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Hydroxyapatite (HAP), which is the main inorganic component of human bones and teeth, has received much attention for its use as an implant material. Doping foreign ions into the HAP lattice struct...

Single-component and competitive adsorption of tetracycline (TC) and Zn(II) on an NH4Cl-induced magnetic ultra-fine buckwheat peel powder biochar (NH4Cl-BHP-char/Fe3O4) was investigated in batch experiments. NH4Cl-BHP-char/Fe3O4 exhibited a large surface area of 1119.097 m2 g−1 and a total pore volume of 0.139 cm3 g−1 and was easily separated from aqueous solution using a magnet. Also, adsorption was endothermic, spontaneous, and highly pH-dependent. The optimum pH of the single-component adsorption of TC and Zn(II) was 4.0 and 6.5, respectively, and the optimum pH of co-adsorption was 6.0. The kinetics studies showed the prepared biochar could be rapidly adsorbed within 60 min, and chemical adsorption was dominant. For single-component adsorption, the maximum adsorption capacities of TC and Zn(II) were 106.38 and 151.52 mg g−1, respectively, and they underwent monolayer adsorption on the biochar surface. Moreover, for competitive adsorption, maximum TC and Zn(II) adsorption capacities of 126.58 and 357.14 mg g−1 were achieved. Both film diffusion and intra-particle diffusion were found to be significant processes to facilitate adsorption. TC and Zn(II) promoted the adsorption of each other. The proposed biochar could be used repeatedly for at least four cycles. All these results demonstrated that developed NH4Cl-BHP-char/Fe3O4 was regarded as a low-cost alternative adsorbent to remove the heavy metal ions and antibiotic pollutants from water or wastewater.

Biochar conversion from corn stover was evaluated under various process conditions, and the absorption capacity of biochar was investigated for the removal of oxytetracycline in wastewater. Biochar was prepared at lower carbonization temperatures (200–500 °C) and was used in three different concentrations of chemical oxygen wastewater. The results showed that the biochar prepared at the temperature range of 200–500 °C had a faster sorption rate and shorter sorption equilibrium time compared to biochar produced at higher temperatures. The longest time to reach sorption equilibrium was 9 h for biochar obtained at 200 °C. However, the biochar prepared at 500 °C required only 0.5 h to reach the sorption equilibrium. The corn stover-biochar had the highest sorption capacity of 246.3 mg/g for oxytetracycline at 30 °C. The adsorption kinetics was consistent with pseudo–second-order kinetics. This study provides a theoretical basis for the conversion of corn stover into biochar as efficient sorbents.

Fenton reaction has been widely used for pretreatment of lignocellulose with the advantages of simple operation, a rapid reaction rate, and less pollution. In this study, batch and fed-batch Fenton...

A photonic quasi-crystal fiber (PQF) with high birefringence based on ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is described. There are two elliptical air holes in the core to increase birefringence and the outer air hole array has a twelve-fold Stampfli-type quasi-crystal structure. ZBLAN reduces absorption loss in the infrared region resulting in higher birefringence. The birefringence and confinement loss of the PQF are analyzed numerically by the full-vector finite element method. Birefringence is higher than that of conventional polarization-maintaining fibers due to the two elliptical air holes in the center and reaches the maximum of 4.15×10−2 at a wavelength of 2 μm. The novel structure has great potential in high-performance optical devices.

Micro electrical discharge machining (micro EDM) provides an alternative in generating complex 3-D micro features in difficult-to-machine materials. The micro EDM performance depends not only on machining parameters but also on the microstructures and micro-characteristics of materials. The effect of free surface layer of austenitic stainless steel on the micro EDM performance is investigated in this paper. Experiments are carried out by machining multilayer stainless steel workpieces without and with surface treatment (acid pickling and oxidation treatment). Surface layer model is built to demonstrate the increasing influence of surface layer on micro EDM performance when the size of workpiece is decreased. The surface free energies of AISI 304 workpieces are estimated by measuring the contact angles. The results show that the steel workpiece with oxidation treatment has the highest surface free energy and the highest material removal rate compared with those without treatment and with acid pickling treatment. The influence of surface layer of steel workpiece on micro EDM performance is more significant when the discharge energy is lower due to size effects. Taper ratio of machined holes on steel workpiece without treatment is much higher than those of holes on steel workpieces with acid pickling and oxidation treatment. As a conclusion, surface treatment of steel workpiece before machining is an effective method to improve the machining efficiency and machining precision of micro EDM, especially when involving the sub-micro or nano-machining where machining is conducted on the workpiece surface.

Achieving galloping gait in quadruped robots is challenging, because the galloping gait exhibits complex dynamical behaviors of a hybrid nonlinear under-actuated dynamic system. This paper presents a learning approach to quadruped robot galloping control. The control function is obtained through directly approximating real gait data by learning algorithm, without consideration of robot’s model and environment where the robot is located. Three motion control parameters are chosen to determine the galloping process, and the deduced control function is learned iteratively with modified Locally Weighted Projection Regression (LWPR) algorithm. Experiments conducted upon the bioinspired quadruped robot, AgiDog, indicate that the robot can improve running performance continuously along the learning process, and adapt itself to model and environment uncertainties.

A promising UV nonlinear optical material, beryllium-free nitrate Ba2NO3(OH)3, has been synthesized via modified high-temperature solid state reactions in a self-made high-pressure apparatus which exhibits a perfect balance of a large second harmonic generation coefficient, an appropriate birefringence for phase matching, a short UV absorption cutoff edge and physicochemical stabilities.

A novel CeO2-MoO3-WO3/TiO2 (CMWT) catalyst was prepared by a single step sol-gel (SG) method. It exhibited 93.8%–98.9% of NO conversion at 275–450 °C and high tolerance to 10% H2O and 1000 ppm SO2 at a gas hourly space velocity (GHSV) of 90,000 h− 1. Superior SCR activity of CMWT catalyst could be attributed to the presence of more Ce3 + and chemisorbed oxygen, higher redox ability, stronger adsorption capacity of NH3 species and the strong interaction among ceria, molybdenum, tungsten and titania.

With the development of micro electro mechanical system (MEMS), the application of micro components is becoming increasingly wide. Micro electrical discharge machining (micro EDM) is one of the most effective manufacturing processes for micro components. During past few decades, some innovative methods for improving micro EDM performance have been proposed. Using special-shaped electrode is just one of them. Although micro EDM with helical electrode has been proposed and the availability has been proved for several years, relatively little is known about the precise effect of helical electrode rotation on micro EDM performance. In this study, micro through-holes were machined on Ti6Al4V sample with a cylindrical electrode and helical electrode. The helical electrode achieves better machining performance overall compared to the cylindrical electrode due to its favorable debris removal ability. The higher the rotational speed of helical electrode, the higher the material removal rate (MRR). When using the cylindrical electrode, the MRR first increases and then decreases after reaching a peak at 3000 rpm. Higher MRR is obtainable with the helical electrode with reverse rotation; with forward rotation, it yields higher machining precision (lower overcut and taper rate).

This paper presents a control approach for bounding gait of quadruped robots by applying the concept of Virtual Constraints (VCs). A VC is a relative motion relation between two related joints imposed to the robots in terms of a specified gait, which can drive the robot to run with desired gait. To determine VCs for highly dynamic bounding gait, the limit cycle motions of the passive dynamic model of bounding gait are analyzed. The leg length and hip/shoulder angle trajectories corresponding to the limit cycles are parameterized by leg angles using 4 th-order polynomials. In order to track the calculated periodic motions, the polynomials are imposed on the robot as virtual motion constraints by a high-level state machine controller. A bounding speed feedback strategy is introduced to stabilize the robot running speed and enhance the stability. The control approach was applied to a newly designed lightweight bioinspired quadruped robot, AgiDog. The experimental results demonstrate that the robot can bound at a frequency up to 5 Hz and bound at a maximum speed of 1.2 m·s−1 in sagittal plane with a Froude number approximating to 1.

To further study the discharge characteristics and machining mechanism of micro-electrical discharge machining (micro-EDM), the variation trends of the discharge energy and discharge crater size with actual discharge duration are discussed based on single-pulse experiments. The polarity effect of micro-EDM was analyzed according to the motion characteristics of electrons and ions in the discharge plasma channel. The results show that the discharge current and voltage of micro-EDM were independent of the discharge width and open-circuit voltage. The energy utilization rate of the short-pulse discharge was relatively high, and the energy utilization rate decreased gradually as the discharge duration increased. Even if the mass of the positive ion was much larger than that of the electron, the kinetic energy of the positive ion was still less than that of the electron when bombarding the surface of the electrode. The acceleration and speed of electrons were very high, and the number of times that electrons bombarded the surface of positive electrode was more than 600 times that of positive ions bombarding the surface of the negative electrode during the same time.

As a novel catalyst for oxygen reduction reaction (ORR), nitrogen-doped carbon xerogel was prepared via a sol-gel followed by the subsequent pyrolysis in ammonia atmosphere and post-treatment process. The resultant catalysts were characterized by BrunauereEmmetteTeller (BET), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis and electrochemical measurements. The role of metal in the catalyst was studied by comparing catalytic activities of the catalysts with and without post-treatment. Results show that the catalyst with nitrogen doped on the surface possesses an amorphous microstructure. The catalysts with and without post-treatment showed almost the same ORR electrocatalytic activities, which clearly demonstrated the negligible influence of metal removal on ORR performance. The catalyst with post-treatment displayed comparable ORR activity to that of Pt/C in alkaline medium as well as superior stability. A maximum power density of 115 mW cm −2 at 40 °C was achieved on the single cell with the as-prepared catalyst as cathode, demonstrating its application as promising alternative for Pt-based electrocatalysts in direct borohydride fuel cells.

Porous metals and alloys are ideal lightweight and damping materials which have garnered significant research attention owing to their superior mechanical and metallurgical characteristics. Micro electrical discharge machining (micro EDM) is an alternative method for machining porous metals. In this study, experiments on porous stainless steel (PSS) were conducted to determine the micro EDM performance of austenitic stainless steel (AISI 304) and PSS samples with various porosities and pore sizes. The results were analyzed based on the thermal conduction theory of porous materials. PSS achieved better machining performance overall compared to AISI 304 due to its porosity; further, porosity and pore size were shown to have a significant influence on the machining characteristics of PSS. The larger the porosity and pore size, the higher the material removal rate (MRR) and the lower the relative tool wear ratio (RTWR). Thermal conductivity decreases due to the existence of pores, causing less heat to be lost by heat conduction and more energy to be consumed in order to remove the material. High capacitance in the experimental circuit proved suitable for machining PSS, while high open circuit voltage appeared to be more suitable for machining AISI 304.

The material removal process of micro electrical discharge machining is based on the instantaneous ultra-high temperature generated by a series of repetitive discharge pulses. Due to the size effects, the polycrystal cannot be considered as continuous and homogeneous material when machining is in micron scale, and the effects of material microstructure should not be neglected. In this article, the thermoelectric characteristics of grain and grain boundary are discussed, and the influence of grain size on the machining performances in micro electrical discharge machining is researched. Two kinds of austenitic stainless steels (AISI 304) which are different in grain size are chosen as the workpieces in experiments. It is verified by both theory models and experimental results that the smaller the grain size, the higher the material removal rate, under the same discharge conditions. Both thermal conductivity and melting point of the grain boundary are lower than those of the grain because of the grain boundary segregation. The effective thermal conductivity and local effective melting point of polycrystalline materials vary with their grain sizes since the grain boundary volume fractions change. As a consequence, the material removal rate of micro electrical discharge machining has direct relationship with grain size of the workpiece.

Graphitic mesoporous carbon xerogel (GMCX) with high surface area and comparable mesoporous structure is prepared via a sol–gel process with cobalt acetate, followed by the subsequent pyrolysis in nitrogen flow at 1800 °C. 20 wt.% Pt/GMCX catalyst is synthesized using the as-prepared GMCX powder as support. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations for Pt/GMCX indicate that Pt nanoparticles dispersed on GMCX have a much smaller average nanoparticle size and narrower size distribution than Pt nanoparticles grown on commercial XC-72 carbon black and GCX powder which we reported before. The results of linear sweep voltammetry (LSV) test demonstrate that the Pt/GMCX catalyst exhibits a higher oxygen reduction reaction (ORR) electrocatalytic activity than commercial Pt/C and Pt/GCX. The corrosion resistance of the catalysts was evaluated by potential cycling accelerated aging test (AAT). Pt/GMCX catalyst exhibits very nearly the same Pt electrochemical active surface area (EASA) retention as Pt/GCX (53.3% for Pt/GMCX and 53.0% for Pt/GCX), which is higher than that of commercial Pt/C (39.2%). Combined with its facile synthesis process, GMCX powder is a promising substitute for commercial Pt electrocatalyst support in achieving high catalytic activity and good durability for ORR.

Electrical discharge machining (EDM) and emerging electro-arc machining (EAM) are machining processes sharing a similar material erosion mechanism. However, the input parameters and the output responses of them exhibit significant differences. To gain a deeper understanding of these differences, a study was performed adopting single pulse discharges and machining parameters covering EDM and EAM. A full factorial experiment including 50 trials with consideration of the polarity, the discharge current, and the pulse duration, was designed and carried out. For more detailed research and for the sake of comparison, the trials were divided into die-sinking EDM, short pulse EAM, normal EAM, and low current EAM. While the crater geometries including the heat affected zone diameter, the crater depth, the white layer thickness, the removal volume, and the removal ratio, were acquired as results and analyzed. The heat affected zone diameter under both polarities grew with increasing the discharge current and longer the pulse duration. The crater geometry of EDM and EAM was similar when positive polarity was adopted. The crater under negative polarity became shallower as the discharge current decreased and as the pulse duration increased: this led to a significant difference between EDM and EAM. Furthermore, the removal volume and the removal ratio exhibited similar trends. The shallow craters of negative polarity with little removal volume were likely to appear in the normal EAM and low current EAM trials. The characteristics of EAM are such that the high discharge current and the long pulse duration together result in a large material removal rate (MRR) while the long pulse duration alone results in a low electrode wear ratio (EWR). However, the removal ratio of EAM is lower than that of EDM.

Electrical discharge machining (EDM) is one of the most promising non-traditional micro-scale machining methods. Because several operating parameters that are insignificant in macro EDM cannot be neglected during micro EDM process, models derived from the macro EDM process may be inappropriate at the micro scale. This paper contains a comprehensive review of size effects in traditional micro-machining and characteristics specific to micro EDM compared to macro EDM techniques. The very concept of size effects in micro EDM is thoroughly defined and three categories of effects are presented: material microstructure, processing parameter and thermal conduction size effects. Future potential research directions on the subject are also summarized. We assert that careful research and precise attention must be given to size effects in micro EDM. Size effect information especially benefits the machining speed and machining precision of micro EDM.

A high-birefringence(HB) photonic quasi-crystal fiber(PQF) with all-circular air holes is designed and ZrF4-BaF2-LaF3-AlF3-NaF(ZBLAN) is used to increase the birefringence and reduce confinement loss of the PQF in the infrared region. The structure of the PQF is analyzed and optimized numerically using the full-vector finite element method by adopting the perfectly matched layer boundary conditions. The PQF possesses higher birefringence in the wavelength range between 1.3 and 1.8μm and the maximum birefringence value of 4.1×10−2 is achieved at 1.55μm. This is the highest birefringence value reported from all-circular-hole PQFs so far suggesting that the novel structure has great potential in high-performance optical devices.

Squaraine core based small molecules in bulk heterojunction organic solar cells have received extensive attentions due to their distinguished photochemical properties in far red and infrared domain. In this paper, combining theoretical simulations and experimental syntheses and characterizations, three major factors (fill factor, short circuit and open-cirvuit voltage) have been carried out together to achieve improvement of power conversion efficiencies of solar cells. As model material systems with D-A-D' framework, two asymmetric squaraines (CNSQ and CCSQ-Tol) as donor materials in bulk heterojunction organic solar cell were synthesized and characterized. Intensive density functional theory computations were applied to identify some direct connections between three factors and corresponding molecular structural properties. It then helps us to predict one new molecule of CCSQ'-Ox that matches all the requirements to improve the power conversion efficiency.

Electrical discharge machining (EDM) gets the advantage of less cutting force. However, a transient force named the impulse force exists in the machining process. The impulse force has effects on the efficiency, stability and accuracy of EDM. The peak current plays a major role in the impulse force, which has been studied and verified. However, the effects of other process parameters on the impulse force are lack of systematically study. Five single-factor experiments adopting different dielectric medium, polarity, gap width, tool geometry, and immersion depth, were designed and carried out. The single pulsed power source used in the experiments had constant discharge durations by detecting and shutting discharge current, which made the experiments to get rid of the randomness of discharge durations and be accurate. However, the vibration characteristics of the force sensor were changed by the dielectric medium, the fixture and the electrode weight, which made the measure of the impulse force to be complicated. The force balance method was simplified and adopted to acquire the maximum impulse force. It was found that these machining parameters had effects on the impulse force. There was little impulse force when the dielectric medium was air. The impulse force of positive polarity was a little higher than that of negative polarity. The impulse force of sphere tools was larger than that of needle tools. The increasing of gap width or immersion depth enlarged the impulse force. Moreover, the gap width had effects on the crater diameter while the depth of immersion did not. It is verified that these process parameters affected the impulse force by their effects on the bubble.

Understanding the effect of processing parameters on the tool electrode wear during micro-electrical discharge machining (micro-EDM) is helpful to predict and compensate the electrode wear, so as to improve the machining precision. In this paper, experiments are carried out and the influences of tool electrode diameter on the micro-EDM process are discussed based on the skin effect and area effect. It is demonstrated that the machining speed, tool wear, and taper rate are different with the increase of tool electrode diameter. Due to the skin effect and area effect, larger electrode diameter results in higher material removal rate along with higher tool wear rate. The electrode material removal increment is more than the workpiece material removal increment with the increase of tool electrode diameter, which leads to the increase of relative tool wear ratio. Discharge energy is concentrated on the tool surface which enhances the possibility of discharge on the side face and the corner of the tool electrod...

Micro electrical discharge machining (micro-EDM) has been widely applied in the field of precision machining, but the machining mechanism is still unclear. In this paper, the relationship between the characteristics of discharge plasma and discharge duration is clarified by analyzing the formation and expansion process of the discharge plasma channel under micro-scale discharge conditions. Based on the experimental results, the effects of discharge duration on the discharge current, discharge voltage and discharge crater size are discussed. The results show that the expansion acceleration, internal pressure, temperature, and electron density of the discharge plasma decrease as the discharge duration increase, while the radius and expansion velocity of the discharge plasma increase, and finally the discharge plasma reaches the state of shape&ndash, position equilibrium. The resistance of discharge plasma is estimated to fluctuate in the range of 38&ndash, 45 &Omega, by the ratio of discharge maintenance voltage to discharge current. The energy utilization rate of micro-EDM is very high when discharge duration is less than 4 &mu, s, and then decreases gradually as the discharge duration increased. There is a positive linear relationship between discharge crater volume and discharge duration. The discharge duration has no significant effect on the discharge crater depth. This study provides a theoretical basis for further study of discharge plasma characteristics in micro-EDM.