Accurate quantitative evaluation of the performance of pneumatic rock drills is important to improve the performance and put the design on a scientific basis.

A rock drill receives energy from a compressor or a hydraulic system and transfers impact energy through the drill and bit to crush rocks. Impact energy, the main performance index of rock drills, was estimated by many researchers in an indirect way because direct measurement is difficult.

Those measurement methods are difficult to apply to the performance tests of mass-produced drills as they require modification of the structure of percussion drills or preparation of standardized rock samples.

In view of these practical requirements, Pak Chol Hyok, a researcher at the Faculty of Mining Engineering, proposed a new structure of impact energy measurement device and analyzed its performance through simulation.

The analysis results show that the stress wave transmitted through the drill rod is converted into the pressure wave of oil filled inside the cylinder. Its maximum value is 15-28MPa, varying with position. Therefore, suitable location of measurement points can raise measurement accuracy while extending the service life of the sensor.

The newly proposed measuring device is more reliable and more convenient to operate than the method of determining the impact energy by stress wave measurement.

Generally, the design of small acoustic devices for mobile phones uses acoustic analysis techniques involving equivalent circuits. This acoustic analysis technique is an approach to find acoustic parameter values on acoustic equivalent circuits from the size values of angular acoustic device by the classical acoustic theory-based acoustic theory equation, and to predict acoustic properties electronically based on their acoustic parameters. Thus, it provides simple modeling and it does not take a long time to interpret. However, this acoustic analysis technique cannot predict exact acoustic characteristics because it cannot represent the variation of acoustic parameters due to the change of the “position relationship” or “geometry” in acoustic devices.

Han Myong U, a researcher at the Faculty of Communication, proposed an acoustic parameter estimation method which verifies, by finite element method, the structure of resonance frequency response due to the acoustic porthole position that could not be explained by the original equivalent circuit analysis method, and explains acoustic weight and acoustic capacity.

A genetic algorithm has been used for traditional acoustic parameter estimation, but it requires a very long time to estimate the correct factor because it depends on the search by mutations around the optimal solution. The proposed estimation method uses a hybrid genetic algorithm that switches to simulated annealing that performs well local retrieval after convergence to some extent around the optimal solution by a genetic algorithm.

He compared the measured results with the simulation results by the proposed method to validate its effectiveness. The results showed that the proposed estimation approach can accurately estimate acoustic capacity with respect to resonant frequency, and acoustic mass parameters, and it is possible to estimate acoustic parameters with respect to the position or shape of a compact acoustic device.

Pyongyang onban is one of the famous traditional dishes of Pyongyang. The name “onban” literally means warm boiled rice.

According to historical records, onban was mentioned in Siuijonso and Kyugonyoram compiled in the 19th century, but it had been widely spread among people much long before.

To make Pyongyang onban, clean and boil polished rice first. Husk mung beans and powder them with a millstone to make pancakes. And hard-boil chicken in cold water and tear it into bite-sized pieces and boil the broth after seasoning with soy sauce and salt. Parboil mushrooms in boiling water and fry and season them with spices. To make spiced sauce, mix soy sauce with beaten spring onion and garlic, pulverized red pepper, sesame oil and powder and some chicken broth.

Put warm boiled rice in a bowl, add chicken, mushrooms, a spoonful of spiced sauce and mung bean pancakes on it as garnish. And then, put finely chopped onion and red pepper and thinly sliced egg on it. It is served after pouring the broth into the bowl or with the broth in another bowl.