Evaluation of the castability of a Co-Cr-Mo-W alloy varying the investing technique

O objetivo deste estudo foi comparar a fusibilidade de ligas de Co-Cr-Mo-W (Remanium 2000), Ni-Cr (Durabond) e Co-Cr-Mo (Vera-PDI), incluídas em revestimentos à base de fosfato, sílica ou utilizando uma técnica mista. Uma rede de nylon quadrada (10 X 10 mm) com 100 espaços abertos serviu de modelo para construção de padrões de cera, que foram incluídos com revestimento à base de sílica, revestimento fosfatado e técnica mista (camada de revestimento fosfatado com 2 mm de espessura + revestimento à base de sílica). Quarenta e cinco espécimes (5 para cada condição experimental) foram fundidos sob chama de gás-oxigênio e a seguir jateados com óxido de alumínio. O número de segmentos fundidos completos foi contado para obter uma percentagem designada como "valor de fusibilidade", representando a precisão da liga em reproduzir os detalhes do molde. A análise estatística por meio de ANOVA a dois critérios e teste Tukey mostrou que, comparando-se as ligas, a Remanium 2000 teve fusibilidade estaticamente semelhante (p>0,05) à da Vera PDI e inferior à da liga Durabond (p<0,05). Considerando os resultados da técnica mista, a liga Remanium 2000 teve menor valor de fusibilidade (p<0,05) que as ligas Durabond e Vera PDI, que apresentaram valores estatisticamente semelhantes entre si (p>0,05). Concluindo, a fusibilidade da liga de Co-Cr-Mo-W (Remanium 2000) foi comparável à da liga de Co-Cr (Vera PDI) e inferior à da liga de Ni-Cr alloy (Durabond). À exceção da liga Remanium 2000, a técnica de inclusão mista aumentou consideravelmente a capacidade das ligas testadas de reproduzir os detalhes do molde, quando comparada à técnica de inclusão em revestimento fosfatado. A técnica de inclusão mista representa uma alternativa para melhorar a fusibilidade de ligas de metais básicos sem afetar a qualidade superficial das peças metálicas.

Evaluation of the castability of a Co-Cr-Mo-W alloy varying the investing technique

O objetivo deste estudo foi comparar a fusibilidade de ligas de Co-Cr-Mo-W (Remanium 2000), Ni-Cr (Durabond) e Co-Cr-Mo (Vera-PDI), incluídas em revestimentos à base de fosfato, sílica ou utilizando uma técnica mista. Uma rede de nylon quadrada (10 X 10 mm) com 100 espaços abertos serviu de modelo para construção de padrões de cera, que foram incluídos com revestimento à base de sílica, revestimento fosfatado e técnica mista (camada de revestimento fosfatado com 2 mm de espessura + revestimento à base de sílica). Quarenta e cinco espécimes (5 para cada condição experimental) foram fundidos sob chama de gás-oxigênio e a seguir jateados com óxido de alumínio. O número de segmentos fundidos completos foi contado para obter uma percentagem designada como "valor de fusibilidade", representando a precisão da liga em reproduzir os detalhes do molde. A análise estatística por meio de ANOVA a dois critérios e teste Tukey mostrou que, comparando-se as ligas, a Remanium 2000 teve fusibilidade estaticamente semelhante (p>0,05) à da Vera PDI e inferior à da liga Durabond (p<0,05). Considerando os resultados da técnica mista, a liga Remanium 2000 teve menor valor de fusibilidade (p<0,05) que as ligas Durabond e Vera PDI, que apresentaram valores estatisticamente semelhantes entre si (p>0,05). Concluindo, a fusibilidade da liga de Co-Cr-Mo-W (Remanium 2000) foi comparável à da liga de Co-Cr (Vera PDI) e inferior à da liga de Ni-Cr alloy (Durabond). À exceção da liga Remanium 2000, a técnica de inclusão mista aumentou consideravelmente a capacidade das ligas testadas de reproduzir os detalhes do molde, quando comparada à técnica de inclusão em revestimento fosfatado. A técnica de inclusão mista representa uma alternativa para melhorar a fusibilidade de ligas de metais básicos sem afetar a qualidade superficial das peças metálicas.

(Table 2) Fatty acid composition of polychaetes sampled during POLARSTERN cruise ANT-XXIV/2

The fatty acid (FA) composition of representatives belonging to 18 polychaete families from the Southern Ocean shelf and deep sea (600 to 5337 m) was analysed in order to identify trophic biomarkers and elucidate possible feeding preferences. Total FA content was relatively low with few exceptions and ranged from 1.0 to 11.6% of total body dry weight. The most prominent FA found were 20:5(n-3), 16:0, 22:6(n-3), 18:1(n-7), 20:4(n-6), 18:0, 20:1(n-11) and 18:1(n-9). For some polychaete families and species FA profiles indicated selective feeding on certain dietary components, like freshly deposited diatom remains (e.g., Spionidae, Fauveliopsidae and Flabelligeridae) or foraminiferans (e.g., Euphrosinidae, Nephtyidae and Syllidae). Feeding patterns were relatively consistent within families at the deep stations, while the FA composition differed between the deep and the shelf stations within the same family. Fatty alcohols, indicative of wax ester storage, were found in almost all families (in proportions of 0.0 to 29.3% of total FA and fatty alcohols). The development of this long-term storage mechanism of energy reserves possibly displays an evolutionary strategy.

(Table 1) Isotopic composition of organic compinents of DSDP Hole 24-231

Plant leaf wax hydrogen isotope (dDwax) reconstructions are increasingly being used to reconstruct hydrological change. This approach is based upon the assumption that variations in hydroclimatic variables, and in particular, the isotopic composition of precipitation (dDP), dominate dDwax. However modern calibration studies suggest that offsets between plant types may bias the dDwax hydrological proxy at times of vegetation change. In this study, I pair leaf wax analyses with published pollen data to quantify this effect and construct the first vegetation-corrected hydrogen isotopic evidence for precipitation (dDcorrP). In marine sediments from Deep Sea Drilling Program Site 231 in the Gulf of Aden spanning 11.4-3.8 Ma (late Miocene and earliest Pliocene), I find 77 per mil swings in dDwax that correspond to pollen evidence for substantial vegetation change. Similarities between dDP and dDcorrP imply that the hydrological tracer is qualitatively robust to vegetation change. However, computed vegetation corrections can be as large as 31 per mil indicating substantial quantitative uncertainty in the raw hydrological proxy. The resulting dDcorrP values quantify hydrological change and allow us to identify times considerably wetter than modern at 11.09, 7.26, 5.71 and 3.89 Ma. More generally, this novel interpretative framework builds the foundations of improved quantitative paleohydrological reconstructions with the dDwax proxy, in contexts where vegetation change may bias the plant-based proxy. The vegetation corrected paleoprecipitation reconstruction dDcorrP, represents the best available estimate as proof-of-concept, for an approach that I hope will be refined and more broadly applied.

Alkenone accumulation rates, stable carbon isotope record, and sea surface temperature reconstruction for IODP Site 306-U1313

Here we present orbitally-resolved records of terrestrial higher plant leaf wax input to the North Atlantic over the last 3.5 Ma, based on the accumulation of long-chain n-alkanes and n-alkanl-1-ols at IODP Site U1313. These lipids are a major component of dust, even in remote ocean areas, and have a predominantly aeolian origin in distal marine sediments. Our results demonstrate that around 2.7 million years ago (Ma), coinciding with the intensification of the Northern Hemisphere glaciation (NHG), the aeolian input of terrestrial material to the North Atlantic increased drastically. Since then, during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials. The close correspondence between aeolian input to the North Atlantic and other dust records indicates a globally uniform response of dust sources to Quaternary climate variability, although the amplitude of variation differs among areas. We argue that the increased aeolian input at Site U1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in North America and the associated strengthening of glaciogenic dust sources. Evolutional spectral analyses of the n-alkane records were therefore used to determine the dominant astronomical forcing in North American ice sheet advances. These results demonstrate that during the early Pleistocene North American ice sheet dynamics responded predominantly to variations in obliquity (41 ka), which argues against previous suggestions of precession-related variations in Northern Hemisphere ice sheets during the early Pleistocene.

Mapping of C4 plant input from North West Africa into North East Atlantic sediments

Mapping the abundance of 13C in leaf-wax components in surface sediments recovered from the seafloor off northwest Africa (0-35°N) reveals a clear pattern of delta13C distribution, indicating systematic changes in the proportions of terrestrial C3 and C4 plant input. At 20°N latitude, we find that isotopically enriched products characteristic of C4 plants account for more than 50% of the terrigenous inputs. This signal extends westward beneath the path of the dust-laden Sahara Air Layer (SAL). High C4 contributions, apparently carried by January trade winds, also extend far into the Gulf of Guinea. Similar distributions are obtained if summed pollen counts for the Chenopodiaceae-Amaranthaceae and the Poaceae are used as an independent C4 proxy. We conclude that the specificity of the latitudinal distribution of vegetation in North West Africa and the pathways of the wind systems (trade winds and SAL) are responsible for the observed isotopic patterns observed in the surface sediments. Molecular-isotopic maps on the marine-sedimentary time horizons (e.g., during the last glacial maximum) are thus a robust tool for assessing the phytogeographic changes on the tropical and sub-tropical continents, which have important implications for the changes in climatic and atmospheric conditions.

Carbon, nitrogen and lipid content and egg and pellet production of female C. hyperboreus in situ and during incubation experiments

The effects of temperature and food availability on feeding and egg production of the Arctic copepod Calanus hyperboreus were investigated in Disko Bay, western Greenland, from winter to spring 2009. The abundance of females in the near bottom layer and the egg production of C. hyperboreus prior to the spring bloom document that reproduction relies on lipid stores. The maximum in situ egg production (± SE) of 54 ± 8 eggs female/d was recorded in mid-February at chlorophyll a concentrations below 0.1 µg/l, whereas no egg production was observed in mid-April when the spring bloom developed. After reproduction, the females migrated to the surface layer to exploit the bloom and refill their lipid stores. In 2 laboratory experiments, initiated before and during the spring bloom, mature females were kept with and without food at 5 different temperatures ranging from 0 to 10°C and the fecal pellet and egg production were monitored. Food had a clear effect on fecal pellet production but no effect on egg production, while temperature did not have an effect on egg or fecal pellet production in any of the experiments. Analyses of carbon and lipid content of the females before and after the experiments did not reflect any effect of food or temperature in the pre-bloom experiment, whereas in the bloom experiment a clear positive effect of food was detected in female biochemical profiles. The lack of a temperature response suggests a future warmer ocean could be unfavorable for C. hyperboreus compared to smaller Calanus spp. which are reported to exploit minor temperature elevations for increased egg production.

(Table 1) Lipid and kerogen content at DSDP Leg 64 Holes

Diatomaceous mud and an organically-rich claystone from holes at Sites 474 and 476 at the mouth of the Gulf of California were analyzed by organic geochemical methods to characterize their organic matter. The lipids of all three samples are primarily marine autochthonous, with the exception of Sample 474-5-3, 105-107 cm, which also contains some vascular plant wax. Based on the lipid composition, the sediment was deposited mainly under oxic environmental conditions. The kerogens were aliphatic and autochthonous marine. Two lignite fragments were also analyzed, and the data indicate that they are driftwood that absorbed marine bitumen from the surrounding sediment during coalification.

Terrigenous input and marine productivity for the Pacific sector of the Southern Ocean based on lipid biomarkers

In this study, we present a new multiproxy data set of terrigenous input, marine productivity and sea surface temperature (SST) from 52 surface sediment samples collected along E-W transects in the Pacific sector of the Southern Ocean. Allochtonous terrigenous input was characterized by the distribution of plant wax n-alkanes and soil-derived branched glycerol dialkyl glycerol tetraethers (brGDGTs). 230Th-normalized burial rates of both compound groups were highest close to the potential sources in Australia and New Zealand and are strongly related to lithogenic contents, indicating common sources and transport. Detection of both long-chain n-alkanes and brGDGTs at the most remote sites in the open ocean strongly suggests a primarily eolian transport mechanism to at least 110°W, i.e. by prevailing westerly winds. Two independent organic SST proxies were used, the UK'37 based on long-chain alkenones, and the TEX86 based on isoprenoid GDGTs. Both, UK'37 and TEX86 indices show robust relationships with temperature over a temperature range between 0.5 and 20°C, likely implying different seasonal and regional imprints on the temperature signal. While alkenone-based temperature estimates reliably reflect modern SST even at the low temperature end, large temperature residuals are observed for the polar ocean using the TEX86 index. 230Th-normalized burial rates of alkenones are highest close to the Subtropical Front and are positively related to lithogenic fluxes throughout the study area. In contrast, highest isoGDGT burial south of the Antarctic Polar Front is not related with dust flux but may be largely controlled by diatom blooms, and thus high opal fluxes during austral summer.

(Table 1) Composition of lipids in particulate matter and bottom sediments of the Baltic Sea

Lipid contents in the upper layer of bottom sediments in the Baltic Sea range from 0.37 to 2.66 mg/g (1.2-25.8% Corg). It is shown that the main factors determining composition of lipids in bottom precipitates are relative roles of different sources of lipids in sediments and conditions of sediment accumulation. Runoff of the Daugava River into the Gulf of Riga contributes simple low-polarity lipids. Sterols and certain bound fatty acids originate in living organic matter. Polar lipids are formed by inheritance of complex phospholipids and glycolipids from plankton and/or by formation of polycondensates.

n-Alkane content and compound-specific d13C values of soil samples, river samples, and marine surface samples

Southwestern Africa's coastal marine mudbelt, a prominent Holocene sediment package, provides a valuable archive for reconstructing terrestrial palaeoclimates on the adjacent continent. While the origin of terrestrial inorganic material has been intensively studied, the sources of terrigenous organic material deposited in the mudbelt are yet unclear. In this study, plant wax derived n-alkanes and their compound-specific d13C in soils, flood deposits and suspension loads from regional fluvial systems and marine sediments are analysed to characterize the origin of terrestrial organic material in the southwest African mudbelt. Soils from different biomes in the catchments of the Orange River and small west coast rivers show on average distinct n-alkane distributions and compound-specific d13C values reflecting biome-specific vegetation types, most notably the winter rainfall associated Fynbos Biome of the southwestern Cape. In the fluvial sediment samples from the Orange River, changes in the n-alkane distributions and compound-specific d13C compositions reveal an overprint by local vegetation along the river's course. The smaller west coast rivers show distinct signals, reflecting their small catchment areas and particular vegetation communities. Marine surface sediments spanning a transect from the northern mudbelt (29°S) to St. Helena Bay (33°S) reveal subtle, but spatially coherent, changes in n-alkane distributions and compound-specific d13C, indicating the influence of Orange River sediments in the northern mudbelt, the increasing importance of terrigenous input from the adjacent western coastal biomes in the central mudbelt, and contributions from the Fynbos Biome to the southern mudbelt. These findings indicate the different sources of terrestrial organic material deposited in the mudbelt, and highlight the potential the mudbelt has to preserve evidence of environmental change from the adjacent continent.

n-alkane carbon isotope ratios in plants and recent lake sediments from Cameroon

Trees and shrubs in tropical Africa use the C3 cycle as a carbon fixation pathway during photosynthesis, while grasses and sedges mostly use the C4 cycle. Leaf-wax lipids from sedimentary archives such as the long-chain n-alkanes (e.g., n-C27 to n-C33) inherit carbon isotope ratios that are representative of the carbon fixation pathway. Therefore, n-alkane d13C values are often used to reconstruct past C3/C4 composition of vegetation, assuming that the relative proportions of C3 and C4 leaf waxes reflect the relative proportions of C3 and C4 plants. We have compared the d13C values of n-alkanes from modern C3 and C4 plants with previously published values from recent lake sediments and provide a framework for estimating the fractional contribution (areal-based) of C3 vegetation cover (fC3) represented by these sedimentary archives. Samples were collected in Cameroon, across a latitudinal transect that accommodates a wide range of climate zones and vegetation types, as reflected in the progressive northward replacement of C3-dominated rain forest by C4-dominated savanna. The C3 plants analysed were characterised by substantially higher abundances of n-C29 alkanes and by substantially lower abundances of n-C33 alkanes than the C4 plants. Furthermore, the sedimentary d13C values of n-C29 and n-C31 alkanes from recent lake sediments in Cameroon (-37.4 per mil to -26.5 per mil) were generally within the range of d13C values for C3 plants, even when from sites where C4 plants dominated the catchment vegetation. In such cases simple linear mixing models fail to accurately reconstruct the relative proportions of C3 and C4 vegetation cover when using the d13C values of sedimentary n-alkanes, overestimating the proportion of C3 vegetation, likely as a consequence of the differences in plant wax production, preservation, transport, and/or deposition between C3 and C4 plants. We therefore tested a set of non-linear binary mixing models using d13C values from both C3 and C4 vegetation as end-members. The non-linear models included a sigmoid function (sine-squared) that describes small variations in the fC3 values as the minimum and maximum d13C values are approached, and a hyperbolic function that takes into account the differences between C3 and C4 plants discussed above. Model fitting and the estimation of uncertainties were completed using the Monte Carlo algorithm and can be improved by future data addition. Models that provided the best fit with the observed d13C values of sedimentary n-alkanes were either hyperbolic functions or a combination of hyperbolic and sine-squared functions. Such non-linear models may be used to convert d13C measurements on sedimentary n-alkanes directly into reconstructions of C3 vegetation cover.

Stable carbon isotopic analyses of n-alkanes and the calculated C4 plant-derived fractions in the dust samples

Atmospheric dust samples collected along a transect off the West African coast have been investigated for their lipid content and compound-specific stable carbon isotope compositions. The saturated hydrocarbon fractions of the organic solvent extracts consist mainly of long-chain n-alkanes derived from epicuticular wax coatings of terrestrial plants. Backward trajectories for each sampling day and location were calculated using a global atmospheric circulation model. The main atmospheric transport took place in the low-level trade-wind layer, except in the southern region, where long-range transport in the mid-troposphere occurred. Changes in the chain length distributions of the n-alkane homologous series are probably related to aridity, rather than temperature or vegetation type. The carbon preference of the leaf-wax n-alkanes shows significant variation, attributed to a variable contribution of fossil fuel- or marine-derived lipids. The effect of this nonwax contribution on the d13C values of the two dominant n-alkanes in the aerosols, n-C29 and n-C31 alkane, is, however, insignificant. Their d13C values were translated into a percentage of C4 vs. C3 plant type contribution, using a two-component mixing equation with isotopic end-member values from the literature. The data indicate that only regions with a predominant C4 type vegetation, i.e. the Sahara, the Sahel, and Gabon, supply C4 plant-derived lipids to dust organic matter. The stable carbon isotopic compositions of leaf-wax lipids in aerosols mainly reflect the modern vegetation type along their transport pathway. Wind abrasion of wax particles from leaf surfaces, enhanced by a sandblasting effect, is most probably the dominant process of terrigenous lipid contribution to aerosols.

Widespread exploitation of the honeybee by early Neolithic farmers

The pressures on honeybee (Apis mellifera) populations, resulting from threats by modern pesticides, parasites, predators and diseases, have raised awareness of the economic importance and critical role this insect plays in agricultural societies across the globe. However, the association of humans with A. mellifera predates post-industrial-revolution agriculture, as evidenced by the widespread presence of ancient Egyptian bee iconography dating to the Old Kingdom (approximately 2400 bc)1. There are also indications of Stone Age people harvesting bee products; for example, honey hunting is interpreted from rock art2 in a prehistoric Holocene context and a beeswax find in a pre-agriculturalist site3. However, when and where the regular association of A. mellifera with agriculturalists emerged is unknown4. One of the major products of A. mellifera is beeswax, which is composed of a complex suite of lipids including n-alkanes, n-alkanoic acids and fatty acyl wax esters. The composition is highly constant as it is determined genetically through the insect’s biochemistry. Thus, the chemical ‘fingerprint’ of beeswax provides a reliable basis for detecting this commodity in organic residues preserved at archaeological sites, which we now use to trace the exploitation by humans of A. mellifera temporally and spatially. Here we present secure identifications of beeswax in lipid residues preserved in pottery vessels of Neolithic Old World farmers. The geographical range of bee product exploitation is traced in Neolithic Europe, the Near East and North Africa, providing the palaeoecological range of honeybees during prehistory. Temporally, we demonstrate that bee products were exploited continuously, and probably extensively in some regions, at least from the seventh millennium cal bc, likely fulfilling a variety of technological and cultural functions. The close association of A. mellifera with Neolithic farming communities dates to the early onset of agriculture and may provide evidence for the beginnings of a domestication process.