Jo Aug 8, 2024
Unijunction transistor (UJT) is a semiconductor with two ohmic base contacts and an emitter p-n junction, so it is called double-base diode. Its static(S-shaped) I-V characteristic has a region with negative differential resistances. Therefore, UJTs are used in pulse generators, sawtooth generators and converters. UJT-based circuits are well known to be simpler and more reliable than those based on diodes and bipolar transistors.
Recently, transducers where the output signal frequency depends on physical quantities such as temperature, light, magnetic field, stress, concentration of gas and radiation level, have been designed with UJTs. Thus, improvement of the switching characteristic of UJT leads to that of the characteristics of these transducers.
To improve the switching characteristic of UJT, a number of researchers have investigated the radiation effect on it. To the best of our knowledge, there are no reports in the literature regarding how the neutron irradiation of UJT affects its peak point voltage.
Pae Kyong Il, a researcher at the Semiconductor Institute, has proposed a new analytical expression for the peak point voltage of UJT considering the effect of neutron irradiation, and proved its validity by comparing the calculated values and those measured from the neutron irradiation on an Si planar UJT.
His study has shown that the calculated values of the peak point voltage of UJT are in good agreement with the measured ones, that the peak point voltage of UJT decreases after neutron irradiation, and that the peak point voltage of UJT decreases gradually with the growing intensity of neutron fluence.
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Jo Aug 4, 2024
The silicon steel plate is widely used as core materials of various devices such as a transformer and an electromotor. However, in order to solve the energy problem, it is very important to develop soft magnetic materials with less iron loss.
Fe-based amorphous and nano-crystalline alloys are widely used because of its low cost and iron loss about one fifth to one third of silicon steel plates. But, they are restricted to some degree in application because the value of maximum flux density of these materials is about 80% of silicon steel plates. Therefore, researches to develop soft magnetic materials with higher maximum flux density and lower core loss have been performed. As a result, new Fe-based nano-crystal soft magnetic materials have been developed. Among them, Fe-Cu-B system nano-crystalline soft magnetic materials are attracting a great deal of attention.
In most studies, the experimental results of the influence of copper, silicon and boron on the magnetic properties were analyzed, but the thermodynamic changing process was not described in detail.
Jo Chol Min, a researcher at the Faculty of Materials Science and Technology, has conducted a study to thermodynamically solve the influence of Cu addition on the crystallization of the Fe-based nano-crystalline soft magnetic alloy fabricated by the melt spinning method. In addition, he has analyzed the influence of silicon and boron on the magnetic properties of Fe-based nano-crystalline soft magnetic alloys to determine the reasonable composite.
He found that the crystallization activation energy of Fe-based alloys containing copper was lower than copper-free alloys, which indicates that copper is effective to accelerate the crystallization of alloys and increase the magnetic property. He also demonstrated that in crystallization heat treatment, the maximum flux density and coercive force of the Fe-based nano-crystalline soft magnetic alloy containing copper were the best with 2% of Si.
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Jo Jul 30, 2024
People want to live in a cleaner environment and more developed living conditions. Various harmful substances such as toxic materials, gas, dust and dirt come into being from the daily life of people. These substances pollute air, water, soil, etc. and destroy ecological environment, thus doing direct or indirect harm to people.
As an acidic igneous rock containing quartz, feldspars and mica as essential minerals, granite is widely used for decoration of the outer walls of buildings. However, during the processing of granite, granite waste in which 30% is dust is generated. This waste is used as construction filler for building materials, but most of it is left in the open air or landfilled. Consequently, soil, underground water and source of stream are polluted and the concentration of dust in the air is increased. Especially, the particle size of fine granite dust (FGD) is so small that exerts severe harmful influence on the environment.
Recycling of this FGD into eco-friendly material can be very profitable to the economy as well as environment protection.
Ri Chol Ju, a researcher at the Faculty of Earth Science and Technology, has proposed a method of synthesizing zeolite from waste granite powder with low energy (fusing at the temperature of 800℃) and at low cost (using an effective solvent-sodium carbonate).
The results showed that 13X zeolite can be successfully synthesized through pretreatment at the relatively low temperature from what is manufactured by separating chemically stable quartz from FGD.
This method could be applied to all the waste produced from the processing of other rocks containing crystalline quartz.
If you need some more information, please refer to his paper “Hydrothermal synthesis of 13X zeolite by using feldspars separated from waste granite powder” in “International journal of environmental science and technology” (SCI).
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Jo Jul 28, 2024
Development and use of natural energy plays an important role in guaranteeing the sustainable development of economy and satisfying the energy demands. In this field, study on the solar energy is particularly important. Recently, the efficiency of perovskite solar cells (PSCs) which have become the focus of solar energy development almost reached the efficiency of silicon solar cells and therefore a lot of efforts are being made to ensure the stability of solar cells.
The stability of PSCs primarily depends on the stability of perovskite which performs the function of light absorber in devices. For this reason, many researchers are trying to improve the heat and humidity stability of perovskite.
Recently, it has been found that ion liquid, which has been studied in several fields including medicine due to its special properties such as high viscosity, low vapor pressure and incombustibility, can be used as an additive or a solvent for perovskite precursor to improve the performance and stability of PSCs.
Ion liquid, well known as an eco-friendly harmless solvent, has polarity that can solve perovskite precursor, so it can replace the toxic DMF or DMSO that have been conventionally used for fabrication of PSCs.
Kang Jin Hyok, a researcher at the Faculty of Information Science and Technology, investigated the influence of ion liquid methylammonium acetate (MAAc) on the characteristics of perovskite and the performance of hole transport material (HTM)-free PSCs with carbon electrode when it is used as a solvent of precursor for preparing perovskite.
The perovskite was prepared by solid–gas reaction between dimethylammonium lead iodide (DMAPbI3) and methylamine (MA). DMAPbI3 was solved by ion liquid MAAc instead of DMF and it was used as a precursor.
The perovskite film based on ion liquid was more uniform and denser than the one based on DMF, thus improving the crystallinity and crystal size of perovskite. The analysis result showed that the nonradiative recombination of cells decreased and the open circuit voltage could be improved when using MAAc instead of DMF.
For further details, you can refer to his paper “The characteristics of hole-transport material-free perovskite solar cells with carbon electrode made by using ion liquid methylammonium acetate solvent” in “Results in Optics” (SCI).
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Jo Jul 26, 2024
Increasing the measurable distance and the displacement measurement limit of a self-mixing displacement sensor poses one of the most important problems to improve the sensor’s performance.
In order to solve the problem, there has to be found an estimation method of the optical feedback factor for a strong feedback regime.
The hardship of the estimation in this regime is brought about by a strong speckle noise and the restriction of normalization methods presented hitherto.
Kim Chol Hyon, a section head at the Faculty of Physical Engineering, has found an approach to improving the accuracy of the self-mixing sensor, which can work even for long range and large displacement, by deciding the region of the optical feedback factor based on the ratio of fringe height and by using it and the fringe counting method.
The experiments showed that the SM displacement sensor based on the new approach will be a great help to the enlargement of the measurement range of the sensor.
If further information is needed, please refer to his paper “Amelioration of accuracy of displacement measurement in strong feedback regime based on region decision: enlargement of measurement range of self-mixing displacement sensor” in “Optics Communications” (SCI).
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Jo Jul 25, 2024
To raise the speed and accuracy of displacement retrieval by overcoming the weakness of time-consuming parameter estimation and complex displacement retrieval algorithm is very important in improving the real-time quality of measurement.
Kim Il Hyok, a student at the Faculty of Physical Engineering, has proposed a new method for parameter estimation and displacement retrieval which does not require complex normalization and is of high precision of displacement retrieval and incomparably less time-consuming than existing data fitting based methods.
It is a high-speed and high-precision method of displacement reconstruction based on data-fitting method in the near-half-fringe zone collaborating with the fringe-counting method. The method proposed is applicable to any optical feedback level and to any motion. The method provides the fastest estimation and the highest precision of displacement retrieval. Its displacement reconstruction error is less than 16nm and its estimation speed is over 30 times as fast as conventional methods.
You can find the details in his paper “Betterment of displacement retrieval method based on data fitting in near-half-fringe zone” in “Applied optics” (SCI).
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