939 resultados para Surface Organometallic Chemistry on Metals


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The collection of ferromanganese nodules at Naturhistoriska Riksmuseet, Stockholm, Sweden has been donated by Pr. Boström, K. and Ingri, J. from the Technical University of Lulea. They have been collected in the Bothnia Gulf, the Baltic Sea anfd the Barents sea from 1976 until 1985. In 1997 it is was put to the care custody of the Laboratory for Isotope Geology (LIG) of NRM. As part of the Access Project at LIG, Curt Boman has gone through the collection and established a database with detailed information about the samples it contains. Ferromanganese nodules typically display a rounded shape and are formed by redox processes at the interface between the seabed sediment and water. In addition to iron and manganese they also contain other metal elements. Nodules chemical composition reflects the substances found in the sediment to which they are associated. Since the nodules grow continuously, they reflect changes in the sedimentary environment chemistry on a yearly basis, which makes them very interesting as environmental archives. The nodules can be found locally in large quantities and due to their metal content they are also economically interesting as a source of raw materials.

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Siliciclastic turbidites represent huge volumes of sediments, which are of particular significance for (1) petroleum researchers, interested in their potential as oil reservoirs and (2) sedimentologists, who aim at understanding sediment transport processes from continent to deep-basins. An important challenge when studying marine turbidites has been to establish a reliable chronology for the deposits. Indeed, conventional marine proxies applied to hemipelagic sediments are often unreliable in detrital clays. In siliciclastic turbidites, those proxies can be used only in hemipelagic intervals, providing a poor constraint on their chronology. In this study, we have used sediments from the Rhône Neofan (NW Mediterranean Sea) to demonstrate that pollen grains can provide a high-resolution chronostratigraphical framework for detrital clays in turbidites. Vegetation changes occurring from the end of Marine Isotopic Stage 3 to the end of Marine Isotopic Stage 2 (from ~30 to ~18 ka cal. BP) are clearly recorded where other proxies have failed previously, mainly because the scarcity of foraminifers in these sediments prevented any continuous Sea Surface Temperature (SST) record and radiocarbon dating to be obtained. We show also that the use of palynology in turbidite deposits is able to contribute to oceanographical and sedimentological purposes: (1) Pinus pollen grains can document the timing of sea-level rise, (2) the ratio between pollen grains transported from the continent via rivers and dinoflagellate cysts (elutriating) allows us to distinguish clearly detrital sediments from pelagic clays. Finally, taken together, all these tools show evidence that the Rhône River disconnected from the canyon during the sea-level rise and thus evidence the subsequent rapid starvation of the neofan at 18.5 ka cal. BP. Younger sediments are hemipelagic: the frequency of foraminifers allowed to date sediments with radiocarbon. First results of Sea Surface Temperature obtained on foraminifers are in good agreement with the dinoflagellate cysts climatic signal. Both provide information on the end of the deglaciation and the Holocene.

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The objective of the present thesis was to use the manipulation of oocytes enclosed in preantral follicles (MOEPF) as a tool for the female gametes rescue and optimization, from wild species of Caatinga biome. The thesis was divided into 4 experiments. At first experiment, it was performed the estimative and description of the agouti (Dasyprocta leporina) preantral follicles (PF) histologic and ultrastructural features, in which it was estimated 4419.8 ± 532.26 and 5397.52 ± 574.91 follicles for the right and left ovary, respectively, and the majority (86,63%) belonged to the primordial follicles category (P<0.05). Most of the population consists of morphologically normal follicles (70.78%), presenting a large and central nuclei and uniform cytoplasm. At ultrastructural evaluation it was verified the presence of a great number of round mitochondrias associated to lipid droplets. In the second experiment, it was performed the estimative and description of yellow-toothed cavies (Galea spixii) PF characteristics, also, the evaluation of the effect of solid surface vitrification (SSV) on the in situ PF morphology. The total of 416.0 ± 342.8 PF was estimated for the ovary pair and the presence of a large quantity of primary follicles (P<0.05) was evidenced. Most of the PF was morphologically normal (94.6%), in which the oocyte nuclei presented condensed granules of heterochromatin. Round or elongated shaped mitochondria constituted the most abundant organelles. In regard of the SSV, the protocol using the dimethylsulfoxide (DMSO) 3M possibility the preservation of 69.5% of morphologically normal PF, which was evidenced by the light and transmission electronic microscopy. At third experiment, the evaluation of the SSV procedure on the morphology and viability in situ PF form collared peccaries (Pecari tajacu) was performed. No differences were observed among treatments, in which the use of DMSO, ethylene glycol (EG) and dimethylformamide (DMF) as cryoprotectants, regardless its concentration, promoted the morphology preservation of much than 70% of PF. Concerning the PF viability, the DMSO and EG promoted the best preservation. The fourth experiment aimed to evaluate the effect of α MEM+ or TCM199 associated or not to 50 ng of FSHr on the morphology, activation and growth of collared peccaries PF, in vitro cultured (IVC) during 1 or 7 days and the effect on the extracellular matrix (ECM). After 7 days of IVC only the use of TCM199/FSH maintained the proportion of intact PF, similar to day 1(63.2%), however, no differences were observed among treatments (P>0.05). Also, an improvement of the proportion of intact growing PF was verified (P>0.05). By the Ag-NOR analysis it was observed that only the treatment using TCM199/FSH promoted the maintenance of cell proliferation similar to day 1 (P>0.05). The picrosirius red stain revealed that ECM remained intact in all treatments (P>0.05). Thus, as the general conclusion, the use of MOEPF in the refereed species allowed the knowledge of aspects related to its reproductive morphology and physiology, enabling the germplasm conservation, with the possibility of germplasm bank formation, as the elucidation of mechanisms related to the PF survive and in vitro development.

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In educational observed difficulty in train teachers to meet the medium and higher education needs, and one reason for this is the different experiences in the training of educators in relation to those found in the classroom. So often arise criticisms related to relevance and efficiency of degree courses, as regards the performance of its natural mission, which weakens the teacher training. Thus, improving the quality of education is very dependent on the initiatives of teachers, creating teaching alternatives to strengthen their performance in school. From this reflection, it is concluded that teacher training needs new educational proposals that qualify, and so can promote the formation of his students more adequately. Among the educational proposals as alternatives to initial teacher training may use the scientific theater (TC). Considering this possibility, this work has been proposed as investigate and discuss the influence of TC combined with experimentation in the initial training of future teachers in Chemistry who participate in the Groups Fanatics chemistry Theatre (UERN) and Chemistry on Stage (UFRN). Therefore, there was, in a first stage, theatrical essays based on the theater of the oppressed, and written dramaturgical scripts, a collaborative proposal. To incorporate experimentation in chemistry to theater rehearsals, there was a systematic literature search and after content analysis, were selected categories, materials and reagents easily accessible, easy procedures and implementation with low risk of accidents and easy care chemical waste. In the second part we identified: a) the beliefs of student teachers in the use of TC ally trial for initial training of chemistry teachers; b) the influence of TC ally to trial on learning of chemical concepts of high school students who attended the shows; c) the reasons for using or not TC ally to trial by chemistry teachers who participated in the TC group and currently work in the classroom. In this study, questionnaires and interviews were used, compounds, respectively, by a Likert scale and open questions. Quantitative data were analyzed by classical statistics the media, using as centrality measures the average, the concordance argument and the average deviation. Qualitative data were discussed according to content analysis, with categories that emerged from reading the answers. These analyzes concluded that the licensees have a positive view on the use of scientific theater for disclosure of the chemical for use in the learning of chemical concepts, pedagogical and disciplinary knowledge, and to form promotion strategy for research and extension at the University. They credit improvements in their initial training on the use of scientific theater combined with experimentation. The TC provides motivation for the construction of conceptual thinking in an informal way of chemical communication, allowing the student to expand their knowledge, not only favoring the phenomenological approach, but also the construction of chemical knowledge and the internalization of scientific concepts.

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We present records of biogenic opal percentage and burial rate in 12 piston cores from the Atlantic and Indian sectors of the Southern Ocean. These records provide a detailed, quantitative description of changing patterns of opal deposition over the last 450 kyr. The striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal, and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the Southern Ocean under different global climate conditions. Three broad depositional patterns can be distinguished. Northernmost records (39°-42°S latitude) are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity. Records from cores just north of the present Antarctic Polar Front (46°-49°S) show even larger increases in opal burial rate during glacial intervals, but have variance concentrated in the 100 and 23 kyr bands. Southernmost records (51°-55°S) are completely out of phase with those to the north, with greatly reduced opal burial rates during glacial periods. Taken as a whole, the opal records show no evidence for the increased total Antarctic productivity predicted by recent geochemical models of atmospheric CO2 variability. The areal expansion of Southern Ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial-interglacial opal patterns. The excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region. However, local circulation changes may act to modify this basic signal, possibly accounting for the observed differences in the opal variance spectra.

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This thesis analyzes the Chow motives of 3 types of smooth projective varieties: the desingularized elliptic self fiber product, the Fano surface of lines on a cubic threefold and an ample hypersurface of an Abelian variety. For the desingularized elliptic self fiber product, we use an isotypic decomposition of the motive to deduce the Murre conjectures. We also prove a result about the intersection product. For the Fano surface of lines, we prove the finite-dimensionality of the Chow motive. Finally, we prove that an ample hypersurface on an Abelian variety possesses a Chow-Kunneth decomposition for which a motivic version of the Lefschetz hyperplane theorem holds.

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This review discusses synthesis of enantiopure sulfoxides through the asymmetric oxidation of prochiral sulfides. The use of metal complexes to promote asymmetric sulfoxidation is described in detail, with a particular emphasis on the synthesis of biologically active sulfoxides. The use of non-metal-based systems, such as oxaziridines, chiral hydroperoxides and peracids, as well as enzyme-catalyzed sulfoxidations is also examined.

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Stable isotope data from eastern equatorial Pacific (EEP) core TR163-19 (2°15'N, 90°57'W, 2348 m) are presented for the surface-dwelling foraminifers Globigerinoides ruber and G. sacculifer and thermocline-dwelling Globorotalia menardii and Neogloboquadrina dutertrei. Using species-specific normalization factors derived from experimental and plankton tow data, we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles. We demonstrate that G. ruber maintains a mixed layer habitat throughout the entire record, while G. sacculifer records a mixture of thermocline and mixed layer conditions and G. menardii and N. dutertrei record thermocline properties. We conclude that G. sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients. Results suggest that this region of the EEP had a thicker mixed layer and deeper d13CDIC boundary between the surface and equatorial undercurrent during the last two glacial periods. A shift in N. dutertrei and G. sacculifer geochemistry prior to ~185 kyr suggests water column structure and chemocline gradients changed, possibly due to a shift in the position of the undercurrent relative to this site. The timing and magnitude of glacial-interglacial d13C variations between species indicates that near-surface carbon chemistry is controlled by changes in productivity, atmospheric circulation, and advected intermediate water sources north of the Antarctic polar front. These results demonstrate that when properly calibrated for species differences, multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past.

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Upwelling intensity in the South China Sea has changed over glacial-interglacial cycles in response to orbital-scale changes in the East Asian Monsoon. Here, we evaluate new multi-proxy records of two sediment cores from the north-eastern South China Sea to uncover millennial-scale changes in winter monsoondriven upwelling over glacial Terminations I and II. On the basis of U/Th-based speleothem chronology, we compare these changes with sediment records of summer monsoondriven upwelling east of South Vietnam. Ocean upwelling is traced by reduced (UK'37-based) temperature and increased nutrient and productivity estimates of sea surface water (d13C on planktic foraminifera, accumulation rates of alkenones, chlorins, and total organic carbon). Accordingly, strong winter upwelling occurred north-west of Luzon (Philippines) during late Marine Isotope Stage 6.2, Heinrich (HS) and Greenland stadials (GS) HS-11, GS-26, GS-25, HS-1, and the Younger Dryas. During these stadials, summer upwelling decreased off South Vietnam and sea surface salinity reached a maximum suggesting a drop in monsoon rains, concurrent with speleothem records of aridity in China. In harmony with a stadial-to-interstadial see-saw pattern, winter upwelling off Luzon in turn was weak during interstadials, in particular those of glacial Terminations I and II, when summer upwelling culminated east of South Vietnam. Most likely, this upwelling terminated widespread deep-water stratification, coeval with the deglacial rise in atmospheric CO2. Yet, a synchronous maximum in precipitation fostered estuarine overturning circulation in the South China Sea, in particular as long as the Borneo Strait was closed when sea level dropped below -40 m.

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Recent research has increasingly advocated a role for the North Pacific Ocean in modulating global climatic changes over both the last glacial cycle and further back into the geological record. Here a diatom d18O record is presented from Ocean Drilling Program Site 882 over the Pliocene/Quaternary boundary from 2.73 Ma to 2.52 Ma (MIS G6-MIS 99). Large changes in d18Odiatom of c. 4 per mil from 2.73 Ma onwards are documented to occur on a timeframe broadly coinciding with glacial-interglacial cycles. These changes are primarily attributed to large scale inputs of meltwater from glacials surrounding the North Pacific Basin and the Bering Sea. Despite these inputs and associated change in surface water salinity, on the basis of existing opal and UK37 temperature data and new modelled water column densities, no evidence exists to suggests a removal of the halocline stratification or a resumption of the high productivity system similar to that which prevailed prior to 2.73 Ma. The permanence of the halocline suggests that the region played a key role in driving global climatic changes over the early glacial-interglacial cycles that followed the onset of major Northern Hemisphere Glaciation by inhibiting deep water upwelling and ventilation of CO2 to the atmosphere.

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The hydrologic system beneath the Antarctic Ice Sheet is thought to influence both the dynamics and distribution of fast flowing ice streams, which discharge most of the ice lost by the ice sheet. Despite considerable interest in understanding this subglacial network and its affect on ice flow, in situ observations from the ice sheet bed are exceedingly rare. Here we describe the first sediment cores recovered from an active subglacial lake. The lake, known as Subglacial Lake Whillans, is part of a broader, dynamic hydrologic network beneath the Whillans Ice Stream in West Antarctica. Even though "floods" pass through the lake, the lake floor shows no evidence of erosion or deposition by flowing water. By inference, these floods must have insufficient energy to erode or transport significant volumes of sediment coarser than silt. Consequently, water flow beneath the region is probably incapable of incising continuous channels into the bed and instead follows preexisting subglacial topography and surface slope. Sediment on the lake floor consists of till deposited during intermittent grounding of the ice stream following flood events. The fabrics within the till are weaker than those thought to develop in thick deforming beds suggesting subglacial sediment fluxes across the ice plain are currently low and unlikely to have a large stabilizing effect on the ice stream's grounding zone.

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This thesis presents details of the design and development of novel tools and instruments for scanning tunneling microscopy (STM), and may be considered as a repository for several years' worth of development work. The author presents design goals and implementations for two microscopes. First, a novel Pan-type STM was built that could be operated in an ambient environment as a liquid-phase STM. Unique features of this microscope include a unibody frame, for increased microscope rigidity, a novel slider component with large Z-range, a unique wiring scheme and damping mechanism, and a removable liquid cell. The microscope exhibits a high level of mechanical isolation at the tunnel junction, and operates excellently as an ambient tool. Experiments in liquid are on-going. Simultaneously, the author worked on designs for a novel low temperature, ultra-high vacuum (LT-UHV) instrument, and these are presented as well. A novel stick-slip vertical coarse approach motor was designed and built. To gauge the performance of the motor, an in situ motion sensing apparatus was implemented, which could measure the step size of the motor to high precision. A new driving circuit for stick-slip inertial motors is also presented, that o ffers improved performance over our previous driving circuit, at a fraction of the cost. The circuit was shown to increase step size performance by 25%. Finally, a horizontal sample stage was implemented in this microscope. The build of this UHV instrument is currently being fi nalized. In conjunction with the above design projects, the author was involved in a collaborative project characterizing N-heterocyclic carbene (NHC) self-assembled monolayers (SAMs) on Au(111) films. STM was used to characterize Au substrate quality, for both commercial substrates and those manufactured via a unique atomic layer deposition (ALD) process by collaborators. Ambient and UHV STM was then also used to characterize the NHC/Au(111) films themselves, and several key properties of these films are discussed. During this study, the author discovered an unexpected surface contaminant, and details of this are also presented. Finally, two models are presented for the nature of the NHC-Au(111) surface interaction based on the observed film properties, and some preliminary theoretical work by collaborators is presented.

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The drag on a nacelle model was investigated experimentally and computationally to provide guidance and insight into the capabilities of RANS-based CFD. The research goal was to determine whether industry constrained CFD could participate in the aerodynamic design of nacelle bodies. Grid refinement level, turbulence model and near wall treatment settings, to predict drag to the highest accuracy, were key deliverables. Cold flow low-speed wind tunnel experiments were conducted at a Reynolds number of 6∙〖10〗^5, 293 K and a Mach number of 0.1. Total drag force was measured by a six-component force balance. Detailed wake analysis, using a seven-hole pressure probe traverse, allowed for drag decomposition via the far-field method. Drag decomposition was performed through a range of angles of attack between 0o and 45o. Both methods agreed on total drag within their respective uncertainties. Reversed flow at the measurement plane and saturation of the load cell caused discrepancies at high angles of attack. A parallel CFD study was conducted using commercial software, ICEM 15.0 and FLUENT 15.0. Simulating a similar nacelle geometry operating under inlet boundary conditions obtained through wind tunnel characterization allowed for direct comparisons with experiment. It was determined that the Realizable k-ϵ was best suited for drag prediction of this geometry. This model predicted the axial momentum loss and secondary flow in the wake, as well as the integrated surface forces, within experimental error up to 20o angle of attack. SST k-ω required additional surface grid resolution on the nacelle suction side, resulting in 15% more elements, due to separation point prediction sensitivity. It was further recommended to apply enhanced wall treatment to more accurately capture the viscous drag and separated flow structures. Overall, total drag was predicted within 5% at 0o angle of attack and 10% at 20o, each within experimental uncertainty. What is more, the form and induced drag predicted by CFD and measured by the wake traverse shared good agreement. Which indicated CFD captured the key flow features accurately despite simplification of the nacelle interior geometry.

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This report documents the development of the initial dynamic policy mixes that were developed for assessment in the DYNAMIX project. The policy mixes were designed within three different policy areas: overarching policy, land-use and food, and metals and other materials. The policy areas were selected to address absolute decoupling in general and, specifically, the DYNAMIX targets related to the use of virgin metals, the use of arable land and freshwater, the input of the nutrients nitrogen and phosphorus, and emissions of greenhouse gases. Each policy mix was developed within a separate author team, using a common methodological framework that utilize previous findings in the project. Specific drivers and barriers for resource use and resource efficiency are discussed in each policy area. Specific policy objectives and targets are also discussed before the actual policy mix is presented. Each policy mix includes a set of key instruments, which can be embedded in a wider set of supporting and complementary policy instruments. All key instruments are described in the report through responses to a set of predefined questions. The overarching mix includes a broad variety of key instruments. The land-use policy mix emphasizes five instruments to improve food production through, for example, revisions of already existing policy documents. It also includes three instruments to influence the food consumption and food waste. The policy mix on metals and other materials primarily aims at reducing the use of virgin metals through increased recycling, increased material efficiency and environmentally justified material substitution. To avoid simply shifting of burdens, it includes several instruments of an overarching character.