ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymer. The organization has 16969 authors who have published 23758 publications receiving 535713 citations. The organization is also known as: Exxon Mobil Corporation & Exxon Mobil Corp..

Diffusing-wave-spectroscopy measurements of viscoelasticity of complex fluids

Abstract: We present a new use of dynamic light scattering that permits the determination of the viscoelastic behavior of a complex fluid. By describing the motion of a scattering particle in a viscoelastic medium in terms of a generalized Langevin equation with a memory function, we relate the time evolution of its mean-square displacement to the frequency-dependent storage and loss moduli of the medium. The utility of this technique is illustrated through the application of diffusing-wave spectroscopy to probe the viscoelastic behavior of two complex fluids. The properties of a concentrated suspension of colloidal particles interacting as hard spheres are shown to be strongly influenced by the incipient colloidal glass transition, which leads to an extended range of frequencies over which they behave like an elastic solid. Similar elasticity is observed in a compressed emulsion, resulting in this case from the additional interfacial energy of the deformed droplets. In both cases diffusing-wave spectroscopy is used to measure the frequency dependence of the storage and loss moduli, and these results are compared with those from mechanical measurements. Besides providing a purely optical method for measuring mechanical properties, this technique provides new insight into the origin of the viscoelastic behavior.

Rapid fluvial incision along the Yellow River during headward basin integration

Abstract: The onset of fluvial erosion in an area of tectonic uplift is thought to reflect the timing of the uplift. Geomorphological data from the Yellow River in Tibet, indicate that the rapid incision of this river channel occurred as a result of climate change, at least six million years after the onset of plateau uplift.

Strength, porosity, and permeability development during hydrostatic and shear loading of synthetic quartz-clay fault gouge

Abstract: [1] The strength and permeability of fault zones must be quantified in order to accurately predict crustal strength and subsurface fluid migration To this end, we performed experiments on mixtures of fine-grained quartz and kaolinite incremented at 10 wt% intervals between the two end-member components (analogues for natural fault gouge) in order to establish their strength and fluid flow properties during hydrostatic and shear loading Hydrostatically compacted samples exhibited permeability reduction on increasing effective pressures from 5 MPa to 50 MPa, with the rate of reduction displaying strong dependency on the synthetic fault gouge composition The permeability decreases continuously with increasing kaolinite content Porosity exhibits a distinct minimum that evolves with increasing effective pressure according to the relative compaction of the quartz and kaolinite end-members Porosity evolution with increasing clay content is predicted satisfactorily by a simple ideal packing model At the highest effective pressure (50 MPa), permeability reduced log-linearly over 4 orders of magnitude with increasing clay content Mechanically, sheared gouge samples showed a continuous reduction in frictional strength with increasing clay fraction Permeability decreased further on shear loading after initial hydrostatic compaction to 50 MPa This was most evident for the pure quartz end-member, with two orders of magnitude additional reduction, whereas the clay-rich samples were reduced only tenfold, mostly before a shear strain of 5 Variation of permeability with both clay content and shear deformation may be adequately described by previously published empirical predictors for fault zone permeability Clay content has the largest effect on permeability, and shear deformation affects permeability of quartz-rich gouges more than clay-rich gouges

Antiferromagnetism in YBa2Cu

Abstract: Neutron diffraction has been used to study antiferromagnetic ordering in $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ as a function of $x$. Evidence for such ordering has been observed only in the tetragonal, nonsuperconducting phase ($x\ensuremath{\lesssim}0.4$). The magnetic origin of the superlattice reflections has been confirmed with polarized beam measurements. A single antiferromagnetic structure was observed throughout the ordered phase, with a maximum N\'eel temperature of \ensuremath{\sim}500 K and average ordered moment of ${(0.66\ifmmode\pm\else\textpm\fi{}0.07)}_{\mathrm{\ensuremath{\mu}}\mathit{B}}$ per magnetic Cu atom at $x\ensuremath{\approx}0$. Magnetic susceptibility measurements suggest that two-dimensional correlations are strong, as in ${\mathrm{La}}_{2}\mathrm{Cu}{\mathrm{O}}_{4\ensuremath{-}y}$, and may survive into the orthorhombic phase.