• Journal of Microbiology and Biotechnology
• /
• v.21 no.9
• /
• pp.979-987
• /
• 2011

Culture pH change has some important roles in signal transduction and secondary metabolism. We have already reported that acidic pH shock enhanced actinorhodin production in Streptomyces coelicolor. Among many potential governing factors on pH variation, the putative $Na^+/H^+$ antiporter (sha) genes in S. coelicolor have been investigated in this study to elucidate the association of the sha on pH variation and secondary metabolism. Through the transcriptional analysis and overexpression experiments on 8 sha genes, we observed that most of the sha expressions were promoted by pH shock, and in the opposite way the pH changes and actinorhodin production were enhanced by the overexpression of each sha. We also confirmed that sha8 especially has a main role in maintaining cell viability and pH homeostasis through $Na^+$ extrusion, in salt effect experiment under the alkaline medium condition by deleting sha8. Moreover, this gene was observed to have a function of pH recovery after pH variation such as the pH shock, being able to cause the sporulation. However, actinorhodin production was not induced by the only pH recovery. The sha8 gene could confer on the host cell the ability to recover pH to the neutral level after pH variation like a pH drop. Sporulation was closely associated with this pH recovery caused by the action of sha8, whereas actinorhodin production was not due to such pH variation patterns alone.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.14 no.4
• /
• pp.495-502
• /
• 2014

Fast recovery diodes (FRDs) were developed using the $p^{{+}{+}}/n^-/n^{{+}{+}}$ epitaxial layers grown by low temperature epitaxy technology. We investigated the effect of electrostatic discharge (ESD) stresses on their electrical and switching properties using current-voltage (I-V) and reverse recovery time analyses. The FRDs presented a high breakdown voltage, >450 V, and a low reverse leakage current, < $10^{-9}$ A. From the temperature dependence of thermal activation energy, the reverse leakage current was dominated by thermal generation-recombination and diffusion, respectively, at low and high temperature regions. By virtue of the abrupt junction and the Pt drive-in for the controlling of carrier lifetime, the soft reverse recovery behavior could be obtained along with a well-controlled reverse recovery time of 21.12 ns. The FRDs exhibited excellent ESD robustness with negligible degradations in the I-V and the reverse recovery characteristics up to ${\pm}5.5$ kV of HBM and ${\pm}3.5$ kV of IEC61000-4-2 shocks. Likewise, transmission line pulse (TLP) analysis reveals that the FRDs can handle the maximum peak pulse current, $I_{pp,max}$, up to 30 A in the forward mode and down to - 24 A in the reverse mode. The robust ESD property can improve the long term reliability of various power applications such as automobile and switching mode power supply.

• Journal of dental hygiene science
• /
• v.11 no.4
• /
• pp.375-380
• /
• 2011

This study evaluated whether fluoride treatment can affect recovery of the irregularity of enamel surface after tooth whitening with a high concentration of hydrogen peroxide (HP) activated by plasma arc light. A total of 36 bovine teeth stained with coke were used in this experiment. The specimens were classified into following three groups (two different commercial plasma arc groups and a control group without light curing source): (1) 35% HP gel only, (2): 35% HP gel and Plasma arc A, and (3) 35% HP gel and Plasma arc B. To measure color changes and surface morphologies before and after the bleaching, colorimeter and scanning electron microscopy were used, respectively. When the specimens were bleached with hydrogen peroxide and plasma arc lights, the bleaching effect was greater than when only hydrogen peroxide gels were used (Kruskal-Wallis test, p<0.05). In addition, plasma arc B showed the more color changes than plasma arc A (Bonferroni post-hoc test, p<0.05). The surfaces of the teeth treated with fluoride gel after the whitening treatment came to be smooth. Therefore, the results of this study suggested that the fluoride application for patients who got tooth whitening therapy with a high concentration of hydrogen peroxide gels activated by plasma arc light will be effective to recover rough enamel surfaces.

• Journal of Hydrogen and New Energy
• /
• v.13 no.4
• /
• pp.304-312
• /
• 2002

In this study, the performance of the $5Nm^3/hr$ compact type steam reformer which was developed for application of fuel cell or hydrogen station was evaluated in terms of gas process efficiency. For these purposes, reforming efficiency and total efficiency with system load change were analyzed. The reforming efficiency was calculated from the total molar flow of hydrogen output over total fuel flow input to the reformer and the burner on the higher heating value(HHV). In the case of the total efficiency, recovered heat at the heat recovery exchanger was considered. From the results, it was known that system performance was stable, because methane conversion showed the a slight decline which is about 2% though increasing system load to full. Reforming efficiency was increased from 20% to 58%, respectively as increasing system load from 10% to 90%. It was found that total efficiency was higher then reforming efficiency because of terms of heat recovered. As a results, it was known that total efficiency was increased form 75% to 83% at the 10% and 90% system load, respectively. From these results, it is concluded that compact steam reformer which is composed of stacking plate-type reactors is suitable to on-site hydrogen generator or to fuel cell application because of quick start within 1 hr and good performance.

• Journal of Hydrogen and New Energy
• /
• v.16 no.2
• /
• pp.136-141
• /
• 2005

Li-doped NiO was synthesized by molten salt method. $LiNO_3$-LiOH flux was used as a source for Li doping. $NiCl_2$ was added to the molten Li flux and then processed to make the Li-doped NiO material. Li:Ni ratios were maintained from 5:1 to 30:1 during the synthetic procedure and the Li doping amount of synthesized materials were found between 0.086-0.190 as a Li ion to Ni ion ratio. Li doping did not change the basic cubic structural characteristics of NiO as evidenced by XRD studies, however the lattice parameter decreased from 0.41769nm in pure NiO to 0.41271nm as Li doping amount increased. Hydrogen gas sensors were fabricated using these materials as thick films on alumina substrates. The half surface of each sensor was coated with the Pt catalyst. The sensor when exposed to the hydrogen gas blended in air, heated up the catalytic surface leaving rest half surface (without catalyst) cold. The thermoelectric voltage thus built up along the hot and cold surface of the Li-doped NiO made the basis for detecting hydrogen gas. The linearity of the voltage signal vs $H_2$ concentration was checked up to 4% of $H_2$ in air (as higher concentrations above 4.65% are explosive in air) using Li doped NiO of Li ion/Ni ion=0.111 as the sensor material. The response time T90 and the recovery time RT90 were less than 25 sec. There was minimum interference of other gases and hence $H_2$ gas can easily be detected.

• Resources Recycling
• /
• v.3 no.3
• /
• pp.7-11
• /
• 1994

The recovery of copper from $\alpha$-Etchent waste and pure copper solution was studied by the $H_2$reduction process. The results of test were as following: 1) The recovery of copper was increased with increasing hydrogen pressure and stirring speed up to 300 psi and 500 rpm, respectively, and was decreased in the higher values. But the recovery of copper from the fresh copper solution and $\alpha$-Etchent solution reached 90% and 60%, respectively. And in all tests the copper recovery from pure copper solution is higher by 30~40% than that from $\alpha$Etchent solution. 2) The recovery of copper was increased up to 30 minute of reaction time, and after then it became constant. The copper particles prepared in the initial 30 min have the needle-like shapes and in the longer reaction time than 30 min the shape was changed into noudle-like form. The average particle size was about $2~3\mu\textrm{m}$.

• Journal of Hydrogen and New Energy
• /
• v.12 no.3
• /
• pp.211-217
• /
• 2001

From wood to coal and petroleum, mankind has used various fuel. Since using such fuel, mankind has developed power source of mechanism. We obtain numerous power from caloric force. Present energy supply is based on the fossil fuel. Fossil fuel has high energy density and is convenient for transportation and storage. Human being prepared countermeasure of energy economy, high energy efficiency and substitution energy for limits of fossil fuel. High energy efficiency among them is very important. This research will improve total output by physical exergy recovery of $LH_2$-fuel cell system.

• Journal of Hydrogen and New Energy
• /
• v.29 no.5
• /
• pp.490-496
• /
• 2018

Recently, the power and refrigeration cogeneration based on Kalina cycle has attracted much attention for more efficient utilization of low-grade energy. This study presents a thermodynamic performance analysis of a cogeneration cycle of power and absorption refrigeration based on Kalina cycle. The cycle combines Kalina cycle (KCS-11) and absorption cycles by adding a condenser and an evaporator between turbine and absorber. The effects of ammonia mass fraction and separation pressure were investigated on the system performance of the system. Results showed that the energy utilization of the system could be greatly improved compared to the basic Kalina cycle.

• Journal of Hydrogen and New Energy
• /
• v.30 no.1
• /
• pp.58-66
• /
• 2019

Static compound parabolic collectors (CPCs) have advantages such as ease for fabrication and lower cost compared with other concentrating collectors. In this study, thermal performance analysis of CPC employing heat storage tank was carried out. The clearness index and capacity of heat storage tank are taken as the main parameters for numerical simulation. The effects of the parameters on the hourly and daily system performances ncluding the useful energy, heat loss, and collector efficiency were numerically investigated. Results showed that the system has a potential for efficient recovery of solar thermal energy.

• Journal of Hydrogen and New Energy
• /
• v.30 no.3
• /
• pp.289-295
• /
• 2019

Effects of various reaction factors such as pressure, time, and temperature on clathrate formation were investigated for hydroquinone with $CO_2$ and $N_2$. Experimental and spectroscopic results indicate that $CO_2$ plays more preferential role in forming hydroquinone clathrates than $N_2$. These results can be used in application of selective $CO_2$ separation from flue gases with the formation of clathrate compounds.