3,209 research outputs found
Damage in porous media due to salt crystallization
We investigate the origins of salt damage in sandstones for the two most
common salts: sodium chloride and sulfate. The results show that the observed
difference in damage between the two salts is directly related to the kinetics
of crystallization and the interfacial properties of the salt solutions and
crystals with respect to the stone. We show that, for sodium sulfate, the
existence of hydrated and anhydrous crystals and specifically their dissolution
and crystallization kinetics are responsible for the damage. Using magnetic
resonance imaging and optical microscopy we show that when water imbibes sodium
sulfate contaminated sandstones, followed by drying at room temperature, large
damage occurs in regions where pores are fully filled with salts. After partial
dissolution, anhydrous sodium sulfate salt present in these regions gives rise
to a very rapid growth of the hydrated phase of sulfate in the form of clusters
that form on or close to the remaining anhydrous microcrystals. The rapid
growth of these clusters generates stresses in excess of the tensile strength
of the stone leading to the damage. Sodium chloride only forms anhydrous
crystals that consequently do not cause damage in the experiments
Uniqueness of solutions of the stochastic Navier-Stokes equation with invariant measure given by the enstrophy
A stochastic Navier-Stokes equation with space-time Gaussian white noise is
considered, having as infinitesimal invariant measure a Gaussian measure
\mu_{\nu} whose covariance is given in terms of the enstrophy. Pathwise
uniqueness for \mu_{\nu}-a.e. initial velocity is proven for solutions having
\mu_{\nu} as invariant measure.Comment: Published by the Institute of Mathematical Statistics
(http://www.imstat.org) in the Annals of Probability
(http://www.imstat.org/aop/) at http://dx.doi.org/10.1214/00911790400000037
On the origin of the extremely different solubilities of polyethers in water
The solubilities of polyethers are surprisingly counter-intuitive. The best-known example is the difference between polyethylene glycol ([–CH2–CH2–O–]n) which is infinitely soluble, and polyoxymethylene ([–CH2–O–]n) which is completely insoluble in water, exactly the opposite of what one expects from the C/O ratios of these molecules. Similar anomalies exist for oligomeric and cyclic polyethers. To solve this apparent mystery, we use femtosecond vibrational and GHz dielectric spectroscopy with complementary ab initio calculations and molecular dynamics simulations. We find that the dynamics of water molecules solvating polyethers is fundamentally different depending on their C/O composition. The ab initio calculations and simulations show that this is not because of steric effects (as is commonly believed), but because the partial charge on the O atoms depends on the number of C atoms by which they are separated. Our results thus show that inductive effects can have a major impact on aqueous solubilities
Detection of Volatile Organic Compounds in Upland peat by Means of Proton-transfer-reaction Mass Spectrometry
This research represents the results of the detection of volatile organic compounds (VOCs) in the sphagnum moss and peat from two upland bogs located in Germany. Proton-transfer-reaction mass spectrometry (PTR-MS), used for the research, is a high-sensitive method, which permit to detect low concentrations of VOCs in ambient air. Along with natural VOCs of peat plants (generally sphagnum moss), the results of the study showed the presence of anthropogenic VOCs emissions like butanol, toluene, and benzene. This fact testifies about the capability of peat moss to accumulate these compounds. Possible sources of these VOCs in the peat samples can be agricultural machines and the traffic of the nearest roads
Aging of rotational diffusion in colloidal gels and glasses
We study the rotational diffusion of aging Laponite suspensions for a wide
range of concentrations using depolarized dynamic light scattering. The
measured orientational correlation functions undergo an ergodic to non-ergodic
transition that is characterized by a concentration-dependent
ergodicity-breaking time. We find that the relaxation times associated with
rotational degree of freedom as a function of waiting time, when scaled with
their ergodicity-breaking time, collapse on two distinct master curves. These
master curves are similar to those previously found for the translational
dynamics; The two different classes of behavior were attributed to colloidal
gels and glasses. Therefore, the aging dynamics of rotational degree of freedom
provides another signature of the distinct dynamical behavior of colloidal gels
and glasses.Comment: 12 pages, 7 figure
Nonmonotonic Friction due to Water Capillary Adhesion and Hydrogen Bonding at Multiasperity Interfaces
Nonmonotonic Friction due to Water Capillary Adhesion and Hydrogen Bonding at Multiasperity Interfaces
Counteracting Interfacial Energetics for Wetting of Hydrophobic Surfaces in the Presence of Surfactants
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