PVDF cantilever, this device is extremely sensitive to vibration and can harvest weak vibration energy. Both simulation and experimental results have approved that this device can operate at very low frequency which is about 20 Hz and can effectively harvest energy from 15–50 Hz. The peak of the output voltage can reach 1.8 V with the acceleration of 0.2 g. This is a promising harvester for powering the wireless sensors in the future.

Enhancing ductility of the Al-Si coating on hot stamping steel by controlling the Fe-Al phase transformation during austenitization

Abstract: In this study, austenitizing heat treatment before hot stamping of Al-10% Si coated boron steel is first investigated through environment scanning electron microscopy (ESEM) equipped with energy dispersive x-ray analysis (EDAX). The cracking behavior of the coating was evaluated using Gleeble 3500, a thermo-mechanical simulator under uniaxial plastic deformation at elevated temperatures. The extent and number of cracks developed in the coating were carefully assessed through an optical microscope. The coating layer under hot-dipped condition consists of an Al-Si eutectic matrix, Fe2Al7Si, Fe3Al2Si3 and Fe2Al5, from the coating surface to the steel substrate. The coating layer remains dense, continuous and smooth. During austenitization, the Al-rich Fe-Al intermetallics in the coating transform to more Fe-rich intermetallics, promoted by the Fe diffusion process. The coating finally shows the coexistence of two types of Fe-Al intermetallics, namely, FeAl2 and FeAl. Microcracks and Kirkendall voids occur in the coating layer and diffusion zone, respectively. The coating is heavily cracked and broken into segments during the hot tensile tests. Bare steel exposed between the separate segments of the coating is oxidized and covered with a thin FeO x layer. The appearance of the oxide decreases the adhesion of the Al-Si coating. It is found that the ductile FeAl is preferred as a coating microstructure instead of the brittle FeAl2. Therefore, the ductility of the Al-Si coating on hot stamping boron steel could be enhanced by controlling the ductile Fe-rich intermetallic phase transformations within it during austenitization. Experiments indicate that a higher austenitizing temperature or longer dwell time facilitate the Fe-rich intermetallics transformation, increasing the volume fraction of FeAl. This phase transformation also contributes to reducing the crack density and depth.

Potassium-induced bifurcations and chaos of firing patterns observed from biological experiment on a neural pacemaker

Abstract: Changes of neural firing patterns and transitions between firing patterns induced by the introduction of external stimulation or adjustment of biological parameter have been demonstrated to play key roles in information coding. In this paper, bifurcation processes of bursting patterns were observed from an experimental neural pacemaker, through the adjustment of potassium parameter including ion concentration and calcium-dependent channel conductance. The adjustment of calcium-dependent potassium channel conductance was achieved by changing the extracellular tetraethylammonium concentration. The deterministic dynamics of chaotic bursting patterns induced by period-doubling bifurcation and intermittency, and lying between two periodic bursting patterns in a period-adding bifurcation process was investigated with a nonlinear prediction method. The bifurcations included period-doubling and period-adding bifurcations of bursting patterns. The experimental bifurcations and chaos closely matched those previously simulated in the theoretical neuronal model by adjusting potassium parameter, which demonstrated the simulation results of the theoretical model. The experimental results indicate that the potassium concentration and conductance of calcium-dependent potassium channel can induce bifurcations of the neural firing patterns. The potential role of these bifurcation structures in neural information coding mechanism is discussed.

Use of lime mud from paper mill as a heterogeneous catalyst for transesterification

Abstract: Lime mud (LM), a solid waste from the paper mill, is used as an economic and environmental friendly heterogeneous basic catalyst for transesterification, which is accompanied by characterization of X-ray fluorescence, thermogravimetric-differential thermal analysis, X-ray diffraction, N2 adsorption, and Hammett indicator method. To investigate the performance of the achieved catalyst, which is activated through calcination, the aspects of calcination temperature, reaction time, mole ratio of methanol to oil, catalyst addition percentage, and reaction temperature are concerned. Characterization of catalyst reveals that LM could be activated through calcination to transform the carbonate and hydrate of calcium into the oxide forms and higher calcination temperature could lead to stronger basic strength. However, N2 adsorption results indicate that higher temperature causes the sintering of the catalyst and shrinkage of the catalyst grains. When LM is activated at 800°C (LM-800) and the reaction is carried out at 64°C with a methanol to oil mole ratio of 15:1, catalyst addition percentage of 6%, and reaction time of 2 h, the maximum transesterification conversion of 94.35% could be achieved. Reusability of LM-800 is also investigated compared with laboratory grade CaO in five reaction cycles and the results indicate that the catalysts derived from LM can be used as an economic and efficient catalyst for biodiesel production.

Interferometry observations of low-latitude E-region irregularity patches using the Sanya VHF radar

Abstract: Interferometry plays an important role in revealing fine-scale structures of ionospheric irregularity By placing an additional receiving array of four 5-element Yagi antennas in the north of the main East-West array of the Sanya VHF radar, multiple interferometry baselines with components parallel and perpendicular to the magnetic meridian are formed These baselines allow us to study the three-dimensional (3D) behavior of low-latitude ionospheric field-aligned irregularity (FAI) over Sanya Using multiple non-collinear receiving baselines, an experiment for which the Sanya VHF radar operated as an interferometer was performed on 10 July 2013 Ionospheric E-region FAI echoes with periods of several minutes were observed during 0745-0915 UT; mean Doppler velocity was around −30 m/s with spectral widths of about 50 m/s The interferometry results show fine-scale structures of E-region FAI with a zonal scale size of 15 km or less In addition, we found that the periodic variations of echo intensity shown in radar range-time-intensity (RTI) maps were produced by spatially separated E-region irregularity patches The patches drifted westward with a velocity of about 40–60 m/s and could be associated with propagating gravity waves These results provide a clearer picture of the characteristics of FAI and thus help to investigate the generation and dynamics of low-latitude ionospheric irregularities in the Chinese sector

Anisotropic diffusion filtering for ultrasound speckle reduction

Abstract: Speckle noise has long been known as a limiting factor for the quality of an ultrasound B-mode image. In this study, anisotropic diffusion filtering is proposed as an effective method for ultrasound speckle reduction. This article provides a brief description of anisotropic diffusion filtering proposed by Perona and Malik, and compares its speckle filtering effects with other filtering methods including median, moving average, and frequency domain Gaussian low-pass. In this study, multiple filters are implemented in Matlab. For each filter, three different types of noisy images with speckle noise are tested. The results show that anisotropic filter can reduce the noise more effectively and meanwhile preserve the boundaries of the objects. In addition, this filter has more controllable filtering parameters and is independent on the information of the noise.

Preliminary studies on the basic factors of bionics

Abstract: The bionic consciousness, idea, and practice opened a unique path for the progress of mankind, the development of the society, and the innovation of science and technology from the subconscious bionic activities of the ancient humans to the significant bionic designs in modern engineering Nowadays, driven by the practical demand of human beings, bionics becomes an important factor for the sustainable development of technology A lot of new and outstanding innovations have been produced through the effective interactions between bionics, technology, and demand The stronger the interactions, the greater the innovation success would be In this article, the basic factors such as the connotation, characteristics, and interactions of bionic demands, bionic models, bionic simulations, and bionic products were explained, which are the indispensable basic knowledge for improving the ability of innovation especially for the original one, realizing the design and innovation of new technology and manufacturing for better bionic products

Response of sediment yield to vegetation restoration at a large spatial scale in the Loess Plateau

Abstract: The impact of vegetation coverage on erosion and sediment yield in the Loess Plateau has been extensively studied, but the research has been primarily based on observations from slope runoff plots or secondary forest regions; the scaling method remains unresolved when it is applied at a large spatial scale, and it is difficult to apply to regions with severe soil and water loss given the predominance of herbs and shrubs. To date, there is little data on the quantitative impact of changes to vegetation on sediment concentration at a large spatial scale. This paper is based on vegetation information from remote sensing images, measured rainfall and sediment data over nearly 60 years, and results from previous runoff and sediment variation research on the Yellow River. We introduce the concepts of a sediment yield coefficient and the percentage of effective vegetation and erodible area, analyze the impact of different vegetation conditions on the flood sediment concentration and sediment yield, and evaluate the effect of rainfall intensity on sediment yield under different vegetation conditions at the watershed scale. We propose models to evaluate the impact of vegetation on sediment yield in the loess gully hilly region, which are based on remote sensing data and support an application at a large spatial scale. The models can be used to assess sediment reduction that results from the current significant improvement of vegetation in the Loess Plateau.

Temperature-induced deformation of CRTS II slab track and its effect on track dynamical properties

Abstract: Two finite-element models of the CRTS II slab track are presented to simulate temperature-induced deformations of the concrete track slab with no deterioration or with a deteriorated cement asphalt mortar (CAM). One model, which considers the fully bonding interface between the slab and the CAM layer, could applied to a track that is in good condition; the other model uses cohesive zone elements to simulate the deteriorated CAM with some possible interfacial separation and slip. Utilizing both of the models, temperature-induced warp deformations of track under various temperature loads are investigated. The influence of temperature deformation on the dynamic properties of the track is analyzed based on the train-track coupled dynamics. Numerical results show that the deteriorated CAM layer can significantly increase temperature deformations of a CRTS II track slab, which would produce tiny rail irregularities. There are clear differences between the deformation shapes of the track slabs that have an inseparable mortar layer and those have a separable mortar layer. The track slab with a deteriorated mortar layer showed more open curl distortion than the track slab in good condition. The dynamical response index of the slab track is intensified to a certain level due to the temperature deformation; with an increase of the train speed, the track dynamical responses increased linearly. However, rail irregularities due to the temperature deformations are very tiny. Even if a track is exposed to extreme temperature loads and the mortar layer is deteriorated, temperature deformation can have a negligible effect on the track’s dynamical properties.