Giant spin Hall Effect in two-dimensional monochalcogenides

One of the most exciting properties of two dimensional materials is their sensitivity to external tuning of the electronic properties, for example via electric field or strain. Recently discovered analogues of phosphorene, group-IV monochalcogenides (MX with M = Ge, Sn and X = S, Se, Te), display several interesting phenomena intimately related to the in-plane strain, such as giant piezoelectricity and multiferroicity, which combine ferroelastic and ferroelectric properties. Here, using calculations from first principles, we reveal for the first time giant intrinsic spin Hall conductivities (SHC) in these materials. In particular, we show that the SHC resonances can be easily tuned by combination of strain and doping and, in some cases, strain can be used to induce semiconductor to metal transitions that make a giant spin Hall effect possible even in absence of doping. Our results indicate a new route for the design of highly tunable spintronics devices based on two-dimensional materials

The growth of ZnO crystals from the melt

The peculiar properties of zinc oxide (ZnO) make this material interesting for very different applications like light emitting diodes, lasers, and piezoelectric transducers. Most of these applications are based on epitaxial ZnO layers grown on suitable substrates, preferably bulk ZnO. Unfortunately the thermochemical properties of ZnO make the growth of single crystals difficult: the triple point 1975 deg C., 1.06 bar and the high oxygen fugacity at the melting point p_O2 = 0.35 bar lead to the prevailing opinion that ZnO crystals for technical applications can only be grown either by a hydrothermal method or from "cold crucibles" of solid ZnO. Both methods are known to have significant drawbacks. Our thermodynamic calculations and crystal growth experiments show, that in contrast to widely accepted assumptions, ZnO can be molten in metallic crucibles, if an atmosphere with "self adjusting" p_O2 is used. This new result is believed to offer new perspectives for ZnO crystal growth by established standard techniques like the Bridgman method.Comment: 6 pages, 6 figures, accepted for J. Crystal Growt

Paleotocas gigantes na Região Metropolitana de Porto Alegre (estado do Rio Grande do Sul, Brasil).

Tunnels dug by semi-fossorial mammals of the South American Cenzoic megafauna are known as paleoburrows and are generally described from isolated records or very restricted regions. A particularly favorable set of conditions allowed the systematic mapping of paleoburrows over more than a decade in the Porto Alegre metropolitan area (Rio Grande do Sul state, Brazil), covering more than 10,000 km2. Through digital prospecting, media strategies and fieldwork, more than 400 paleoburrows were found in this region, usually in large-scale anthropogenic excavations. The structures may consist of a single one or several tunnels, reaching up to two or three dozen. Burrows can be opened or filled with sediments to variable extent. More than 80% of the tunnels are completely filled with sediment, thus classified as crotovines. Their widths range between 0.5 and 3.0 m and their heights are between 0.5 and 2.0 m. Tunnels with a diameter of 1.4 m, with original estimated lengths of more than 50 m, are frequent. Excavation traces on burrow walls and roofs are common, but fossils have not been found. In very flat areas like floodplains or areas with very uneven relief (mountainous), paleoburrows are rare to absent. The largest amount of tunnels were found in regions of hilly and relatively stable relief, dug in different lithotypes except unconsolidated sediments or unaltered magmatic or metamorphic rocks. It is possible that each hill may have several paleoburrows, isolated or in groups, around its base. Thus, the region can be considered the one with the highest known density of paleoburrows of this type in the world so far.Túneis cavados por mamíferos semi-fossoriais da megafauna do Cenzóico da América do Sul são conhecidos como paleotocas e geralmente são descritos de registros isoladas ou de regiões bastante restritas. Condições especialmente favoráveis permitiram o mapeamento sistemático das paleotocas da Região Metropolitana de Porto Alegre (estado do Rio Grande do Sul, Brasil) ao longo de mais de uma década, cobrindo uma área de mais de 10 mil km2. Através de prospecção digital, estratégias de mídia e trabalho de campo foram encontrados mais de 400 túneis nesta região, geralmente em escavações antropogênicas de grande porte. Um registro com túneis pode compor-se de um túnel apenas ou por vários túneis, alcançando até duas ou três dezenas. Os túneis podem estar abertos ou então entulhados por sedimentos em maior ou menor grau. Mais de 80% dos túneis estão completamente preenchidos com sedimentos, sendo então classificados como crotovinas. Suas larguras variam entre 0.5 e 3.0 m e suas alturas entre 0.5 e 2.0 m. Frequentes são túneis com 1.4 m de diâmetro, cujo comprimentos originais foram estimados mais de 50 m. Traços de escavação nas paredes laterais e no teto são comuns, mas fósseis não foram encontrados. Em áreas muito planas como planícies de inundação ou em regiões de relevo muito acidentado (montanhoso) as paleotocas são raras a ausentes. A maior quantidade de túneis foi encontrada em regiões de relevo ondulado, relativamente estável, em diversos litotipos exceto sedimentos inconsolidados ou rochas magmáticas ou metamórficas inalteradas. É possível que cada colina ali tenha várias paleotocas, isoladas ou em grupos, ao redor de sua base. Assim, a região pode ser considerada a que possui a maior densidade conhecida de paleotocas desse tipo no mundo até agora

Advanced modeling of materials with PAOFLOW 2.0:New features and software design

Recent research in materials science opens exciting perspectives to design novel quantum materials and devices, but it calls for quantitative predictions of properties which are not accessible in standard first principles packages. PAOFLOW, is a software tool that constructs tight-binding Hamiltonians from self consistent electronic wavefunctions by projecting onto a set of atomic orbitals. The electronic structure provides numerous materials properties that otherwise would have to be calculated via phenomenological models. In this paper, we describe recent re-design of the code as well as the new features and improvements in performance. In particular, we have implemented symmetry operations for unfolding equivalent k-points, which drastically reduces the runtime requirements of first principles calculations, and we have provided internal routines of projections onto atomic orbitals enabling generation of real space atomic orbitals. Moreover, we have included models for non-constant relaxation time in electronic transport calculations, doubling the real space dimensions of the Hamiltonian as well as the construction of Hamiltonians directly from analytical models. Importantly, PAOFLOW has been now converted into a Python package, and is streamlined for use directly within other Python codes. The new object oriented design treats PAOFLOW's computational routines as class methods, providing an API for explicit control of each calculation.</p

Biomarkers Signal Contaminant Effects on the Organs of English Sole (Parophrys vetulus) from Puget Sound

Fish living in contaminated environments accumulate toxic chemicals in their tissues. Biomarkers are needed to identify the resulting health effects, particularly focusing on early changes at a subcellular level. We used a suite of complementary biomarkers to signal contaminant-induced changes in the DNA structure and cellular physiology of the livers and gills of English sole (Parophrys vetulus). These sediment-dwelling fish were obtained from the industrialized lower Duwamish River (DR) in Seattle, Washington, and from Quartermaster Harbor (QMH), a relatively clean reference site in south Puget Sound. Fourier transform–infrared (FT-IR) spectroscopy, liquid chromatography/mass spectrometry (LC/MS), and gas chromatography/mass spectrometry (GC/MS) identified potentially deleterious alterations in the DNA structure of the DR fish livers and gills, compared with the QMH fish. Expression of CYP1A (a member of the cytochrome P450 multigene family of enzymes) signaled changes in the liver associated with the oxidation of organic xenobiotics, as previously found with the gill. The FT-IR models demonstrated that the liver DNA of the DR fish had a unique structure likely arising from exposure to environmental chemicals. Analysis by LC/MS and GC/MS showed higher concentrations of DNA base lesions in the liver DNA of the DR fish, suggesting that these base modifications contributed to this discrete DNA structure. A comparable analysis by LC/MS and GC/MS of base modifications provided similar results with the gill. The biomarkers described are highly promising for identifying contaminant-induced stresses in fish populations from polluted and reference sites and, in addition, for monitoring the progress of remedial actions

Genesis and variation spatial of Podzol in depressions of the Barreiras formation, northeastern Espírito Santo State, Brazil, and its implications for Quaternary climate change

Variations in relief associated with pedogenetic processes promote different intensities in weathering of sediments of the Barreiras Formation and may thus lead to the formation of different soil types, like Podzols, Acrisols and Ferralsols. The Podzols of tropical regions contain important information on climate and vegetation changes that occurred mainly in late Pleistocene and Holocene; however few studied, regarding their spatial variation, that can be investigated through ground penetrating radar (GPR). The aim was to study morphological, physical, chemical, stable C isotopic properties and spatial distribution of soils within depressions of the Barreiras Formation and characterize the 14C chronology of two Podzols and their B spodic horizons, along a transect grassland to forest in northeastern Espírito Santo State, Brazil. The profiles encompass a sequence of A-E-Bhm horizons, except for P3 and P6 with histic H and A-Bt, respectively. The GPR images showed patterns corresponding to these soil horizons, and the GPR data reveal the presence of diagnostic subsurface horizons characteristic of spodic horizons with cemented layers. The influence of relief factors and original materials was observed, associated with ferrolysis and podzolisation as main actors in the genesis of soils studied. The monomorphic organic matter filling the voids evidences the processes of imobilization, illuviation and precipitation, with the genesis of the spodic horizon. The Podzols profiles of Pleistocene organic matter ages accumulated compounds of C3 plants from the vegetation cover in the B spodic horizons of the profiles P4 and P1, since at least 14,251 and 38,890 cal BP, respectively, suggesting the dominance of a humid climate at least during the studied period in the region

Diversity of Meiofauna from the 9°50′N East Pacific Rise across a Gradient of Hydrothermal Fluid Emissions

Background: We studied the meiofauna community at deep-sea hydrothermal vents along a gradient of vent fluid emissions in the axial summit trought (AST) of the East Pacific Rise 9 degrees 50'N region. The gradient ranged from extreme high temperatures, high sulfide concentrations, and low pH at sulfide chimneys to ambient deep-sea water conditions on bare basalt. We explore meiofauna diversity and abundance, and discuss its possible underlying ecological and evolutionary processes. Methodology/Principal Findings: After sampling in five physico-chemically different habitats, the meiofauna was sorted, counted and classified. Abundances were low at all sites. A total of 52 species were identified at vent habitats. The vent community was dominated by hard substrate generalists that also lived on bare basalt at ambient deep-sea temperature in the axial summit trough (AST generalists). Some vent species were restricted to a specific vent habitat (vent specialists), but others occurred over a wide range of physico-chemical conditions (vent generalists). Additionally, 35 species were only found on cold bare basalt (basalt specialists). At vent sites, species richness and diversity clearly increased with decreasing influence of vent fluid emissions from extreme flow sulfide chimney (no fauna), high flow pompei worm (S: 4-7, H-loge': 0.11-0.45), vigorous flow tubeworm (S: 8-23; H-loge': 0.44-2.00) to low flow mussel habitats (S: 28-31; H-loge': 2.34-2.60). Conclusions/Significance: Our data suggest that with increasing temperature and toxic hydrogen sulfide concentrations and increasing amplitude of variation of these factors, fewer species are able to cope with these extreme conditions. This results in less diverse communities in more extreme habitats. The finding of many species being present at sites with and without vent fluid emissions points to a non endemic deep-sea hydrothermal vent meiofaunal community. This is in contrast to a mostly endemic macrofauna but similar to what is known for meiofauna from shallow-water vents

Generational Association Studies of Dopaminergic Genes in Reward Deficiency Syndrome (RDS) Subjects: Selecting Appropriate Phenotypes for Reward Dependence Behaviors

Abnormal behaviors involving dopaminergic gene polymorphisms often reflect an insufficiency of usual feelings of satisfaction, or Reward Deficiency Syndrome (RDS). RDS results from a dysfunction in the “brain reward cascade,” a complex interaction among neurotransmitters (primarily dopaminergic and opioidergic). Individuals with a family history of alcoholism or other addictions may be born with a deficiency in the ability to produce or use these neurotransmitters. Exposure to prolonged periods of stress and alcohol or other substances also can lead to a corruption of the brain reward cascade function. We evaluated the potential association of four variants of dopaminergic candidate genes in RDS (dopamine D1 receptor gene [DRD1]; dopamine D2 receptor gene [DRD2]; dopamine transporter gene [DAT1]; dopamine beta-hydroxylase gene [DBH]). Methodology: We genotyped an experimental group of 55 subjects derived from up to five generations of two independent multiple-affected families compared to rigorously screened control subjects (e.g., N = 30 super controls for DRD2 gene polymorphisms). Data related to RDS behaviors were collected on these subjects plus 13 deceased family members. Results: Among the genotyped family members, the DRD2 Taq1 and the DAT1 10/10 alleles were significantly (at least p < 0.015) more often found in the RDS families vs. controls. The TaqA1 allele occurred in 100% of Family A individuals (N = 32) and 47.8% of Family B subjects (11 of 23). No significant differences were found between the experimental and control positive rates for the other variants. Conclusions: Although our sample size was limited, and linkage analysis is necessary, the results support the putative role of dopaminergic polymorphisms in RDS behaviors. This study shows the importance of a nonspecific RDS phenotype and informs an understanding of how evaluating single subset behaviors of RDS may lead to spurious results. Utilization of a nonspecific “reward” phenotype may be a paradigm shift in future association and linkage studies involving dopaminergic polymorphisms and other neurotransmitter gene candidates