Jo Oct 11, 2024
Coal is a main energy resource and many households in our country use honeycomb briquettes made of coal for heating and cooking. In summer honeycomb briquettes are mainly used as fuel for cooking. But they reveal some shortcomings such as difficulty in ignition and low combustion efficiency due to the need for high ignition temperature.
The most important thing is to reduce the time and energy needed for ignition of honeycomb briquette as much as possible, and to raise the combustion rate up to the level of gas combustion for instant cooking. 150 to 200 grams of wood sticks are needed for ignition of honeycomb briquettes. If the calorific value of wood is 16MJ/kg, as much energy as 2 400 to 3 200kJ is consumed for ignition alone. What is more, a large amount of flame and harmful gases are released due to the difference in the activation energy between coal and biomass, which pollutes the environment.
Therefore, many researchers have conducted studies to lower the ignition temperature and raise the combustion rate by lowering combustion activation energy of coal. To this end, they added combustion additive to coal or mixed coal and biomass. To prevent the release of much flame during ignition with wood sticks, some researchers have developed double-layer or multi-layer ignition honeycomb briquettes to be ignited with a sheet of paper or a match stick. The problem is that if biomass like raw sawdust is added to the upper sides of briquettes as it is, it produces smoke and exerts bad influence on coking power.
Jon Chol, a researcher at the Faculty of Mining Engineering, on the basis of the analysis of biomass ignition characteristics for its size, has studied the ignition and combustion characteristics of upper side ignition honeycomb briquettes and determined appropriate crushing size and blending rate of biomass.
The results showed that the upper side ignition honeycomb briquette added with biomass has ignition time of two to three minutes on average, combustion time of 75 minutes and combustion rate of 156.12g/min, and that the most appropriate biomass crushing size is 125㎛.
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Jo Oct 10, 2024
Fishing started in Korea thousands of years ago.
Spears and hooks made of bone and stone, and sinkers made of broken earthenware are often found from the Neolithic remains in all parts of the country that have been known so far.
These fishing tools demonstrate that the Korean ancestors started fishing before the Neolithic Age.
Fishing tools developed into various types through a long course of history.
According to the archaeological discoveries, it is guessed that a wooden sailing boat must have come into being in the Bronze Age.
A big heavy sinker for deep sea fishing, an implement for spearing a fish caught in the net, scallop shells in the deep sea, etc. were found from the Chodo Remains (remains of the Bronze and Iron Ages) in Rason City. All these prove that fishing on a sailing boat in the deep sea already started in this period.
The Korean people developed the fishing method in a more efficient and diverse way over a long period of time, considering the nature and habitat of fish. They also devised a way of pickling, freezing and drying the fish for effective storage and processing.
From olden times, the Korean people have steadily developed fishery while fishing in conformity with the nature and terrain of the country.
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Jo Oct 8, 2024
In order to protect critical electronic equipment against damped sine transient currents induced into its cables due to transient electromagnetic fields, switching phenomena, platform resonances, etc., a proper measure should be taken.
In any major equipment, there must be several individual units (LRUs), which are interconnected by cable harnesses in varying lengths. When such equipment is used in severe electromagnetic (EM) environment, the loops consisting of the shields of cable harnesses, the grounded chasses of LRUs at the two ends and the ground path provide coupling with the interfering fields. The induced voltages, particularly due to the current in the cable shields, can cause temporary upset or permanent damage to the LRUs connected at either end of the cable harnesses.
To ensure satisfactory performance of the LRUs under such conditions, it is necessary to simulate appropriate conditions in a laboratory and conduct an evaluation.
In order to protect the critical electronic equipment against damped sine transient currents, Jong Hak Chol, a section head at the Faculty of Electrical Engineering, generated and induced the necessary damped sine currents into the cables of the electromagnetic compatibility test (EMCT) equipment in the laboratory. Then he developed a test equipment CS116 of Standard 461E/F and measured other factors using this equipment.
Many approaches using LC discharge have been investigated as a general way of producing damped sine current waves, but those need tiny amount of inductance and capacitance and they tend to cause wave distortion and power loss. Especially, demanding value of inductance for building a damped sine wave generator for 30MHz and 100MHz are around 5 to 14nH.
Thus, he designed and manufactured a damped sine wave generator with small inductance and capacitance, and conducted some experiments to verify its output.
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Jo Oct 6, 2024
Kkaktugi is a kind of kimchi that Korean people usually make for winter.
It is a mixture of cubed radish or cucumber with seasonings like pepper or garlic. The name kkaktugi has been said to imitate the sound heard when radish is being cubed.
Old records say that Kuryo people regarded radish as a main ingredient together with bean paste and kelp and that foodstuff preservation technique was on a high level in those days, which demonstrates that Korean ancestors processed radish and other vegetables in several ways from olden times.
A lot of seasonings added to kkaktugi make it look delicious and taste strong, which improves appetite even more.
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Jo Oct 3, 2024
The least mean square algorithm is widely used in many areas due to its simplicity and robustness. Within the LMS algorithm, the tap-length of the filter, defined as the number of tap coefficients of the adaptive filter, is an important factor that influences the performance and complexity of the LMS adaptive filter. If the tap-length is too long, it causes heavy computational burden and slows convergence rate, whereas if the tap-length is underestimated, the mean squared error (MSE) tends to increase. Therefore, segmented filter LMS (SF-LMS) algorithm, gradient descent LMS (GD-LMS) algorithm, and fractional tap-length LMS (FT-LMS) algorithm have been used to regulate the tap-length of filters. Among these variable LMS algorithms, the fractional tap-length least mean square (FT-LMS) algorithm has attracted attentions recently due to its less computational complexity and better convergence performance than other variable tap-length algorithms.
According to the steady-state performance analysis of the FT-LMS algorithm, correct choice of the step size for tap-length adaptation is very important. It provides a trade-off between the convergence rate and the steady-state bias of tap-length.
Jon Kwan Hak, a section head at the Faculty of Communications, has proposed an improved variable tap-length algorithm with variable step size for tap-length adaptation γ.
He confirmed the performance of the proposed algorithm by simulations for high and low noises, respectively. The results showed that for both noise conditions, the proposed algorithm obtains both fast convergence rate of the tap-length and small steady-state tap-length fluctuation.
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Jo Oct 2, 2024
Proverbs are known to have been widely used in Korea since the period of Three Kingdoms.
The proverb found in “Samgukyusa” (“Chronicles of the Three Kingdoms”) is the first one in all the existing historical documents. At that time it was called “rion”. After that it was given the name “sangon” and it has been called “soktam” (Korean pronunciation of “proverb”) since the middle years of the feudal Joson dynasty.
The first book of proverbs in Korea is “Sunoji” (by Hong Man Jong) published in the seventeenth century. It has a collection of more than 130 proverbs that were popular in those days. Later, “Paekonhae” (by Ri Ik), “Yangyopki” (by Ri Tok Mu), “Idamsokchan” (by Jong Yak Yong), etc. were compiled.
The first proverb dictionary written in Korean is “Joson Rion” compiled by Choe Won Sik in 1913, which has over 900 proverbs. Later, several proverb books were compiled.
After liberation, “Book of Korean Idioms and Proverbs”, “Book of Korean Proverbs”, “Korean Proverbs”, “Dictionary of Korean Idioms and Proverbs”, etc. were compiled and published.
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