225,935 research outputs found
Ultrasonic sound speed of hydrating calcium sulphate\ud hemihydrate; part 2, the correlation of sound velocity to\ud hydration degree
In this article the sound velocity through a mix is correlated to the hydration degree of\ud
the mix. Models are presented predicting the sound velocity through fresh slurries and\ud
hardened products. These two states correspond to the starting and finishing point of the\ud
hydration process. The present research shows that a linear relation between the amount\ud
of hydration-product (gypsum) formed (Smith et al., 2002) and sound velocity can be\ud
used to describe this process. To this end, the amount of hydration-product formed is\ud
determined by the using the equations of Schiller (1974) for the hydration process and\ud
of Brouwers (2010) for the volume fractions of binder, water and hydration products\ud
during the hydration process. The presented model shows that the induction time and\ud
gypsum growth rate are linear related to the water/gypsum-ratio
The use of artificial neural networks in adiabatic curves modeling
Adiabatic hydration curves are the most suitable data for temperature calculations in concrete hardening structures. However, it is very difficult to predict the adiabatic hydration curve of an arbitrary concrete mixture. The idea of modeling adiabatic temperature rise during concrete hydration with the use of artificial neural networks was introduced in order to describe the adiabatic hydration of an arbitrary concrete mixture, depending on factors which influence the hydration process of cement in concrete. The influence of these factors was determined by our own experiments. A comparison between experimentally determined adiabatic curves and adiabatic curves, evaluated by proposed numerical model shows that artificial neural networks can be used to predict adiabatic hydration curves effectively. This model can be easily incorporated in the computer programs for prediction of the thermal fields in young concrete structures, implemented in the finite element or finite difference codes. New adiabatic hydration curves with some other initial parameters of the concrete mixture can be easily included in this model in order to expand the range of suitability of artificial neural networks to predict the adiabatic hydration curves. (C) 2008 Elsevier B.V. All rights reserved
A shrinking core model for steam hydration of CaO-based sorbents cycled for CO2 capture
Calcium looping is a developing CO2 capture technology. It is based on the reversible carbonation of CaO
sorbent, which becomes less reactive upon cycling. One method of increasing the reactivity of unreactive
sorbent is by hydration in the calcined (CaO) form. Here, sorbent has been subjected to repeated cycles of
carbonation and calcination within a small fluidised bed reactor. Cycle numbers of 0 (i.e., one calcination),
2, 6 and 13 have been studied to generate sorbents that have been deactivated to different extents.
Subsequently, the sorbent generated was subjected to steam hydration tests within a thermogravimetric
analyser, using hydration temperatures of 473, 573 and 673 K. Sorbents that had been cycled less prior to
hydration hydrated rapidly. However, the more cycled sorbents exhibited behaviour where the hydration
conversion tended towards an asymptotic value, which is likely to be associated with pore blockage. This
asymptotic value tended to be lower at higher hydration temperatures; however, the maximum rate of
hydration was found to increase with increasing hydration temperature. A shrinking core model has been
developed and applied to the data. It fits data from experiments that did not exhibit extensive pore blockage
well, but fits data from experiments that exhibited pore blockage less well
Accurate Evaluation of Charge Asymmetry in Aqueous Solvation
Charge hydration asymmetry (CHA)--a characteristic dependence of hydration
free energy on the sign of the solute charge--quantifies the asymmetric
response of water to electric field at microscopic level. Accurate estimates of
CHA are critical for understanding hydration effects ubiquitous in chemistry
and biology. However, measuring hydration energies of charged species is
fraught with significant difficulties, which lead to unacceptably large (up to
300%) variation in the available estimates of the CHA effect. We circumvent
these difficulties by developing a framework which allows us to extract and
accurately estimate the intrinsic propensity of water to exhibit CHA from
accurate experimental hydration free energies of neutral polar molecules.
Specifically, from a set of 504 small molecules we identify two pairs that are
analogous, with respect to CHA, to the K+/F- pair--a classical probe for the
effect. We use these "CHA-conjugate" molecule pairs to quantify the intrinsic
charge-asymmetric response of water to the microscopic charge perturbations:
the asymmetry of the response is strong, ~50% of the average hydration free
energy of these molecules. The ability of widely used classical water models to
predict hydration energies of small molecules correlates with their ability to
predict CHA
Hydration Water Dynamics and Instigation of Protein Structural Relaxation
The molecular mechanism of the solvent motion that is required to instigate
the protein structural relaxation above a critical hydration level or
transition temperature has yet to be determined. In this work we use
quasi-elastic neutron scattering (QENS) and molecular dynamics simulation to
investigate hydration water dynamics near a greatly simplified protein surface.
We consider the hydration water dynamics near the completely deuterated
N-acetyl-leucine-methylamide (NALMA) solute, a hydrophobic amino acid side
chain attached to a polar blocked polypeptide backbone, as a function of
concentration between 0.5M-2.0M, under ambient conditions. In this
Communication, we focus our results of hydration dynamics near a model protein
surface on the issue of how enzymatic activity is restored once a critical
hydration level is reached, and provide a hypothesis for the molecular
mechanism of the solvent motion that is required to trigger protein structural
relaxation when above the hydration transition.Comment: 2 pages, 2 figures, Communicatio
Ultrasonic sound speed analysis of hydrating calcium sulphate hemihydrate \ud
This article focuses on the hydration, and\ud
associated microstructure development, of b-hemihydrate\ud
to dihydrate (gypsum). The sound velocity is used to\ud
quantify the composition of the fresh slurry as well as the\ud
hardening and hardened—porous—material. Furthermore,\ud
an overview of available hydration kinetic and volumetric\ud
models for gypsum is addressed. The presented models\ud
predict the sound velocity through slurries and hardened\ud
products. These states correspond to the starting and ending\ud
times of the hydration process. The present research shows\ud
that a linear relation between the amount of hydrationproduct\ud
(gypsum) formed and sound velocity (Smith et al.,\ud
J Eur Ceram Soc 22(12):1947, 2002) can be used to\ud
describe this process. To this end, the amount of hydrationproduct\ud
formed is determined using the equations of\ud
Schiller (J Appl Chem Biotechnol 24(7):379, 1974) for the\ud
hydration process and of Brouwers (A hydration model of\ud
Portland cement using the work of Powers and Brownyard,\ud
2011) for the volume fractions of binder, water and\ud
hydration products during the hydration proces
Kinetic, Spectroscopic, and X-Ray Crystallographic Evidence for the Cooperative Mechanism of the Hydration of Nitriles Catalyzed by a Tetranuclear Ruthenium-ÎĽ-oxo-ÎĽ-hydroxo Complex
The tetranuclear ruthenium-oxo-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(μ4-O)(μ3-OH)(μ2-OH)} (1) was found to be a highly cooperative catalyst for the nitrile hydration reaction. The cooperative mechanism of the hydration of benzonitrile was established by Hill inhibition kinetics. The treatment of a nitrile substrate with complex 1 led to the catalytically relevant nitrile-coordinated tetraruthenium complex 3. The X-ray structure of the nitrile-coordinated complex 3 showed a considerably “relaxed” tetrameric core structure compared to that of 1. The hydration of para-substituted benzonitriles p-X-C6H4CN with an electron-withdrawing group (X = Cl, Br, CO2H, CF3) exhibited cooperative kinetics, as indicated by the sigmoidal saturation kinetics, while the hydration of nitriles with an electron-donating group (X = OH, OMe, t-Bu, CH3) obeyed Michaelis–Menten saturation kinetics. The formation of a ruthenium hydride species was observed during the hydration of methacrylonitrile, and its monomeric nature was established by using DOSY NMR techniques
Inclusion of Enclosed Hydration Effects in the Binding Free Energy Estimation of Dopamine D3 Receptor Complexes
Confined hydration and conformational flexibility are some of the challenges
encountered for the rational design of selective antagonists of G-protein
coupled receptors. We present a set of C3-substituted (-)-stepholidine
derivatives as potent binders of the dopamine D3 receptor. The compounds are
characterized biochemically, as well as by computer modeling using a novel
molecular dynamics-based alchemical binding free energy approach which
incorporates the effect of the displacement of enclosed water molecules from
the binding site. The free energy of displacement of specific hydration sites
is obtained using the Hydration Site Analysis method with explicit solvation.
This work underscores the critical role of confined hydration and
conformational reorganization in the molecular recognition mechanism of
dopamine receptors and illustrates the potential of binding free energy models
to represent these key phenomena.Comment: This is the first report of using enclosed hydration in estimating
binding free energies of protein-ligand complexes using implicit solvatio
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