Magnetic properties of Yb2Mo2O7 and Gd2Mo2O7 from rare earth Mossbauer measurements

Using 170-Yb and 155-Gd Mossbauer measurements down to 0.03K, we have examined the semiconducting pyrochlore Yb2Mo2O7 where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd2Mo2O7 where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and 172-Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb2Mo2O7 and modest in Gd2Mo2O7. Magnetic irreversibilities occur at 17K in Yb2Mo2O7 and at 75K in Gd2Mo2O7 and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd2Mo2O7, we observe the steady state Gd hyperfine populations at 0.027K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic.Comment: 9 pages, 9 figure

Water flow between soil aggregates

Aggregated soils are structured systems susceptible to non-uniform flow. The hydraulic properties depend on the aggregate fabric and the way the aggregates are assembled. We examined the hydraulic behavior of an aggregate packing. We focused on conditions when water mostly flows through the aggregates, leaving the inter-aggregate pore space air-filled. The aggregates were packed in 3mm thick slabs forming a quasi two-dimensional bedding. The larger aggregates were wetted with water and embedded in smaller aggregates equilibrated at a lower water content. The water exchange between wet and drier aggregates was monitored by neutron radiography. The three-dimensional arrangement of the aggregates was reconstructed by neutron tomography. The water flow turned out to be controlled by the contacts between aggregates, bottle-necks that slow down the flow. The bottle-neck effect is due to the narrow flow cross section of the contacts. The water exchange was simulated by considering the contact area between aggregates as the key parameter. In order to match the observed water flow, the contact area must be reduced by one to two orders of magnitude relative to that obtained from image analysis. The narrowness of the contacts is due to air-filled voids within the contact

Water flow between soil aggregates

Aggregated soils are structured systems susceptible to non-uniform flow. The hydraulic properties depend on the aggregate fabric and the way the aggregates are assembled. We examined the hydraulic behavior of an aggregate packing. We focused on conditions when water mostly flows through the aggregates, leaving the inter-aggregate pore space air-filled. The aggregates were packed in 3mm thick slabs forming a quasi two-dimensional bedding. The larger aggregates were wetted with water and embedded in smaller aggregates equilibrated at a lower water content. The water exchange between wet and drier aggregates was monitored by neutron radiography. The three-dimensional arrangement of the aggregates was reconstructed by neutron tomography. The water flow turned out to be controlled by the contacts between aggregates, bottle-necks that slow down the flow. The bottle-neck effect is due to the narrow flow cross section of the contacts. The water exchange was simulated by considering the contact area between aggregates as the key parameter. In order to match the observed water flow, the contact area must be reduced by one to two orders of magnitude relative to that obtained from image analysis. The narrowness of the contacts is due to air-filled voids within the contact

MR fluoroscopy in vascular and cardiac interventions (review)

Vascular and cardiac disease remains a leading cause of morbidity and mortality in developed and emerging countries. Vascular and cardiac interventions require extensive fluoroscopic guidance to navigate endovascular catheters. X-ray fluoroscopy is considered the current modality for real time imaging. It provides excellent spatial and temporal resolution, but is limited by exposure of patients and staff to ionizing radiation, poor soft tissue characterization and lack of quantitative physiologic information. MR fluoroscopy has been introduced with substantial progress during the last decade. Clinical and experimental studies performed under MR fluoroscopy have indicated the suitability of this modality for: delivery of ASD closure, aortic valves, and endovascular stents (aortic, carotid, iliac, renal arteries, inferior vena cava). It aids in performing ablation, creation of hepatic shunts and local delivery of therapies. Development of more MR compatible equipment and devices will widen the applications of MR-guided procedures. At post-intervention, MR imaging aids in assessing the efficacy of therapies, success of interventions. It also provides information on vascular flow and cardiac morphology, function, perfusion and viability. MR fluoroscopy has the potential to form the basis for minimally invasive image–guided surgeries that offer improved patient management and cost effectiveness