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

Diversity in CO2 concentrating mechanisms among chemolithoautotrophs from genera Hydrogenovibrio, Thiomicrorhabdus, and Thiomicrospira, ubiquitous in sulfidic habitats worldwide

Members of Hydrogenovibrio, Thiomicrospira and Thiomicrorhabdus fix carbon at hydrothermal vents, coastal sediments, hypersaline lakes, and other sulfidic habitats. The genome sequences of these ubiquitous and prolific chemolithoautotrophs suggest a surprising diversity of mechanisms for dissolved inorganic carbon (DIC) uptake and fixation; these mechanisms are verified here. Carboxysomes are apparent in transmission electron micrographs of most of these organisms; lack of carboxysomes in Thiomicrorhabdus sp. Milos T2 and Tmr. arctica, and an inability to grow under low DIC conditions by Thiomicrorhabdus sp. Milos T2 are consistent with an absence of carboxysome loci in their genomes. For the remaining organisms, potential DIC transporters from four evolutionarily distinct families (Tcr0853/0854, Chr, SbtA, SulP) are located downstream of carboxysome loci. Transporter genes collocated with carboxysome loci, as well as some homologs located elsewhere on the chromosomes, had elevated transcript levels under low DIC conditions, as assayed by qRT-PCR. DIC uptake was measureable via silicone oil centrifugation when a representative of each of the four types of transporter was expressed in Escherichia coli. Expression of these genes in carbonic anhydrase-deficient E. coli EDCM636 enabled it to grow under low DIC conditions, consistent with DIC transport by these proteins. The results from this study expand the range of DIC transporters within the SbtA and SulP transporter families, verify DIC uptake by transporters encoded by Tcr_0853 and Tcr_0854 and their homologs, and introduce DIC as a potential substrate for transporters from the Chr family. IMPORTANCE Autotrophic organisms take up and fix DIC, introducing carbon into the biological component of the global carbon cycle. The mechanisms for DIC uptake and fixation by autotrophic Bacteria and Archaea are likely to be diverse, but have only been well-characterized among "Cyanobacteria". Based on genome sequences, members of Hydrogenovibrio, Thiomicrospira and Thiomicrorhabdus have a variety of mechanisms for DIC uptake and fixation. We verified that most of these organisms are capable of growing under low DIC conditions, when they upregulate carboxysome loci and transporter genes collocated with these loci on their chromosomes. When these genes, which fall into four evolutionarily independent families of transporters, are expressed in E. coli, DIC transport is detected. This expansion in known DIC transporters across four families, from organisms from a variety of environments, provides insight into the ecophysiology of autotrophs, as well as a toolkit for engineering microorganisms for carbon-neutral biochemistries of industrial importance

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

Badanie usuwania manganu w procesie rekultywacji wód kopalnianych

In this work a comparative study of manganese removal from pre-treated acid mine drainage is described. Manganese removal by three ways was realized. At the first method sodium hydroxide was added to raise pH of processed AMD to the 9.5 to promote the abiotic oxidation of soluble divalent species to insoluble form of manganese. Potassium permanganate was used at pH near neutrality for elimination of manganese from AMD by oxidative precipitation in the second process. A third method, as electrowinning, was applied, finalized to the anodic Mn recovery under MnO2 form. The results showed that the three methods are effective and manganese were removed from acid mine drainage for values that comply with environmental requirements. However, when sodium hydroxide was used as reagent, coprecipitation of manganese and magnesium present in AMD was observed. In the second experiment enhanced selectivity of the process and purity of obtained precipitates were achieved. In the process of electrowinning – over 95% of Mn removal under MnO2 form, with a high degree of purity (about 99%) was attained.W pracy tej opisano porównawcze badanie usuwania manganu z przygotowanego drenażu kwaśnych wód kopalnianych. Usuwanie manganu odbyło się na trzy sposoby. Po pierwsze, dodano wodorotlenek sodu aby podnieść pH przerabianego AMD do 9.5 aby spowodować abiotyczne utlenianie rozpuszczalnych dwuwartościowych gatunków do nierozpuszczalnej formy manganu. Nadmanganian potasu zastosowano przy pH bliskim poziomu neutralnego aby wyeliminować mangan z kwaśnych wód kopalnianych poprzez tlenowe strącanie w drugiej metodzie. Trzecia metoda, jako elektrolityczna, została zastosowana do anodowego odzysku Mn w formie MnO2. Wyniki wskazały, że trzy metody są efektywne i mangan został usunięty z drenażu kwaśnych wód kopalnianych w ilościach porównywalnych z wymaganiami środowiskowymi. Jednakże, przy zastosowaniu wodorotlenku sodu zaobserwowano wzajemne strącanie manganu i magnezu obecnego w kwaśnych wodach kopalnianych. W drugim eksperymencie zwiększona została selektywność procesu i czystość otrzymanych substancji. W procesie elektrolitycznym – ponad 95% Mn zostało usuniętych w postaci MnO2, przy dużym stopniu czystości (około 99%)