Synthesis process of Ba-ferrites from α-FeOOH and γ-FeOOH and investigation of magnetic properties

The claviform BaFe₁₂O₁₉ crystals were synthesized by the precipitation-toptactic reaction method using α-FeOOH and γ-FeOOH as raw materials respectively. The synthesis processes of BaFe₁₂O₁₉, studied by XRD, SEM, EDS, FT-IR, and TG-DTA techniques, included preparations of precursor γ and precursor α, formations of α-Fe₂O₃ and BaFe₂O₄, and production of rod-like BaFe₁₂O₁₉ through dehydroxylation of pod-like FeOOH, followed by reactions of α-Fe₂O₃ with BaCO₃ and BaFe₂O₄. The crystallinity of α-Fe₂O₃ and BaCO₃ from precursor α was better than from precursor γ due to the direct dehydroxylation of α-FeOOH, resulting in a lower nucleation rate and better crystallinity of BaFe₂O₄. BaFe₁₂O₁₉ prepared from precursor α showed lower crystallinity and purity with a higher length-diameter ratio than from precursor γ. The VSM results proved that the appearance of final products had an important influence on magnetic properties.     

Temperature-induced fractionation of oxygen isotopes of diatom frustules and growth water in Lake Sihailongwan in Northeast China

Diatom oxygen isotopes have been widely applied in quantitative reconstruction of the paleoclimate and paleoenvironment, but have rarely been reported in China. In the present study, Lake Sihailongwan in Northeast China was selected for detailed investigation of oxygen isotopic fractionation between diatom frustules and lake water induced by growth temperature. This study involved a 2-year period of field monitoring of the lake water temperature at multiple depths and biweekly collections of traps for both sediment and water at shallow and bottom depths (7 and 49 m below the lake surface, respectively), diatom separation and purification of the trap sediments, and oxygen isotope measurement for diatom silica and lake water samples. The conditioned experiment conducted herein demonstrated that the laboratory device, methods and techniques used in this study were capable of generating reliable data for the typical oxygen isotope composition of diatom frustules. The data obtained revealed a prominent linear relationship between the oxygen isotope composition of the modern diatom and lake temperature during growth. The fractionation coefficient was about −0.185‰/°C−0.238‰/°C in the temperature range of 3.6–24°C, which is consistent with the observations from various aquatic environments and laboratory culture with different diatom taxa. These findings provide strong support for the dominant control of the growth temperature on the oxygen isotope fractionation between the diatom frustules and ambient water. A notable difference in the fractionation coefficient was observed between the surface and bottom diatom oxygen isotopes, suggesting that various depositional processes and taphonomic effects influenced the surface and bottom trap samples. Another factor leading to this difference may be that enrichment by evaporation and dilution by rainfall have a stronger influence on the surface. Overall, the results presented here demonstrate significant progress in evaluation of diatom oxygen isotopes in China and draw attention to the differences between surface and bottom diatom oxygen isotope compositions.     

Controllable stereoselective synthesis of pyrano[3,2-<Emphasis Type=Italic>c</Emphasis>]quinolines by lanthanide halides catalyzed aza-Diels-Alder reactions

An efficient method for the synthesis of tetrahydroquinoline derivatives via lanthanide halides catalyzed domino reactions of arylamines with dihydropyran is described. Either the cis or the trans isomer can be obtained as the major product in good yield by changing the catalyst and reaction conditions.     

Chiral pyrrolidine-azole conjugates: Simple and efficient asymmetric organocatalysts for Michael addition to nitrostyrenes

Simple pyrrolidine-azole conjugates have been synthesized and found to be efficient catalysts for asymmetric Michael addition to nitrostyrenes. The identified optimal catalysts, pyrrolidine-azoles 2, 8 and 13, could catalyze the asymmetric Michael addition of a range of Michael donors and nitrostyrenes in high yields (up to 99%) and excellent stereoselectivities (up to 99:1 dr and 97% ee).     

Radioprotectors from pyrodextrins

Cornstarch heated in the range of 230–280°C depolymerized into pyrodextrins characterized by two-component EPR signals of relatively stable free radicals. These thermally generated radicals could serve as efficient scavengers for free radicals generated from pyrodextrins with the 200 Gy dose of γ-radiation. The most efficient traps/scavengers were produced from cornstarch at 250–280°C. IR data indicated incorporation of the OH groups to the pyrodextrins. These groups most probably originated from the OH· radicals formed by the radiolysis of water. EPR spectra provided evidence for trapping free radicals generated by γ-irradiation and for their subsequent annihilation on contact with pyrodextrins. Water affected radical processes occurring in pyrodextrins caused by γ-irradiation.     

Temporal and spatial distribution of tropospheric CO<Subscript>2</Subscript> over China based on satellite observations

Mid-troposphere CO₂ data retrieved by the AIRS (atmospheric infrared sounder) were validated with five ground-based stations and aircraft measurements in the Northern Hemisphere. AIRS CO₂ products show good agreement with ground and aircraft observations. The data had a monthly average accuracy better than 3 ppmv. In this study, the spatial and temporal distribution of mid-troposphere CO₂ from January 2003 to December 2008 was analyzed based on this satellite product. The average concentration of atmospheric CO₂ was higher in the Northern Hemisphere than in the Southern Hemisphere. The yearly average results show a gradual increase from 2003 to 2008. In China, the annual growth rate was about 2 ppmv/a, similar to the United States, Europe, Australia and India, but was slightly lower than Canada and Russia. Mid-troposphere CO₂ concentrations were higher over northern China than over southern areas, due to differences in natural conditions and industrial layout. There were four centers of high CO₂ concentration between 35° and 45°N over China, with low concentrations over Yunnan Province. There was a significant seasonal CO₂ variation with peak concentration in spring and the lowest concentration in autumn.     

Synthesis and photo-responsive behaviors of hollow polyazobenzene micro-spheres

By means of distillation precipitation polymerization, the silica-hybrid particles with polyazobenzene shell (PAzo@SiO₂) micro-spheres were prepared with 6-(4-methoxy-4′-oxy-azobenzene) hexyl methacrylate (Azo-M) as monomer, divinylbenzene (DVB) as cross-linker, and ~250 nm vinylated sol-gel silica particles as template. Hollow polyazobenzene microspheres were further developed after selective removal of the silica cores with HF solution. When the content of DVB related to Azo-M is 20 wt%, the acetonitrile is 200 mL, and the polymerization time is 4.5 h, the hollow PAzo microspheres with about 20 nm shell are successfully fabricated. These hollow PAzo microspheres have excellent reversible photoisomerization, and their first-order rate constant of trans-cis isomerization only decreases 11.8% compared with homopolymer of azobenzene (Homo-PAzo).     

Language clusters based on linguistic complex networks

To investigate the feasibility of using complex networks in the study of linguistic typology, this paper builds and explores 15 lin-guistic complex networks based on the dependency syntactic treebanks of 15 languages. The results show that it is possible to classify human languages by means of the following main parameters of complex networks: (a) average degree of the node, (b) cluster coefficients, (c) average path length, (d) network centralization, (e) diameter, (f) power exponent of degree distribution, and (g) the determination coefficient of power law distributions. The precision of this method is similar to the results achieved by means of modern word order typology. This paper tries to solve two problems of current linguistic typology. First, the language sample of a typological study is not real text; second, typological studies pay too much attention to local language structures in the course of choosing typological parameters. This study performs better in global typological features of language and not only enhances typological methods, but it is also valuable for developing the applications of complex networks in the humanities, social, and life sciences.     

Solidification microstructure and phase constitution of Fe-7.5%Mo-16.5%Si ternary quasiperitectic alloy

Solidification of Fe-7.5%Mo-16.5%Si ternary quasiperitectic alloy is investigated by using differential scanning calorimetry (DSC) and drop tube containerless processing techniques.The primary phase is identified as R (Fe5Mo3Si2) and the quasiperitectic phases are τ1 (Fe5MoSi4) and Fe3Si.With the decrease of droplet diameter, the cooling rate and undercooling of the droplets in-crease rapidly.The experiment result indicates that the solidification microstructure is composed of remnant primary phase, qua-sip...     

Hydrothermal synthesis and photoluminescence behavior of CeO<Subscript>2</Subscript> nanowires with the aid of surfactant PVP

Well-crystalline CeO₂ nanowires were prepared via a surfactant-assisted hydrothermal process. Reaction temperature and reaction time were changed for the determination of optimal synthesis parameters. The as-obtained products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM). The results show that single crystal CeO₂ nanowires with high yield and good uniformity can be obtained hydrothermally at 180°C for 12 h with the aid of 2.0 g surfactant (polyvinyl pyrrolidone, PVP). The role of PVP was then discussed and a possible growth mechanism was proposed. Moreover, room temperature photoluminescence (PL) spectra were obtained for these CeO₂ nanowires, which are believed to be related to the abundant defects in these nanostructures.