Strain‐Visualization with Ultrasensitive Nanoscale Crack‐Based Sensor Assembled with Hierarchical Thermochromic Membrane

As eidetic signal recognition has become important, displaying mechanical signals visually has imposed huge demands for simple readability and without complex signal processing. Such visualization of mechanical signals is used in delicate urgent medical or safety‐related industries. Accordingly, chromic materials are considered to facilitate visualization with multiple colors and simple process. However, the response and recovery time is very long, such that rapid regular signals are unable to be detected, i.e., physiological signals, such as respiration. Here, the simple visualization of low strain ≈2%, with ultrasensitive crack‐based strain sensors with a hierarchical thermochromic layer is suggested. The sensor shows a gradient color change from red to white color in each strain, which is attributed to the hierarchical property, and the thermal response (recovery) time is dramatically minimized within 0.6 s from 45 to 37 °C, as the hierarchical membrane is inspired by termite mounds for efficient thermal management. The fast recovery property can be taken advantage of in medical fields, such as monitoring regular respiration, and the color changes can be delicately monitored with high accuracy by software on a mobile phone.     

Engineering of charge transport materials for universal low optimum doping concentration in phosphorescent organic light-emitting diodes

A universal low optimum doping concentration of below 5% was demonstrated in phosphorescent organic light-emitting diodes (PHOLEDs) by managing the energy levels of charge transport materials. The device performances of PHOLEDs could be optimized at a low doping concentration of 3% irrespective of the host material in the emitting layer. The suppression of charge trapping and hopping by the dopant through charge transport layer engineering optimized the device performance at low doping concentration. In addition, it was revealed that PHOLEDs with low optimum doping concentration show better quantum efficiency, low efficiency roll-off and low doping concentration dependency of the device performance.     

A preliminary study on the development of an easy method for beef freshness using a cyclic voltammetric system

This study was carried out to develop an easy method for beef freshness using a cyclic voltammetric system. Prime graded (USDA) beef loin at 48 h postmortem was cut into pieces 3 cm thick, packaged into commercial plastic zipper bag, and then stored at 4 °C for 0, 3, 6 and 9 days. A commercial cyclic voltammetry and data processing software were used for this study and the interdigitated electrode was fabricated according to semiconductor manufacturing. The homogenated beef was filtered through Whatman No. 1 filter paper and 250 μL of the filtrate was applied on the interdigitated electrode sensor chip for electrochemical detection. Electrochemical signals changed as storage periods increased. The shape of the cyclic voltammogram changed from a roundish curve to a shapely curve. Redox values (V) also increased during storage. Electrochemical signals matched well with lipid oxidation values (Thiobarbituric acid reactive substances: TBARS). A linear relationship between redox value and TBARS was obtained with a correlation factor of 0.957. Thus, the electrochemical signal of a cyclic voltammetric system can be used as an indicator of beef freshness.     

Development of bismuth tellurium selenide nanoparticles for thermoelectric applications via a chemical synthetic process

Bismuth tellurium selenide (Bi₂Te_ySe_3−y) nanoparticles for thermoelectric applications are successfully prepared via a water-based chemical reaction under atmospheric conditions. The nanostructured compound is prepared using a complexing agent (ethylenediaminetetraacetic acid) and a reducing agent (ascorbic acid) to stabilize the bismuth precursor (Bi(NO₃)₃) in water and to favor the reaction with reduced sources of tellurium and selenium. The resulting powder is smaller than ca. 100 nm and has a crystalline structure corresponding to the rhombohedral Bi₂Te_2.7Se_0.3. The nanocrystalline powder is sintered via a spark plasma sintering process to obtain a sintered body composed of nano-sized grains. Important transport properties of the sintered body are measured to calculate its most important characteristic, the thermoelectric performance. The results demonstrate a relationship between the nanostructure of the sintered body and its thermal conductivity.     

Studies on the heating capacity control of a multi-type heat pump system applying a multi-input multi-output (MIMO) method

This paper describes a method to control capacity of a multi-type heat pump system. Because indoor units are interconnected, alteration of the heating or cooling setting of one indoor unit can influence the performance of the other indoor units. Proportional-integral (PI) controllers were used to assess system performance, and the PI controllers’ gain values were optimized by using a genetic algorithm. A system model was established following a system identification optimization process, and a pseudo random binary sequence was selected as the system identification input signal. A multi-input multi-output (MIMO) controller was more effective in reducing such cross-coupling effects than a single-input single-output (SISO) controller. The temperature at the secondary fluid outlet in the condenser and the saturation pressure at the evaporator were selected as the control variables in the MIMO controller. The experimental results showed that an optimized MIMO controller could reduce overshoot by up to 40% compared with the results using a SISO controller.     

Preparation and photoluminescence properties of γ-KCaPO4: Eu phosphors for near UV-based white LEDs

Novel whitish-blue phosphors based on a phosphate host matrix, γ-KCaPO₄: Eu²⁺, were prepared by a conventional solid-state reaction method using slightly phosphorus deficient conditions and their photoluminescence properties were investigated. The concentration quenching process, temperature dependence of the luminescence and decay curve were also investigated. The γ-KCaPO₄: Eu²⁺ phosphor was efficiently excited by UV-Visible light at wavelengths of 200-450 nm and exhibited a bright whitish-blue emission with a maximum peak wavelength of 473 nm. All of these characteristics suggest that the γ-KCaPO₄: Eu²⁺ phosphors combined with red phosphors could be applicable to near UV-based white LEDs, i.e., only two kinds of phosphor powders are needed for the formation of white light.     

Microstructures,Mechanical and Chemical Properties of TLP-Bonded Joints in a Duplex Stainless Steel with Amorphous Ni-Based Insert Alloys

The changes in tensile strength and pitting corrosion resistance of transient liquid-phase (TLP)-bonded joints for a duplex stainless steel with MBF-80, MBF-30, and MBF-35 as functions of holding time and filler were interpreted with respect to the bond microstructure. Using MBF-80 after 300 seconds, the fracture strength of the joint reached the maximum value. The failure was dependent on the interplay between the reduction in residual liquid and the increase in interface precipitates. After 3600 seconds, the joint strength had the minimum value. At the same conditions, the tensile strength for MBF-80 was low compared with MBF-35 and MBF-30. In contrast with the tensile strength, the joint produced with MBF-80 for 3600 seconds exhibited the best corrosion resistance. Among the fillers used, the corrosion resistance of the joint using MBF-80 close to that of the substrate could be related intimately to the existence of Cr in this filler.     

A risk management approach to safety assessment of trenchless technologies for culvert rehabilitation

Proper functioning of culverts is not only critical to protecting the transportation system from flooding but also critical to maintaining the expected service life of the overall transportation system. During the service life of culverts, they deteriorate due to many reasons such as corrosion caused by road salt, blockage by debris and sediment, poor construction techniques, etc. Trenchless technologies have been used by several State Departments of Transportation (DOTs) to rehabilitate deteriorated drainage structures without disrupting the traffic and within a relatively short span of time. These technologies provide many benefits in terms of cost, time, quality, and expected service life. However, the safety aspects of these techniques have not been discussed and documented in detail probably due to the complexity and the lack of safety standards and specifications directly associated with the techniques. This paper discusses the application of a risk assessment framework to assess potential safety issues of currently available trenchless technologies for culvert rehabilitation. The findings of the study will provide additional information to improve the decision making process in selecting and planning culvert rehabilitation projects.