• 한국가시화정보학회:학술대회논문집
• /
• 2007.11a
• /
• pp.134-137
• /
• 2007

The temporal evolution of wake behind a circular cylinder oscillating rotationally with a relatively high forcing frequency has been investigated experimentally using a dynamic PIV technique. Experiments were carried out with varying the frequency ratio $F_R\;(=f_f/f_n)$ in the range from 0.0 (stationary) to 1.6 at oscillation amplitude of ${\theta}_A=30^{\circ}$ and Reynolds number of $Re=4.14{\times}10^3$. Depending on the forcing condition ($F_R$), the flow was divided into three regimes; non-lock-on ($F_R=0.4$), transition ($F_R=0.8$, 1.6) and lock-on regimes ($F_R=1.0$) with markedly different flow structure in the near-wake region behind the cylinder. When the frequency ratio was less than 1.0 ($F_R{\le}1.0$), the rotational oscillatory motion of the cylinder decreased the length of the vortex formation region and enhanced the mutual interaction between large-scale vortices across the wake centerline. The entrainment of ambient fluid seemed to play an important role in controlling the near-wake flow and shear-layer instability. However, the flow characteristics changed markedly beyond the lock-on flow regime ($F_R=1.0$) due to high-frequency forcing. At $F_R=1.6$, the mutual interactions between the vortices shed from both sides of the cylinder were not so strong. Thereby, the flow entrainment and momentum transfer into the wake center region were reduced. In addition, the size of the large-scale vortices decreased since the lateral extent of the wake was suppressed.

• Bulletin of the Korean Mathematical Society
• /
• v.59 no.3
• /
• pp.643-657
• /
• 2022

Let R be a ring and S a multiplicative subset of R. An R-module T is called u-S-torsion (u-always abbreviates uniformly) provided that sT = 0 for some s ∈ S. The notion of u-S-exact sequences is also introduced from the viewpoint of uniformity. An R-module F is called u-S-flat provided that the induced sequence 0 → A ⊗_R F → B ⊗_R F → C ⊗_R F → 0 is u-S-exact for any u-S-exact sequence 0 → A → B → C → 0. A ring R is called u-S-von Neumann regular provided there exists an element s ∈ S satisfying that for any a ∈ R there exists r ∈ R such that sα = rα². We obtain that a ring R is a u-S-von Neumann regular ring if and only if any R-module is u-S-flat. Several properties of u-S-flat modules and u-S-von Neumann regular rings are obtained.

• Bulletin of the Korean Mathematical Society
• /
• v.58 no.3
• /
• pp.659-668
• /
• 2021

Let R be a semiprime ring with maximal right ring of quotients Q_mr(R), and let n₁, n₂, …, n_k be k fixed positive integers. Suppose that R is (n₁+n₂+⋯+n_k)!-torsion free, and that f : 𝜌 → Q_mr(R) is an additive map, where 𝜌 is a nonzero right ideal of R. It is proved that if [[…[f(x), x^n₁], …], x^n_k] = 0 for all x ∈ 𝜌, then [f(x), x] = 0 for all x ∈ 𝜌. This gives the result of Beidar et al. [2] for semiprime rings. Moreover, it is also proved that if R is p-torsion, where p is a prime integer with p = Σ^k_i=1 n_i and if f : R → Q_mr(R) is an additive map satisfying [[…[f(x), x^n₁], …], x^n_k] = 0 for all x ∈ R, then [f(x), x] = 0 for all x ∈ R.

• Journal of Life Science
• /
• v.21 no.4
• /
• pp.502-508
• /
• 2011

The purpose of this study was to evaluate the methods of identifying zygotic seedlings of crosses between 'Morita unshiu' (Citrus. unshiu Marc.) and 'Ponkan' (C. reticulata Blanco). In order to investigate the frequency and position of zygotic seedlings and to determine the efficiency of zygotic seedling identification, random amplified polymorphic DNA (RAPD) and sequence-related amplified polymorphism (SRAP) were performed using UBC (9, 27, 229, 230, and 254) primers and F4/R27, F7/R14, F12/R10, and F44/R62 primer sets, respectively. A total of 37 putative zygotic seedlings out of 55 individuals were selected by RAPD and SRAP. The F7/R14 primer pair showed a screening ability of 45.5% (25/55), whereas the primer UBC27 revealed the highest efficiency of zygotic seedling identification (50.9%, 28/55). When both UBC27 and F7/R14 were properly used for selection of hybridized seedlings of 'Morita unshiu' (C. unshiu Marc.) and 'Ponkan' (C. reticulata Blanco), screening efficiency was increased to 60% (33/55) for putative zygotic seedlings. Thus, it is possible to select putative hybrid zygotic seedlings in an accurate and effective manner by RAPD and SRAP.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.10
• /
• pp.735-741
• /
• 2007

An axial F.R.P. fan model for cooling tower is developed. The fan is designed using the equations for one dimensional inviscid flow through the fan blade. Fan shape is swept forward with a parabolic function. Calculations of the three dimensional turbulent flow around the fan are carried out to investigate performance of the fan. Data of the total pressure rise and hydraulic efficiency can be obtained for the various setting angles. Calculated values of the total pressure rise and hydraulic efficiency at the design point are less than those of the design specification. The prototype of the F.R.P. fan is made by laminating of the fiberglass and epoxy resins on the mold of fan shape.

• Journal of the Korean Society for Heat Treatment
• /
• v.3 no.1
• /
• pp.1-7
• /
• 1990

To investigate the influence of r.f. power and electrode distance on the TiN deposition, TiN films were deposited onto STC3, STD11 steel and Si-wafer from gas mixtures of $TiC_4/N_2/H_2$ using the radio frequency plasma assisted chemical vapor deposition. The crystallinity of TiN film could be improved by the increase of r.f. power and the decrease of electrode distance. The TiN coated layer contains chlorine, its content were decreased with increasing r.f. power as well as decreasing electrode distance. And the thickness of deposited TiN was largely affected by r.f. power and electrode distance. The hardness of deposited TiN reached a maximum value of about Hv 2,000.

• IE interfaces
• /
• v.21 no.3
• /
• pp.254-261
• /
• 2008

Connected-(r,s)-out of-(m,n) : F system is an important topic in redundancy design of the complex system reliability and it's maintenance policy. Previous studies applied Monte Carlo simulation and genetic, simulated annealing algorithms to tackle the difficulty of maintenance policy problem. These algorithms suggested most suitable maintenance cycle to optimize maintenance pattern of connected-(r,s)-out of-(m,n) : F system. However, genetic algorithm is required long execution time relatively and simulated annealing has improved computational time but rather poor solutions. In this paper, we propose the ant colony optimization approach for connected-(r,s)-out of-(m,n) : F system that determines maintenance cycle and minimum unit cost. Computational results prove that ant colony optimization algorithm is superior to genetic algorithm, simulated annealing and tabu search in both execution time and quality of solution.

• The Journal of the Acoustical Society of Korea
• /
• v.13 no.1
• /
• pp.93-98
• /
• 1994

This study aims to find the theoretical consideration of the basic simularity rule between scale model experiment and real building as a results ; 1. In the case of room acoustics, $f_m=n\cdot{f_r}\;T_m=T_r/n\; \alpha_m(f_m)=\alpha_r(f_r)$ 2. That of sound Insulation : $TL_m(f_m)=TL_r(f_r)$

• Journal of the Korean Society of Safety
• /
• v.6 no.1
• /
• pp.26-30
• /
• 1991

Flammability, and released toxic halogen gases during combustion about two kinds of flame-retardant flexible foam(F.R. flexible PV foam) were investigated. One of the above was F.R. flexible PU foam with the containment of halogen and the other was manufactured with pure flexible PU foam in aqueous solution of alumina trihydrate(ATH) and dried 4 hours at 10$0^{\circ}C$. Flammability by L.O.I and UL94 HF-1 of the two materials were similarly shown. And combustion gases were analyzed with GC-Mass. HCI, CI$_2$ and HF were detected at both halogen being contained F.R. flexible PU foam and ATH dolng one The reason, to find halogen gases from burning ATH-containing F, R. flexible PU foam which wasn't used for any halogenated F.R., could be considered as by using trichlorofluoromethane with blowing agent to make PU foam. The relative quanity of relesed halogen gases of F.R. flexible PU foam with the containment of halogen had been indicated tree times HCI and CI$_2$, two times HF than ATH containing, respectively.

• Communications of the Korean Mathematical Society
• /
• v.10 no.1
• /
• pp.207-213
• /
• 1995

Let $(\Omega, F, P)$ be a probability space with F a $\sigma$-algebra of subsets of the measure space $\Omega$ and P a probability measure on $\Omega$. Suppose $a > 0$ and let $(F_t)_{t \in [0,a]}$ be an increasing family of sub-$\sigma$-algebras of F. If $r > 0$, let $J = [-r,0]$ and $C(J, R^n)$ the Banach space of all continuous paths $\gamma : J \to R^n$ with the sup-norm $\Vert \gamma \Vert = sup_{s \in J}$\mid$\gamma(s)$\mid$$ where $$\mid$\cdot$\mid$$ denotes the Euclidean norm on $R^n$. Let E,F be separable real Banach spaces and L(E,F) be the Banach space of all continuous linear maps $T : E \to F$.