Noble gas as a functional dopant in ZnO

Owing to fully occupied orbitals, noble gases are considered to be chemically inert and to have limited effect on materials properties under standard conditions. However, using first-principles calculations, we demonstrate herein that the insertion of noble gas (i.e., He, Ne, or Ar) in ZnO results in local destabilization of electron density of the material driven by minimization of an unfavorable overlap of atomic orbitals of the noble gas and its surrounding atoms. Specifically, the noble gas defect (interstitial or substitutional) in ZnO pushes the electron density of its surrounding atoms away from the defect. Simultaneously, the host material confines the electron density of the noble gas. As a consequence, the interaction of He, Ne, or Ar with O vacancies of ZnO in different charge states q (ZnO:VOq) affects the vacancy stability and their electronic structures. Remarkably, we find that the noble gas is a functional dopant that can delocalize the deep in-gap VOq states and lift electrons associated with the vacancy to the conduction band.Comment: 15 pages, 4 figure

Band Gap Modulation of SrTiO3 upon CO2 Adsorption

CO2 chemisorption on SrTiO3(001) surfaces is studied using ab initio calculations in order to establish new chemical sensing mechanisms. We find that CO2 adsorption opens the material band gap, however, while the adsorption on the TiO2-terminated surface neutralizes surface states at the valence band (VB) maximum, CO2 on the SrO-terminated surfaces suppresses the conduction band (CB) minimum. For the TiO2-terminated surface, the effect is explained by the passivation of dangling bonds, whereas for the SrO-terminated surface, the suppression is caused by the surface relaxation. Modulation of the VB states implies a more direct change in charge distribution, and thus the induced change in band gap is more prominent at the TiO2 termination. Further, we show that both CO2 adsorption energy and surface band gap are strongly dependent on CO2 coverage, suggesting that the observed effect can be utilized for sensing application in a wide range of CO2 concentrations

Tailoring electronic properties of multilayer phosphorene by siliconization

Controlling a thickness dependence of electronic properties for two-dimensional (2d) materials is among primary goals for their large-scale applications. Herein, employing a first-principles computational approach, we predict that Si interaction with multilayer phosphorene (2d-P) can result in the formation of highly stable 2d-SiP and 2d-SiP$_2$ compounds with a weak interlayer interaction. Our analysis demonstrates that these systems are semiconductors with band gap energies that can be governed by varying the thickness and stacking order. Specifically, siliconization of phosphorene allows to design 2d-SiP$_x$ materials with significantly weaker thickness dependence of electronic properties than that in 2d-P and to develop ways for their tailoring. We also reveal the spatial dependence of electronic properties for 2d-SiP$_x$ highlighting difference in effective band gaps for different layers. Particularly, our results show that central layers in the multilayer 2d systems determine overall electronic properties, while the role of the outermost layers is noticeably smaller

The in vitro effect of a tooth bleaching agent on coffee and wine stained teeth

Magister Scientiae Dentium - MSc(Dent)Summary: Aim: The aim of this laboratory study is to assess the efficacy of a tooth bleaching agent by evaluating the degree of color change with the use of a spectrophotometer and not by the usual subjective, visual methods. Methodology: Twenty specimens of human teeth will be collected, polished and divided into two groups. A baseline color measurement by the CIE L* a* b* with a spectrophotometer against a white background will be taken before one group is immersed in coffee and the other in red wine for two weeks. Bleaching of the specimens will be done according to manufacturer’s instructions for two weeks. Color readings will be taken before bleaching, weekly during bleaching and 1 and 2 weeks after the bleaching treatment. Color change (ΔE) will be calculated mathematically as Δ E = [ (Δ L*)2 + (Δ a*)2 + (Δ b*)2 ]1/2. An observation of whether the baseline color reading will be regained by the bleaching process will be made. Results: Data collected will be recorded on an Excel spreadsheet. Advice from a qualified statistician will be sought to analyze the data. Results will be discussed in comparison with the existing literature on this subject.South Afric

Социально-экономические детерминанты идентификации институтов государственности Украины

Аргументовано пріоритетність розбудови інституту держави для досягнення суспільного добробуту в Україні. Визначено специфіку формування антикризового управління в Україні з урахуванням політичного та соціально-економічного розвитку. Обґрунтовано стратегічно важливі проблеми та визначальні дилеми ідентифікації інститутів державності для України.The author argues that in order to achieve social welfare in Ukraine the priority must be given to the development of the institution of State. He determines the specific form of its crisis management by taking the political and socio-economic context into account. In order to find ways to overcome the global challenges in front of Ukraine, he justifies the important identification dilemmas of the institution of State associated with the timing of the state approval and privatization, uncertain property rights, the vector of civilization development, specification of state functions and anti-corruption activities of society.Аргументирована приоритетность развития института государства для достижения общественного благосостояния в Украине. Определена специфика формирования антикризисного управления в Украине с учетом политического и социально-экономического развития. Обоснованы важные проблемы и определяющие дилеммы идентификации институтов государственности для Украины

Dispersion forces stabilise ice coatings at certain gas hydrate interfaces which prevent water wetting

Gas hydrates formed in oceans and permafrost occur in vast quantities on Earth representing both a massive potential fuel source and a large threat in climate forecasts. They have been predicted to be important on other bodies in our solar systems such as Enceladus, a moon of Saturn. CO$_2$-hydrates likely drive the massive gas-rich water plumes seen and sampled by the spacecraft Cassini, and the source of these hydrates is thought to be due to buoyant gas hydrate particles. Dispersion forces cause gas hydrates to be coated in a 3-4 nm thick film of ice, or to contact water directly, depending on which gas they contain. These films are shown to significantly alter the properties of the gas hydrate clusters, for example, whether they float or sink. It is also expected to influence gas hydrate growth and gas leakage