A hybrid approach to computing electrostatic forces in fluidized beds of charged particles

In particulate flow devices particles acquire electric charge through triboelectric charging, and resulting electrostatic forces can alter hydrodynamics. To capture this effect, the electrostatic force acting on individual particles in the device should be computed accurately. Electrostatic force is calculated using a hybrid approach consisting of: (1) long‐range contributions from an Eulerian electric field solved using the Poisson equation (2) short‐range contributions calculated using a truncated pairwise sum and (3) a correction to avoid double counting. Euler‐Lagrange simulation of flows incorporating this hybrid approach reveals that bed height oscillations in small fluidized beds of particles with monopolar charge decreases with increasing charge level, which is related to lateral segregation of particles. A ring‐like layer of particles, reported in experimental studies, forms at modestly high charge levels. Beds with equal amounts of positively and negatively charged particles are fluidized in a manner similar to uncharged particles. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2282–2295, 2016     

Electrical impedance tomography problem with inaccurately known boundary and contact impedances

In electrical impedance tomography (EIT) electric currents are injected into a body with unknown electromagnetic properties through a set of contact electrodes at the boundary of the body. The resulting voltages are measured on the same electrodes and the objective is to reconstruct the unknown conductivity function inside the body based on these data. All the traditional approaches to the reconstruction problem assume that the boundary of the body and the electrode-skin contact impedances are known a priori. However, in clinical experiments one usually lacks the exact knowledge of the boundary and contact impedances, and therefore, approximate model domain and contact impedances have to be used in the image reconstruction. However, it has been noticed that even small errors in the shape of the computation domain or contact impedances can cause large systematic artefacts in the reconstructed images, leading to loss of diagnostically relevant information. In a recent paper (Kolehmainen , 2006), we showed how in the 2-D case the errors induced by the inaccurately known boundary can be eliminated as part of the image reconstruction and introduced a novel method for finding a deformed image of the original isotropic conductivity using the theory of TeichmÜller mappings. In this paper, the theory and reconstruction method are extended to include the estimation of unknown contact impedances. The method is implemented numerically and tested with experimental EIT data. The results show that the systematic errors caused by inaccurately known boundary and contact impedances can efficiently be eliminated by the reconstruction method.      

Triboelectric charging of monodisperse particles in fluidized beds

To investigate the interplay between particle charging and hydrodynamics in fluidized beds, models for triboelectric charging and electrostatic forces were built into a computational fluid dynamics‐discrete element method model. Charge transfer was governed by the difference in effective work function between contacting materials as well as the electric field at the point of contact. Monodisperse particles were fluidized with an effective work function difference between the particles and the conducting walls. For smaller work function differences, hydrodynamics were not changed significantly as compared with an uncharged case. In these simulations, the average charge saturated at a value much lower than the value anticipated based on the work function difference, and a unimodal distribution of charges was observed. For larger work function differences, particles stuck to walls and bed height oscillations due to slugging were less pronounced. For these cases, a bimodal distribution of charges emerged due to effects from strong electric fields. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1872–1891, 2017     

Mid‐infrared spectroscopy and multivariate curve resolution for analyzing human adipose tissue triacylglycerols

The aim of this study was to evaluate use of infrared spectroscopy for measuring adipose tissue triacylglycerols (TAGs) with analysis by multivariate curve resolution (MCR). The mid‐infrared spectrum was measured with an attenuated total reflection accessory from a lipid droplet pressed from adipose tissue. The obtained spectra were characteristic of pure TAG spectra and water and protein contamination could be easily identified from specific spectral regions. MCR analysis of the olefinic (?C? H) stretch (3006 cm^?1), resolved the different contributions of monounsaturated (MUFA) and polyunsaturated (PUFA) double bonds. Similar MCR analysis of the trans (HC?CH? ) region (966 cm^?1), resolved the differing contributions of isolated trans isomers (transFA) and CLA. The PUFA double bond content of 16 subjects was negatively correlated with concentrations of serum total cholesterol R = ?0.498 (p = 0.050) and triacylglycerols R = ?0.609, (p = 0.016). The transFA content exhibited a negative, although non‐significant, correlation to high‐density lipoprotein (HDL)‐cholesterol (R = ?0.483, p = 0.068). The present study shows that MCR analysis of adipose tissue TAG infrared spectra can be used to estimate differences in the fatty acid (FA) profiles in population studies. Infrared spectroscopy in combination with MCR provides a robust method for assessing a FA profile of human adipose tissue. Practical applications: This study has highlighted the use of MCR to enhance the information obtained from infrared spectra. This new approach provides a robust method for assessing a FA profile of human adipose tissue lipids.     

Extracellular enzyme activities and nutrient availability during artificial groundwater recharge

Natural organic matter (NOM) removal is the main objective of artificial groundwater recharge (AGR) for drinking water production and biodegradation plays a substantial role in this process. This study focused on the biodegradation of NOM and nutrient availability for microorganisms in AGR by the determination of extracellular enzyme activities (EEAs) and nutrient concentrations along a flow path in an AGR aquifer (Tuusula Water Works, Finland). Natural groundwater in the same area but outside the influence of recharge was used as a reference. Determination of the specific α-d-glucosidase (α-Glu), β-d-glucosidase (β-Glu), phosphomonoesterase (PME), leucine aminopeptidase (LAP) and acetate esterase (AEST) activities by fluorogenic model substrates revealed major increases in the enzymatic hydrolysis rates in the aquifer within a 10 m distance from the basin. The changes in the EEAs along the flow path occurred simultaneously with decreases in nutrient concentrations. The results support the assumption that the synthesis of extracellular enzymes in aquatic environments is up and down regulated by nutrient availability. The EEAs in the basin sediment and pore water samples (down to 10 cm) were in the same order of magnitude as in the basin water, suggesting similar nutritional conditions. Phosphorus was likely to be the limiting nutrient at this particular AGR site. Furthermore, the extracellular enzymes functioned in a synergistic and cooperative way.     

Simultaneous estimation of spatially distributed thermal conductivity,heat capacity and surface heat transfer coefficient in thermal tomography

In thermal tomography, the thermal properties of a target are estimated as spatially distributed parameters based on non-invasive measurements of surface temperatures. In the measurement setup, the target is sequentially heated at different source locations and the induced temperature evolutions are measured at several measurement locations on the surface. In [V. Kolehmainen, J. Kaipio, H. Orlande, Reconstruction of thermal conductivity and heat capacity using a tomographic approach, Int. J. Heat Mass Transfer 50 (25–26) (2007) 5150–5160], it was demonstrated with simulations that simultaneous estimation of spatially distributed thermal conductivity and volumetric heat capacity from transient boundary data is feasible when the boundary heat flux from the target to the surrounding medium is known all over the target boundary. In this article, we extend the computational methods towards the more practical setup of imaging targets, where the boundary heat flux from the target to the surrounding medium is not known. We model the surface heat transfer coefficient as a spatially distributed parameter on the target boundary and estimate it simultaneously with the spatially distributed thermal conductivity and volumetric heat capacity using the statistical (Bayesian) inversion framework. The feasibility of the approach is evaluated with simulations.     

点光源的亮度表象

汽车里照明设备的要求通常通过如光强等参数来定义。反之,对信号灯的感知则由信号灯的亮度决定。为了引入新的光源(如LED)必须考虑一个新的因素———亮度的均匀度。1测量任务本实验中以刹车灯和车尾位置灯为例,在实验室和实际交通场景中对不同信号灯进行研究。图1举例说明了具     

Computational calibration method for optical tomography

We propose a computational calibration method for optical tomography. The model of the calibration scheme is based on the rotation symmetry of source and detector positions in the measurement setup. The relative amplitude losses and phase shifts at the optic fibers are modeled by complex-valued coupling coefficients. The coupling coefficients can be estimated when optical tomography data from a homogeneous and isotropic object are given. Once these coupling coefficients have been estimated, any data measured with the same measurement setup can be corrected for the relative variation in the data due to source and detector losses. The final calibration of the data for the source and detector losses and the source calibration between the data and the forward model are obtained as part of the initial estimation for reconstruction. The calibration method was tested with simulations and measurements. The results show that the coupling coefficients of the sources and detectors can be estimated with good accuracy. Furthermore, the results show that the method can significantly improve the quality of reconstructed images.     

Effects of α-tocopherol and ascorbyl palmitate on the isomerization and decomposition of methyl linoleate hydroperoxides

In order to study antioxidant action on lipid hydroperoxide decomposition, the effects of α-tocopherol (TOH) and ascorbyl palmitate on the decomposition rate and reaction sequences of 9- and 13-cis,trans methyl linoleate hydroperoxide (cis,trans ML-OOH) decomposition in hexadecane were studied at 40°C. Decomposition of cis,trans ML-OOH as well as the formation and isomeric configuration of methyl linoleate hydroxy and ketodiene compounds were followed by high-performance liquid chromatographic analysis. TOH effectively inhibited the decomposition of ML-OOH. The decomposition rate was two times slower at 0.2 mM and more than 10 times slower at 2 and 20 mM of TOH. Ascorbyl palmitale (0.2, 2, and 20 mM) slightly accelerated the decomposition of ML-OOH. Both compounds had an effect on the reaction sequences of ML-OOH decomposition. At high levels TOH inhibited the isomerization of cis,trans ML-OOH to trans,trans ML-OOH through peroxyl radicals and increased the formation of hydroxy compounds. Further, the majority of the hydroxy and ketodiene compounds formed had a cis,trans configuration, indicating that cis,trans ML-OOH decomposed through alkoxyl radicals without isomerization. These results suggest that when inhibiting the decomposition of hydroperoxides, TOH can act as a hydrogen atom donor to both peroxyl and alkoxyl radicals. In the presence of ascorbyl palmitate, cis,trans ML-OOH decomposed rapidly but without isomerization. In contrast to TOH, the majority of hydroxy compounds were cis,trans, but the ketodiene compounds were trans,trans isomers. This indicates that ascorbyl palmitate reduced cis,trans ML-OOH to the corresponding hydroxy compounds. However, the simultaneous formation of trans,trans ketodiene compounds suggests that ML-OOH decomposition, similar to the control sample, also occurred in these samples. Thus, under these experimental conditions, the reduction of ML-OOH to more stable hydroxy compounds did not occur to an extent significant enough to inhibit the radical chain reactions of ML-OOH decomposition.