Performance of β-galactosidase pretreated with lactose to prevent activity loss during the enzyme immobilisation process

In this study, Kluyveromyces lactis β-galactosidase was pretreated with lactose to prevent loss of activity during the immobilisation process, and glutaraldehyde was used as a linker to immobilise β-galactosidase on the surface of a silica gel. The pretreatment of β-galactosidase strongly improved its activity after immobilisation. Specifically, the activity of pretreated immobilised β-galactosidase was 2.6 times greater than that of non-pretreated immobilised β-galactosidase. The optimal temperature, pH and ionic strength of buffer for pretreated immobilised β-galactosidase were 37 °C, pH 7.5 and 20 mM potassium phosphate buffer, respectively. These values were shifted by 5 °C and pH by 0.5 when compared to the soluble β-galactosidase. Moreover, the pretreated immobilised β-galactosidase showed a better reusability than did non-pretreated immobilised β-galactosidase, with 63.9% of its original activity being retained after 10 reuses.     

水蒸气跨音速流动中非平衡现象的数值模拟

研究了水蒸气跨音速流动过程中的非平衡相变及凝结冲波现象,揭示了气动激波与非平衡凝结流动之间相互作用的非定常流动规律。采用欧拉形式的控制方程求解两相凝结流动,建立了二维可压缩守恒型计算模型对水蒸气跨音速非平衡流动进行了数值模拟．捕获到了凝结冲波现象,揭示了凝结冲波的非平衡热力学机理,并探讨了尺度效应对两相非平衡流动的影响。研究了凝结冲波与气动激波之间的不同热力学特性和形成机理,并探讨了气动激波与非平衡凝结流动之间相互作用的非定常流动规律。     

Flame-synthesis limits and self-catalytic behavior of carbon nanotubes using a double-faced wall stagnation flow burner

Flame-synthesis limits of carbon nanotubes (CNTs) are measured using a double-faced wall stagnation flow (DWSF) burner that shows potential in mass production of CNTs. With nitrogen-diluted premixed ethylene-air flames established on the nickel-coated stainless steel double-faced plate wall, the limits of CNT formation are determined using field-emission scanning and transmission electron microscopies and Raman spectroscopy. Also, self-catalytic behavior of the synthesized CNTs is evaluated using the DWSF burner with a CNT-deposited stainless steel double-faced plate wall. Results show narrow fuel-equivalence ratio limits of multi-walled CNT (MWCNT)-synthesis at high flame stretch rates and substantially extended limits at low flame stretch rates. This implies that the synthesis limits are very sensitive to the fuel-equivalence ratio variation for the high stretch rate conditions, yielding a lot of impurities and soot rather than MWCNTs. The enhanced ratio of tube inner diameter to wall thickness of the MWCNTs synthesized using a CNT self-catalytic flame-synthesis process is observed, indicating that the quality of metal-catalytic, flame-synthesized MWCNTs can be much improved via the process. Thus, using a DWSF burner with the CNT self-catalytic process has potential in mass production of MWCNTs with improved quality.     

Numerical simulation on the behavior of a liquid jet into an air flow

A numerical simulation has been performed to clarify the effects of turbulence in a liquid on the deformation of the liquid jet surface into an air flow. The turbulences in the liquid jet were simulated by the Rankin vortices, and the liquid jet surface was tracked numerically by the volume of fluid method. By numerical simulations, the onset of the protrusions on the liquid jet surface is caused by the vortices in the liquid, and the surrounding air flow plays an important role in the amplification of the protrusions. The amplification rate of the trough displacement is proportional to the air‐to‐liquid velocity ratio. At large imposed vortex intensities, the trough displacement increases with the vortex intensity. On the other hand, at small imposed vortex intensities, the amplification of the trough displacement is also affected by factors other than vortex intensity. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 473–484, 2001     

Optimization of two-stage fractionation process for lignocellulosic biomass using response surface methodology (RSM)

A two-stage process using aqueous ammonia and hot-water has been investigated to fractionate corn stover. To maximize hemicelluloses recovery and purity in the liquid hydrolyzate by optimizing the fractionation process, the experiments were carried out employing response surface methodology (RSM). A central composite design (CCD) was used to evaluate and confirm the effectiveness and interactions of factors. The optimal fractionation conditions were determined to be as follow: (1) First-stage reactor operated in batch mode using a 15% NH₄OH solution (w_NH3 = 15%) at 1:10 solid:liquid ratio, 60 °C, and 24 h; (2) second stage percolation reactor operated using hot-water at 20 cm³ min⁻¹, 200 °C, and 10 min.The model predicted 51.5% xylan recovery yield and 82.4% xylan purity under these conditions. Experiments confirmed the maximum xylan recovery yield and purity were 54.7% and 83.9% respectively under the optimal reaction conditions.With the solids resulting from the two-stage treatment, 87%-98% glucan digestibilities were obtained with 15 FPU of GC 220 per g-glucan and 30 CBU of Novo 188 per g-glucan enzyme loadings. Xylan digestibility of xylooligomer hydrolysates reached 76% with 8000 GXU per g-xylan of Multifect-Xylanase loading. In the simultaneous saccharification and fermentation (SSF) test using treated solids and Saccharomyces cerevisiae (D₅A), 86 % to 98% of ethanol yield was obtained on the basis of the glucan content in the treated solids.     

Establishment of risk-based accident scenarios using the master logic diagram related to LILW management in the temporary storage facility

The initiating event, which is the first step in the establishment of risk-based accident scenarios, was derived by master logic diagram (MLD) method based on the fault tree analysis (FTA), and then the risk-based accident scenarios were developed by the event tree analysis (ETA) through the derived initiating events. The main initiating events led to the arbitrary operational accident: the dropping of a drum and fire were derived from the MLD method. Consequently, based on two main initiating events, four heading events were derived, and then the 12 risk-based accident scenarios concerning the LILW management in the temporary storage facility were finally established by the ETA method.     

Experimental study on mitigating the cathode flooding at low temperature by adding hydrogen to the cathode reactant gas in PEM fuel cell

Severe flooding can be critical in a fuel cell vehicle operating at a high current density, and in a fuel cell vehicle at the initial stage of start up. It is often difficult to remove the condensed water from the cathode gas diffusion layer (GDL) of the fuel cell because of the surface tension between the water and the GDL. In this research, in order to remove the condensed water from the cathode GDL, a small amount of hydrogen was injected into the cathode reactant gases. The results showed that the hydrogen addition method successfully removed the liquid water from the cathode GDL. Water removal was verified for various hydrogen flow rates and hydrogen addition durations. Furthermore, the dew point temperature of the outlet gas at the cathode was observed to determine the amount of water removed from the cathode GDL. In addition, the water droplet in the cathode gas flow channel was visualized by using a transparent cell. Furthermore, degradation tests are also performed. Considering the degradation test, the hydrogen addition method is expected to be effective in mitigating cathode flooding.     

Efficiency enhancement in large-area organic photovoltaic module using theoretical power loss model

For efficiency enhancement of a large-area monolithic organic photovoltaic (OPV) module, we studied the influence of the OPV cell geometry parameters using theoretical and experimental methods. For this work, a unit OPV cell as a reference device and four types of monolithic OPV module with different active cell lengths were fabricated together on a glass substrate. The characteristics of the fabricated unit OPV cell were measured and the voltage (V_mp) and current density (J_mp) at the maximum power point were extracted. The parasitic power losses were calculated from the extracted parameters and the material parameters using a theoretical power loss model, taking into consideration the series resistance, contact resistance, and shading (or dead area) losses at the calculated maximum power of the monolithic OPV module. To analyze the influence of OPV cell layout on efficiency of the large-area monolithic OPV module, the power conversion efficiency of the four type monolithic OPV modules with different active cell lengths was measured and compared with the calculated power conversion efficiency. The calculated PCE ratio of the monolithic OPV module with three cells was approximately 78%, and the measured PCE ratio of the fabricated monolithic OPV module with three cells was also approximately 78%. The measured PCE ratio of fabricated monolithic OPV modules with two, four, and five cells also exhibited this tendency for the calculated PCE ratio. Thus, a large-area monolithic OPV module with optimum electrical power loss and an appropriate number of OPV cells can be designed by extracting the parameters of the unit OPV cell and calculating the electrical power loss using the proposed theoretical power loss model.     

Effect of electrode configuration on the thermal behavior of a lithium-polymer battery

A thermal modeling was performed to study the effect of the electrode configuration on the thermal behavior of a lithium-polymer battery. It was examined the effect of the configuration of the electrodes such as the aspect ratio of the electrodes and the placing of current collecting tabs as well as the discharge rates on the thermal behavior of the battery. The potential and current density distribution on the electrodes of a lithium-polymer battery were predicted as a function of discharge time by using the finite element method. Then, based on the results of the modeling of potential and current density distributions, the temperature distributions of the lithium-polymer battery were calculated. The temperature distributions from the modeling were in good agreement with those from the experimental measurement for the batteries with three different types of electrodes at the discharge rates of 1C, 3C, and 5C.     

Reduction characteristics of CuFe2O4 and Fe3O4 by methane; CuFe2O4 as an oxidant for two-step thermochemical methane reforming

The reduction characteristics of CuFe₂O₄ and Fe₃O₄ by methane at 600–900 °C were determined in a thermogravimetric analyzer for the purpose of using CuFe₂O₄ as an oxidant of two-step thermochemical methane reforming. It was found that the addition of Cu to Fe₃O₄ largely affected the reduction kinetics and carbon formation in methane reduction. In the case of CuFe₂O₄, the reduction kinetics was found to be faster than that of Fe₃O₄. Furthermore, carbon deposition and carbide formation from methane decomposition were effectively inhibited. In case of Fe₃O₄, Fe metal formed from Fe₃O₄ decomposed methane catalytically, that lead to the formation of graphite and Fe₃C phases. It is deduced that Cu in CuFe₂O₄ enhanced reduction kinetics, decreased reduction temperature and prevented carbide and graphite formation. Additionally, methane conversion and CO selectivity in the syngas production step with CuFe₂O₄ were in the range of 33.5–55.6% and 54.9–59.6%, respectively.