• Journal of the Korean Mathematical Society
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• v.59 no.4
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• pp.685-697
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• 2022

Recently, Gireesh, Shivashankar, and Naika [11] found some infinite classes of congruences for the 3- and the 9-regular cubic partitions modulo powers of 3. We extend their study to all the 3^k-regular cubic partitions. We also find new families of congruences.

• Journal of the Korean Mathematical Society
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• v.56 no.1
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• pp.169-181
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• 2019

In [9], Geramita, Harbourne, and Migliore find a graded minimal free resolution of the 2nd order symbolic power of the ideal of a linear star configuration in ${\mathbb{P}}^n$ n of any codimension r. In [8], Geramita, Galetto, Shin, and Van Tuyl extend the result on a general star configuration in ${\mathbb{P}}^n$ but for codimension 2. In this paper, we find a graded minimal free resolution of the 2nd order symbolic power of the ideal of a general star configuration in ${\mathbb{P}}^n$ of any codimension r using a matroid configuration in [10]. This generalizes both the result on a linear star configuration in ${\mathbb{P}}^n$ of codimension r in [9] and the result on a general star configuration in ${\mathbb{P}}^n$ of codimension 2 in [8].

• Journal of the Korean Mathematical Society
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• v.58 no.2
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• pp.283-308
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• 2021

In [30] the author finds a graded minimal free resolution of the 2-nd order symbolic power of a star configuration in ℙn of any codimension r. In this paper, we find that of any m-th order symbolic power of a star configuration in ℙn of codimension 2, which generalizes the result of Galetto, Geramita, Shin, and Van Tuyl in [15, Theorem 5.3]. Furthermore, we extend it to the m-th order symbolic power of a star configuration in ℙn of any codimension r for m = 3, 4, which also generalizes the result of Biermann et al. in [1, Corollaries 4.6 and 5.7]. We also suggest how to find a graded minimal free resolution of the m-th order symbolic power of a star configuration in ℙn of any codimension r for m ≥ 5.

• Journal of the Korean Mathematical Society
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• v.54 no.1
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• pp.177-191
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• 2017

In this note we consider the right unit-duo ring property on the powers of elements, and introduce the concept of weakly right unit-duo ring. We investigate first the properties of weakly right unit-duo rings which are useful to the study of related studies. We observe next various kinds of relations and examples of weakly right unit-duo rings which do roles in ring theory.

• Journal of the Korean Statistical Society
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• v.27 no.1
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• pp.57-66
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• 1998

In the analysis of time series it is an important issue to determine whether a time series under study is stationary. For the test of the stationary of the time series the Dickey-Fuller (DF) type tests have been mainly used. In this paper, we consider the regular unit root tests and seasonal unit root tests based on the generalized Durbin-Watson (DW) statistics when the errors are independent. The limiting distributions of the proposed DW-type test statistics are the functionals of standard Brownian motions. We also obtain the finite distributions and powers of the DW-type test statistics and compare the performances with the DF-type tests. It is observed that the DW-type test statistics have good behaviors against the DF-type test statistics especially in the nonzero (seasonal) mean model.

• The Pure and Applied Mathematics
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• v.25 no.1
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• pp.31-38
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• 2018

In [4], the authors show that if ${\mathbb{X}}$ is a ${\mathbb{k}}-configuration$ in ${\mathbb{P}}^2$ of type ($d_1$, ${\ldots}$, $d_s$) with $d_s$ > $s{\geq}2$, then ${\Delta}H_{m{\mathbb{X}}}(md_s-1)$ is the number of lines containing exactly $d_s-points$ of ${\mathbb{X}}$ for $m{\geq}2$. They also show that if ${\mathbb{X}}$ is a ${\mathbb{k}}-configuration$ in ${\mathbb{P}}^2$ of type (1, 2, ${\ldots}$, s) with $s{\geq}2$, then ${\Delta}H_{m{\mathbb{X}}}(m{\mathbb{X}}-1)$ is the number of lines containing exactly s-points in ${\mathbb{X}}$ for $m{\geq}s+1$. In this paper, we explore a standard ${\mathbb{k}}-configuration$ in ${\mathbb{P}}^2$ and find that if ${\mathbb{X}}$ is a standard ${\mathbb{k}}-configuration$ in ${\mathbb{P}}^2$ of type (1, 2, ${\ldots}$, s) with $s{\geq}2$, then ${\Delta}H_{m{\mathbb{X}}}(m{\mathbb{X}}-1)=3$, which is the number of lines containing exactly s-points in ${\mathbb{X}}$ for $m{\geq}2$ instead of $m{\geq}s+1$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.2
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• pp.285-290
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• 2010

We investigate the outage probability in terms of QoS (quality of service) in indoor PLC network. We consider various kinds of appliances for realistic indoor PLC network. For estimation of the outage probability, we calculate the time-varying channel responses considering the loading conditions based on regular human activities and include the additive noise. We calculate the outage probability for each terminal and investigate relationship between the outage probability and the channel length, and transmit powers. Our results suggest that the outage probability is increased when the channel length becomes longer because more appliances affect the amount of reduced channel capacity and is not improved distinctly for very high and low outage threshold by increasing the transmit power. However, we can see outage probability improvement for 30% outage threshold case by increasing the transmit power.

• Journal of Electrical Engineering and Technology
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• v.8 no.2
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• pp.271-281
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• 2013

In order to improve the performance of analysis, it is important to consider the nonlinearity in power system. The Carleman embedding technique (linearization procedure) provides an effective approach in reduction of nonlinear systems. In the approach, a group of differential equations in which the state variables are formed by the original state variables and the vector monomials one can build with products of positive integer powers of them, is constructed. In traditional Carleman linearization technique, the tensor matrix is truncated to form a square matrix, and then regular linear system theory is used to solve the truncated system directly. However, it is found that part of nonlinear information is neglected when truncating the Carleman model. This paper proposes a new approach to solve the problem, by combining the Poincar$\acute{e}$ transformation with the Carleman linearization. Case studies are presented to verify the proposed method. Modal analysis shows that, with traditional Carleman linearization, the calculated contribution factors are not symmetrical, while such problems are avoided in the improved approach.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.4
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• pp.707-716
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• 2009

The levels of psychosocial stresses and fatigue of firemen were analyzed to reveal the various factors related to them. The self-administered questionnaires were performed to 262 firemen ill Cheonsju City. In terms of various levels of psychosocial stresses, 12.2% were under potential stresses, 87.8% were under high-level of stress, but healthy group was not found. The levels of fatigue symptoms divided by the median of total scores was 51.1% of low levels, and 48.9% of high levels. Multiple stepwise analysis revealed that the factors or influence on psychosocial stresses with explanatory powers of 11.5% included subjective health status, job satisfaction, job demand and alcohol drinking habits. The factors of influence on fatigue symptoms with explanatory powers of 9.0% included subjective health and regular exercises. The study results indicate that the level of stress or fatigue is so complicatedly influenced by variable factors. Thus the effective strategy for stress and fatigue reduction among firemen should include additional programs focusing on health promotion.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4493-4501
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• 2011

This study was performed to determine the levels of MMSE-K among the elderly people affiliated with long-term care insurance services in rural areas, and to reveal its association with related variables. The interviews were performed, during the period from March 1st, to May 31th, 2009, to 410 elderlies in rural areas. As a results, The prevalence of cognitive functions among all subjects were 80.5% of severe cognitive impairment, 11.7% of mild cognitive impairment, and 7.8% of normal. The prevalence of cognitive functions were lower according to the higher grade of long-term care insurance. And the prevalence of cognitive functions were lower in the group of lower educational level, unemployed, live alone, lower monthly income, bear for living expenses by sons and daughters and medical aid, lower visual acuity, with urinary incontinence, with amnesia, without regular exercise and lower frequency of going out than their respective counterparts. The hierarchial multiple regression analysis was used to reveal the explanatory powers of factors influencing on the cognitive functions level. Such factors as age, bear for living expenses, visual acuity, urinary incontinence, amnesia, regular exercise and grade of long-term care services were significantly influenced with cognitive functions. especially the factors of health status were significantly influenced with cognitive functions.