50,857 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
Early egg traits in Cancer setosus (Decapoda, Brachyura): effects of temperature and female size
No full textPrevious study on Cancer setosus (Molina, 1782) had shown that latitudinal changes in temperature control the number of annual egg masses. This study focused on the effects of pre-oviposition temperature and female size on egg-traits in C. setosus from Northern (Antofagasta 23ºS) and Central-Southern (Puerto Montt 41ºS) Chile. Blastula eggs produced in nature ranged in dry mass (DM) from 9.1 to 15.1 µg, in carbon (C) from 4.8 to 8.4 µg, in nitrogen (N) from 1.0 to 1.6 µg, in C:N ratio between 4.7 and 5.4, and in volume (V) between 152 and 276 mm3 x 10-4 per female. Blastula eggs from females caught early in the reproductive season in Puerto Montt (09/2006) were significantly higher in DM, C, N, and V than those of females caught two months later (11/2006), reflecting a seasonal increase in water temperature. In Puerto Montt “early” and “late” season blastula eggs were about 32% and 20% higher in DM, C, N, and V as eggs from Antofagasta, respectively. Subsequent egg masses produced in captivity in Puerto Montt followed this pattern of smaller eggs with lower DM, C, and N content at higher pre-oviposition temperatures. In Antofagasta no significant difference in DM, C, N and V between eggs produced in nature and subsequent eggs produced in captivity was found and all egg traits were significantly positively affected by maternal size. Reproductive plasticity in C. setosus helps explaining the species wide latitudinal distribution range
Acute outpatient surgery for superficial thrombophlebitis
No full textAim: Superficial thrombophlebitis is a common complication of advanced varicosis. Besides the symptomatic complaints patients have a considerable risk of thromboembolic events. The aim therapy is the reduction of both the inflammatory pain and the thromboembolic risk. The two common types of surgical treatment are the ligation of the greater saphenous vein at the saphenofemoral junction or ligation plus stripping of the phlebitic vein. According to recent studies the latter shows better symptomatic outcomes. Patients and method: The present study describes an outpatient, primary operation technique using cryo-stripping. Between 1998 and 200165 patients were treated: 44 patients showed a stadium I according to Verrel, 20 patients a stadium II, and 1 patient a stadium IV. Results: No relevant complications after operation occurred. After one week 97% of the patients were almost free of complaints. In more than 90% of the cases the phlebitis was almost cured. Three patients needed additional stripping. After three months one woman developed a deep vein thrombosis. A factor V Leiden mutation was detected later. Conclusion: According to our data the outpatient stripping using cryo-technique is a safe and rapidly relieving treatment of superficial thrombophlebitis
Acute outpatient surgery for superficial thrombophlebitis
No full textAim: Superficial thrombophlebitis is a common complication of advanced varicosis. Besides the symptomatic complaints patients have a considerable risk of thromboembolic events. The aim therapy is the reduction of both the inflammatory pain and the thromboembolic risk. The two common types of surgical treatment are the ligation of the greater saphenous vein at the saphenofemoral junction or ligation plus stripping of the phlebitic vein. According to recent studies the latter shows better symptomatic outcomes. Patients and method: The present study describes an outpatient, primary operation technique using cryo-stripping. Between 1998 and 200165 patients were treated: 44 patients showed a stadium I according to Verrel, 20 patients a stadium II, and 1 patient a stadium IV. Results: No relevant complications after operation occurred. After one week 97% of the patients were almost free of complaints. In more than 90% of the cases the phlebitis was almost cured. Three patients needed additional stripping. After three months one woman developed a deep vein thrombosis. A factor V Leiden mutation was detected later. Conclusion: According to our data the outpatient stripping using cryo-technique is a safe and rapidly relieving treatment of superficial thrombophlebitis
Estudo de catalisadores de ferro fundido para a síntese Fischer-Tropsch
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Curso de Pós-Graduação em Físico-Químic
Wave turbulence of a rotating array of quantized vortices in the T → 0 temperature limit
No full textThe dynamics of quantized vortices in the zero temperature limit is currently of great interest, particularly in the case of the Fermi superfluid He-B. Here we study wave turbulence, generated by the librating motion of a rotating cylindrical container filled with He-B, in the limit of vanishing viscous forces at temperatures . The polarization of the quantized vortices with respect to the axis of rotation is measured using non-invasive NMR techniques. We observe a decrease of the polarization when the librating motion is started, and a two-stage relaxation process when the modulation of the rotation velocity is stopped. The first relaxation process is associated with the dissipation of large-scale flow stored in inertial waves and the solid body rotation of the vortex array. From the decay of these energy reservoirs we determine the rate of energy dissipation of large-scale flow. The later second process is related to the relaxation of Kelvin waves on individual vortices. This process is monitored by the recovery of the polarization. The existence of a Kelvin wave cascade at the lowest temperatures is currently a central open question. We supply some evidence for the cascade
Design and Analysis of a Distributed TRIC concept Seamless Smart Morphing Wing
No full textThis thesis embarked upon establishing and validating a design process to build and control a distributed TRIC concept seamless smart morphing wing to achieve simultaneous load alleviation, flutter suppression and drag minimization capabilities. A novel aeroelastic simulation tool was built to carry out composite wing skin optimization, with prototype testing carried out to design a flexible connection between modules. The work output was a fully built morphing wing which was successfully tested in the TU Delft Open Jet Facility. Control of the wing was partially made feasible through the development of a surrogate model of the system which was also validated with DIC testing.https://www.youtube.com/watch?v=SdagIiYRWyA&t=1s Smart-X Alpha DemonstratorAerospace Engineerin
Carbidization and size effects of unsupported nanosized iron in the low temperature Fischer-Tropsch process
No full textIncludes abstract.Includes bibliographical references.In the process of developing the most efficient production of fuels from coal or natural gas, there have been major advances in the development of the catalysts used. Previous work at the Centre for Catalysis Research, at the University of Cape Town, has shown great potential and provided a much deeper under- standing of the workings of the Fischer-Tropsch catalyst. The research has found that the catalyst crystallite size plays a crucial part in the product selectivity and requires strict control in order to obtain a certain desired product spectrum. The aim of this project is to provide insight on the behavior of various iron oxide crystallite sizes when placed in a CO concentrated environment during catalyst pretreatment. It will also clarify whether the sizes of the nano-crystallites will increase or decrease when the different phases form and which size carbides faster
Suspicion of deep vein thrombosis: diagnostic strategy at the interface of general practice and specialist care
No full textAim: We describe characteristics of patients with suspected deep vein thrombosis (DVT) referred to specialists by their general practitioner (GP) and the further proceeding by the specialist. Patients and method: From August 2001 to April 2003 all 114 patients (age 15 to 91, 72 women) with suspected symptoms of DVT were prospectively recruited in a specialist practice for vascular surgery/phlebology. Symptoms and clinical findings were documented by a standard procedure. Results: 40% of the patients received a compression therapy and 18% an anticoagulation with heparin by their GP. Pain (88%) and swelling (71%) were the leading patient complaints. Physical examination revealed calf pressure pain (40%) and differences in calf circumference (56%) as the dominant results. The clinical signs were not specific enough to exclude DVT. DVT was diagnosed in 12 patient (10.5%). Varicosis (30%) and (pseudo-) radikulaere pain (20%) were the most frequent differential diagnoses. Conclusion: The proportion of diagnosed DVT in patients referred by their GPs was low. Clinical examination alone turned out as unsuitable to detect DVT. Therefore, GPs are not capable to exclude the diagnosis DVT without technical diagnostics. The determination of D-dimer concentration in connection with clinical signs could be an alternative for GPs to reduce referrals, although this concept has not been evaluated yet
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