Search results for "Barium"
showing 10 items of 262 documents
The transport of ions across monoolein bilayers mediated by synthetic macrocyclic carriers
1989
The efficiency as carriers for the alkali and the alkaline earth ions across monoolein bilayers of three macrocyclic compounds has been investigated by conductometric measurements. The results show that although the three compounds have the optimum cavity size for fitting potassium and barium cations, their efficiency in ionic transport is quite different. These discrepancies are rationalized on the basis of the overlap of the water-diazacrown and cation-ligand interactions on the carrier mechanism.
Caracterización de barita cubana y su reducción carbotérmica en horno de microondas
2007
The Cuban Barite (BaSO4) is characterized by X ray diffraction, chemical analysis and scanning electron microscopy. The principal components are identified and its characteristic morphology is shown. Its carbothermic reduction under microwave irradiation is carried out with the purpose of to improve the yield of this stage during the mineral transformation process in reagent of barium of diverse applications. La barita cubana (BaSO4) se ha caracterizado por difracción de rayos X, análisis químico y microscopía electrónica de barrido. Se han identificado sus componentes mayoritarios y así mismo se muestra su morfología característica. Se ha realizado su reducción carbotérmica en horno de mic…
Effect of sodium to barium substitution on the space charge implementation in thermally poled glasses for nonlinear optical applications
2009
Thermally poled niobium borophosphate glasses in the system 0.55(0.95-y) NaPO{sub 3}+y/2 Ba(PO{sub 3}){sub 2}+0.05Na{sub 2}B{sub 4}O{sub 7})+0.45Nb{sub 2}O{sub 5} were investigated for second order optical nonlinear (SON) properties. Bulk glasses were studied by Raman spectroscopy, thermal analysis, optical and dielectric measurements. The sodium to barium substitution does not lead to significant changes in optical properties, crystallization of glasses and coordination environment of polarizable niobium atoms. However, the ionic conductivity decreases drastically with the increase of barium concentration. Secondary ion mass spectroscopy has been used to determine the element distribution …
High-pressure and high-temperature X-ray diffraction studies of scheelite BaWO4
2009
International audience; We carried out high-pressure (HP) and high-temperature (HT) in situ ADXRD synchrotron measurements in barium tungstate (BaWO4 ) up to 7.5 GPa and 800 K. Coexistence of the scheelite and fergusonite structures was found beyond 7 GPa, both at room temperature and HT, suggesting a polymorphism zone in the P –T phase diagram. The experiments are complemented by thermodynamic calculations within the quasi-harmonic approximation. At ambient pressure, a volume thermal expansivity of 9.5 × 10− 6 K−1 was obtained for scheelite BaWO4 . At HP, the thermal expansivity of the fergusonite doubles that of scheelite. Theoretical equation of state curves at HP and HT are also present…
Antispasmodic effect of 4'-methylepigallocatechin on guinea pig ileum.
2012
AbstractThe antispasmodic effect of 4′-methylepigallocatechin (MEC), which was isolated from Maytenus rigida Mart (Celestraceae), was investigated in vitro in guinea pig intestinal segments. In the isolated ileum, MEC (1 nM–100μM) did not modify the ileal spontaneous tonus or the electrically elicited contractions. MEC (8μM) significantly (p<0.01) reduced the submaximal contractions induced by histamine (2μM), carbachol (100μM) and BaCl2 (0.03M). An additive relaxing action (p<0.001) was observed by co-incubation of verapamil (10 nM) and MEC (8μM). Although MEC (1nM–100μM) did not modify the contractions elicited by 60mM KCl, it significantly reduced the CaCl2 contractile response without c…
Ruiša pūķgalve Latvijas Universitātes Muzeja herbārijā
2020
Par Gada augu 2020 tika izvēlēts Latvijas aizsargājamais augs ruiša pūķgalve, ko Latvijā pirmo reizi atradis dabaspētnieks Eduards Lēmanis (1841 – 1902) 1883. gadā Antonopolē. Tas kopā ar citiem ruiša pūķgalves herbārija paraugiem glabājas Latvijas Universitātes Muzeja Botānikas un mikoloģijas kolekcijās. Tie ir gan Latvijā, gan Igaunijā ievākti eksemplāri laika posmā no 1848. līdz 1977. gadam.
A study of thin surface layers by multilayer Mössbauer spectroscopy /MMS/
1990
A stacking Mossbauer technique, MMS has been applied for studying thin surface layers. The surface layers formed on the57Fe film in aqueous solutions of corrosion inhibitors, such as zinc phosphate and barium metaborate, and in distilled water was studied by this method. It has been found that the corrosion is much slower in the presence of zinc phosphate and barium metaborate. XPS analysis suggests the formation of a mixed iron zinc phosphate on the surface of the57Fe film after corrosion in a zinc phosphate solution.
Quantitative XPS analysis of leached layers on optical glasses
1993
The corrosion of optical glasses often reduces the utility of uncoated glasses as well as the adhesion of resistive coatings deposited onto corroded glasses. Photoelectron spectroscopy (XPS) was applied to study glass surfaces with respect to their surface corrosion. In particular, leaching by the influence of polish slurries, pure water, air and even residual gases inside a vacuum device was studied in detail. Pure quartz glass and different sodium and barium silicate glasses were broken in ultrahigh vacuum (4 × 10−10 mbar) for the determination of sensitivity factors of the different XPS signals. It was found that a quantitative determination of the surface composition of corroded and lea…
Kristāliska bārija diborāta iegūšanas iespējas ūdens šķīdumos
2019
Kristāliska bārija diborāta iegūšanas iespējas ūdens šķīdumos. Ponomarjovs D., zinātniskais vadītājs Dr. ķīm., asoc. prof. Švirksts J. Bakalaura darbs, 34 lappuses, 14 attēli, 16 tabulas, 17 literatūras avots. Latviešu valodā. Kursa darbā tika sintezēts bārija diborāts, kurš tika iegūts apmaiņas reakcijā ūdens šķīdumā. Tika izmantotas dažādas izejvielu attiecības. Iegūtie savienojumi tika analizēti izmantojot titrametriju. Pēc iegūtiem datiem tika aprēķinātas vielu molārās attiecības un noteiktas vielu formulas.
<strong>Nomenclatural types of <em>Hieracium</em> (Asteraceae) species described from the Balearic Islands (Spain) and several rela…
2021
A nomenclatural revision of the genus Hieracium in the Balearic Islands (Spain) is presented and the typification of five names: H. aragonense Scheele, H. balearicum Arvet‑Touvet, H. elisaeanum Arvet-Touvet ex Willkomm, H. majoricanum Arvet-Touvet and H. microscapum Arvet-Touvet, is discussed. The names are lectotypified using specimens preserved at COI, GRM, and P herbaria. Several comments for the names H. cataractarum Arvet-Touvet & Huter and H. praecox subsp. brachypus Freyn in Porta & Rigo are also provided.