Search results for " atom"
showing 10 items of 1526 documents
Ab initio calculations of pure and Co+2-doped MgF2 crystals
2020
This research was partly supported by the Kazakhstan Science Project № AP05134367«Synthesis of nanocrystals in track templates of SiO2/Si for sensory, nano- and optoelectronic applications», as well as by Latvian Research Council project lzp-2018/1-0214. Calculations were performed on Super Cluster (LASC) in the Institute of Solid State Physics (ISSP) of the University of Latvia. Authors are indebted to S. Piskunov for stimulating discussions.
Large numbers of cold positronium atoms created in laser-selected Rydberg states using resonant charge exchange
2016
Lasers are used to control the production of highly excited positronium atoms (Ps*). The laser light excites Cs atoms to Rydberg states that have a large cross section for resonant charge-exchange collisions with cold trapped positrons. For each trial with 30 million trapped positrons, more than 700 000 of the created Ps* have trajectories near the axis of the apparatus, and are detected using Stark ionization. This number of Ps* is 500 times higher than realized in an earlier proof-of-principle demonstration (2004 Phys. Lett. B 597 257). A second charge exchange of these near-axis Ps* with trapped antiprotons could be used to produce cold antihydrogen, and this antihydrogen production is e…
H-He collision-induced satellite in the Lyman alpha profile of DBA white dwarf stars
2020
The spectra of helium-dominated white dwarf stars with hydrogen in their atmosphere present a distinctive broad feature centered around 1160~\AA\/ in the blue wing of the Lyman-$\alpha$ line. It is extremely apparent in WD 1425+540 recently observed with HST COS. With new theoretical line profiles based on ab initio atomic interaction potentials we show that this feature is a signature of a collision-induced satellite due to an asymptotically forbidden transition. This quasi-molecular spectral satellite is crucial to understanding the asymmetrical shape of Lyman-$\alpha$ seen in this and other white dwarf spectra. Our previous work predicting this absorption feature was limited by molecular…
Nuclear anapole moment interaction in BaF from relativistic coupled-cluster theory
2018
We present high accuracy relativistic coupled cluster calculations of the P-odd interaction coefficient $W_A$ describing the nuclear anapole moment effect on the molecular electronic structure. The molecule under study, BaF, is considered a promising candidate for the measurement of the nuclear anapole moment, and the preparation for the experiment is now underway [Altunas et al., Phys. Rev. Lett. 120, 142501 (2018)]. Influence of various computational parameters (size of the basis set, treatment of relativistic effects, and treatment of electron correlation) on the calculated $W_A$ coefficient is investigated and a recommended value of 147.7 Hz with an estimated uncertainty of 1.5% is prop…
Makro- un mikroelementu sastopamības variācijas mellenēs Vaccinium Myrtillus L.) un augsnē
2020
Darbā tika analizēts dzelzs, cinka, vara, kālija un fosfātjonu saturs mellenēs (Vaccinium myrtillus L.), krūmmellenēs (Vaccinium corymbosum) un to augsnē. Melleņu un augsnes paraugi tika ievākti meža teritorijā, kur tika mēslots ar vieglajiem koksnes pelniem. Krūmmelleņu ogu un augsnes paraugi tika ievākti privātmājas teritorijā, kur netika izmantots nekāds mēslojums. Veicot sauso mineralizāciju, ar liesmas atomabsorbciometrijas metodi noteikts dzelzs, cinka un vara saturs, fotometriski tika noteikts fosfātjonu saturs un ar liesmas fotometriju tika noteikts kālija saturs. Iegūtie rezultāti tika apstrādāti, izvērtēts noteikto elementu saturs mellenēs un krūmmellenēs, kā arī iegūtie rezultāti…
Augsnes piesārņojuma ar smagajiem metāliskajiem elementiem izvērtējums dzelzceļa apkārtnē
2018
Augsnes piesārņojuma ar smagajiem metāliskajiem elementiem izvērtējums dzelzceļa apkārtnē. Jansons Ā., zinātniskais vadītājs Dr. chem., doc. Osīte A. Bakalaura darbs, 52 lappuses, 21 attēls, 7 tabulas, 25 literatūras avoti, 5 pielikumi. Latviešu valodā. Darba ietvaros ir veikta smago metālisko elementu – dzelzs, mangāna, vara, cinka, niķeļa un svina jonu kvantitatīvā analīze augsnes paraugos, kas ievākti Torņakalna, Jāņavārtu, Dārziņu un Kūdras dzelzceļa staciju apkārtnē – blakus stacijai (vilcienu bremzēšanas ceļa sākumā) un atstatus no tās. Vispirms tika veikta ievākto augsnes paraugu sagatavošana mineralizācijai (žāvēšana, homogenizēšana, sijāšana). Augsnes paraugu matricas sagraušana ti…
Metālisko elementu saturs augsnē Liepājas Ziemeļu Fortu teritorijā
2019
Metālisko elementu saturs augsnē Liepājas Ziemeļu fortu teritorijā. Butkus D., darba vadītāja Mg. chem., lektore Balcerbule Z. Bakalaura darbs, 45 lappuses, 21 attēls, 18 tabulas, 32 literatūras avoti, 4 pielikumi. Latviešu valodā. Darbā ir veikta metālisko elementu analīze Ziemeļu fortu teritorijā ņemtajos augsnes paraugos. Augsnes izvilkumi gatavoti HNO3 šķīdumos, veikta arī mineralizācija ar mikroviļņu enerģiju. Elementu koncentrācijas tika noteiktas ar liesmas atomabsorbciometrijas un ICP – MS metodēm. Iegūtie rezultāti tika salīdzināti ar LR MK augsnes un grunts kvalitātes normatīviem un literatūrā pieejamiem datiem.
Kinetics of the intestinal uptake of zinc acexamate in normal and zinc-depleted rats.
1990
Abstract The uptake of zinc as acexamic acid salt in the small intestine of the anaesthetized rat was shown to be a two-phase process in normal animals. The first phase is rapid mucosal binding which satisfies the Freundlich isotherm equation and which involves about 30 per cent of the initially perfused zinc. The second phase was characterized as an apparent absorption step which obeys Michaelis-Menten and first-order combined kinetics, with the following parameters: Vm = 6.51 mg h−1; Km = 2.96 mg; ka = 0.306 h−1. In largely non-saturated conditions, an apparent global rate constant of about 2.50 h−1 was calculated. No significant interference due to endogenous zinc excretion into the smal…
Investigation of water sorption and aluminum releases from high viscosity and resin modified glass ionomer.
2019
Background High viscosity glass ionomer cement (HVGIC) and resin-modified glass ionomer cement (RMGIC) have recently been clinically preferred thanks to their numerous advantages. However, initial moisture contamination has a negative effect on the mechanical and physical properties of these cements. The aim of this study was in vitro of HVGICs and RMGICs, with and without surface protection, on water sorption, solubility and release of aluminum. Material and Methods In this study, as HVGICs; Equia Forte, IonoStar Plus, Riva Self Cure; as RMCIS, Ionolux and Riva Light Cure; and as control, Z250 universal composite was used. Equia coat, Voco varnish and Riva coat were chosen as surface prote…
External pressure and composition effects on the atomic and electronic structure of SnWO4
2015
The atomic and electronic structure of tin tungstates, α-SnWO4, α-Sn1.03W0.99O4 and β-SnWO4 ,w as studied by the W L3-edge X-ray absorption spectroscopy and first-principles linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange-correlation density functional (DFT)/ Hartree–Fock (HF) scheme. It was found that the crystal structure of both α-phases is built up of strongly distorted WO6 octahedra, whereas that of β-SnWO4 is composed of nearly regular WO4 tetrahedra. In addition, there are distorted SnO6 octahedra in both α- and β-phases. The metal–oxygen octahedra distortion is explained by the second-order Jahn–Teller effect. The influence of pressure on the st…