Dynamic modeling and control of hopping robot in planar space

The paper presents two-mass inverted pendulum (TMIP) model and its control scheme for hopping robot. Unlike the conventional spring-loaded inverted pendulum (SLIP) model, the proposed TMIP model is able to provide the functions of energy storing and releasing by using a linear actuator. Also it becomes more accurate comparing to the conventional SLIP model by taking the foot mass into consideration. Furthermore how to determine both takeoff angle and velocity for hopping is analytically suggested to accomplish the desired stride and height of hopping robot. The control method for the TMIP model is also presented in the paper. Finally, the effectiveness of the proposed model and control scheme is verified through the simulation.     

Less conservative robust stabilization conditions for the uncertain polynomial fuzzy system under perfect and imperfect premise matching

By introducing some slack matrices, this paper proposes less conservative robust stabilization conditions for the polynomial fuzzy system with parametric uncertainties. In the proposed methods, no inverse polynomial matrices are chosen as the decision variables so that each element of the gain and the Lyapunov matrices can be guaranteed to strictly be a polynomial function. Therefore, the hardware implementation cost of operating the proposed controller is reduced because no rational functions need to be computed. Moreover, the fuzzy controllers are designed under perfect and imperfect premise matching conditions to enhance the design flexibility. Finally, some numerical examples are given to demonstrate the effectiveness of the proposed methods.

     

Magnetoresistance of Sr1−x K x BiO3: a second-family of bismuth-oxide-based superconductors

The superconducting Sr _1–x K _x BiO ₃ samples with x = 0.45 – 0.6 were synthesized by the high-pressure-high-temperature technique in a belt type apparatus (2 GPa, 700 °C, 1 h, Pt capsules) with stoichiometric mixtures of Sr ₂ Bi ₂ O ₅ , Bi ₂ O ₃ and KO ₂ as described earlier. ¹ The X-ray diffraction results appear as a single perovskite-like phase. The superconductivity occurs at T _c 12 K in the A. C. susceptibility measurement. The onset (zero resistivity) temperature of superconductivity in resistivity measurement of the investigated sample was . The transition temperature region was a little bit broad and a shoulder was present about 11.3 K indicating probably the existence of crystallites of different K content. The particularly interesting point is that the resistance begins to reappear at T < 6 K at zero magnetic field. As the external magnetic field is applied, the reentrant resistance disappears and superconductivity is recovered until the applied magnetic field becomes higher than 0.65 Tesla. The superconductivity for T < 6 K is destroyed for the higher magnetic field. The T_c onset decreases as the magnetic field increases like in the BCS type superconductors. The transition region becomes broader under the magnetic field, which indicate a kind of vortex transition as in the case of high T _c cuprates.     

Selective Dissolution-Derived Nanoporous Design of Impurity-Free Bi2Te3 Alloys with High Thermoelectric Performance

Thermoelectric technology, which has been receiving attention as a sustainable energy source, has limited applications because of its relatively low conversion efficiency. To broaden their application scope, thermoelectric materials require a high dimensionless figure of merit (ZT). Porous structuring of a thermoelectric material is a promising approach to enhance ZT by reducing its thermal conductivity. However, nanopores do not form in thermoelectric materials in a straightforward manner; impurities are also likely to be present in thermoelectric materials. Here, a simple but effective way to synthesize impurity-free nanoporous Bi_0.4Sb_1.6Te₃ via the use of nanoporous raw powder, which is scalably formed by the selective dissolution of KCl after collision between Bi_0.4Sb_1.6Te₃ and KCl powders, is proposed. This approach creates abundant nanopores, which effectively scatter phonons, thereby reducing the lattice thermal conductivity by 33% from 0.55 to 0.37 W m⁻¹ K⁻¹. Benefitting from the optimized porous structure, porous Bi_0.4Sb_1.6Te₃ achieves a high ZT of 1.41 in the temperature range of 333–373 K, and an excellent average ZT of 1.34 over a wide temperature range of 298–473 K. This study provides a facile and scalable method for developing high thermoelectric performance Bi₂Te₃-based alloys that can be further applied to other thermoelectric materials.     

A study on the electrical properties of Pb(Zr, Ti)O3 thin films crystallized by the electrical resistive heating of Pt thin film

The electrical properties of Pb(Zr, Ti)O₃ thin films annealed by Pt thin film heater were investigated. By the thin film heater, we successfully crystallized Pb(Zr, Ti)O₃ thin films at a high temperature above 750 °C in a few seconds. The thin film heater has some advantages, such as a low thermal budget, little Pb-loss and enhanced surface morphology compared with the conventional furnace because it has a fast heating rate. The electrical properties of the Pb(Zr, Ti)O₃ thin film crystallized by thin film heater improved considerably comparing to those crystallized in conventional furnace. The remanent polarization, breakdown field, and leakage current density measured to be 22.7 μC/cm², 853 kV/cm, and 6.93 × 10⁻⁷ A/cm², respectively.     

Controlling nanoparticle location via confined assembly in electrospun block copolymer nanofibers

Coaxial nanofibers with poly(styrene-block-isoprene) (PS-b-PI)/magnetite nanoparticles as core and silica as shell are fabricated using electrospinning.1-4 Thermally stable silica helps to anneal the fibers above the glass transition temperature of PS-b-PI and form ordered nanocomposite morphologies. Monodisperse magnetite nanoparticles (NPs; 4 nm) are synthesized and surface coated with oleic acid to provide marginal selectivity towards an isoprene domain. When 4 wt% nanoparticles are added to symmetric PS-b-PI, transmission electron microscopy (TEM) images of microtomed electrospun fibers reveal that NPs are uniformly dispersed only in the PI domain, and that the confined lamellar assembly in the form of alternate concentric rings of PS and PI is preserved. For 10 wt% NPs, a morphology transition is seen from concentric rings to a co-continuous phase with NPs again uniformly dispersed in the PI domains. No aggregates or loss of PI selectivity is found in spite of interparticle attraction. Magnetic properties are measured using a superconducting quantum interference device (SQUID) magnetometer and all nanocomposite fiber samples exhibit superparamagnetic behavior.     

Effects of packaging parameters on the microbial decontamination of Korean steamed rice cakes using in-package atmospheric cold plasma treatment

Food Science and Biotechnology - The effects of packaging materials, package shape, and secondary packaging on the inactivation of indigenous mesophilic aerobic bacteria in Korean steamed rice...     

Recent trends in development of hematite (α-Fe2O3) as an efficient photoanode for enhancement of photoelectrochemical hydrogen production by solar water splitting

Solar-assisted water splitting using photoelectrochemical (PEC) cell is an environmentally benign technology for the generation of hydrogen fuel. However, several limitations of the materials used in fabrication of PEC cell have considerably hindered its efficiency. Extensive efforts have been made to enhance the efficiency and reduce the hydrogen generation cost using PEC cells. Photoelectrodes that are stable, efficient and made of cost-effective materials with simple synthesizing methods are essential for commercially viable solar water splitting through PEC technology. To this end, hematite (α-Fe₂O₃) has been explored as an excellent photoanode material to be used in the application of PEC water oxidation owing to its suitable bandgap of 2.1 eV that can utilize almost 40% of the visible light. In this study, we have summarized the recent progress of α-Fe₂O₃ nanostructured thin films for improving the water oxidation. Strategic modifications of α-Fe₂O₃ photoanodes comprising nanostructuring, heterojunctions, surface treatment, elemental doping, and nanocomposites are highlighted and discussed. Some prospects related to the challenges and research in this innovative research area are also provided as a guiding layout in building design principles for the improvement of α-Fe₂O₃ photoanodes in photoelectrochemical water oxidation to solve the increasing environmental issues and energy crises.