The frequency is an important operating parameter of power systems and electrical equipment, and the frequency measurement is the basis of the operation and monitoring of power systems and electrical equipment and of relaying protection. The frequency of power systems is an important index of power quality, and it is very important for the fault diagnosis of power systems. Larger power system capacity increases the stability requirement of power systems, which consequently leads to higher measurement accuracy of the frequency of power systems.

Many frequency measurement theories and calculation methods have been developed so far. Although they can be used in real applications with relatively accurate frequency measurements and small measurement errors, they are all based on discrete Fourier transform (DFT) under asynchronous samples, and approximate computational methods have been employed for real frequency measurement calculations.

Im Jung Bin, a researcher at the Faculty of Electrical Engineering, used vector theory to accurately measure the frequency under asynchronous sampling conditions for sinusoidal signals with constant frequency offset. He proposed a frequency measurement principle based on the vectors at three sampling points and calculated the frequency based on the calculation of the real and imaginary parts at each sampling point using DFT transform. Likewise, he proposed a frequency calculation method under asynchronous sampling and verified through simulation that the frequency measurement method under asynchronous sampling using three sampling values is accurate.

This provides a method for accurately and quickly measuring the frequency in the development of power measuring devices and protective devices.

The reliability problems of shock tube initiation systems have been a focus in mining and demolition blasting. Current blasting practices widely use shock tubes as a non-electrical initiation means. Shock tube initiation systems typically consist of shock tubes coupled with a donor detonator. Shock tubes are used to transmit an initiation impulse to the target detonators. The shock tubes are initiated and detonated by the adiabatical pressing of the mixture of explosive material and air due to the explosion shock by detonators.

Reliability is the most important for any initiation system, and efficient initiation of shock tubes is an important factor.

There has been some research on initiating a bunch of shock tubes so far. However, all the researchers have concentrated on the experimental study of lateral coupling mode.

Choe Yong Chol, a researcher at the Faculty of Mining Engineering, numerically investigated the influence of coupling modes on the explosion shocks and their propagation to shock tubes, and validated it through the test results of the initiation reliability of shock tubes in bunch.

He used lateral and frontal bunch-series coupling modes for the numerical simulations and tests.

The results showed that the peak pressures of explosion shock acting on the inside of shock tubes, and initiation rates were higher for frontal bunch-series coupling mode than for lateral mode, and that the peak pressures acting on the inside of shock tubes by numerical analysis were in good relation with the initiation rate of shock tubes in bunch by tests.

Sujonggwa, or dried persimmon punch, is a traditional drink the Korean people have prepared and enjoyed since olden times.

The details of sujonggwa are explained in such books compiled in the period of the feudal Joson dynasty as Rimwonsimnyukji (1825), Tongguksesigi (first half of the 19th century) and Siuijonso (late 19th century) and such books compiled in modern times as Cuisine of Korea.

According to Rimwonsimnyukji, the food made by preserving fruits in honey is called jonggwa and the drink made with jonggwa is called sujonggwa. This tells that various fruits were used originally to make sujonggwa. Later, only dried persimmon was used in preparing the drink.

The ingredients of sujonggwa are ginger, cinnamon, honey, dried persimmon and pine nut.

Sujonggwa is refreshing, sweet and fragrant.

The Korean people prepared and enjoyed the drink mainly on lunar New Year’s Day. It was distinctive as a drink taken on holidays and also renowned as a health drink. The frequent consumption of the drink is good for digestion and especially efficacious for treating bleeding gum.

Sujonggwa, associated with the wisdom and intelligence of the Korean people, is still encouraged as a distinctive drink at present.