Statistical parameters in assessing ecological and geochemical state of the Kolpashevo-Turukhan mineragenic zone eastern part

The relevance. The required statistical identification of natural and anthropogenic biogeochemical anomalies when conducting ecological and geochemical studies on the territories of buried exogenous ores with a weak anthropogenic pressure. The difficulty of their identification according to their sources is related to a similar litho-siderophilic geochemical specialization of sedimentary rocks of iron ore, titanium-zirconium formations and modern soils of taiga zone landscapes. Moreover, the research implemented a method for biomaterial sample preparation. This method is aimed at obtaining the possibility of using a biomaterial sample as a natural indicator to reveal the aeolian and dust aerosol substance intake. As a result, there is an urgent need to involve steps in biogeochemical data statistical processing that allows one qualitatively differentiate the effects of chemical elements concentration via root nutrition and dust accumulation on the leaves. The aim. Statistical assessment of content variability and relationships of chemical elements in aspen leaves in the zone of anthropogenic influence of transport roads crossing the localization areas of buried iron ore deposits of the Bakcharsko-Kolpashevo ore district, Kolpashevo-Turukhan mineragenic zone. Qualitative biogeochemical identification of biomaterial enrichment through root and dust in areas of anomalous concentration of chemical elements using data on accumulation of rare earth elements. Objects. Soil, leaves of common aspen (Populus tremula L., 1753). Methods. Regional biogeochemical and lithochemical sampling was carried out in three profiles along local roads with asphalt and unpaved surfaces at the entrances to settlements. The sampling points common for the methods were shifted off the roads at a distance of at least 20 m to undisturbed landscapes. After sample preparation, the concentration of 28 chemical elements in the samples was determined by instrumental neutron activation analysis. The interpretation of geochemical data was based on the results of multicomponent statistical analysis. Results. The studied territories along the lines of regional research are characterized by the background biogeochemical and lithochemical values. The revealed biogeochemical anomaly is caused by a dust halo that accompanies the unpaved road. The rare earth elements levels show the influence of fine dust-aerosol and aeolian material intake

Study of semi-polar gallium nitride grown on m-sapphire by chloride vapor-phase epitaxy

In this study, we analyzed the result of the influence of the non-polar plane of a sapphire substrate on the structural, morphological, and optical properties and Raman scattering of the grown epitaxial GaN film. It was found that selected technological conditions for the performed chloride-hydride epitaxy let us obtain the samples of structurally qualitative semi-polar wurtzite gallium nitride with (11¯22) orientation on m-sapphire. Using a set of structural and spectral methods of analysis the structural, morphological, and optical properties of the films were studied and the value of residual bi-axial stresses was determined. A complex of the obtained results means a high structural and optical quality of the epitaxial gallium nitride film. Optimization of the applied technological technique in the future can be a promising approach for the growth of the qualitative GaN structures on m-sapphire substrates

Expanded syringe exchange programs and reduced HIV infection among new injection drug users in Tallinn, Estonia

<p>Abstract</p> <p>Background</p> <p>Estonia has experienced an HIV epidemic among intravenous drug users (IDUs) with the highest per capita HIV prevalence in Eastern Europe. We assessed the effects of expanded syringe exchange programs (SEP) in the capital city, Tallinn, which has an estimated 10,000 IDUs.</p> <p>Methods</p> <p>SEP implementation was monitored with data from the Estonian National Institute for Health Development. Respondent driven sampling (RDS) interview surveys with HIV testing were conducted in Tallinn in 2005, 2007 and 2009 (involving 350, 350 and 327 IDUs respectively). HIV incidence among new injectors (those injecting for < = 3 years) was estimated by assuming (1) new injectors were HIV seronegative when they began injecting, and (2) HIV infection occurred at the midpoint between first injection and time of interview.</p> <p>Results</p> <p>SEP increased from 230,000 syringes exchanged in 2005 to 440,000 in 2007 and 770,000 in 2009. In all three surveys, IDUs were predominantly male (80%), ethnic Russians (>80%), and young adults (mean ages 24 to 27 years). The proportion of new injectors decreased significantly over the years (from 21% in 2005 to 12% in 2009, p = 0.005). HIV prevalence among all respondents stabilized at slightly over 50% (54% in 2005, 55% in 2007, 51% in 2009), and decreased among new injectors (34% in 2005, 16% in 2009, p = 0.046). Estimated HIV incidence among new injectors decreased significantly from 18/100 person-years in 2005 and 21/100 person-years in 2007 to 9/100 person-years in 2009 (p = 0.026).</p> <p>Conclusions</p> <p>In Estonia, a transitional country, a decrease in the HIV prevalence among new injectors and in the numbers of people initiating injection drug use coincided with implementation of large-scale SEPs. Further reductions in HIV transmission among IDUs are still required. Provision of 70 or more syringes per IDU per year may be needed before significant reductions in HIV incidence occur.</p

Local structure, chemical bond parameters and hyperfine magnetic interactions of 57Fe and doped 119Sn atoms in the orthoferrites TlFeO3 and TlFe0.99Sn0.01O3

Mössbauer spectroscopy has been applied to study the magnetic hyperfine interactions of 57Fe and 119Sn probe atoms within TlFeO3 and TlFe0.99Sn0.01O3 ferrites. According to the magnetic measurements, the magnetic ordering temperature TN (= 560 K) for TlFeO3 is much lower than that for any other orthoferrites RFeO3 (R = rare earth). It is suggested that such difference in TN may be explained by different characteristics of the Tl–O and R–O chemical bonds involved and the induced competition with the Fe–O bonds. The effects of covalency and overlap distortion on the spin and charge densities at 57Fe nuclei are discussed in relation with the hyperfine interactions observed. By using cluster molecular orbital (MO) calculations, it was shown that the low value of the hyperfine magnetic field HFe(= 538 kOe) at 57Fe nuclei in TlFeO3 is strongly associated with a decrease of the covalent mixing parameter (bσ)2 = 0.048 and (bπ)2 = 0.009 values, which characterize the Fe–O bond covalence. It was elucidated that the value of super-transferred hyperfine field (HSTHF) at 119Sn nuclei in TlFe0.99Sn0.01O3 is sensitive mainly to the angle of the Sn–O–Fe bonds

Synthesis, structure, and magnetic and dielectric properties of magnetoelectric BaDyFeO4 ferrite

BaDyFeO4 was prepared by a conventional solid-state method in air at 1573 K. It crystallizes in space group Pnma (No. 62) with a = 13.16861(1) angstrom, b = 5.70950(1) angstrom, and c = 10.26783(1) angstrom, and it is isostructural with BaYFe0 4 . Three magnetic transitions were found in BaDyFeO4 at T-N3 = 9 K, T-N2 = 23 K, and T-N1 =47 K in zero magnetic field in comparison with two magnetic transitions observed in BaYFeO4. Magnetic-field-induced transitions were also detected in BaDyFeO4 at 18 and 28 kOe (at T= 1.8 K). Frequency-dependent broad dielectric peaks were observed in BaDyFeO4 spanning between T-N2 and T-N and centred at 35 K - this temperature does not coincide with any T-N. No dielectric anomalies were found at T-N1 and T-N3, while very weak frequency-independent dielectric anomalies were detected at T-N2. Positive and negative magnetodielectric effects were measured in BaDyFeO4 (within a range of -0.8 and + 0.4% up to 90 kOe) reflecting magnetic-field dependence of dielectric constant. Pyroelectric current measurements did not detect any ferroelectricity in BaDyFeO4 under measurement conditions used. No dielectric anomalies and no magnetodielectric effects were found in BaYFeO4. (C) 2019 Elsevier B.V. All rights reserved

Electronic state of 57Fe used as Mössbauer probe in the perovskites LaMO3 (M=Ni and Cu)

For the first time a comparative study of rhombohedral LaNiO3 and LaCuO3 oxides, using 57Fe Mössbauer probe spectroscopy (1% atomic rate), has been carried out. In spite of the fact that both oxides are characterized by similar crystal structure and metallic properties, the behavior of 57Fe probe atoms in such lattices appears essentially different. In the case of LaNi0.99Fe0.01O3, the observed isomer shift (δ) value corresponds to Fe3+ (3d5) cations in high-spin state located in an oxygen octahedral surrounding. In contrast, for the LaCu0.99Fe0.01O3, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe4+(3d4) cations in octahedral coordination within Fe(IV) perovskite-like ferrates. To explain such a difference, an approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that in the case of LaNi0.99Fe0.01O3, electronic state of nickel is dominated by the d7 configuration corresponding to the formal ionic “Ni3+–O2−” state. On the other hand, in the case of LaCu0.99Fe0.01O3 a large amount of charge is transferred via Cu–O bonds from the O:2p bands to the Cu:3d orbitals and the ground state is dominated by the d9L configuration (“Cu2+−O” state)..

Local Environment and Electronic Structure in K2NiF4-type La2Li0.50Cu0.50O4 Doped by 57Fe

The 57Fe M¨ossbauer spectrum of the oxide La2Li0.50Cu0.50O4 doped with 57Fe (1 at.-%) underlines at 300 K the presence of three different components: two corresponding to the substitution of 57Fe probe atoms for respectively “Cu3+” [Fe(1)] and Li+ [Fe(3)] and the third [Fe(2)] attributed to 57Fe associated with oxygen vacancies. A decrease of the temperature down to 77 K does not lead to essential changes of the M¨ossbauer parameters corresponding to the Fe(1) and Fe(2) sub-spectra. On the contrary, a drastic change occurs in the Fe(3) sub-spectrum which has been interpreted by a displacement of the charge-transfer equilibrium Fe4+(3) + O2− →Fe3+(3) + O(L) at the Li+ sites

Local Environment and Electronic Structure in K2NiF4-type La2Li0.50Cu0.50O4 Doped by 57Fe

The 57Fe M¨ossbauer spectrum of the oxide La2Li0.50Cu0.50O4 doped with 57Fe (1 at.-%) underlines at 300 K the presence of three different components: two corresponding to the substitution of 57Fe probe atoms for respectively “Cu3+” [Fe(1)] and Li+ [Fe(3)] and the third [Fe(2)] attributed to 57Fe associated with oxygen vacancies. A decrease of the temperature down to 77 K does not lead to essential changes of the M¨ossbauer parameters corresponding to the Fe(1) and Fe(2) sub-spectra. On the contrary, a drastic change occurs in the Fe(3) sub-spectrum which has been interpreted by a displacement of the charge-transfer equilibrium Fe4+(3) + O2− →Fe3+(3) + O(L) at the Li+ sites

Electronic state of 57Fe Mössbauer probe atoms in Cu(III) oxides with perovskite and perovskite-related structures

Mössbauer spectroscopy studies were developed in order to obtain an evaluation of different physico-chemical factors characterizing the electronic structure of the local sites (CuO6) into three copper(III) oxides: LaCuO3 having a three-dimensional (3D) perovskite structure; SrLaCuO4 and La2Li0.50Cu0.50O4 with a two-dimensional (2D) K2NiF4-type structure. All these matrixes have been doped with 57Fe (1 at.%) Mössbauer probe atoms. Such evaluation was based on analysis of the 57Fe Mössbauer parameters (isomer shift and quadrupole splitting) characterizing the formal oxidation state and the local structure of the 57Fe probe atoms. The obtained results underline that four main factors play an important role in the stabilization of formally trivalent “Cu3+” ions: (i) the involved preparation process (in particular the oxygen pressure level able to impede the formation of oxygen vacancies); (ii) the dimensionality (3D or 2D) of the lattice; (iii) the chemical surrounding and (iv) the local structural distortion of the transition metal site (CuO6), both last factors governing the local crystal field energy, orbital ordering and a possible charge transfer Cu3+–O2− ↔ Cu2+–O−(L)