• Proceedings of the Optical Society of Korea Conference
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• 1990.02a
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• pp.73-78
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• 1990

1.3${\mu}{\textrm}{m}$ DFB with absorption grating of 1.55${\mu}{\textrm}{m}$ InGaAsP layer was fabricated. This new type of DFB laser shows self-plusation for DC operation. At low level of injection the relation between the pulsation frequency and the injection current shows similar behavior with the relaxation oscillation of ordinary laser and at high level of injection the pulsation frequency decreases compared to the relaxation oscillation. Period doubling, period 3 and 4 were observed for AC modulation. In case of period doubling the waveform shows only one pulse within a period without any accompanying subsidiary pulses and the oscillation frequency was quite stable. The pulse widths as short as 58.5 ps was achieved with AC modulation. We propose the time division multiplexing application of this kind of DFB laser.

• Journal of the Korean Society of Combustion
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• v.17 no.3
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• pp.9-16
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• 2012

Nonlinear dynamics of pulsating instability in radiating counterflow diffusion flames is numerically investigated by imposing Damk$\ddot{o}$hler number perturbation. Stable limit-cycle solutions occur in small ranges of Damk$\ddot{o}$hler numbers past bifurcation point of instability. Period doubling cascade and chaotic behaviors appear just before dynamic extinction occurs. Nonlinear dynamics is also studied when large disturbances are imposed to flames. For weak steady flames, the dynamic extinction range shrinks as the magnitudes of disturbances are increased. However, strong steady flames can overcome relatively large disturbances, thereby the dynamic extinction range extending. Stable limit-cycle behaviors reappears prior to dynamic extinction when the steady flames are strong enough.

• Environmental Analysis Health and Toxicology
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• v.16 no.4
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• pp.205-209
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• 2001

Lemna gibba was newly cultured and provided for toxicity tests. In this study, the chromate toxicity tests for Lemna gibba were performed according to the OECD Lemna growth inhibition test guideline. The test species was Lemna gibba, and the tests were repeated 5 times. To evaluate the toxicity test results, the average specific growth rate, EC50, 95％ confidential limit, and variances were calculated. The test performance was analyzed by the doubling time and test statistics. The average values of EC50 data determined by logistic and linear interpolation curves were 25.9 ppm and 35.4 ppm respectively (by chromate concentration). The doubling time of all controls were below 2.5 day, so all tests passed the criteria for the test performance. This study introduced a new test method, Lemna growth inhibition test, which is provided for the hazard assessment of aquatic environment.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1994-2003
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• 2003

The vibration of a flexible cantilever tube with nonlinear constraints when it is subjected to flow internally with fluids is examined by experimental and theoretical analysis. These kinds of studies have been performed to find the existence of chaotic motion. In this paper, the important parameters of the system leading to such a chaotic motion such as Young's modulus and the coefficient of viscoelastic damping are discussed. The parameters are investigated by means of system identification so that comparisons are made between numerical analysis using the design parameters and the experimental results. The chaotic region led by several period-doubling bifurcations beyond the Hopf bifurcation is also re-established with phase portraits, bifurcation diagram and Lyapunov exponent so that one can define optimal parameters for system design.

• East Asian mathematical journal
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• v.31 no.5
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• pp.743-751
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• 2015

In this paper, we consider a discrete ratio-dependent predator-prey system with harvesting effect. In order to investigate dynamical behaviors of this system, first we find out all fixed points of the system and then classify their stabilities by using their Jacobian matrices and local stability method. Next, we display some numerical examples to substantiate theoretical results and finally, we show numerically, by means of a bifurcation diagram, that various dynamical behaviors including cycles, periodic doubling bifurcation and chaotic bands can be existed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.121-128
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• 1995

The results are summarized as what follows: 1) The modeling of thin beams, which is a continuous system, into a two DOF system yields satisfactory results for the chaotic vibrations. 2) The concept of "natural forcing function" derived from the eigenfunction of the bifurcation mode is very useful for the natural responses of the system. 3) Among the perturbation techniques, HBM is a good estimate for the response when the geometry of motion is known. 4) It is known that there exist periodic solutions of coupled mode response for somewhat large damping and forcing amplitude, as well as weak damping and forcing. 5) The route-to-chaos related with lateral instability in thin beams is composed of period-doubling and quasiperiodic process and finally follows discontinuous period-doubling process. 6) The chaotic vibrations are verified by using Poincare maps, FFT's, time responses, trajectories in the configuration space, and the very powerful technique Lyapunov characteristics exponents.exponents.

• Journal of the Korean Mathematical Society
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• v.55 no.6
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• pp.1423-1433
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• 2018

This paper is concerned about several quasilinear elliptic systems with m-Laplacians. According to the Liouville theorems of those systems on ${\mathbb{R}}^n$, we obtain the singularity estimates of the positive $C^1$-weak solutions on bounded or unbounded domain (but it is not ${\mathbb{R}}^n$ and their decay rates on the exterior domain when ${\mid}x{\mid}{\rightarrow}{\infty}$. The doubling lemma which is developed by Polacik-Quittner-Souplet plays a key role in this paper. In addition, the corresponding results of several special examples are presented.

• Journal of Communications and Networks
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• v.12 no.1
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• pp.1-4
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• 2010

As a countermeasure to simple power attack, the unified point addition codes for the elliptic curve cryptosystem were introduced. However, some authors proposed a different kind of power attacks to the codes. This power attack uses the observation that some internal operations in the codes behave differently for addition and doubling. In this paper, we propose a new countermeasure against such an attack. The basic idea of the new countermeasure is that, if one of the input points of the codes is transformed to an equivalent point over the underlying finite field, then the code will behave in the same manner for addition and doubling. The new countermeasure is highly efficient in that it only requires 27(n-1)/3 extra ordinary integer subtractions (in average) for the whole n-bit scalar multiplication. The timing analysis of the proposed countermeasure is also presented to confirm its SPA resistance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.495-500
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• 2003

The vibration of a flexible cantilever tube with nonlinear constraints when it is subjected to flow internally with fluids is examined by experiment and theoretical analysis. These kind of studies have often been performed that finds the existence of chaotic motion. In this paper, the important parameters of the system leading to such a chaotic motion such as Young's modulus and coefficient of viscoelasticity in tube material are discussed. The parameters are investigated by means of a system identification so that comparisons are made between numerical analysis using the parameters of a handbook and the experimental results. The chaotic region led by several period-doubling bifurcations beyond the Hopf bifurcation is also re-established with phase portraits and bifurcation diagram so that one can define optimal parameters for system design.

• Korean Journal of Microbiology
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• v.29 no.4
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• pp.263-266
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• 1991

The growth of T. novellus in auto trophic and geterotrophic media was studied to determine the time required for cells to enter stationary phase and relative percentage of ribosomal proteins. When T. novellus was grown autotrophically, growth proceeded at a slow rate characteristic of autotrophs and did not enter log phase until the end of the first day. Logarithmic growth proceeded for 3-4 days at which time the cells entered the stationary phase. In particular, logarithmic growth was accompanied by decreasing pH of culture media and in the stationary phase the pH levelled off at 6.0, a decrease of 1.6 pH value compared to original pH of media. The pH decrease was greatest during log phase when cells oxidized thiosulfate to $H_{2}$$SO_{4}$. The doubling time was about 26h. In heterotrophic media growth proceeded at a much faster rate and cells entered stationary phase 20-22h after inoculation. The doubling time was 3h. The protein content of the ribosomes in T. novellus grown heterotrophically was 4.2% greater than those from the organism grown autotrophically.