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161.
Coro Echeverria Pedro L. Almeida Oscar F. Aguilar Gutierrez Alejandro D. Rey Maria Helena Godinho 《Journal of Polymer Science.Polymer Physics》2017,55(10):821-830
The shear rate dependence of material functions such as shear viscosity (η) and the first normal stress difference (N1) were given and interpreted earlier by Kiss and Porter. Their widely accepted work revealed the possibility of having a negative minimum of N1 for polymeric liquid crystals. In this work, we disclose for the first time the evidence of two negative N1 minima on a sheared cellulosic lyotropic system. The lower shear rate minimum is ascribed to the uncoiling of the cholesteric helix, as theoretically predicted earlier. Our findings contribute also to the understanding of the other minimum already reported in the literature and attributed to the nematic director tumbling mode. Moreover, the elastic change that the LC‐HPC sample undergoes during the helix unwinding of the cholesteric structure is also by means of oscillatory measurements. This study is a contribution for the understanding of the structure‐properties relationship linked with the complex rheological behavior of chiral nematic cellulose‐based systems and may help to improve their further processing. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 821–830 相似文献
162.
Roca M Marcos MD Amorós P Beltrán-Porter A Edwards AJ Beltrán-Porter D 《Inorganic chemistry》1996,35(19):5613-5621
A general synthetic approach to rationalize the solution preparative chemistry of oxovanadium phosphates containing organic species as structural directing agents is presented. Careful attention is payed to the hydrolysis and condensation processes involving the ionic species in solution, and a simple restatement of the partial charge model (PCM) has been used in order to organize the experimental results. The structure of a new V(IV)-Fe(III) bimetallic oxovanadium phosphate, [H(3)N(CH(2))(2)NH(3)](2)[H(3)N(CH(2))(2)NH(2)] [Fe(III)(H(2)O)(2)(V(IV)O)(8)(OH)(4)(HPO(4))(4)(PO(4))(4)].4H(2)O, has been determined by X-ray single crystal diffraction methods. This compound crystallizes in the monoclinic system, space group P2(1)/n and the cell dimensions are as follows: a = 14.383(3) ?, b = 10.150(2) ?, c = 18.355(4) ?, and beta = 90.39(3) degrees (Z = 2). The existence of a complex intercrossing channel system, including a very large channel of 18.4 ? of diameter (in which both water molecules and ethylenediamine species are located), is the more interesting feature of this structure. Thermal decomposition, including the dehydration/rehydration process, has been studied by thermal analysis and variable temperature X-ray powder diffraction techniques. A complementary SEM study of the different intermediate decomposition products is presented. 相似文献
163.
Brandão Pedro Francisco Ramos Rui Miguel Rodrigues José António 《Analytical and bioanalytical chemistry》2018,410(26):6873-6880
Analytical and Bioanalytical Chemistry - Formaldehyde is often applied in the industrial production of different products, such as textiles, insulation materials, or cosmetics, due to its... 相似文献
164.
Pedro Marcos Frugeri Camila Marchioni Ayla Campos do Lago Célio Wisniewski 《Analytical letters》2018,51(10):1492-1504
This work proposes a flow injection analysis system for sulfaguanidine determination in pharmaceutical and food samples. The method was based on the reaction of sulfaguanidine with nitronium ion to produce a colored complex whose absorbance was measured at 545?nm. The flow injection analysis system’s significant parameters were checked by a fractional factorial design 27–2 and optimization by a Doehlert matrix. The flow injection analysis system shows optimum values at 0.28, 2.00, and 0.11% (w/v) for N-naphtil ethylenediamine, ammonium sulfamate, and sodium nitrite concentrations, respectively. The possible interferents present in pharmaceutical and food samples were assessed by a multivariate technique and depicted on probability charts, indicating no significant interferences at the 95% level of confidence interval. The method showed detection and quantification limits of 0.012 and 0.039?mg?L?1, an analytical frequency of 30 readings h?1 and precision always lower than 5.0% expressed as the relative standard deviation. The obtained results were in accordance with those obtained by high-performance liquid chromatography. 相似文献
165.
166.
Häussermann U Berastegui P Carlson S Haines J Léger JM 《Angewandte Chemie (International ed. in English)》2001,40(24):4624-4629
167.
168.
Nuno P. Faísca Pedro M. Saraiva Berç Rustem Efstratios N. Pistikopoulos 《Computational Management Science》2009,6(4):377-397
In this paper, we outline the foundations of a general global optimisation strategy for the solution of multilevel hierarchical
and general decentralised multilevel problems, based on our recent developments on multi-parametric programming and control
theory. The core idea is to recast each optimisation subproblem, present in the hierarchy, as a multi-parametric programming
problem, with parameters being the optimisation variables belonging to the remaining subproblems. This then transforms the
multilevel problem into single-level linear/convex optimisation problems. For decentralised systems, where more than one optimisation
problem is present at each level of the hierarchy, Nash equilibrium is considered. A three person dynamic optimisation problem
is presented to illustrate the mathematical developments. 相似文献
169.
Pedro M Girão 《Comptes Rendus Mathematique》2002,334(2):105-108
Let N?5, a>0, be a smooth bounded domain in , , and 6u62=|?u|22+a|u|22. We prove there exists an α0>0 such that, for all , This inequality implies Cherrier's inequality. To cite this article: P.M. Girão, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 105–108 相似文献
170.
Avalos M Babiano R Cintas P Clemente FR Gordillo R Hursthouse MB Jiménez JL Light ME Palacios JC 《The Journal of organic chemistry》2002,67(7):2378-2381
The present contribution discloses a simple and unexpected acid-catalyzed cleavage of tetrahydrotetrazines leading to 1,2-bis(hydrazones). Incorporation of a chiral fragment derived from carbohydrates enables the rapid preparation of glycosazones, a family of compounds employed by Emil Fischer to elucidate the configuration of sugars. In addition, a mechanistic proposal accounts for experimental observations. 相似文献