The rotor of a steam turbine is a main element for converting thermal energy into mechanical energy, and its lifetime affects the safety of the whole unit. The units in power plants face several constraints during operation. For instance, the start-up time of a steam turbine is affected by thermal stress. Especially, due to the heavy variation of operation environments, some features of a rotor such as thermal stress, apparent expansion and thermal strain get worse. If they exceed the limitation, the corresponding elements are damaged or even destroyed, causing fatal accidents.

For rapid start-up of a unit, it is necessary to find out its appropriate start-up curve, and it should be operated accordingly to improve the safety and economic efficiency of the plant.

Optimization of turbine start-up in power plants has been studied in many aspects so far. Most of the models were built for real-time simulations. They reflected the features of stage groups of turbine using real-time operation database and various equations for quickness, and in most cases, the efficiency of stage groups were considered to be invariable. In order to determine the thermal stress exerted on the rotor during the start-up and shut-down of a turbine, it is necessary to accurately evaluate the inlet and outlet parameters of the nozzle and blades at each stage, not stage groups. Therefore, detailed calculations for each stage should be conducted to determine the pressure and enthalpy at the nozzle and blades, and their relative internal efficiency.

Rim Ju Yong, a researcher at the Faculty of Thermal Engineering, built a model of a 210MW subcritical condensing steam turbine for a power plant to determine the parameters mentioned above, and composed a special program with VC. Then, according to the operation regulation of turbine, he framed various cold start-up schedules. After that, he calculated the steam parameters on the parts of all stages by using the special program, and studied the temperature field and stress field by the finite element method (FEM).

Taking the calculation results as sample data, he established a regression model to determine the stress at the risk point of rotor. Based on the regression model, he determined the optimal cold start-up schedule using genetic algorithm (GA).

The results show that the fatigue lifetime increases by 20% with the decrease in the maximum von Mises stress by 1.4%, and the start-up period of the optimized schedule is reduced by 124min compared to the original one.

In information security systems, a single authentication mechanism plays a very important role in information processing systems as it provides convenient and secure authentication in multi-Web service environments today when service systems are growing rapidly, and thus there is a lot of research on it around the world. In particular, the access control schemes in single authentication mode have been studied a lot worldwide.

Verifying user’s trust in systems and performing a variety of access controls are very important as a large number of attacks on service systems are attributable to the malicious behavior of registered users.

The characteristics of SSO system make it very difficult to apply the traditional RBAC (Role Based Access Control) model directly because the roles of each service system may be the same but the corresponding rights may be different. Thus, there has been a lot of research on applying RBAC models that can facilitate user management to single authentication systems.

However, the previous dynamic access control schemes based on RBAC model failed to propose a detailed access control scheme according to user’s behavior changes.

Having analyzed the characteristics of the single authentication system and the reliability-based access control scheme, Myong Kwang Min, a section head at the Faculty of Information Science and Technology, has proposed a secure and flexible access control system for SSO system by combining the entropy weighting and the reliability-based access control scheme, and evaluated its performance.

The evaluation results show that the proposed access control model is superior to all single authentication schemes and trust-based access control schemes.

Among the traditional dishes that the Korean people have enjoyed from olden times are pickles, which reflect their taste and likings.

The Korean ancestors had long known that salt can prevent food spoilage and used it in their dietary life to pickle such foods as vegetables, fish and meat so as to store them for a long time.

Such practice of pickling has a very long history. According to historical records, Koreans produced salt from ancient times and ate salted fish a lot.

Kimchi can also be said to have started from pickling at first.

There were parsley kimchi, chives kimchi, radish kimchi, leaf mustard kimchi, etc.

These kinds of kimchi are salted foods created by Koreans in the course of making wide use of pickles in their dietary life for a long time.

Pickling was further developed in the period of the feudal Joson dynasty.

Pickles in those days were divided into salt pickles directly preserved in salt, pickles preserved in bean paste or soy sauce, vinegared pickles and bran pickles using rice bran according to pickling agents. They were also divided into vegetable pickles, meat pickles, fish pickles and herb pickles according to ingredients.

Pickles are very good preserved foods that make it possible to store seasonal foods for a long time under the climatic conditions of the DPRK with distinctive seasons.