Defect engineering of ZnO: Review on oxygen and zinc vacancies

ZnO is an important material which has been widely applied in photodetector, catalyst, gas sensor, field emitter, etc. Yet, its inability to absorb visible light, poor charge transport, and low conductivity limit the application of these devices. Recently, it was discovered that introduction of defects such as oxygen and zinc vacancies into ZnO can effectively improve the existing properties or lead to new and unexpected yet highly desirable characteristics. Herein, we present a systematic review on the available approaches to synthesize oxygen- and/or zinc-deficient ZnO with emphasis on their chemical, structural, and electrical particularities. Furthermore, applications of defective ZnO in various nanoscale devices are discussed in terms of their functionality, reliability, and performance. Finally, we summarize major challenges and offer perspectives for further research in this field. We hope that this review would make a valuable contribution to broaden the knowledge of defective ZnO.     

Design of ruthenium-zeolite nanocomposites for enhanced hydrocarbon synthesis from syngas

The purpose of this work is the design of metal-zeolite nanocomposite catalysts for Fischer–Tropsch synthesis, containing ruthenium nanoparticles, uniformly distributed in the hierarchical BEA zeolites. The use of ruthenium avoids the formation of inert hardly reducible inert metal silicates and metal aluminates. Carbon nanotubes with supported metal oxide nanoparticles play the role of sacrificial template, which allows creating mesoporosity and bringing metallic functionality inside the zeolite matrix. Both mesoporosity and larger micropores of the BEA zeolite facilitate the localization of metal nanoparticles within the zeolite structure and diffusion of the reacting molecules. Compared to the conventional zeolite supported metal catalysts, the synthesized hierarchical ruthenium-zeolites exhibited much higher activity and lower methane selectivity in Fischer–Tropsch synthesis.

     

Turing instability in an economic–demographic dynamical system may lead to pattern formation on a geographical scale

Spatial distribution of the human population is distinctly heterogeneous, e.g. showing significant difference in the population density between urban and rural areas. In the historical perspective, i.e. on the timescale of centuries, the emergence of densely populated areas at their present locations is widely believed to be linked to more favourable environmental and climatic conditions. In this paper, we challenge this point of view. We first identify a few areas at different parts of the world where the environmental conditions (quantified by the temperature, precipitation and elevation) show a relatively small variation in space on the scale of thousands of kilometres. We then examine the population distribution across those areas to show that, in spite of the approximate homogeneity of the environment, it exhibits a significant variation revealing a nearly periodic spatial pattern. Based on this apparent disagreement, we hypothesize that there may exist an inherent mechanism that may lead to pattern formation even in a uniform environment. We consider a mathematical model of the coupled demographic-economic dynamics and show that its spatially uniform, locally stable steady state can give rise to a periodic spatial pattern due to the Turing instability, the spatial scale of the emerging pattern being consistent with observations. Using numerical simulations, we show that, interestingly, the emergence of the Turing patterns may eventually lead to the system collapse.     

Ferromagnet/Superconductor Hybridization for Magnonic Applications

In this work, a new hybridization of superconducting and ferromagnetic orders is demonstrated, promising for magnonics. By measuring the ferromagnetic and spin wave resonance absorption spectra of a magnetostatically coupled permalloy/niobium bilayer at different temperatures, magnetostatic spin wave resonances with unconventional dispersion are observed. The mechanism behind the modified dispersion, confirmed with micromagnetic simulations, implies screening of the alternating magnetostatic stray fields of precessing magnetic moments in the ferromagnetic layer by the superconducting surface in the Meissner state.     

Behavior of Tl(2212)-Normal Metal Point Contacts under Microwave Irradiation

Current-voltage characteristics and their derivatives of S-c-N point contacts formed by Tl₂Ba₂CaCu₂O_8–x anvil - niobium needle have been studied in the temperature range from 4.2 to T_c under microwave irradiation of wide frequency range. At frequencies of order 10¹⁰ Hz two types of excess current (I_exc) dependence on irradiation power level P was observed. In one case at temperatures near T/T_c 0.5 an excess current oscillates with increasing of P as the square of zero order Bessel function. In another case closer to the critical temperature (mainly at T/T_c 0.9) the enhancement of I_exc by the microwave power was revealed. Observed effects demonstrate complicated dynamics of quasiparticles in Tl-based HTS.     

Enhanced performance of FeOOH/ZnIn2S4/Au nanosheet arrays for visible light water splitting

Journal of Materials Science: Materials in Electronics - Carrier separation, charge transport, and visible light absorption are the main factors affecting the solar water splitting performance of a...     

Investigation of magnesium fluoride crystals for imaging acousto-optic tunable filter applications

Results of an investigation of acousto-optic (AO) cells using single crystals of magnesium fluoride (MgF2) are presented. Two acousto-optic tunable filter (AOTF) cells for imaging application have been designed and tested in the visible and ultraviolet (UV) regions of the spectrum from 190 to 490 nm. The two imaging filters were developed by using the wide-angle AO interaction geometry in the (010) and (11 0) planes of the crystal. These filters were used to obtain spectral images at the shortest wavelengths achieved so far. Advantages and drawbacks of this crystal are discussed and photoelastic, acoustic, and AO properties of MgF2 are examined. The investigation confirmed that MgF2-based AOTF cells can be used in the deep UV region up to 110 nm.     

Pattern recognition with an adaptive joint transform correlator

An adaptive joint transform correlator for real-time pattern recognition is presented. A reference image for the correlator is generated with a new iterative algorithm. The training algorithm is based on synthetic discriminant functions. The obtained reference image contains the information needed to reliably discriminate a target against known false objects and a cluttered background. Calibration lookup tables of all optoelectronics elements used are included in the design of the adaptive joint transform correlator. Two methods for the implementation of the proposed joint transform correlator in an optodigital setup are considered. Experimental results are provided and compared with those of computer simulations.     

Invited review: Whey proteins as antioxidants and promoters of cellular antioxidant pathways

Oxidative stress contributes to cell injury and aggravates several chronic diseases. Dietary antioxidants help the body to fight against free radicals and, therefore, avoid or reduce oxidative stress. Recently, proteins from milk whey liquid have been described as antioxidants. This review summarizes the evidence that whey products exhibit radical scavenging activity and reducing power. It examines the processing and treatment attempts to increase the antioxidant bioactivity and identifies 1 enzyme, subtilisin, which consistently produces the most potent whey fractions. The review compares whey from different milk sources and puts whey proteins in the context of other known food antioxidants. However, for efficacy, the antioxidant activity of whey proteins must not only survive processing, but also upper gut transit and arrival in the bloodstream, if whey products are to promote antioxidant levels in target organs. Studies reveal that direct cell exposure to whey samples increases intracellular antioxidants such as glutathione. However, the physiological relevance of these in vitro assays is questionable, and evidence is conflicting from dietary intervention trials, with both rats and humans, that whey products can boost cellular antioxidant biomarkers.