1,654 research outputs found
Thermische verkenningen van een dubbelschroefextruder
No full textIn dit verkennend onderzoek is gekeken naar een aantal thermische processen die zich afspelen in een dubbelschroefextruder. Deze processen zijn: de opsmelting van de polymeer (in korrel- of poedervorm), de warmtegeneratie in een C-vormige kamer van de dubbelschroefextruder en in de spleet tussen schroef en barrel. Een aantal temperatuurprofielen zijn gemeten in de smelt vlak achter de schroeven, de verbanden die hiermee gelegd kunnen worden met de procesparameters zijn nog vaag. Een over-all warmtebalans moet inzicht geven in de totale warmtehuishouding van de extruder. Het hele werk zelf toont aan dat regeling en storingsonderdrukking bij een dubbelschroefextruder erg belangrijk is.Applied SciencesFysische Technologi
The SF-36: a simple, effective measure of mobility disability for epidemiological studies
No full textBackgroundMobility disability is a major problem in older people. Numerous scales exist for the measurement of disability but often these do not permit comparisons between study groups. The physical functioning (PF) domain of the established and widely used Short Form-36 (SF-36) questionnaire asks about limitations on ten mobility activities.ObjectivesTo describe prevalence of mobility disability in an elderly population, investigate the validity of the SF-36 PF score as a measure of mobility disability, and to establish age and sex specific norms for the PF score.MethodsWe explored relationships between the SF-36 PF score and objectively measured physical performance variables among 349 men and 280 women, 59-72 years of age, who participated in the Hertfordshire Cohort Study (HCS). Normative data were derived from the Health Survey for England (HSE) 1996.Results32% of men and 46% of women had at least some limitation in PF scale items. Poor SF-36 PF scores (lowest fifth of the gender-specific distribution) were related to: lower grip strength; longer timed-up-and-go, 3m walk, and chair rises test times in men and women; and lower quadriceps peak torque in women but not men. HSE normative data showed that median PF scores declined with increasing age in men and women.ConclusionOur results are consistent with the SF-36 PF score being a valid measure of mobility disability in epidemiological studies. This approach might be a first step towards enabling simple comparisons of prevalence of mobility disability between different studies of older people. The SF-36 PF score could usefully complement existing detailed schemes for classification of disability and it now requires validation against them
Complex calcium ferrites in the blast furnace process: Fluxed sinter formation and SFCA reduction under simulated conditions
No full textCivil Engineering and Geoscience
Oxygen balanced mixotrophy in microalgae
No full textMicroalgae are photosynthetic microorganisms that can reach higher areal productivity than terrestrial plants, do not require arable land or fresh water, and can use fertilizers with almost 100% efficiency. Microalgae-derived products are therefore considered a promising sustainable source of food and other commodities.Microalgae are commonly grown exploiting their photoautotrophic capacity (henceforth referred to as autotrophic), in which cells harvest light energy, use CO2 as a carbon source, and release O2 as a byproduct. CO2 and aeration are provided to prevent carbon limitation and oxygen accumulation. Some microalgae can also be grown heterotrophically, in which organic carbons, such as sugars and organic acids, are used as carbon sources in the absence of light. In this trophic mode, O2 is consumed and CO2 is released as a by-product. Autotrophic and heterotrophic cultivation of microalgae can be combined in mixotrophic cultivation in which light and reduced organic carbons are simultaneously exploited within a single microalgal monoculture.In this thesis we designed a novel mixotrophic process called “oxygen balanced mixotrophy” in which there is no net O2 production. This was possible by tuning the supply of organic carbon to the rate of photosynthesis. When illuminated, the culture did not required any aeration. Due to the internal gas recirculation, about the 90% of the organic carbon provided was converted into biomass making the process almost carbon neutral. The presence of two complementary growth modes within a microalgal monoculture led to doubled biomass productivity and concentration in comparison with an autotrophic reference.Oxygen balanced mixotrophy has been successfully applied to with two industrially relevant microalgal strains: Chlorella sorokiniana and Galdieria sulphuraria. G. sulphuraria had a protein content of over 60% w/w and compared favorably with the FAO dietary requirements for adults regarding amino acid composition. Moreover G. sulphuraria contains a high proportion of sulphurated amino acids compared with Chlorella, Spirulina and soybean protein. Due to its attractive amino acid profile and high protein content, G. sulphuraria proved to be a good candidate for food and feed applications to overcome sulphurated amino acid deficiencies.Mixotrophic cultivation of G. sulphuraria demonstrate to be also a good strategy to produce the blue pigment phycocyanin with superior acid- and thermal stability compared to phycocyanin extracted in Spirulina.Finally the insights of this thesis were combined in a techno-economic model. Projections were made on biomass production costs for a hypothetical 100-hectare facility located in southern Spain. Our projections indicated that mixotrophic cultivation of Chlorella sorokiniana would half microalgal production cost mainly due to the doubling of biomass productivity under mixotrophy. For Galdieria sulphuraria, because of the expected low efficiency of CO2 uptake and the doubling of biomass productivity, mixotrophic biomass production costs would be three times cheaper than autotrophic production. Microalgal protein yield per hectare is expected to be 30-60 times higher than for soy beans while it would require 25-50 times less water. If glucose is used as a substrate for mixotrophic cultivation, the land and water consumption of sugar production substantially increases the overall water and land usage. However, when we consider the land and the water needed for sugar beet production, mixotrophic cultivation still requires 4 times less land and 7 times less water than soy beans. Altogether, this thesis successfully designed and applied oxygen balanced mixotrophy with two industrially relevant microalgal strains proving its effectiveness in reducing microalgal production costs. We are on the right track to achieve an economically feasible protein production from microalgae for food and feed purposes
A liquid foam-bed photobioreactor for microalgae production
No full textMicroalgae are promising sources for the production of food, feed, bulk chemicals and biofuels. Currently, the production of bulk commodities from algal biomass is not yet feasible due to high costs and energy demand of microalgae production processes. In order to reduce the costs and energy demand of microalgae cultivation, a liquid foam-bed photobioreactor was developed. Such a liquid foam-bed photobioreactor has several advantages over traditional photobioreactors. For example, the foam-bed photobioreactor allows for increased biomass concentration, thereby reducing harvesting costs. Furthermore, less energy is required for gassing because of the low pressure in the reactor, and the transfer of carbon dioxide to the microalgae culture is faster and more efficient due to improved gas-liquid contact. This new photobioreactor design relies on continuous foam formation and foam breaking, and therefore several foam breaking techniques and reactor configurations were experimentally evaluated. In addition, our experiments revealed that Pluronic F68 is a suitable foam stabilizing agent for the foam-bed photobioreactor. We showed experimentally the feasibility and potential of such a foam-bed photobioreactor: we maintained > 20 g L-1 biomass density during continuous reactor operation, and we achieved 57 g m-2 d-1 areal biomass productivity. Our calculations show that the energy requirements of microalgae production can be reduced ten-fold when a foam-bed photobioreactor is used instead of a traditional flat panel photobioreactor.</p
Softening in the blast furnace process: Local melt formation as the trigger for softening of ironbearing burden materials
No full textCivil Engineering and Geoscience
Identifying vulnerabilities of chromosomal instability: equal sharing is caring
No full textTo maintain tissue homeostasis, cells need to duplicate and equally divide their genetic information over two new daughter cells. This process is tightly controlled, and for good reason: faulty cell division brings the risk of cell death. In contrast to healthy cells, cancer cells tend to make mistakes during cell division. Often, chromosomes fail to segregate correctly, leading to daughter cells with abnormal chromosome counts. This ongoing process of segregation errors is referred to as chromosomal instability (CIN). CIN has been linked to poor prognosis and increased therapy resistance. However, since this is a cancer cell specific trait, CIN could be a potential target to specifically attack genetically unstable cancer cells.
In this thesis, we took multiple approaches to identify vulnerabilities of chromosomal unstable cancer cells. For this, we utilized a genetic screening platform in human haploid HAP1 cells, and induced CIN by different mechanisms; spindle assembly checkpoint (SAC)-deficiency, replication stress or by chromosome condensation defects. The core aim of the project was to find genes that are important for the survival of CIN cells in general. Therefore, we focused on the genes that hit in all three conditions. Interestingly, we identified 17 genes, under which several kinetochore proteins, ER proteins, ubiquitin ligases, a phosphatase and RNAseH2. These genes could represent genes that are generally important for cells with an unbalanced genome and might encompass interesting targets for the clinic. Unfortunately, the level of synthetic lethality of the overlapping hits was mild. Therefore, we exploited the hits per screen separately. Because we found more optimal targets in each individual unstable background than in all backgrounds combined, we believe that cancer patients will benefit most from identifying the underlying cause of the genetic instability in their tumor, in order to target the tumors vulnerability specifically
Micromilling of hardened tool steels
No full textMiniaturized parts are increasingly demanded in different fields like medical, transportation, environmental, and communication industries. In order to manufacture these parts in an economical way, mass replication methods, such as micro injection molding, have to be applied. Currently, Electro Discharge Machining (EDM) process is mainly used to manufacture the needed moulds for micro injection molding in industries. In order to achieve the final shape, several electrodes have to be made by milling with different levels of geometrical accuracy. Besides, the material removal rate of EDM is relatively low. This results in a long throughput-time and high manufacturing cost. Therefore, industries are looking for alternative technologies to overcome these drawbacks; micromilling is one of the promising technologies. The advantages of the micromilling technology include the applicability of a broad range of materials including hardened tool steels, the capability of manufacturing three dimensional geometries, accurate machining of complex features, and it is economical for small and medium lot sizes, etc. However, although micromilling in principle is a good alternative for the EDM process, it is found in research that some challenges have to be overcome before this technology is ready to be adopted in industrial applications. The literature survey shows that the fundamental micro cutting mechanism has been well investigated and understood through the study of micro orthogonal cutting and ultraprecision machining. Issues related to the application of micromilling have however not yet been well studied. Besides, inconsistent observations are commonly seen in literature. This is because observed results in micromilling are highly dependent on the experimental conditions. Based on the literature survey and initial micromilling tests, the general goal of this research has been defined as to develop and describe a reliable micromilling process for precision machining of hardened tool steels. It was decided to first improve lives of micro endmills to achieve a reliable cutting, and then to improve the performance of the process through process planning. In this research, experiments were mainly done with Ø 0.5 mm square endmills on hardened tool steels (AISI H11, H13, etc.). Experimental investigations were done to identify the main problems in micromilling. It was observed that the used commercial micro tools suffered severe wear, the tool life was too short to conduct a successful task, and the workpiece quality was not achieving the requirements. Investigations were conducted to understand tool wear types and mechanism. The factors which influence the tool performance were analyzed. It was found that the geometry of commercial tools is mainly derived from macro endmills, with which the cutting edge corners have the highest stress level. The machining parameters and tool paths are two factors that have significant effect on the tool performance; however, there was no good method available for the planning of the micromilling process. The geometry of micro endmills was studied theoretically by means of analytical modeling and FEA method. Having understood the relationship between geometrical features of the cutting tool and their influence on the tool performance (stiffness and strength of the cutting edge corners), the geometry of the micro endmill can be designed specifically for a given application to achieve the desired performance. This method was demonstrated by designing the micro square endmill especially for hard milling applications. The newly designed tools were manufactured and validated through experiments in comparison with the commercial tools. The experimental results have shown that the new designs have improved the tool performance as expected. The planning of the micromilling process has been divided into two parts. In the first part, design of experiments has been used to understand the relationship between input variables (machining parameters and tool paths) and process response (tool wear and surface finish). With this method, the significant variables can be identified by means of ANOVA analysis, and the cutting conditions can be planned accordingly to optimize the process output. For example, to have a long tool life is important for the roughing operation, and to achieve a good surface finish is of interest for the finishing operation. In the second part of the process planning, a knowledge-based method is used to plan cutting conditions for the machining of micro features with high aspect ratios. The selection of machining parameters was done by means of a force model, which describes the relation between machining parameters and average forces. The tool paths were tested by a FEM model. An improved tool path was proposed to overcome the disadvantage of the conventional tool path. Experiments were done with conditions chosen by the theoretical analysis, and the results proved the validity of the developed method. Micro ribs with aspect ratios higher than 50 could be machined successfully.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
Design of a Micro Milling Setup with an Active Magnetic Bearing Spindle
No full textThis thesis describes the design of a micro milling setup with an active magnetic bearing spindle. Micro milling is the mechanical removal of material with sub millimeter tools. An active magnetic bearing typically consists of a set of magnetic actuators, a control loop and position sensors. Active Magnetic Bearings enable a very high rotational speed of 150.000 rpm and a high positioning accuracy. The use of bearing signals for process monitoring is a separate research topic in the same project. Special attention has been given to the design of magnetic actuators with low rotating losses. A design with an axial bias flux generated by permanent magnets has been applied. The rotordynamic modelling of the spindle is described as well as the controller design. The spindle has been realized and a rotational speed of 150.000 rpm has been achieved. The spindle has been integrated into a micro milling setup, where the work piece is positioned using an xy stage driven by Lorentz actuators. A novel tool clamping device had to be developed which matches the reduced dimensions of the spindle and which is able to withstand the very high rotational speed. A monolithic tool holder has been designed in which the clamping force increases with increasing rotational speed. The main improvements that can be made require the increase of the rotational speed and an increase of the flexural spindle resonance frequencies. A novel design has been presented to support a short, disk shaped rotor. This rotor shape has required the design of a controller which compensates the strong gyroscopic coupling in a rotating disk.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
The facts don't add up': The questions asked about the information society and emotions in Caryl Churchill's play Love and Information.
No full textThis thesis examines whether or not Caryl Churchill still stays true to a claim she made early in her career namely: “Playwrights don’t give answers, they ask questions” (qtd. in Aston 10) when looking at her latest play, Love and Information. The play’s mainly criticizes the information society and the negative aspects of this society which are, information overload, poverty of attention, the decreasing political awareness, the need for information, and the isolation, while it tries to influence the audience to ask critical questions about society. Churchill stimulates the audience to think critically about these aspects in society but does not force the audience to agree with her she simply poses questions upon the audience. The message of the play is that a balance between love and information is the ideal and this is also embedded in the play’s title as the title exemplifies that love and information c! an both g o together
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