Multistage Growth Research Articles

Reconciling larval and adult sampling methods to model growth across life-stages.

Individual growth rates are intrinsically related to survival and lifetime reproductive success and hence, are key determinants of population growth. Efforts to quantify age-size relationships are hampered by difficulties in aging individuals in wild populations. In addition, species with complex life-histories often show distinct shifts in growth that cannot be readily accommodated by traditional modelling techniques. Amphibians are often characterized by rapid larval growth, cessation of growth prior to metamorphosis, and resumption of growth in the adult stage. Compounding issues of non-linear growth, amphibian monitoring programs typically sample larval and adult populations using dissimilar methods. Here we present the first multistage growth model that combines disparate data collected across life-history stages. We model the growth of the endangered Reticulated Flatwoods Salamander, Ambystoma bishopi, in a Bayesian framework, that accounts for unknown ages, individual heterogeneity, and reconciles dip-net and drift fence sampling designs. Flatwoods salamanders achieve 60% of growth in the first 3 months of life but can survive for up to 13 years as a terrestrial adult. We find evidence for marked variability in growth rate, the timing and age at metamorphosis, and maximum size, within populations. Average size of metamorphs in a given year appeared strongly dependent on hydroperiod, and differed by >10mm across years with successful recruitment. In contrast, variation in the sizes of emerging metamorphs appeared relatively constant across years. An understanding of growth will contribute to the development of population viability analyses for flatwoods salamanders, will guide management actions, and will ultimately aid the recovery of the species. Our model formulation has broad applicability to amphibians, and likely any stage-structured organism in which homogenous data cannot be collected across life-stages. The tendency to ignore stage-structure or omit non-conforming data in growth analyses can no longer be afforded given the high stakes of management decisions, particularly for endangered or at-risk populations.

Development of novel anti-malarial from structurally diverse library of molecules, targeting plant-like CDPK1, a multistage growth regulator of P. falciparum.

Upon Plasmodium falciparum merozoites exposure to low [K+] environment in blood plasma, there is escalation of cytosolic [Ca2+] which activates Ca2+-Dependent Protein Kinase 1 (CDPK1), a signaling hub of intra-erythrocytic proliferative stages of parasite. Given its high abundance and multidimensional attributes in parasite life-cycle, this is a lucrative target for designing antimalarials. Towards this, we have virtually screened MyriaScreenII diversity collection of 10,000 drug-like molecules, which resulted in 18 compounds complementing ATP-binding pocket of CDPK1. In vitro screening for toxicity in mammalian cells revealed that these compounds are non-toxic in nature. Furthermore, SPR analysis demonstrated differential binding affinity of these compounds towards recombinantly purified CDPK1 protein. Selection of lead compound 1 was performed by evaluating their inhibitory effects on phosphorylation and ATP binding activities of CDPK1. Furthermore, in vitro biophysical evaluations by ITC and FS revealed that binding of compound 1 is driven by formation of energetically favorable non-covalent interactions, with different binding constants in presence and absence of Ca2+, and TSA authenticated stability of compound 1 bound CDPK1 complex. Finally, compound 1 strongly inhibited intra-erythrocytic growth of P. falciparum in vitro. Conceivably, we propose a novel CDPK1-selective inhibitor, step towards developing pan-CDPK kinase inhibitors, prerequisite for cross-stage anti-malarial protection.

Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

Due to a lack of direct experimental results, the detailed mechanisms that govern the blistering behavior of tungsten (W) exposed to ITER-relevant condition in nuclear fusion remain unclear. The growth mechanism of hydrogen (H) blisters is one example. In this work, recrystallized W was exposed to H plasma at 50 eV, 1.5×1026m−2, and 573 K. Transmission electron microscopy (TEM) samples were prepared using plasma-focused ion beam (FIB) followed by flash-polishing to effectively remove surface damages induced by FIB. The TEM images revealed that the general blisters observed on the exposed surface are associated with underlying cavities. A considerable amount of dislocations were found in the vicinity of the cavities. Prismatic dislocation loop arrays were observed, including small size 'coffee-bean' prismatic loops and large size prismatic loops. Near the tip of surfaces cavities, evidences for the emission of shear loops were also found. Based on the experimental findings, a multi-stage growth mechanism of H cavities was proposed. The loop-punching mechanism is operative for both very small cavities and cavities with sizes larger than several hundreds of nanometers. Whereas at intermediate sizes, cavities grow by emitting shear loops from the cavity tip.

Extremely light K in subducted low-T altered oceanic crust: Implications for K recycling in subduction zone

In order to investigate the behavior of potassium (K) isotopes during metamorphic dehydration and to further constrain its implications for K recycling in the subduction zone, we measured K isotopic compositions of whole-rocks and separated minerals (phengite, omphacite, amphibole) from Sumdo eclogites, Tibet, using a recently established high-precision analysis method. Our data reveal that the δ41K (‰) of the whole-rock eclogites (−1.64 to −0.24) displays dramatically lower values than observed in fresh mid-ocean ridge basalts (MORB) (−0.43 ± 0.17) and altered MORB (−0.76 to −0.11). In addition, the δ41K values of eclogites show a positive correlation with both K2O contents and K/Nb ratios, which suggests that the low δ41K values were most likely caused by dehydration during subduction. Thus, isotopically heavy K may be released into the mantle wedge, while the light component is subducted into the deep mantle. Therefore, the K isotope systems have the potential to trace subducted crustal materials and to create heterogeneity within the mantle.Mineral separates from Sumdo eclogites are highly heterogeneous in K isotopic compositions, ranging from −0.98 to +0.23 in phengite, from −1.25 to −1.10 in omphacite and from −1.16 to −0.09 in amphibole. The K isotope fractionations between amphibole and phengite and between amphibole and omphacite vary from −0.30 to +0.25 and from −0.04 to +0.63, respectively, indicating K isotopic disequilibrium between amphibole and omphacite/phengite, which might result from the multistage growth of minerals during subduction metamorphism. However, generally phengites show heavier K isotopic compositions than the coexisting omphacite (Δ41Kphengite-amphibole = +0.25) and amphibole (Δ41Kphengite-amphibole = +0.03 ∼ +0.30, except TB193 is −0.25), which may imply that the K isotopic fractionation is controlled by the difference in coordination numbers of K between phengite (6) and omphacite (7 to 8)/amphibole (8).

Flower-Shaped Trapiche Ruby from Mong Hsu, Myanmar: A Revised Growth Mechanism

Two polished slices of flower-shaped trapiche ruby from Mong Hsu were analysed by X-ray computed tomography and X-ray micro-fluorescence. They are characterised by the presence of a core overgrown by two layers of ruby (with the outer one forming the ‘petal’ shape), and these three domains were previously attributed by Liu (2015) to a multi-stage growth mechanism. The present research indicates that these specimens show textural sector zoning associated with chemical sector zoning. In agreement with literature data, three different growth sectors are identified: a pinacoidal growth sector (corresponding to the core) and two sets of dipyramidal growth sectors with different inclinations with respect to the c-axis. The core, middle and outer layers are thus growth sectors of the same crystal, and no successive stages are needed to explain their formation. Therefore, the growth model proposed for other trapiche rubies from Myanmar also applies to the formation of these flower-shaped specimens. The distinctive shape of these rubies is due to weathering of the growth sectors and the sector boundaries.

Fault-fluid evolution in the Xitian W–Sn ore field (South China): Constraints from scheelite texture and composition

Understanding fault-fluid evolutionary processes is crucial for understanding the genesis of vein-type deposits. Scheelite and quartz are common hydrothermal minerals in W–Sn ore field faults. In the Xitan ore field (Nanling Range, South China), scheelite textural and compositional features were studied and two types of scheelite were identified: Type I (represented by scheelite in the Xihu fault) is intergrown with quartz, has oscillatory zonation, variable zonation band width and is homogeneous light grey color in cathodoluminescence images; and Type II (represented by scheelite in the Goudalan fault) is intergrown with quartz that shows multi-stage growth, has oscillatory zonation and each zonation band is the same width. Scheelite grains of both types have homogeneous major element distribution (e.g., W and Ca), however trace element contents (e.g., Mg, Nb) are slightly variable, and rare earth element (REE) and Y contents gradually decrease by an order of magnitude from the core to the rim in both types of scheelite. From core to rim, the chondrite-normalized REE patterns of Type I scheelite change from flat curves with no or slightly positive Eu anomalies to intense concave shapes with intense positive Eu anomalies. The middle REEs gradually become depleted, indicating the MREE fractionation associated with early scheelite precipitation in a relatively closed fault-fluid system. In contrast, the chondrite-normalized REE patterns of Type II scheelite grains are similar, all showing weak MREE depletion from the core to rim, implying recurrent fluid pulses in an open fault-fluid system. The REE patterns in the cores of the Type I scheelite are similar to those of the scheelite from Jurassic granites related to the W–Sn mineralization, suggesting that the initial ore-forming fluids were exsolved from the Jurassic magma. The REE patterns in the rims of Type II scheelite are consistent with those of scheelite from the Goudalan W deposit, suggesting that the fault-fluid system experienced a similar evolution to the ore-forming fluid system. Combining the results of this work with previous quartz H-O isotopic and fluid inclusion studies, it can be concluded that fluid mixing occurred in both the fault-fluid system and the ore-forming fluid system, triggering large-scale W precipitation.

Zoned orthopyroxenes in the Ni-Co sulfide ore-bearing Xiarihamu mafic-ultramafic intrusion in northern Tibetan Plateau, China: Implications for multiple magma replenishments

The Xiarihamu mafic-ultramafic intrusion is situated in the East Kunlun Orogenic Belt (E-KOB), northern Tibetan Plateau, China, with Ni-Co sulfide mineralization mainly in orthopyroxenite and olivine orthopyroxenite. Whole-rock and mineral compositions show cyclic variations in drill-hole intersections through the Xiarihamu mafic-ultramafic intrusion. Microbeam X-ray fluorescence (XRF) mapping shows reverse zoning (Cr-poor core, Cr-rich rim) and oscillatory zoning (Cr-poor core, Cr-rich mantle and Cr-poor rim) in orthopyroxene of olivine orthopyroxenite and orthopyroxenite. Zoned orthopyroxenes are euhedral or subhedral, and there are relatively sharp interfaces between zones with distinct Cr contents. Crystal-size distribution (CSD) curves of orthopyroxenes in olivine orthopyroxenite show concave-upward curvature at size larger than 3.0 mm, and larger orthopyroxenes commonly display zoning, implying a secondary recrystallization and grain growth of larger orthopyroxenes. Quantitative analyses show that Cr and enstatite contents of cores are relatively lower, but incompatible element (e.g., Ti, Zr, Ga and Sr) contents of cores are higher than rims in reverse zoned orthopyroxenes, and chemical profiles of unzoned orthopyroxenes resemble those of rims (but different from those of cores) in reverse zoned orthopyroxenes.Chemical profiles of orthopyroxenes indicate that Cr zoning is not due to the change in Cr partitioning behavior between orthopyroxene and silicate melt, which shows significant temperature and redox dependence. Textural feature and crystal-size distribution of orthopyroxenes suggest the formation of Cr-rich zones attests to the multi-stage growth in the process of magma replenishment, rather than a reactive liquid flow model or in-situ trapped liquid overgrowth. Orthopyroxene zoning, together with compositional variation and intrusive relationship between olivine orthopyroxenite and orthopyroxenite imply that the Xiarihamu mafic-ultramafic intrusion was formed by multiple magma replenishments with magma varying roughly from a more evolved to a more primitive composition.

New observations of Tin Mineralization Potential Vis-à-Vis Ore Petrographic, Alteration and Geochemistry in the Southeastern part of Bastar Craton, Central India

The Tin mineralizations occur around the Katekalyan area, hosted in the acid magmatic rocks. The evolution differentiating granitic magma shows residual melt enrichment where end products intruded as pegmatites into the rocks. The different kind of pegmatite occur as simple unzoned, recrystallized (granitic pegmatite), and metasomatic greisenised and albitised pegmatites which emplaced within the pre-existing rocks of metabasic intrusive, granite (KG), granite gneiss (KGG). Sometimes it also found in metasediments as mineralised and non-mineralised characters along the fractures and foliation planes trending N-S, E-W and more frequently are observed NNW-SSE trends. Cassiterite is most important Tin-ore mineral and associated with pegmatites. Some cassiterite samples exhibit colourless to brown shades zoning which indicate multi stage growth. The cassiterite samples contain significant amounts of Sn, Nb, Ta with minor W.
 The partial melting model shows that the variation 5 to 50% partial melting of bulk continental crust for KG as well as KGG rocks but bulk distribution coefficient for Sr (DSr) shows low i.e. <<10. The upper limit of partial melting of bulk crust estimates ~50 % for KG and KGG rocks are consistent with required rheological, critical melt percentage to leave the source region has decreased granite melt which were capable to mineralised tin ore elements. It is interesting to note that the SnF4 and SnCl4 probably not stable in presence of water under geologically reasonable conditions.

Effect of Temperature on Annealing Products of Synthesized Opal Matrices

In this paper, we describe the synthesis of opal matrices by the sol-gel method and the α-cristobalite production from them by high-temperature annealing. Both the conditions for preparing synthetic opal matrices by the hydrolysis of tetraethoxysilane in a binary ethanol-water solvent using an ammonia solution as a catalyst and the reagent concentrations for this process are described in detail. The silica particles were prepared by multistage growth to the required size at addition of tetraethoxysilane to the reaction mixture. A temperature regime for drying the siliceous xerogel with the production of porous matrices for further use and annealing to obtain high-purity α-cristobalite is proposed. Structural adjustments, such as an increase in the matrix density, their hardening, and a temperature-dependent change in the matrix porosity, are described. Open-pore matrices consisting of amorphous silicon dioxide are prepared by annealing up to 1100°C. The prepared matrices can later be used for their impregnation with various compositions to obtain various types of sensors, composite materials, and inverted matrices. The transition of a silica xerogel from an amorphous state to a crystalline state with the formation of low-temperature α-cristobalite with an α-tridymite admixture by drying and annealing at 1300°C is shown. Further annealing at 1650°C leads to the formation of a transparent nonporous sample of α-cristobalite. All processes were performed under the control of scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis.

Deciphering the zircon Hf isotope systematics of Eoarchean gneisses from Greenland: Implications for ancient crust-mantle differentiation and Pb isotope controversies

Abstract We report a Hf isotope investigation of zircons from four Eoarchaean orthogneisses from the Godthabsfjord region of southern West Greenland by laser ablation MC-ICPMS, to elucidate crust-mantle differentiation processes in the early Earth. Zircon crystals of all samples record a complex, multi-stage growth and disturbance history, and these discrete growth phases also exhibit disparate Lu-Hf isotope systematics. The oldest (3.84–3.82 Ga) zircon cores have tightly clustered 176Hf/177Hf ratios that are consistent with derivation of their tonalitic precursors from chondritic mantle at this time, with no evidence of input from older crustal or depleted mantle sources. Younger (3.67–3.62 Ga) zircon overgrowths have subchondritic Hf and plausibly grew from small fraction partial melts of the tonalitic host, involving variable dissolution of the older zircon cores. The Neoarchean (ca. 2.7 Ga) zircon component in some samples extends to significantly higher 176Hf/177Hf than the >3.65 Ga zircon, a feature that is interpreted to reflect addition of radiogenic Hf from the rock matrix during metamorphic zircon growth and recrystallisation at 2.7 Ga. The strongly positive eHf (3.82 Ga) values obtained by dissolution of GGU110999 zircons are interpreted to be an artifact of calculating eHf values at ages that are too old, and also from the inclusion of radiogenic younger domains in the analysed multi-grain fractions, rather than to a contribution from depleted Eoarchean mantle. Such data – from zircon grains with multiple age and isotopic components – should not be used to define the evolution of crust-mantle reservoirs. A re-interpretation of the existing Pb isotope data, incorporating the new Hf isotope constraints, posits that the protoliths to the Godthabsfjord gneisses were influenced by radiogenic Pb introduced as a fluid mobile component during recycling of a high-μ stagnant basaltic lid at ≥3.8 Ga. The destruction of this mafic protocrust, with attendant fluid release into chondritic mantle, may have been instrumental for the generation of stable Eoarchean tonalitic crust from ca. 3.8 Ga.

Effect of Si(1 1 1)√3 × √3-Bi template structure on growth mode and electrical conductance of Au overlayers

Growth of ultra-thin Au films on Si(1 1 1)√3 × √3-Bi surfaces was studied using low energy electron diffraction, scanning tunneling microscopy and in situ measurements of surface conductivity. The Si(1 1 1)√3 × √3-Bi surfaces were represented either by the Si(1 1 1)-α-√3 × √3-Bi phase with 0.33 ML (monolayers) of Bi adatoms or by the Si(1 1 1)-β-√3 × √3-Bi phase with 1.0 ML of Bi atoms arranged into trimers. Structure of the template surface was found to affect greatly the growth mode and conductance of the overgrown Au films in the thickness range from 0.1 to 3.0 ML of Au. Growth of Au films on Si(1 1 1)-β-√3 × √3-Bi follows the Vollmer-Webber mode, while in case of Au films on Si(1 1 1)-α-√3 × √3-Bi the complicated multi-stage growth occurs where formation of Stranski-Krastanov wetting layer is successively followed by island growth and vice versa. Surface conductivity of the samples was found to be dictated by Au film morphology. In the Au/Si(1 1 1)-β-√3 × √3-Bi sample, surface conductivity remains essentially unchanged due to lacking of electrical connections between Au islands. In the Au/Si(1 1 1)-α-√3 × √3-Bi sample, surface conductivity grows with Au thickness starting from overcoming of percolation threshold at ∼0.6 ML of Au.

Technology Evolution and Growth Potential for Printed Electronic Papers.

Electronic paper is now closer than ever to changing the way we read, write, and study. This was hailed as a revolution so profound that some see it as second only to the invention of the printing press in the 15th century. In this study, four analytical methods, which included statistical analysis, technology decomposition, multistage technological evolution and growth potential analysis were used. Results showed that technological research on business has great potential for development and vast market, and it would be another 16 years before the limit could be reached for patents. A great deal of technology breakthrough has been achieved during 1992 and 2012. The four major countries for printed electronic paper development are Japan, USA, South Korea and China. However, China has a gap compared with other countries, as the key technology was held by large enterprises. The apparatus for printed electronic paper has been the major focus in China. The key point for research on printed electronic paper was focused on devices for presentation and light emission, and related semiconductor devices.

Identification of drought tolerant populations at multi-stage growth phases in temperate maize germplasm

Drought is one of the main abiotic stresses in agriculture worldwide. Drought could increase under the predicted scenario of climate change, particularly in the Mediterranean area. Breeding for drought tolerance requires screening of germplasm in order to identify sources of tolerance; therefore, were evaluated 51 diverse open-pollinated maize populations from various temperate regions under increasing levels of drought at germination, seedling establishment and early growth. There was genetic variability for drought tolerance among populations at all growth phases. Several populations from diverse origins and germplasm groups exhibited high germination across stress treatments. Some of those populations had high ability to sustain root development and showed differential performance depending on the stage of development and the phenotypic aspect considered. In general, BS17 showed high germination rate, fast seedling growth and early vigor under drought. Longlellow and Grano de trigo showed high germination and growth establishment rates, whereas AS3(HT)C3 showed high germination rate and early vigor under drought. The photosynthetic rate, stomatal conductance and transpiration of Enano Levantino/Hembrilla (ELH) and BS17 populations were not affected by drought. Water use efficiency of BS17, ELH, Northwestern Dent (NWD) and Viana was not affected by drought. Some of these populations are promising sources of drought tolerance which can provide different mechanisms of drought tolerance at different stages of plant development. Therefore, these results open new possibilities of breeding for drought tolerance by combining those mechanisms through crosses among potential donors. Furthermore, these findings indicate that it is worthwhile to study the genetic and biological basis of such mechanisms.

Mass-transfer and differential element mobility in metapelites during multistage metamorphism of the Yenisey Ridge, Siberia

Abstract Pelitic gneisses and schists from the Garevka Complex (Yenisey Ridge) at the western margin of the Siberian craton contain zoned garnet porphyroblasts that show clear evidence of multistage growth. The three discrete stages define a counter-clockwise pressure–temperature ( P–T ) path involving initial prograde low pressure heating followed by near-isothermal medium-pressure compression and post-peak retrograde synexhumation decompression and cooling. The combined study of the variations of in-situ major and trace element mineral compositions of coexisting minerals and mineral modes with changing P and T conditions and metamorphic reactions in rocks allowed detailed investigation of metamorphic processes. A significant increase in pressure during prograde collision-related metamorphism correlates with an abrupt increase of Ca in garnets, which in turn is accompanied by a significant decrease in heavy rare earth elements (HREE) and Y contents. Decrease in temperature and pressure during retrograde metamorphism led to an increase in the HREE and Y content in garnets with concomitant decrease of grossular component of garnet. A pronounced systematic negative correlation between HREE including Y content and Ca content in garnet can be attributed to substitution of trivalent rare earth elements (REE) and Y for divalent Ca cations on eightfold sites. The main reasons for the sharp increase in Ca content in garnets during collisional metamorphism are either (1) the redistribution between garnet and plagioclase, which led to less calcium in composition, or (2) consequence of epidote breakdown. A mass balance of major and trace elements between the reactants and products of metamorphic reactions yield very good matches between the measured and reconstructed modal abundances in all cases, indicating that collisional metamorphism was essentially isochemical with respect to most elements, with the exception of HREE. The minimum equilibration volume for the major elements was c. 1 mm 3 . The total HREE balance requires a rather greater reaction volume involved in the redistribution of HREEs, of the order of 3–8 mm 3 which provides evidence for their relatively higher migration mobility during metamorphism in comparison with other REE.

Multi-stage growth and fluid evolution of a hydrothermal sulphide chimney in the East Pacific Ridge 1–2° S hydrothermal field: constraints from in situ sulphur isotopes

AbstractSulphur isotopes can be used as a powerful tool to trace fluid evolution and explore the formation of chimneys. To clarify the in situ S isotopic variations of sulphides at the micro-scale, we analyzed a sulphide chimney collected from the hydrothermal field in the East Pacific Rise 1–2° S using a sensitive high-mass-resolution ion micro-probe for stable isotopes (SHRIMP SI). Three mineral zones can be identified in the chimney: an external outer wall of porous anhydrite and colloform pyrite, an internal middle zone of sub-euhedral pyrite and massive chalcopyrite, and an inner zone of massive pyrite. The δ34SV-CDT values of the sulphides fall within the range 1.83–7.51 ‰ (avg. 4.05 ‰, n = 16), and S isotopic values increase from the core (3.09 ‰, n = 3) to the middle (3.78 ‰, n = 11) to the edge (6.99 ‰, n = 2). These results illustrate mineral crystallization processes and the mixing between seawater-derived S and magmatic–hydrothermal fluids during the growth of the chimney. The zones from the edge to the core are characterized by crystal morphologies of colloform/anhedral pyrite to massive pyrite with decreasing δ34S values, revealing multi-stage mineral deposition and sulphur isotopic fractionation. In contrast to the increase in δ34S values from the core to the edge in one profile (profile A), anomalously low δ34S values in fine-grained pyrite relative to chalcopyrite in another profile (profile B) in the middle zone result from S isotopic exchange between seawater SO42− and fluid H2S due to different fluid–seawater mixing, possibly caused by variations in permeability and porosity across the chimney.

Identifying multi-stage nanocrystal growth using in situ TEM video data

ABSTRACTThe in situ transmission electron microscopy technique is receiving considerable attention in material science research, as its in situ nature makes possible discoveries that ex situ instruments are unable to make and provides the capability of directly observing nanocrystal growth processes. As incresing amounts of dynamic transmission electron microscopy (TEM) video data become available, one of the bottlenecks appears to be the lack of automated, quantitative, and dynamic analytic tools that can process the video data efficiently. The current processing is largely manual in nature and thus laborious, with existing tools focusing primarily on static TEM images. The absence of automated processing of TEM videos does not come as a surprise, as the growth of nanocrystals is highly stochastic and goes through multiple stages. We introduce a method in this article that is suitable for analyzing the in situ TEM videos in an automated and effective way. The method learns and tracks the normalized particle size distribution and identifies the phase-change points delineating the stages in nanocrystal growth. Using the outcome of the change-point detection process, we propose a hybrid multi-stage growth model and test it on an in situ TEM video, made available in 2009 by Science.

Synthesis of thick gallium nitride layers by method of multi-stage growth on substrates with column structure

Subject of Research.The paper deals with processes of formation and transformation of defects during multi-stage growth of thick gallium nitride layers with hydride vapor phase epitaxy on GaN/Al2O3 substrates with buried column pattern formed with the use of metal-organic vapor phase epitaxy. Methods. The growth of initial GaN layers was performed with the use of metal-organic vapor phase epitaxy. On the surface of the initial layers columns with the height of 800 nm were generated by means of ion etching. These columns were overgrown with 3-4 µm-thick GaN layers. On thus formed substrate multi-stage growth of GaN layers was performed with the use of hydride vapor-phase epitaxy. The total thickness of GaN layers was 100-1500 µm. The grown layers were studied by optical and electron microscopy and Raman spectroscopy. Main Results. Density of threading dislocations in the layers grown by hydride vapor-phase epitaxy was (3-6)·107 cm-2, that was one order of magnitude lower than in the used substrate, and two to three orders lower than dislocation density in typical GaN layers grown on commercial sapphire substrates. Raman spectroscopy data were indicative of low level of mechanical stress in the layers and their high structural uniformity. It was established that under multi-stage growth conditions, non-catastrophic cracks (those that do not cause sample destruction) are able to transform into macropores and appear to be an important st ructural element, serving to stress relaxation in the bulk of thick gallium nitride layers grown on foreign substrates. Practical Relevance. The results of the study can be used in the development of III-nitride heterostructures for optoelectronics and high-power and high-frequency microelectronics.

Synsedimentary, Diagenetic, and Metamorphic Pyrite, Pyrrhotite, and Marcasite at the Homestake BIF-Hosted Gold Deposit, South Dakota, USA: Insights on Au-As Ore Genesis from Textural and LA-ICP-MS Trace Element Studies

The Paleoproterozoic Homestake deposit, northern Black Hills, South Dakota, is the largest banded iron-formation (BIF)-hosted gold deposit in the world and one of the largest single gold deposits globally (~1,300 t Au mined at an average grade of 8.4 g/t). The origin of the deposit has remained in dispute from its discovery, with views broadly falling into two groups: (1) the gold and associated elements were externally sourced and deposited in a suitable structural and/or chemical trap (e.g., iron formation), and (2) gold was indigenous to the host iron formation, from which it was remobilized into dilatant structural zones during deformation and metamorphism. In recent times, most workers have favored the former model, appealing to the broad synchroneity of Paleoproterozoic metamorphism, felsic magmatic activity, and gold event timing. LA-ICP-MS analysis of synsedimentary to early diagenetic sulfides at Homestake and surrounding area indicates that the Au in the orebodies may have originally had a significant syngenetic component. In particular, LA-ICP-MS mapping of multistage pyrites from carbonaceous shale in the upper Poorman Formation shows that Au and a suite of trace elements (Co, Ni, Cu, Zn, Se, Mo, Ag, Sb, Te, Au, Hg, Tl, Pb, and Bi), similar to those in diagenetic pyrite from around the globe, are contained in anhedral, sponge-textured cores and nodules surrounded by relatively trace element barren, Au-poor, euhedral pyrite rims. Furthermore, interelement ratios (e.g., Co/Ni, Ni/Ag) of the trace element-rich spongy and nodular pyrites are also similar to those of typical diagenetic pyrite. LA-ICP-MS imaging of pyrrhotite in the same rocks reveals multistage growth in this mineral as well, with the earlier generation having higher concentrations of Ag, Sb, Pb, Tl, and Bi than its presumed metamorphic counterpart. Imaging of marcasite in the shales of the upper Poorman Formation demonstrates this mineral’s high abundance of W and Tl relative to all generations of pyrite and pyrrhotite. Mass-balance calculations indicate that the volume of upper Poorman Formation in the mine area (approx. 12 km3) could potentially yield ~4,500 t of Au, a value greater than the total mined resource by more than a factor of three. These geochemical data and calculations suggest that a significant portion of the gold at Homestake may have been sourced from the relatively thick carbonaceous and sulfidic black shale facies in the stratigraphic footwall to the host iron formation, in a manner similar to other sediment-hosted gold districts.

The Borodinskii Massif of potassium porphyric granite: Results of U–Pb dating and its tectonic position (Fennoscandian Shield)

It has been demonstrated for the first time that the Svecofennian crustal porphyric granites in the southeastern part of the Fennoscandian Shield are clearly subdivided into two age groups of 1.87 and 1.80 Ga. The representative of the first group is the Kuznechenskii Massif of porphyric granites with a U–Pb age of 1874 ± 4 Ma belongs to the group of plutons formed during the orogenic stage of Svecofennide evolution. The Borodinskii Massif with an age of 1797 ± 2 Ma is a member of the second group: these plutons were formed under tectonically stable (epiplatform) conditions. Therefore, the formation of porphyric granites occurred as the result of repeated generation of crustal magmas during multistage accretional growth of the Svecofennian crust.

High Temperature Corrosion studies on Pulsed Current Gas Tungsten Arc Welded Alloy C-276 in Molten Salt Environment

Alloy C-276 is widely used in the power plant environment due to high strength and corrosion in highly aggressive environment. The investigation on high- temperature corrosion resistance of the alloy C-276 PCGTA weldment is necessary for prolonged service lifetime of the components used in corrosive environments. Investigation has been carried out on Pulsed Current Gas Tungsten Arc Welding by autogenous and different filler wires (ERNiCrMo-3 and ERNiCrMo-4) under molten state of K2SO4-60% NaCl environment at 675oC under cyclic condition. Thermogravimetric technique was used to establish the kinetics of corrosion. Weight gained in the molten salt reveals a steady-state parabolic rate law while the kinetics with salt deposits displays multi-stage growth rates. PCGTA ERNiCrMo-3 shows the higher parabolic constant compared to others. The scale formed on the weldment samples upon hot corrosion was characterized by using X-ray diffraction, SEM and EDAX analysis to understand the degradation mechanisms. From the results of the experiment the major phases are identified as Cr2O3, Fe2O3, and NiCr2O4. The result showed that weld fabricated by ERNiCrMo-3 found to be more prone to degradation than base metal and ERNiCrMo-4 filler wire due to higher segregation of alloying element of Mo and W in the weldment