The crystal structure of thermostable mutants of chimeric 3-isopropylmalate dehydrogenase, 2T2M6T

A chimeric 3-isopropylmalate dehydrogenase (IPMDH), 2T2M6T,was produced by replacing the amino acid sequences of the Thermusthermophilus enzyme with those of the Bacillus subtilis enzymefrom residues 75 to 113. Decreased thermostability of the chiaiericenzyme was recovered by either evolutionary engineering (I93L)or site-directed mutagenesis (S82R). The 3-D structures of themutants have been determined by X-ray diffraction at 2.1 Åresolution. Although S82R was refined routinely, (I93L) requiredthe preliminary rigid-body refinement of each domain. The X-factorswere reduced to 0.18 for both mutants. Removal of the unfavorabletorsion angle at isoleucine 93 may have made I93L more thermostablethan 2T2M6T. In the case of S82R, the replaced arginine residuecontributed to the extra hydrogen bond with water molecules.The large replaced residue decreased the entropy of the solvent,which may have caused the improvement in enzyme thermostability.Denatu ration by heating may be interpreted from these structuralresults.     

Effect of preparation conditions on the characteristics of exfoliated graphite

Exfoliated graphite (EG) was prepared from graphite intercalation compounds (GICs) synthesized electrochemically with different electricity consumption from 10.83 to 40.00 A h/kg. Effects of electricity consumption on the synthesis of GICs and of exfoliation temperature on different parameters of EG, i.e. exfoliation volume, volatile content, specific surface area and pore volume measured by mercury porosimetry, length and width of worm-like particles, and distance between neighboring balloons based on the zigzag model for worm-like particles of EG, were studied. These parameters were found to depend strongly on the electricity consumption and also on exfoliation temperature. Exfoliation volume, volatile content, specific surface area and pore volume on EG prepared at 1000 °C increased with increasing electricity consumption, but the distance between neighboring balloons was found to decrease. These results reveal marked development of pores in EG samples. Raising exfoliation temperature increased exfoliation volume, specific surface area and pore volume up to 800 °C. Above this temperature these parameters tended to be stable.     

Dynamic analysis and simulation of a helium-heated steam reformer

This paper deals with the dynamic characteristics of a helium-heated heat-exchanger type steam reformer with catalyst tubes of industrial size. A nonlinear dynamic model was developed based on algebraic and ordinary differential equations which describe material, component and energy balances. This model was numerically linearized around an operating point. In addition, an auto-regressive model was obtained from experimental input-output data in which the inputs were perturbed simultaneously using pseudo-random binary sequences. Experimental data obtained by step and PRBS testing were used for comparison with the simulated responses. The comparison showed that the simulated responses agreed reasonably well with the experimental data.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

The ion-exchange mechanism between copper and alkali ions, when 20R₂O · 10Al₂O₃· 70SiO₂ (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl₂, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl₂ decomposes into CuCl and Cl₂ at 550°C and the Cu⁺ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl₂ acts as an oxidizing agent just like oxygen. In the case of molten CuSO₄─₂SO₄, a small amount of Cu⁺ which is present in the molten state plays a primary role in the Cu ⇌ R⁺ ion exchange process, although the contribution of direct Cu²⁺⇌ 2R⁺ ion exchange cannot be ignored.     

A memory‐in‐pixel reflective‐type LCD using newly designed system and pixel structure

A 7.03‐in. extended graphics array reflective LCD prototype has been developed by using memory‐in‐pixel (MIP) technologies with a newly designed system and pixel structure. The MIP system comprising a MIP backplane and a display driver has been optimized to reduce power consumption. The MIP backplane has specific circuits that allow accessing row drivers randomly, and the display driver manages which row should be accessed. Thus, the system is capable of showing a mixture of still and moving images, resulting in low power consumption. A dithering block embedded in the display driver enables to select an appropriate dithering algorithm according to the types of images and the position on the screen. In addition, the novel pixel structure, “three divided patterns”, has been designed to improve image quality and to provide visibility in dark environments. The latter is based on a novel approach; interpixel area is used for an aperture to transmit light from the backlight, and the fringe field from adjacent pixel electrodes is used to control LC directions. The feature of the pixel structure is also effective for obtaining equivalent gamma between reflective and transmissive images.     

Protective Effects of Voluntary Exercise on Hepatic Fat Accumulation Induced by Dietary Restriction in Zucker Fatty Rats

Weight control based on dietary restriction (DR) alone can cause lipid metabolic failure and progression to fatty liver. This study aimed to investigate the effect of exercise on preventing DR-induced hepatic fat accumulation in Zucker fatty (ZF) rats by focusing on the relationship between adipose tissue lipolysis and hepatic fat uptake. Six-week-old male ZF rats were randomly assigned to obese, DR, or DR with exercise (DR + Ex) groups. The DR and DR + Ex groups were fed a restricted diet, with the latter also undergoing voluntary exercise. After 6 weeks, hepatic fat accumulation was observed in the DR group, whereas intrahepatic fat was markedly reduced in the DR + Ex group. Compared with the obese (Ob) group, the DR group exhibited 2.09-fold expression of hepatic fatty acid translocase (FAT)/CD36 proteins (p < 0.01) and 0.14-fold expression of hepatic fatty acid-binding protein (FABP)1 (p < 0.01). There were no significant differences between the DR + Ex group and the Ob group. FAT/CD36 and hepatic triglyceride (TG) expression levels were strongly positively correlated (r = 0.81, p < 0.001), whereas there was a strong negative correlation between FABP1 and hepatic TG expression levels (r = −0.65, p < 0.001). Our results suggest that hepatic fat accumulation induced by DR in ZF rats might be prevented through exercise-induced modifications in FAT/CD36 and FABP1 expression.     

Preparation of Sn‐Doped Zinc Phosphate Amorphous Thin Film and its Emission Properties

Using liquid‐phase synthesis, SnO – ZnO – P₂O₅ amorphous coating films exhibiting broad emission of Sn²⁺ center were prepared. It is found that the P – O – Zn bonds of the film were generated during the heat‐treatment. The emission property due to Sn²⁺ depended on the heat‐treatment temperature, which correlated with the residual chloride ion content. Although the peak position of the photoluminescence (PL) excitation band was almost constant, that of PL red‐shifted with increasing amount of SnO, which was quite different from the result observed for SnO – ZnO – P₂O₅ bulk glass containing Sn²⁺ center.     

Fabrication of Sr0.5Ba0.5Nb2O6 Nanocrystallite‐Precipitated Transparent Phosphate Glass‐Ceramics

Transparent (Sr_0.5Ba_0.5)Nb₂O₆ (SBN50) nanocrystallite‐precipitated phosphate glass‐ceramics were prepared by a conventional glass‐ceramic process. x(SrO–BaO–2Nb₂O₅) ? (100–4x)P₂O₅ (xSBNP) glasses with a refractive index of 1.9–2.0 exhibited high water resistance owing to the presence of Q⁰ and Q¹ phosphate units. Both bulk and surface crystallization of the SBN50 phase were observed in 20SBNP and 21SBNP glass‐ceramics. Although the nominal content of SBN50 crystals in the 21SBNP glass was larger than that in the 20SBNP glass, the latter exhibited better crystallinity of SBN50 and a higher number density of precipitated SBN nanocrystallites. By tuning the two‐step heat‐treatment and the chemical composition, transparent SBN50‐precipitated glass‐ceramics were successfully obtained. Given that no remarkable increase of the relative dielectric constants was observed after crystallization of the SBN50 nanocrystallites, it is postulated that the relative dielectric constant of the bulk is mainly governed by the amorphous phosphate region, and that the contribution of precipitation of the SBN50 nanocrystallites to the dielectric constant is not very significant in this system.     

Domain switching characteristics of lead zirconate titanate piezoelectric ceramics during mechanical compressive loading

To better understand the domain switching characteristics of lead zirconate titanate (PZT) ceramics, the orientations of domains have been directly investigated during loading and unloading using various experimental techniques. Upon loading, linear and non-linear fracture mechanics of the PZT ceramics are observed. The slope of the stress–strain response is attributed mainly to lattice strain and domain switching strain. During the loading process, electrical activity also occurs several times in the PZT ceramics. This activity is related to a lightning-like phenomenon and consists of a bright flash with a click. This electrogenerative event is caused by severe domain switching. The characteristics of domain switching and reverse switching are detected during the loading and unloading processes. The amount of domain switching depends on the grain, due to different stress levels. In addition, two patterns of 90° domain switching systems are characterized, namely (i) 90° turn about the tetragonal c-axis and (ii) 90° rotation of the tetragonal a-axis.