• The KIPS Transactions:PartB
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• v.10B no.7
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• pp.735-742
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• 2003

In the information retrieval system, document clustering technique is to provide user convenience and visual effects by rearranging documents according to the specific topics from the retrieved ones. In this paper, we clustered documents using K-Means algorithm and present the effect of index terms weighting scheme on the document clustering. To verify the experiment, we applied Latent Semantic Indexing approach to illustrate the clustering results and analyzed the clustering results in 2-dimensional space. Experimental results showed that in case of applying local weighting, global weighting and normalization factor, the density of clustering is higher than those of similar or same weighting schemes in 2-dimensional space. Especially, the logarithm of local and global weighting is noticeable.

• Journal of the Korea Society of Computer and Information
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• v.18 no.8
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• pp.87-93
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• 2013

A baby-step giant-step algorithm divides n by n blocks that possess $m={\lceil}\sqrt{n}{\rceil}$ elements, and subsequently computes and stores $a^x$ (mod n) for m elements in the 1st block. It then calculates mod n for m blocks and identifies each of them with those in the 1st block of an identical elemental value. This paper firstly proposes a modified baby-step giant-step algorithm that divides ${\lceil}m/2{\rceil}$ blocks with m elements applying $a^{{\phi}(n)/2}{\equiv}1(mod\;n)$ and $a^x(mod\;n){\equiv}a^{{\phi}(n)+x}$ (mod n) principles. This results in a 50% decrease in the process of the giant-step. It then suggests a reverse baby-step giant step algorithm that performs and saves ${\lceil}m/2{\rceil}$ blocks firstly and computes $a^x$ (mod n) for m elements. The proposed algorithm is found to successfully halve the memory and search time of the baby-step giant step algorithm.

• Convergence Security Journal
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• v.18 no.1
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• pp.13-18
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• 2018

Efficiency is one of the most important factors in cryptographic systems. Cheon et al. proposed a new exponent form for speeding up the exponentiation operation in discrete logarithm based cryptosystems. It is called split exponent with the form $e_1+{\alpha}e_2$ for a fixed element ${\alpha}$ and two elements $e_1$, $e_2$ with low Hamming weight representations. They chose $e_1$, $e_2$ in two unbalanced subsets $S_1$, $S_2$ of $Z_p$, respectively. We achieve efficiency improvement making $S_1$, $S_2$ balanced subsets of $Z_p$. As a result, speedup for exponentiations on binary fields is 9.1% and speedup for scalar multiplications on Koblitz Curves is 12.1%.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.31 no.3
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• pp.533-544
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• 2021

Using Shor algorithm, factoring and discrete logarithm problem can be solved effectively. The public key cryptography, such as RSA and ECC, based on factoring and discrete logarithm problem can be broken in polynomial time using Shor algorithm. NIST has been conducting a PQC(Post Quantum Cryptography) standardization process to select quantum-resistant public key cryptography. The multivariate quadratic based signature scheme, which is one of the PQC candidates, is suitable for IoT devices with limited resources due to its short signature and fast sign and verify process. We analyzes classic attacks and quantum attacks for Rainbow which is the only multivatiate quadratic based signature scheme to be finalized up to the round 3. Also we compute the attack complexity for the round 3 Rainbow parameters, and analyzes the security level of Rainbow, one of the PQC standardization candidates.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.5
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• pp.15-20
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• 2023

Until now, Pollard's Rho algorithm has been known as the most efficient way for discrete algebraic problems to decrypt symmetric keys. However, the algorithm is being studied on how to further reduce the complexity of O(${\sqrt{p}}$) performance, along with the disadvantage of having to store the giant stride m=⌈${\sqrt{p}}$⌉ data. This paper proposes an array method for cycle detection in discrete logarithms. The proposed method reduces the number of updates of stack memory by at least 73%. This is done by only updating the array when (x_i<0.5x_i-1)∩(x_i<0.5(p-1)). The proposed array method undergoes the same number of modular calculation as stack method, but significantly reduces the number of updates and the execution time for array through the use of a binary search method.

• Safety and Health at Work
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• v.15 no.1
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• pp.59-65
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• 2024

Background: Different job strain formulations based on the Job Demand-Control model have been developed. This study evaluated longitudinal associations between job strain and psychological distress and whether associations were influenced by six formulations of job strain, including quadrant (original and simplified), subtraction, quotient, logarithm quotient, and quartile based on quotient, in randomly selected Japanese workers. Methods: Data were from waves I and II of the Survey of Midlife in Japan (MIDJA), with a 4-year followup period. The study sample consisted of 412 participants working at baseline and had complete data on variables of interest. Associations between job strain at baseline and psychological distress at follow-up were assessed via multivariable linear regression, and results were expressed as β coefficients and 95% confidence intervals including R² and Akaike information criterion (AIC) evaluation. Results: Crude models revealed that job strain formulations explained 6.93-10.30% of variance. The AIC ranged from 1475.87 to 1489.12. After accounting for sociodemographic and behavioral factors and psychological distress at baseline, fully-adjusted models indicated significant associations between all job strain formulations at baseline and psychological distress at follow-up: original quadrant (β: 1.16, 95% CI: 0.12, 2.21), simplified quadrant (β: 1.01, 95% CI: 0.18, 1.85), subtraction (β: 0.39, 95% CI: 0.09, 0.70), quotient (β: 0.37, 95% CI: 0.08, 0.67), logarithm quotient (β: 0.42, 95% CI: 0.12, 0.72), and quartile based on quotient (β: 1.22, 95% CI: 0.36, 2.08). Conclusion: Six job strain formulations showed robust predictive power regarding psychological distress over 4 years among Japanese workers.

• Journal of Microbiology and Biotechnology
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• v.6 no.5
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• pp.352-357
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• 1996

The partition of proteins in the salt-rich phase of polyethylene glycol (pEG)/salt aqueous two-phase systems is limited by the salting-out effects of salt. The logarithm of the concentration of proteins partitioned in the salt-rich phase decreases linearly with increases in the concentration of salt in the salt-rich phase (salting-out). Therefore, the partition of a given protein in the salt-rich phase of aqueous two-phase systems can be estimated from the salting-out constant. The slope of the solubility line (salting-out con-stant) for a given protein is determined by the type of salt in the two-phase systems.

• Journal of the Korean Society of Tobacco Science
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• v.4 no.2
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• pp.57-61
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• 1982

For evaluating kinetic parameters of various reactions and materials a straight- forward method has been studied by the variable heating rate method in DSC analysis. Based on the linear relationship between the logarithm of the heating rate and reciprocal Peak temperature, this method allows calculation of activation energy and the Arrhenius frequency factor by only one observation of the peak temperature versus the heating rate. According to tile D function, D=-In P(x)/dx, to x(=$\frac{E}{RT}$) we can calculate reasonably accurate activation energy, tile Arrhenius factor and the rate constant, and predict half-life times of various materials from the kinetic calculation.

• Korean Journal of Materials Research
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• v.4 no.8
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• pp.927-933
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• 1994

The effect of particle shape and size on the settling characteristics in monodisperse suspensions of non-spherical particles was investigated. The slope index n values which was obtained from the plot of logarithm of settling rate vs. voidage were increased with the decrease of particle size because different amount of liquid could be adsorbed on irregular particle shape and/or size at same volume concentration. From the experimental results, an equation, $n_{i}=n(a+b/d_{v})$ where n is value of spherical particles, dv is minimum particle diameter and a, b are constants for characteristic of particles.

• Honam Mathematical Journal
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• v.32 no.3
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• pp.525-536
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• 2010

Let $X_1,X_2,\cdots$ be identically distributed $\rho$-mixing random variables with mean zeros and positive finite variances. In this paper, we prove $$\array{\lim\\{\in}\downarrow0}{\in}^2 \sum\limits_{n=3}^\infty\frac{1}{nlogn}P({\mid}S_n\mid\geq\in\sqrt{nloglogn}=1$$, $$\array{\lim\\{\in}\downarrow0}{\in}^2 \sum\limits_{n=3}^\infty\frac{1}{nlogn}P(M_n\geq\in\sqrt{nloglogn}=2 \sum\limits_{k=0}^\infty\frac{(-1)^k}{(2k+1)^2}$$ where $S_n=X_1+\cdots+X_n,\;M_n=max_{1{\leq}k{\leq}n}{\mid}S_k{\mid}$ and $\sigma^2=EX_1^2+ 2\sum\limits{^{\infty}_{i=2}}E(X_1,X_i)=1$.