A planar Bi-Sb multijunction thermal converter with small ac-dctransfer differences

A planar Bi-Sb multijunction thermal converter was fabricated on the LPCVD Si₃N₄/SiO₂/Si₃N ₄-diaphragm, prepared by silicon bulk micromachining, which thermally isolated a bifilar Pt- or NiCr-heater and the hot junctions of a Bi-Sb thermopile from the silicon substrate. The voltage responsivity, the ac-dc transfer difference, and the fluctuations of the output thermoelectric voltage and heater resistance were discussed to investigate the design factors of a thermal converter. The respective voltage responsivities in air and in a vacuum of the thermal converter with a built-in NiCr-heater were about 14.0 mV/mW and 54.0 mV/mW. The ac-dc voltage and the current transfer differences in air were about ±0.60 ppm and ±0.11 ppm in the dc reversing frequency range from 10 Hz to 10 kHz. They are sufficiently small to be used as practical ac standards. Compared to the thermal converter with a built-in Pt-heater, the thermal converter with a built-in NiCr-heater demonstrated a higher voltage responsivity and smaller ac-dc transfer differences, while exhibiting slightly larger fluctuations in output thermoelectric voltage and in heater resistance     

Electron scattering profiles in SOS films measured by temperature-dependent Hall effect

The electron scattering mechanisms at every depth in heteroepitaxial SOS films have been investigated by measuring the temperature dependence of Hall mobility. It appears that, above the `critical? temperature Tc=120 K, lattice scattering prevails only in the proximity of 1/SiO, while ionised impurity scattering becomes dominant near the substrate (2000 ? from Si/Al2O3) even at room temperature.     

Cyclic seismic testing of steel moment connections reinforced with welded straight haunch

A simplified seismic design procedure as well as force transfer model for seismic steel moment connections using a welded straight haunch was recently proposed. As a follow-up study, cyclic seismic testing was conducted to verify the proposed procedure and to develop strategies that would prevent cracking at the haunch tip. All the specimens based on the proposed procedure effectively pushed the plastic hinging of the beam outside the haunch and developed satisfactory connection ductility with no fracture. A sloped edge combined with a drilled hole near the haunch tip, or a pair of stiffeners that partially or fully extended from the beam web, successfully prevented crack initiation at the haunch tip. The strut action of the haunch web, which had been predicted from the previous analytical study, was also identified through the strain gage readings in this experiment.     

Graphene-based flexible and stretchable thin film transistors

Graphene has been attracting wide attention owing to its superb electronic, thermal and mechanical properties. These properties allow great applications in the next generation of optoelectronics, where flexibility and stretchability are essential. In this context, the recent development of graphene growth/transfer and its applications in field-effect transistors are involved. In particular, we provide a detailed review on the state-of-the-art of graphene-based flexible and stretchable thin film transistors. We address the principles of fabricating high-speed graphene analog transistors and the key issues of producing an array of graphene-based transistors on flexible and stretchable substrates. It provides a platform for future work to focus on understanding and realizing high-performance graphene-based transistors.     

Effects of poly‐γ‐glutamic acid on the physicochemical characteristics of skim milk yoghurt

The physicochemical and sensory properties of skim milk yoghurts containing poly‐γ‐glutamic acid (PGA) at different levels (0.0025, 0.005 and 0.01%) were evaluated. Addition of PGA up to 0.01% to reconstituted skim milk (11%, w/v) did not affect the growth of lactic acid bacteria or the development of titratable acidity in yoghurt, whereas full‐fat control yoghurt had reduced acid production. No changes were found in viable cell counts of PGA yoghurts during storage (4 weeks at 4 °C). The addition of PGA (0.005%) significantly decreased syneresis in skim milk yoghurt and did not cause any undesirable effects in sensory acceptability.     

Accelerated test analysis of reversal potential caused by fuel starvation during PEMFCs operation

The performance of polymer electrolyte membrane fuel cells (PEMFCs) was reduced due to the degradation of the catalyst layer when reverse potential was generated by fuel starvation in PEMFCs. Detailed analysis was performed through accelerated reversal potential tests. The electrochemical impedance spectroscopy (EIS) measurement results showed that the charge transfer resistance increased and the electrochemical active surface area (ECSA) reduction was confirmed through the cyclic voltammetry (CV) measurements. Corrosion of the carbon used as the catalyst support was detected by confirming the CO peak in the 1st cyclic voltammogram in the CV measurements. Growth of the Pt catalyst due to the agglomeration and sintering of Pt was confirmed during increasing cycles of the accelerated reversal potential through X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses.     

Pd-doped Sn-Ag-Cu-In solder material for high drop/shock reliability

Pd was chosen as a minor alloying element in a new Sn-1.2Ag-0.7Cu-0.4In solder alloy to improve the drop/shock reliability. The tensile properties and drop/shock reliability of the new Sn-1.2Ag-0.7Cu-0.4In-0.03Pd solder alloy was compared with those of the Sn-1.0Ag-0.5Cu and Sn-3.0Ag-0.5Cu alloys. The UTS, yield strength and elongation of Sn-1.2Ag-0.7Cu-0.4In-0.03Pd were superior to those of the other alloys tested. Sn-1.2Ag-0.7Cu-0.4In-0.03Pd showed outstanding drop/shock reliability compared to the representative Pb-free solder, Sn-3.0Ag-0.5Cu. Therefore, the Sn-1.2Ag-0.7Cu-0.4In-0.03Pd composition is assessed to be an alternative Pb-free solder composition that may replace Sn-3.0Ag-0.5Cu.     

Complementary Logic Gates and Ring Oscillators on Plastic Substrates by Use of Printed Ribbons of Single-Crystalline Silicon

CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by transfer printing of p-type and n-type single crystalline ribbons of silicon. The gain and the sum of high and low noise margins of the inverters were as high as ~150 and 4.5 V at supply voltages of 5 V, respectively. The frequencies of the ring oscillators reached 2.6 MHz at supply voltages of 10 V. These results, as obtained with devices that have relatively large critical dimensions (i.e., channel lengths in the several micrometer range), taken together with good mechanical bendability, suggest promise for the use of this type of technology for flexible electronic systems.     

Improvement of SiCf/SiC density by slurry infiltration and tape stacking

SiC fiber-reinforced SiC–matrix ceramic composites (SiC_f/SiC) were fabricated by vacuum infiltration of a SiC slurry into Tyranno™-SA grade-3 fabrics coated with a 200 nm-thick pyrolytic carbon (PyC) layer followed by hot pressing using a transient eutectic-phase. The density of the composite was improved using a special infiltration apparatus with a pressure gradient and alternating tape insertion between fabrics. Their overall properties were compared with those of monolithic SiC and composite containing chopped fibers. Although the density of the composites decreased with increasing fiber fraction, SiC_f/SiC containing 50 vol.% fibers had a density of 3.13 g/cm³, which is the highest reported thus far. The composites containing continuous fibers had a maximum flexural strength of 607 MPa and a step increase in the stress–displacement behavior during the three-point bending test due to fiber reinforcement, which was not observed in the monolith.