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931.
Leonardo Sena Gomes Teixeira Antônio Celso Spínola Costa Júlio César Rosa Assis Sérgio Luis Costa Ferreira Mauro Korn 《Mikrochimica acta》2001,137(1-2):29-33
A new sensitive method exploiting solid-phase spectrophotometry is proposed for the determination of cobalt in pharmaceutical
preparations. The chromogenic reagent 1-(2-thiazolylazo)-2-naphthol (TAN) was immobilized on C18 bonded silica loaded into
a home-made cell with 1.5 mm of optical path for cobalt determination. Cobalt(II) reacts with TAN on C18 material, at pH 6.0–7.5,
to give a coloured complex which has maximum absorption at 572 nm. In this way, the sample was passed through the cell and
Co(II) ions were quantitatively retained on the solid-phase. After the direct measurement of light-absorption in the solid
phase, only the cobalt was eluted with 0.1 mol L−1 hydrochloric acid. The cell was washed with water and then another sample solution could be passed through the cell. The
procedure allowed the determination of cobalt in the range of 10–160 μg L−1 with coefficient of variation of 4.7% (n=10) and apparent molar absorptivity of 2.62 × 106 L mol−1 cm−1 using sample volume of 3-mL.
Received May 15, 2000. Revision August 28, 2000. 相似文献
932.
Fernando Ferreira 《Mathematical Logic Quarterly》1999,45(3):399-407
We study, within the framework of intuitionistic logic, two well-known general results of (classical logic) bounded arithmetic. Firstly, Parikh's theorem on the existence of bounding terms for the provably total functions. Secondly, the result which states that adding the scheme of bounded collection to (suitable) bounded theories does not yield new II2 consequences. 相似文献
933.
Effect of different donors on kinetics of Zn catalysts and molecular weight of the obtained polypropylene 总被引:2,自引:0,他引:2
María Lujn Ferreira Daniel E. Damiani 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):53-69
This paper studies MgCl2/internal donor/TiCl4//external donor/AlEt3 catalytic systems where ethyl benzoate (E.B.) or 2,2,6,6 tetramethylpiperidine (TMPiP) are used as internal and external donors. E.B. as external donor does not change the molecular weight of the product with TMPiP as internal donor. The molecular weight of polypropylene decreases drastically and global productivity and stereoselectivity are very low with MgCl2/internal Donor/TiCl4//external donor/AlEt3 when TMPiP is the external and internal donor. In this case the insoluble fraction in n-heptane is highly stereospecific and the molecular weight is similar to commercial products. We present a new explanation of these results, based on Ystenes proposal, comparing both precatalysts. 相似文献
934.
J. A. M. Ferreira J. D. M. Costa P. N. B. Reis 《Theoretical and Applied Fracture Mechanics》1999,31(1):759
This paper is concerned with fatigue of polypropylene/glass-fibre thermoplastic composites produced from a bi-directional woven cloth mixture of E glass fibres and polypropylene fibres. The latter becomes the matrix after the application of heat and pressure. This composite was manufactured with a fibre volume fraction Vf of 0.338. The effect of layer design on the static and fatigue performance was investigated. The S–N curves, the rise in the temperature of the specimens during the tests and the loss of stiffness, were obtained and discussed. The loss of stiffness was related to the rise of temperature and stress release observed in the material. The effect of load rate on the static properties was also studied and discussed accordingly. 相似文献
935.
Using simulated annealing, we examine a bipartitioning of small worlds obtained by adding a fraction of randomly chosen links to a one-dimensional chain or a square lattice. Models defined on small worlds typically exhibit a mean-field behavior, regardless of the underlying lattice. Our work demonstrates that the bipartitioning of small worlds does depend on the underlying lattice. Simulations show that for one-dimensional small worlds, optimal partitions are finite size clusters for any fraction of additional links. In the two-dimensional case, we observe two regimes: when the fraction of additional links is sufficiently small, the optimal partitions have a stripe-like shape, which is lost for a larger number of additional links as optimal partitions become disordered. Some arguments, which interpret additional links as thermal excitations and refer to the thermodynamics of Ising models, suggest a qualitative explanation of such a behavior. The histogram of overlaps suggests that a replica symmetry is broken in a one-dimensional small world. In the two-dimensional case, the replica symmetry seems to hold, but with some additional degeneracy of stripe-like partitions. 相似文献
936.
Tiwari Ashutosh Prasad Sridhar B. Boshoff Helena I. Arora Kriti Gautham Shenoy G. Vandana K. E. Varadaraj Bhat G. 《Molecular diversity》2020,24(4):1265-1279
Molecular Diversity - Diphenyl ether derivatives inhibit mycobacterial cell wall synthesis by inhibiting an enzyme, enoyl-acyl carrier protein reductase (InhA), which catalyses the last step in the... 相似文献
937.
Tnia Laranjeira Ana Costa Catarina Faria-Silva Daniela Ribeiro Jos Miguel P. Ferreira de Oliveira Sandra Simes Andreia Ascenso 《Molecules (Basel, Switzerland)》2022,27(5)
Tomato producing and processing industries present undoubted potential for industrial discarded products valorization whether due to the overproduction of fresh tomatoes or to the loss during processing. Although tomato by-products are not yet considered a raw material, several studies have suggested innovative and profitable applications. It is often referred to as “tomato pomace” and is quite rich in a variety of bioactive compounds. Lycopene, vitamin C, β-carotene, phenolic compounds, and tocopherol are some of the bioactives herein discussed. Tomato by-products are also rich in minerals. Many of these compounds are powerful antioxidants with anti-inflammatory properties besides modulating the immune system. Several researchers have focused on the possible application of natural ingredients, especially those extracted from foods, and their physiological and pharmacological effects. Herein, the effects of processing and further applications of the bioactive compounds present in tomato by-products were carefully reviewed, especially regarding the anti-inflammatory and anti-cancer effects. The aim of this review was thus to highlight the existing opportunities to create profitable and innovative applications for tomato by-products in health context. 相似文献
938.
THE EFFECT OF MEMORY TERMS IN DIFFUSION PHENOMENA 总被引:1,自引:0,他引:1
In this paper the effect of integral memory terms in the behavior of diffusion phenomenais studied.The energy functional associated with different models is analyzed and stabilityinequalities are established.Approximation methods for the computation of the solutionof the integro-differentiaI equations are constructed.Numerical results are included. 相似文献
939.
A method for the simultaneous determination of major (10-200 mg/l) and minor (0.1-10 mg/l) volatile compounds from wine has been optimised and validated. A 3-ml volume of wine is diluted with water (7 ml), salted with 4.5 g of ammonium sulfate and extracted with 0.2 ml of dichloromethane. The extract is injected in the split mode in a GC system, separated on a Carbowax 20M capillary column and detected by flame ionisation detection. Volatiles from wine are divided into four groups according to their behaviour in the extraction, and a specific internal standard has been selected for each group. The method allows satisfactory determination of more than 30 volatile compounds of wine. Compounds analysed include acetaldehyde, diacetyl, acetoine (3-hydroxy butanone), fusel alcohols and their acetates, and fatty acids and their ethyl esters. The linear dynamic range of the method covers the normal range of occurrence of analytes in wine and extends from at least one magnitude order to more than two, with typical r2 between 0.9938 and 0.9998. Reproducibility ranges from 3.1 to 10% (as RSD) with 5.5% as the average. The analysis of spiked samples has shown that matrix effects do not significantly affect method performance. 相似文献
940.
Aleksander Kravos Andreja
gajnar Gotvajn Urka Lavren
i
tangar Borislav N. Malinovi Helena Prosen 《Molecules (Basel, Switzerland)》2022,27(6)
Advanced oxidation processes (AOPs) have been introduced to deal with different types of water pollution. They cause effective chemical destruction of pollutants, yet leading to a mixture of transformation by-products, rather than complete mineralization. Therefore, the aim of our study was to understand complex degradation processes induced by different AOPs from chemical and ecotoxicological point of view. Phenol, 2,4-dichlorophenol, and pentachlorophenol were used as model pollutants since they are still common industrial chemicals and thus encountered in the aquatic environment. A comprehensive study of efficiency of several AOPs was undertaken by using instrumental analyses along with ecotoxicological assessment. Four approaches were compared: ozonation, photocatalytic oxidation with immobilized nitrogen-doped TiO2 thin films, the sequence of both, as well as electrooxidation on boron-doped diamond (BDD) and mixed metal oxide (MMO) anodes. The monitored parameters were: removal of target phenols, dechlorination, transformation products, and ecotoxicological impact. Therefore, HPLC–DAD, GC–MS, UHPLC–MS/MS, ion chromatography, and 48 h inhibition tests on Daphnia magna were applied. In addition, pH and total organic carbon (TOC) were measured. Results show that ozonation provides by far the most suitable pattern of degradation accompanied by rapid detoxification. In contrast, photocatalysis was found to be slow and mild, marked by the accumulation of aromatic products. Preozonation reinforces the photocatalytic process. Regarding the electrooxidations, BDD is more effective than MMO, while the degradation pattern and transformation products formed depend on supporting electrolyte. 相似文献