Development of co-continuous structure in liquid crystalline polyester

We investigated liquid crystallization of liquid crystalline polyester BB-5 during isothermal annealing by digital high-fidelity microscope and light scattering. A liquid crystalline spherical domain having a radius of micrometers appeared by annealing at around 180 °C. The domain grew dendritically in all directions. Neighboring liquid crystalline regions coalesced and then interconnected. The interconnected structure changed to a co-continuous two-phase structure with increasing ordering of the liquid crystalline phase, and the interface between the liquid crystalline phase and the isotropic phase became smoother over time. Liquid crystallization stopped before volume filling the whole space, and the liquid crystalline phase and isotropic phase coexisted. The liquid crystalline region became narrower with an increase in the temperature of the liquid crystallization. Such structural development is different from the liquid-liquid phase separation via spinodal decomposition, and it may be attributed to the segregation of non-liquid crystallizable low molecular weight molecules from the growth front by fractionation of the molecular weight distribution during the liquid crystallization in terms of the instability of the diffusion-controlled interface.     

Determination of a new podophyllotoxin derivative, TOP-53, and its metabolite in rat plasma and urine by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method was developed for the determination of a new podophyllotoxin derivative, TOP-53 (I), and TOP-53 glucuronide (II) as its major metabolite in rat plasma and urine. For the analysis of I, the sample was chromatographed on a reversed-phase C18 column with electrochemical detection after consecutive two-step liquid-liquid extractions. Compound II was determined as I after enzymatic hydrolysis of II. This method was validated sufficiently with respect to specificity, accuracy, and precision. The limits of quantitation for both I and II were 2 ng/ml in plasma and 10 ng/ml in urine. The method is thus useful for the pharmacokinetic study of I.     

Substitution of an aspartic acid results in constitutive activation of c-kit receptor tyrosine kinase in a rat tumor mast cell line RBL-2H3

The c-kit protooncogene encodes a receptor tyrosine kinase that mediates signals required for differentiation, proliferation and survival of mast cells. We have already shown the constitutive activation of c-kit receptor tyrosine kinase (KIT) in a human mast cell leukemia line (HMC-1) and a murine mastocytoma cell line (P-815). We here examined whether such constitutive activation of KIT occurred in the rat tumor mast cell line RBL-2H3 as well, which is frequently used as a tool for studying functions of mast cells. In RBL-2H3 cells, KIT was constitutively phosphorylated on tyrosine and activated in the absence of autocrine production of its ligand, stem cell factor (SCF). Sequencing analysis revealed that one of c-kit genes of RBL-2H3 cells had a point mutation, resulting in amino acid substitution of Tyr for Asp in codon 817. When rat wild-type c-kit cDNA and mutant-type c-kit cDNA encoding KITTyr817 were transfected into cells of a human embryonic kidney cell line (293T), only mutant form KITTyr817 was constitutively phosphorylated on tyrosine and activated in the absence of SCF. Since mutations at the same Asp codon constitutively activated KIT in all the human HMC-1, murine P-815, and rat RBL-2H3 cell lines, and since the incorporation of antisense oligonucleotides of c-kit messenger RNA significantly suppressed the proliferation of RBL-2H3 cells, the activating mutations in the Asp codon of the c-kit gene appeared to be involved in neoplastic growth of mast cells.     

Genetic analysis of double-strand break repair in Escherichia coli

We had reported that a double-strand gap (ca. 300 bp long) in a duplex DNA is repaired through gene conversion copying a homologous duplex in a recB21 recC22 sbcA23 strain of Escherichia coli, as predicted on the basis of the double-strand break repair models. We have now examined various mutants for this repair capacity. (i) The recE159 mutation abolishes the reaction in the recB21C22 sbcA23 background. This result is consistent with the hypothesis that exonuclease VIII exposes a 3'-ended single strand from a double-strand break. (ii) Two recA alleles, including a complete deletion, fail to block the repair in this recBC sbcA background. (iii) Mutations in two more SOS-inducible genes, recN and recQ, do not decrease the repair. In addition, a lexA (Ind-) mutation, which blocks SOS induction, does not block the reaction. (iv) The recJ, recF, recO, and recR gene functions are nonessential in this background. (v) The RecBCD enzyme does not abolish the gap repair. We then examined genetic backgrounds other than recBC sbcA, in which the RecE pathway is not active. We failed to detect the double-strand gap repair in a rec+, a recA1, or a recB21 C22 strain, nor did we find the gap repair activity in a recD mutant or in a recB21 C22 sbcB15 sbcC201 mutant. We also failed to detect conservative repair of a simple double-strand break, which was made by restriction cleavage of an inserted linker oligonucleotide, in these backgrounds. We conclude that the RecBCD, RecBCD-, and RecF pathways cannot promote conservative double-strand break repair as the RecE and lambda Red pathways can.     

Impulse breakdown voltages of triggered multistage vacuum gap

Several sealed-off triggered vacuum gaps are connected in series to improve hold-off voltage. The characteristics of impulse breakdown voltage of these series-connected gaps are investigated experimentally. The sum hold-off voltage of series-connected gaps decreases to a unit hold-off voltage when the maximum value of voltage division ratio across the gaps increases to unity. Self-breakdown probability of the series-connected gaps is always higher than that of a single gap under the same conditions. Hence, stage efficiency of the multistage gap decreases with increasing number of stages. Its value is 90 percent with 2-stage gap and 75 percent with 5-stage gap, respectively, under the same voltage division ratio and the same gap length (2.0 mm) in each stage. Triggered breakdown voltage of 2- or 3- stage gap is several hundred volts when all gaps are triggered simultaneously at the peak of the main impulse wave and a working voltage range is nearly 100 percent in this case. The working voltage range decreases with number of stages. Its value is 45 percent with 3-stage gap and 15 percent with 5-stage gap, respectively, when one triggered gap is fired for switching.     

Modern interpretation on the high-stretching of natural rubber attained by the classic ‘racking’ method

To investigate the mechanism of high elongation of natural rubber attained by the ‘racking method’, a strip of smoked-sheet was elongated up to 150 times in length, by stretching rapidly at room temperature and forcing to shrink at 75-80 °C repeatedly. On X-ray diffraction, a typical fibre pattern with an amorphous ring appeared already at ×10 (stretch ratio=10). The degree of crystallinity increased to the level of 17-18% at ×20 and turned to decrease after ×60, but the degree of crystallite orientation reached at a high level already at ×10 and did not change significantly and the half-height width of reflection profiles stayed almost at a constant level, while the Young's modulus increased up to ca. 300 MPa at ×100 and then fell rather discontinuously. It was assumed that some fractions of chain segments between entanglements were gradually broken in each step of stretching operation, rather than disentangled and slipped.     

Stress intensity factors of microstructurally small crack

The stress intensity factor (SIF) is widely used for evaluating integrity of cracked components. Averaging the anisotropy of each crystal, the macroscopic behavior of polycrystalline materials is isotropic and homogenous in terms of elastic deformation. However, the anisotropic and/or inhomogeneous property influences on the stress field around a crack if the crack size is small in comparison with the grain. Thus, the SIF of the microstructurally small crack may differ from that in the isotropic body. In present study, the effect of anisotropic/inhomogeneous elasticity on the SIF is investigated by using the finite element analysis (FEA). At first, the SIFs of semi-circular crack in a single crystal and a polycrystalline material are calculated. These reveal that the magnitude of SIF is dependent not only on the crystal orientation but also on the deformation constraint by the neighboring crystals. Then, the statistical scatter of SIF due to the random orientation of crystal orientation in a polycrystal is examined by a Monte Carlo simulation.     

Effect of 8 MeV electron irradiation on electrical properties of CuInSe2 thin films

Radiation damages due to 8 MeV electron irradiation in electrical properties of CuInSe₂ thin films have been investigated. The n-type CuInSe₂ films in which the carrier concentration was about 3×10¹⁶ cm⁻³, were epitaxially grown on a GaAs(0 0 1) substrate by RF diode sputtering. No significant change in the electrical properties was observed under the electron fluence <3×10¹⁶ e cm⁻². As the electron fluence exceeded 10¹⁷ e cm⁻², both the carrier concentration and Hall mobility slightly decreased. The carrier removal rate was estimated to be about 0.8 cm⁻¹, which is slightly lower than that of III–V compound materials.     

Accelerator Analysis of Tributyltin Adsorbed onto the Surface of a Tributyltin Resistant Marine Pseudoalteromonas sp. Cell

Tributyltin (TBT) released into seawater from ship hulls is a stable marine pollutant and obviously remains in marine environments. We isolated a TBT resistant marine Pseudoalteromonas sp. TBT1 from sediment of a ship’s ballast water. The isolate (10^{9.3 ± 0.2} colony-forming units mL⁻¹) adsorbed TBT in proportion to the concentrations of TBTCl externally added up to 3 mM, where the number of TBT adsorbed by a single cell was estimated to be 10^8.2. The value was reduced to about one-fifth when the lysozyme-treated cells were used. The surface of ethanol treated cells became rough, but the capacity of TBT adsorption was the same as that for native cells. These results indicate that the function of the cell surface, rather than that structure, plays an important role to the adsorption of TBT. The adsorption state of TBT seems to be multi-layer when the number of more than 10^6.8 TBT molecules is adsorbed by a single cell.