Efficient attack strategy for legitimate energy-powered eavesdropping in tactical cognitive radio networks

Wireless Networks - The cognitive radio network (CRN) is not only considered a useful medium for users, but it is also an environment vulnerable to proactive attackers. This paper studies an attack...     

Accurate evaluation of hydrogen crossover in water electrolysis systems for wetted membranes

In fuel cell and electrolysis systems, hydrogen crossover is a phenomenon where hydrogen molecules (H₂) permeate through a membrane, lowering the overall process efficiency and generating a potential safety risk. Many works have been reported to mitigate this undesired phenomenon, but it is yet difficult to accurately measure the rate of hydrogen crossover, particularly when the membrane is fully wetted in water. In this work, we investigated the pressure decay method as a simple, convenient, and low-cost method to characterize hydrogen crossover through wetted membranes for water electrolysis systems. Three different ion exchange membranes were analyzed: Nafion 212, Nafion 115, and in-house sulfonated poly(arylene ether sulfone). We rigorously confirmed our method and data by comparing it to the ANSI dataset with the current state-of-the-art equations of state (EOS) to account for the nonideality of high pressure hydrogen systems. The error from the gas non-ideality was less than 0.03%. As expected, the rate of hydrogen crossover showed high dependency on the temperature; more importantly, hydrogen crossover increased significantly when the membrane was fully soaked in water. For dry membranes, the proposed pressure decay method corroborated well with the literature data measured using other known methods. Moreover, for wetted membranes, the obtained data showed high similarity compared to the GC method which is currently the most reliable method in the literature. We attempted to predict the hydrogen permeability of wetted membranes using the solution diffusion model. The model based on the given thermodynamic parameters overestimated the hydrogen permeability, which can be used to estimate the ion channel tortuosity.     

Anisotropic Properties of Quasi-1D In4Se3: Mechanical Exfoliation,Electronic Transport,and Polarization-Dependent Photoresponse

Theoretical and experimental investigations of various exfoliated samples taken from layered In₄Se₃ crystals are performed. In spite of the ionic character of interlayer interactions in In₄Se₃ and hence much higher calculated cleavage energies compared to graphite, it is possible to produce few-nanometer-thick flakes of In₄Se₃ by mechanical exfoliation of its bulk crystals. The In₄Se₃ flakes exfoliated on Si/SiO₂ have anisotropic electronic properties and exhibit field-effect electron mobilities of about 50 cm² V⁻¹ s⁻¹ at room temperature, which are comparable with other popular transition metal chalcogenide (TMC) electronic materials, such as MoS₂ and TiS₃. In₄Se₃ devices exhibit a visible range photoresponse on a timescale of less than 30 ms. The photoresponse depends on the polarization of the excitation light consistent with symmetry-dependent band structure calculations for the most expected ac cleavage plane. These results demonstrate that mechanical exfoliation of layered ionic In₄Se₃ crystals is possible, while the fast anisotropic photoresponse makes In₄Se₃ a competitive electronic material, in the TMC family, for emerging optoelectronic device applications.     

Porous Hollow‐Structured LaNiO3 Stabilized N,S‐Codoped Graphene as an Active Electrocatalyst for Oxygen Reduction Reaction

A nanohybrid based on porous and hollow interior structured LaNiO₃ stabilized nitrogen and sulfur codoped graphene (LaNiO₃/N,S‐Gr) is successfully synthesized for the first time. Such a nanohybrid as an electrocatalyst shows high catalytic activity for oxygen reduction reaction (ORR) in O₂‐saturated 0.1 m KOH media. In addition, it demonstrates a comparable catalytic activity, longer working stability, and much better alcohol tolerance compared with commercial Pt/C behavior in same experiment condition. The obtained results are attributed to synergistic effects from the enhanced electrocatalytic active sites on the rich pore channels of porous hollow‐structured LaNiO₃ spheres and heteroatom doped efficiency on graphene structure. In addition, N,S‐Gr can meritoriously stabilize monodispersion of the LaNiO₃ spheres, and act as medium bridging for high electrical conductivity, thereby providing large active surface area for O₂ adsorption, accelerating reduction reaction, and improving electrochemical stability. Such a hybrid opens an interesting class of highly efficient non‐Pt catalysts for ORR in alkaline media.     

Scalability and homogeneity of slot die‐coated metal oxide semiconductor for TFTs

An indium oxide‐based precursor solution has been developed by spin coating method. In order to apply this material to mass production, material, process, and equipment optimizations for slot die coating have been implemented. Slot die coating is a cost‐effective and scalable process and already applied to photoresist materials in the display industry. The indium oxide‐based precursor solution has been coated on bare glasses and thin‐film transistor substrates by a mass production‐type slot die coater. Mobility of over 10 cm²/Vs is achieved for the first time for a large area at an annealing temperature of 350 °C. The homogeneity of the film will be presented.     

Streptomycetes cultured on glass beads: Sample preparation for SEM

We demonstrate the preparation of samples of streptomycetes (Streptomyces coelicolor, S. aureofaciens) cultured on glass beads (balotina) for scanning electron microscopy. The main trick of the method consists in immobilization of glass beads with low-melting agarose. The samples are then fixed in OsO(4) vapors followed by dehydration in vapors of absolute ethanol. No air-to-liquid transition during the sample preparation occurs. Consequently, whole cell cycle of streptomycetes in the term of mycelial morphology can readily be studied by this method.     

Liquid water transport in PEMFC cathode with symmetrical biomimetic flow field design based on Murray's law

Water management in the flow field as well as the flooding process in the gas diffusion and catalyst layers enormously influence proton exchange membrane fuel cells (PEMFCs) performance and reliability. Researchers have developed many different designs for flow channels that can be used to distribute fuel or oxidant in PEMFCs (proton exchange membrane fuel cells). Among these designs, novel biomimetic designs have captured special attentions from researchers due to their capability of distributing fluids effectively. This study presents an investigation of the liquid water transport within a porous layer and a symmetrical biomimetic flow field based on Murray's law. The volume of fluid (VOF) method is employed, and the dynamic contact angle (DCA) effects are also considered for better prediction of water distribution. The water transport process and water distribution inside the porous layer and flow field are obtained from the simulation results. Recommendations are given for this type of flow field design based on the behaviors of liquid water in the porous layer and flow field.     

Synthesis of β-MoO3 whiskers by the thermal evaporation method with flowing oxygen gas

β-MoO₃ is a monoclinic phase of MoO₃; it has been shown to be a promising material that can replace α-MoO₃ in chemical, optical, electronic, and electrochromic applications. However, the difficulty in synthesizing β-MoO₃ with a one-dimensional (1D) morphology has limited its use in applications requiring a large specific surface area. In the present work, β-MoO₃ whiskers were prepared by thermally evaporating α-MoO₃ powder in a tube furnace at temperatures (T_f) from 750 to 1000°C and under flowing O₂ gas. The collected samples were identified as mainly β-MoO₃ by X-ray diffraction measurements, and the highest purity β-MoO₃ was obtained at T_f = 1000°C. Scanning and transmission electron microscopy observations showed that whiskers with a width of 10 nm were successfully synthesized by this method. The whiskers were confirmed to be β-MoO₃ via lattice image analysis. Measurements of the temperature distribution in the tube furnace and comparisons with the Mo–O phase diagram led to the conclusion that the whiskers formed via a vapor–solid route. Prepared β-MoO₃ whiskers were compared with α-MoO₃ powder via the X-ray photoelectron spectroscopy characterization method. By elucidating the β-MoO₃ whisker synthesis mechanism, this research provides guidance for the large-scale production of β-MoO₃ whiskers.