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Quantification of intragranular porosity in sand-size material from an aquifer on Cape Cod, Massachusetts, by scanning electron microscopy, mercury injection, and epifluorescence techniques shows that there are more reaction sites and that porosity is greater than indicated by standard short-term laboratory tests and measurement techniques. Results from laboratory and field tracer tests show solute nonequilibrium for a reacting ion consistent with a model of diffusion into, and exchange within, grain interiors. These data indicate that a diffusion expression needs to be included in transport codes, particularly for simulation of the transport of radioactive and toxic wastes. 相似文献
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Kraemer C Nikseresht N Piatek JO Tsyrulin N Dalla Piazza B Kiefer K Klemke B Rosenbaum TF Aeppli G Gannarelli C Prokes K Podlesnyak A Strässle T Keller L Zaharko O Krämer KW Rønnow HM 《Science (New York, N.Y.)》2012,336(6087):1416-1419
Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF(4), establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field H(c|| = 4.0 ± 0.1 kilo-oersteds. We discovered non-mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h(4) universality class; in accord with this, the quantum phase transition at H(c) exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations. 相似文献
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PC Sereno AL Beck DB Dutheil B Gado HCE Larsson GH Lyon JD Marcot OWM Rauhut RW Sadleir CA Sidor DD Varricchio GP Wilson JA Wilson 《Science (New York, N.Y.)》1998,282(5392):1298-1302
Fossils discovered in Lower Cretaceous (Aptian) rocks in the Tenere Desert of central Niger provide new information about spinosaurids, a peculiar group of piscivorous theropod dinosaurs. The remains, which represent a new genus and species, reveal the extreme elongation and transverse compression of the spinosaurid snout. The postcranial bones include blade-shaped vertebral spines that form a low sail over the hips. Phylogenetic analysis suggests that the enlarged thumb claw and robust forelimb evolved during the Jurassic, before the elongated snout and other fish-eating adaptations in the skull. The close phylogenetic relationship between the new African spinosaurid and Baryonyx from Europe provides evidence of dispersal across the Tethys seaway during the Early Cretaceous. 相似文献
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