One spring day Chairman Kim Jong Il visited the park of Mangyongdae Schoolchildren’s Palace (then) for memorial tree-planting.
Lest the Chairman, who was always busy with the state affairs, should waste much time ...
In January, Juche 104 (2015), the respected Comrade Kim Jong Un visited the newly built Pyongyang Mushroom Farm (then).
Enjoying the panoramic view of the farm, he said with affection that a glance ...
It happened when the respected Comrade Kim Jong Un was inspecting a building-materials production base.
One of the leading officials of the factory courteously expressed his determination to not only produce more building ...
The geometry of TICS has an influence on the output signal of sensors. This relation is determined by the cell constant given by the size of a sensor.
Several researchers demonstrated three methods to determine the cell constant of TICS― experimental method using standard solutions with known conductivity, single-loop calibration method and analytical method by rough approximation. They pointed out that in order to measure the lower ranges of conductivity which require a smaller cell constant, the diameter of sensor and measuring container must be enlarged.
But until now it has not been suggested to deal with the influence of the geometric parameter of a sensor on the cell constant and the regulation band of the cell constant with the size of a sensor. So, it is worthwhile to do some research on the relation between the cell constant and the size of a sensor.
Jang Hyon, a researcher at the Faculty of Electronics, has analyzed the relation between the geometry of a TICS (inner radius r1, outer radius r2 and height t of the sensor toroid) and its cell constant through simulations by the finite element method and experiments.
Taking account of actual conditions, he considered the sizes (r1, r2 and t) of a sensor within several tens of millimeters.
A key factor which influences the cell constant is the hole diameter (2r1) of the sensor toroid. The effective superior limit of inner radius of the sensor toroid that can give the smallest cell constant is about 30 mm.
The theoretical results on the cell constants of sensors in different sizes coincided with the experiment results with less than about 5% relative error.
The conductivity below limit value that can be adjusted by cell constant is about 0.36 times the lowest bound value of conductance measurement range.
Satellite-based free space optical quantum key distribution system is being considered as a very promising technique which is capable of overcoming the transmission limits of fiber-based QKD system and constructing a global quantum communication network.
It was demonstrated that laser beam has orbital angular momentum generated from spiral topological structure of itself in addition to spin angular momentum polarization property. In this case, unlike polarized quantum state, a photon may have a number of quantum states. Using optical orbital angular momentum as information carriers, information can be modulated in the infinite dimensional space. Furthermore, there is a possibility of increasing data throughput efficiently and enhancing the stability of system. Consequently, applying the orbital angular momentum to quantum key distribution, it is possible to increase the quantum key generation rate remarkably and this mode is suitable for free space optical quantum communication.
Some researchers considered polarization coding in FSO QKD system which is one of the good ways to realize quantum communication in free space. For convenience of analysis, they assumed that the air is in a steady state when QKD is performed between two parties in free space. However, the air is in a dynamic state of continuous flow rather than in a fixed state. It is known that there is a possibility of upgrading the performance of FSO QKD system when orbital angular momentum is applied to QKD.
O Ju Hyok, a researcher at the Faculty of Communications, has investigated more suitable QKD protocols for FSO quantum communication and analyzed the impact of atmospheric turbulence on quantum bit error rate of QKD system. He has also developed two QKD protocols suitable for FSO QKD system (one formed by combining random phase modulation with BB84 protocol and the other by combining entanglement modulation using photon orbital angular momentum with BB84 protocol) and analyzed the effects of atmospheric turbulence on the performance of FSO QKD system.
The simulation results demonstrate two facts. First, QBER of FSO QKD system increases with increase in air refraction index structural constant, that is, the intensity of atmospheric turbulence. Second, for FSO QKD, entanglement-based OAM QKD is more suitable than random phase modulation method.
Since the ocean covers over 70% of the earth’s surface and marine transportation has many advantages, it is continuously increasing and shipbuilding is still considered as an important industry. This is constantly increasing the demands for ships as well as for the efficiency improvement of shipbuilding. Therefore, shipbuilding field is widely introducing advanced techniques including computer programs for ship design and shipbuilding to raise its modernization level.
Some processes such as seam landing of hull surface are carried out on computers, but they are mainly based on the skills and experiences of designers.
Seam or butt landing (simply seam landing) of shell plates in the hull lofting process which is the first step of shipbuilding plays an important role in raising the speed and quality of shipbuilding and lowering its cost. However, this work has not been modernized until now because of its complexity and it has been done manually on paper and on mold lofts by the skills and experiences of designers.
Some computer programs for ship design and shipbuilding such as AVEVA, Ship Constructor, Maxsurf, etc. give help with seam landing of shell plate. These programs contain some graphics processing functions for seam landing in ship surfaces. However, seam landing of hull surface by computers still depends on the skills and experiences of designers. Therefore, the result of seam landing of hull surface is dependent on designer’s ability and this work lacks scientific accuracy. The main reason for low scientific accuracy of this work is its complexity.
Pae Ho Rim, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has proposed an optimization model for seam landing and a solving method by GA. On this basis, he has confirmed the validity of the proposed method.
First, for the optimum seam landing, he built an optimization model with the sum of cutting, shearing, forming and welding cost as an objective function. As obvious in the objective function, costs of cutting, shearing, forming and welding depend on seam landing.
Second, he proved that the optimization problem for seam landing of hull surface is a topological optimization one when the number and form of seams are design variables and it is a form optimization one when only the form is a design variable.
Finally, he demonstrated that optimization method using GA gives a better solution than the seam landing of an existing ship and that by Taguchi’s method.