Developing a monitoring psychological stress index system via photoplethysmography

The purpose of this work was to assess the psychological stress index (PSI) by using oxyhemoglobin saturation by SpO₂ [i.e., the plethysmograph (PPG) signal], which can be measured easily and conveniently. We use the plethysmograph amplitude (PPGA) and the heart-beat interval (HBI) extracted from the SpO₂ waveform to obtain the stress index and to quantify it from 0 to 100. The respiration rate can also be extracted from the heart-rate interval, as shown in our previous research. Therefore, the PPG signal can display the heart rate, SpO₂ waveform, SpO₂ concentration, respiration rate, and psychological stress index. This methodology was tested on nine volunteer Taiwanese students under the stress of an English presentation. The experiment, which takes 30 min for each student, was separated into three stages: preparation, presentation, and discussion, and relaxation. The PSI values of these three stages were 49 ± 10, 60 ± 11, and 56 ± 10, respectively. The results were very successful, and showed PSI values changing from low, to high, and back to low during these three stages. In the near future, we hope to implement this system into a robotic wheelchair in order to monitor the PSI of elderly patients in a nursing home, and to evaluate their psychological condition based on this method.     

Noise Characteristics of ZnO-Nanowire Photodetectors Prepared on ZnO:Ga/Glass Templates

In this paper, we report the fabrication of vertically well-aligned ZnO nanowire ultraviolet (UV) photodetectors on ZnO:Ga/glass templates. With 1 V applied bias, it was found that dark current density of the device was only 1.37times10^-7 A/cm². It was also found that UV-to-visible rejection ratio of the fabricated photodetector was around 1000 with a maximum quantum efficiency of 12.6%. It was also found that noise equivalent power and normalized detectivity of the ZnO nanowire photodetector were 5.73times10^-11 W and 6.17times10⁹ cmHz^0.5W^-1, respectively.     

Impact mechanical response and microstructural evolution of Ti alloy under various temperatures

A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behaviour and microstructural evolution of a Ti alloy (Ti–1.1Mo–5.2Zr–2.9Al–0.35Fe–0.05N–0.20 O–0.02H in wt.%) deformed at strain rates ranging from 8 × 10² s^?1 to 8 × 10³ s^?1 and temperatures between 25 °C and 900 °C. In general, the results indicate that the mechanical behaviour and microstructural evolution of the alloy are highly sensitive to both the strain rate and the temperature conditions. The flow stress curves are found to include both a work-hardening region and a work-softening region. The strain rate sensitivity parameter, β, increases with increasing strain and strain rate, but decreases with increasing temperature. The activation energy varies inversely with the flow stress, and has a low value at high deformation strain rates or low temperatures. The microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result primarily of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. Correlating the mechanical properties of the current Ti alloy with the TEM observations, it is concluded that the precipitation of α phase dominates the fracture strain. TEM observations reveal that the amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current loading conditions.     

A Case Study to Evaluate the Productivity Changes of the Thermal Power Plants of the Taiwan Power Company

This paper developed an approach based on data envelopment analysis and Malmquist productivity index to investigate the performance of power plants and conducted an empirical study with eight thermal power plants in Taiwan. The analysis results show the productivity improvements, and thus, help Taiwan Power Company to monitor and diagnose changes in the productivity of its thermal power plants. Furthermore, this study also provides specific directions for improvements to increase competitiveness in the face of the continuing liberalization of the Taiwanese power generation market.     

Flow–obstacle interaction in rapid granular avalanches: DEM simulation and comparison with experiment

This paper investigates the interaction between rapid granular flow and an obstacle. The distinct element method (DEM) is used to simulate the flow regimes observed in laboratory experiments. The relationship between the particle properties and the overall flow behaviour is obtained by using the DEM with a simple linear contact model. The flow regime is primarily controlled by the particle friction, viscous normal damping and particle rotation rather than the contact stiffness. Rolling constriction is introduced to account for dispersive flow. The velocity depth-profiles around the obstacles are not uniform but varying over the depth. The numerical results are compared with laboratory experiments of chute flow with dry granular material. Some important model parameters are obtained, which can be used to optimize defense structures in alpine regions.     

Antireflective coating for ITO films deposited on glass substrate

The refractive index n of radio-frequency (r.f.) magnetron sputtered indium tin oxide (ITO) films varies with sputtering parameters, such as sputtering power and oxygen percentage in the sputtering ambient. In this study, the feasibility to fabricate multilayer antireflective (AR) coating with a single ITO target by controlling the sputtering conditions is explored. Reduction in the reflectance can be achieved by using a one-quarter-wavelength inner layer ITO with a refractive index n = 1.87 and a one-quarter-wavelength outer layer ITO with n = 2.17. Hence, a single ITO target suffices in the preparation of multilayer AR coating. This simplifies the deposition processes and equipment for the fabrication of AR coating. Surface corrugation, another approach to the reduction of reflectance, is also discussed.     

On the InGaP/InxGa1−xAs pseudomorphic high electron-mobility transistors for high-temperature operations

The high-temperature characteristics of a novel InGaP/In_xGa_1−xAs pseudomorphic transistor with an inverted delta-doped channel are reported. Due to the presented wide-gap InGaP Schottky layer and the V-shaped In_xGa_1−xAs channel structure, the degradation of device performance with increasing the temperature is not so significant. Experimentally, for a 1×100 μm² device, the gate–drain voltages at a gate leakage current of 260 μA/mm and the maximum transconductances g_m,max are 30 (22.2) V and 201 (169) mS/mm at the temperature of 300 (450) K, respectively. Meanwhile, broad and flat drain current operation regimes for g_m, f_T and f_max are obtained.     

Broad-band single-patch circularly polarized microstrip antennawith dual capacitively coupled feeds

New design of a circular microstrip antenna with dual capacitively coupled feeds for broad-band circular polarization radiation is presented. The dual feeds are with a small top-loaded disk and are connected to a Wilkinson power divider with a 90° phase shift between its two output feedlines. The radiating circular patch, printed on a thin substrate, is supported by nonconducting posts on a conducting ground plane and is excited capacitively through the dual feeds. With a distance less than 10% times the center operating wavelength between the circular patch and the ground plane, the present proposed antenna can provide an impedance bandwidth (VSWR ⩽2) of about 49% and a 3-dB axial-ratio bandwidth of about 35%. The antenna gain bandwidth, defined to be within 1-dB gain variation in the axial-ratio bandwidth, is as large as 28%, with the antenna gain level at about 7.0 dBi     

Unified dual-field multiplier in GF(P) and GF(2k)

A scalable unified multiplier for both prime fields GF(P) and binary extension fields GF(2^k), where P=2^m-1 and GF(2^k) is generated by an irreducible all one polynomial. The proposed unified dual-field multiplier uses the LSB-first bit-serial architecture for multiplication in GF(P) and GF(2^k) other than the Montgomery multiplication algorithm, which has been employed by most existing dual-field multipliers. The proposed unified dual-field multiplier costs little space and time complexities. The new multiplier is scalable for operands of any size while other existing dual-field multipliers are only scalable for operands with multiples of m. Furthermore, the proposed multiplier has simplicity, regularity, modularity and concurrency and is very suitable to be implement in VLSI.