http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
개별검색 DB통합검색이 안되는 DB는 DB아이콘을 클릭하여 이용하실 수 있습니다.
통계정보 및 조사
예술 / 패션
<해외전자자료 이용권한 안내>
- 이용 대상 : RISS의 모든 해외전자자료는 교수, 강사, 대학(원)생, 연구원, 대학직원에 한하여(로그인 필수) 이용 가능
- 구독대학 소속 이용자: RISS 해외전자자료 통합검색 및 등록된 대학IP 대역 내에서 24시간 무료 이용
- 미구독대학 소속 이용자: RISS 해외전자자료 통합검색을 통한 오후 4시~익일 오전 9시 무료 이용
※ 단, EBSCO ASC/BSC(오후 5시~익일 오전 9시 무료 이용)
Catalytic performance of various acids in the coupling reaction of formaldehyde and methyl formate to produce methyl glycolate and methyl methoxy acetate has been studied. The influence of reaction conditions, such as catalyst amount, reaction temperature, reaction time, and molar ratio of formaldehyde to methyl formate, has also been investigated. The results showed that the acid strength had great influence on the reaction, namely, stronger acds had higher activities. It was also found that the reaction temperature and time had significant effect on the reaction, and the preferable conditions were quite different as different acids were used.
<P><B>Abstract</B></P> <P>This paper reports Seebeck effects from optically-induced intramolecular proton-transfer HPI-Cbz molecules based on vertical electrode/organic film/electrode thin-film devices. We observed large Seebeck coefficients of 428μV/K and 390μV/K from HPI-Cbz based thin-film devices at 60°C when proton-transfer was induced by the photoexcitation of a 325nm laser with an intensity of 12mW/cm<SUP>2</SUP> and 6mW/cm<SUP>2</SUP> respectively. Under dark condition without proton transfer occurring, the Seebeck coefficient was measured to be 342μV/K at 60°C. The Seebeck coefficient enhancement by the induced intramolecular charge transfer can be attributed to the enhanced polarization difference between high- and low-temperature surface due to the stronger electron–phonon coupling followed with the proton-transfer in HPI-Cbz under photoexcitation, and the strength of electron–phonon coupling is proportional to the photoexcitation intensity. The enhanced temperature-dependent electrical polarization between the high and low-temperature surfaces acts as an additional driving force to diffuse the majority charge carriers for the development of a large Seebeck effect. Therefore, using intramolecular proton-transfer presents an effective approach of enhancing Seebeck effect in organic materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photoinduced proton-transfer states lead to enhancement on Seebeck coefficients. </LI> <LI> Photoinduced proton-transfer states lead to enhancement on electrical conductivity. </LI> <LI> Temperature-dependent polarization acts as a new driving force for Seebeck effect. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
The mass transfer from the matrix to the fracture face is driven by both concentration and pressure differences. In this work, high-temperature high-pressure (HPHT) systems for diffusion experiments with only concentration differences were used to determine the diffusion coefficient, and flow experiments with only pressure differences were also conducted; and the magnitude of gas molecular diffusion and its contribution to production were analyzed in this study. The results show as follows: (1) Gas flow from the matrix to the fracture system is driven by the combined effect of gas molecular diffusion and seepage. The pore structure characteristics of the reservoir and the contribution of the diffusion to the yield can vary greatly. (2) In tight reservoirs with an average permeability of 0.3067 mD, the contribution of gas molecular diffusion to the total gas mass flux is only 0.08%, while in shale reservoirs, the average permeability is 0.0015 mD; the contribution of diffusion to the total gas mass flux could be as large as 1%. (3) The contribution of molecular diffusion to gas production is closely related to the pore sizes of the porous medium. The smaller the pore sizes are, the greater the contribution of molecular diffusion to gas production.
The development practice of polymer flooding shows that the injection profile easily inverses during the process of single slug polymer flooding. The low effective or ineffective circulation of abundant injecting water in high permeability layer, low producing degree of low permeability layer and large polymer volume have influenced the sweep efficiency and oil recovery of polymer flooding. In view of these questions, the alternative injection method of various viscosity polymer slugs is studied. This paper explains the theory of enhanced oil recovery of multi-slug polymer alternative injection. The experiment results show that the alternative injection of high and low viscosity polymer slugs has a better effect than single slug polymer flooding. The mobility differences between high-low permeability layers can be effectively reduced. For a multi-layer heterogeneous reservoir, there is an optimal alternative cycle. Reasonable slug size can not only inhibit dominant channel forming in high permeability layer but also can effectively produce low permeability layer and control profile inversion to a certain extent. This provides a technical support for studying the controlling methods of profile inversion.
Hydraulic fracture is a key technology for high-efficiency development of shale gas, and the flow mechanism of fractured well with Stimulated Reservoir Volume (SRV) is complex in shale gas. In this paper, an apparent permeability model is proposed, which can not only reflect the multi-scale flow characteristics in shale gas but also characterize the variation of permeability with effective stress. In addition, a composite model for a fractured well with SRV is established, which comprises multiscale, geomechanics and adsorption phenomenon. The object of this paper is to investigate some important impacts on a fractured well with SRV. The results reveal that the cumulative gas production will decrease sharply when the shale gas reservoir stress-sensitive coefficient increases. Additionally, the gas production rate and cumulative gas production will increase with the increase of SRV permeability. And, the adsorption phenomenon has an influence on shale gas seepage and sorption capacity, the larger Langmuir volume, the richer adsorption gas content in shale gas. And, more adsorbed gas will be exploited into free gas, which slows down the production decline of gas wells. The production of gas well will increase with the increase of perforation thickness of gas reservoir.
Polymer flooding is becoming more common and more successful, and has made a great contribution to EOR. However, the statistical analysis of water injection profile data shows that the injection profile easily inverses during the process of single slug polymer flooding in heterogeneous reservoir. It is unfavorable for enhancing oil recovery. According to seepage mechanics theory, the cognition is determined that the injection rate distribution in high and low permeability layers depends on reservoir heterogeneity and physicochemical property of polymer. The basic reason of profile inversion lies in the different dynamic variation of resistance factors in the high and low permeability layers. In order to use existing reservoir simulation software to accurately describe the profile inversion characteristics, a processing method is submitted which is that different polymer characteristic parameters and relative permeability curves are assigned to different regions according to the distributions of reservoir characteristics during polymer flooding. Then, this processing method is used for systematically studying the profile inversion laws of different permeability ratio, polymer concentration and injecting-polymer occasion. The results show that these factors have great influence on the profile inversion. This provides a technical support for studying the profile inversion rules and corresponding improvement method.
Free lipase-mediated biodiesel production has been considered to be promising due to its advantages of high catalytic efficiency and lower preparation cost. Exploring the feasibility of free lipase to convert potential low quality oil feedstock into biodiesel is of great significance for further reducing the cost of biodiesel production. However, it is reported that low quality oils usually contain high concentration of phospholipids. Our previous study showed that the presence of high phospholipids content in oil feedstock would lead to poor catalytic performance of free lipase NS81006.Thereby, in order to improve the process, a combined catalysis together with phospholipase Lecitase Ultra and lipase NS81006 was developed in this paper. First, the effect of different factors involved in the process on Lecitase Ultra’s catalytic performance was investigated, then a two-step method via phospholipase-catalyzed phospholipids degradation followed by lipase-catalyzed methanolysis was further attempted to promote the conversion of phospholipids-containing oils for biodiesel production. When using oil containing 2,235 ppm initial phosphorus as feedstock, the final biodiesel yield could reach 96.4%, while the yield without phospholipase was only 76.6%. This work demonstrates that the combined catalysis of phospholipase and free lipase has a great prospect in biodiesel production from high phospholipids-containing oil feedstocks.
This study, for the first time, reports the functional expression of lipase B derived from the yeast Candida antarctica (CALB) in Corynebacterium strain using the Escherichia coli plasmid PK18. The CALB gene fragment encoding a 317-amino-acid protein was successfully obtained from the total RNA of C. antarctica. CALB was readily produced in the Corynebacterium strain without the use of induction methods described in previous studies. This demonstrated the extracellular production of CALB in the Corynebacterium strain. CALB produced in the Corynebacterium MB001 strain transformed with pEC-CALB recombinant plasmid exhibited maximum extracellular enzymatic activity and high substrate affinity. The optimal pH and temperature for the hydrolysis of 4-nitrophenyl laurate by CALB were 9.0 and 40℃, respectively. The enzyme was stable at pH 10.7 in the glycine-KOH buffer and functioned as an alkaline lipase. The CALB activity was inhibited in the presence of high concentration of Mg2+, which indicated that CALB is not a metalloenzyme. These properties are key for the industrial application of the enzyme.
This study, for the first time, reports the functional expression of lipase B derived from the yeast Candida antarctica (CALB) in Corynebacterium strain using the Escherichia coli plasmid PK18. The CALB gene fragment encoding a 317-amino-acid protein was successfully obtained from the total RNA of C. antarctica. CALB was readily produced in the Corynebacterium strain without the use of induction methods described in previous studies. This demonstrated the extracellular production of CALB in the Corynebacterium strain. CALB produced in the Corynebacterium MB001 strain transformed with pEC-CALB recombinant plasmid exhibited maximum extracellular enzymatic activity and high substrate affinity. The optimal pH and temperature for the hydrolysis of 4-nitrophenyl laurate by CALB were 9.0 and 40℃, respectively. The enzyme was stable at pH 10.7 in the glycine-KOH buffer and functioned as an alkaline lipase. The CALB activity was inhibited in the presence of high concentration of Mg<sup>2+</sup>, which indicated that CALB is not a metalloenzyme. These properties are key for the industrial application of the enzyme.