Incremental Determination and Hierarchy-Matrix-Desc...

Jo Dec 24, 2024

Formal Concept Analysis (FCA) is one of the major formats for knowledge extraction, reduction, representation and analysis. FCA is formulated based on a formal context represented by a binary relation between a set of objects and a set of attributes. Formal concept lattice is the core of the mathematical theory of FCA.

Applying FCA methods to large formal contexts could bring many challenges, because the algorithm to extract formal concepts can have an exponential complexity in the worst case. Hence, the determination problem has been widely discussed in many scientific works ever since, which leads to the development of many efficient algorithms. In general, these algorithms can be divided into two categories, i.e. batch algorithms and incremental algorithms. Batch algorithms usually construct the lattice in a bottom-up (or top-down) approach, while incremental algorithms compute the lattice by adding objects (or attributes) to a given context one by one.

Among all types of lattice construction algorithms, incremental algorithms have a unique advantage. The input formal context may not be fixed in a realistic application of FCA, which means the present lattice has to be updated or a new lattice should be computed from scratch. Obviously, computing the corresponding changes only and updating the current lattice should be a better choice, which can be handled by incremental algorithms.

Generating all extents of the generalized one-sided concept lattice by the incremental algorithm is usually based on the operation of Galois connection, and the operation needs to scan the formal context. This becomes a significant computing overhead, especially when the formal context is large.

With respect to the description problem, the researcher who formulated FCA mentioned that the most communicative description is given by Hasse diagrams. However, it is difficult to autonomously understand the hierarchy of the concepts from Hasse diagrams for any information retrieval software. Thus, Pak Chol Hong, a researcher at the Faculty of Applied Mathematics, has proposed methods of describing the hierarchy of a concept lattice by using a hierarchy-matrix, estimating the connectivity of concepts by the hierarchy-matrix and describing the Hasse diagram via a hierarchy-matrix.

If there is a method of determining the generalized one-sided concept lattice and describing its Hierarchy-matrix sequentially, the more useful software with autonomous intelligence, which is based on FCA from the generalized one-sided formal context, can be built. On this basis, he has presented a new efficient incremental algorithm that performs the operation of Galois connection for determining the generalized one-sided concept lattice only once and describes its hierarchy-matrix sequentially. In addition, he has evaluated the feature and effectiveness of the proposed algorithms.

Preparation of Mg-Al-La Master Alloys using Molten ...

Jo Dec 22, 2024

Mg-Al alloys are widely used in various fields such as architecture and aviation due to their low density, high specific strength, good corrosion resistance and ease of processing. The components applied to special vehicles need to have high temperature creep resistance. The addition of a small amount of rare earth elements in the Mg-Al alloy can meet this requirement.

The research group led by Jang Pok Nam, an institute head at the Faculty of Metal Engineering, has already worked on the preparation of Mg-Al-La master alloy by chloride-fluoride molten salt electrolysis in MgCl₂-KCl-AlF₃-La₂O₃ system. In this method, AlF₃ exists in a solid state in molten salts and it is consumed through chemical reactions going with electrolysis. However, the separation of this solid fluoride and the resulting master alloy is not easy and evaporation loss of chlorides is big due to relatively high electrolytic temperature.

Therefore, the research group has proposed a method of preparing Mg-Al-La master alloy by chloride electrolysis to reduce electrolytic temperature and facilitate the separation of electrolytes and alloys.

No studies have been reported on the preparation of Mg-Al-La master alloys by molten salt electrolysis in MgCl₂-KCl-AlCl₃ molten salts.

After preparing the Mg-Al-La master alloy by molten salt electrolysis in MgCl₂-KCl-AlCl₃ ternary molten salt, they have investigated the factors affecting the element contents and current efficiencies in the production of Mg-Al-La master alloy, such as electrolysis temperature, cathode current density and electrolysis time.

He has found that increasing electrolytic temperature favors the increase in the contents of Al and La in the alloy, and the optimum electrolytic temperature is 600-650℃, and that as cathodic current density and electrolytic time increase, the content of Mg in the alloy also increases steadily but the content of La decreases.

Study on the Distribution of Hydrothermal Alteratio...

Jo Dec 20, 2024

Research for new deposits using the satellite image analysis method has already been carried out by many previous researchers. Studies to predict mineral prospecting sites by satellite image analysis have been mostly conducted to identify mineralized alteration zones and to detect linear structures.

Satellite image analysis generally begins with remote sensing. The integrated data is prepared for the user. In this stage, the integrated data is interpreted by various methods. In data interpretation, images are interpreted to identify various phenomena with regard to their importance.

It is widely accepted that hydrothermal alteration plays an important role in ore formation. The desirable distribution of alteration zones around the limited borders of an ore body facilitates outdoor exploration activities. Generally, hydrothermal alteration processes lead to emanation of clay and other silicate minerals, including kaolinite, sericite, quartz, chlorite, epidote, and calcite. The application of both spectral and statistical analyses of remotely sensed data can identify the above-mentioned minerals and explore the buried deposits. Hydrothermal alteration zones can be recognized from the spectral characteristics of main mineral assemblages.

Based on the spectral characteristics of main mineral assemblages, Ra Chung Yol, a section head at the Faculty of Earth Science and Technology, has determined the distribution of the hydrothermal alteration zone in the study area, using band-ratio analysis, principal component analysis, and colorimetric synthesis methods.

He has concluded that the hydrothermal alteration zone in the study area was widely distributed over an area of 2 000m×200m above the surface under the control of the ore-bringer structure, especially at the contact with the alkaline rock mass.