Search results for "Impedance"
showing 10 items of 432 documents
Influence of the scalp thickness on the intracranial contribution to rheoencephalography
2004
In spite of the great efforts made by the scientific community, up to now there is no agreement about the rheoencephalography (REG) capability to reflect cerebral blood flow (CBF). Moreover, a standard procedure and the optimal electrode arrangement have not been established yet. In a previous study, we found, using a classical four-shell spherical model of the head and solving it by numerical methods that, theoretically, there could exist an electrode arrangement to register an REG II free of extracranial contribution. In this paper, we have studied the influence of scalp thickness on the intracranial contribution to REG II. The study has been performed by solving the head model, using in …
Effect of temperature on the passive state of Alloy 31 in a LiBr solution: Passivation and Mott-Schottky analysis
2015
The passive behaviour of Alloy 31, a highly-alloyed austenitic stainless steel (UNS N08031), has been investigated in a LiBr heavy brine (700 g/l) at different temperatures using potentiostatic polarisation and Mott-Schottky analysis. Cation vacancies have been found to be the dominant defect in the passive films formed on Alloy 31. An increase in temperature enhanced the generation of cation vacancies at the film/solution interface and raised the steady-state passive current density. The density of defects within the passive film also increased significantly with temperature, making the film more conductive and less protective against localised attacks.
Litija sāļu – imidazolija jonu šķidrumu elektrolītu jonu vadītspēja un termiskā stabilitāte
2016
Litija sāļu - imidazolija jonu šķidrumu elektrolītu jonu vadītspēja un termiskā stabilitāte Singatulovs J., zinātniskais vadītājs Dr. chem., doc. Vaivars G. bakalura darbs, 38 lappuses, 21 attēli, 25 literatūras avoti. Latviešu valodā. Darbā tika sintezēti divi jonu šķidrumi: 1-butil-3-metilimidazolija dimetilfosfāts un 1,3-dimetilimidazolija dimetilfosfāts. Vadītspēja un elektroķīmiskā stabilitāte atkarībā no temperatūras tika noteiktas tīriem jonu šķidrumiem un jonu šķidrumu - litija nitrāta elektrolītiem. Tika izstrādāta vadītspējas atkarības no temperatūras noteikšanas metodika. Ar impedances spektroskopiju tika noteikti vadītspēju ietekmējoši faktori.
SPĒĒK kompozītmembrānu īpašību pētījumi pielietojumam CO2 elektroķīmiskajos pārveidotājos
2019
Šajā darbā ir veikta sulfonēta poli(ēter ēter ketona) (SPĒĒK) sintēze ar sulfonēšanas pakāpēm 0,87; 0,82; 0,74. No iegūtā SPĒĒK tika izgatavotas kompozītmembrānas ar atšķirīgu aktīvās ogles saturu: 0; 0,15; 0,3; 0,5; 0,6; 0,8; 1,0; 2,0; 3,0 %. Iegūto membrānu īpašības tika izpētītas ar dažādām metodēm. Kompozītmembrānām tika noteikta ūdens uzņemšana un uzbriešanas pakāpe. Impedances analīzi veica ar diferenciālo un vienas membrānas metodi. Tika pētītas arī virsmas dzeta potenciāla izmaiņas. Kompozītmembrānu termiskās īpašības analizēja ar termogravimetrisko metodi. Membrānu virsmas morfoloģiju pētīja ar skenējošās elektronu mikroskopijas metodi. SPĒĒK membrāna tika notestētas CO2 elektroķīm…
An approach to As(III) and As(V) bioavailability studies with Caco-2 cells
2005
Foods and drinking water are the main sources of human exposure to inorganic arsenic [As(III) and As(V)]. After oral ingestion, the intestinal epithelium is the first barrier to absorption of these species. A human intestinal cell line (Caco-2) was used to evaluate cell retention and transport of As(III) (15.6-156.0 microM) and/or As(V) (15.4-170.6 microM). Cell monolayer integrity, cell viability, membrane damage and effects on cell metabolism were evaluated. Only the highest concentrations assayed [As(III): 156.0 microM; As(V): 170.6 microM] produced a cytotoxic effect with different cellular targets: As(III) altered the permeability of tight junctions, and As(V) caused uncoupling of the …
Odorant binding changes the electrical properties of olfactory receptors at the nanoscale
2021
Olfactory receptors (ORs) comprise the largest multigene family in the vertebrates. They belong to the class A (rhodopsin-like) family of G protein-coupled receptors (GPCRs), which are the most abundant membrane proteins, having widespread, significant roles in signal transduction in cells, and therefore, they are a major pharmacological target. Moreover, ORs displayed high selectivity and sensitivity towards odorant detection, a characteristic that raised the interest for developing biohybrid sensors based on ORs for the detection of volatile compounds. The transduction of odorant binding into cellular signaling by ORs is not well understood and knowing its mechanism would enable developin…
Studying the Neurovascular Unit: An Improved Blood–Brain Barrier Model
2009
The blood–brain barrier (BBB) closely interacts with the neuronal parenchyma in vivo. To replicate this interdependence in vitro, we established a murine coculture model composed of brain endothelial cell (BEC) monolayers with cortical organotypic slice cultures. The morphology of cell types, expression of tight junctions, formation of reactive oxygen species, caspase-3 activity in BECs, and alterations of electrical resistance under physiologic and pathophysiological conditions were investigated. This new BBB model allows the application of techniques such as laser scanning confocal microscopy, immunohistochemistry, fluorescent live cell imaging, and electrical cell substrate impedance se…
Nanoscale Mapping of the Physical Surface Properties of Human Buccal Cells and Changes Induced by Saliva
2019
International audience; The mucosal pellicle, also called salivary pellicle, is a thin biological layer made of salivary and epithelial constituents, lining oral mucosae. It contributes to their protection against microbiological, chemical, or mechanical insults. Pellicle formation depends on the cells’ surface properties, and in turn the pellicle deeply modifies such properties. It has been reported that the expression of the transmembrane mucin MUC1 in oral epithelial cells improves the formation of the mucosal pellicle. Here, we describe an approach combining classical and functionalized tip atomic force microscopy and scanning microwave microscopy to characterize how MUC1 induces change…
Electric field enhanced water dissociation at the bipolar membrane junction from ac impedance spectra measurements
1998
Abstract Preliminary experimental results of the ac impedance spectra of a bipolar ion-exchange membrane are reported and interpreted on the basis of a previous theoretical model based on the Nernst–Planck/Poisson equations. It is shown that the experiments can provide valuable electrochemical information about the bipolar junction structure and the electric-field enhanced water dissociation phenomenon that occurs at this junction, although the high number of unknown parameters involved makes it difficult to obtain accurate values for the parameters characteristic of this phenomenon.
Electrical impedance spectroscopy of ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate (ECOENG™ 110)
2011
Abstract Ionic liquid “ECOENG™ 110”, a promising electrolyte for electrochemical devices, was investigated by impedance spectroscopy. Metallic electrodes (Pt, Cu, Ag, and Mo) as well as carbon were used for the electrochemical characterization. The dependences of the real and imaginary impedance, polarization resistance and electrochemical capacity of the double layer on the electrode potential were investigated using electrical equivalent circuits of R1(QR2) and R1[Q(R2W)] types.