The effect of natural flow of aquifers and associated dispersion on the onset of buoyancy‐driven convection in a saturated porous medium

Carbon dioxide injection into deep saline aquifers is an important option for managing CO₂ emissions. Injected CO₂ dissolves into formation brines from above, increasing brine density and creating an unstable hydrodynamic state favorable for natural convection. Long‐term buoyancy‐driven flow of high‐density CO₂‐saturated brine leads to faster trapping through improved dissolution and can reduce the risk of CO₂ leakage from storage sites. We investigate the role of natural flow of aquifers and associated dispersion on the onset of convection. A linear stability analysis of a transient concentration field in a laterally infinite, horizontal, and saturated porous layer with steady horizontal flow is presented. The layer is subjected to a sudden rise in CO₂ concentration from the top and is closed from the bottom. Solution of the stability equations is obtained using a Galerkin technique and the resulting equations are integrated numerically. We found simple scaling relationships that follow t_Dc～60(1 + Pe_T)Ra^‐2 for the onset time of convection and a～0.05Ra/(1 + Pe_T) for the wavenumber of the initial instabilities. Results reveal that transverse dispersion increases the time to onset of convection for the entire range of Ra. Furthermore, transverse dispersion decreases the critical wavenumber of the instabilities. These results facilitate screening candidate sites for geological CO₂ storage. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Determination of picomolar silver concentrations by differential pulse anodic stripping voltammetry at a carbon paste electrode modified with phenylthiourea-functionalized high ordered nanoporous silica gel

This study introduces the design of an anodic stripping voltammetric (ASV) method for the silver ion determination at a carbon paste electrode (CPE), chemically modified with phenylthiourea-nanoporous silica gel (Tu-SBA-15-CPE). The electroanalytical pro includes two steps: preconcentration of metal ions at an electrode surface, followed by quantification of the accumulated species by differential pulse anodic stripping voltammetric methods. Factors affecting the performance of the anodic stripping were investigated, including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The most sensitive and reliable electrode contained 10% Tu-SBA-15 and 90% carbon paste. The accumulation potential and time were set at, −200 mV and 300 s, respectively, and the scan rate at 50 mV s⁻¹ in the scan range of −200 to 700 mV. The resulting electrode demonstrated a linear response over range of silver ion concentration of 8.0-80 pmol/L with detection limit (S/N = 3) of 5 pmol/L. The prepared electrodes were used for the silver determination in sea and tap water samples and very good recovery results were obtained. The accuracy was assessed through recovery experiments and independent analysis by graphite furnace atomic absorption spectrometry.     

Effects of yoghurt butter oils on rat plasma lipids,haematology and liver histology parameters in a 150‐day study

Although yoghurt butter oil as a fermented dairy product is widely consumed in several countries, its metabolic effects have not been fully elucidated. In this study, male Wistar rats were treated with standard diet, standard diet enriched with 10% or 20% (W/W) of either cow yoghurt butter oil (CYBO), sheep yoghurt butter oil (SYBO) or cottonseed oil (COT) for 20 weeks. Treatment of rats with CYBO or SYBO (at both concentrations) did not significantly influence haematological parameters, plasma lipids and liver histological structure. However, in contrast to popular belief, COT treatment at the higher dose induced leukocytosis, dyslipidaemia and liver steatosis.     

A novel compound fast fractional integral sliding mode control and adaptive PI control of a MEMS gyroscope

Microsystem Technologies - This study considers a novel compound fast fractional integral sliding mode control and adaptive PI control (APIFFOISMC) of a MEMS gyroscope. MEMS gyroscope has been...     

Stochastic collocation-based nonlinear analysis of concrete bridges with uncertain parameters

This paper focuses on the stochastic response of concrete bridges considering uncertainty in bearing and abutment stiffness. A multi-span simply supported bridge with concrete girders is selected. A 3D-dimensional model is prepared, and nonlinear response history analyses are performed. For the numerical dynamic simulation, the non-sampling stochastic method based on generalized polynomial chaos (gPC) expansion is utilised. The uncertain parameters include the vertical and shear stiffness of bearings and the lateral stiffness of abutments are presented by the truncated gPC expansions. Furthermore, the system response such as base shear, acceleration, velocity and displacement in different columns is presented by gPC expansion with unknown deterministic coefficients. The stochastic Galerkin projection is employed to calculate a set of deterministic equations. A non-intrusive solution, as a set of collocation points, determines the unknown gPC coefficients of the system response and the results are compared with Monte Carlo simulations. The key advantage of spectral discretization is the combination of the mentioned method with the spatial discretization, e.g. finite element model. This study also emphasises the accuracy in results and time efficiency of the proposed non-sampling method for uncertainty quantification of stochastic systems comparing to sampling procedure (e.g. Monte Carlo simulation).     

Barium promoted manganese oxide catalysts in low-temperature methane catalytic combustion

In this study, a series of BaO-MnO_x mixed oxide catalysts were synthesized by the mechanochemical method and employed in lean methane catalytic combustion (MCC) at low temperatures. The synthesized catalysts were characterized by XRD, BET, TGA, FT-IR, H₂-TPR, O₂-TPD, and FESEM analyses. The results indicated that the 10 wt% BaO-MnO_x catalyst with a BET surface area of 25 m² g^?1 possessed the best catalytic performance. The higher activity of the 10 wt% BaO-MnO_x catalyst was due to the higher ability to supply oxygen through the components during the MCC process. The light-off temperature corresponding to 50% of the methane conversion was about 330 °C, which was about 50 °C lower than the pure MnO_x. Moreover, for the BaO(10)-MnO_x catalyst, the 10 and 90% of methane conversion temperatures were about 305 and 427 °C, respectively. Also, the 10 wt% BaO-MnO_x catalyst exhibited high catalytic stability under dry feed condition at 450 °C for 50 h. Furthermore, the influence of various parameters such as calcination temperature, feed ratio, GHSV, pretreatment condition, and presence of water vapor in the feedstock was studied on the catalytic performance.     

A High Voltage Line Driver for Subscriber Loop Interfaces in a Low Voltage Submicron BiCMOS Technology

This paper presents a 30 V line driver for short loop subscriber line interface circuit applications. The high voltage line drivers was implemented in a low-voltage 0.8 m BiCMOS process using 30 V extended-drain MOS transistors, fully compatible with the low voltage technology. Using a Quasi-Current Mirror architecture for the output stage, the line driver is capable of delivering more than 30 mA current into the lines with an idle current as low as 1 mA, satisfying the short loop requirements. With less than 0.24 mm² area, the circuit can be easily integrated with low-voltage circuitry on a single chip.