Improved radiation damage tolerance of titanium nitride ceramics by introduction of vacancy defects

TiN and TiN_0.7 were irradiated using a 100 keV Ar-ion beam at 600 °C to target doses of 3 × 10¹⁷ ions cm⁻². SRIM estimation, GIXRD and fluorescence analysis have been performed to evaluate the effect of pre-existing vacancy defect on the radiation tolerance. The lattice parameter of TiN increased after irradiation due to interstitial atoms and vacancies in as-irradiated TiN. In contrary, the lattice parameter decreased for as-irradiated TiN_0.7, which indicates that the nitrogen atom vacancies in TiN_0.7 acted as sinks for displacement atoms generated by irradiation to limit interstitial atoms existing. The intensity of peaks in fluorescence spectrum of as-irradiated TiN was higher than that of as-irradiated TiN_0.7. That attributed to the presence of color centers formed by Frenkel defects in as-irradiated TiN. All of the results indicate that introducing vacancy defect in materials would offer capability to realize self-heal of irradiation damage.     

A synergistic approach to light-free catalysis using zinc oxide embedded multi-walled carbon nanotube paper

Nanoparticle embedded carbon nanotube papers can produce flexible functional films, whose function is based on the electronic coupling of the nanoparticles with the network of carbon nanotubes. Here we report on the expansion of a synergistic light-free catalyst system that requires both the molecular wire capability of multi-walled carbon nanotubes and the piezoelectric properties of ZnO nanoparticles. The electron–hole pairs can be induced by the piezoelectric effect of ZnO nanoparticles under the effect of pressure. The strong oxidizing radicals interact with the electron–hole pairs and aqueous solution to induce the degradation of methylene blue without the requirement of light. This study highlights the use of nanoparticles for the piezoelectric – light free catalyst system and the limitations of increased nanoparticle loading on the catalytic degradation of methylene blue.     

An optimal filter based MPC for systems with arbitrary disturbances

In this study, a linear model predictive control (MPC) approach with optimal filters is proposed for handling unmeasured disturbances with arbitrary statistics. Two types of optimal filters are introduced into the framework of MPC to relax the assumption of integrated white noise model in existing approaches. The introduced filters are globally optimal for linear systems with unmeasured disturbances that have unknown statistics. This enables the proposed MPC to better handle disturbances without access to disturbance statistics. As a result, the effort required for disturbance modeling can be alleviated. The proposed MPC can achieve offset-free control in the presence of asymptotically constant unmeasured disturbances. Simulation results demonstrate that the proposed approach can provide an improved disturbance õrejection performance over conventional approaches when applied to the control of systems with unmeasured disturbances that have arbitrary statistics.     

NSGA-II-based nonlinear PID controller tuning of greenhouse climate for reducing costs and improving performances

The traditional tuning scheme of proportional, integral, and derivative (PID) controller parameters usually lay more emphasis on control performances than economic profits. As a result, the corresponding control performance is improved, but such case may lead to high production costs. In this paper, a new tuning methodology for multiple PID controllers from an economic point of view by incorporating multiple performance measures and production costs based on nondominated sorting genetic algorithm-II (NSGA-II) is presented. A model of nonlinear thermodynamic laws between numerous system variables affecting the greenhouse climate is formulated. The proposed tuning scheme is tested through step responses for greenhouse climate control by minimizing the indices of overall performance and production cost in a simulation experiment. The results show that the controllers by tuning the gain parameters can achieve good control performance at a relatively low cost. Maybe it is a quite effective and promising tuning method by using this method in the complex greenhouse production.     

Simultaneous strengthening and toughening of reduced graphene oxide/alumina composites fabricated by molecular-level mixing process

Reduced graphene oxide/alumina composite powders were prepared by mixing of graphene oxides and aluminum ions at the molecular-level. It was found that the composite consolidated from the powders showed that reduced graphene oxide were homogeneously dispersed and strongly bonded with the alumina matrix by oxygen atoms presenting at reduced graphene oxide/alumina interfaces. Both the hardness and the toughness of the composites were enhanced simultaneously by the addition of reduced graphene oxide, which act as bridges to restrain the propagation of cracks in the alumina matrix. It is clarified that graphenes can be utilized as promising reinforcements for enhancement in mechanical properties of ceramic materials when the molecular-level mixing process is applied.     

Blind velocities mitigation for MIMO GMTI radar with Doppler division multiple access waveforms

Multiple-input multiple-output (MIMO) radar with multiple transmitters and multiple receivers can achieve a larger virtual antenna array and more system degrees of freedom; thus applying it to ground moving target indication (GMTI) radar can improve the performance of GMTI. Doppler division multiple access (DDMA) waveforms are approximately orthogonal providing good minimum detectable velocity (MDV) performance. However, in such DDMA systems, a sufficient pulse repetition frequency (PRF) design freedom is required. Furthermore, these waveforms suffer from blind velocities which are serious problems, especially in radar systems with high carrier frequency or low PRF. This paper analyses the blind velocities problem and show that blind velocities are relative to variation of the PRF and/or the carrier frequency. Variable PRF techniques are widely used in conventional GMTI radar including multiple PRFs and variable pulse repetition intervals (PRI). Combined with the characteristics of the DDMA MIMO GMTI radar, this paper proposed two methods to mitigate blind velocities: “multi-PRF DDMA” which employs multiple PRFs over successive coherent processing intervals, and “PRI-dithered DDMA” which employs nonuniform sampling by dithered PRI in slow time. Simulation results demonstrate that both the methods are effective ways to mitigate blind velocities in DDMA MIMO GMTI radar systems.     

Efficient and robust visible light photocatalytic H2 production based on CdSe quantum dots sensitized titania

In this work, cadmium selenide quantum dots (CdSe QDs) with different sizes were synthesized and employed as visible light sensitizers of titania, in comparison with other organic molecules based sensitizers, including the well-known ruthenium complex sensitizer, tris(4,4-dicarboxy-2,2-bipyridyl)ruthenium(II) chloride, phenolic-formaldehyde resin and poly (4-vinylphenol). The different sensitizers are linked to titania via different molecular linkages through self-assemble processes. CdSe QDs adsorbed onto titania via stabilization ligand (mercaptopropionic acid) are more stable and efficient in terms of photocatalytic H₂ generation and photocurrent generation. The CdSe QDs with a diameter of 2.5 nm exhibits a strong absorption peak centred at 500 nm (CdSe500) and shows the best photocatalytic performance than other QDs with larger size and organic sensitizers. The turnover number of CdSe500 QDs for H₂ generation reaches ca. 9000 after 96 h reaction, with a 0.6% quantum yield under irradiation at 450 nm (light intensity = 35 mW/cm²). During the initial 3.0 h reaction, the turnover numbers of different types of sensitizers are estimated about 4.3, 52.5, 323.2 and 16.5 for phenolic-formaldehyde resin, poly (4-vinylphenol), CdSe500 QDs and ruthenium complex, respectively. These results highlights the advantages of utilizing CdSe QDs as stable visible light sensitizers for solar energy conversion.     

Cobalt-doped cerium oxide nanoparticles: Enhanced photocatalytic activity under UV and visible light irradiation

CeO₂ nanoparticles (NPs) were synthesized by coprecipitation using cerium(III) nitrate hexahydrate as the precursor and ethanol as the solvent. Different concentration of cobalt-doped cerium oxide NPs (3mol % and 6 mol %) were prepared by adding various concentrations of cobalt chloride to cerium nitrate. The as-synthesized NPs were characterized through X-ray diffraction (XRD) measurements, ultraviolet (UV)–visible spectroscopy, Photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). XRD results reveal that the as-prepared CeO₂ NPs had a face-centered cubic structure with crystallite size in the range of 5–8 nm. TEM analyses showed that the CeO₂ NPs and Co-doped CeO₂ NPs had a homogenous size distribution (sizes were within 5–12 nm). Band-edge absorption of CeO₂ NPs redshifted upon increasing the Co concentration as compared to undoped CeO₂ NPs. PL spectra reveal a peak shift of CeO₂ emission upon cobalt doping, which were due to an increase in oxygen defects localized between the Ce4f and O2p energy levels (i.e., via formation of Ce³⁺ states). Photocatalytic degradation of methylene blue in aqueous solution under UV and visible (sunlight) irradiation in the presence of pure CeO₂ NPs and of Co-doped CeO₂ NPs was investigated. The efficiency of photocatalytic degradation of CeO₂ NPs increased with the Co concentration both under UV irradiation and under visible light. Co-doped CeO₂ NPs (6 mol%) showed degradation efficiencies of 98% and 89% at 420 min of exposure to UV irradiation and to visible light, respectively.     

Static and dynamic high voltage limitation of series and parallel bimorph actuators

The series and parallel bimorph actuators were investigated to identify the limiting factors at high voltage operations. In the static condition, the series and parallel bimorph exhibit polarization-shaped and three-looped hysteresis curve, respectively. The parallel bimorph shows much larger magnitude of saturated and remnant polarization than the series bimorph. The series bimorph is mainly restricted by the breakdown voltage in contrast to the parallel bimorph, which is limited by the domain reorientation. In the dynamic condition, both types of actuators are mainly limited by the maximum stress and domain reorientation. The actuator tends to fracture at the location of maximum stress near the resonance when the voltage is increased to a certain degree. Further increasing the voltage, domain reorientation may happen at frequencies lower than the resonance. Comparatively, the series bimorph has higher resistance to the domain reorientation than the parallel bimorph.     

Joint relay selection and resource allocation in cooperative device-to-device communications

Device-to-device (D2D) communications allow proximate cellular user equipments (UEs) to communicate with each other directly under the control of base station (BS). In this paper, considering the selection relaying (SR) rule which allows a subset of potential relays to forward the source’s data to the corresponding destination, we first establish a multi-relay system model where a D2D UE can act as not only a source but also a potential relay for another D2D link, and then analyze the cooperation behaviors among selfish UEs. Next a simple strategy is proposed to deal with the relay selection problem, and then the fair and efficient resource sharing problem among cooperating D2D UEs is formulated as a bargaining game. Since the game function is non-convex, we turn to an iterative method by introducing an auxiliary function to get the proportional fair resource allocation results. The system efficiency and fairness are proved by numeral simulation results.