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121.
In self-preserving turbulent wall flows, both measurements and direct numerical simulations indicate that the mean square vorticity in the outer region does not depend only on and U
. It also depends on the Reynolds number.RAA is grateful to St. Francis Xavier University (Antigonish) for their support while on study leave there. The support of ARC is gratefully appreciated. 相似文献
122.
Cotton Cellulose Ageing in Sealed Vessels. Kinetic Model of Autocatalytic Depolymerization 总被引:1,自引:0,他引:1
In this paper, we propose a new kinetic model that describes the depolymerization of pure cotton cellulose, applicable to
ageing experiments in sealed vessels. By recording the pH of the salt solutions used for controlling the relative humidity
inside the vessels, we demonstrate that volatile acidic species are produced during the ageing of pure cellulose. Based on
the proposition that the acids produced must have an autocatalytic effect on the depolymerization of cellulose, we theoretically
developed equations describing the time dependence of the percentage of the broken glycosidic bonds, the folding endurance,
tensile strength, tensile energy absorption, stretch at break and the L* and b* coordinates of the CIEL*a*b* color system.
The experimentally determined values of these pure cellulose paper properties were fit into the model equations by use of
a computer statistical package. The very high values of the regression coefficients indicate that the model equations work
quite well. The experimental data and the model equations indicate that for long ageing times (up to 150 days at 80 °C), the
deterioration of the sample properties accelerates and finally brings about an abrupt breakdown of the samples. Under the
light of these findings, we believe that the useful life of the historical paper stored in archives and libraries is less
than predicted by the existing models, and steps for its preservation should be taken immediately. As an additional preservation
measure, we propose the ventilation of the storage areas so that the volatile acidic products of paper deterioration that
accelerate its ageing are removed. 相似文献
123.
Kava (Piper methysticum) dietary products have been sold worldwide for treatment of nervous anxiety, tension, and restlessness. Recent reports showed potential association of kava usage and liver injuries. This study was conducted to develop simple and reliable methodologies for the extraction and determination of 6 major kavalactones: (+)-methysticin, (+)-dihydromethysticin, (+)-kavain, (+)-dihydrokavain, yangonin, and desmethoxyyangonin. Ultrasonic extraction techniques and isocratic reversed-phase liquid chromatography (LC) were optimized for different types of samples, including capsules containing kava root extract or root powder, raw root material, tea bags, and snack bar. A suitable internal standard, 5,7-dihydroxyflavone, was used for LC calibration. Kavalactones were completely separated in 30 min using a Luna C18-2 column at 60 degrees C with an isocratic mobile phase consisting of 2-propanol-acetonitrile-water-acetic acid (16 + 16 + 68 + 0.1, v/v/v/v). Within-laboratory, intraday, and interday method variation (% relative standard deviation) for most samples extracted by methanol or methanol-water mixture were <5%. Lower levels of kavalactone contents and higher variations were observed for tea bags from water extraction or infusion as compared to methanol extraction. Labeling information of tea bags based on methanol extraction could be misleading to consumers. Analytical recoveries of snack bar fortified at 10 and 20 microg/g were >84% with RSD values <8%. Methods developed in this study offer a simple and reproducible means for analysis of kavalactones in various matrixes of dietary products. 相似文献
124.
125.
Brunetti FG Herrero MA Muñoz Jde M Díaz-Ortiz A Alfonsi J Meneghetti M Prato M Vázquez E 《Journal of the American Chemical Society》2008,130(25):8094-8100
We describe a new synthetic strategy to produce multifunctionalized carbon nanotubes using a combination of two different addition reactions, the 1,3-dipolar cycloaddition of azomethine ylides and the addition of diazonium salts, both via a simple and fast microwave-induced method. The presence of multifunctionality on the SWNTs has been confirmed using the most useful techniques for the characterization of carbon nanotubes. The doubly functionalized SWNTs can be considered potentially useful for many interesting applications. 相似文献
126.
Montserrat Alfonso Antonia Neels Helen Stoeckli-Evans 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(10):1144-1146
The new nickel(II) coordination polymer poly[diaquanickel(II)-μ-(pyrazine-2,3,5,6-tetracarboxylato)-tetraaquanickel(II)], {[{Ni(C8N2O8)(H2O)2}Ni(H2O)4]}n, has been synthesized and characterized both spectroscopically and crystallographically, by X-ray powder diffraction analysis. In this two-dimensional coordination polymer, NiII ions are bridged by pyrazine-2,3,5,6-tetracarboxylic acid, coordinating in a bis-bidentate manner, so forming one-dimensional polymeric chains. The chains are linked by a second NiII ion, via an O atom of the coordinated carboxylate group, resulting in the formation of a two-dimensional layer-like polymer. The remaining coordination sites of the two independent octahedral NiII ions are occupied by water molecules. The layers are connected via hydrogen bonds involving all six coordinated water molecules. 相似文献
127.
Ritamaria di Lorenzo Antonietta Bernardi Lucia Grumetto Antonia Sacchi Carmen Avagliano Serena Coppola Anna Fiorenza de Giovanni di Santa Severina Cristina Bruno Lorella Paparo Sonia Laneri Irene Dini 《Molecules (Basel, Switzerland)》2021,26(21)
Human skin is colonized by diverse commensal microbes, making up the skin microbiota (SM), contributing to skin integrity and homeostasis. Many of the beneficial effects aroused by the SM are exerted by microbial metabolites such as short-chain fatty acids (SCFAs), including butyric acid. The SCFAs can be used in cosmetic formulations against skin diseases to protect SM by preserving and/or restoring their natural balance. Unpleasant sensorial properties and unfavorable physico-chemical properties of butyrate strongly limit its cosmetic use. In contrast, some butyrate derivatives, including phenylalanine butyramide (C13H18N2O2, FBA), a solid form of butyric acid, are odorless while retaining the pharmacokinetic properties and safety profile of butyric acid. This study assessed the FBA’s permeation across the skin and its soothing and anti-reddening potential to estimate its cosmetic application. The dosage method used to estimate FBA’s levels was validated to be sure of analytical results. The FBA diffusion tests were estimated in vitro using a Franz-type vertical diffusion cell. The soothing action was evaluated in vivo by Colorimeter CL400, measuring the erythema index. The results suggest that the FBA represents an innovative way to exploit the benefits of butyric acid in the cosmetic fields since it cannot reach the bloodstream, is odorless, and has a significative soothing action (decrease the erythema index −15.7% after 30′, and −17.8% after 60′). 相似文献
128.
Priscilla Augusta de Sousa Fernandes Raimundo Luiz Silva Pereira Antonia Thassya Lucas dos Santos Henrique Douglas Melo Coutinho Maria Flaviana Bezerra Morais-Braga Viviane Bezerra da Silva Adrielle Rodrigues Costa Maria Elizete Machado Generino Maraiza Gregorio de Oliveira Saulo Almeida de Menezes Luciano Temoteo dos Santos Abolghasem Siyadatpanah Polrat Wilairatana Tain Machado Aguiar Portela Ma Aparecida Barbosa Ferreira Gonalo Jos Weverton Almeida-Bezerra 《Molecules (Basel, Switzerland)》2022,27(10)
One of the main global problems that affect human health is the development of bacterial resistance to different drugs. As a result, the growing number of multidrug-resistant pathogens has contributed to an increase in resistant infections and represents a public health problem. The present work seeks to investigate the chemical composition and antibacterial activity of the essential oil of Syzygium cumini leaves. To identify its chemical composition, gas chromatography coupled to mass spectrometry was used. The antibacterial activity test was performed with the standard strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 25853 and Staphylococcus aureus ATCC 25923 and multidrug-resistant clinical isolates E. coli 06, P. aeruginosa 24 and S. aureus 10. The minimum inhibitory concentration (MIC) was determined by serial microdilution as well as the verification of the modulating effect of the antibiotic effect. In this test, the oil was used in a subinhibitory concentration. The test reading was performed after 24 h of incubation at 37 °C. The results show that the major chemical constituent is α-pinene (53.21%). The oil showed moderate activity against E. coli ATCC 25922, with the MIC of 512 µg/mL; there was no activity against the other strains. The oil potentiated the effect of antibiotics demonstrating possible synergism when associated with gentamicin, erythromycin and norfloxacin against E. coli 06 and S. aureus 10. 相似文献
129.
Cazorla-Reyes R Fernández-Moreno JL Romero-González R Frenich AG Vidal JL 《Talanta》2011,85(1):183-196
A new multiresidue method has been developed and validated for the simultaneous extraction of more than two hundred pesticides, including non-polar and polar pesticides (carbamates, organochlorine, organophosphorous, pyrethroids, herbicides and insecticides) in urine at trace levels by gas and ultra high pressure liquid chromatography coupled to ion trap and triple quadrupole mass spectrometry, respectively (GC-IT-MS/MS, UHPLC-QqQ-MS/MS). Non-polar and polar pesticides were simultaneously extracted from urine samples by a simple and fast solid phase extraction (SPE) procedure using C18 cartridges as sorbent, and dichloromethane as elution solvent. Recovery was in the range of 60-120%. Precision values expressed as relative standard deviation (RSD) were lower than 25%. Identification and confirmation of the compounds were performed by the use of retention time windows, comparison of spectra (GC-amenable compounds) or the estimation of the ion ratio (LC-amenable compounds). For GC-amenable pesticides, limits of detection (LODs) ranged from 0.001 to 0.436 μg L−1 and limits of quantification (LOQs) from 0.003 to 1.452 μg L−1. For LC-amenable pesticides, LODs ranged from 0.003 to 1.048 μg L−1 and LOQs ranged from 0.011 to 3.494 μg L−1. Finally, the optimized method was applied to the analysis of fourteen real samples of infants from agricultural population. Some pesticides such as methoxyfenozide, tebufenozide, piperonyl butoxide and propoxur were found at concentrations ranged from 1.61 to 24.4 μg L−1, whereas methiocarb sulfoxide was detected at trace levels in two samples. 相似文献
130.
Gonzalo Gurrea Ysasi Juan Carlos Moreno María Antonia Serrano 《Photochemistry and photobiology》2014,90(5):1170-1173
This article analyzes Ultraviolet Erythematic Radiation (UVER) dose received by several golf players in winter in Valencia. Playing golf involves spending several hours outdoors because of the length of golf matches and training. Moreover, in Valencia there are many golf players coming from northern Europe, with a phototype very sensitive (I–II). For that reason, these people have an increasing risk while playing. This article shows that harmful effects coming from UVER radiation may occur not only in summer time but also in winter, especially at these latitudes. VioSpor dosimeters have been used to develop this analysis over several golf players on January 2013 between 10:00 h and 15:00 h, local time. 相似文献