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81.
Wang Z Lau BP Tague B Sparling M Forsyth D 《Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment》2011,28(6):799-806
A sensitive and selective isotope dilution ion chromatography/tandem mass spectrometry (ID IC-MS/MS) method was developed and validated for the determination of perchlorate in infant formula. The perchlorate was extracted from infant formula by using 20 ml of methanol and 5 ml of 1% acetic acid. All samples were spiked with (18)O(4) isotope-labelled perchlorate internal standard prior to extraction. After purification on a graphitised carbon solid-phase extraction column, the extracts were injected into an ion chromatography system equipped with an Ionpac AS20 column for separation of perchlorate from other anions. The presence of perchlorate in samples was quantified by isotope dilution mass spectrometry. Analysis of both perchlorate and its isotope-labelled internal standard was carried out on a Waters Quattro Ultima triple quadrupole mass spectrometer operating in a multiple reaction monitoring (MRM) negative ionisation mode. The method was validated for linearity and range, accuracy, precision, sensitivity, and matrix effects. The limit of quantification (LOQ) was 0.4 μg l(-1) for liquid infant formula and 0.95 μg kg(-1) for powdered infant formula. The recovery ranged from 94% to 110% with an average of 98%. This method was used to analyse 39 infant formula, and perchlorate concentrations ranging from 相似文献
82.
Y.M. Lau I. Roghair N.G. Deen M. van Sint Annaland J.A.M. Kuipers 《Chemical engineering science》2011,(14):48
The present paper describes an Euler–Lagrange model utilizing a drag closure derived from direct numerical simulations (front-tracking model) for (i) single isolated bubbles and (ii) bubbles rising in bubble swarms, expressed as a function of the local gas fraction. The model is applied to the prediction of an air/water system in a bubble column and for which experimental data is available. The effect of variation in size of the mapping window for the interphase coupling between the Eulerian and Lagrangian framework is investigated for both closure relations. It is found that the drag closure as a function of the local gas fraction is an improvement over the use of the drag closure for isolated single bubbles for the prediction of bubbly flow. 相似文献
83.
Francis C. Lau James A. Joseph Jane E. McDonald Wilhelmina Kalt 《Journal of Functional Foods》2009,1(3):274-283
Treatment of BV2 microglial cells with blueberry extracts has been shown to be effective in reducing lipopolysaccharide (LPS)-induced proinflammatory mediators such as nitric oxide (NO), tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), inducible NO synthase (iNOS), and cyclooxygenase 2 (COX2). The current study explored the possibility that the down-regulation of iNOS and COX2 by blueberry extracts was mediated through NF-κB signaling pathway. A column-purified fraction of polyphenol-enriched blueberry extract (PC18) was used to treat LPS-activated BV2 cells. The results thus far showed that blueberry polyphenols significantly suppressed iNOS and COX2 promoter activities. In addition, blueberry polyphenols inhibited NF-κB nuclear translocation in LPS-activated BV2 cells. These findings suggested that the beneficial effects of blueberries may involve direct modulation of oxidative stress and/or inflammatory signaling cascades. 相似文献
84.
Cornelius B. Bavoh Bhajan Lal Omar Nashed Muhammad S. Khan Lau K. Keong Mohd. Azmi Bustam 《中国化学工程学报》2016,24(11):1619-1624
Recently ionic liquids(ILs) are introduced as novel dual function gas hydrate inhibitors. However, no desired gas hydrate inhibition has been reported due to poor IL selection and/or tuning method. Trial error as well as selection based on existing literature are the methods currently employed for selecting and/or tuning ILs. These methods are probabilistic, time consuming, expensive and may not result in selecting high performance ILs for gas hydrate mitigation. In this work, COSMO-RS is considered as a prescreening tool of ILs for gas hydrate mitigation by predicting the hydrogen bonding energies(E_(HB)) of studied IL inhibitors and comparing the predicted E_(HB) to the depression temperature(?) and induction time. Results show that, predicted EHBand chain length of ILs strongly relate and significantly affect the gas hydrate inhibition depression temperature but correlate moderately(R = 0.70) with average induction time in literature. It is deduced from the results that, ? increases with increasing IL EHBand/or decreases with increasing chain length. However, the cation–anion pairing of ILs also affects IL gas hydrate inhibition performance. Furthermore, a visual and better understanding of IL/water behavior for gas hydrate inhibition in terms of hydrogen bond donor and acceptor interaction analysis is also presented by determining the sigma profile and sigma potential of studied IL cations and anions used for gas hydrate mitigation for easy IL selection. 相似文献
85.
86.
Mohsen Soleimani Sheraz Khan David Mendenhall Willie Lau Mitchell A. Winnik 《Polymer》2012,53(13):2652-2663
We describe fluorescence resonance energy transfer (FRET) studies of film formation by a new type of two-component latex particles. These particles consist of a miscible blend of two components that have a similar composition but very different molecular weights. In our approach, we used sequential seeded emulsion polymerization to generate (in situ) a fraction of oligomer in poly(butyl acrylate-co-methyl methacrylate) P(BA-MMA) seed particles that contained a relatively high molecular weight (high-M) dye-labeled polymer. In this way we could systematically change the molecular weight distribution of polymer inside the particles. We varied the amount and the molecular weight of the oligomers. For latex films cast from these two-component particles, we studied the diffusion rate of the high molecular weight polymer by FRET. These measurements revealed that oligomers promoted diffusion rate during latex film formation (oligoplasticization). We analyzed our diffusion data in terms of the Fujita–Doolittle free-volume model and showed that higher molecular weight oligomers are less efficient as plasticizers. In separate experiments, oligomers with similar molecular weights as those in the two-component particles were introduced via latex blending. We compared oligoplasticization in latex blends films with that in the two-component particles films. Finally, we investigated the rheological behavior of the two-component polymers with compositions adjusted to have a common Tg (2 °C). The higher the molecular weight of the oligomer, the more that had to be added to achieve Tg = 2 °C. All of the oligomers were much shorter than the entanglement length and act as diluents of the entanglements in the high-M polymer. We found that incorporating larger amounts of oligomers with a higher molecular weight resulted in a more pronounced drop in polymer viscosity, associated with the decrease in the entanglement density. 相似文献
87.
Understanding the process of self-assembly of peptides has been important in various biomedical engineering applications. This work focuses on the effect of peptide concentration on the molecular self-assembly of an ionic-complementary peptide, EAK16-I (AEAKAEAKAEAKAEAK), in aqueous solution. The surface tension and self-assembled nanostructures were determined for a wide range of peptide concentrations using axisymmetric drop shape analysis-profile (ADSA-P) and atomic force microscopy (AFM), respectively. Surface tension measurements revealed a critical self-assembly concentration of 0.3 mg peptide/ml water, below which the surface tension decreased rapidly with increasing peptide concentration, and above which the surface tension remained at a constant, plateau value. There were two structural transitions observed with increasing peptide concentration: the first was from globular nanostructures to fibrils, and the second from the fibrils to relatively thick fibers. The second structural transition occurred at the critical self-assembly concentration as determined by the surface tension measurements. The nanostructural behavior of EAK16-I was compared with that of EAK16-II, which has the same amino acid composition but a different charge distribution. Salt effects were also examined by adding NaCl to the peptide solution. The salt addition facilitated the formation of peptide fibrils at low peptide concentrations but increased the critical self-assembly concentration, which occurred at 0.8 mg peptide/ml water in the presence of 20 mM NaCl. The structural transitions involved in the self-assembly of EAK16-I resemble those from protofibrils to fibrils observed with numerous naturally occurring peptides. An understanding of this structural transition may have relevance in the analysis and treatment of peptide/protein conformational diseases and have application in the production of self-assembled protein nanostructures. 相似文献
88.
This paper discusses a rapid GC-FID technique for the simultaneous quantitative analysis of FFA, MAG, DAG, TAG, sterols, and
squalene in vegetable oils, with special reference to palm oil. The FFA content determined had a lower SE compared with a
conventional titrimetric method. Squalene and individual sterols, consisting of β-sitosterol, stigmasterol, campesterol, and
cholesterol, were accurately quantified without any losses. This was achieved through elimination of tedious conventional
sample pretreatments, such as saponification and preparative TLC. With this technique, the separation of individual MAG, consisting
of 16∶0, 18∶0, and 18∶1 FA, and the DAG species, consisting of the 1,2(2,3)- and 1,3-positions, was sufficient to enable their
quantification. This technique enabled the TAG to be determined according to their carbon numbers in the range of C44 to C56. Comparisons were made with conventional methods, and the results were in good agreement with those reported in the literature. 相似文献
89.
Study of Low-Temperature Thermocompression Bonding
in Ag-In Solder for Packaging Applications 总被引:1,自引:0,他引:1
Riko I Made Chee Lip Gan Li Ling Yan Aibin Yu Seung Wook Yoon John H. Lau Chengkuo Lee 《Journal of Electronic Materials》2009,38(2):365-371
Low-temperature solders have wide applications in integrated circuits and micro-electromechanical systems packaging. In this
article, a study on Ag-In solder for chip-to-chip thermocompression bonding was carried out. The resulting joint consists
of AgIn2 and Ag9In4 phases, with the latter phase having a melting temperature higher than 400°C. Complete consumption of In solder into a Ag-rich
intermetallic compound is achieved by applying a bond pressure of 1.4 MPa at 180°C for 40 min. We also observe that the bonding
pressure effect enables a Ag-rich phase to be formed within a shorter bonding duration (10 min) at a higher pressure of 1.6 MPa.
Finally, prolonged aging leads to the formation of the final phase of Ag9In4 in the bonded joints. 相似文献
90.
A polyester composite based on betelnut fibres was fabricated and its adhesive wear and frictional performance studied using a block on disk machine at different applied loads and sliding distances at 2.8 m/s sliding velocity under dry/wet contact conditions. SEM was used to study worn surface morphology. The results revealed that betelnut fibre reinforced polyester (BFRP) composite had better wear and frictional performance under wet contact condition compared to dry. The wear mechanism of the BFRP composite was predominated by micro and macro-cracks in the polyester regions and debonding of fibres. 相似文献