Mixed Zone Research Articles

Distribution, properties and origin of viscous-flow features in the McMurdo Dry Valleys, Antarctica

Satellite images and high resolution air photos, coupled with field examinations, were used to examine 24 rock glaciers/debris-covered glaciers and 25 gelifluction sheets, collectively referred to as viscous-flow features, in the McMurdo Dry Valleys, Antarctica. Debris-covered glaciers are the dominant form and are longer (mean length=2.5km), wider (mean width=0.8km), and less steep (mean slope=12°) than similar features reported in most arctic and alpine environments. The catchment areas tend to be large, averaging over 9km2. Most of the debris-covered glaciers are tongue-shaped, and where excavation was possible, the ice core was readily observable. Gelifluction sheets primarily occur at the base of valley sidewalls below talus on slopes ranging from 5 to 30° (average=13°) and contain a very thin active layer (normal range 20 to 40cm). Both viscous-flow forms occur on the north- and south-facing slopes of the east–west trending valleys and are concentrated in the inland mixed zone and stable upland microclimatic zone; these lobes were not found in the coastal thaw zone. Gelifluction sheets result from the melting of snow high on the valley walls, subsurface flow of meltwater on top of the permafrost, and slow movement downslope. They are readily observable from nonsorted polygons that are stretched into rectangles that are perpendicular to the slope and contain raised polygon rims upslope. The movement of gelifluction sheets can be detected from upturned stones containing carbonate coatings. Rates of horizontal surface flow of the viscous-flow features are comparable to those reported elsewhere in Antarctica and in the alpine and arctic regions of the world. Some of the viscous-flow features appear to be inactive, possibly reflecting the recession of alpine glaciers in high elevation cirques.

Growth rate variation and potential paleoceanographic proxies in Primnoa pacifica: Insights from high-resolution trace element microanalysis

Red tree coral, Primnoa pacifica, is one of the more common habitat-forming deep-sea gorgonian corals in the northeast Pacific Ocean, growing in colonies up to 2m high and living for decades to hundreds of years. Growth characteristics of P. pacifica were studied in Dixon Entrance, northern British Columbia, and the Olympic Coast National Marine Sanctuary, Washington State, USA, based on samples collected in July 2008. To minimize the impact of scientific sampling on coral populations, only dead coral skeletons and dislodged live corals were collected. Ages and growth rates were measured using band counts, and checked against AMS-14C ages of gorgonin rings. Ba/Ca, Mg/Ca, Na/Ca and Sr/Ca ratios in the calcite cortex were measured using radial Secondary Ion Mass Spectrometer (SIMS) transects with a spot size of <20μm and separation distance of 25μm. Growth banding was consistent in width between the central mixed zone consisting of calcite and gorgonin and the dominantly calcite cortex. Average annual radial growth rate of the nine corals analysed ranged from 0.23 to 0.58mm/yr, with an average growth rate of 0.32mm/yr in Dixon Entrance and 0.36m/yr in OCNMS. These growth rates are slightly higher than P. pacifica growth rates from the Gulf of Alaska, and more than four times the growth rates of sister species Primnoa resedaeformis in the northwest Atlantic. Primary productivity is likely a more important driver of geographic variation in Primnoa growth rates than temperature or current strength. Both Dixon Entrance and OCNMS are areas with high primary productivity and strong tidal currents. Lack of post-Atomic Bomb radiocarbon in all but one of the gorgonin samples, and long radiocarbon reservoir ages in the Northeast Pacific, made radiocarbon-based verification of coral ages and growth rates difficult due to wide errors in calibrated age estimates. Mg/Ca and Sr/Ca ratios were inversely correlated in two of the three corals analyzed, and showed evidence of interannual variation. Mg/Ca ratios ranged from 70 to 136mmolmol−1, and Sr/Ca ratios from 2.041 to 3.14mmolmol−1. Previously published relationships between gorgonian calcite Mg/Ca and seawater temperature yielded average temperatures matching ambient measurements, but the intra- and inter-annual variation in apparent temperature based on the Mg/Ca ratios was more than double the observed variation in modern seawater temperature ranges in the region. Annual variation in Mg/Ca and Sr/Ca could be related to seasonal changes in precipitation efficiency, which is likely a function of short-term fluctuations in coral growth rate, in turn related to variation in primary productivity. Seasonal and interannual variations in food availability, driven by primary productivity, may affect skeletal growth rate, hence Mg/Ca and Sr/Ca ratios. Primnoid coral skeletal microgeochemistry probably records temporal changes in both temperature and primary productivity.

Earthworm density and biomass in relation to plant diversity and soil properties in a Palouse prairie remnant

Earthworms are important soil animals in grassland ecosystems and are considered to be important to soil quality. The overall impact of earthworms on soil properties and plant diversity, however, depends on earthworm species, functional group and the type of ecosystem. The primary purpose of this study was to document the relationship among earthworms, key soil properties and native and exotic plant diversity in the little studied, Palouse prairie grassland (Idaho, USA). A secondary objective was to determine the effectiveness of three methods commonly used to sample earthworms. A hillslope characterized by Palouse prairie vegetation, well-expressed, hummocky (mounded) topography and known to support both exotic and native earthworm species was selected for study. The hillslope was divided into three zones [annual-dominated (AD), mixed (MX) and perennial-dominated (PD)] based on characteristics of the inter-mound plant communities described in previous research. Total earthworm biomass in the MX zone (53.5gm−2) was significantly greater than in the PD zone (14.7gm−2) (P=0.0384), but did not differ from the AD zone. Earthworm density ranged from 52 to 81.1individualsm−2 but was not significantly different across zones. Total C and N at 0 to 10 and 30 to 50cm depths were significantly greater in the AD and PD zones as compared to the same depths in the MX zone. Soil textural class was silt loam within all zones and the soil silt fraction was positively correlated with total exotic earthworm density (R=0.783, P=0.0125) and biomass (R=0.816, P=0.0072). Native earthworms were only found in the zone with the greatest total and native plant diversity (PD). Total soil C and N were not correlated to earthworm density, but soil total C and N were significantly negatively correlated with exotic plant density, which indicates that invasive plants may be decreasing soil total C (R=−0.800) and N (R=−0.800). Calculated earthworm densities using data from the electroshocker were generally lower than those based on the hand-sorting method. Electroshocking, however, created lower disturbance and was the only method that resulted in the collection of the deep-burrowing, native species Driloleirus americanus.

Enrichment of Rare Earth Elements during magmatic and post-magmatic processes: a case study from the Loch Loyal Syenite Complex, northern Scotland

Concern about security of supply of critical elements used in new technologies, such as the Rare Earth Elements (REE), means that it is increasingly important to understand the processes by which they are enriched in crustal settings. High REE contents are found in syenite-dominated alkaline complexes intruded along the Moine Thrust Zone, a major collisional zone in north-west Scotland. The most northerly of these is the Loch Loyal Syenite Complex, which comprises three separate intrusions. One of these, the Cnoc nan Cuilean intrusion, contains two mappable zones: a Mixed Syenite Zone in which mafic melasyenite is mixed and mingled with leucosyenite and a Massive Leucosyenite Zone. Within the Mixed Syenite Zone, hydrothermal activity is evident in the form of narrow altered veins dominated by biotite and magnetite; these are poorly exposed and their lateral extent is uncertain. The REE mineral allanite is relatively abundant in the melasyenite and is extremely enriched in the biotite–magnetite veins, which have up to 2 % total rare earth oxides in bulk rock analyses. An overall model for development of this intrusion can be divided into three episodes: (1) generation of a Light Rare Earth Element (LREE)-enriched parental magma due to enrichment of the mantle source by subduction of pelagic carbonates; (2) early crystallisation of allanite in melasyenite, due to the saturation of the magma in the LREE; and (3) hydrothermal alteration, in three different episodes identified by petrography and mineral chemistry, generating the intense enrichment of REE in the biotite–magnetite veins. Dating of allanite and titanite in the biotite–magnetite veins gives ages of c. 426 Ma, overlapping with previously published crystallisation ages for zircon in the syenite.

English

Variances in the natural-environmental and artificial factors of the mining industry and of mining production were analyzed to achieve scientifically the ecological restoration of the Lu’an mining land system. The eco-environmental pressure of the evaluation index system was established. Each unit of land system was exposed to a different eco-environmental pressure, which resulted in differences in land eco-function performance. The land system can be categorized into the productive, protective, consumptive, and mixed land types based on eco-environmental performance. The Lu’an mining area was divided into four regions, namely, the uncultivated land consumptive zone (23.33 km2, 4.09%), the wetland and mining subsidence protective zone (109.23 km2, 19.16%), the flatland productive zone (373.89 km2, 65.57%), and the artificial mixed zone (63.76 km2, 11.18%), and a total of eleven eco-function types. The regions’ area ratios were 6.50, 19.16, 8.77, and 65.57%, respectively. Productive and consumptive land was oversized, whereas mixed and protective land was very small, indicating an undesirable land use system. Based on the analysis, an integrated model involving 19 models (e.g, shrub and grassland rehabilitation, steep slope protection, ecological village building model, etc.) was proposed for the development of the local eco-environment based on the eco-function type of mining land. Key words: Mining area, ecological division, eco-function type, eco-environmental pressure, China,

STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWOKEPLERTARGETS

Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

Hidrogeoquímica de cursos de água: influência da ocupação humana sobre parâmetros físico-químicos no Município de Porto Alegre, RS

Neste trabalho são apresentados resultados de avaliação de impacto ambiental em três sub-bacias hidrográficas, situadas em diferentes contextos urbano-paisagísticos, na cidade de Porto Alegre/RS. A influência de atividades humanas sobre a composição química de águas e sedimentos, coletados sazonalmente, foi determinada a partir da análise em laboratório de parâmetros físico-químicos, tais como Fe, Mn, Al, Cu, Zn, Cr, Cd, Pb, Hg, DBO5, DQO e matéria orgânica, além de parâmetros in situ como potencial hidrogeniônico-pH, temperatura-T, potencial de redução-Eh, condutividade elétrica-CE e oxigênio dissolvido-OD, de modo a estabelecer distinção entre dejetos gerados em cada cenário. Os resultados revelam que os contextos urbano-paisagísticos influenciam sensivelmente a composição química dos cursos d’água. Por outro lado, a sazonalidade parece exercer papel secundário, considerando que não houve variação signiticativa na concentração de poluentes no período de superávit hídrico, compreendido entre Abril e Outubro. Desse modo, constatamos que os graus de poluição seguem a sequência lógica dos padrões de urbanização: Periurbana é a zona em que a produção de dejetos é menor, a zona Urbana Mista é aquela onde há adensamento populacional e presença de indústrias e outras atividades potencialmente poluidoras, e Urbana Rarefeita é a zona que apresenta características intermediárias. Ao mesmo tempo, verifica-se que, em ambos os cenários, o ambiente fluvial está exposto a processos contínuos de degradação,considerando que dejetos são lançados diretamente na água, fato que contribui para o aumento dos gastos com seu tratamento.

Effects of Thermal Discharge from a Coastal Power Plant on Phytoplankton in Zhanjiang Bay

Effects of thermal discharge from a coastal power plant on phytoplankton community were determined in subtropical Zhanjiang Bay. Two sampling transects were chosen up and down the Zhanjiang Plant in the Zhanjiang Bay, Nine stations were located along the two transects, which were divided into four zones. Monthly boat cruises were undertaken in the bay at spring up here, tide ebb slack, neap rise open and neap tide ebb slack respectively, during the period April-October 2012. Species diversity (H') showed a distinct increasing gradient from the most thermally polluted zone to the healthy zone. The more distinct gradient occurred at spring tide. Species diversity fluctuated during April-October 2011 and four sampling tide times with no visible patterns. Evenness showed indistinct gradient from the heated water source to the control zone, and fluctuated during April-October 2011 and four sampling tide times with no visible patterns. Species richness, cell count and Chl a concentration at mixed and healthy zones were significantly higher than that at heated zones, with the maximum value recorded at mixed zone, and showed seasonal and tidal changes with no obvious pattern.

Is the sulphur anomaly in planetary nebulae caused by the s-process?

Motivated by unexplained observations of low sulphur abundances in planetary nebulae (PNe) and the PG1159 class of post asymptotic giant branch (AGB) stars, we investigate the possibility that sulphur may be destroyed by nucleosynthetic processes in low-to-intermediate mass stars during stellar evolution. We use a 3 Msun, Z=0.01 evolutionary sequence to examine the consequences of high and low reaction rate estimates of neutron captures onto sulphur and neighbouring elements. In addition, we have tested high and low rates for the neutron producing reactions C13(alpha,n)O16 and Ne22(alpha,n)Mg25. We vary the mass width of a partially mixed zone (PMZ), which is responsible for the formation of a C13 pocket and is the site of the C13(alpha,n)O16 neutron source. We test PMZ masses from zero up to an extreme upper limit of the entire He-intershell mass at 10^-2 Msun. We find that the alternative reaction rates and variations to the partially mixed zone have almost no effect on surface sulphur abundances and do not reproduce the anomaly. To understand the effect of initial mass on our conclusions, 1.8 Msun and 6 Msun evolutionary sequences are also tested with similar results for sulphur abundances. We are able to set a constraint on the size of the PMZ, as PMZ sizes that are greater than half of the He-intershell mass (in the 3 Msun model) are excluded by comparison with neon abundances in planetary nebulae. We compare the 1.8 Msun model's intershell abundances with observations of PG1159-035, whose surface abundances are thought to reflect the intershell composition of a progenitor AGB star. We find general agreement between the patterns of F, Ne, Si, P, and Fe abundances and a very large discrepancy for sulphur where our model predicts abundances that are 30-40 times higher than is observed in the star.

The provenance of sub-cratonic mantle beneath the Limpopo Mobile Belt (South Africa)

Petrological, whole rock major element and mineral chemical analysis of mantle xenoliths from the Venetia kimberlite pipes (533Ma) in South Africa reveals an apparently stratified cratonic mantle beneath the Central Zone of the Limpopo Mobile Belt (LMB) that separates the Kaapvaal and Zimbabwe Cratons. Combined pressure–temperature (P–T) data and petrographic observations indicate that the mantle consists of an upper layer of Low-T coarse-equant garnet+spinel lherzolite (~50 to ~130km depth). This layer is underlain by a region of mixed garnet harzburgites and garnet lherzolites that are variably deformed (~130 to ~235km depth). An equilibrated geotherm did not exist at the time of kimberlite eruption (533Ma) and a localised heating event involving the introduction of asthenospheric material to the High-T lithosphere below 130km is inferred.Low-T garnet–spinel lherzolites are highly melt depleted (40% on average). In contrast, the High-T lithosphere (mostly at diamond stable conditions) consists of a mixed zone of variably sheared and melt depleted (30% on average) garnet harzburgite and mildly melt depleted (20% on average) garnet lherzolite. The chemistry of the High-T xenoliths contrasts with that of minerals included in diamond originating from the same depth. Inclusions suggest diamond crystallisation in a more melt depleted lithosphere than represented by either Low- or High-T xenoliths. High-T xenoliths are proposed to represent formerly melt depleted lithosphere, refertilised by asthenosphere-derived melts during the diapiric rise of a proto-kimberlitic melt pocket. This process is coupled to the positive temperature perturbation observed in the High-T xenoliths and may represent a common process in the lower lithosphere related to localised but intense tectono-magmatic events immediately preceding kimberlite eruption.The presence of clinopyroxene, garnet and abundant orthopyroxene in the Low-T lherzolite implies a history of melt depletion followed by metasomatic addition of Si–Al–Ca, forming high-temperature orthopyroxene from which clinopyroxene and garnet exsolved. Si enrichment is a characteristic feature of the majority of the Kaapvaal Craton to the south of the LMB but not of the Zimbabwe Craton to the north, implying a Kaapvaal origin. The provenance of the High-T lithosphere beneath the LMB is less well constrained as it is intensely modified by kimberlitic magmatism and diamond inclusion chemistry does not show significant systematic variation across the cratons. The presence of rare, mildly silica enriched high-temperature harzburgites suggests that a Kaapvaal origin for the entire lithosphere beneath the LMB is most likely.

The structure and petrology of the Cnoc nan Cuilean Intrusion, Loch Loyal Syenite Complex, NW Scotland

AbstractIn NW Scotland, several alkaline intrusive complexes of Silurian age intrude the Caledonian orogenic front. The most northerly is the Loch Loyal Syenite Complex, which is divided into three separate intrusions (Ben Loyal, Beinn Stumanadh and Cnoc nan Cuilean). Mapping of the Cnoc nan Cuilean intrusion shows two main zones: a Mixed Syenite Zone (MZ) and a Massive Leucosyenite Zone (LZ), with a gradational contact. The MZ forms a lopolith, with multiple syenitic lithologies, including early basic melasyenites and later felsic leucosyenites. Leucosyenite melts mixed and mingled with melasyenites, resulting in extreme heterogeneity within the MZ. Continued felsic magmatism resulted in formation of the relatively homogeneous LZ, invading western parts of the MZ and now forming the topographically highest terrane. The identification of pegmatites, microgranitic veins and unusual biotite-magnetite veins demonstrates the intrusion's complex petrogenesis. Cross-sections have been used to create a novel 3D GoCad™ model contributing to our understanding of the intrusion. The Loch Loyal Syenite Complex is known to have relatively high concentrations of rare earth elements (REEs), and thus the area has potential economic and strategic value. At Cnoc nan Cuilean, abundant REE-bearing allanite is present within melasyenites of the MZ. Extensive hydrothermal alteration of melasyenites here formed steeply dipping biotite-magnetite veins, most enriched in allanite and other REE-bearing accessories. This study has thus identified the area of greatest importance for further study of REE enrichment processes in the Cnoc nan Cuilean intrusion.

CFD Analysis of Combustion and Pollutant Formation Phenomena in a Direct Injection Diesel Engine at Different EGR Conditions

In this work, exhaust gas recirculation (EGR) is varied in a direct injection constant speed diesel engine using extended coherent flame model for 3-zones by CFD. The three zones are unmixed fuel zone, mixed gases zone, unmixed air plus EGR zone. The three zones are too small to be resolved by the mesh and are therefore modeled as sub-grid quantities. The mixed zone is the result of turbulent and molecular mixing between gases in the other two zones, where combustion takes place. Grid and time independent tests are carried out further to find the appropriate space and time steps respectively. The preliminary studies are carried out to validate the model with the experiments. The present study is conducted towards varying the EGR in the cylinder. CFD results indicate that as EGR increases, nitrogen oxides decreases in a general trend observed in diesel engines. The predicted model shows that flame temperature is lowered in the combustion chamber with the increase in EGR. However, as oxides of nitrogen decreases, soot increases due to lowered oxygen concentration. Reaction variable and temperature contours in the cylinder reveal that combustion regresses as EGR is increased.

Таксономічна і синекологічна характеристика асамблей ногохвісток болотних біотопів Волинського Полісся

Bog’s springtails (Collembola), the habitants of Volyn Polissja region, were studied. Untill this time, there was no information about fauna and population of soil invertebrates in the bog’s edafotop of Western Polissja study greatly enriched with fauna of Collembola. 32 species which were not previously reported in this region were found. Two of these species were first marked as Collembola fauna in Ukraine, 18 species – at the territory of the Ukrainian Polissja region, 8 new species were discovered at the Western Polissja region, and 4 types – at Volyn Polissja region. An important feature defected is the dominance of Collembola caenoassambley, species richness, and number of Isotomidae family. That facts suggest some similarities between the studied bog fauna of the western part of Polissja lowland located in mixed forests zone and fauna of “izotomoidnyi“ type, which is for the Palaearctic fauna of common of northern latitudes. The following factors of the caenoassambley Collembola were analyzed: species composition, quantity, dominated structure, biotope groups spectrum, field hihropreferendum, life forms. Fauna of the oligotrophic bog springtails is characterized by large variety of species, which makes 89% of whole species richness of Collembola in bog plant communities. It was found that north-european and boreo-montanni species are regionally specific dominants. Keywords: Collembola, Volyn Polissja, fauna, bog’s biotops, structure of caenoassambley.

A review of geomorphic processes and landforms in the Dry Valleys of southern Victoria Land: implications for evaluating climate change and ice-sheet stability

Abstract The Dry Valleys are subdivided into three microclimate zones on the basis of summertime measurements of atmospheric temperature, soil moisture, relative humidity and wind-speed/ direction. Subtle variations in these climate parameters result in considerable differences in process geomorphology and in the development of unique landforms within each zone. The mapped zones include a coastal thaw zone, an inland mixed zone and a stable upland zone. Landforms within each zone are subdivided into macroscale features (e.g. valleys, slopes and gullies), mesoscale features (e.g. polygons and viscous-flow features) and microscale features (e.g. rock and near-surface soil features, including the effects of salt weathering, wind erosion and pitting). We present a review of landscape development in the Dry Valleys with implications for long-term climate change and ice-sheet stability. Chronological control is afforded by 40 Ar/ 39 Ar dating of volcanic ash-fall deposits and cosmogenic nuclide analyses of surface boulders. Collectively, the data call for persistent cold and dry conditions in the stable upland zone for approximately the last 14 Ma, although some level of climatic amelioration and landform modification may have occurred within low-lying regions and in the inland mixed zone.

Artificial upwelling to stimulate growth of non-toxic algae in a habitat for mussel farming

Large-scale artificial upwelling was tested as a method to enhance the environmental conditions for the growth of non-toxic algae in a Norwegian fjord (61°0′N, 6°22′E). The experiment was designed to evaluate if nutrient-rich seawater, brought up from below the mixed zone of a stratified fjord to the euphotic zone by air bubbling, would stimulate the growth of non-toxic relative to toxic algae. Pumping 44 m3 min−1 of air at 1 atm through a pipe diffuser submerged at 40 m depth formed a buoyancy flux that lifted 60 m3 s−1 of deep water to the upper 17 m over a period of 21 days. The supply of silicate, inorganic nitrogen and phosphate to the upper 10 m in the fjord increased, and a significant increase in the biomass of non-toxic algae was observed. The upwelling gave an increased growth of the non-toxic dinoflagellates Ceratium furca and C. tripos. After termination of the experiment, the phytoplankton biomass decreased significantly, whereas a distinct increase occurred in the relative biomass of the potentially toxic Dinophysis spp. The result is considered promising when it comes to creating controlled geographical areas with non-toxic food for mussel production.

Effects of tool positioning on joint interface microstructure and fracture strength of friction stir lap Al-to-steel welds

Friction stir lap welding (FSLW) experiments have been conducted to study the effects of tool positioning on microstructures formed in the Al-to-steel interface region and on joint strength, defined as maximum applied force over the width (F m/w s) of the test sample, of the welds. Various pin positioning and speed conditions were used in the FSLW experiments followed by microstructure examination on the interface regions and tensile-shear testing on the welds, including an examination on crack propagation in mixed stir zone. It was found that when the pin was close to the bottom steel piece, Al-to-steel reaction occurred resulting in intermetallic outbursts formed along the interface. This represents the case of incomplete metallurgical joint. When the pin was lowered to just reach the steel, a thin and continued interface intermetallic layer formed. Evidences and consideration on growth kinetics have suggested that the layer could only remain thin (≤2.5 μm) during FSLW. This layer could bear a high load during tensile-shear testing and the adjacent aluminium deformed and fractured instead. The resulting F m/w s was high. When the pin penetrated to steel, F m/w s reduced due to brittle fracture being dominant inside mixed stir zone. Evidences have shown that the amount of penetration and speed condition during FSLW do not have large effects on F m/w s.

Assessment of Cyclic Lifetime of NiCoCrAlY/ZrO2-Based EB-PVD TBC Systems via Reactive Element Enrichment in the Mixed Zone of the TGO Scale

The chemical composition of the alumina-zirconia mixed zone (MZ) of an electron beam physical vapor deposited thermal barrier coating (EB-PVD TBC) system is affected by service conditions and by the interdiffusion of elements from the substrate alloy below and the zirconia top coat. Three NiCoCrAlY bond-coated Ni-base substrates with YPSZ or CeSZ EB-PVD TBCs were subjected to a cyclic furnace oxidation test (FCT) at 1373 K (1100 °C) in order to provide experimental evidence of a link between chemistry of the MZ, the substrate alloy, the ceramic top coat, and the time in the FCT. Energy dispersive spectroscopy of the MZ revealed preferred accumulation of Cr, Zr, Y, and Ce. The concentration of the reactive elements (RE = Ce + Y + Zr) was related to the respective average lifetimes of the TBC systems at 1373 K (1100 °C). The RE content in the MZ turned out to be a life-limiting parameter for YPSZ and CeSZ TBC systems which can be utilized to predict their relative lifetimes on the individual substrates. Conversely, the TBC failure mechanisms of YPSZ and CeSZ TBC systems are dissimilar.

Corrosion of AA6061 Brazed with an Al-Si Alloy: Effects of Si on Metallurgical and Corrosion Behavior

Aluminum alloy (AA)6061 (UNS A96061) and AA4047 (UNS A94047) were brazed to construct a tapered model braze joint with variable braze clearances. Isolated AA6061-T6 was also exposed to the thermal cycle of a typical dip brazing process without applying filler metal. The braze, mixed, and heat-affected zones were modeled by thermochemical computations and characterized experimentally. Corrosion exposures were conducted in accordance with BS 11846 Method B for detection of intergranular corrosion (IGC). Each zone developed its own corrosion morphology traced to the unique chemical composition and metallurgical characteristics. The brazing thermal cycle promoted IGC of isolated AA6061. Moreover, the Al-Si braze and AA6061 joint promoted additional intergranular corrosion in the Si-enriched mixed zone exacerbated by grain boundary Q (Al4Cu2Mg8Si7) and β phases as well as eutectically formed Si needles at solidification boundaries. Pitting occurred in the Al-Si braze zone. Anodic and cathodic polarization scan...

Age, Nd–Hf isotopes, and geochemistry of the Vijayan Complex of eastern and southern Sri Lanka: A Grenville-age magmatic arc of unknown derivation

The ca. 1.0–1.1 Ga Vijayan Complex (VC) of eastern and southeastern Sri Lanka is one of three high-grade metamorphic terranes making up the basement of the island and is in tectonic contact with the adjacent, older Highland Complex. It consists predominantly of granitoid gneisses ranging in composition from diorite to leucogranite, with a distinct calc-alkaline geochemical signature, and is interpreted as a magmatic arc. Strong ductile deformation has obliterated almost all original intrusive relationships. High-grade metamorphism during the Pan-African event at ca. 610–520Ma has produced widespread granulite-facies assemblages that are now largely retrogressed and were affected by extensive late metamorphic K-metasomatism. In southern Sri Lanka the Vijayan gneisses are tectonically interlayered with rocks of the Highland Complex in a so-called mixed zone. We report zircon ages, whole-rock Nd and Hf-in-zircon isotopic systematics and geochemical data for a large selection of Vijayan gneissses in order to better characterize this complex and its tectonic setting. The zircon ages are predominantly in the range 1100–1000Ma with a few early Neoproterozoic intrusions, and identify the VC as a Grenville-age magmatic arc. Many zircons experienced minor to significant lead-loss at about 580Ma. The Nd and Hf isotopic data confirm a generally primitive origin for most Vijayan gneisses, but significant variations in both isotopic systems argue for source heterogeneities and the possible involvement of minor amounts of older continental material in their genesis. Immobile trace and rare earth element distributions favour an origin of the gneiss protoliths through melting at relatively shallow depth, and the chemical variation from diorite and tonalite via granodiorite to granite in the VC can be explained by increasing fractionation of plagioclase and biotite, accompanied by amphibole and accessory phases. The VC may be comparable, in some respect, to the composition and evolution of the Kohistan Arc in Pakistan. The unique composition, age and isotopic characteristics of the VC find no convincing counterpart in other fragments of the Gondwana supercontinent, and its origin therefore remains exotic and enigmatic.

Analytical Model for Zones Distributions in Non-Horizontal Miscible WAG Injection

The advantages of WAG (water-alternating-gas) injection compared to gas injection and waterflooding, from technical and economical points of view, are results of creating a mixed zone in which both water and gas are flowing simultaneously. Previously, an analytical model was developed in the literature to evaluate complete segregation distance and zone distributions for horizontal miscible WAG injection models. Even though this analytical model is derived using simplifying assumptions, it still gives good insight into the design of new projects when the lack of data does not allow a detailed full field reservoir simulation to be carried out. On the other hand, the advantages and disadvantages of applying WAG injection in dipped reservoirs, and up-dip or down-dip patterns are still in question while there isn’t any analytical model available for analyzing process in this type of reservoir. This paper develops analytical equations for a non-horizontal model and investigates the effect of dip angle on segregation effects in miscible WAG injection process. Up-dip versus down-dip WAG injection is another subject which will be discussed in this paper.