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排序方式: 共有862条查询结果,搜索用时 15 毫秒
711.
Aleksandra Mielewczyk-Gryń Sebastian Wachowski Agnieszka Witkowska Kacper Dzierzgowski Wojciech Skubida Konrad Świerczek Anna Regoutz David J. Payne Stephen Hull Hangfeng Zhang Isaac Abrahams Maria Gazda 《Journal of the American Ceramic Society》2020,103(11):6575-6585
X-ray and neutron diffraction have been utilized to analyze the crystalline and electronic structure of lanthanum orthoniobate substituted by antimony. Using X-ray absorption spectroscopy and photoelectron spectroscopy, changes in the electronic structure of the material upon substitution have been analyzed. The structural transition temperature between fergusonite and scheelite phases for 30 mol% antimony substitution was found to be 15°C. Based on the neutron data, the oxygen nonstoichiometry was found to be relatively low. Moreover no influence on the position of the valence band maximum was observed. The influence of the protonation on the electronic structure of constituent oxides has been studied. Absorption data show that the incorporation of protonic defects into the lanthanum orthoniobate structure leads to changes in lanthanum electronic structure and a decrease in the density of unoccupied electronic states. 相似文献
712.
713.
Aleksandra M. Torbica Biljana S. Pajin Radovan P. Omorjan Ivana S. Lončarević Jelena M. Tomić 《Journal of the American Oil Chemists' Society》2014,91(1):39-48
In this study, the fat phase of chocolate samples which contained cocoa butter from Ghana and cocoa butter equivalent (CBE) of moderate hardness was analyzed. Physical properties and shelf life of chocolate depend on the fat phase behavior as well as the amount and composition of added CBE. The laboratory-made chocolate samples were tempered at three different pre-crystallization temperatures (25, 27 and 29 °C), with three different concentrations of CBE, amounting to 3, 5 and 7 %, calculated on chocolate. The color and other physical attributes of chocolate samples were investigated by the following analytical methods: thermoreographic measurement, solid fat content (SFC) of chocolate, Blooming test (thermo-cycle test 32/20 °C) and color measurement. It was found that using CBE of moderate hardness did not change the melting properties of chocolate in relation to the investigated cocoa butter from Ghana (of moderate hardness). It was found that all three applied temperatures of pre-crystallization are optimum for the chocolate mass with the addition of the investigated CBE under the given measurement conditions. At all these temperatures, the chocolate had excellent fat bloom resistance. 相似文献
714.
715.
Charlotte Nilsson Gunno Renman Lena Johansson Westholm Agnieszka Renman Aleksandra Drizo 《Water research》2013
The organic matter released from septic tanks can disturb the subsequent step in on-site wastewater treatment such as the innovative filters for phosphorus removal. This study investigated the effect of organic load on phosphorus (P) and bacteria removal by reactive filter materials under real-life treatment conditions. Two long-term column experiments were conducted at very short hydraulic residence times (average ∼5.5 h), using wastewater with high (mean ∼120 mg L−1) and low (mean ∼20 mg L−1) BOD7 values. Two alkaline filter materials, the calcium-silicate material Polonite and blast furnace slag (BFS), were tested for the removal capacity of total P, total organic carbon (TOC) and Enterococci. Both experiments showed that Polonite removed P significantly (p < 0.01) better than BFS. An increase in P removal efficiency of 29.3% was observed for the Polonite filter at the lower concentration of BOD7 (p < 0.05). Polonite was also better than BFS with regard to removal of TOC, but there were no significant differences between the two filter materials with regard to removal of Enterococci. The reduction in Enterococci was greater in the experiment using wastewater with high BOD7, an effect attributable to the higher concentration of bacteria in that wastewater. Overall, the results demonstrate the importance of extensive pre-treatment of wastewater to achieve good phosphorus removal in reactive bed filters and prolonged filter life. 相似文献
716.
Toxicity of Metal Oxide Nanoparticles: Mechanisms,Characterization, and Avoiding Experimental Artefacts
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Aleksandra B. Djurišić Yu Hang Leung Alan M. C. Ng Xiao Ying Xu Patrick K. H. Lee Natalie Degger R. S. S. Wu 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(1):26-44
Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non‐toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity. 相似文献
717.
Edward I. Evstigneyev Anton S. Mazur Aleksandra V. Kalugina Andrey V. Pranovich 《木材化学与工艺学杂志》2018,38(2):137-148
Several lignin preparations (Freudenberg lignin, Björkman lignin, and Pepper lignin), technical lignins (soda, soda-AQ, Kraft, Kraft-AQ, and hydrolysis), dimeric lignin model compounds, and different polysaccharides (galactoglucomannan, arabinogalactan, xylan, and arabinan) were analyzed by means of solid-state 13C CP/MAS NMR. Signals assignment in solid-state NMR lignin spectra was performed on the basis of the conducted studies and earlier published data. It was established that there exists strong linear correlation (r = 0.985) between Alkyl-O-Aryl inter-unit bond content in lignin and integral signals intensity in NMR spectra in the range of chemical shifts of 96–68 ppm. The integral signals intensity was measured in correlation with the reference integral signals in the range of chemical shifts of 162–102 ppm, typical for aromatic carbon atoms. To eliminate the effect, caused by carbohydrates contained in lignin, the correction factor of 0.67% of the area of integration per 1% of carbohydrates was determined. It was shown that the solid-state 13C CP/MAS NMR method allowed to determine Alkyl-O-Aryl bond content in both soluble and insoluble lignin preparations, and also to determine methoxyl groups content in soluble preparations. 相似文献
718.
Silvana?Rossy?de?Brito Aleksandra?do?Socorro da SilvaEmail author Eulália?Carvalho?da?Mata Nandamudi?Lankalapalli?Vijaykumar Cláudio?Alex?Jorge?da?Rocha Maurílio?de?Abreu Monteiro Jo?o?Crisóstomo?Weyl?Albuquerque?Costa Carlos?Renato?Lisboa?Francês 《Information Systems Frontiers》2018,20(4):883-899
Despite advances in the quality and availability of information and communication technologies (ICT), the level of access and skill in using these resources remains unequal. This is particularly evident in developing countries. To reduce the gap between these levels of ICT use, organizations (both public and private) invest in the expansion of infrastructure by providing ICT access and ICT training. In this study, we demonstrate that there is a gap in current approaches to monitor and evaluate large-scale ICT training interventions. Thus, we propose an approach based on social network analysis and data mining techniques, and apply it to an online training program conducted in different regions of Brazil. The results allow us to examine different aspects of the program, such as the region of participants, the institutions driving the intervention, local indicators of telecommunications infrastructure, and local socioeconomic conditions. 相似文献
719.
The passivity of AISI 304L and AISI 316L stainless steels in a borate buffer solution, with and without the addition of chloride ions, was studied using cyclic voltammetry and potentiodynamic measurements. The passive layers formed by electrochemical oxidation at different passivation potentials on both the stainless steels were studied by X-ray photoelectron spectroscopy, their compositions were analysed as a function of depth, and the cationic fraction of the passive film was determined. The passive films established on the two stainless steels in the borate buffer solution at pH = 9.3 contained the oxides of two main elements, i.e., Fe and Cr. The oxides of the alloying elements Ni and, optionally, Mo, also contribute to the passive layer. In the presence of chloride ions a strong chromium enrichment was observed in the passive layers. 相似文献
720.
Magdalena Gawęda Piotr Jeleń Elżbieta Długoń Aleksandra Wajda Magdalena Leśniak Wojciech Simka Maciej Sowa Rainer Detsch Aldo R. Boccaccini Maciej Sitarz 《Journal of the American Ceramic Society》2018,101(2):590-601
Black glasses are amorphous materials based on silicon oxycarbide. The use of precursors in the form of ladder‐like silsesquioxanes enables the control of the amount of carbon ions in the glass network by adjusting ratios of T to D structural units in precursors. In this study, four different sols precursors of four different layers of black glasses on titanium substrates were prepared. The materials were analyzed with the use of various spectroscopic and microscopic methods. Formation of continuous and hermetic layers resistant to corrosion was proven. The black glasses layers were examined as materials for biomedical applications. Therefore, preliminary tests of their bioactivity and biocompatibility were performed. The best results were obtained for the material of lower contribution of carbon ions. 相似文献