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231.
The effects of four washing procedures on the concentrations of manganese, iron, copper, zinc and cadmium and were investigated for three pooled samples of human head hair. The solutions evaluated were a non-ionic detergent (Triton X-100), an ionic detergent (sodium lauryl sulfate), acetone and a complexing agent (EDTA). The results indicate that for every element determined there is a level below which the concentration cannot be reduced by further washings. The numbers of washings required to reach these levels vary considerably. This effect must be considered in the trace element analysis of hair. 相似文献
232.
We consider a Galerkin finite element method that uses piecewisebilinears on a modified Shishkin mesh for a model singularlyperturbed convectiondiffusion problem on the unit square.The method is shown to be convergent, uniformly in the perturbationparameter , of order N1in a global energy norm, providedonly that N1, where O(N2)mesh points are used. Thuson the new mesh the method yields more accurate results thanon Shishkins original piecewise uniform mesh, whereit is convergent of order N1lnN. Numerical experiments support our theoretical results.
Received 14 September, 1998. Revised 24 September, 1999. 相似文献
233.
Olga Zhytniakivska Valeriya Trusova Galyna Gorbenko Elena Kirilova Inta Kalnina Georgiy Kirilov Julian Molotkovsky Jukka Tulkki Paavo Kinnunen 《Journal of fluorescence》2014,24(3):899-907
Förster resonance energy transfer (FRET) between anthrylvinyl-labeled phosphatidylcholine (AV-PC) as a donor and newly synthesized benzanthrones (referred to here as A8, A6, AM12, AM15 and AM18) as acceptors has been examined to gain insight into molecular level details of the interactions between benzanthrone dyes and model lipid membranes composed of zwitterionic lipid phosphatidylcholine and its mixtures with anionic lipids cardiolipin (CL) and phosphatidylglycerol (PG). FRET data were quantitatively analyzed in terms of the model of energy transfer in two-dimensional systems taking into account the distance dependence of orientation factor. Evidence for A8 location in phospholipid headgroup region has been obtained. Inclusion of CL and PG into PC bilayer has been found to induce substantial relocation of A6, AM12, AM15 and AM18 from hydrophobic membrane core to lipid-water interface. 相似文献
234.
Chiral topological phases and fractional domain wall excitations in one-dimensional chains and wires
According to the general classification of topological insulators, there exist one-dimensional chirally (sublattice) symmetric systems that can support any number of topological phases. We introduce a zigzag fermion chain with spin-orbit coupling in magnetic field and identify three distinct topological phases. Zero-mode excitations, localized at the phase boundaries, are fractionalized: two of the phase boundaries support ±e/2 charge states while one of the boundaries support ±e and neutral excitations. In addition, a finite chain exhibits ±e/2 edge states for two of the three phases. We explain how the studied system generalizes the Peierls-distorted polyacetylene model and discuss possible realizations in atomic chains and quantum spin Hall wires. 相似文献
235.
Lokki T Pätynen J Tervo S Siltanen S Savioja L 《The Journal of the Acoustical Society of America》2011,129(6):EL223-EL228
Strong, exciting, and engaging sound is perceived in the best concert halls. Here, it is shown that wideband early reflections that preserve the temporal envelope of sound contribute to the clear and open acoustics with strong bass. Such reflections are fused with the direct sound due to the precedence effect. In contrast, reflections that distort the temporal envelope render the sound weak and muddy because they partially break down the precedence. The presented findings are based on the earlier psychoacoustics research, and confirmed by a perceptual evaluation with six simulated concert halls that have same monaural room acoustical parameter values according to ISO3382-1. 相似文献
236.
Crosslinking is a feasible way to prepare biodegradable polymers with potential in biomedical applications such as controlled release of active agents and tissue engineering. A synthesis route in which functional telechelic aliphatic polyester oligomers are used as precursors for the preparation of crosslinked polyesters and poly(ester anhydride)s is described. Mechanical properties, degradation characteristics and rate, and bioactivity can be modified widely by controlling the chemical composition and architecture of the crosslinkable oligomers. In tissue engineering, photocrosslinking allows to use crosslinkable oligomers in advanced manufacturing techniques like micromolding in capillaries, stereolithography and two-photon polymerization. 相似文献
237.
A new class of liquid crystalline thermosets (LCTs) was successfully produced containing lyotropic cellulose nanocrystals (CNCs) as the primary mesogenic component (up to 72 wt%) by the addition of non-mesogenic epoxy monomers. Cellulose-based LCTs were produced by totally aqueous processing methods and ultimately cured at elevated temperatures to produce ordered networks of ‘frozen’ liquid crystalline (LC) phases. Various degrees of birefringence were obtained via self-assembly of CNCs into oriented phases as observed by polarized optical microscopy and transmission electron microscopy. X-ray diffraction measurements highlighted the effects of texture of CNCs within LCT films compared to lyophilized CNCs. Cellulose-based LCT films uniquely exhibited thermo-mechanical properties of both traditional LCTs and LC elastomers, such as high elastic modulus (~1 GPa) under ambient conditions and low glass transition temperature (~?25 °C), respectively. The development of LCTs based on CNCs and aqueous processing methods provides a renewable pathway for designing high performance composites with ordered network structures and unique optical properties. 相似文献
238.
Zhuo-Lin Wang Kari Hiltunen Petri Orava Jukka Seppälä Yu-Yen Linko 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):599-612
Abstract The use of lipase as biocatalyst in polyesterification of aliphatic diacids or their derivatives, and diols in an organic solvent has been discussed. We have demonstrated that bis(2-chloroethyl) esters of succinic, fumaric, and maleic acid, and bis(2,2,2-trifluoroethyl) sebacate and -dodecanedioate can be polymerized by lipase-catalyzed polytransesterification. Maleate was isomerized to fumarate even under mild reaction conditions, resulting in poly(1,4-butyl fumarate). In order to obtain a high mass-average molar mass of the polyester, solid Mucor miehei lipase was found to be the best lipase and diphenyl ether the best solvent of several investigated. There was no clear relationship with the log P value of the solvent and the polyesterification activity of lipase. The highest degree of polymerization (DP = 184) of poly(1,4-butyl sebacate) with a mass-average molar mass of 46,600 g·mol?1 was obtained in polytransesterification of bis(2,2,2-trifluoroethyl) sebacate and 1,4-butanediol using a programmed vacuum profile. However, a mass-average molar mass as high as about 42,000 g·mol?1 (DP = 167) was also obtained with free sebacic acid when vacuum was employed to remove the water formed during esterification. The mass average molar mass of the polyester increased with an increase in the relative quantity of lipase up to 1 g per 1.5 mmol of diacid, with an increase in the molar mass of the aliphatic diol up to 1,5-pentanediol, and with an increase in the concentration of substrates up to 0.83 M. 相似文献
239.
Nikolaos Pahimanolis Ulla Hippi Leena-Sisko Johansson Tapio Saarinen Nikolay Houbenov Janne Ruokolainen Jukka Seppälä 《Cellulose (London, England)》2011,18(5):1201-1212
In the present work, amino functionalized nanofibrillated cellulose (NFC) was prepared using click-chemistry in aqueous reaction
conditions. First, reactive azide groups were introduced on the surface of NFC by the etherification of 1-azido-2,3-epoxypropane
in alkaline water/isopropanol-mixture at ambient temperature. Then the azide groups were reacted with propargyl amine utilizing
copper catalyzed azide-alkyne cycloaddition (CuAAC), leading to pH-responsive 1,2,3-triazole-4-methanamine decorated NFC.
The reaction products were characterized using Fourier transform infrared spectroscopy, elemental analysis and X-ray photoelectron
spectroscopy. The presence of the attached azide groups was also confirmed by reacting them with 5-(dimethylamino)-N-(2-propyl)-1-naphthalenesulfonamide
by CuAAC, yielding highly fluorescent NFC. In addition, atom force microscopy and rheology studies confirmed that the original
NFC nanostructure was maintained during the synthesis. 相似文献
240.
Yun-Hsin Liao Kalle Levon Jukka Laakso Jan-Erik
sterholm 《Macromolecular rapid communications》1995,16(5):393-397
Water solubility of electro-active polymers in their doped state may provide a possibility for environmentally feasible manufacturing processes. Because previous results in this direction require expensive modifications or impractical template polymerization methods, we created a simple method of mixing components with a large molecular weight difference. The polymer which acts as an acidic dopant and provides water solubility, has to have the higher molecular weight. The formed complex resembles a block copolymer but in this case the polyaniline block is attached to the sulfonated polystyrene chain by strong physical interactions instead of chemical end-to-end linkage. 相似文献