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排序方式: 共有196条查询结果,搜索用时 31 毫秒
41.
Anamaria Iulia Torok Erika Andrea Levei Silviu Constantin Oana Teodora Moldovan Marin Senila Oana Cadar Dorina Casoni Simion Bogdan Angyus Claudiu Tanaselia Eniko Covaci Tiberiu Frentiu 《Molecules (Basel, Switzerland)》2021,26(22)
The aim of the study was to develop the hydrogeochemical profiling of caves based on the elemental composition of water and silty soil samples and a multivariate statistical analysis. Major and trace elements, including rare earths, were determined in the water and soil samples. The general characteristics of water, anions content, inorganic and organic carbon fractions and nitrogen species (NO3− and NH4+) were also considered. The ANOVA—principal component analysis (PCA) and two-way joining analysis were applied on samples collected from Cloșani Cave, Romania. The ANOVA-PCA revealed that the hydrogeochemical characteristics of Ca2+-HCO3− water facies were described by five factors, the strongest being associated with water-carbonate rock interactions and the occurrence of Ca, Mg and HCO3− (43.4%). Although organic carbon fractions have a lower influence (20.1%) than inorganic ones on water characteristics, they are involved in the chemical processes of nitrogen and of the elements involved in redox processes (Fe, Mn, Cr and Sn). The seasonal variability of water characteristics, especially during the spring, was observed. The variability of silty soil samples was described by four principal components, the strongest influence being attributed to rare earth elements (52.2%). The ANOVA-PCA provided deeper information compared to Gibbs and Piper diagrams and the correlation analysis. 相似文献
42.
Mihaela Monica Constantin Ctlina Gabriela Corbu Sorin Mocanu Elena Irina Popescu Marin Micutz Teodora Staicu Raluca omoghi Bogdan Tric Vlad Tudor Popa Aurica Precupas Iulia Matei Gabriela Ionita 《Molecules (Basel, Switzerland)》2022,27(1)
Riboflavin under UVA radiation generates reactive oxygen species (ROS) that can induce various changes in biological systems. Under controlled conditions, these processes can be used in some treatments for ocular or dermal diseases. For instance, corneal cross-linking (CXL) treatment of keratoconus involves UVA irradiation combined with riboflavin aiming to induce the formation of new collagen fibrils in cornea. To reduce the damaging effect of ROS formed in the presence of riboflavin and UVA, the CXL treatment is performed with the addition of polysaccharides (dextran). Hyaluronic acid is a polysaccharide that can be found in the aqueous layer of the tear film. In many cases, keratoconus patients also present dry eye syndrome that can be reduced by the application of topical solutions containing hyaluronic acid. This study presents physico-chemical evidence on the effect of riboflavin on collagen fibril formation revealed by the following methods: differential scanning microcalorimetry, rheology, and STEM images. The collagen used was extracted from calf skin that contains type I collagen similar to that found in the eye. Spin trapping experiments on collagen/hyaluronic acid/riboflavin solutions evidenced the formation of ROS species by electron paramagnetic resonance measurements. 相似文献
43.
Adina Arvinte Mika Mahosenaho Mariana Pinteala Adama-Marie Sesay Vesa Virtanen 《Mikrochimica acta》2011,174(3-4):337-343
The electrochemical oxidation of p-nitrophenol (p-NP) has been studied comparatively on a graphene modified electrode and a multiwall carbon nanotube (MWNT) electrode by using cyclic and differential pulse voltammetry. The sensors were fabricated by modifying screen-printed electrodes with graphene and MWNT nanomaterials, respectively, both dispersed in Nafion polymer. p-NP is irreversibly oxidized at +0.9?V (vs. the Ag/AgCl) in solutions of pH 7. The height and potential of the peaks depend on pH in the range from 5 to 11. In acidic media, p-NP yields a well-defined oxidation peak at +0.96?V which gradually increases in height with the concentration of the analyte. In case of differential pulse voltammetry in sulfuric acid solution, the sensitivity is practically the same for both electrodes. The modified electrodes display an unusually wide linear response (from 10???M to 0.62?mM of p-NP), with a detection limit of 0.6???M in case of the graphene electrode, and of 1.3???M in case of the MWNT electrode. Figure
DPV responses of graphene and MWNT electrodes to increasing concentrations of p-NP in H2SO4 20?mM solution. Inset: liniar plot of oxidation peak currents with the concentration of p-NP. 相似文献
44.
45.
Adina Luminita Sasu Bogdan Sasu 《Proceedings of the American Mathematical Society》2004,132(12):3653-3659
We introduce and characterize the stability radius of systems whose state evolution is described by linear skew-product semiflows. We obtain a lower bound for the stability radius in terms of the Perron operators associated to the linear skew-product semiflow. We generalize a result due to Hinrichsen and Pritchard.
46.
We present necessary and sufficient conditions for uniform exponential expansiveness of discrete skew-product flows, in terms
of uniform complete admissibility of the pair (c
0(N, X), c
0(N, X)). We give discrete and continuous characterizations for uniform exponential expansiveness of linear skew-product flows,
using the uniform complete admissibility of the pairs (c
0(N, X), c
0(N, X)) and (C
0(R
+, X), C
0(R
+, X)), respectively. We generalize an expansiveness theorem due to Van Minh, R?biger and Schnaubelt, for the case of linear skew-product
flows. 相似文献
47.
Ryckebusch A Gilleron P Millet R Houssin R Lemoine A Pommery N Grellier P Sergheraert C Hénichart JP 《Chemical & pharmaceutical bulletin》2005,53(10):1324-1326
Protein farnesyltransferase of Plasmodium falciparum is a potential target in the treatment of malaria for which increased drug resistance is observed. The design, synthesis and evaluation of a series of N-(4-piperidinyl)benzamides is reported. The most potent compounds showed in vitro activity against the parasite at submicromolar concentrations. 相似文献
48.
Lazar A Da Silva E Navaza A Barbey C Coleman AW 《Chemical communications (Cambridge, England)》2004,(19):2162-2163
The solid-state structure of the complex of para-sulfonatocalix[4]arene with d-arginine, contains a water channel diagonal to a zigzag bilayer of the host, within the bilayer six crystallographically independent molecules of arginine are present, four being included in the calix cavities. 相似文献
49.
Vitamin B12 supported on graphene oxide: As a bio‐based catalyst for selective aerobic oxidation of alcohols
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Ahmad Shaabani Adina Rashidi Vahid Shabnam Shaabani Reza Mohammadian Mohammad Taghi Nazeri Mina Keramati Nejad 《应用有机金属化学》2018,32(10)
The environmental impact of chemical processes has now opened new windows of opportunity for bio‐based catalysts. In this paper a highly active bio‐based catalyst of vitamin B12 supported on graphene oxide nanosheets is reported for the selective aerobic oxidation of alcohols to the corresponding carbonyl compounds. Operational simplicity, mild reaction conditions, high yield and selectivity, non‐hazardous nature, commercial availability and affordability are the main advantages of this novel catalytic system. 相似文献
50.
Mariana Loredana Dianu Angela Kriza Adina Magdalena Musuc 《Journal of Thermal Analysis and Calorimetry》2013,112(2):585-593
A bidentate/tridentate 5-bromosalycilaldehyde isonicotinoylhydrazone Schiff base was synthesized by condensing 5-bromosalycilaldehyde with isonicotinoylhydrazine. Cu(II), Co(II), Ni(II), Mn(II) and Zn(II) complexes of this chelating ligand were synthesized using nitrates of these metals. The ligand and the complexes were characterized by elemental analysis, UV–Vis, IR and EPR spectroscopy, conductance and magnetic susceptibility measurements, fluorescence, cyclic voltammetry and thermogravimetric analysis. The ligand and Zn(II) complex exhibits solid-state photoluminescence at room temperature. 相似文献