• Journal for History of Mathematics
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• v.17 no.3
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• pp.13-22
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• 2004

In this paper, we consider two conjectures, the Bieberbach Conjecture that was proved true and the Lu Qi-Keng Conjecture that was proved not true. We inspect them historically and introduce the interesting results. From them we find that the deep theory of mathematics comes from continuous conjectures.

• Microbiology and Biotechnology Letters
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• v.41 no.4
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• pp.469-471
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• 2013

In this study, we measured the anti-bacterial activity of radioisotope Lu-177 using a new laboratory instrument. The disk method used for the measurement of existing anti-bacterial antibiotics is drug diffusion into the medium. To measure the antimicrobial activity of a radioisotope, a new type of laboratory instrument is necessary to prevent the drug from spreading and the present invention was thus tested. In the medium, a space isolated separately for radioisotope injection was used to prevent the radioisotope from spreading and radioisotopes are actually injected by this system. We found that the antibacterial activity increased according to the radiation dose increases. It is expected that, through the present study, measuring the antibacterial activity of the other radioisotopes easily in the laboratory will be possible.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.1
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• pp.523-549
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• 2018

The increasing number of subscribers and demand of multiplicity of services has turned Multi-Server Authentication (MSA) into an integral part of remote authentication paradigm. MSA not only offers an efficient mode to register the users by engaging a trusted third party (Registration Centre), but also a cost-effective architecture for service procurement, onwards. Recently, Lu et al.'s scheme demonstrated that Mishra et al.'s scheme is unguarded to perfect forward secrecy compromise, server masquerading, and forgery attacks, and presented a better scheme. However, we discovered that Lu et al.'s scheme is still susceptible to malicious insider attack and non-compliant to perfect forward secrecy. This study presents a critical review on Lu et al.'s scheme and then proposes a secure multi-server authentication scheme. The security properties of contributed work are validated with automated Proverif tool and proved under formal security analysis.

• Current Optics and Photonics
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• v.4 no.3
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• pp.238-246
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• 2020

The heat distribution in crystals in a 2-㎛ acousto-optic Q-switched Tm:LuAG laser pumped by pulsed-laser-diode (pulsed-LD) intermittent-pumping technology was analyzed using COMSOL software. The thermal lensing effect of the Tm:LuAG crystal can be mitigated by pulsed-LD intermittent-pumping techniques. An experimental setup using this kind of approach achieved maximum output energy of 8.31 mJ, minimum pulse width of 101.9 ns, and highest peak power of 81.55 kW, reached at a Q-switched repetition rate of 200 Hz. It offers significant improvement of performance of the output laser beam, compared to pulsed-LD double-ended pumping technology at the same repetition rate.

• Korean Journal of Materials Research
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• v.30 no.8
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• pp.413-420
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• 2020

Lu₃Al_5-xGa_xO₁₂:Ce³⁺,Cr³⁺ powders are prepared using a solid-state reaction method. To determine the crystal structure, Rietveld refinement is performed. The results indicate that Ga³⁺ ions preferentially occupied tetrahedral rather than octahedral sites. The lattice constant linearly increases, obeying Vegard's law, despite the strong preference of Ga³⁺ for the tetrahedral sites. Increasing x led to a blue-shift of the Ce³⁺ emission band in the green region and a change in the emission intensity. Persistent luminescence is observed from the powders prepared with x = 2-3, occurring through a trapping and detrapping process between Ce³⁺ and Cr³⁺ ions. The longest persistent luminescence is achieved for x = 2; its lifetime is at least 30 min. The findings are explained using crystal structure refinement, crystal field splitting, optical band gap, and electron trapping mechanism.

• Advances in Computational Design
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• v.8 no.3
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• pp.219-236
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• 2023

In this paper, finite element modeling of the laser ultrasonics (LU) process in ablation regime is of interest. The momentum resulting from the removal of material from the specimen surface by the laser beam radiation in ablation regime is modeled as a pressure pulse. To model this pressure pulse, two equations are required: one for the spatial distribution and one for the temporal distribution of the pulse. Previous researchers have proposed various equations for the spatial and temporal distributions of the pressure pulse in different laser applications. All available equations are examined and the best combination of the temporal and spatial distributions of the pressure pulse that provides the most accurate results is identified. This combination of temporal and spatial distributions has never been used for modeling laser ultrasonics before. Then by using this new model, the effects of variations in pulse duration and laser spot radius on the shape, amplitude, and frequency spectrum of ultrasonic waves are studied. Furthermore, the LU in thermoelastic regime is simulated by this model and compared with LU in ablation regime. The interaction of ultrasonic waves with a defect is also investigated in the LU process in ablation regime. Good agreement of the results obtained from the new finite element model and available experimental data confirms the accuracy of the proposed model.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.123-125
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• 2023

As deep learning has become an essential part of human lives, the requirement for Deep Learning as a Service (DLaaS) is growing. Since using remote cloud servers induces privacy concerns for users, a Fully Homomorphic Encryption (FHE) arises to protect users' sensitive data from a malicious attack in the cloud environment. However, the FHE cannot support several computations, including the most popular activation function, Rectified Linear Unit (ReLU). This paper analyzes several polynomial approximation methods for ReLU to utilize FHE in DLaaS.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.2
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• pp.112-121
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• 2013

An approach for composing a performance optimized computational code is suggested for the latest microprocessors. The concept of the code optimization, termed localization, is maximizing the utilization of the second level cache that is common to all the latest computer systems, and minimizing the access to system main memory. In this study, the localized optimization of the LU-SGS (Lower-Upper Symmetric Gauss-Seidel) code for the solution of fluid dynamic equations was carried out in three different levels and tested for several different microprocessor architectures widely used these days. The test results of localized optimization showed a remarkable performance gain of more than two times faster solution than the baseline algorithm for producing exactly the same solution on the same computer system.

• Journal of applied mathematics & informatics
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• v.3 no.2
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• pp.217-234
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• 1996

This report introduces a faster parallel LU decomposi-tion algorithm that gives a speedup almost equal to the number of nodes used. The new algorithm takes an advantage of an important C feature that lays out a matrix using a row major scheme and is based on the currently widely used LU decomposition algorithm with one major modification to eliminate most of the communication overhead. Empirical results are included in this report. For example solving a dense matrix that contains 100,000,000 elements gives a speedup of 50 when executed on 50 nodes of an intel Paragon in parallel.

• Journal of computational fluids engineering
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• v.9 no.3
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• pp.39-48
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• 2004

In the present study, an efficient implementation technique of the van Leer's implicit operator is suggested in accordance with the Roe's explicit operator. By using an efficient treatment of the off-diagonal terms, which occupy most of the memory requirement for the linear system of equations, it is shown that the improved scheme only requires less than 30% of memory and is approximately 10-20% faster than the baseline scheme.