Comment on AC frequency characteristics of coplanar impedance sensors as design parameters by Jongin Hong, Dae Sung Yoon, Sung Kwan Kim, Tae Song Kim, Sanghyo Kim, Eugene Y. Pak and Kwangsoo No, Lab Chip, 2005, 5, 270

In their article, ‘‘AC frequency characteristics of coplanar impedance sensors as design parameters’’, Hong et al.1 present an analytical model for the calculation of the resistance between two electrodes in a microchannel. However, their measurements fit poorly with their suggested model, and they attribute the discrepancies to electrode thickness and a ‘fringing effect’. In this note we show that the discrepancies are due to the neglected channel height in their model, and that by including two additional transforma ions, the resistance between tw

Grey wolf genomic history reveals a dual ancestry of dogs

The grey wolf (Canis lupus) was the first species to give rise to a domestic population, and they remained widespread throughout the last Ice Age when many other large mammal species went extinct. Little is known, however, about the history and possible extinction of past wolf populations or when and where the wolf progenitors of the present-day dog lineage (Canisfamiliaris) lived(1-8). Here we analysed 72 ancient wolf genomes spanning the last 100,000 years from Europe, Siberia and North America. We found that wolf populations were highly connected throughout the Late Pleistocene, with levels of differentiation an order of magnitude lower than they are today. This population connectivity allowed us to detect natural selection across the time series, including rapid fixation of mutations in the gene IFT8840,000-30,000 years ago. We show that dogs are overall more closely related to ancient wolves from eastern Eurasia than to those from western Eurasia, suggesting a domestication process in the east. However, we also found that dogs in the Near East and Africa derive up to half of their ancestry from a distinct population related to modern southwest Eurasian wolves, reflecting either an independent domestication process or admixture from local wolves. None of the analysed ancient wolf genomes is a direct match for either of these dog ancestries, meaning that the exact progenitor populations remain to be located.Peer reviewe

Origins and genetic legacy of prehistoric dogs

Dogs were the first domestic animal, but little is known about their population history and to what extent it was linked to humans. We sequenced 27 ancient dog genomes and found that all dogs share a common ancestry distinct from present-day wolves, with limited gene flow from wolves since domestication but substantial dog-to-wolf gene flow. By 11,000 years ago, at least five major ancestry lineages had diversified, demonstrating a deep genetic history of dogs during the Paleolithic. Coanalysis with human genomes reveals aspects of dog population history that mirror humans, including Levant-related ancestry in Africa and early agricultural Europe. Other aspects differ, including the impacts of steppe pastoralist expansions in West and East Eurasia and a near-complete turnover of Neolithic European dog ancestry

Chemical-Looping Combustion of Solid Fuels — Operational Experiences in 100kW Dual Circulating Fluidized Bed System

AbstractResults from the first year of operation of a 100kW chemical-looping combustor for solid fuels are presented. Gas measurements showed the presence of unconverted gas from the fuel reactor. With bituminous coal the gas conversion was up to 84%, and significantly higher with low-volatile fuel and char. The gas conversion was strongly dependent on solids inventory in the fuel reactor. A CO2 capture up to 98-99% was reached.The unit worked well and operation was stable. The operation shows the viability of this technology, which has unique potential for breakthrough in cost and energy penalty of CO2 capture

Chemical-looping combustion of solid fuels – Design and operation of a 100 kW unit with bituminous coal

Chemical-looping combustion is a novel technology with inherent capture of CO2 when burning gaseous, liquid or solid fuels. By using two interconnected fluidised beds with a bed material capable of transferring oxygen from air to the fuel, a nitrogen-free stream of CO2 can be obtained with no direct efficiency loss. Here, approximately 20 h of experimental results from a 100 kW unit for solid fuels are presented. Using ilmenite oxygen carrier and a Colombian bituminous coal (Cerrejón coal), five periods of operation were conducted at 940-980°C in the fuel reactor for 1.5-6 h. The unit worked well and stable operation was easily reached. The investigation involves variations of operational parameters to see the effect on performance. It was shown that an oxygen demand below 16% and a CO2 capture above 99% can be reached during extended periods at close to optimal conditions. By replacing the steam fluidisation with inert nitrogen, the influence of the carbon stripper with respect to the steam gasification was tested. It was shown that CO2 capture decreased from 98.5% to 95.5% without the gas conversion provided by the carbon stripper. Finally, pressure profiles from two experiments are presented and compared to a pressure profile predicted from cold-flow model experiments. The work shows the first extended operation of chemical-looping combustion with solid fuels in the 100 kW scale and the operational experience gives strong indication that the process is viable

Analytical expression for electric filed between two facing strip electrodes in microchannels

An analytical solution is presented for the electric field between two facing strip electrodes situated in a microchannel, as frequently used in impedance cytometry applications. The measured change in resistance as induced by a 5 mm bead moving through the microchannel is in good agreement with the model. It is also demonstrated that the centre sensitivity is maximal for an electrode width equal to ~56% of the channel height

Operation of a 100 kW chemical-looping combustor with Mexican petroleum coke and Cerrejón coal

This study describes the design and operation of a 100 kW chemicallooping combustor for solid fuels. Six experiments of continuous operation, varying between 8 and 32 minutes in length, have been conducted. The fuels investigated were a Mexican petroleum coke and a bituminous coal from Cerrejón in Colombia. Overall, it was found that operation was stable and loss of char to the air reactor was small, meaning that the CO2 capture efficiency was high (up to 90% at temperatures close to 950°C in the fuel reactor). Gas concentration measurements showed the presence of unconverted CO, H2 and CH4 corresponding to an oxygen demand of around 20%, depending on the fuel reactor temperature. In addition, a residence-time analysis was conducted from a batch experiment, enabling an estimation of the mass flow of oxygen carriers through the system using the riser pressure drop in the air reactor

Analytical model of gas conversion in a 100 kW chemical-looping combustor for solid fuels—Comparison with operational results

This study analyses results from a 100 kWth chemical-looping combustor, consisting of two interconnected circulating fluidised-bed reactors, for use with solid fuels. The fuel reactor has an internal circulation loop, whereas the circulation loop of the air reactor leads to the fuel reactor. Operation of the unit is flexible, as it is possible to vary key operational parameters in a wide range to investigate the response in system behaviour and performance. Results from a previous study have shown that by varying the fluidisation velocity in three different sections of the unit, a phenomenological relation between gas conversion, fuel reactor bed inventory and global solids circulation can be found. This relation is here studied in more depth, clearly indicating that high gas conversion can only be reached if the fuel reactor bed inventory is large. Furthermore, an analytical model describing gas conversion is applied to the fuel reactor. It is shown that the model predicts the effect of variations in solids inventory well. Corrections to the model based on circulation, temperature and time of operation were assessed, but the effect was small under the present conditions. Data for the analysis are compiled from four operational periods, ranging from 2.4 h to 5.9 h of continuous fuel feeding. The oxygen carrier used was ilmenite, and the fuel a bituminous coal from Colombia