Polytechnic University

Reverse power flow from a photovoltaic (PV) power generation system to distribution system is limited below a certain limit value. The behavior of a power conditioning system (PCS) for large capacity PV power generation system when the output power approached the output power limit value was experimentally estimated. Under the condition, the PCS became uncontrollable. It was pointed out that this phenomenon was caused by the maximum power point tracking (MPPT) control of the PCS. Furthermore, some methods to avoid the uncontrollable condition of PCS were shown.

This study concerned placement of the beam joints in frame design of conventional wooden houses. It clarified effect of beam joints placed near the angle tie on the strength performance and fracture properties of the horizontal structure with angle ties. The results of in-plane shear tests and structural analysis showed when the beam joint is placed near the angle tie, beam joint break before the angle tie. Furthermore, maximum load was reduced depending on how beam joints were reinforced. Besides, an analytical model of horizontal structure with angle ties with beam joint is proposed, which agrees well with experimental results.

Reverse power flow from a photovoltaic power generation system to distribution system is limited below a certain limit value. The behavior of a power conditioning system (PCS) for large capacity photovoltaic power generation system when the output power approached the output power limit value was experimentally estimated. Under the condition, the PCS became uncontrollable. It was pointed out that this phenomenon was caused by maximum power point tracking (MPPT) control of the PCS. Furthermore, some methods to avoid the uncontrollable condition of PCS were shown.

Lateral load tests were conducted with crushed dimensions as experimental variables for the purpose of investigating the maximum lateral strength and bending moment equation for RC columns in demolition. 1. Percentage of Maximum lateral strengths tended to decrease as the amount of crushing in the depth direction increased. 2. Experimental values of the maximum Lateral strength at disassembly can be estimated using the proposed bending moment calculation equation. When calculated using the average of the crushed cross sections and the length of the neutral axis of RC columns determined by theory, the proposed bending moment equation adequately evaluates the experimental values. 3. The length of the neutral axis of RC columns determined by theory tended to increase with increasing depth of crushed for the same crushed height direction. Those values ranged from 43% to 57% of the column depth.

The contributions of magnetohydrodynamic (MHD) vortexes to chiral electrodeposition in a vertical magnetic field were theoretically examined based on the three-generation model of the 2D nucleus, 3D nucleus, and screw dislocation; for the vortexes to rotate in the second and third-generation, the kinematic viscosity must be at least 10−18 and 10−30 times lower than the ordinary value in the first generation, i.e., almost equal to zero. This implies that the ionic vacancy created on the electrode surface works as an atomic-scale lubricant. At the same time, the vortexes played three roles: promotion and suppression of nucleation, and transport of the chirality from the upper generation to the lower generation through precessional motion. Then, the rule of the chirality transfer was established, and finally, the relationship between the chiral activity and magnetic field was clarified in the presence and absence of chloride ions.

Blue light emitted during arc welding is known to potentially cause photoretinopathy. To help prevent retinal injury, it is important to identify the hazards associated with various welding conditions. The present work conducted experiments involving gas metal arc welding of mild steel under various conditions, and measured the spectral radiance of the arcs. The effective radiance values, as used by the American Conference of Governmental Industrial Hygienists (ACGIH) to quantify exposure level of blue light, were subsequently calculated from the data. The resulting values were in the range of 5.0–118 W/cm²/sr, corresponding to hazardous levels according to ACGIH guidelines. The effective radiance was increased at higher welding currents and when pulsed currents were used rather than steady currents. The blue light hazard was also affected by the type of shielding gas employed. These data confirm that it is very hazardous to stare at arcs during gas metal arc welding of mild steel. As such, appropriate eye protection is necessary during arc welding, and directly staring at the arc should be avoided.

More than 90% of wooden frame houses are made up of components processed by pre-cutting. The drawings for pre-cutting are prepared by the designers of structural design offices and pre-cutting factories. In this study, interviews, drawing surveys, and questionnaires were conducted in order to understand the tendency of the joint arrangement of horizontal members of the framing designers. As a result of the survey, it was found that there were some cases where joints had to be placed at these locations, although they were designed not to be placed at push up part of the brace or inside the angle-tie.

In this report, the effect of shade caused by slits on the surface of cementitious materials on the brightness (L* value) of the surface of the cementitious materials was investigated, and the modeling of the brightness (L* value) based on the irradiation angle and the irradiation area was proposed. Furthermore, the applicability of the above model was confirmed by the trial work of designing and construction.

Compressive strength and pozzolanic reaction of specimens mixed with fine milled fly ash were examined. Mortar specimens mixed with three types of fine milled fly ash were cured under high-temperature condition in early ages. It was clarified that smaller particle size of the fly ash improved the early strength development of mortar. Moreover, both of finely milling fly ash particle and high-temperature curing in early ages remarkably accelerated the pozzolanic reaction of fly ash. The synergistic effect provided the acceleration of the strength development of mortar.

In this study, flow observation in friction stir welding using a transparent fluid followed by PIV analysis were conducted to discuss and verify the relationship between the thread shape of the probe and the layered microstructure. Subsequently, friction stir welding of 6061 aluminium alloy were conducted to confirm the validity of the verification. In the flow observation, the tracer swirled around the probe was observed to be discharged from the probe tip and formed a layered deposit behind the probe. This layered deposition showed different periodicity depending on the tool screw geometry. The PIV analysis showed that the tracer was discharged from the threaded part at the probe tip. Therefore, it is considered that the discharge from the probe tip contributes to the layered deposition. In the joining experiments, the spacing of the layered microstructure appeared on the cross-section altered depending on the thread shape of the tool. Therefore, it is considered that the layered microstructure is strongly related to the geometry of thread of welding tool.

In this study, flow observation in friction stir welding using a transparent fluid followed by PIV analysis were conducted to discuss and verify the relationship between the thread shape of the probe and the layered microstructure. Subsequently, friction stir welding of 6061 aluminum alloy were conducted to confirm the validity of the verification. In the flow observation, the tracer swirled around the probe was observed to be discharged from the probe tip and formed a layered deposit behind the probe. This layered deposition showed different periodicity depending on the tool screw geometry. The PIV analysis showed that the tracer was discharged from the threaded part at the probe tip. Therefore, it is considered that the discharge from the probe tip contributes to the layered deposition. In the joining experiments, the spacing of the layered microstructure appeared on the cross-section altered depending on the thread shape of the tool. Therefore, it is considered that the layered microstructure is strongly related to the geometry of thread of welding tool.

Objectives: This study aimed to evaluate the efficacy and adverse events of favipiravir in COVID-19 patients. Methods: Our protocol was registered on PROSPERO (CRD42020206305). Fourteen databases were searched until February 8th, 2021. An update search for new RCTs was done on March 2nd, 2022. Meta-analysis was done for randomized controlled trials (RCTs) and non-RCTs. Results: Overall, 157 studies (24 RCTs, one non-RCT, 21 observational studies, two case series, and 106 case reports) were included. On hospitalized patients, in comparison to standard of care, favipiravir showed a higher rate of viral clearance at day 5 (RR=1·60, p=0·02), defervescence at day 3-4 (RR=1·99, p<0·01), chest radiological improvement (RR=1·33, p<0·01), hospital discharge at day 10-11 (RR=1·19, p<0·01), and shorter clinical improvement time (MD=-1.18, p=0.05). Regarding adverse events, favipiravir groups had higher rates of hyperuricemia (RR=9·42, p<0·01), increased alanine aminotransferase (RR=1·35, p<0.01), but lower rates of nausea (RR=0·42, p<0·01) and vomiting (RR=0·19, p=0·02). There were no differences regarding mortality (RR=1·19, p=0.32), and increased aspartate aminotransferase (RR=1·11, p=0·25). On non-hospitalized patients, no significant differences were reported. Conclusion: Adding favipiravir to the standard of care provides better outcomes for hospitalized COVID-19 patients. Pregnant, lactating women, and patients with a history of hyperuricemia should avoid using favipiravir.

The present study emphasizes the importance of the direct evaluation of the athermal strength of structural materials, which is the time-independent material strength that corresponds to the basic capability to bear stresses caused by external forces permanently, and we call it the “permanent strength.” The present experimental study, taking FCC metals processed by severe plastic deformation (SPD), shows that the permanent strength is unexpectedly much lower than the flow stress temporally observed in a standard tensile test. More than half of the observed flow stress corresponds to the time-dependent thermal strength. Furthermore, the grain refinement associated with SPD processing never contributes to the augmentation of the permanent strength, i.e., the Hall–Petch relation is not applicable to as-SPDed materials. In contrast to aluminum, for copper, the low permanent strength produced by SPD is never revived by subsequent annealing. These observations elicit the general view that we should know the permanent strength of structural materials, not limited to SPD-processed metals, because we must confirm that the permanent strength is higher than the allowable stress in structural design to ensure the use of the structure within its elastic range in normal environments.

The purpose of this study is to show the validity of the simulation result for particle charge and trajectory in an ESP with multiple wire electrodes, and the effect of the number of wire electrodes on the relationship between collection efficiency and discharge power. The ESP in this study has wires-and-plates configuration composed of three high-voltage application wire electrodes placed between grounded plate electrodes with a gap of 15 mm. The charged particle trajectory in the ESP was calculated by equations, and measured using a particle image velocimetry. In addition, the analysis and the experimental collection efficiencies as a function of input power in the ESPs with a single wire electrode and three wire electrodes were compared, and the effect of the number of wire electrodes on the power consumption was investigated. As a result, the x and y components of particle velocity measured using PIV almost agreed with the simulated result. The validity of the simulation result for charged particle trajectory, which was calculated by fitting the analyzed corona current to the experimental value, in the gas flow considering the ionic flow in an ESP with multiple wire electrodes was indicated. Also, both analysis and experimental collection efficiencies at the ESP with three wire electrodes were greater than that with the single wire electrode at the same input power. An analysis revealed that this was because the residence time of particles in the ESP with three wire electrodes was longer than that with the single wire electrode.

Visualization of skills is one of the possible methods for efficient acquisition of skills. The goal of this study is to propose teaching methods for the efficient acquisition of these tasks for basic carpentry skills. For each task, a survey of existing literature is conducted to understand the known tips and tricks. In addition, a questionnaire survey of skilled technicians will be conducted to ascertain the tips and tricks recognized by skilled technicians themselves. Next, movement analysis is conducted on skilled and unskilled workers to ascertain the presence or absence of tricks that have not been described in the literature (tacit knowledge) and that are not recognized by the skilled workers themselves, based on the differences in their movements. Furthermore, we confirm whether the operation tips obtained from the literature survey and the skill questionnaire survey are consistent with the actual motions. Based on the results of the literature survey, skills questionnaire survey, and motion analysis, we create evaluation criteria for the work and visualize the skills. By using these evaluation criteria, we evaluate the movements of unskilled workers and provide them with guidance on how to improve their work in accordance with the actual conditions of each individual worker to improve the efficiency of skill acquisition. As a first step, this paper reports on the results of a literature review and skills questionnaire survey with the aim of identifying the known tricks of chisel blade sharpening operations and the tricks recognized by skilled workers. The results from the literature survey and skills questionnaire survey within the scope of this study are summarized below. (1) There was no difference between the literature survey and the questionnaire survey in terms of working posture, wrist condition, vertical angle of the chisel to the grinding wheel, working motion, and application of force. (2) Although the technical manual described tips for reducing the chisel travel distance, the results of the questionnaire survey showed that skilled workers worked with a larger chisel movement distance. (3) The results of the questionnaire survey and the technical manual differed in the tips for applying force. The technical manual stated that blade sharpening was done by applying a large amount of force. On the other hand, in the questionnaire survey, the respondents answered that they sharpened the blade without applying a large amount of force.

This article presents a method to estimate the average torque of a V / f -controlled induction motor (IM) accurately from stator flux linkage and stator current vectors. This method is based on stator flux linkage calculation by a dc-offset-less approximation integrator with error compensator considering not only no-load iron and mechanical losses but also stray load loss. Based on loss analysis, we point out the necessity of considering the iron loss, mechanical loss, and stray load loss caused by the fundamental wave power as additional losses in order to improve the torque estimation accuracy of the proposed method. This article also shows a new method to take the stray load loss into account using linearity of torque and rotor current. The proposed method can be performed without a torque meter and is applicable to both sinusoidal and inverter drives. The proposed torque estimation is implemented on two squirrel-cage IMs: a semiclosed rotor machine and a closed-slot rotor machine, fed by sinusoidal-, square-, and pulsewidth-modulation-wave drives. The result of the estimated torque is verified by comparing the estimated and measured torques.