Nucleation, growth and retrogrowth of oxidation induced stacking faults in thin silicon-on-insulator

The nucleation, growth, and retrogrowth of stacking faults were investigated for thermally oxidized silicon-on-insulator substrates formed by the separation by implanted oxygen (SIMOX) method. It has been observed that for high oxidation temperatures (T >1150°C) oxidation induced stacking faults (OISFs) undergo a retrogrowth (shrinkage) process at noticeably lower temperatures than in bulk silicon. The retrogrowth process in thin film SIMOX substrates starts at approximately 1190°C for the 2 h thermal oxidations. In this paper, a model for the retrogrowth process is proposed based on the assumption that at high oxidation temperatures vacancies may be injected from the thermal oxide/top silicon interface. We suggest that the vacancy injection reduces the self-interstitial supersaturation and as a direct consequence, attenuates the OISF growth. We also propose that the self-interstitial supersaturation is reduced through point defect recombination inside the silicon overlayer and at the top-silicon/buried-oxide interface where a high density of steps and kink sites are found.     

Differences in DNA recognition and conformational change activity between boxes A and B in HMG2 protein

High mobility group (HMG) 2 is a sequence-nonspecific DNA-binding protein consisting of a repeat of DNA-binding domains called HMG1/2 boxes A and B and an acidic C-terminal. To understand the mode of HMG2 interaction with DNA, we expressed various HMG2 peptides containing HMG1/2 box(es) in Escherichia coli cells and purified them. Gel retardation and DNA supercoiling assay indicated that the region essential for the preferential binding of HMG2 with negatively supercoiled DNA and DNA unwinding activity is located in box B, but not sufficient alone. The flanking C-terminal basic region or box A linked by a linker region is necessary to express activities. The SPR measurements certified that the intrinsic DNA binding affinity of box B is weaker (Kd = 170 microM), and these adjoining regions largely strengthen the affinity (Kd 相似文献   

Effect of a phase-transfer catalyst on the chemical modification of poly(vinyl chloride) by substitution with thiocyanate as a nucleophile

This study examined the effect of the phase-transfer catalysts tetrabutylammonium bromide (TBAB) and tetrabutylammonium hydrogen sulfate (TBAHS) on the chemical modification of poly(vinyl chloride) (PVC) by substitution with thiocyanate as a nucleophile. TBAB accelerated the dechlorination of PVC in SCN/ethylene glycol (EG) solution. Furthermore, the addition of TBAB to SCN/EG solution improved the substitution of the Cl in PVC with SCN in solution. The addition of TBAB or TBAHS to SCN/H₂O solution promoted the dechlorination of PVC, whereas dechlorination did not occur without the catalyst. The catalysts preferred substitution to the elimination of HCl in SCN/H₂O solution, and TBAB was slightly superior to TBAHS in terms of the degree and selectivity of the substitution. The addition of nitrobenzene to SCN/H₂O solution with TBAB increased the degree of substitution. Consequently, phase-transfer catalysts, particularly TBAB, were very effective at promoting the substitution of Cl in PVC with SCN in solution.     

Gender-specific frequency of background somatic mutations at the hypoxanthine phosphoribosyltransferase locus in cord blood T lymphocytes from preterm newborns

Limited information is available regarding the frequency, spectrum, and clinical relevance of somatic mutations in the developing fetus. The goal of this study was to determine somatic mutant frequencies (Mfs) at the hypoxanthine phosphoribosyltransferase (HPRT) reporter gene in cord blood T lymphocytes from preterm infants to gain insight into in utero mutational events. Mf determinations were made by using the HPRT T cell cloning assay on cord blood samples from 52 preterm infants. Natural logarithm Mfs (lnMfs) from preterm infants were compared with results from our database for full-term infants. Our analysis revealed higher lnMfs in cord blood T lymphocytes from preterm compared with full-term infants (P = 0.008). In addition, preterm females had significantly higher lnMfs compared with full-term females (P < 0.001), whereas preterm males were found to have significantly lower lnMfs than preterm females (P = 0.005). Regression analyses also demonstrate a significant relationship between lnMf and gestational age for preterm females that does not exist for preterm males. These results demonstrate the gender-specific association between Mf and age in humans.     

Three‐dimensional numerical analysis of a liquid metal MHD generator

Three‐dimensional numerical analysis of a liquid metal MHD generator has been carried out. The three‐dimensional structures of the electromagnetic field and fluid flow in the MHD generator have been clarified, and the effect of the electrode width on the performance has also been examined, taking account of the current flow in the electrode. Structures of the electromagnetic field and fluid flow are complicated owing to the three‐dimensional current flow, induced magnetic field, and Lorentz force. The highest performance is found to be obtained when the width of the electrode is equal to that of the generator. The performance predicted from three‐dimensional analysis is somewhat lower than that from two‐dimensional analysis because of the larger input power. The increase in the input power is attributed to the increase in Lorentz force caused by less reduced magnetic flux density and to the additional friction loss on the insulator walls (x?y plane). © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 19–26, 2007; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/eej.20282     

Thermal, Mechanical, and Chemical Properties of Sintered Xenotime-Type RPO4 (R = Y, Er, Yb, or Lu)

Xenotime-type RPO₄ (R = Y, Er, Yb, or Lu) powder was dry-pressed into disks and bars. The disks and bars could be sintered to a relative density of greaterthan equal to98% in air without cracking at 1300° (R = Yb or Lu) or 1500°C (R = Y or Er), depending on the grain size. The linear thermal expansion coefficient (at 1000°C), thermal conductivity (at 20°C), and bending strength (at 20°C) of the xenotime-type RPO₄ ceramics were 6.2 10^-6/°C, 12.02 W(mK)^-1, and 95 ± 29 MPa for R = Y; 6.0 10^-6/°C, 12.01 W(mK)^-1, and 100 ± 21 MPa for R = Er; 6.0 10^-6/°C, 11.71 W(mK)^-1, and 135 ± 34 MPa for R = Yb; and 6.2 10^-6/°C, 11.97 W(mK)^-1, and 155 ± 25 MPa for R = Lu. The xenotime-type RPO₄ ceramics did not react with SiO₂, TiO₂, Al₂O₃, ZrO₂, or ZrSiO₄, even at 1600°C for 3 h in air, and were stable in aqueous solutions of HCl, H₂SO₄, HNO₃, NaOH, and NH₄OH at 20°C.     

Hybrid inorganic/organic composites of Mg-Al layered double hydroxides intercalated with citrate, malate, and tartrate prepared by co-precipitation

Inorganic/organic composite materials composed of Mg-Al layered double hydroxides (Mg-Al LDHs) intercalated with citrate (C₆H₅O₇³⁻), malate (C₄H₄O₅²⁻), or tartrate (C₄H₄O₆²⁻) anions were prepared by a co-precipitation technique and characterized by X-ray diffraction and compositional analyses. The molecular orientation of the organic component in the interlayer space was determined. At low intercalation levels, citrate ion was inclined at an angle of 26° relative to the brucite-like layers of Mg-Al LDH. At higher solution concentrations, both the Mg(C₆H₅O₇)⁻ complex and free C₆H₅O₇³⁻ were isotropically oriented in the interlayer space. For both malate·Mg-Al LDH and tartrate·Mg-Al LDH, the organic anions were inclined at 26° relative to the Mg-Al LDH layers regardless of anion concentration.     

Efficient cleavage of RNA at high temperatures by a thermostable DNA-linked ribonuclease H

To construct a DNA-linked RNase H, which cleaves RNA site-specificallyat high temperatures, the 15-mer DNA, which is complementaryto the polypurine-tract sequence of human immunodeficiency virus-1RNA (PPT-RNA), was cross-linked to the unique thiol group ofCys135 in the Thermus thermophilus RNase HI variant. The resultantDNA-linked enzyme (d15-C135/TRNH), as well as the d15-C135/ERNH,in which the RNase H portion of the d15-C135/TRNH is replacedby the Escherichia coli RNase HI variant, cleaved the 15-merPPT-RNA site-specifically. The mixture of the unmodified enzymeand the unlinked 15-mer DNA also cleaved the PPT-RNA but ina less strict manner. In addition, this mixture cleaved thePPT-RNA much less effectively than the DNA-linked enzyme. Theseresults indicate that the cross-linking limits but acceleratesthe interaction between the enzyme and the DNA/RNA substrate.The d15-C135/TRNH cleaved the PPT-RNA more effectively thanthe d15-C135/ERNH at temperatures higher than 50°C. Thed15-C135/TRNH showed the highest activity at 65°C, at whichthe d15-C135/ERNH showed little activity. Such a thermostableDNA-linked RNase H may be useful to cleave RNA molecules withhighly ordered structures in a sequence-specific manner.     

Thermal imaging system applying two‐color thermometry

This study proposes a new thermal imaging system using the principle of two‐color thermometry to determine the temperature of objects. The system can provide a thermal image of objects without being assigned their emissivity. Applying two‐color thermometry to a thermograph is performed by dividing the detectable wavelength range of a radiation detector into two different ranges using respective bandpass filters. A thermal image is constructed from the two energy distributions of radiation which are measured after passing through each filter. In this study, in order to evaluate the accuracy of imaged temperature in the present system, an error analysis for imaged temperature is carried out and the accuracy of the imaged temperature in the present system is compared with those in a conventional thermograph. This study also demonstrates the performance of the present system by imaging the temperature of objects with different emissivities and at different temperatures. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(6): 473–488, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10104