Effects of sulfate ligand on uranyl carbonato surface species on ferrihydrite surfaces

Understanding uranium (U) sorption processes in permeable reactive barriers (PRB) are critical in modeling reactive transport for evaluating PRB performance at the Fry Canyon demonstration site in Utah, USA. To gain insight into the U sequestration mechanism in the amorphous ferric oxyhydroxide (AFO)-coated gravel PRB, U(VI) sorption processes on ferrihydrite surfaces were studied in 0.01 M Na(2)SO(4) solutions to simulate the major chemical composition of U-contaminated groundwater (i.e., [SO(4)(2-)] ~13 mM L(-1)) at the site. Uranyl sorption was greater at pH 7.5 than that at pH 4 in both air- and 2% pCO(2)-equilibrated systems. While there were negligible effects of sulfate ligands on the pH-dependent U(VI) sorption (<24 h) in both systems, X-ray absorption spectroscopy (XAS) analysis showed sulfate ligand associated U(VI) surface species at the ferrihydrite-water interface. In air-equilibrated systems, binary and mono-sulfate U(VI) ternary surface species co-existed at pH 5.43. At pH 6.55-7.83, a mixture of mono-sulfate and bis-carbonato U(VI) ternary surface species became more important. At 2% pCO(2), there was no contribution of sulfate ligands on the U(VI) ternary surface species. Instead, a mixture of bis-carbonato inner-sphere (38%) and tris-carbonato outer-sphere U(VI) ternary surface species (62%) was found at pH 7.62. The study suggests that the competitive ligand (bicarbonate and sulfate) coordination on U(VI) surface species might be important in evaluating the U solid-state speciation in the AFO PRB at the study site where pCO(2) fluctuates between 1 and 2 pCO(2)%.     

A double wall-ring geometry for interfacial shear rheometry

The rheological properties of complex fluid interfaces are of prime importance in a number of technological and biological applications. Whereas several methods have been proposed to measure the surface rheological properties, it remains an intrinsically challenging problem due to the small forces and torques involved and due to the intricate coupling between interfacial and bulk flows. In the present work, a double wall-ring geometry to measure the viscoelastic properties of interfaces in shear flows is presented. The geometry can be used in combination with a modern rotational rheometer. A numerical analysis of the flow field as a function of the surface viscoelastic properties is presented to evaluate the non-linearities in the surface velocity profile at a low Boussinesq number. The sensitivity of the geometry, as well as its applicability, are demonstrated using some reference Newtonian and viscoelastic fluids. Oscillatory and steady shear measurements on these reference complex fluid interfaces demonstrate the intrinsic sensitivity, the accuracy, and the dynamic range of the geometry when used in combination with a sensitive rheometer.     

Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

An integrated microfluidic device for influenza and other genetic analyses

An integrated microfluidic device capable of performing a variety of genetic assays has been developed as a step towards building systems for widespread dissemination. The device integrates fluidic and thermal components such as heaters, temperature sensors, and addressable valves to control two nanoliter reactors in series followed by an electrophoretic separation. This combination of components is suitable for a variety of genetic analyses. As an example, we have successfully identified sequence-specific hemagglutinin A subtype for the A/LA/1/87 strain of influenza virus. The device uses a compact design and mass production technologies, making it an attractive platform for a variety of widely disseminated applications.     

Chemical network algorithms for the risk assessment and management of chemical threats

A network of chemical threats: Current regulatory protocols are insufficient to monitor and block many short-route syntheses of chemical weapons, including those that start from household products. Network searches combined with game-theory algorithms provide an effective means of identifying and eliminating chemical threats. (Picture: an algorithm-detected pathway that yields sarin (bright red node) in three steps from unregulated substances.).     

Empirical correction of crosstalk in a low-background germanium γ–γ analysis system

The Pacific Northwest National Laboratory (PNNL) is currently developing a custom software suite capable of automating many of the tasks required to accurately analyze coincident signals within gamma spectrometer arrays. During the course of this work, significant crosstalk was identified in the energy determination for spectra collected with a new low-background intrinsic germanium (HPGe) array at PNNL. The HPGe array is designed for high detection efficiency, ultra-low-background performance, and sensitive γ–γ coincidence detection. The first half of the array, a single cryostat containing seven HPGe crystals, was recently installed into a new shallow underground laboratory facility. This update will present a brief review of the germanium array, describe the observed crosstalk, and present a straight-forward empirical correction that significantly reduces the impact of this crosstalk on the spectroscopic performance of the system.     

Field-induced anisotropy in concentrated systems of rigid particles and macromolecules

This paper presents experimental results on the use of spectroscopic optical polarimetry to study structure in dense systems of rigid particles and rigid polymer liquid crystals. These measurements probe microstructural anisotropy induced by the application of electric fields in the case of dense suspensions of rigid spheres, or flow fields in the case of polymer liquid crystals. It is demonstrated that conservative linear dichroism can measure moments of the particle pair distribution function in dense suspensions. In liquid crystals, the dichroism is a result of field-induced anisotropy in the defect structure of the material.     

Some experimental results on the development of Couette flow for non-Newtonian fluids

This paper reports some experimental results on the time development of a Couette flow following the start-up of shear flow using the technique of two-color flow birefringence. Measurements obtained on collagen solutions are consistent with two theoretical studies which predict that for some viscoelastic liquids, momentum is transferred from the moving Couette cell boundary to the interior of the fluid through a velocity wave propagating and reflecting between the cell boundaries. This non-Newtonian phenomenon, exhibited as an oscillatory response in the measured birefringence and orientation angle, is observed at shear rates above a critical value when the response time of the polymer solution approaches the flow development time in the Couette flow cell.