• 한국재료학회지
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• 제3권2호
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• pp.185-192
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• 1993

본 연구에서는 분극성을 갖는 미세분말/유전유체 분산계내의 전기유변효과를 mechanism을 중심으로 고찰하였다. 전기유변효과를 일으키는 mechanism을 (1)입자표면전도(surface conductance) (2)입자내부전도(bulk conductance(3) 유도분극(induced polarization)으로 구분하여 설명하였다. 소수성(anhydrous-base)전기유변유체 내의 미세분말 입자간 상호인력을 예측할 수 있도록 유도분극 mechanism을 적용하여 수학적으로 모델화 함으로써 전기유변효과를 향상 시키기 위한 재료선정의 기초로 하였다. 전기유변유체의 미세입자로 이용될 수 있다고 여겨지는 ceramic, ferrite 및 polymer등 7가지 재료를 선정하여 계산한 결과 ceramic및 ferrite입자가 입자간 상호인력이 큰것으로 나타났다.

• Wind and Structures
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• 제10권5호
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• pp.421-435
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• 2007

A two-dimensional flutter analysis method (2d-3DOF method) was developed to simultaneously investigate the relationship between oscillation parameters and aerodynamic derivatives of three degrees of freedom, and to clarify the coupling effects of different degrees of freedom in flutter instability. With this method, the flutter mechanism of two typical bridge deck sections, box girder section and two-isolated-girder section, were numerically investigated, and both differences and common ground in these two typical flutter phenomena are summarized. Then the flutter stabilization effect and its mechanism for long-span bridges with box girders by using central-slotting were studied by experimental investigation of aerodynamic stability and theoretical analysis of stabilizing mechanism. Possible explanation of new findings in the evaluation trend of critical wind speed through central vent width is finally presented.

• 대한기계학회논문집
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• 제18권12호
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• pp.3109-3117
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• 1994

To operate a flexible mechanism in high speed its weight must be reduced as far as the structural strength does not decrease too much, but a light-weighted mechanism causes undesirable elastodynamic responses deteriorating the system performance. Besides, clearance within the connections of mechanisms causes rapid wear, increased noise and vibration. Even if the problems described above must be considered in the initial design stage, there has been no effective design process which takes account of the correlation between dynamic characteristics of flexible mechanism and the clearance effect at the joint. In this study, the generalized elastodynamic governing equations which include dynamic characteristics and boundary conditions of flexible mechanism are derived by variational calculus and solved by using FFM theory. To take the clearance effect at joint into account a new dynamic model is presented and also the method of modified stiffness/damping matrix is proposed to activate the dynamic clearance model, which cooperates with the developed governing equation very easily. As the results of this study, the proposed method(modified stiffness/damping matrix) to calculate clearance effect was proved to be superior to the existing one(force reaction method) in solution convergency and calculation performance. Besides this method can be easily adopted to the complex shape joint without calculation of reaction force direction.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3811-3816
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• 2013

Nucleophilic substitution reactions of ethyl methyl (2), ethyl propyl (4) and diisopropyl (7) chlorothiophosphates with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at $55.0^{\circ}C$. A concerted mechanism is proposed based on the selectivity parameters. The deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are secondary inverse ($k_H/k_D=0.66-0.99$) with 2, primary normal and secondary inverse ($k_H/k_D=0.78-1.19$) with 4, and primary normal ($k_H/k_D=1.06-1.21$) with 7. The primary normal and secondary inverse DKIEs are rationalized by frontside attack involving hydrogen bonded, four-center-type transition state, and backside attack involving in-line-type transition state, respectively. The anilinolyses of ten chlorothiophosphates are examined based on the reactivity, steric effect of the two ligands, thio effect, reaction mechanism, DKIE and activation parameter.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
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• pp.718-721
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• 1996

In this work, an effective stiffness generated by internal loading for a planar 3 degrees of freedom RCC mechanism is investigated. For this purpose, the internal kinematic analysis and antagonistic stiffness modeling for this mechanism are performed. It is shown that the antagonistic stiffness could be effectively created at the center of the mechanism in its symmetric configuration.

• Journal of Chest Surgery
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• 제27권1호
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• pp.9-14
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• 1994

Substance P[SP] has been known to be a peptide which may be plays a role as a neurotransmitter in central nervous system as well as peripheral autonomic nervous system. It has been reported that SP was widely distributed in the nerve of the tracheal smooth muscle and induced the muscle contraction. However, definite action mechanism of SP in the tracheal smooth muscle was not clear, yet. Thus, present experiment was performed to elucidate an effect of substance P and an action mechanism on contraction of the smooth muscle in rabbits. In order to find a neural mechanism to the effect of SP on the tracheal smooth muscle contraction, atropine sulfate, tetrodotoxin, propranol and phentolamine were administered at 10 min before the addition of SP. Otherwise,to find effect of SP antagonists on the action of SP, [D-Pro2, D-Try7,9]SP, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP and [D-Pro4, D-Trp7,9]SP were administered as a same fashion. These following results were obtained. 1] SP induced contraction of the tracheal smooth muscle under resting condition and the contraction was increased dose-dependently. 2] Cholinergic blocker[atropine], neural blocker[tetrodotoxin] and adrenergic blocker[propranol and phentolamine] didn`t have an effect on the contractile response. 3] Three SP antagonists inhibited the contractile response. 4] Isoproterenol relaxed the contraction induced by SP. The above results suggested that SP induced contraction of the tracheal smooth muscle directly act to the smooth muscle in rabbits. The autonomic nervous system did not seem to participate in the SP action.

• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.2909-2912
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• 2009

The amines studied in this study are less reactive toward ethyl propiolate (3) in MeCN than in H$_2$O although they are 7 to 9 pK$_a$ units more basic in the aprotic solvent. The reactivity of morpholine and deuterated morpholine toward 3 is found to be identical, indicating that proton transfer occurs after rate-determining step (RDS). The fact that kinetic isotope effect is absent excludes a stepwise mechanism in which proton transfer occurs in RDS as well as a concerted mechanism in which nucleophilic attack and proton transfer occur concertedly through a 4-membered cyclic transition state (TS). Thus, the reactions have been concluded to proceed through a stepwise mechanism in which proton transfer occurs after RDS. Brønsted-type plots are linear with small ${\beta}_{nuc}$ values, i.e., ${\beta}_{nuc}$ = 0.29 in H$_2$O and ${\beta}_{nuc}$ = 0.51 in MeCN, indicating that bond formation is not advanced significantly in RDS. The small ${\beta}_{nuc}$ value also supports the conclusion drawn from the study of kinetic isotope effect.

• 대한화학회지
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• 제47권4호
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• pp.432-436
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• 2003

• Bulletin of the Korean Chemical Society
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• 제32권spc8호
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• pp.2955-2959
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• 2011

Second-order rate constants for nucleophilic substitution reactions of 2,4-dinitrophenyl benzenesulfonate 1a with a series of alicyclic secondary amines in MeCN have been measured spectrophotometrically and compared with those reported previously for the corresponding reactions performed in aqueous medium to investigate the effect of medium on reactivity and reaction mechanism. The amines employed in this study are found to be more reactive in the aprotic solvent than in $H_2O$. The reactions of 1a in MeCN result in a linear Br${\o}$nsted-type plot with ${\beta}_{nuc}$ = 0.58, which contrasts to the curved Br${\o}$nsted-type plot reported previously for the corresponding reactions performed in the aqueous medium (i.e., ${\beta}_2$ = 0.86 and ${\beta}_1$ = 0.38). Accordingly, it has been concluded that the reaction mechanism changes from a stepwise mechanism to a concerted pathway upon changing the medium from $H_2O$ to MeCN. Reactions of Y-substituted phenyl benzenesulfonates 1a-c with piperidine in MeCN result in a linear Br${\o}$nsted-type plot with ${\beta}_{lg}$ = -1.31, indicating that expulsion of the leaving group is significantly more advanced than bond formation in the transition state. The trigonal bipyramidal intermediate ($TBPy^{\pm}$) proposed previously for the reactions in $H_2O$ would be highly unstable in MeCN due to strong repulsion between the negative charge in $TBPy^{\pm}$ and the negative dipole end of MeCN. Thus, destabilization of $TBPy^{\pm}$ in MeCN has been concluded to change the reaction mechanism from a stepwise mechanism to a concerted pathway.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2002년도 춘계학술대회
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• pp.221-225
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• 2002

Machinability improvement by the use of liquid nitrogen in cryogenic machining has been reported in various studies. This has been mostly attributed to the cooling effect of liquid nitrogen. However, No study has been found in discussion on whether liquid nitrogen possesses lubrication effect in cryogenic cutting. This paper presents lubrication mechanism related to chip microstructure. The friction reduction was further reflected In larger shear angle and less secondary deformation in the chip microstructures.