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91.
Three new tetracyclic polyisoprenylated xanthones, named oxy-guttiferones M, K2, and I, along with oxy-guttiferone K and guttiferone M, have been isolated from the fruits of Garcinia cambogia. Their structures were elucidated by MS and NMR spectroscopic experiments. The absolute configurations of oxy-guttiferone K, taken as a model of tetracyclic xanthones, and guttiferone M, as a model of polyisoprenylated benzophenones, have been determined by comparison of their experimentally measured circular dichroism (CD) curves with the TDDFT-predicted curves. 相似文献
92.
Sonia de Almeida Evaneide N. Lima Marisa S. Crespi Clóvis A. Ribeiro Valdir Schalch 《Journal of Thermal Analysis and Calorimetry》2009,97(2):529-533
Urban solid residues are constituted of food remaining, grass leaves, fruit peelings, paper, cardboard, rubber, plastic, etc.
The organic fraction formed represents about 50% during the decomposition yields biogas and leachate, which are sources of
pollution. Residue samples were collected from the landfill in different and cells from several ages and the corresponding
leachate, both after treatments, were submitted to thermal analysis. Kinetic parameters were determined using Flynn–Wall–Ozawa
method. The linear relation between the two kinetic parameters (ln A and E) was verified for organic residue urban’s samples, but not for leachate’s sample. The occurred difference can be attributed
to the constituents present in leachate. 相似文献
93.
Mayté Paredes Zaldivar Norma Galego Fernández Cristina Gastón Peña Manuel Rapado Paneque Sonia Altanés Valentín 《Journal of Thermal Analysis and Calorimetry》2011,106(3):725-730
A new polyacrylic acid/polyhydroxybutyrate semi-interpenetrating polymer network hydrogel, the s-IPN/PAA-PHB, was prepared
by a gamma radiation-induced polymerization. Thermal behavior was studied by thermogravimetric analysis (TG) and Differential
scanning calorimetry (DSC), while the s-IPNs composition, FTIR spectra, and swelling kinetics were also determined. It was
found that the DSC curve showed a melting point which is attributed to polyhydroxybutyrate. The TG curves showed various stages
of degradation which are in correspondence of the presence of crosslinked polyacrylic acid and confirmed the higher thermal
stability of the polymer network. The s-IPN/PAA-PHB composition was 10% of PHB and 90% of PAA. Moreover, the network reached
approximately 600% of swelling in water, so it behaves like a superabsorbent hydrogel. 相似文献
94.
Sonia Senra-Ferreiro 《Analytica chimica acta》2010,668(2):195-65
A novel, simple and low cost method for the determination of nitrite using headspace single-drop microextraction and cuvetteless ultraviolet-visible micro-spectrophotometry is described. A Griess reagent-containing aqueous microdrop exposed to the headspace was used as extractant of the volatile nitrogen oxides generated from nitrite by direct acidification of the aqueous sample. Experimental parameters affecting the headspace single-drop microextraction performance such as composition and volume of the extractant phase, sample volume, concentration of acetic acid, ionic strength, sample agitation, temperature and microextraction time were systematically examined. Measurements were carried out at 540 nm under optimized conditions. A detection limit of 1.5 μg L−1 and an enrichment factor of 193 were achieved. Intra-day repeatability and inter-day reproducibility, expressed as relative standard deviation, were 3.5% (n = 7) and 10.6% (three consecutive days), respectively. The proposed method, characterized by its enhanced sensitivity and selectivity in comparison with the standardized colorimetric assay, was successfully applied to the analysis of several environmental water samples. 相似文献
95.
Oreste Senofonte Nicola Violante Sonia D'Ilio Stefano Caimi Antonio Peri Sergio Caroli 《Microchemical Journal》2001,69(3)
In the framework of the Human Biology and Medicine Project of the National Program for Research in Antarctica (Programma Nazionale di Ricerche in Antartide, PNRA) a study was undertaken to explore the suitability of trace element determination in human hair as a tool for the early detection of the impact of extreme environmental conditions on the health of members of the Italian and French expeditions. This study included three campaigns, namely, the 1995–1996 expedition to the Italian base of Terra Nova Bay, as well as the 1997–1998 and 1998–1999 expeditions to both the Italian base of Terra Nova Bay and the Italian–French base of Dome C. Sampling of hair of participants in the expeditions was carried out both prior to departure and at the end of the period spent at the bases. As regards storage, pre-treatment and analysis of hair samples they were performed in accordance with previously established procedures. Acid-assisted microwave digestion was adopted as the best approach for preparing solutions for subsequent analysis by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. In the first part of this study, only the elements Ca, Cu, Fe, Mg and Zn were selected, while at a later stage it was decided to also include Co, Cr, Mn, Mo and Ni. Experimental results were subjected to basic statistical analysis to detect possible significant differences in element concentrations that occurred during the sojourn at the bases, with a view to identify possible remedial action to minimize adverse consequences. 相似文献
96.
Sara M. Resnizky Rita R. Plá Raquel C. Jasan Sonia E. Hevia Mónica A. Moreno Rodrigo Invenizzi 《Accreditation and quality assurance》2006,10(11):590-593
The implementation of a quality system based on the ISO/IEC 17025:1999 standard is a growing necessity for analytical laboratories to demonstrate their technical competence. In 2001, the Nuclear Analytical Techniques Group of the Argentine Atomic Energy Commission obtained the recognition of the International Atomic Energy Agency in the application of neutron activation analysis and the accreditation by the national accreditation body. The importance of the participation of the group in the Agency's Regional Programme for Latin America, ARCAL XXVI on Quality Assurance in Analytical laboratories is discussed, as well as the activities performed to attain these objectives. Some improvements worth mentioning resulted from the implementation of the quality system and, following the premise of continuous improvement, changes were introduced aiming at the laboratory re-accreditation. 相似文献
97.
Sonia Freire H. Casas Esther Rilo Luisa Segade O. Cabeza E. Jiménez 《Journal of Thermal Analysis and Calorimetry》2005,80(2):285-288
Summary In this paper we present excess molar volumes and excess molar enthalpies of binary and ternary mixtures containing propyl propanoate, hexane and cyclohexane as components at 298.15 K. Excess molar volumes were calculated from the density of the pure liquids and mixtures. The density was measured using an Anton Paar DMA 60/602 vibrating-tube densimeter. Excess molar enthalpies were obtained using a Calvet microcalorimeter 相似文献
98.
99.
Sonia Mazzucchi Valter Moretti Ivan Remizov Oleg Smolyanov 《Mathematische Nachrichten》2023,296(3):1244-1284
Chernoff approximations of Feller semigroups and the associated diffusion processes in Riemannian manifolds are studied. The manifolds are assumed to be of bounded geometry, thus including all compact manifolds and also a wide range of non-compact manifolds. Sufficient conditions are established for a class of second order elliptic operators to generate a Feller semigroup on a (generally non-compact) manifold of bounded geometry. A construction of Chernoff approximations is presented for these Feller semigroups in terms of shift operators. This provides approximations of solutions to initial value problems for parabolic equations with variable coefficients on the manifold. It also yields weak convergence of a sequence of random walks on the manifolds to the diffusion processes associated with the elliptic generator. For parallelizable manifolds this result is applied in particular to the representation of Brownian motion on the manifolds as limits of the corresponding random walks. 相似文献
100.
A Bis‐Sulfonyl O,C,O Aryl Pincer Ligand and its Tin(II) Complex: Synthesis,Structural Studies,and DFT Calculations 下载免费PDF全文
Mohammad El Ezzi Romaric Lenk Dr. David Madec Dr. Jean‐Marc Sotiropoulos Sonia Mallet‐Ladeira Dr. Annie Castel 《Angewandte Chemie (International ed. in English)》2015,54(3):805-808
The efficiency of the deprotonated aryl bis‐sulfone [2,6‐{(p‐tolyl)SO2}2C6H3]? as an O,C,O‐coordinating pincer‐type ligand was described. The bis‐sulfone precursor was synthesized using a straightforward palladium‐catalyzed cross‐coupling reaction. As a result of directed ortho metalation (DoM) through sulfonyl groups, a selective lithiation of the aryl group was achieved and the corresponding carbanion was isolated and its structure determined by single‐crystal X‐ray diffraction analysis. A heteroleptic tin(II) complex has been prepared by a nucleophilic substitution reaction. Crystallographic analysis and DFT calculations indicate that the bis‐sulfonyl moiety acts as a new O,C,O‐coordinating pincer‐type ligand with intramolecular S?O coordination to a tin(II) center. The cis form with the two nonbonded oxygen atoms of the sulfonyl groups on the same side is preferentially obtained. 相似文献