• Korean Journal of Mathematics
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• v.28 no.4
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• pp.907-913
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• 2020

Let R be a commutative ring with identity and let M be a w-module over R. Denote by ℱM the set of all w-submodules of M such that (M/N)w is w-cofinitely generated. Then it is shown that M is w-Artinian if and only if ℱM is closed under arbitrary intersections, if and only if ℱM satisfies the descending chain condition.

• Journal of the Korean Mathematical Society
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• v.51 no.3
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• pp.509-525
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• 2014

Let R be a commutative ring with identity. An R-module M is said to be w-projective if $Ext\frac{1}{R}$(M,N) is GV-torsion for any torsion-free w-module N. In this paper, we define a ring R to be w-semi-hereditary if every finite type ideal of R is w-projective. To characterize w-semi-hereditary rings, we introduce the concept of w-injective modules and study some basic properties of w-injective modules. Using these concepts, we show that R is w-semi-hereditary if and only if the total quotient ring T(R) of R is a von Neumann regular ring and $R_m$ is a valuation domain for any maximal w-ideal m of R. It is also shown that a connected ring R is w-semi-hereditary if and only if R is a Pr$\ddot{u}$fer v-multiplication domain.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.5
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• pp.504-515
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• 1997

In this paper, interference of non-GSO/MSS system into M/W radio stations has been analyzed as two aspects. One is that PDF(Power Flux Density) levels, which are received by M/W radio stations from non-GSO satellites, were simulated and compared with the threshold level specified in ITU-R SF.357. The other is that C/I values, which have been utilized in estimating interference between conventional fixed services, were simulated and analyzed by means of calculating excess time percent and duration below the C/I protection ratio. As the results, it was shown that interference levels received by M/W stations from non- GSO/MSS satellites don't exceed above the threshold level at all, even if changing parameters related with M/W stations. In addition, the excess percent time below the interference protection ratio is a long term of 32% in the case of Iridium interfering into a M/W stations route, but only a short term of 1.71% in the case of Globalstar interfering into a M/W stations route.

• The Journal of Engineering Geology
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• v.33 no.3
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• pp.403-411
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• 2023

The possibility of utilizing radiant solar energy as a renewable energy resource in Tajikistan was investigated by assessing solar irradiance using XGBoost algorithm. Through training, validation, and testing, the seasonality of solar irradiance was clear in both actual and predicted values. Calculation of hourly values of solar irradiance on 1 July 2016, 2017, 2018, and 2019 indicated maximum actual and predicted values of 1,005 and 1,009 W/m², 939 and 997 W/m², 1,022 and 1,012 W/m², 1,055 and 1,019 W/m², respectively, with actual and predicted values being within 0.4~5.8%. XGBoost is thus a useful tool in predicting solar irradiance in Tajikistan and evaluating the possibility of utilizing radiant solar energy.

• Bulletin of the Korean Mathematical Society
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• v.59 no.1
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• pp.213-226
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• 2022

Let R be a ring and M an R-module. Then M is said to be regular w-flat provided that the natural homomorphism I ⊗_R M → R ⊗_R M is a w-monomorphism for any regular ideal I. We distinguish regular w-flat modules from regular flat modules and w-flat modules by idealization constructions. Then we give some characterizations of total quotient rings and Prüfer v-multiplication rings (PvMRs for short) utilizing the homological properties of regular w-flat modules.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.224-227
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• 2006

We have chained 459nm blue laser radiation generated by intracavity sum frequency generation( SFG ) due to the mixing of the 1064 nm laser output of a Nd:YVO4 pumped by diode and the 809nm radiation from higg-power semiconductor laser(500mW). The maximum blue output power of 0.95 mW was obtained using 400 mW input power of semiconductor laser at the type II phase matching condition (${\psi}=90^{\circ}\;{\theta}=90^{\circ}$). The threshold input power of blue laser generation was 120 mW.

• KIEAE Journal
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• v.15 no.4
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• pp.21-28
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• 2015

Purpose: Although security lights are used to secure pedestrian visibility and safety at nighttime, they can generate light trespass in the neighboring residential space. To prevent this, standards for acceptance limits on vertical illuminance and light pollution by the windows of residential buildings are presented. Method: This study thus representatively selected three types of lamps and, through an evaluation and analysis of the physical and subjective discomfort glare per lamp, proposed a discomfort glare index for each lamp. The evaluation and analysis according to the lamps were conducted through experiments. The variables were the security lights' lamps (NH 100W, MH 70W, LED 50W), installation angles ($0^{\circ}$, $20^{\circ}$), and installation distances (3m, 5m, 7m, 9m). Result: According to the results of the discomfort glare evaluation depending on the angles and distances of the security lights, the following minimum standards are proposed: for NH 100W, a discomfort glare index of 30 and an installation distance of 4m; for MH 70W, a discomfort glare index of 32 and an installation distance of 4m; and, for LED 50W, a discomfort glare index of 31 and an installation distance of 6m, respectively. In addition, this paper recommends the use of MH 70W, when the road width is 4m-6m, and LED 50W, when the road width is over 6m, respectively.

• Bulletin of the Korean Mathematical Society
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• v.56 no.5
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• pp.1187-1198
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• 2019

Let R be a domain with its field Q of quotients. An R-module M is said to be weak w-projective if $Ext^1_R(M,N)=0$ for all $N{\in}{\mathcal{P}}^{\dagger}_w$, where ${\mathcal{P}}^{\dagger}_w$ denotes the class of GV-torsionfree R-modules N with the property that $Ext^k_R(M,N)=0$ for all w-projective R-modules M and for all integers $k{\geq}1$. In this paper, we define a domain R to be w-Matlis if the weak w-projective dimension of the R-module Q is ${\leq}1$. To characterize w-Matlis domains, we introduce the concept of w-Matlis cotorsion modules and study some basic properties of w-Matlis modules. Using these concepts, we show that R is a w-Matlis domain if and only if $Ext^k_R(Q,D)=0$ for any ${\mathcal{P}}^{\dagger}_w$-divisible R-module D and any integer $k{\geq}1$, if and only if every ${\mathcal{P}}^{\dagger}_w$-divisible module is w-Matlis cotorsion, if and only if w.w-pdRQ/$R{\leq}1$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.1
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• pp.115-125
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• 1998

This paper examined the feasibility of adding a new NGSO/MSS(Non-Geostationary orbit/Mobile satellite service) service link to a frequency band which is already allocated to fixed-service microwave(M/W) system. To achieve this goal, the NGSO/MSS handset performance under the influence of the M/W multiple stations and the influence of handsets on the M/W station were both analyzed. Sharing criterions were also obtained by means of coordination contour in the former case, and handset capacity in the latter case. As the results, it was proven that sharing was feasible only when the vertical distance between handset and trendline was above 4 km except front and back points of M/W antenna bore sight under influence of 9 hops(the distance between hops = 50 km) M/W system on the NGSO/MSS handset, and only when the capacity of handset was below $7.0\times10^{-14}$ handsets/ $m^{2}$ under influence of handsets on the M/W station.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.196-206
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• 1999

In this paper, we have estimated the interference effects between the NGSO/MSS system and the fixed-service M/W system for sharing the NGSO/MSS system into the frequency band operated by the existing M/W system. Between above two systems, the interference effects must be analyzed in the following three points. That is, PFD(Power Flux Density) level must be obtained in the case of the interference from NGSO satellites into M/W stations, C/I(Carrier-to-Interference Ratio) and the coordination contour in the case of the interference between NGSO/MSS feeder link and a M/W station, and the interference power level and coordination contour in the case of the interference between NGSO/MSS service link(handsets) and M/W stations. Therefore, in order to obtain above three criteria, we have developed the analytical model, introduced the related equations and estimated the system performance by means of the simulation and the theoretial analysis. It is expected that the results will be utilized in setting the criterion for sharing between the NGSO/MSS system and the M/W station.