Increasing the Durability of Piezoelectric Impact-based Micro Wind Generator in Real Application

AbstractThe purpose of this study is to increase the durability of piezoelectric impact-based micro wind generator (PIMWG) in real application. Using new PIMWG design, numerical simulation, and experimental comparison analysis, we improved the durability of PIMWGs in real application. The experimental results show that the optimized PIMWG generated 2.4 mW (RMS value), and it did not crack within 40h. In this study, we improved the durability of PIMWGs for real application

Dinosaur track-bearing deposits of the Cretaceous Gyeongsang Supergroup, Korea: Stratigraphic occurrences and paleoecological implications

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Influence of the waist diameters on transmission characteristics and strain sensitivity of microtapered long-period fiber gratings

Transmission characteristics of microtapered long-period fiber gratings (MTLPGs) and their strain and temperature sensitivities with variations in the waist diameters are investigated theoretically and experimentally. Transmission characteristics of MTLPGs strongly depend on the waist diameter of the tapered optical fiber (TOF) because of the modification of the effective index difference between the core and the cladding modes. Based on the photoelastic effect, the resonant wavelengths of MTLPGs with variations in strain shift to shorter wavelengths. The strain sensitivity of the MTLPG with a waist diameter of 25 μm is improved by a factor of 20 compared with that of a 125 μm long-period fiber grating. The temperature sensitivities of MTLPGs are also enhanced by reducing the waist diameter of the TOF

Enhancing photoluminescence quantum efficiency of metal halide perovskites by examining luminescence-limiting factors

Metal halide perovskites (MHPs) show superior optoelectronic properties, which give them the great potential for use in next generation light-emitting diodes (LEDs). In particular, their narrow emission linewidths can achieve ultrahigh color purity. However, the reported luminescence efficiency (LE) values are not high enough to be commercialized in displays and solid-state lightings. Moreover, the operational stability of LEDs associated with the overshooting of luminance and the high relative standard deviation of reported external quantum efficiencies are still problematic. In this perspective, we review photophysical factors that limit the photoluminescence quantum efficiency of perovskite-based LEDs. These factors are categorized into (i) weak exciton binding, (ii) nonradiative recombinations, (iii) slow cooling of long-lived hot carriers, (iv) deep-level defects, and (v) interband transition rates. We then present various physicochemical methods to effectively overcome these luminescence-limiting factors. We finally suggest some useful research directions to further improve the LE of MHP emitters as core components in displays and solid-state lightings.

Characteristics of interval gastric neoplasms detected within two years after negative screening endoscopy among Koreans

Background In Korea, where gastric cancer is highly prevalent, biennial endoscopy is recommended among individuals over 40. Even under regular screening, some are still diagnosed at advanced stages. We aimed to identify characteristics of interval gastric neoplasms (IGNs) with rapid progression. Results Newly-diagnosed gastric neoplasms detected in screening endoscopy between January 2004 and May 2016 were reviewed. Among them, those who had previous endoscopy within 2 years were enrolled. Endoscopic findings, family history of gastric cancer, smoking, and H. pylori status were analysed. Totally, 297 IGN cases were enrolled. Among them, 246 were endoscopically treatable IGN (ET-IGN) and 51 were endoscopically untreatable IGNs (EUT-IGN) by the expanded criteria for endoscopic submucosal dissection. Among EUT-IGNs, 78% were undifferentiated cancers (40/51) and 33% showed submucosal invasion (13/40). They were median 2.0 cm in size and more commonly located in the proximal stomach than ET-IGNs (70.6% vs. 41.9%, p < 0.001). EUT-IGN was independently related with age < 60 (OR, 2.09; 95%CI, 1.03–4.26, p = 0.042), H. pylori (OR, 2.81; 95%CI, 1.20–6.63, p = 0.018), and absent/mild gastric atrophy (OR, 2.67; 95%CI, 1.25–5.72, p = 0.011). Overall and disease-specific survival were not significantly different between the two groups, however EUT-IGN tended to have short disease-specific survival (overall survival, p = 0.143; disease-specific survival, p = 0.083). Conclusions Uniform screening endoscopy with two-year interval seems not enough for rapid-growing gastric neoplasms, such as undifferentiated cancers. They tended to develop in adults younger than 60 with H. pylori infection without severe gastric atrophy. More meticulous screening, especially for proximal lesions is warranted for adults younger than 60 with H. pylori infection before development of gastric atrophy

A Study on the Burn Pattern Experiments in Structure Fire

The fire has created tremendous damage, yet skilled fire investigators can read the fire patterns left by the fire. Through the fire patterns interpretation and analysis, fire investigators should be able to determine exactly how and where the fire or explosion started. Fire patterns can help the fire investigator trace fire movement back to the point of origin. The origin and cause investigation for is attempting to determine the first material ignited, the source of ignition, and how the two brought together to cause the ignition. The investigators should read the fire scene to establish the area of origin. In this study, through burn pattern experiments, fire behavior in the compartment, fire pattern formation mechanism, fire patterns reproducibility, fire patterns persistence through flashover and full room involvement condition, fire scene reconstruction for fire origin determination, and other fire pattern’s temperature will be discussed and analyzed in depth. Burn test was conducted to recognize and analyze fire patterns created in the phase of pre flashover or post flashover in the compartment (container house). In addition, fire pattern experiments are designed to test combustible material, including polyurethane foam with a lower thermal inertia or wooden chair with a higher thermal inertia. During these experiments, through the thermocouple fire pattern’s temperature will be measured in the stage of pre flashover or post flashover.

Understanding the accelerator from resources-based perspective

Purpose - This study aims to explore Accelerators and their practices in sustaining start-ups within their innovative programs for these companies based on the resource-based perspective. Moreover, with an ever-increasing demand for Accelerators amongst start-up companies, this study also demonstrates the importance of Accelerators, as it pertains to new venture creation. Design/methodology/approach - This research uses an exploratory case study approach to examine a comparative view of leading Accelerator companies in the USA and Korea based on resource support. Findings - The results of this study show that there are a number of differences between Accelerators of the two countries in terms of the resources they support for early-stage start-ups. The findings also show some similarities. However, in Korea, the Accelerator landscape is limited, where mentorship, resources and investments are not readily accessible, resulting in low success rates for Korean start-up companies. These limitations have had a negative trickle-down effect when providing entrepreneurs with strong access to resources and investors, which highly affects the success rates of early-stage start-ups. Practical implications - In terms of the resource-based theory, this study contributes to the growth of early start-ups by emphasizing the role of the accelerator and suggesting the extent and impact that entrepreneurs have access to resources and investors. Originality/value - With significant growth in start-ups around the world, the necessity for start-up funding and mentorship has increased drastically. Start-up companies need various types of assets, systems, knowledge and information to achieve their goals. In Accelerators, start-ups receive all the aforementioned resources while also improving their entrepreneurial skills. Start-up companies have many options in seeking investors who support both tangible and intangible resources to boost growth. While there is a wealth of information on traditional funding methods, there are few studies that shed light on the role of Accelerators from the resource-based point of view