• 대한임상검사과학회지
• /
• 제44권1호
• /
• pp.31-37
• /
• 2012

Many mammals in temperate zones are affected by the distinctive changes of the four seasons in these zones. Their reproductive status is active in the summer climate and inactive during severe winter weather. The golden hamster (Mesocricetus auratus) is seasonal breeding animal whose sexual activities are regulated by photoperoidism. The reproduction and metabolism are activated by long summer days (LD) and inhibited by short winter days (SD). After several months of SD, animals become refractory to this inhibitory photoperiod and spontaneously revert to LD-like physiology. The suprachiasmatic nuclei (SCN) house the primary circadian oscillator in mammals. Seasonal changes in the photic input to this structure control many annual physiological rhythms via SCN-regulated pineal melatonin secretion, which provides an internal endocrine signal representing photoperiod. The aim of this study was to assess the variation in the morphology of the testis in relation to the natural photoperiod in male golden hamsters. The hamsters were castrated at different weeks (2, 5, 8, and 15). The cell numbers of tubules with spermatogonia (SG), spermatocyte (SC), spermatids (ST), and spermatozoa (SZ) were recorded in each sample. The results showed that testicular regression of golden hamsters occurred in the SD-treated animals. The present investigation determines that the effects of the photoperiod on the reproduction of male golden hamsters. It was also found that the circadian period increases the rate of reproductive inhibition in animals exposed to inhibitory photoperiods.

• 한국세라믹학회지
• /
• 제42권9호
• /
• pp.637-644
• /
• 2005

In order to find a proper buffering material which can prohibit an unwanted interfacial reaction between anode and electrolyte of LSGM-based SOFC, we examined a gadolinium doped ceria and scandium doped zirconia as a candidate. For this examination, we investigated the microstructural and phase stability of the interface under different buffering layer conditions. According to the investigation, ceria based material induced a serious La diffusion out of the LSGM electrolyte resulted in the formation of very resistive $LaSrGa_3O_7$ phase at the interface. On the other hand zirconia based material was directly reacted with LSGM electrolyte and thus produced very resistive reaction products such as $La_2Zr_2O_7,\;Sr_2ZrO_4,\;LaSrGaO_4\;and\;LaSrGa_3O_7$. From this study we found that an improper buffering material induced the higher internal cell resistance rather than an interfacial stability.

• 한국세라믹학회지
• /
• 제42권12호
• /
• pp.808-815
• /
• 2005

[ $Bi_xCe_{l-x}O_{2-x/2}$ ](BD C : Bismuth Doped Ceria) powders with x = 0.1, 0.2, and 0.3 were synthesized using the Glycine Nitrate Process (GNP). They were then calcined at $500^{\circ}C$ for 2 hand sintered in a pellet or rod form at 900, 1000 or $1100^{\circ}C$ for 4 h for characterization as the alternative electrolyte material for intermediate temperature solid oxide fuel cells. The BDC powder consisted of a single phase of $CeO_2-Bi_2O_3$ solid solution in the as-synthesized state as well as in the as-calcined state with a mean powder size of 4.5nm in the former state and 6.5 - 10.1nm in the latter. On the contrary, the second phase of $\alpha-Bi_2O_3$ was observed to have been formed in the sinter with its amount increasing roughly with increasing temperature or $Bi_2O_3$ content. The BOC powder was superior in sinterability to other alternative electrolyte materials such as GDC, ScSZ, and LSGM with the minimum sintering temperature for a relative density of $95\%$ or larger as low as $1100^{\circ}C$. The ionic conductivity of BOC increased with $Bi_2O_3$ content and the maximum value of 0.119 S/cm was obtained at $800^{\circ}C$ for $Bi_{0.3}Ce_{0.7}O_{1.85}$.

• 전기화학회지
• /
• 제10권4호
• /
• pp.288-294
• /
• 2007

Modified oxalate method에 의해 합성한 중온형 Solid Oxide Fuel Cell 용 LSCF cathoded의 pH 변화에 따른 분말특성 및 여러 종류의 전해질에 따른 전극특성에 대해 연구하였다. LSCF를 합성하기 위한 출발물질로는 La, Sr, Co 및 Fe의 염화물과 oxalic acid, ethanol 및 $NH_4OH$를 사용하여, $80^{\circ}C$ 에서 pH 2, 6, 7, 8, 9 및 10에서 합성하였다. 합성한 LSCF 분말은 pH $2{\sim}9$까지는 단일상의 LSCF 결정상을 생성하였다. 그러나, PH 10에서는 LSCF결정상 외에 이차상인 $La_2O_3$ 결정상이 나타났으며, 또한 $800^{\circ}C$에서 4시간 하소한 경우 50 nm정도의 작은 크기를 나타내었다. 합성한 LSCF cathode 분말의 전기전도도는 pH 7에서 합성한 LSCF 분말의 경우 $600^{\circ}C$부터 $900^{\circ}C$까지 측정하였을 때 약 950 S/cm의 높은 값을 나타내었다. 또한 분극저항의 경우 같은 합성 조건에서 합성한 LSCF 분말이라도 하소조건에 따라 다른 결과를 나타내었는데, $800^{\circ}C$에서 하소한 분말의 경우 $1200^{\circ}C$에서 하소한 분말 보다 낮은 분극저항을 나타내었다. 특히 $800^{\circ}C$에서 4시간 하소하여 합성한 LSCF 분말은 $600^{\circ}C$에서 Scandia Stabilized Zirconia (ScSZ), yttria (8mol.%)-stabilized zirconia(8Y-YSZ) 및 Gadolinium Doped Ceria(GDC) 전해질을 사용하였을 때, 전극면적이 $0.5\;cm^2$일 때 각각 2.52, 1.54 및 $2.58\;{\Omega}$을 나타내었다.