The short-time rotational dynamics of colloidal silica tracer spheres in suspensions of rigid silica rods is investigated, using time-resolved phosphorescence anisotropy, as a function of tracer radius aT , rod volume fraction f, and the range k 21 of the double-layer repulsions between the like-charged rods and tracer spheres. A large tracer size aT and a small screening length k 21 appear to ...

A mathematical method has been developed by which the cerebral extraction fraction of oxygen (OEF) administered in a bolus can be quantitatively measured and compared with a previously established method by Mintun et al. Successive injection of three tracers are required: 15O-labeled O2 as a test tracer, a diffusible tracer as a reference tracer and also as a flow tracer, and a tracer for cereb...

Tracer-particles, massless particles that are advected throughout the flow domain, are an important factor in computational solutions. The utility of tracer-particles, which sample and report relevant solution data, is predicated upon an accurate advection algorithm. The objective of this research was to investigate the ability of existing techniques, physical-space and logical-space advection,...

Introduction Dynamic susceptibility contrast (DSC) MR perfusion is based on the indicator dilution theorem for non-diffusible tracers.[1,2] A common misconception is that tracer recirculation cannot occur in order to make use of the underlying theory (i.e., analysis of the tracer kinetics must be “firstpass”).[3-13] As a result, there have been a number of approaches suggested for removing trac...

The accurate modeling of cascades to unresolved scales is an important part of the tracer transport component of dynamical cores of weather and climate models. This paper aims to investigate the ability of the advection schemes in the National Center for Atmospheric Research’s Community Atmosphere Model version 5 (CAM5) to model this cascade. In order to quantify the effects of the different ad...

Geophysical turbulent fluids are characterized by the presence of organized energetic structures which control tracer transport and stirring, while enabling a tracer cascade down to the smallest scales. In order to understand the physical mechanisms involved in this turbulent tracer cascade, we focus on the dynamics underlying the formation of tracer gradients which are necessarily associated t...

People spend the majority of their time indoors and therefore the quality of indoor air is worthy of investigation; indoor air quality is affected by indoor sources of pollutants and from pollutants entering buildings from outdoors. In this study, unique perfluorocarbon tracers were released in five experiments at a 100 m and ~2 km distance from a large university building in Manchester, UK and...

The present study compares and quantitates both solvent drag and solute drag forces in a system with both heteropore and homopore membranes. It is shown that tracer solute permeability can be increased if solution flow or driver solute flux is in the direction of tracer diffusion. Either force can decrease tracer permeability if the force can decrease tracer permeability if the force is opposit...

The capability of using imperfect stochastic reduced-order models to capture crucial passive tracer statistics such as tracer energy spectrum, tracer intermittency, and eddy diffusivity is investigated. The passive scalar field is advected by a two-layer baroclinic turbulent flow which can generate various representative regimes in atmosphere and ocean. Much simpler and more tractable linear Ga...