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121.
Traces amounts of arsenic and antimony in water samples were determined by gas chromatography with a photoionization detector after liquidnitrogen cold trapping of their hydrides. The sample solution was treated with sodium hydroborate (NaBH4) under weak-acid conditions for arsenic(III) and antimony(III) determination, and under strong-acid conditions for arsenic(III+V) and antimony(III+V) determination. Large amounts of carbon dioxide (CO2) and water vapor obscured determination of arsine and stibine. Better separation from interference could be achieved by removing CO2 and water vapor in two tubes containing sodium hydroxide pellets and calcium chloride, respectively. The detection limits of this method were 1.8 ng dm?3 for arsenic and 9.4 ng dm?3 for antimony in the case of 100-cm3 sample volumes. Therefore, it is suitable for determination of trace arsenic and antimony in natural waters. 相似文献
122.
Smooth Fe78Si10B12 thin films were prepared by r.f. sputtering with the very slow deposition rate of 0.59 nm/min. The as-deposited films were not fully amorphous, instead α-Fe(Si) nanocrystallites were found to be embedded in the amorphous matrix. The saturation magnetostriction λs of the as-deposited film is about 6.5 × 10−6. After annealing at 540 °C for 1 h in an ultrahigh vacuum (4.5 × 10−5 Pa), the fraction of α-Fe(Si) crystalline phase largely increased, and correspondingly the λs decreased to 4.5 × 10−7. Ripple domain structures were observed in the as-deposited film, while dense stripe domains were observed in the annealed sample, characterized by a very narrow domain width of 80 nm. (1 1 0) texture and island-like configuration of α-Fe(Si) nanocrystallites formed by the annealing treatment are responsible for the perpendicular anisotropy. For the as-deposited film, the magnetization curves increased linearly with the increase of the magnetic field, and showed the very small hysteresis. On the other hand, the annealed sample clearly showed a very steep jump near the origin, which is due to the switch process of the dense stripe domain. 相似文献
123.
124.
Yoshikazu Shizuri Jiro Ohtsuka Seiji Kosemura Yukimasa Terada Shosuke Yamamura 《Tetrahedron letters》1984,25(48):5547-5550
Some macrocyclic diterpenes derived from euphohelioscopin A and euphornin have been stereoselectively converted into the jatropholane- and daphnane-type compounds and the known tricyclic compound which has been treated with phCOCl - pyridine to afford euphohelionone, the new type of diterpene isolated from euphorbia helioscopia L. 相似文献
125.
Steven Altschuler Sigurd B. Angenent Yoshikazu Giga 《Journal of Geometric Analysis》1995,5(3):293-358
In this paper, we study generalized “viscosity” solutions of the mean curvature evolution which were introduced by Chen, Giga,
and Goto and by Evans and Spruck. We devote much of our attention to solutions whose initial value is a compact, smooth, rotationally
symmetric hypersurface given by rotating a graph around an axis. Our main result is the regularity of the solution except
at isolated points in spacetime and estimates on the number of such points. 相似文献
126.
To demonstrate the neighbouring-group participation of the 2-benzyloxy group in the glycosidation of phenols and of strongly acidic alcohols by the diazirine 1 , we examined the glycosidation of 4-nitrophenol, 4-methoxyphenol, (CF3)2CHOH, MeOH, and i-PrOH by the diazirine 11 , derived from the 2-deoxypyranose 6 . Oxidation of the oximes 7 yielded (E)- and (Z)- 8 . In solution, (E)- 8 isomerised to (Z)- 8 . Similarly, the (E)-configurated mesylate 9 , prepared from 8 , underwent acid-catalysed isomerisation to (Z)- 9 . Treatment of (Z)- 9 with NH3, followed by oxidation of the resulting diaziridine 10 with I2, yielded the desired diazirine 11 . Glycosidation by 11 of the above mentioned hydroxy compounds yielded the glycosides 12–21 . In agreement with the postulated neighbouring-group participation, these glycosidation proceeded without, or with a very low diastereoselectivity, favouring the axial anomers. 相似文献
127.
Nobumoto?NagasawaEmail author Shugo?Ikeda Aiko?Shimoda Takeshi?Waki Yoshikazu?Tabata Hiroyuki?Nakamura Hisao?Kobayashi 《Hyperfine Interactions》2016,237(1):39
The 57Fe Mössbauer spectra of the single crystalline and the finely ground Sr1?x La x Fe12?y Co y O19 (x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe2+ ions in the Fe3+ ions were not observed in our Sr1?x La x Fe12?y Co y O19 samples. In SrFe12O19, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr0.544La0.456Fe11.775Co0.225O19. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co2+ ion for the Fe3+ ion changes the center shifts of the Fe3+ ions near the Co2+ ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co2+ ions occupy the 4f 1 and the 4f 2 sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe3+ ions. 相似文献
128.
Sintering behavior and bioactivity of diopside, CaMgSi2O6, prepared by a coprecipitation process were examined for its biomedical applicability. As-prepared powder was synthesized by adding aqueous ammonia to an ethanol solution containing Ca(NO3)2·4H2O, Mg(NO3)2·6H2O, and Si(OC2H5)4 and characterized by means of TG–DTA, XRD, and TG–MS. The dried powder was X-ray amorphous and crystallized into diopside at 845.5 °C. The glass network formation by SiO4 tetrahedra was almost completed below 800 °C. The bioactivity of the diopside prepared by sintering the compressed powder at 1100 °C for 2 h was evaluated by immersion of the sintered body in a simulated body fluid (SBF) at 36.5 °C. Leaf-like apatite particles were found to be formed on the surface of the sintered body and grew with passage of soaking time. This apatite-forming behavior in the SBF is related to the dissolution of Ca(II) ions from the sintered body in the early stage of immersion. Thus, diopside prepared by the coprecipitation process using the metal alkoxide and the metal salts was found to have an apatite-forming ability. 相似文献
129.
Summary: Specific temperature‐responsive biodegradable hydrogels were synthesized and characterized in terms of their regulation of enzymatic accessibility based on the physical properties of the temperature‐responsive polymers. The hydrogels consist of glycidyl methacrylate‐modified dextran grafted with the poly(N‐isopropylacrylamide) (PNIPAAm) homopolymer, and cross‐linked by co‐polymerization with NIPAAm and N,N‐dimethylacrylamide (DMAAm). The coil‐globule change in the grafted poly(NIPAAm) chains and only a slight dehydration of the poly(NIPAAm‐co‐DMAAm) cross‐linkers are effective in controlling the enzymatic degradation over a specific temperature range.
130.
Ito T Masuda Y Abe N Oyama M Sawa R Takahashi Y Chelladurai V Iinuma M 《Chemical & pharmaceutical bulletin》2010,58(10):1369-1378
Comprehensive re-investigation of the chemical constituents in the leaves of Vateria indica (Dipterocarpaceae) resulted in the isolation of a novel resveratrol dimeric dimer having a C(2)-symmetric structure, vateriaphenol F (1), and two new O-glucosides of resveratrol oligomers, vateriosides A (2) (resveratrol dimer) and B (4) (resveratrol tetramer), along with a new natural compound (3) and 33 known compounds including 26 resveratrol derivatives. The absolute structures were elucidated by spectroscopic analysis, including two dimensional NMR and circular dichroism (CD) spectra. 相似文献