4,125 research outputs found
Vanadia Promoted Co-AI20 3 Fischer-Tropsch Catalysts
No full textBibliography: leaves 117-124.The primary aim of this work was to study systematically V20 5 promotion on yAI203 supported cobalt-based Fischer-Tropsch catalysts. The y-Ah03 support was modified by addition of varying amounts of vanadia and was subsequently loaded with the same Co content (10 wt-%). The modified supports and catalysts were characterised using conventional characterisation methods. The physio-chemical properties of the vanadia promoted supports and catalysts were characterised using Atomic Adsorption Spectroscopy (AAS), zeta-potential measurements, and BET measurements, X-ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Transmission Electron Microscopy (TEM), and CO chemisorption. Catalyst performance in the Fischer-Tropsch synthesis was tested in fixed bed reactor. A catalysts synthesised from plain y-A1203 was used as a base catalyst. Characterization results show that modification of y-Ab03 support to obtain V205 loadings beyond 1-monolayer vanadia coverage was difficult when using ion exchange. Ion-exchange equilibrium limitations might have caused the poor vanadia loadings beyond 1-monolayer coverage. The supports net surface charge as measured using zeta potential, was decreased by vanadia content in the supports. CO chemisorption results were complex and could only be modelled using dual site Langmuir model assuming the presence of two different sites absorbing CO on the Co-V-AI catalyst system. This made extraction of physical properties from this method rather difficult. Fischer Tropsch synthesis reaction was carried out at typical industrial conditions (T=220°C, P=20 bar (a), H2/CO=2 Xco-60 mol-%) for cobalt catalysts. Vanadia promoted catalysts showed a marked decrease in initial activity. However, the overall deactivation rate was lower with increasing vanadia content. The vanadia content did not affect the chain growth kinetic behavior of the catalyst in the Fischer-Tropsch synthesis hence C5+ selectivity in the Fischer-Tropsch synthesis was unperturbed by vanadia content. Increasing the vanadia content in the catalyst resulted in high n-olefin content and high 1-olefin content. The observed increase in olefin content might be due to the low catalytic activity observed for the catalysts with high vanadia loadings. The most pronounced effect of vanadia promotion on Fischer Tropsch synthesis was in the oxygenate content in the Fischer-Tropsch product. Catalysts with high vanadia loading yielded high amounts of oxygenate products; mainly alcohols and aldehydes
The effect of metal type and loading on n-paraffin hydrocracking conversion and selectivity
No full textIncludes bibliographical references.With the continued decline in global oil reserves, there is a growing need to develop alternative sources of conventional fuels to complement the current dependence on crude oil feedstocks. Natural gas, coal and biomass have been identified for this purpose. The distinctive advantage of using natural (stranded) gas is that it is turned into a useful product, thereby increasing its value and reducing the environmental impact of simply flaring it. The value-added work up of natural gas is effected by Gas-to-Liquid conversion via the Fischer-Tropsch Synthesis. Long-chain hydrocarbon waxes are produced and these are subsequently hydrocracked into the required middle distillate fuels, preferably diesel, as diesel engines are more efficient than their petrol counterparts. Hydrocracking may be carried out using a bifunctional catalyst, consisting of metal and acid components. Industrially, hydrocracking is used to crack heavy crude oil fractions into the desired fuel range, however, the catalysts used are sulphided transition metals. These are less suitable for cracking Fischer-Tropsch waxes as they would introduce sulphur into a clean feedstock. Moreover, at reaction temperatures of around 250°C, transition metal sulphide catalysts display little activity. Thus, one may consider noble metals such as palladium or platinum, whilst shape selective zeolites may be used as the acid component
Hydrography and flow in the rift valley of the Mid-Atlantic Ridge
No full textSlow-spreading mid-ocean ridges such as the Mid-Atlantic Ridge are characterized by deep axial rift valleys which are isolated from the water on the ridge flanks. Topographic effects therefore have a significant impact on the rift-valley hydrography and dynamics but little is known about the details. Known processes of global importance acting near the axes of midocean ridges include high rates of diapycnal mixing associated with the rough topography and high-temperature hydrothermal circulation, a major source for a number of chemical constituents of the ocean.Physical data sets from the rift valley of two connected segments of the Mid-Atlantic Ridge, which include the largest known hydrothermal vent field of the Atlantic, were analyzed to investigate the segment-scale hydrography, dynamics and geothermal fluxes. The data include two quasi-synoptic hydrographic and particle plume surveys (one year apart) and one-year-long records from an array of moored current meters.The hydrographic properties of the rift-valley water were similar during the two surveys, suggesting a stable state characterized by inflow from the eastern ridge flank, unidirectional along-segment flow (directly observed during an entire year), and monotonic along-valley hydrographic gradients consistent with high rates of diapycnal mixing. Geothermal processes do not appear to contribute significantly to these patterns. The data contain signaturesof a range of dynamical processes consistent with high rates of diapycnal mixing, including hydraulically controlled sill flows, topographic lee waves and high-energy tidal flows.The spatial distribution of the light-scattering anomalies associated with the dispersing hydrothermal particle plume are consistent with the dynamical observations. Close to the vent field the particle distribution is highly inhomogeneous but density-averaged profiles indicate that the mean plume is Gaussian in depth. To quantify the fluxes associated with the hydrothermal plume the corresponding hydrographic anomalies were determined. The complexity of the hydrography within the rift valley precludes the application of "standard" methods ho that a new method had to be developed resulting in the first quantitative hydrographic anomaly measurements of an Atlantic hydrothermal plume. The hydrographic and particle anomalies of this plume are linearly correlated, indicating that the particles behave conservatively in the near field.Estimates for the heat flux associated with the hydrothermal plume were derived using two established methods, one based on plume-rise modeling and the other on the advection of heat anomalies away from the vent field. Height-of-rise modeling yields values which are an order of magnitude too low because the plume model relies on a point-source assumption which is violated by the geometry of the vent field. The uncertainties associated with the advection method are particularly small at the site studied because of the uni-directionality of the flow field, the small uncertainties of the hydrographic anomaly measurements, and the Gaussian shape of the averaged near-field plume. The resulting estimate for the heat flux associated with the particle plume is 2.5 GW.Mass and heat budgets of the rift valley indicate that high diapycnal diffusivities are required to account for the hydrographic observations and suggest that a portion of the water flowing along the rift valley may be lost to the overlying water column. Inspired by the observations a simple analytical and numerical model for the flow within the rift valley was developed. The results indicate that the rift valley acts as an efficient low-pass filter with characteristic time scales of weeks to months, providing a plausible explanation for the persistence of the along-segment flow
Models of stress at mid-ocean ridges and their offsets
No full textThis thesis aims to investigate the stresses at mid-ocean ridge offsets, and particularly at the particular class of offsets represented by oceanic microplates. Amongthese, the Easter microplate is one of the best surveyed. This thesis first studies the stress field associated with mid-ocean ridges and simple types of ridge offsets, and then uses the stress field observed at Easter to constrain the driving mechanism of microplates. Two-dimensional finite element modelling is used to predict the lithospheric stress indicators, which are then compared with observations. Extensional structures at high angles (> 35 ) to ridge trends are often observed at ridge-transform intersections and non-tranform offsets, but remained unexplained until now. This study proposes that the topographic loading created by the elevation of mid-ocean ridges relative to old seafloor is a source of ridge parallel tensile stresses, and shows they can be explained by the rotation of ridge parallel tensile stresses at locked offsets. The elasto-plastic rheology is used to investigate the evolution of normal faults near mid-ocean ridges. It is shown that variations in the lithospheric strength, caused entirely by variations in the brittle layer thickness, can account for the observed variations in fault character with spreading rate and along-axis position. Plasticity is shown to prevent the achievement of large fault throws in thin brittle layers. Consequently, it may be important at fast spreading ridges. A new dynamic model is proposed for Easter microplate. It mainly consists of: 1) driving forces along the East and West Rifts, resulting from the combination of a regional tensile stress with an increasing ridge strength towards rift tips, 2) mantle basal drag resisting the microplate rotation, and contributing with less than 20% to the total resisting torque, and 3) resisting forces along the northern and southern boundaries. To explain both the earthquake focal mechanism evidence and theexistence of compressional ridges in the Nazca plate, the boundary conditions alongthe northern boundary are required to change with time, from completely locked tolocked in the normal direction only. This study does not invalidate the microplate kinematic model proposed by Schouten et al. (1993), but shows that normal resisting forces along the northern and southern boundaries of Easter microplate must exist in order to explain the stress observations. Also, it suggests that ridge strength variations play an important role in the dyamics of mid-ocean ridge overlap regions
Virtual Human Problem Solving Environments
No full textAbstract. Interest in complex integrated digital or virtual human modeling has seen a significant increase over the last decade. Coincident with that increased interest, Oak Ridge National Laboratory (ORNL) initiated the development of a human simulation tool, the Virtual Human. The Virtual Human includes a problem-solving environment (PSE) for implementing the integration of physiological models in different programming languages and connecting physiological function to anatomy. The Virtual Human PSE (VHPSE) provides the computational framework with which to develop the concept of a "Virtual Human." Supporting the framework is a data definition for modeling parameters, PhysioML, a Virtual Human Database (VHDB), and a Web-based graphical user interface (GUI) developed using Java. Following description of the VHPSE, we discuss four example implementations of models within the framework. Further expansion of a human modeling environment was carried out in the Defense Advanced Research Projects Agency Virtual Soldier Project. SCIRun served as the Virtual Soldier problem solving environment (VSPSE). We review and compare specific developments in these projects that have significant potential for the future of Virtual Human modeling and simulation. We conclude with an evaluation of areas of future work that will provide important extensions to the VHPSE and VSPSE and make possible a fully-integrated environment for human anatomical and physiological modeling: the Virtual Human
Ridge Preservation im Seiten- und Frontzahnbereich
No full textZiel: Darstellung und Diskussion verschiedener Behandlungskonzepte zur Versorgung von kompromittierten Extraktionsalveolen im Front- und Seitenzahnbereich.
Material und Methode: Anhand zweier klinischer Fallbeispiele werden unterschiedliche Herangehensweisen und Materialkombinationen primär zur Versorgung von defizitären Alveolen aufgezeigt. In beiden Fällen erfolgte eine Augmentation im Sinne einer gesteuerten Knochenregeneration (GBR). Dazu wurde im Seitenzahnbereich eine kreuzvernetzte Membran exponiert belassen. Im Frontzahnfall wurde mithilfe eines Bindegewebstransplantats gleichzeitig eine Verdickung der Weichgewebe und der Verschluss der Alveole erzielt. Neben der knöchernen Rekonstruktion wurde die Vermeidung einer Verschiebung der Mukogingivalgrenze mit den dargestellten Techniken angestrebt.
Schlussfolgerung: Individuelle defekt-bezogene Konzepte zur Ridge Preservation (RP) können auch komplexe alveoläre Defekte nach Extraktion erfolgreich regeneriert werden. Aus Behandler- und Patientensicht reduziert sich somit nicht nur die Behandlungszeit, sondern auch die Notwendigkeit für komplexe, gestufte Augmentationsverfahren
Application of advanced notch stress approaches to assess fatigue strength of ship structural details: consolidation and dissemination of results
No full textThis report summarizes research activities carried out in compliance with the extension period of the research project proposed to and funded by the A. Von Humboldt Stiftung. Outline of the activities is reported in the work plan for the fifth period of exchange of the fellowship (extension) of the first author, at the beginning of the present report. Reference is made to previous reports describing activities of former periods.
Thereafter, activities are outlined as they were carried out during the stay in Hamburg of the first author.
Similarly to previous reports, this report is co-authored by Dipl.-Ing. Claas Fischer, actually Doktorand at TUHH and working on similar topics, as the reported research activities were carried out in strict cooperation
Application of advanced notch stress approaches to assess fatigue strength of ship structural details: benchmarks on complex geometries and laboratory tests
No full textThis report summarizes research activities carried out in compliance with Task #3, #4 and #5 of the research project proposed to and funded by the A. Von Humboldt Stiftung. Outline of the activities is reported in the work plan for the third period of exchange of the fellowship of the first author at the beginning of the present report, briefly summarizing the findings from the previous work and looking forward to future developments.
Thereafter, activities are outlined as they were carried out during the stay in Hamburg of the first author. Advices for future activities are also provided for both, numerical and experimental analyses. Updating of literature review about N-SIF based approaches is finally reported.
Similarly to a previous report, this report is co-authored by Dipl.-Ing. Claas Fischer, actually doktorand at TUHH and working on similar topics, as the reported research activities were carried out in strict cooperation
Application of advanced notch stress approaches to assess fatigue strength of ship structural details: analysis of tests and evaluation of approaches for complex geometries
No full textThis report summarizes research activities carried out in compliance with the extension period of the research project proposed to and funded by the A. Von Humboldt Stiftung. Outline of the activities is reported in the work plan for the fourth period of exchange of the fellowship (extension) of the first author, at the beginning of the present report. Reference is made to previous reports describing activities of former periods.
Thereafter, activities are outlined as they were carried out during the stay in Hamburg of the first author.
Similarly to previous reports, this report is co-authored by Dipl.-Ing. Claas Fischer, actually Doktorand at TUHH and working on similar topics, as the reported research activities were carried out in strict cooperation
Prayer Kaddish
No full textKadiš je kratka liturgijska molitva sa eshatološkim fokusom koja se više puta izgovara tokom verske službe (uglavnom na aramejskom) kojom se veliča i slavi Bog. Takođe je i molitva ožalošćenih tokom prve godine žalosti. Kadiš je za sve Jevreje, i pobožne i slobodumne, uzvišen i svet i možda najpopularnija molitva u celokupnoj jevrejskoj liturgiji. Dr Fischer smatra da su njen postanak, razvoj, sadržaj, značaj, jezik i odnos ka spasenju duše malo poznati i da samo moć navike ovoj molitvi daje prividnu snagu. Zbog toga u članku “Molitva Kadiš” želi da protumači sadržaj ove divne molitve i da širu javnost upozna sa njenom istorijom. Govoreći o nastanku ove molitve autor nas upoznaje sa verovatnim izvorima koji se odnose na citate iz Talmuda i Mišne kao i na jednu staru potresnu bajku iz vremena Rab Akibe. Kadiš je prvobitno napisan na hebrejskom jeziku pa se tako citira i pojavljuje u Talmudu. Kasnije je u Vavilonu hebrejski tekst preveden na aramejski ali su odlomci starog hebrejskog teksta očevidno zadržani u delu molitve, koji se i danas govori subotom i praznicima pri iznošenju Tore. Dr Fischer smatra da je neobično da se ova najpoznatija i najčešće izgovarana molitva slabo ili nikako može razumeti te stoga analizira svaki stih posebno dajući nam potrebna objašnjenja i tumačenja. Na kraju rada govori o promenama koje se su događale tokom vremena i poredi prvobitni i savremeni sadržaj Kadiša.Kaddish is a short liturgical prayer with an eschatological focus that is pronounced several times during a religious service (mostly in Aramaic) which praises and glorifies God. There is also the prayer of the grieving during the first year of mourning. For all Jews, both religious and free-spirited, Kaddish is sublime and holy, and perhaps the most popular prayer in the entire Jewish liturgy. Dr. Fischer believes that its origin, development, content, significance, language, and attitude towards the salvation of the soul are slightly known and that only the power of habit gives this prayer illusory strength. That is why in the article "Prayer Kaddish" he wants to interpret the content of this wonderful prayer and to acquaint the general public with its history. Speaking about the origin of this prayer, the author introduces us to probable sources that refer to quotations from the Talmud and the Mishnah, as well as to an old shocking fairy tale from the time of Rab Akiba. Kaddish was originally written in Hebrew, so it is quoted and appears in the Talmud. Later, in Babylon, the Hebrew text was translated into Aramaic, but excerpts from the old Hebrew text were apparently retained in the part of the prayer, which is still spoken today on Saturdays and holidays during the presentation of the Torah. Dr. Fischer finds it unusual that this most famous and most often pronounced prayer can be poorly or not at all understood and therefore analyzes each verse separately giving us the necessary explanations and interpretations. At the end of the paper, he talks about the changes that have taken place over time and compare the original and modern content of Kaddish.Dr Leopold Fischer (1886-1941) bio je rabin u Daruvaru a potom nadrabin u Vršcu. Uređivao je "Jevrejski almanah" godišnjak Saveza rabina Kraljevine SHS, koji je izlazio od 1925 do 1930. Bio je član Glavnoga odbora Saveza jevrejskih opština Jugoslavije i član Upravnoga odbora biblioteke i muzeja grada Vršca. Autor je knjiga i tekstova koji i danas predstavljaju važan izvor u talmudskim studijama. Bio je osoba izuzetnog obrazovanja, govorio je 9 jezika, imao dva doktorata, dopisivao se s brojnim poznatim i uglednim ličnostima (Šalom Alejhem, Šalom Aš, Rabindranat Tagore). Nakon sloma Kraljevine Jugoslavije uhvaćen je i sa ostalim beogradskim Jevrejima deportovan u logor Topovske Šupe u Beogradu, gdje je stradao.Dr. Leopold Fischer (1886-1941) was a rabbi in Daruvar and senior rabbi in Vršac. He was edited "Jewish Almanac" - the yearbook of the Association of Rabbis of the Kingdom of Serbs, Croats and Slovenes, which was published from 1925 to 1930. He was a member of the Main Board of the Federation of Jewish Communities of Yugoslavia and a member of the Board of the Library and Museum of Vršac. He is the author of books and texts that still represent an important source in Talmudic studies. He was a person of exceptional education, he spoke nine languages, he had two doctorates, and he corresponded with many famous and respectable people (Shalom Aleichem, Shalom Ash, Rabindranath Tagore). After the collapse of the Kingdom of Yugoslavia, he was captured and deported with other Belgrade Jews to the Topovske Šupe camp in Belgrade, where he died
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