Jo Jun 25, 2024
The genus Sinamia currently comprises about 8 species, all recorded in China.
Sinamia zdanskyi was first described by Stensiö, and subsequently, a great number of Sinamia were found in Gansu, Shannxi, Ningxia and Inner Mongolia around the Ordos Plateau.
A new specimen of Sinamiidae was collected from the Upper Cretaceous Seson Formation, the Democratic People’s Republic of Korea. It is similar to Sinamia liaoningensis in the shape of the more arched preopercle, relatively smaller size of the infraorbitals, more caudal fin rays, more scale rows between the origin of the anal fin and the dorsal margin of the body, and lack of serrated scales.
This discovery not only extends the geographic distribution of sinamiids, but also fills a blank in the sinamiid study in the DPRK.
You can find more information in the essay by Kim Pyong Song, an institute head at the Faculty of Earth Science and Technology, “First Occurrence of Sinamia (Amiiformes, Sinamiidae) from the Upper Cretaceous Seson Formation, Democratic People’s Republic of Korea” in “Cretaceous Research” (SCI).
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Jo Jun 23, 2024
All the digital data stored, copied and distributed on the network have their own unique information, and especially, digital images, as one of the fastest multimedia formats that can deliver their information in visual way, have a lot of information.
Most of the digital images transmitted through the network are private and, especially, digital images with sensitive information, such as medical diagnostic images, can lead to irrevocable disaster when they are disclosed to be abused. Therefore, it is very important for digital images to be digitally secured.
In general, digital images, when compared to text data, have characteristics of very large capacity, high overlap and strong correlation between adjacent pixels. In the meanwhile, digital image data require strong real-time property in communication, storage and distribution. Hence, it requires fast and secure image encryption algorithms. From this necessity, many previous researchers have proposed improved chaotic maps and applied them to various image encryption algorithms.
Chaotic map is generally classified into one-dimensional and high-dimensional ones. The former has advantages of simple structure, easy hardware and software implementation and low computational cost, while it has disadvantages of narrow chaotic behavior and non-uniform distribution of output chaotic sequences. The latter is difficult to implement in hardware and software due to its complex structure and multi-control parameters, and it also has computational complexity. In recent years, one-dimensional or multidimensional chaotic maps with good chaotic characteristics are proposed by combining the existing 1D chaotic maps that are fast and easy to implement in software and hardware.
Based on the analysis of the prior works, Pak Chan Il, a section head at the IT Institute, has designed a two-dimensional chaotic map with better chaotic performance than the prior ones and built a simple and fast pixel-level image encryption algorithm.
To start with, he configured a new 2D-ICCM (2D Infinite Collapse Coupling Map) with better chaotic performance by combining two 1D infinite collapse maps which have the best chaotic characteristics of all previous 1D chaotic maps. He confirmed through various experiments that the proposed 2D-ICCM has better chaotic performance than previous 2D chaotic maps.
Next, he proposed a new pixel-level image encryption algorithm which combined simple-structured pixel-level permutation and diffusion, and tested the performance by applying the proposed 2D-ICCM. The simulation and experimental results showed that the proposed image encryption scheme has excellent performance against various cyberattacks.
If further information is needed, please refer to his paper “A new image encryption algorithm using 2D infinite collapse coupling map” in “Multimedia Tools and Applications” (SCI).
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Jo Jun 20, 2024
Addition of Zn element into CdS improves the short circuit current density and open circuit voltage to increase the efficiency of hetero-junction based solar cells such as CdTe and CIGS, decreasing the absorption losses of the window materials in p-n junction devices and the lattice mismatch.
Over the past three decades, there have been a number of reports on the deposition and properties of Cd1-xZnxS ternary compound with a various range of Zn concentration (low Zn content, midst content and overall Zn content), using different methods like chemical bath deposition, spray pyrolysis, SILAR, vacuum evaporation, MOCVD, RF sputtering, vapor zinc chloride treatment, etc.
Ki Tong Hun, a student at the Faculty of Electronics, has deposited Cd1-xZnxS thin films (0<x<1) by the CBD method and investigated the influence of Zn content on the structural, morphological, optical and electrical properties of films by using XRD, SEM, UV-VIS spectroscopy and other analysis instruments.
The analysis results can be summarized as follows;
XRD studies revealed that the crystal phase of Cd1-xZnxS thin film changed from the hexagonal to hexagonal/cubic mixed phase at lower Zn contents, and then transformed to cubic ZnS phase as Zn content further increased.
Through the SEM measurements, he could observe certain-sized granules formed by the agglutination of Cd and Zn compounds around the nucleus due to the absorption of Cd2+ and Zn2+ ions with initial increase of Zn concentration. On the other hand, for the Zn content greater than 0.6, Cd1-xZnxS particle size decreased and the mixture phase in thin film became stable.
For further details, please refer to his paper “Investigation on the influence of Zn content on the structural, optical, morphological and electrical properties of ternary compound Cd1-xZnxS window layer for CdTe solar cell” in “Functional Materials Letters” (SCI).
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Jo Jun 18, 2024
There have been some studies related to the chemical and electrochemical behaviour of cerium in molten salts. The eutectic LiCl-KCl, the eutectic NaCl-KCl, the eutectic LiF-KF-NaF and room temperature AlCl3-1-methyl-3-ethylimidazolium chloride are used most for this kind of study, and some differences have been found in the stability and the electrochemical properties of cerium ions in these media.
Kim Pyong Hun, a section head at the General Assay Office, has studied the electrochemical reduction of CeO2 in eutectic CaCl2-NaCl melt by means of the cyclic voltammetry and the constant voltage electrolysis.
One cathodic current peak in the cyclic voltammogram was observed and a one-step electrochemical reduction mechanism of CeO2 appeared. For different hours of electrolysis at the temperature 800℃ and at the constant voltage 3.0V, the products of CeOCl and CeO2 were observed by XRD. This result confirms the electrochemical reduction sequence: CeO2→CeOCl.
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Jo Jun 17, 2024
Redox flow battery (RFB) has been developed in popularity since 1970s and become a promising large-scale energy storage system recently. RFB is an electrochemical device that stores and releases energy through redox reactions of active ion species in electrolyte. The main advantage of RFB over other electrochemical devices such as lead acid battery and lithium ion battery is that the power system could be made very flexible because of the independence of its power from its energy and that its cost per energy in high-capacity systems is particularly low. The drawback is that the ion selective membrane for these RFBs is very expensive and it should satisfy very strict requirements for several aspects including ion selectivity, electric conductivity and chemical stability.
This has led to the recent trend of not using membranes. The advantage of the soluble lead flow battery is the absence of a membrane because only one electrolyte is used.
Kim Ju Song, a researcher at the Faculty of Chemistry, has suggested lead fluoroborate dissolved in aqueous solution of fluoroboric acid as electrolyte of SLFB and investigated the electrochemical characteristics. He chose paste of waste lead acid batteries as a source of lead and investigated its effects on the performance of electrolyte.
The results are as follows.
The conductivity of 1.5 mol/L electrolyte prepared with recycled lead has a peak when the concentration of HBF4 is less than 1.0 mol/L. The kinetic characteristics of Pb2+/Pb and Pb2+/PbO2 are almost the same in both reagent grade lead and recycled lead electrolytes. When electrolytes prepared from recycled lead are used, the average charging efficiency and the average voltage efficiency are all shown to be superior to those of methanesulfonic acid cells.
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Jo Jun 16, 2024
Electrospinning is a method of producing micro/nano fibers by injecting polymer solutions in electrostatic fields. In an electric field, the polymer droplets at the nozzle tip form a Taylor cone. When the electric field force to overcome the surface tension of the polymer solution is applied, a fine spinning flow is emitted from the tip of the Taylor cone, and during its flying towards the collector, solvent evaporation and cooling of the melt result in solid nanofibers deposited onto the collector.
Recently, highly productive electrospinning methods such as multi-nozzle electrospinning and needleless elecrospinning have been proposed. Multi-nozzle electrospinning is a method with many overlapped nozzles. It is difficult to realize stable and continuous spinning because corona discharge is created by strong electrical interaction between the nozzles, due to the nonuniform distribution of the electric field at the nozzle tip. Therefore, creating a uniform electric field between nozzles is very important for multi-nozzle electrospinning. Prediction of the diameter of electrospun fibers is also important in their applications.
Not only some methods of controlling the structure and diameter of electrospun fibers by changing the structure and arrangement of nozzles, but also a number of attempts to improve the structure and orientation degree of electrospun fiber by changing the setup of collectors have been proposed. However, few attempts have been made to obtain uniform electrospun fibers by changing the shape of collector geometry.
Pak Yong Ho, a researcher at the Nano Physics Engineering Institute, has determined a new type of curved profile for a collector to obtain uniform fibers in an arched multi-nozzle electrospinning device.
Applying the calculation model for polymer jet in an electrostatic field using Calculating Fluid Dynamics (CFD), he calculated the velocity field distribution in electrospun polymer jet fluid, and determined the uniform velocity profile. Taking a curved surface determined by the uniform velocity profile as a collector, he constructed an arched multi-nozzle electrospinning system. To obtain uniform electrospun nanofiber membranes suitable for preparation of nanofiber ion exchange membrane for electrodialysis applications, he proposed an equation of the curve for collector geometry. Curved collectors need no additional means for obtaining electrospun fibres in uniform diameter.
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