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21.
The acid-catalyzed decomposition of unusually stable 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazenes in either aqueous perchloric acid or an aqueous mixture of perchloric and acetic acid was studied under pseudo-first order reaction conditions at 25 °C. Different products were obtained according to substitution on nitrogen N-3. For a triazene carrying hydrogen, the corresponding 3-amino-2,1-benzisothiazole and benzenediazonium salts were formed whereas in the case of substitution by an alkyl group (methyl and n-butyl) the 2,1-benzisothiazole-3-diazonium salt and N-alkylaniline were obtained. The observed rate constant (kobs) of the acid-catalyzed decomposition increased, initially, nonlinearly with increasing concentration of acid. Subsequently, kobs decreased slightly and at high acid concentration, increased steeply once again. An A-SE2 mechanism in which protonation of the triazene nitrogen proceeds simultaneously with cleavage of the N–N bond is proposed. Tautomerism of 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazene was investigated using 1H NMR spectroscopy. 相似文献
22.
Mohammad Norouzi Masoud Soleimani Iman Shabani Fatemeh Atyabi Hana H. Ahvaz Abusaeed Rashidi 《Polymer International》2013,62(8):1250-1256
The main purpose of tissue engineering is the preparation of fibrous scaffolds with similar structural and biochemical cues to the extracellular matrix in order to provide a substrate to support the cells. Controlled release of bioactive agents such as growth factors from the fibrous scaffolds improves cell behavior on the scaffolds and accelerates tissue regeneration. In this study, nanofibrous scaffolds were fabricated from biocompatible and biodegradable poly(lactic‐co‐glycolic acid) through the electrospinning technique. Nanofibers with a core–sheath structure encapsulating bovine serum albumin (BSA) as a model protein for hydrophilic bioactive agents were prepared through emulsion electrospinning. The morphology of the nanofibers was evaluated by field‐emission scanning electron microscopy and the core–sheath structure of the emulsion electrospun nanofibers was observed by transmission electron microscopy. The results of the mechanical properties and X‐ray diffraction are reported. The scaffolds demonstrated a sustained release profile of BSA. Biocompatibility of the scaffolds was evaluated using the MTT (3(4,5‐ dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay for NIH‐3T3 fibroblast cells. The results indicated desirable biocompatibility of the scaffolds with the capability of encapsulation and controlled release of the protein, which can serve as tissue engineering scaffolds. © 2013 Society of Chemical Industry 相似文献
23.
Pacaiova Hana 《Frontiers of Mechanical Engineering in China》2010,5(2):184-188
Maintenance management requirements have another dimension in the present as in the past. Looking for the optimal tools of
decision processing is hard. The current concepts have represented the integration of theoretical, technical, and management
tools whose applications need actual modification. Technical measurements are expensive and take a long time/term, and it
is hard to estimate the economical returns. This paper presents the concept of a maintenance management task and its function
in preventing major accidents. The importance of considering the reliability of maintenance tasks and the method to reach
it are also discussed in this paper. 相似文献
24.
Tae Woo Kim Hana Yoo In Young Kim Hyung‐Wook Ha Ah Reum Han Jong‐San Chang Ji Sun Lee Seong‐Ju Hwang 《Advanced functional materials》2011,21(12):2301-2310
Manganese oxide nanocrystals are combined with aluminum oxide nanocrystals to improve their crystallinity via calcination without a significant increase of crystal size. A nanocomposite, consisting of two metal oxides, can be synthesized by the reaction between permanganate anions and aluminum oxyhydroxide keggin cations. The as‐prepared manganese oxide–aluminum oxide nanocomposite is X‐ray amorphous whereas heat‐treatment gives rise to the crystallization of an α‐MnO2 phase at 600 °C and Mn3O4/Mn2O3 and γ‐Al2O3 phases at 800 °C. Electron microscopy and N2 adsorption‐desorption‐isotherm analysis clearly demonstrate that the as‐prepared nanocomposite is composed of a porous assembly of monodisperse primary particles with a size of ~20 nm and a surface area of >410 m2 g?1. Of particular interest is that the small particle size of the as‐prepared nanocomposite is well‐maintained up to 600 °C, a result of the prevention of the growth of manganate grains through nanoscale mixing with alumina grains. The calcined nanocomposite shows very‐high catalytic activity for the oxidation of cyclohexene with an extremely high conversion efficiency of >95% within 15 min. The present results show that the improvement of the crystallinity without significant crystal growth is very crucial for optimizing the catalytic activity of manganese oxide nanocrystals. 相似文献
25.
Hana Ross 《Nicotine & tobacco research》2004,6(1):181-189
This critique analyzes the methodology used in a study of the economic burden imposed on public finances in the Czech Republic by the consumption of cigarettes. The study was prepared by a consulting firm on behalf of the Phillip Morris Company. This critique, by using economic theory and a cost-benefit methodology, refutes the conclusion of the Phillip Morris study that smoking represents an economic benefit to Czech state finances. In fact, the correction of only one among numerous errors in assumptions and calculations in the Phillip Morris study leads to the opposite conclusion: Instead of savings of $150 million per year, smoking drains at least $373 million from the state budget annually, nearly.8% of the Czech gross domestic product. The net loss to the society is even greater if all pertinent costs and benefits are calculated properly. The critique demonstrates how to craft a rigorous economic response to common industry attempts to influence public opinion in which the industry employs specious or erroneous assumptions and data. 相似文献
26.
Transport of L -leucine into Schizosaccharomyces pombe cells from the stationary phase of growth (after preincubation for 60 min with 1% glucose) proceeds uphill, practically unidirectionally, and is mediated by at least two systems: a high-affinity system with a KT of 0·045 mmol 1?1 and Jmax of 3·3 nmol min?1 (mg dry weight)?1 and a low-affinity system with a KT of 1·25 mmol 1?1 and Jmax of 16·0 nmol min?1 (mg dry weight)?1. The high-affinity system has a pH optimum at 3.2, the accumulation ratio is highest at a cell density of 2–4 mg dry weight per ml and decreases with increasing leucine concentration. Transport of leucine by the high-affinity system is strongly inhibited by proton conductors, ammonium ions and by most amino acids, but only L -phenylalanine, L -isoleucine, L -valine and L -cysteine behave as fully competitive inhibitors. Systems of L -leucine transport in S. pombe are not constitutive. Transport activity appears only after preincubation of cells with a suitable source of energy. If cycloheximide is added during preincubation with glucose, no transport systems for leucine are synthesized. After removal of glucose, the activity of transport systems decays with a half-time of about 20 min. The presence of cyclic AMP increases the initial rate of leucine uptake only in cells preincubated with glucose and in the absence of cycloheximide. 相似文献
27.
Martina Stekrova Hana Minarikova Eliska Vyskocilova Jiri Kolena Libor Cerveny 《Journal of Porous Materials》2014,21(5):757-767
The presented report focuses on the testing of heterogenized methyltrioxorhenium (MTO) in indene epoxidation. A range of mesoporous materials with different SiO2/Al2O3 ratios, namely aluminosilicates type Siral and MCM-41 silica and fumed silica, were used as supports for immobilization of MTO. The tested support materials and prepared catalytic systems exhibited high surface area, well-defined regular structure and narrow pore size distribution of mesopores and therefore represent good quality catalysts for various reactions. The immobilized MTO on various supports was tested for the preparation of 1,2-epoxyindane using two forms of hydrogen peroxide as oxidation agents, namely aqueous solution of hydrogen peroxide and its anhydrous form, urea-hydrogen peroxide. The prepared catalysts were successfully used for the preparation of 1,2-epoxyindane with achieved 100 % selectivities to the desired product at high conversions of indene. 相似文献
28.
29.
30.
Salwan K. J. Al-Ani Raid A. Ismail Hana F. A. Al-Ta’ay 《Journal of Materials Science: Materials in Electronics》2006,17(10):819-824
Optoelectronic properties of CdS:In/Si anisotype heterojunction photodetector fabricated by depositing of polycrystalline
CdS and indium doped CdS films used thermal resistive technique on clean monocrystalline p-type silicon substrates are presented. The effect of In diffusion
temperature(T
d)in CdS layer on the optoelectronic characteristics of these devices has been studied. Two peaks situated at 650 and 800 nm
with values of 0.32 and 0.43 A/W, respectively, were observed in the responsivity plot. Other optoelectronics properties such
as detectivity, photovoltaic, and response time are also presented. 相似文献