Search results for "element"
showing 10 items of 13601 documents
Metālu biopieejamība un imobilizācija barības ķēdes segmentā augsne-augs
2015
Maģistra darba mērķis – izvērtēt vidi piesārņojošo metālisko elementu mobilitāti un biopieejamību barības ķēdes segmentā augsne-augs atkarībā no dažādu augsnes piedevu, piemēram, sapropelis, māls un arī uz sapropeļa un māla bāzes veidotu piedevu pievienošanas augsnēm. Sapropeļa kā augsnes piedevas ietekme uz augu attīstību tika vērtēta pēc dīgšanas un augu agrīnās attīstības testiem, izmantojot trīs kultūraugu (gurķu, tomātu, ganību airenes) sēklas. Darbā tika novērtēta Zn, Pb, Cd un Cu imobilizācija un biopieejamība, izmantojot augsnes ūdens un NH4NO3 ekstrakciju metodes. Augsnes piedevu faktiskā ietekme uz elementu biopieejamību tika noteikta piesārņotā augsnē ar pievienotām piedevām kult…
Protonus vadošu uz Nafion polimēra balstītu kompozītmateriālu sintēze un pētījumi izmantošanai degvielas šūnās
2015
Kurināmā elementi izraisa lielu interesi, jo ļauj pārveidot degvielu (piemēram, ūdeņradi, metanolu, metānu) bez Karno cikla ierobežojumiem, sasniedzot augstu lietderības koeficientu. Polimēru elektrolīts ļauj izveidot kurināmā elementu, kas strādā pie pietiekami zemām temperatūrām, optimālām izmantošanai portatīvo enerģijas avotu un autotransporta jomās. Izstrādājot šo darbu, uz protonus vadošā polimēra (Nafions) bāzes sintezēti jauni paraugi, pievienojot polimēram oksīdus, kas ļauj uzlabot materiāla spējas vadīt protonus pie paaugstinātām temperatūrām un relatīvā mitruma zem 100%. Tika veikti sintezēto materiālu fizikālķīmisko īpašību pētījumi, tādi kā: termogravimetrijas analīze, impedanc…
Piezoelectric bimorph response with imperfect bonding conditions
2008
The effect of the finite stiffness bonding between the piezoelectric plies of bimorph devices has been investigated. A boundary integral formulation for piezoelasticity, based on a multidomain technique with imperfect interface conditions, has been developed. The imperfect interface conditions between the piezoelectric layers are described in terms of linear relations between the interface tractions, in normal and tangential directions, and the respective discontinuity in displacements. Continuity of the electric potential at the interface is also assumed and an iterative procedure is implemented to avoid interface interference. Numerical analysis has been performed on bimorph configuration…
Characterization of Rabbit Mesenchymal Cell Attachment on Calcium Phosphate Surface
2014
In the current study, the effect of three different treated surfaces of hydroxyapatite and β-tricalcium phosphate on mesenchymal cell attachment has been investigated. Calcium phosphate powders have been synthesized, uniaxially pressed, polished and sintered. Mesenchymal cells have been seeded onto unpolished, polished and polished-thermally etched ceramic samples. The ceramic samples have been characterized by XRD, FTIR and SEM. Results have shown that the best cell attachment and morphology are on the unpolished surface indicating that relatively rough surface is better for cell application.
Optimal Heating of an Indoor Swimming Pool
2020
This work presents the derivation of a model for the heating process of the air of a glass dome, where an indoor swimming pool is located in the bottom of the dome. The problem can be reduced from a three dimensional to a two dimensional one. The main goal is the formulation of a proper optimization problem for computing the optimal heating of the air after a given time. For that, the model of the heating process as a partial differential equation is formulated as well as the optimization problem subject to the time-dependent partial differential equation. This yields the optimal heating of the air under the glass dome such that the desired temperature distribution is attained after a given…
Salt release monitoring with specific sensors in "in vitro" oral and digestive environments from soft cheeses
2012
International audience; The objective of the present work is to demonstrate the interest and the feasibility of the measurement of NaCl concentrations in soft cheeses and in particular an in vitro digestion process by the use of chemical sensors. The analyzed matrices were the commercial Italian mozzarella cheeses and domestic cheese base models. The classification of mozzarellas was performed according to their salinity, while the breakdown of cheese base models has been followed both at initial steps of digestion in artificial mouth dispositive mimicking the oral sphere and in a gut-imitating digester (TIM-1). During the breakdown of soft cheese in the digester, the estimated values for N…
Novel Porous Carbon Material for the Detection of Traces of Volatile Organic Compounds in Indoor Air
2021
International audience; A highly sensitive and selective silicon-based microanalytical prototype was used to identify a few ppb of volatile organic compounds (VOCs) in indoor air. Herein, a new nonactivated tannin-derived carbon synthesized by an environmentally friendly method, DM2C, a MIL-101(Cr) MOF, and a DaY zeolite were selected for the preconcentration of BTEX compounds (i.e., benzene, toluene, ethylbenzene, and xylenes). Integrating a small amount of these nanoporous solids inside a miniaturized preconcentration unit led to excellent preconcentration performance. By taking advantage of the high adsorption−desorption capacities of the DM2C adsorbent, concentrations as low as 23.5, 30…
Air Quality Assessment by the Determination of Trace Elements in Lichens (Xanthoria calcicola) in an Industrial Area (Sicily, Italy)
2022
This study provides data on variation in the content of metals and metalloids measured in the lichens (Xanthoria calcicola Oxner) collected in the Syracusan petrochemical complex (Sicily, Italy) which is considered one of the largest in Europe. Concentrations of eighteen trace elements measured in the lichens that were collected from 49 different points were analyzed using an inductively coupled plasma (ICP-MS) device. The concentrations of the typical elements of industrial emissions (As, Cr, Ni, and V) highlight the environmental criticality that exists in the study area. The interpretation of the data in terms of multi-element statistical analysis (FA) and enrichment factor (EFs) proved …
Acylative Dynamic Kinetic Resolution of Secondary Alcohols: Tandem Catalysis by HyperBTM and Bäckvall's Ruthenium Complex.
2021
Non-enzymatic dynamic kinetic resolution (DKR) of secondary alcohols by enantioselective acylation using an isothiourea-derived HyperBTM catalyst and racemization of slowly reacting alcohol by Backvall's ruthenium complex is reported. The DKR approach features high enantioselectivities (up to 99:1), employs easy-to-handle crystalline 4-nitrophenyl isobutyrate as the acylating reagent, and proceeds at room temperature and under an ambient atmosphere. The stereoinduction model featuring cation-π system interactions between the acylated HyperBTM catalyst and π electrons of an alcohol aryl subunit has been elaborated by DFT calculations.
Palladium-Catalyzed Hydroxycarbonylation of Aryl and Vinyl Bromides by Mixed Acetic Formic Anhydride
2006
The palladium-catalyzed hydroxycarbonylation of aryl and vinyl bromides in the presence of acetic anhydride and lithium formate as a carbon monoxide source has been developed. The combination of palladium(II) acetate with 1,1'-bis(diphenylphosphino)ferrocene (dppf) is an efficient catalytic system when the reaction is carried out at 120 °C.