Effect of Damping on the Natural Frequencies of Linear Dynamic Systems

An analysis is presented of the effect of weak damping on the natural frequencies of linear dynamic systems. It is shown that the highest natural frequency is always decreased by damping, but the lower natural frequencies may either increase or decrease, depending on the form of the damping matrix

Glutamate cycling may drive organic anion transport on the basal membrane of human placental syncytiotrophoblast

The organic anion transporter OAT4 (SLC22A11) and organic anion transporting polypeptide OATP2B1 (SLCO2B1) are expressed in the basal membrane of the placental syncytiotrophoblast. These transporters mediate exchange whereby uptake of one organic anion is coupled to efflux of a counter-ion. In placenta, these exchangers mediate placental uptake of substrates for oestrogen synthesis as well as clearing waste products and xenobiotics from the fetal circulation. However, the identity of the counter-ion driving this transport in the placenta, and in other tissues, is unclear. While glutamate is not a known OAT4 or OATP2B1 substrate, we propose that its high intracellular concentration has the potential to drive accumulation of substrates from the fetal circulation. In the isolated perfused placenta, glutamate exchange was observed between the placenta and the fetal circulation. This exchange could not be explained by known glutamate exchangers. However, glutamate efflux was trans-stimulated by an OAT4 and OATP2B1 substrate (bromosulphothalein). Exchange of glutamate for bromosulphothalein was only observed when glutamate reuptake was inhibited (by addition of aspartate). To determine if OAT4 and/or OATP2B1 mediate glutamate exchange, uptake and efflux of glutamate were investigated in Xenopus laevis oocytes. Our data demonstrate that in Xenopus oocytes expressing either OAT4 or OATP2B1 efflux of intracellular [14C]glutamate could be stimulated by conditions including extracellular glutamate (OAT4), estrone-sulphate and bromosulphothalein (both OAT4 and OATP2B1) or pravastatin (OATP2B1). Cycling of glutamate across the placenta involving efflux via OAT4 and OATP2B1 and subsequent reuptake will drive placental uptake of organic anions from the fetal circulation.<br/

Predicting and Controlling Resolution and Surface Finish of Ceramic Objects Produced by Stereodeposition Processes

Stereodeposition techniques are well suited for the Solid Freeform Fabrication of dense ceramic components. As opposed to forming a pattern in a particle bed or polymer bath, stereodeposition processes deposit material directly onto the previously created layer. The key to stereodeposition is a material's ability to be dispensed as a fluid, yet rapidly stiffen to hold the shape of the object. This is accomplished by either solidification of a thermoplastic binder upon cooling from a melt (Fused Deposition) or by polymerization of a binder (Reactive Stereodeposition). We are developing both techniques for the production of functional ceramic and engineering polymer objects. A key issue in developing a successful stereodeposition system is controlling the rate of bead transformation from liquid to solid. Control is critical to achieving high resolution and low surface roughness of the finished product, but is made complex by the large number of parameters involved. These include binder parameters (surface tension, gelling characteristics), slurry parameters (viscosity, particle loading and size distribution), and process parameters (deposition rate, temperature). Current efforts at the University of Arizona are focused on modeling and controlling the deposition and transformation of ceramic slurries used in the Reactive Stereodeposition process.Mechanical Engineerin

Offshore Conversion of Wind Power to Gaseous Fuels: Feasibility Study in a Depleted Gas Field

A proof-of-concept study is presented of a Power-to-Gas system that is located fully offshore. This paper analyses how such a system would perform if based at the depleted Kinsale Gas Field in the Celtic Sea Basin off the south coast of Ireland. An offshore wind farm is proposed as the power source for the system. Several conversion technologies are examined in detail in terms of resource efficiency, technological maturity, and platform area footprint, the aim being to ascertain their overall applicability to an offshore Power-to-Gas system. The technologies include proton exchange membrane electrolysers for electrolysis of water to release H2. Bipolar membrane electro-dialysis and electronic cation exchange module processes are also considered for the extraction of CO2 from seawater. These technologies provide the feedstock for the Sabatier process for the production of CH4 from H2 and CO2. Simulations of the end-to-end systems were carried out using Simulink, and it was found that the conversion of offshore wind power to hydrogen or methane is a technically feasible option. Hydrogen production is much closer to market viability than methane production, but production costs are too high and conversion efficiencies too low in both cases with present-day technology to be competitive with current wholesale natural gas prices