3,485 research outputs found
Standards for material handling and facilities equipment proofload testing
Document provides information on verifying the safety of material handling and facilities equipment /MH/FE/, ranging from monorail systems to ladders and non-powered mobile equipment. Seven catagories of MH/FE equipment are defined
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
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
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
Phase Separation by Entanglement of Active Polymerlike Worms
We investigate the aggregation and phase separation of thin, living T.
tubifex worms that behave as active polymers. Randomly dispersed active worms
spontaneously aggregate to form compact, highly entangled blobs, a process
similar to polymer phase separation, and for which we observe power-law growth
kinetics. We find that the phase separation of active polymerlike worms does
not occur through Ostwald ripening, but through active motion and coalescence
of the phase domains. Interestingly, the growth mechanism differs from
conventional growth by droplet coalescence: the diffusion constant
characterizing the random motion of a worm blob is independent of its size, a
phenomenon that can be explained from the fact that the active random motion
arises from the worms at the surface of the blob. This leads to a fundamentally
different phase-separation mechanism that may be unique to active polymers.Comment: 4 pages, 4 figure
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