Rashba spin-splitting control at the surface of the topological insulator Bi2Se3

The electronic structure of Bi2Se3 is studied by angle-resolved photoemission and density functional theory. We show that the instability of the surface electronic properties, observed even in ultra-high-vacuum conditions, can be overcome via in-situ potassium deposition. In addition to accurately setting the carrier concentration, new Rashba-like spin-polarized states are induced, with a tunable, reversible, and highly stable spin splitting. Ab-initio slab calculations reveal that these Rashba state are derived from the 5QL quantum-well states. While the K-induced potential gradient enhances the spin splitting, this might be already present for pristine surfaces due to the symmetry breaking of the vacuum-solid interface.Comment: A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/BiSe_K.pd

Review of nanomaterials in dentistry: interactions with the oral microenvironment, clinical applications, hazards, and benefits.

Interest in the use of engineered nanomaterials (ENMs) as either nanomedicines or dental materials/devices in clinical dentistry is growing. This review aims to detail the ultrafine structure, chemical composition, and reactivity of dental tissues in the context of interactions with ENMs, including the saliva, pellicle layer, and oral biofilm; then describes the applications of ENMs in dentistry in context with beneficial clinical outcomes versus potential risks. The flow rate and quality of saliva are likely to influence the behavior of ENMs in the oral cavity, but how the protein corona formed on the ENMs will alter bioavailability, or interact with the structure and proteins of the pellicle layer, as well as microbes in the biofilm, remains unclear. The tooth enamel is a dense crystalline structure that is likely to act as a barrier to ENM penetration, but underlying dentinal tubules are not. Consequently, ENMs may be used to strengthen dentine or regenerate pulp tissue. ENMs have dental applications as antibacterials for infection control, as nanofillers to improve the mechanical and bioactive properties of restoration materials, and as novel coatings on dental implants. Dentifrices and some related personal care products are already available for oral health applications. Overall, the clinical benefits generally outweigh the hazards of using ENMs in the oral cavity, and the latter should not prevent the responsible innovation of nanotechnology in dentistry. However, the clinical safety regulations for dental materials have not been specifically updated for ENMs, and some guidance on occupational health for practitioners is also needed. Knowledge gaps for future research include the formation of protein corona in the oral cavity, ENM diffusion through clinically relevant biofilms, and mechanistic investigations on how ENMs strengthen the tooth structure

Odzysk złota z odpadów górniczych

Purpose: the metals and industrial minerals contained in the tailings produced by mining and quarrying activities, are cause of environmental damage. The objective of this experimental work is the application of innovative technologies for the treatment and exploitation of mining tailings in Romania, in order to recover materials high grade raw to be placed on the market, reducing the volume of the wastes. Further objective, is to optimize some parameters relating to the dissolution of gold and the subsequent recovery from purified solutions, determining beforehand the technical feasibility of the scheme of process developed on a laboratory scale. Methods: the study is focused on hydrometallurgical process for the recovery of gold. The innovative treatment chosen is the thiosulphate process that, compared to conventional cyanide, has several advantages, first of all the most eco-friendly and non- toxic to humans. The conventional process shows operating limits in the case of auriferous minerals refractory materials, such as Romanian wastes object of the study. Another fundamental characteristic of the ammoniacal thiosulphate solutions, is the best selectivity towards gold, not attacking the majority of the gangue mineral constituents. Results: the dissolution rates of gold reached a final value of 70% Au – working at room temperature – with recoveries of the global process of about 65%, in line with the conventional process. Main conclusions: these results are very encouraging, considering that this is an innovative process, applied to a low content gold ore. The optimization of parameters and operating conditions, and the industrial treatment, continuous and scale greater would certainly permit to reach the best results in terms of process yields and energetic and reagents consumption.Cel: metale i minerały zawarte w odpadach powstających w wyniku działalności górniczej i wydobywczej są przyczyną szkód w środowisku. Celem prac eksperymentalnych jest zastosowanie innowacyjnych technologii do obróbki i eksploatacji odpadów wydobywczych w Rumunii, w celu odzyskania wysokiej jakości surowców, które zostaną wprowadzone do obrotu, zmniejszając ilość deponowanych odpadów. Dalszym celem jest optymalizacja niektórych parametrów związanych z rozpuszczaniem złota i późniejsze odzyskiwanie z oczyszczonych roztworów, z określeniem technicznej wykonalności schematu procesu opracowanego w skali laboratoryjnej. Metoda: badanie koncentruje się na procesie hydrometalurgicznym odzyskiwania złota. Innowacyjnym sposobem jest zastosowanie do ługowania tiosiarczanu, który w porównaniu z tradycyjnym cyjankiem ma wiele zalet, przede wszystkim jest bardziej przyjazny dla środowiska i nietoksyczny dla ludzi. Konwencjonalny proces daje ograniczone wyniki dla badanych odpadów złotonośnych. Podstawową zaletą amoniakalnych roztworów tiosiarczanu jest lepsza selektywność w stosunku do złota, a nie ługowanie wszystkich składników mineralnych skały płonnej. Wyniki: wskaźniki rozpuszczania złota osiągnęły wartość 70% Au - w temperaturze pokojowej - w porównaniu do odzysku z procesu konwencjonalnego około 65%. Główne wnioski: wyniki są bardzo zachęcające, proces jest innowacyjny, zastosowany do rudy o niskiej zawartości złota. Optymalizacja parametrów i warunków pracy oraz wdrożenie w skali przemysłowej pozwoli osiągnąć lepsze wyniki pod względem wydajności procesu oraz zużycia energii i odczynników