• 대한수학회보
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• 제51권2호
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• pp.457-478
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• 2014

In this paper, a 3D autonomous system, which has only stable or non-hyperbolic equilibria but still generates chaos, is presented. This system is topologically non-equivalent to the original Lorenz system and all Lorenz-type systems. This motivates us to further study some of its dynamical behaviors, such as the local stability of equilibrium points, the Lyapunov exponent, the dissipativity, the chaotic waveform in time domain, the continuous frequency spectrum, the Poincar$\acute{e}$ map and the forming mechanism for compound structure of its special cases. Especially, with the help of the Project Method, its Hopf bifurcation of codimension one is in detailed formulated. Numerical simulation results not only examine the corresponding theoretical analytical results, but also show that this system possesses abundant and complex dynamical properties not solved theoretically, which need further attention.

• International Journal of Precision Engineering and Manufacturing
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• 제6권4호
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• pp.60-66
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• 2005

In this paper, we propose the basic measurement method of a 3D digitizer using a CCD camera in detail. In the localization measurement with a CCD camera, the effect of the background light and the sensitivity consideration are always problems in realizing a high precision. In this research, a new measurement principle is proposed in which the pulse compression technique known in radar is used to eliminate the effect of background light even under a low intensity light source, and the coordinate values on the CCD camera image plane are determined accurately. From the quantitative evaluation of the S/N ratio improvement and the fundamental experiment, it is verified that a substantial improvement in the S/N ratio is realized for both the background noise and the pixel noise and that a resolution of less than the pixel is sufficiently possible.

• Journal of Magnetics
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• 제20권4호
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• pp.331-335
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• 2015

The ferromagnetic and electronic structure for the $Al_xGa_{1-x}P$ and Mn-doped $AlGaP_2$ was studied by using the self-consistent full-potential linear muffin-tin orbital method. The lattice parameters of un-doped $Al_xGa_{1-x}P$ (x = 0.25, 0.5, and 0.75) were optimized. The band-structure and the density of states of Mn-doped $AlGaP_2$ with or without the vacancy were investigated in detail. The P-3p states at the Fermi level dominate rather than the other states. Thus a strong interaction between the Mn-3d and P-3p states is formed. The ferromagnetic ordering of dopant Mn with high magnetic moment is induced due to the (Mn-3d)-(P-3p)-(Mn-3d) hybridization, which is attributed by the partially filled P-3p bands. The holes are mediated with keeping their 3d-characters, therefore the ferromagnetic state is stabilized by this double-exchange mechanism.

• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3355-3360
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• 2011

The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $-15.0^{\circ}C$. The studied substrate of 1,2-phenylene phosphorochloridate is cyclic five-membered ring of phosphorus ester, and the anilinolysis rate of 1 is much faster than its acyclic analogue (4: ethyl phenyl chlorophosphate) because of extremely small magnitude of the entropy of activation of 1 compared to 4. The Hammett and Bronsted plots exhibit biphasic concave upwards for substituent X variations in the nucleophiles with a break point at X = 3-Me. The values of deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) change from secondary inverse ($k_H/k_D$ < 1) with the strongly basic anilines to primary normal ($k_H/k_D$ > 1) with the weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the transition state (TS) variation from a predominant backside attack to a predominant frontside attack, in which the reaction mechanism is a concerted $S_N2$ pathway. The primary normal DKIEs are substantiated by a hydrogen bonded, four-center-type TS.

• 대한기계학회논문집B
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• 제22권11호
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• pp.1571-1581
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• 1998

A flow visualization study was carried out for the branch pipe mixing flow in which a jet was issued normally to the fully developed pipe flow. An instantaneous laser tomographic method was used for cross flow Reynolds numbers based on the cross flow diameter D ranged $Re_{cf}=5.26{\times}10^3{\sim}1.13{\times}10^4$, diameter ratios d/D = 0.1 ~ 0.2 and velocity ratios R = 0.5 ~ 10. Oil mist with the size of about $10{\mu}m$ diameter was used for the scattering particle. The main purpose of this study was to reveal the physical mechanism and the structure of vortices formation with varying the velocity ratios and diameter ratios in the branch pipe flow. It was found that the physical mechanism and the structures of vortices formation were quite different depending on the velocity ratios. Particularly in the case of R < 1, the typical vortex shows single loop shape and that for the case of R > 1 depicts mushroom-like structure in the cross flow jet.

• Bulletin of the Korean Chemical Society
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• 제23권10호
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• pp.1445-1450
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• 2002

Solvolytic rate constants at 25 $^{\circ}C$ are reported for solvolysis of chlorodithioformate (1) in binary mixtures of water with acetone, ethanol, methanol, methanol-d, 50%methanol-d/50%D2O, and 2,2,2-trifluroethanol (TFE), and also in TFE-ethanol mixtures. The Grunwald-Winstein plot shows that the three aqueous mixtures exhibit dispersions into separate line. The correlation is improved only slightly by additional parameters NT for solvent nucleophilicity and/or I for aromatic ring parameter. Rate ratios in solvents of the same $Y_cl$ value, having different nucleophilicity provide measures of the minimum extent of nucleophilic solvent assistance, and the value of 3.35 for $[$k_{40EW}$/$k_97TFE$]_Y$ (EW = ethanol-water), is consistent with an essentially SN1 reaction mechanism. This study has shown that the magnitude of l, m and h values associated with a change of solvent composition is able to predict the SN1 reaction mechanism. log(k/$k_o$) = mY + lN + hI

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1879-1884
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• 2012

The kinetic studies on the reactions of dipropyl chlorophosphate (3O) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) have been carried out in acetonitrile at $55.0^{\circ}C$. The obtained deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are primary normal ($k_H/k_D$ = 1.09-1.01) with the strongly basic anilines while secondary inverse ($k_H/k_D$ = 0.74-0.82) with the weakly basic anilines. The steric effects of the two ligands on the rates are extensively discussed for the anilinolyses of the ($R_1O$)($R_2O$)P(=O or S)Cl-type chlorophosphates and chlorothiophosphates. A concerted mechanism is proposed with a frontside nucleophilic attack involving a hydrogen-bonded four-center-type transition state for the strongly basic anilines and with a backside attack transition state for the weakly basic anilines on the basis of the DKIEs, primary normal and secondary inverse with the strongly and weakly basic anilines, respectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2434-2453
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• 2019

To improve the separation performance of time-frequency overlapped radar and communication signals from a single channel, this paper proposes an effective separation method based on an improved empirical wavelet transform (EWT) that introduces a fast boundary detection mechanism. The fast boundary detection mechanism can be regarded as a process of searching, difference optimization, and continuity detection of the important local minima in the Fourier spectrum that enables determination of the sub-band boundary and thus allows multiple signal components to be distinguished. An orthogonal empirical wavelet filter bank that was designed for signal adaptive reconstruction is then used to separate the input time-frequency overlapped signals. The experimental results show that if two source components are completely overlapped within the time domain and the spectrum overlap ratio is less than 60%, the average separation performance is improved by approximately 32.3% when compared with the classic EWT; the proposed method also improves the suitability for multiple frequency shift keying (MFSK) and reduces the algorithm complexity.

• Geomechanics and Engineering
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• 제31권1호
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• pp.71-86
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• 2022

In Taiwan, an efficient approach for enhancing the stability of colluvium slopes is the drilled shaft method. For slopes with drilled shafts, the soil arching effect is one of the primary factors influencing slope stability and intertwines to the failure mechanism of the pile-soil system. In this study, the contribution of soil arching effect to slope stability is evaluated using the FEM software (Plaxis 3D) with the built-in strength reduction technique. The result indicates the depth of the failure surface is influenced by the S/D ratio (the distance to the diameter of piles), which can reflect the contribution of the soil arching effect to soil stability. When α (rock inclination angles)=β (slope angles) is considered and the S/D ratio=4, the failure surface of the slope is not significantly influenced by the piles. Overall, the soil arching effect is more significant on α=β, especially for the steep slopes. Additionally, the soil arching effect has been included in the proposed stability charts. The proposed charts were validated through two case studies, including that of the well-known Woo-Wan-Chai field in Taiwan. The differences in safety factor (FoS) values between the referenced literature and this study was approximately 4.9%.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.52-57
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• 1993

In this study, the inclined endmilling process with a 3-axis machining center using inalined jigs is introduced for the purpose of reducing overall Dies/Molds machining time and improving the machining accuracies. In order to analyse the cutting mechanism of a given endmill more accurateky, the unification of the cutting mechanism model of 3-different-kind endmills is examined by using the mose radius as a parameter. By adding radial runouts as a parameter which influences on surface roughness, the superposition method which defines the effective cusp heigh superposing the cutter mark height and the conventional cusp height is modified. And 3-D surface topography predicted in this paper looks like the surface normally observed in practice. Through machining experiments, the adequacy of the superposition algorithm was confirmed.