Role of Si in the Luminescence of AlN:Eu,Si Phosphors

The luminescence properties of Si,Eu-codoped AlN phosphors were investigated by means of cathodoluminescence. The concentration of Eu was kept constant, while that of Si was varied from 0 to 9.0 at.% using two different Si-source starting powders, Si₃N₄ and SiC. The luminescence of Eu²⁺ in AlN is only observed for samples doped with Si. On the other hand, a concentration quenching is observed for samples doped with high amount of Si from Si₃N₄ while not for those doped from SiC. These results show the importance of Si in the luminescence properties of Eu²⁺-doped AlN.     

Antimicrobial Face Shield: Next Generation of Facial Protective Equipment against SARS-CoV-2 and Multidrug-Resistant Bacteria

Transparent materials used for facial protection equipment provide protection against microbial infections caused by viruses and bacteria, including multidrug-resistant strains. However, transparent materials used for this type of application are made of materials that do not possess antimicrobial activity. They just avoid direct contact between the person and the biological agent. Therefore, healthy people can become infected through contact of the contaminated material surfaces and this equipment constitute an increasing source of infectious biological waste. Furthermore, infected people can transmit microbial infections easily because the protective equipment do not inactivate the microbial load generated while breathing, sneezing or coughing. In this regard, the goal of this work consisted of fabricating a transparent face shield with intrinsic antimicrobial activity that could provide extra-protection against infectious agents and reduce the generation of infectious waste. Thus, a single-use transparent antimicrobial face shield composed of polyethylene terephthalate and an antimicrobial coating of benzalkonium chloride has been developed for the next generation of facial protective equipment. The antimicrobial coating was analyzed by atomic force microscopy and field emission scanning electron microscopy with elemental analysis. This is the first facial transparent protective material capable of inactivating enveloped viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in less than one minute of contact, and the methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis. Bacterial infections contribute to severe pneumonia associated with the SARS-CoV-2 infection, and their resistance to antibiotics is increasing. Our extra protective broad-spectrum antimicrobial composite material could also be applied for the fabrication of other facial protective tools such as such as goggles, helmets, plastic masks and space separation screens used for counters or vehicles. This low-cost technology would be very useful to combat the current pandemic and protect health care workers from multidrug-resistant infections in developed and underdeveloped countries.     

Performance of proposed thin‐wire model in finite difference time domain method

Thin‐wire approximation in the finite difference time domain (FDTD) method is important in saving computer resources and truncating central processing unit (CPU) time. Previously, thin wires were mainly realized using the true thin wire (TTW) model, in which electric field components along the wire axis are set at zero, and three methods, in which electric field components along the wire axis are also set at zero and the medium around thin wires is replaced depending on wire radius, are hereafter called the RM model. The former is the most conventional and widely used method; however, its resultant radius is 0.23Δs, supposing that the space under consideration is divided by cubic cells with a Δs of the side length of FDTD cells. The first method of the RM model can realize thin wires having a radius of about 0.15Δs under the conditions we used, in which the time interval is set at a value which is slightly less than Δt_c, e.g. 0.9999t_c, where Δt_c is defined by the Courant condition; in the case of a thin wire having a radius less than 0.15Δs, the FDTD computation suffers from numerical instability. The second method can realize a thin wire having a radius of about 10⁻⁴Δs. We need some changes in the numerical electromagnetic analysis program based on the FDTD method to employ these models. The third of the RM model, which has already been proposed by the author and in which the relative permittivity and relative permeability of four FDTD cells closest to a thin wire are replaced according to the radius of the thin wire and Δs, could realize thin wires having a radius of about 10⁻⁶Δs without changing the program and numerical instability. In this paper, the third model is extensively investigated and it is demonstrated that we can deal with a thin wire with a radius of about 10⁻⁹Δs without numerical instability. The maximum difference in the evaluation of the surge impedance of an open‐ended horizontal wire located 5 m above a perfectly conducting ground is less than 5%. We can easily use the third model even though the program, which is available, has no the specific function of thin‐wire approximation. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Improvement of thermal stability of Ni silicide on N-Si by direct deposition of group III element (Al, B) thin film at Ni/Si interface

The direct deposition of a thin Al or B layer at Ni/Si interface was proposed as a new method to solve a problem of degraded thermal stability of Ni silicide on heavily doped N⁺-Si substrates. Significant improvement of thermal stability evaluated by the sheet resistance vs. silicidation temperature properties was observed. The improvement is attributed to suppression of agglomeration of the silicide layers. The Al layer was effective only when it was located at the Ni/Si interface before the silicidation process. The deposited Al and B layers under Ni layer segregated at the surface after the silicidation process. The use of B layer was preferable to control the phase transition from NiSi to NiSi₂.     

Development and experimental validation of automatic conversion procedure from mechanical to electrical connection for MEMS equivalent circuit

This paper describes equivalent circuit for micro electromechanical system (MEMS) using a type of behavior model for expressing mechanical and electromechanical element within circuit simulation, in order to simulate their dynamic behaviors easily. To fully treat the equivalent circuit as the behavior model, the equivalent interconnection expression for mechanical splice is required. In this work, a new approach has been proposed for converting the system composed of mechanical and electromechanical elements to equivalent circuit expression. This approach consists of substitution of unit equivalent elements and conversion of each equivalent interconnection for mechanical splices. We applied graph theory for equivalent interconnection. With this approach, complex MEMS consisting of a number of transducers and mechanical elements can be easily converted into equivalent circuits. In order to validate this approach, the resonant property of electrostatic comb-drive actuator was simulated using the equivalent circuit generated and measured experimentally. The simulated resonant frequency was in good agreement with the measurement and the admittance characteristics were well described using this circuit with a consideration of coupling capacitances at the comb electrodes. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A Thermal Decomposition Model of Aminoguanidium 5,5′‐Azobis‐1H‐Tetrazolate and the Effect of Pressure and Particle Size on the Rate of Decomposition

The temperature histories of aminoguanidinium 5,5′‐azobis‐1H‐tetrazolate (C₄H₁₄N₁₈, AGAT) were measured in order to construct a thermal decomposition model of the compound. The effects of chamber pressure and AGAT particle size were also examined. The results of the study suggest that the thermal decomposition of AGAT occurs in three phases: solid phase, condensed phase, and residue. It was found that the condensed phase consists of decomposition zone I where dramatic temperature rise occurs, decomposition zone II where gradual temperature rise occurs, and the cooling zone where decomposition and temperature stop rising. It was also suggested that the temperature of the decomposition surface which is the interface of the solid phase and the condensed phase was ∼500 K, and that N₂ and NH₃ were suggested to occur in the vicinity of the decomposition surface of decomposition zone I. In addition, it was suggested that the thickness of the decomposition zones I and II decreases and that the maximum‐temperature‐reached increases with an increase in atmospheric pressure. The rate of decomposition of AGAT was found to follow Vieille's equation and the rate of decomposition increases with an increase in pressure. The rate of decomposition increased slightly with an increase in particle size.     

Application of elastic salmon collagen gel to uniaxial stretching culture of human umbilical vein endothelial cells

In this study, we investigated the potential of an elastic salmon collagen gel (e-gel) for use as stretching culture scaffold. First, human umbilical vein endothelial cells (HUVECs) were cultured on the e-gel under static condition, and their growth was evaluated by DNA content measurement, MTT test, and scanning electron microscopy. The results demonstrated steady increases in cell number with culture time. Next, HUVECs were cultured on the e-gel under static condition for 2 d, then uniaxially stretched at a constant frequency (10% elongation at 1 Hz). After the stretching culture for 2 h, the cells oriented perpendicularly to the stretch direction. Moreover, the interleukin-6 and interleukin-8 productions of the cells significantly increased under the stretch condition compared with those under the static condition. These results were in good agreement with the published data in which an elastic silicone membrane was used as a scaffold. In conclusion, the e-gel can be used for stretching culture for vascular tissue engineering.     

Potential sources of microbial contamination of satsuma mandarin fruit in Japan, from production through packing shed

Potential sources of microbial contamination of satsuma mandarin fruit were investigated from production through the packing shed in the 2005 season. Microbial counts in the peel and flesh during the fruit development stage were below 2.4 log CFU/g for bacteria and 3 log CFU/g for fungi, except for the peel in August and September. In the field environment, the highest microbial counts were found in fallen leaves on the ground, followed by soil, organic fertilizer, and agricultural water. Only the pesticide solution collected in July was positive for Salmonella, while no verotoxin-producing Escherichia coli was detected from any of the samples. The bacterial and mold flora in the peel comprised phytopathogenic organisms such as bacteria genus Pantoea and mold genus Mycosphaerella and soilborne organisms such as bacteria genus Bacillus and mold genus Cladosporium, which were found in soil, fallen leaves, agricultural water, and cloth mulch throughout the production season. After fruit harvest and sorting, microbial counts of the peel increased, while those of the flesh remained below the lower limit of detection. Although some of the preharvest sources could also be postharvest sources, some packing shed equipment was assumed to be postharvest sources, because Bacillus cereus was not identified from the fruit in the production field but was detected on the peel after sorting and on equipment such as gloves, plastic harvest basket, and size sorter. These results suggest that using sanitizers for agricultural water and packing sheds to prevent cross-contamination would be useful in a good agricultural practices program of the satsuma mandarin in Japan.     

Control of carrier concentration of p-type transparent conducting CuScO2(0001) epitaxial films

Excess oxygen and 1-at% Mg co-doped CuScO₂[3R](0001) epitaxial films were prepared on a-plane sapphire substrates by combining two-step deposition and post-annealing techniques. The optical and electrical transport properties of the co-doped epitaxial films were compared with those of the CuScO₂[3R](0001) epitaxial films. No significant increase in optical absorption was observed in the co-doped epitaxial films, and the energy gap for direct allowed transition was estimated at 3.7 eV. The carrier concentration of CuScO₂[3R](0001) epitaxial films was controlled from ~ 10¹⁶ cm^- 3 to ~ 10¹⁸ cm^- 3 at room temperature by adjusting the excess oxygen and Mg co-doping. The electrical conductivity, carrier concentration, and Hall mobility of the most conductive film were 3.6 × 10^- 2 Scm^- 1, 8.5 × 10¹⁷ cm^- 3 and 2.6 × 10^- 1 cm²V^- 1 s^- 1 at room temperature, respectively. The temperature dependence of the electrical transport properties of the film exhibited semiconducting characteristics, and the activation energy estimated from the temperature dependence of the carrier concentration was 0.50 eV.