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111.
A simple, reliable, trace determination of selenomethionine (Semet) based on a direct hydride generation atomic absorption spectrometric method was developed using sodium tetrahydroborate (0.3% in 0.2% NaOH) and hydrochloric acid (3 M). The method excluded any chemical pretreatment prior to hydride generation (HG). The optimized HG system was successfully coupled with the HPLC system. The detection limit (3σ of blank; n=5), reproducibility (R.S.D. of three successive analyses/day, performed on three different days), and repeatability (R.S.D. of three successive analyses) of the method were 1.08 ng ml−1, 9.8% for 9.04 ng ml−1 and 2.1–9.5% for 30.0–1.27 ng ml−1 Semet as Se (standards prepared in Milli-Q water). Calibration graph was linear up to 30 ng ml−1. This HPLC-HG-AAS method is very promising and successfully determined Semet (spiked) in human urine. 相似文献
112.
Himanshu Joshi Arpit Agarwal Bhalchandra Puranik Chang Shu Amit Agrawal 《国际流体数值方法杂志》2010,62(4):403-427
The lattice Boltzmann method (LBM) has established itself as an alternative approach to solve the fluid flow equations. In this work we combine LBM with the conventional finite volume method (FVM), and propose a non‐iterative hybrid method for the simulation of compressible flows. LBM is used to calculate the inter‐cell face fluxes and FVM is used to calculate the node parameters. The hybrid method is benchmarked for several one‐dimensional and two‐dimensional test cases. The results obtained by the hybrid method show a steeper and more accurate shock profile as compared with the results obtained by the widely used Godunov scheme or by a representative flux vector splitting scheme. Additional features of the proposed scheme are that it can be implemented on a non‐uniform grid, study of multi‐fluid problems is possible, and it is easily extendable to multi‐dimensions. These features have been demonstrated in this work. The proposed method is therefore robust and can possibly be applied to a variety of compressible flow situations. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
113.
Amit Kumar Gupta Kumkum Kumari Neetu Singh Dushyant Singh Raghuvanshi Krishna Nand Singh 《Tetrahedron letters》2012,53(6):650-653
An environmentally benign, ionic liquid promoted multicomponent protocol to benzopyrano(2,3-d)pyrimidines and 4H-chromenes has been developed at room temperature. Results of the reaction depend on the nature of the nucleophile used in the reaction. Secondary amines result in the formation of benzopyrano(2,3-d)pyrimidines, whereas thiols give rise to 4H-chromenes under the same set of reaction conditions. 相似文献
114.
Wei Shyy Young-Chang Cho Amit Gupta Chien-Chou Tseng Ann Marie Sastry 《Acta Mechanica Sinica》2011,27(6):845-865
Successful modeling and/or design of engineering systems often requires one to address the impact of multiple "design variables" on the prescribed outcome.There are often multiple,competing objectives based on which we assess the outcome of optimization.Since accurate,high fidelity models are typically time consuming and computationally expensive,comprehensive evaluations can be conducted only if an efficient framework is available.Furthermore,informed decisions of the model/hardware’s overall performance rely on an adequate understanding of the global,not local,sensitivity of the individual design variables on the objectives.The surrogate-based approach,which involves approximating the objectives as continuous functions of design variables from limited data,offers a rational framework to reduce the number of important input variables,i.e.,the dimension of a design or modeling space.In this paper,we review the fundamental issues that arise in surrogate-based analysis and optimization,highlighting concepts,methods,techniques,as well as modeling implications for mechanics problems.To aid the discussions of the issues involved,we summarize recent efforts in investigating cryogenic cavitating flows,active flow control based on dielectric barrier discharge concepts,and lithium(Li)-ion batteries.It is also stressed that many multi-scale mechanics problems can naturally benefit from the surrogate approach for "scale bridging." 相似文献
115.
Nisha Preschilla A. S. Abdul Rasheed Swayajith Sahadevan Amit Biswas Jayesh R. Bellare Subarna Shyamroy 《Journal of Polymer Science.Polymer Physics》2010,48(16):1786-1794
Effect of very small quantities of organically modified layered silicate clay on the nucleation of polypropylene (PP), as an additive at ppm levels dosage was investigated, in combination with two of the most commercially exploited organic nucleating agents, one of which is a cyclic aromatic phosphinate salt and the other is bis(3,4‐dimethylbenzylidene) sorbitol, each representing a separate class of nucleating molecules by itself. Substitution of a considerable fraction of either of these organic nucleating agents with organically modified inorganic nanoclay was seen to result in a unique synergy between the two in nucleating PP. Polarized light microscopy studies of these synergistic formulations with organoclay to nucleating agent ratios of 1:1 and 1:3 totaling 0.2 weight percent in PP showed significant reduction in spherulite size from that of non‐nucleated PP, and compared with the samples containing exclusive organic nucleating agent at similar loading. Differential scanning calorimetric studies provided evidence and insight into such synergistic behavior. Crystallization and supercooling temperatures for the synergistic formulations were comparable for those formulations containing only organic nucleating agents, indicating comparable nucleation efficiency, whereas organoclay alone, although showing some extent of nucleation, was clearly poorer in efficiency. Wide and small angle X‐ray scattering studies further explained these observations. An increase in the gamma polytype fraction was seen in samples that contained both organoclay and nucleating agent, pointing to the role of organoclay as a gamma nucleator. Organoclay was found to be completely exfoliated in these synergistic formulations and was seen as well‐dispersed, single platelets in the PP matrix. A hybrid network consisting of exfoliated organoclay platelets and organic nucleating agent molecules was proposed, which is more stable and stiffer than the network formed by nucleating agent alone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1786–1794, 2010 相似文献
116.
Abanti Nag 《Journal of Physics and Chemistry of Solids》2005,66(1):191-199
SrAl12O19:Pr3+, Ti4+ phosphor suitable for field emission displays is prepared by the wet chemical gel-carbonate method and the mechanism of enhancement in red photoluminescence (PL) intensity with Ti4+ therein has been investigated. The PL spectra of Pr3+ show both 1D2-3H4 and 3P0-3H6 emission in the red region with very weak intensity when excited at 355 nm. The emission intensity has increased by about 100 times at room temperature in the compositional range SrAl12−xTixO19+x/2:Pr3+, with 0.1≤x≤0.3 in comparison to Ti-free SrAl12O19:Pr3+. TEM investigations show the presence of exsolved nanophase of SrAl8Ti3O19, the precipitation of which is preceded by the presence of defect centers at the interfacial regions between the semicoherent transient phase and the parent SrAl12O19 matrix. The presence of transitional nanophase and the associated defects modify the excitation-emission process by way of formation of electronic sub-levels at lower energy (3.5 eV) than the band gap of SrAl12O19 (∼7 eV) followed by non-resonance energy transfer to Pr3+ level, leading to magnetic-dipole related red emission with enhanced intensity. The PL intensity of Pr3+ decreases at high Ti4+ concentrations (x>0.3) due to higher extent of segregation of non-emissive SrAl8Ti3O19:Pr3+ phase. 相似文献
117.
In this paper we report a new method of fabrication of surface tensionconfined microfluidic devices on glass. We have also
successfully carried out some well-known chemical reactions in these fluidic channels to demonstrate the usefulness of these
wall-less microchannels. The confined flow path of liquid was achieved on the basis of extreme differences in hydrophobic
and hydrophilic characters of the surface. The flow paths were fabricated by making parallel lines using permanent marker
pen ink or other polymer on glass surfaces. Two mirror image patterned glass plates were then sandwiched one on top of the
other, separated by a thin gap-created using a spacer. The aqueous liquid moves between the surfaces by capillary forces,
confined to the hydrophilic areas without wetting the hydrophobic lines, achieving liquid confinement without physical side-walls.
We have shown that the microfluidic devices designed in such a way can be very useful due to their simplicity and low fabrication
cost. More importantly, we have also demonstrated that the minimum requirement of such a working device is a hydrophilic line
surrounded by hydrophobic environment, two walls of which are constituted of air and the rest is made of a hydrophobic surface. 相似文献
118.
Thiol–Ene “Click” Reaction Triggered by Neutral Ionic Liquid: The “Ambiphilic” Character of [hmim]Br in the Regioselective Nucleophilic Hydrothiolation
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Rajesh Kumar Saima Amit Shard Nitin H. Andhare Richa Dr. Arun K. Sinha 《Angewandte Chemie (International ed. in English)》2015,54(3):828-832
Thiol–ene “click” chemistry has emerged as a powerful strategy to construct carbon–heteroatom (C? S) bonds, which generally results in the formation of two regioisomers. To this end, the neutral ionic liquid [hmim]Br has been explored as a solvent cum catalyst for the synthesis of linear thioethers from activated and inactivated styrene derivatives or secondary benzyl alcohols and thiols without the requirement of using a metal complex, base, or free radical initiator. Furthermore, detailed mechanistic investigations using 1H NMR spectroscopy and quadrupole time‐of‐flight electrospray ionization mass spectrometry (Q‐TOF ESI‐MS) revealed that the “ambiphilic” character of the ionic liquid promotes the nucleophilic addition of thiol to styrene through an anti‐Markovnikov pathway. The catalyst recyclability and the extension of the methodology for thiol–yne click chemistry are additional benefits. A competitive study among thiophenol, styrene, and phenyl acetylene revealed that the rate of reaction is in the order of thiol–yne>thiol–ene>dimerization of thiol in [hmim]Br. 相似文献
119.
120.