Effects of Grafting Maleic Anhydride onto Poly-ɛ-caprolactone on Facilitative Enzymatic Hydrolysis

Plastic waste is a global issue because it causes overflowing landfills and pollution, leading to environmental concerns. To address this crisis, materials that can be decomposed in the natural environment are introduced to replace conventional plastics. Poly-ɛ-caprolactone (PCL) is a commonly used plastic that can degrade in natural environments. However, owing to its hydrophobicity, its natural decomposition rate is low. In this study, PCL is modified with maleic anhydride (MA) (PCL-g-MA) to increase hydrophilicity and amorphous region for faster decomposition. To assess the hydrolysis in seawater, lipase hydrolysis is performed to compare the decomposition of PCL-g-MA and PCL. Consequently, in a Pseudomonas lipase-containing PBS solution, it takes 72 and 120 h for complete hydrolyze of PCL-g-MA and PCL, respectively. MA grafted onto PCL increases the amorphous region, where lipase can easily diffuse into PCL-g-MA. Morphological (FESEM and POM images), thermal (TGA and DSC), and structural (FTIR, XRD, and XPS) analyzes support the hydrolysis reaction. The mechanisms proposed in this study confirm that lipase hydrolysis starts in the amorphous regions and then transfers to the crystal regions. This hydrolysis progress is expected to facilitate the creation of eco-friendly low-cost PCL-g-MA composites with high-rate hydrolysis, such as bio-plastics and bio-fibers.     

Crystal structures of mutants of Thermus thermophilus IPMDH adapted to low temperatures

Random mutagenesis on thermophilic 3-isopropylmalate dehydrogenases(IPMDH; EC 1.1.1.85) produced mutant enzymes which adapt tolow temperatures. These mutants had higher activity at lowertemperatures than the wild-type enzyme without losing high thermostability.Here we report three structures of the mutants of Thermus thermophilusIPMDH determined by X-ray diffraction which was adapted to alow-temperature environment. Two of them have unstable coenzymebinding states and the other one probably has a stable substratebinding state. The present research suggests that the adaptationis correlated with the binding of either coenzyme or the substrate.     

A systematized theory of creative concept generation in design: first-order and high-order concept generation

This paper aims to develop a systematized theory on the thinking process at the ‘very early stage of design.’ Here, ‘very’ is used to exaggerate the beginning of design, which includes the time just prior to or the precise beginning of the so-called conceptual design. First, concept generation is segregated into two phases—the problem-driven phase and the inner sense-driven phase. With regard to theoretical approach, the concept generation process is discussed by comparing metaphor, abduction, and general design theory from the perspective of similarities and dissimilarities. In addition, property mapping, concept blending, and concept integration in thematic relation are explained methodologically. So far, these theories and methods have been discussed independently, and the relations among them have not been clarified. As a result, it was found that the concept generation process could be categorized into two types: first-order concept generation and high-order concept generation. Furthermore, it was shown that high-order concept generation is related to the inner sense-driven phase, whereas first-order concept generation is related to the problem-driven phase.     

Analysis of the effect of accumulation of amino acid replacements on activity of 3-isopropylmalate dehydrogenase from Thermus thermophilus

A newly selected cold-adapted mutant 3-isopropylmalate dehydrogenase(IPMDH) from a random mutant library was a double mutant containingthe mutations I11V and S92F that were found in cold-adaptedmutant IPMDHs previously isolated. To elucidate the effect ofeach mutation on enzymatic activity, I11V and six multiple mutantIPMDHs were constructed and analyzed. All of the multiple mutantIPMDHs were found to be improved in catalytic activity at moderatetemperatures by increasing the k_cat with a simultaneous increaseof K_m for the coenzyme NAD⁺. k_cat was improved by a decreasein the activation enthalpy, H. The multiple mutants did notshow large reduction in thermal stability, and one of them showedenhanced thermal stability. Mutation from I11 to V was revealedto have a stabilizing effect. Mutants showed increased thermalstability when the mutation I11V was combined. This indicatesthat it is possible to construct mutants with enhanced thermalstability by combining stabilizing mutation. No additivity wasobserved for the thermodynamic properties of catalytic reactionin the multiple mutant IPMDHs, implying that the structuralchanges induced by the mutations were interacting with eachother. This indicates that careful and detailed tuning is requiredfor enhancing activity in contrast to thermal stability.     

Oxidative Removal of Boron from Molten Silicon by CaO-based Flux Treatment with Oxygen Gas Injection

Oxidative removal of boron from molten silicon has been investigated at 1773 K (1500 °C) by CaO-based flux treatment with oxygen gas injection. Since oxygen gas is injected into the silicon melt after adding CaO- or CaCO₃-CaF₂ flux onto the melt, high oxygen partial pressure is maintained at the flux-O₂-Si interface and the removal of boron proceeds under nonequilibrium conditions. The experimental results clarified that the behavior of boron removal from molten silicon depends on the competition between the oxidation reactions of boron and silicon. On the basis of the results obtained, optimum operating conditions for boron removal by the flux treatment were examined from the viewpoints of initial flux composition, reaction time, oxygen gas flow rate, and orifice size of gas injection nozzle. By repeating the batch operation for 120 seconds three times under the optimum conditions determined in the present study, boron concentration in metallurgical-grade silicon could be reduced from 14 to 7.6 mass ppm efficiently.     

Mathematical modelling for rolling force and microstructure evolution and microstructure controlling with heavy reduction in tandem hot strip rolling

A new mathematical model to predict rolling force and microstructure evolution in hot strip rolling has been proposed. This model is constructed by Orowan's theory, FDM analysis for temperature and incremental theory for the evolution of microstructure. It enables us to predict rolling force accurately, since the flow stress is directly calculated by dislocation density. As the time for computation is quite short, the proposed model can be used to ensure the deviation of grains in the product coils. The proposed model has been used to characterise large reduction tandem hot rolling. There is good relationship between ferrite grain size of the hot strip and dislocation density. Then one can plan the best schedule to roll ultra fine grain strip considering strain, strain rate and rolling temperature. Also, the proposed model is general so that one can predict microstructure in any rolling process to product new steel with correcting material data.     

Absorption and Electrical Conductivity during Electrochemical Reduction in Fullerene Film

The results of in-situ measurements of optical absorption and electrical conductivity in C₆₀/C₇₀ (9/1) film during electrochemical reduction in a cell using solid polymer electrolyte are reported. The drastic change of absorbance and the increase of conductivity upon Li doping were obtained and the results are discussed.     

Smooth Output Reconstruction for Linear Systems with Quantized Measurements

This paper presents a novel approach to reconstruct the output of linear systems in the case where the measured output is uniformly quantized. By fitting the quantized measurements with polynomials in a moving horizon manner, a smooth signal is reconstructed by solving a convex optimization problem with ?₁‐norm regularization. The quantization feature and the system models are taken into account in the optimization. A numerical example is given to show the excellent reconstruction performance of the proposed method. In addition, the proposed method is implemented in a high‐precision linear stage through DSP, and its effectiveness is verified through experiments using a real positioning system.