Jo Nov 17, 2022
Several works have revealed the inclusion properties between the Orlicz spaces, which are complicated in the proof process and very difficult to apply.
Kim Jin Ju, a lecturer at the Faculty of Applied Mathmatics, has formulated a necessary and sufficient condition for the existence of inclusion properties between weighted and weighted weak Orlicz spaces, which is a more generalized space than an Orlicz space, using the characteristic function of a sphere.
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Jo Nov 15, 2022
There may be potential flaws in the whole process of quality formation. The time and expenditure for their control are different according to when they are detected.
Many people found one famous principle while they were summing up their quality management. That is the Law of Ratio 1:10:100.
It means that it takes an hour and 1 won to manage a flaw of quality at the stage of development and design, 10 hours and 10 won at the stage of production, and 100 hours and 100 won at the stage of marketing. That is to say, plan: production: marketing = 1:10:100.
Kang In Song, an institute head at the Faculty of Management of Industrial Economy, has formulated 6 types related to the time of flaw detection and rectification and analyzed the influences of each type on customer satisfaction, time and cost.
Type 1-4: stages of development and design, design examination, production, and test, respectively. In each stage, quality flaws are found and controlled.
Type 5 and 6: stages when quality flaws have been transferred to customers. Type 5 gives priority to troubleshooting and maintenance and also employs refund or exchange of goods. Type 6 is when quality flaws transferred to customers cannot be controlled by enterprises.
Enterprises can choose one of these types to manage quality flaws.
The effects on customer satisfaction, time and cost are:
The enterprise which agrees to Type 1 might make the best choice by giving great satisfaction to the customers and ensuring minimum time and cost. It guarantees preventive management of quality. This enterprise can be said to have quality management level of 6σ.
Any enterprise in favor of Type 2 may give basic satisfaction to the customers and control flaws with comparatively short time and low cost. It has quality management level of 5σ. Its drawback is relative – it is not preventive but has pursuit property and delays the time of starting production.
An enterprise whose quality management goal is Type 3 may have the following advantages. It is preventive and gives partial satisfaction to the demand of the customers. It might ensure production and supply in good time and save a lot of money for equal and continuous improvement even if it needs 10 times as much expenditure. It might have quality management level of 4σ.
An enterprise in favor of Type 4 may not have good points by and large but flaws are not transferred to the customers. It might have quality management level of 3σ. It is not preventive but has pursuit property. It does not satisfy customers’ requirement but ask them for its quality level. It might delay supply and need 10 times its expenditure, in particular in the last stage.
The enterprise in Type 5 might not have good points but if any, it is responsible for flaws and takes measures even though they have already been transferred to the customers. It has quality management level of 2σ. It might always deal with the customers to fix exchange or refund the goods. It has a problem of whom to allocate extra pay – the enterprise or the customers. It might need time for fixing and servicemen and equipment for it.
Any enterprise in Type 6 may have decreased income and legal problems. It might injure its reputation, causing a lot of loss and hardly managing its own business, as flaws are transferred to customers, which makes them disappointed. It is on the verge of bankruptcy. Its quality management level is 1σ.
The 6 types mentioned above let us aware of different effects on customer’s satisfaction, time and cost.
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Jo Oct 30, 2022
Perovskite solar cells (PSCs) are the next generation of photovoltaic technologies that use inorganic-organic hybrid perovskite of ABX3 type structures as light harvesting materials.
Most transparent electrodes for flexible PSCs are made of indium tin oxide (ITO). Although these ITO transparent electrodes have high transparency and conductivity (80% and 15Ω/m2, respectively), they have a number of problems including limited indium sources, high cost due to deposition techniques (sputtering, evaporation and pulsed laser deposition, etc.) and high mechanical brittleness.
Since transparent conductive films based on AgNWs show excellent performance such as high optical transmittance and low sheet resistance along with simple fabrication process and excellent mechanical flexibility, they have been deemed as the most promising alternative to ITO.
However, the transparent electrodes made of bare Ag nanowire networks have a rough surface and the gaps between silver nanowires cause serious parasitic lateral current flow, which leads the performance of devices to the dramatic failure.
Jon Sang Mo, a researcher at the Faculty of Applied Chemistry, has resolved problems with incorporating AgNW networks into PSCs such as smooth surface morphology, space filling and chemical stability, by employing solution-deposition of conductive ATO nanoparticles onto pre-existing AgNW networks at low temperatures.
The PET/AgNW/ATO composite transparent electrodes showed a transmission of 76–82 % in the visible region with an excellent sheet resistance of 18Ω/m2, similar to the commercial PET/ITO plastic substrates.
To build up flexible PSCs, he adopted the simple architecture, in which the CH3NH3PbI3 thin film was sandwiched between ZnO (as the electron-selective layer) and the carbon electrode (as the hole-selective layer) on the AgNW/ATO composite transparent electrodes.
Under AM 1.5 G and 100 mW/cm2 simulated sunlight illumination, the flexible PSCs based on AgNW/ATO composite transparent electrodes achieved PCEs of 5.07 %. JSC, VOC, and FF were 9.8mA/cm2, 835mV and 0.62, respectively.
The new fabrication technique on such a cheap transparent electrode could advance the roll-to-roll mass production of flexible low-cost PSCs.
You can find detailed information about this in his paper “Flexible perovskite solar cells based on AgNW/ATO composite transparent electrodes” presented to the SCI Journal “Synthetic Metals”).
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Jo Oct 28, 2022
Son Won Chol, an institute head at the Faculty of Materials Science and Technology, who successfully developed a new method of hardfacing a worn drill bit by using a build-up electrode with coatings such as nitrided ferrochromium and WC, has been working hard to make further achievements.
In the past, build-up electrodes with Fe-Cr-V-Mo-Ti, Fe-Cr-Mn-V-Ti and Fe-Cr-W-V were used to repair a drill bit for drilling rocks of low strength (f<5).
In general, a hard alloy with high bending strength is used to drill hard rock thanks to its high stability on impact load and that with low bending strength is used for soft rock.
What he used to develop build-up material of the drill bit with high bending strength and toughness was Fe-Cr-Mn-V-Ti-WC system alloy.
He added WC and nitrided high carbon Fe-Cr in coating flux to form a large amount of carbonitride in weld metal for improving the bending strength and toughness.
Based on the effect of the content of ferro-alloys on the hardness and bending strength of weld metal, it was found that the reasonable contents of ferro-alloys to ensure HRC 62 and bending strength of 480MPa were nitride ferrochromium of 37%, ferromanganese of 8%, ferrotitanium of 8%, ferrovanadium of 8% and tungsten carbide of 12%.
Then, considering the effect of weld layers on the microstructure and properties of weld metal and the geometric dimension of the drill bit, he selected two weld layers and heat input 14.20kJ/cm. Finally, he could ensure hardness of weld metal HRC64.
This method can be used to deposit a worn drill bit at coal mines and mines where the strength of rock is medium (f=5~8).
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Jo Oct 26, 2022
In sedimentology, stratigraphic sequences and cycles are ordered by time spans and physical scales such as thickness, and bounded by discontinuities including unconformities or flooding surfaces.
Song Man Hyok, a section head at the Faculty of Earth Science and Technology, has proposed a spectral analysis method based on wavelet transform (WT) maxima and used it as a quantitative tool to identify multiorder stratigraphic boundaries and cycles in well log data.
The proposed spectral analysis is based on quantitative analysis of the center frequencies and resolutions of Gaussian wavelets in time and frequency, and it uses a combination of the WT maxima based on both the first order Gaussian wavelet with a high time resolution and the seventh order Gaussian wavelet with a high frequency resolution.
WT maxima spectra, which can characterize the evolution of WT maxima across scales and periods along WT maxima lines concerned with sequence boundaries, are used to detect dominant spectral peaks corresponding to the time-period domain WT maxima and to determine WT maxima spectral slopes.
The WT maxima spectral slopes are helpful for discriminating sequence boundaries from intrasequence cyclic variations in well log data, and the time-period domain WT maxima are used to relate the detected boundaries to relevant cycles.
He has introduced interval WT maxima spectra and stationary indexes related to the WT maxima spectra as indicators that could be used for hierarchical ordering of the boundaries and cycles.
Application of the proposed method to well log data shows that this method is efficient in identifying multi-order sequences that relate well to the Milankovitch cycles.
The detailed information about this is found in his paper “Spectral Analysis Based on Wavelet Transform Maxima: Identification of Multi-order Stratigraphic Boundaries and Cycles” presented to the SCI Journal “Mathematical Geosciences”.
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Jo Oct 22, 2022
In general, commercialized medium-sized asynchronous wind turbines are fully-automated facilities designed to operate in a parallel connection to the grid; in case of isolated operation, they need to be combined with diesel generators.
Choe Ki Yong, an institute head at the Faculty of Automation Engineering, has studied a method of producing electricity of maximal quality with the wind, by constructing a new stand-alone hybrid (medium-sized asynchronous wind turbines, UPS with battery and photovoltaic array) power system without a diesel generator.
He has proposed a new architecture of a stand-alone hybrid power system which consists of a medium-sized asynchronous wind turbine, a UPS, a current limiter (reactor), a photovoltaic array, and consumer and dump loads; Accordingly, a supervisory control and data acquisition (SCADA) for this system has been suggested along with the operation strategies depending on the output power of the UPS and the wind turbine, consumer load and the battery voltage of UPS.
The case study was confirmed through the simulation results of the operation of a new stand-alone hybrid (two 110 kW asynchronous wind turbines, 250 kVA UPS with battery, reactor, 36 kW photovoltaic array, consumer and dump loads) power system.
The results of the simulation showed that the system frequency change of the new stand-alone hybrid power system was 60±0.5 Hz and that of the wind + diesel stand-alone hybrid system was 60±1 Hz, for the sudden change of consumer load and gust.
More information can be found in his paper “New architecture and SCADA for stand-alone hybrid (medium-sized asynchronous wind turbine + UPS with battery + photovoltaic array) power system without diesel generator” presented to the SCI Journal “Wind Energy”.
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