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41.
In the present work, we compare the influence introduced by the variation of water-to-cement ratio and the presence of different superplasticizers on the hydration process of gray cement using the low-field nuclear magnetic resonance relaxometry. The stages of hydration are identified and a relationship between the ettringite formation during hydration process and the transverse relaxation time is established. It is also demonstrated that the addition of small amounts of superplasticizer in the cement paste significantly expands the dormant period while the hardening period is reduced. On the other side, the increase in the water-to-cement ratio has little influence on the dormant period but can instead increase the porosity of the sample and consequently reduce its strength. 相似文献
42.
The reaction Fe(CN)4(bpy)2? + S2O82? has been studied in aqueous micellar solutions of N‐tetradecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate, SB3‐14. The influence of changes in the surfactant concentration as well as in the peroxodisulfate ions concentration on kobs was investigated. Spectroscopic and conductivity measurements have given information about the distribution of both anionic reagents between the aqueous and micellar pseudophases of the SB3‐14 micellar solutions. A discussion about the adequacy of various equations based on the pseudophase model to rationalize kinetic micellar effects for anion‐anion reactions in sulfobetaine micellar solutions has been done. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 225–231, 2001 相似文献
43.
G. Spacu und A. Pop 《Fresenius' Journal of Analytical Chemistry》1937,111(7-8):254-260
Ohne Zusammenfassung 相似文献
44.
A new approach on MHD natural convection boundary layer flow from a finite flat plate of arbitrary inclination in a rotating
environment, is presented. This problem plays a significant role on boundary layer flow control. It is shown that taking into
account the pressure rise region at the leading edge of the plate leads to avoid separation and the back flow is reduced by
the strong magnetic field. It is also shown that the frictional drag at the leading edge of the plate is reduced when the
inclination angle α=π/4. In the case of isothermal flat plate, the bulk temperature becomes identical for any value of Gr (Grashof number) when the value of M
2 (Hartmann number) and K
2 (rotation parameter) are kept fixed. 相似文献
45.
A conjugate problem of natural convection between two horizontal concentric, isothermal cylinders filled with a fluid-saturated porous medium is studied. The flow field and energy equations are solved under the conditions of equality in temperature but with jump in heat flux at the fluid-solid interface. Numerical results by a finite-difference technique are presented for a large variation in the parameters entering the problem. A comparison of the solution with non-conjugate problem is also given.Das konjugierte Problem der freien Konvektion zwischen zwei horizontalen, konzentrischen, isothermen Zylindern, die mit einem fluid-gesättigten porösen Medium gefüllt sind, wurde hier untersucht.Das Strömungsfeld und die Energiegleichung sind unter den Bedingungen gelöst worden, daß die Temperatur gleich ist, aber ein Wärmeflußsprung am Übergang von der Flüssigkeits- zur Festphase stattfindet. Die numerischen Ergebnisse werden mit dem Finite-Differenzen-Verfahren für viele Parametervariationen dargestellt. Zudem wurde ein Lösungsvergleich mit einem nicht konjugierten Problem gegeben. 相似文献
46.
Davies DL Macgregor SA Poblador-Bahamonde AI 《Dalton transactions (Cambridge, England : 2003)》2010,39(43):10520-10527
Density functional theory calculations have been employed to model ethene hydroarylation using an [Ir(κ(2)-OAc)(PMe(3))Cp](+) catalyst, 1. The reaction proceeds via: (i) an acetate-assisted C-H activation of benzene via an AMLA-6 transition state; (ii) rate-limiting insertion of ethene into the Ir-Ph bond; and (iii) protonolysis of the β-phenylethyl species by HOAc. A range of competing processes are assessed, the most important of which are the C-H activation of ethene at 1 and trapping of the β-phenylethyl intermediate with ethene. The former process gives rise to Ir-vinyl species which can then access further ethene insertion to give stable allyl by-products. A comparison with other ethene hydroarylation catalysts reported in the literature is presented. 相似文献
47.
Roslinda Nazar Mihaela Jaradat Norihan M. Arifin Ioan Pop 《Central European Journal of Physics》2011,9(5):1195-1202
In this paper, the stagnation-point flow and heat transfer towards a shrinking sheet in a nanofluid is considered. The nonlinear
system of coupled partial differential equations was transformed and reduced to a nonlinear system of coupled ordinary differential
equations, which was solved numerically using the shooting method. Numerical results were obtained for the skin friction coefficient,
the local Nusselt number as well as the velocity and temperature profiles for some values of the governing parameters, namely
the nanoparticle volume fraction φ, the shrinking parameter λand the Prandtl number Pr. Three different types of nanoparticles are considered, namely Cu, Al2O3 and TiO2. It was found that nanoparticles of low thermal conductivity, TiO2, have better enhancement on heat transfer compared to nanoparticles Al2O3 and Cu. For a particular nanoparticle, increasing the volume fraction φ results in an increase of the skin friction coefficient and the heat transfer rate at the surface. It is also found that
solutions do not exist for larger shrinking rates and dual solutions exist when λ < −1.0. 相似文献
48.
49.
50.
I Berceanu A Andronic M Duma D MoisĂ M Petrovici A Pop V Simion A del Zoppo G D’Erasmo G Imme G Lanzano A Pagano A Pantaleo G Raciti 《Pramana》1999,53(3):419-424
The excitation function (EF) data for dissipative processes in 19F + 27Al system in the incident energy interval from 113.5 to 130 MeV are used to obtain the dependence of the charge variance and
of the interaction time as a function of the incident energy. Fluctuations are observed in the EFs of both these secondary
observables. Their correlation is supported by a mechanism based on stochastic exchange of nucleons. 相似文献