Jo Jan 15, 2024
In recent years, fractional calculus has been applied in the modeling and control of various kinds of physical systems, as well known and documented in many control theories or in application literature.
In fact, the design of feedback controllers for fractional order systems (FOS) has been approached from generalizations of some classical design methods. For example, the fractional order PID controller can be seen as generalization of a traditional PID controller.
Various engineers designed fractional PID controllers using different designs and tuning methods. However, tuning of a fractional PID controller is a challenging work, because there are five parameters to tune, which means two more parameters than a classical PID controller.
So, Hyon Chung Il, a section head at the Faculty of Automation Engineering, has proposed a design method of a fractional order [proportional derivative] controller for a type of fractional order systems, and verified its effectiveness through comparisons with other controllers such as the traditional integer order PID controller and the fractional order proportional derivative controller.
The comparisons illustrate that the IO-PID controller designed may not always be stable enough to achieve the iso-damping specification and that the proposed FO-[PD] controller outperforms FO-PD controllers.
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Jo Jan 13, 2024
Air flow measurement is an important task in many fields including process control, air conditioning systems, environmental monitoring, medical instrumentation, weather forecasting system and so forth. For many years, flow sensing was accomplished by means of large-scale mechanical flow meters such as anemometers, turbines and Pitot tubes. In recent years, many researchers have applied micromachining processes to realizing micro sensors and arrays for measuring air flow parameters. Many previous studies have demonstrated successful application of micro electro-mechanical system (MEMS) techniques to the fabrication of variety of flow sensors capable of detecting both flow rate and flow direction.
MEMS-based sensors have advantages of small size and light weight. They can briefly be divided into two categories: mechanical sensors and thermal sensors.
Recently, multi-sensor integrated technology has become fashionable in the sensor domain. This sensor shows the merits of both a drag force flow sensor and a thermal flow sensor by integrating them to obtain high sensitivity over a wide range. Although it is sensitive to both low and high rate, it has both mechanical and thermal parts.
Rim Chang Sik, a researcher at the Semiconductor Institute, has proposed a cantilever-based air flow sensor for measuring flow-rate and flow-direction simultaneously using only a mechanical part without a thermal one.
The sensing device is comprised of a standing cylinder-cantilever and an MEMS-based silicon diaphragm with eight diffused piezoresistors as sensing elements.
The device is effective to exactly determine air flow direction angle and to expand operation range with relatively simple structure.
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Jo Jan 11, 2024
The idea of using both gain and phase in robust control theory was proposed and studied by several researchers in 1980s. Especially, the robust control theory based on gain-phase information (GP robust control theory), which started to be studied in 1999 produced new concepts like Ψ-control, H∞/Ψ-control and GP mixed sensitivity control and opened up a new stage for development of robust control theory.
However, all the researches considered only Single Input Single Output (SISO) system. So, it is very important to find a solution to the Ψ-control problem for Multi Input Multi Output (MIMO) system.
Pak Kwang Hae, a researcher at the Faculty of Automation Engineering, has proposed a new solution to Ψ-control problem for SISO system and laid methodological foundations for finding a solution for MIMO system.
To verify the efficiency and applicable possibility of the designed control system, he newly designed an automotive fuel control system and compared it with previous methods through computer simulations.
The results proved that the proposed method is effective and available in practice.
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Jo Jan 9, 2024
Water is commonly used for industry, agriculture and office and domestic consumption. Water shortage is one of the most worrying problems and it is related to poor management and inefficient use of water resources. Therefore, efficient use and monitoring of water are very important. Here, water level sensing is of key importance. Many physical properties of water like relative electrical permittivity, resistivity, thermal conductivity, buoyancy, hydraulic pressure, absorption of radiation, surface reflection of sound or light waves, etc. are used for water level sensing.
Although a variety of structures of capacitive water level sensor and low capacitance probing techniques have been proposed, it is still important to develop a new type which is more convenient, flexible, simple, low-cost and easy to make for widespread application in homes and offices.
Kim Chol Man, a section head at the Faculty of Earth Science and Technology, has proposed a new low-cost capacitance-type water level sensor and low capacitance probing technique. Unlike the conventional low capacitance probing techniques which involve analog circuits such as AC-bridge, negative impedance converter, analog switch, oscillator, multiplexer, phase shifter, etc., his method is based on a direct capacitance-to-time conversion principle by a single microcontroller unit (MCU).
For test and verification, he made a prototype water level controller. The results of the experiments showed that the repeatability and linearity of the sensor are satisfactory within the tolerable limit of 0.5% full scale.
The prototype water level controller is simple and cheap enough for home and office use.
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Jo Jan 8, 2024
Seed mutagenesis can be classified into cross-breeding and artificial mutagenesis.
Crossing, a technique for producing new varieties of seeds by crossing seeds in different genera, species and varieties requires a lot of time and labor although it is cheap.
Artificial mutation, a technique that activates mutagens in seeds, takes less time and labor and it does not cost much to make a device for it. But its drawback is that mutant seeds reveal low availability.
Another artificial mutation method is based on transgenic technique. It is excellent because target genes are injected, but it is very expensive and complicated.
Therefore, Kang Myong Hyok, a researcher at the Faculty of Physical Engineering, based on the analysis of the physical factors of mutation, has developed a device that can serve as a mutagen with simultaneous action of more than two physical factors.
The physical factors he applied are pulsed high-voltage electric field that can change electrical properties of living organisms, shock wave that can momentarily provide energy strong enough to destroy cell membranes, and strong ionization field to make the surrounding environment a strong active field from an inert field stabilized in the growth activity.
He also obtained experimental results for determining suitable operation parameters necessary for mutation.
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Jo Dec 28, 2023
The empirical Bayes approach has become a common method in statistical situations. It is a statistical method for successive Bayes decisions when prior distribution is unknown but many past data are given. The inference for truncation parameters is important for evaluation of upper or lower bounds of population, so it has been studied extensively. Many authors have considered the case of one-sided truncated distribution but in practice, we face the case of two-sided one, too.
Ri Sung Hyon, a section head at the Faculty of Applied Mathematics, has investigated empirical Bayes estimation for truncation parameters of two-sided truncated distribution under squared error loss.
First, he constructed the empirical Bayes estimators of truncation parameters using size two samples and proved the asymptotic optimality of the estimators. Then, he proved that the probability of reverse estimation converges to zero as sample size goes to infinity. Finally, he presented an example to show the soundness of his theoretical results and conducted a simulation on the performance of the proposed empirical Bayes estimators.
The new proposal of using size two samples could be extended to the case of multi-dimensional truncated distributions defined on hyper-cubic domain.
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