• Korean Journal of Mathematics
• /
• 제28권1호
• /
• pp.75-87
• /
• 2020

Category F Rel of fuzzy sets and relations does not form a topos. J. Harding, C. Walker and E. Walker [3] showed that FRel has a tensor product and V. Durov [1] introduced basic definitions related to the notion of vectoid endowed with a tensor product. In this paper, we show that FRel forms a quasi topos. Also we show that there are quasi power objects in FRel. And by the use of the concepts of FRel and quasi topos, we get the logic operators of FRel. Moreover, we show that FRel forms a vectoid.

• 천문학회보
• /
• 제42권2호
• /
• pp.37.1-37.1
• /
• 2017

Since the seminal work of Perrin, physicists have understood in the context of kinetic theory how ink slowly diffuses in a glass of water. The fluctuations of the stochastic forces acting on water molecules drive the diffusion of the ink in the fluid. This is the archetype of a process described by the so-called fluctuation-dissipation theorem, which universally relates the rate of diffusion to the power spectrum of the fluctuating forces. For stars in galaxies, a similar process occurs but with two significant differences, due to the long-range nature of the gravitational interaction: (i) for the diffusion to be effective, stars need to resonate, i.e. present commensurable frequencies, otherwise they only follow the orbit imposed by their mean field; (ii) the amplitudes of the induced fluctuating forces are significantly boosted by collective effects, i.e. by the fact that, because of self-gravity, each star generates a wake in its neighbours. In the expanding universe, an overdense perturbation passing a critical threshold will collapse onto itself and, through violent relaxation and mergers, rapidly converge towards a stationary, phase-mixed and highly symmetric state, with a partially frozen orbital structure. The object is then locked in a quasi-stationary state imposed by its mean gravitational field. Of particular interests are strongly responsive colder systems which, given time and kicks, find the opportunity to significantly reshuffle their orbital structure towards more likely configurations. This presentation aims to explain this long-term reshuffling called gravity-driven secular evolution on cosmic timescales, described by extended kinetic theory. I will illustrate this with radial migration, disc thickening and the stellar cluster in the galactic centre.

• 조명전기설비학회논문지
• /
• 제15권1호
• /
• pp.51-58
• /
• 2001

현재의 DC-DC 컨버터는 스위칭 주파수를 높임에 따라 전체 손실이 현저히 증가하고 있다. 스위칭 손실을 줄이기 위해 사용한 예전의 soft 스위칭기술은 심지어 전압/전류 부담(stress)을 가중시켰다. 이에 대한 대책으로 soft 스위칭을 위한 공진회로를 주전력선에 병렬로 연결하고 보조 스위치를 이용하여 주 스위치의 turn-on 직전에만 공진회로를 동작시키는 유사공진 컨버터(QRC)기술이 발전되었다. 그러나 이 기술을 사용하는 컨버터에서도 손실은 여전히 발생하며 효율에 대한 전체적인 손실량은 알 수 있지만 각 소자에 대한 손실량은 알아볼 수 없었다. 따라서 본 논문에서는 컨버터의 주전력단에 사용되는 반도체 소자들의 선형화 된 손실등가 모델을 만들고 스위칭 시의 전압/전류 파형을 바탕으로 선형 특성을 고려하여 전체 손실에 대한 각 소자의 손실과 스위칭 손실을 분석하였다.

• 대한기계학회논문집A
• /
• 제20권4호
• /
• pp.1123-1132
• /
• 1996

It has been reported that high temperature structural components represent the phenomenon of material degradation according to a long term service under high temperature and pressure. Especially, fossile power plant components using the fossil fuel and heavy oil are affected by dewpoint corrosion of $H_2SO_4$produced during a combustion. Therefore, the service materials subjected to high temperature and pressure may occur the stress corrosion cracking. The object of this paper is to investigate SCC susceptibility according to the material degradation of the high temperature structural materials in dewpoint corrosive environment-$H_2SO_4$.The obtained results are summarized as follows : 1) In case of secondary superheater tube, the fractograph of dimple is observed at the concentration of $H_2SO_4$-5%. When the concentration of $H_2SO_4$ is above 10%, the fracture mode is shifted from a transgranular fracture to an quasi-intergranular fracture according to the increment of concentration. 2) In the relationship between [$\Delta$DBTT]$_sp$ and SCC susceptibility, it is confirmed that the greater material degradation degree is, the higher SCC susceptibility is. In addition, it can be known that SP test is useful test method to evaluate SCC susceptibility for high temperature structural components. 3) When [$\Delta$DBTT]$_sp$ is above 17$17^{\circ}C$ the SCC fracture behavior is definitely observed with SCC susceptibility of above 0.4.