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121.
122.
We propose a method for evaluating the size of the laser-induced breakdown region in water based on the detection and analysis of optodynamic waves. The breakdown region is an optodynamic source of pressure waves that propagate into the surrounding liquid as an ultrasonic pulse. In the experiment the optical breakdown was generated by a standard ophthalmic Nd:YAG laser with a pulse duration of 10 ns and a maximum energy per pulse of 10 mJ. The pulses were detected inside the liquid with a laser-beam deflection probe. The waveforms were captured in the far-field and analyzed. The analysis provides information about the apparent size of the optodynamic source, which is directly related to the size of the breakdown region. The proposed method can be adapted for online monitoring. 相似文献
123.
Koya Shibano Shiro Kubuki Kazuhiko Akiyama Zoltán Homonnay Ernő Kuzmann Stjepko Krehula Mira Ristić Tetsuaki Nishida 《Hyperfine Interactions》2014,226(1-3):489-497
Nanoparticles (NPs) of Fe3O4 and γFe2O3 synthesized by hydrothermal reaction were characterized by X-ray diffractometry (XRD), 57Fe-Mössbauer spectroscopy and field emission scanning electron microscopy (FE-SEM). A decrease in concentration of methylene blue (MB) aqueous solution due to bulk Fe0-NP γFe2O3 mixture with the mass ratio of 3:7 was measured by ultraviolet-visible light absorption spectroscopy (UV-Vis). The Mössbauer spectrum of NP Fe3O4 prepared from hydrothermal reaction was composed of two sextets with absorption area (A), isomer shift (δ) and internal magnetic field (H int) of 56.3 %, 0.34±0.03 mm s???1 and 49.0±0.30 T for tetrahedral (T d) FeIII, and 43.7 %, 0.66±0.11 mm s???1 and 44.0±0.71 T for octahedral (O h) FeII?+?III. The FeII/FeIII ratio was determined to be 0.280 for NP Fe3O4, giving ‘x’ of 0.124 in Fe3???xO4. These results show that NP Fe3O4 prepared by hydrothermal reaction was not regular but nonstoichiometric Fe3O4. Consistent results were observed for XRD patterns of NP Fe3???xO4 indicating sharp intense peaks at 2Θ of 30.2, 35.7 and 43.3° with a large linewidth of 0.44°, yielding the crystallite size of 29–37 nm from the Scherrer’s equation. Iso-thermal annealing of NP Fe3???xO4 at 250 °C for 30 min resulted in the precipitation of NP γFe2O3 with δ of 0.33±0.03 mm s???1 and H intof 46.4±0.27 T due to magnetic tetrahedral FeIII. The Debye temperature of NP Fe3???xO4 was respectively estimated to be 267±5.45 K for Fe $^{\mathrm{III}}(T_{\mathrm{d}})$ and 282±7.17 K for Fe $^{\mathrm{II+III}}(O_{\mathrm{h}})$ , both of which were smaller than that obtained for bulk Fe3O4 of 280±4.15 K and 307±5.70 K, indicating that the chemical environment of iron of NPs is less rigid than that of the bulk compounds. A leaching test using methylene blue (MB) and mixture of bulk Fe0-NP γFe2O3 (3:7) showed a remarkable decrease in MB concentration from 1.90 × 10???2 to 9.49 × 10???4 mM for 24 h with the first order rate constant (k MB) of 2.1 × 10???3 min???1. This result verifies that MB decomposing ability is enhanced by using NP γFe2O3 compared with the k MB of 1.1 × 10???4 min???1 previously obtained from the leaching test using MB and bulk mixture of Fe0???γFe2O3 (3:7). 相似文献
124.
Arjunic acid and arjunolic acid are main bioactive components of Terminalia arjuna stem bark and reported for various biological activities. In this study, microwave-assisted extraction (MAE) of arjunic and arjunolic acid from stem bark of T. arjuna was investigated with developed and validated HPLC-PDA method, which resulted in the isolation of a novel anticancer molecule i.e. arjunic acid. Effects of several experimental parameters, such as type and volume of extraction solvents, microwave power, microwave extraction time, on the extraction efficiencies of arjunic, and arjunolic acid from stem bark of T. arjuna were evaluated. The optimal extraction conditions identified were 5.0 g quantity of stem bark powder, 20 mL of ethyl acetate, preleaching time 10 min, microwave power 600 W, temperature 65°C, and microwave irradiation time 5 min. The results showed that MAE is a more rapid extraction method with higher yield and lower solvent consumptions than reported methods. The HPLC-PDA analysis method was developed and validated to have good linearity, precision, sensitivity, and accuracy. MAE-HPLC-PDA is a faster, convenient, and appropriate method for isolation and determination of arjunic acid and arjunolic acid in the stem bark of T. arjuna. 相似文献
125.
126.
Kharel MK Pahari P Shepherd MD Tibrewal N Nybo SE Shaaban KA Rohr J 《Natural product reports》2012,29(2):264-325
Covering: 1997 to 2010. The angucycline group is the largest group of type II PKS-engineered natural products, rich in biological activities and chemical scaffolds. This stimulated synthetic creativity and biosynthetic inquisitiveness. The synthetic studies used five different strategies, involving Diels-Alder reactions, nucleophilic additions, electrophilic additions, transition-metal mediated cross-couplings and intramolecular cyclizations to generate the angucycline frames. Biosynthetic studies were particularly intriguing when unusual framework rearrangements by post-PKS tailoring oxidoreductases occurred, or when unusual glycosylation reactions were involved in decorating the benz[a]anthracene-derived cores. This review follows our previous reviews, which were published in 1992 and 1997, and covers new angucycline group antibiotics published between 1997 and 2010. However, in contrast to the previous reviews, the main focus of this article is on new synthetic approaches and biosynthetic investigations, most of which were published between 1997 and 2010, but go beyond, e.g. for some biosyntheses all the way back to the 1980s, to provide the necessary context of information. 相似文献
127.
Yasemin ?a?lar Nurhan Gümrük?üo?lu Ece Tu?ba Saka Mira? Ocak Halit Kantekin ümmühan Ocak 《Journal of inclusion phenomena and macrocyclic chemistry》2012,72(3-4):443-447
A tetra-substituted phthalocyanine based on 4-[2-(4-nitrophenoxy)ethoxy]phthalonitrile carrying nitrophenyl group for the sensing of Zn2+ has been prepared and characterized by elemental analysis, FT-IR, 1H and 13C NMR, and MS spectral data. The sensing of Zn2+ is based on the fluorescence quenching of Pc. Both absorbance and fluorescence spectra of ZnPc exhibit distinct changes in visible region in response to treatment with Zn2+ ion in dimethyl sulfoxide. The fluorescence spectrum of the ligand showed quenching in the intensity of the signal at 688?nm for Zn2+. The complex composition of ZnPc was found 1:1 by means of spectrophotometric and spectrofluorimetric titration data. The spectrofluorimetric method showed good sensitivity for Zn2+ with linear range and detection limit of 4.0?×?10?6–4.4?×?10?5 and 2.4×10?7?M, respectively. 相似文献
128.
A novel equilibrium theory is developed for two price markets permitting investors to trade personally designed structured
products. Classical market clearing is enhanced for structured products where the market allows these products to be freely
bought at ask prices or sold for bid prices. Competitive pressures lead the market to lower the ask prices and raise the bid
prices with the market offering individual investors the widest possible set of acceptable risks provided the aggregate counter
cash flow held by the market is consistent with a more conservative prespecified set of acceptable risks. We learn that in
equilibrium heterogeneous investors inherit a common hedging objective of maximizing the bid prices of the final structured
product sold to market or equivalently minimizing the ask price of what is bought. 相似文献
129.
Experiments in a refractive index matched pipe flow facility were conducted using state-of-the-art laser-Doppler anemometry to study turbulent drag reduction by dilute addition of high polymers. The results were analyzed employing the invariant theory of turbulence. It was thus possible to confirm the major conclusion of preceding theoretical work, namely that the mechanism of drag reduction by long-chain polymers is associated with an increase in anisotropy of turbulence at the wall. Furthermore, theoretical considerations based on the elastic behavior of a polymer and spatial intermittency of turbulence at small scales enabled quantitative estimates to be made for the relaxation time of a polymer and its concentration that ensures maximum drag reduction. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
130.
Jayashree Avvadukkam Narayana Badiadka Sarojini B. Kunhanna Madan S. Kumar 《Journal of heterocyclic chemistry》2021,58(3):724-736
A facile three-component reaction of aromatic aldehyde, 2,2-dimethyl-1,3-dioxane-4,6-dione, and 6-amino-1,3-dimethyluracil was developed for the first time using β-cyclodextrin (β-CD) as a macrocyclic host for aldehyde and an efficient catalyst that leads to a batch of novel pyrano[2,3-d:6,5-d′]dipyrimidines ( 4a-k ). The synthesis was accomplished with the aid of microwave irradiations in solvent-free conditions. The product obtained was in contrast to the previous report in which a similar reaction resulted in a mixture of benzylidenepyrimidine and bisaminopyrimidine analogs in the presence of triethylbenzylammonium chloride in an aqueous medium. The formation of the pyrano[2,3-d:6,5-d′]dipyrimidines may be in virtue of the property of β-CD to construct new C C and C X (where X = heteroatom) bonds. Reusability of the catalyst up to three runs without any noteworthy change in catalytic activity is one of the main features of the reaction. Other noteworthy features are good to excellent yields, eco-friendly procedure, non-column chromatographic purification, and mild conditions. 相似文献