| 1. |
- A Asif, Farazee M, 1980-
(författare)
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Circular Manufacturing Systems : A development framework with analysis methods and tools for implementation
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The society today lives on the philosophy of ‘take-make-use-dispose.’ In the long run, this is not sustainable as the natural resources and the waste carrying capacity of the earth are limited. Therefore, it is essential to reduce dependency on the natural resources by decoupling the growth from the consumption. In this venture, both the society and the manufacturing industry have a vital role to play. The society needs to shift towards Circular Economy that rests upon the philosophy of ‘take-make-use-reuse’ and the manufacturing industry has to be a major stakeholder in this shift. Despite being proven to be both economically and environmentally beneficial, successful examples of circular systems are few today. This is primarily due to two reasons; firstly, there is a lack of systemic and systematic approach to guide industries and secondly, there is a lack of analysis methods and tools that are capable of assessing different aspects of circular manufacturing systems. Taking on to these challenges, the objective of this research is to bring forward a framework with methods and decision support tools that are essential to implement circular manufacturing systems. The initial conceptual framework with the systemic approach is developed based on extensive review and analysis of research, which is further adapted for industrial implementation. Systematic analysis methods, decision support and implementation tools are developed to facilitate this adaptation. This development has been supported by four cases from diverse manufacturing sectors. Behind each decision support tool, there are analysis methods built upon mainly system dynamics principles. These tools are based on simulation platforms called Stella and Anylogic. Among other things, these tools are capable of assessing the performance of closed-loop supply chains, consequences of resource scarcity, potential gains from resource conservation and overall economic and environmental performance of circular manufacturing systems.
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| 2. |
- A. M. Naiini, Maziar, 1980-
(författare)
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Horizontal Slot Waveguides for Silicon Photonics Back-End Integration
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the development of integrated silicon photonic devices. These devices are compatible with the present and near future CMOS technology. High-khorizontal grating couplers and waveguides are proposed. This work consists of simulations and device design, as well as the layout for the fabrication process, device fabrication, process development, characterization instrument development and electro-optical characterizations.The work demonstrates an alternative solution to costly silicon-on-insulator photonics. The proposed solution uses bulk silicon wafers and thin film deposited waveguides. Back-end deposited horizontal slot grating couplers and waveguides are realized by multi-layers of amorphous silicon and high-k materials.The achievements of this work include: A theoretical study of fully etched slot grating couplers with Al2O3, HfO2 and AIN, an optical study of the high-k films with spectroscopic ellipsometry, an experimental demonstration of fully etched SiO2 single slot grating couplers and double slot Al2O3 grating couplers, a practical demonstration of horizontal double slot high-k waveguides, partially etched Al2O3 single slot grating couplers, a study of a scheme for integration of the double slot Al2O3 waveguides with selectively grown germanium PIN photodetectors, realization of test chips for the integrated germanium photodetectors, and study of integration with graphene photodetectors through embedding the graphene into a high-k slot layer.From an application point of view, these high-k slot waveguides add more functionality to the current silicon photonics. The presented devices can be used for low cost photonics applications. Also alternative optical materials can be used in the context of this photonics platform.With the robust design, the grating couplers result in improved yield and a more cost effective solution is realized for integration of the waveguides with the germanium and graphene photodetectors.
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| 3. |
- A. Manneh, Ilana, 1970-
(författare)
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Supporting Learning and Teaching of Chemistry in the Undergraduate Classroom
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is agreement in research about the need to find better ways of teaching chemistry to enhance students’ understanding. This thesis aims to contribute to the understanding of how we better support teaching and learning of undergraduate chemistry to make it meaningful and intelligible for students from the outset. The thesis is concerned with examining the interactions between student, specific content and teacher in the undergraduate chemistry classroom; that is, the processes making up the three relations of the didactic triangle. The data consists of observations of students and tutors during problem-solving activities in an introductory chemistry course and interviews with graduate students.Systematic analyses of the different interactions between the student, the chemistry content, and the tutor are made using the analytical tool of practical epistemology analysis. The main findings of the thesis include detailed insights into how undergraduate chemistry students deal with newly encountered content together with didactic models and concrete suggestions for improved teaching and for supporting continuity and progression in the undergraduate chemistry classroom. Specifically, I show how students deal with the chemistry content through a complex interaction of knowledge, experiences, and purposes on different levels invoked by both students and tutors as they interact with each other. Whether these interactions have a positive or negative effect on students’ learning depends on the nature of knowledge, experiences and purposes that were invoked. Moreover, the tutor sometimes invoked other purposes than the ones related to the task at hand for connecting the activity to the subject matter in general. These purposes were not always made continuous with the activity which resulting in confusion among students. The results from these analyses were used for producing hypotheses and models that could support continuity and progression during the activity. The suggested models aim to make the content more manageable and meaningful to students, enabling connections to other experiences and purposes, and helping teachers and tutors to analyze and reflect on their teaching. Moreover, a purpose- and activity-based progression is suggested that gives attention to purposes in chemistry education other than providing explanations of chemical phenomena. The aim of this ‘progression in action’ is to engage students in activities were they can see the meaning of chemical concepts and ideas through their use to accomplish different chemical tasks. A general conclusion is that detailed knowledge about the processes of teaching and learning is important for providing adequate support to both undergraduate students and university teachers in the chemistry classroom.
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| 4. |
- A Monfared, Behzad, 1983-
(författare)
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Magnetic Refrigeration for Near Room-Temperature Applications
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Refrigeration plays a crucial role in many different sectors and consumes about 17% of the electricity produced globally. This significant energy consumption implies large share of refrigeration in primary energy consumption and other environmental impacts. In addition to the environmental impacts associated with energy consumption, the vapor-compression systems contribute in global warming due to the release of their gaseous refrigerants into the atmosphere. As an alternative technology for near room-temperature applications, magnetic refrigeration is proposed by some researchers to eliminate the release of gaseous refrigerants into the atmosphere and to reduce the energy consumption. This thesis is a compilation of a number of studies done on magnetic refrigeration for room-temperature applications.In the first study, the environmental impacts associated to magnetic refrigeration are looked at closely through a life cycle assessment. The life cycle assessment indicates that because of the environmental burdens related to the rare-earth materials used in magnetic refrigeration, the reduction in the environmental impacts is not guaranteed by switching to magnetic refrigeration technology. Accordingly to avoid the extra environmental impacts the magnetic refrigeration systems should use magnetic materials frugally, which requires an optimized design. In addition, operation with higher efficiency compared to vapor-compression systems is necessary to have environmental advantages, at least in some impact categories.A practical method to optimize the design of magnetic refrigeration systems, e.g. to have a compact design or high efficiency, is utilizing a flexible software model, with which the effect of varying different parameters on the performance of the system can be simulated. Such a software model of the magnetic refrigeration system is developed and validated in this project. In developing the model one goal is to add to the precision of the simulated results by taking more details into consideration. This goal is achieved by an innovative way of modeling the parasitic heat transfer and including the effect of the presence of magnetocaloric materials on the strength of the field created by the magnet assembly. In addition, some efforts are made to modify or correct the existing correlations to include the effect of binding agents used in some active magnetic regenerators. Validation of the developed software model is done using the experimental results obtained from the prototype existing at the Department of Energy Technology, KTH Royal Institute of Technology.One of the parameters that can be modified by the developed software model is the choice of the magnetocaloric materials for each layer in a layered active magnetic regenerator. Utilizing the software model for optimizing the choice of the materials for the layers reveals that materials with critical temperatures equal to the cyclic average temperature of the layers in which they are used do not necessarily result in the desired optimum performance. In addition, for maximizing different outputs of the models, such as energy efficiency or temperature lift sustained at the two ends of the regenerators, different choice of materials for the layers are needed. Therefore, in other studies seeking to improve one of the outputs of a system, the choice of the transition or critical temperatures of the materials for each layer is an additional parameter to be optimized.The prototype existing at the Department of Energy Technology, KTH Royal Institute of Technology, was initially designed for replacing the vapor-compression system of a professional refrigerator. However, it could not fulfil the requirements for which it was initially designed. The aforementioned developed simulation model is used to see how much the choice of the materials, size of the particles, and number of layers can enhance the performance while the operation frequency and flow rate of the heat transfer fluid are at their optimum values. In other words, in that study the room for improvement in the performance without applying major changes in the system such as the geometry of the regenerator, which implies redesigning the whole magnet assembly, is investigated. In the redesign process the effect of binding agent and the limitations associated to different properties of it is also investigated theoretically. Nevertheless, the study did not show that with keeping the geometry of the regenerators and the currently existing magnetocaloric materials the initial goals of the prototype can be achieved.In the next study more flexible choice of geometries and magnetocaloric materials are considered. In fact, in this study it is investigated how much the magnetocaloric materials need to be improved so that magnetic refrigeration systems can compete with vapor-compression ones in terms of performance. For the two investigated cases, the magnetic-field dependent properties of the currently existing materials are enough provided that some other issues such as low mechanical stability and inhomogeneity of the properties are solved. Nevertheless, for more demanding design criteria, such as delivering large cooling capacity over a considerable temperature span while the magnetic materials are used sparingly, the magnetic-field dependent properties need to be enhanced, as well.A less explored area in room-temperature magnetic refrigeration is the subject of another study included in the thesis. In this study, solid-state magnetic refrigeration systems with Peltier elements as heat switches are modeled. Since the Peltier elements consume electricity to pump heat, the modeled systems can be considered hybrid magnetocaloric-Peltier cooling systems. For such systems the detailed transient behavior of the Peltier elements together with layers of magnetocaloric materials are modeled. The mathematical model is suitable for implementation in programing languages without the need for commercial modeling platforms. The parameters affecting the performance of the modeled system are numerous, and optimization of them requires a separate study. However, the preliminary attempts on optimizing the modeled system does not give promising results. Accordingly, focusing on passive heat switches can be more beneficial.
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| 5. |
- Aaboen, Lise, 1978
(författare)
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Incubators and incubation -Resources and activities in relation to different actors
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- ABSTRACTIncubators prepare new technology-based firms (NTBFs) for the obstacles ahead, they complement and develop the entrepreneurial ability of the firm founder, advise regarding financing, as well as providing structure and credibility to the firm. Incubators accelerate the development of the firms towards growth, create an entrepreneurial and innovative climate in the region, and contribute to the commercialization of research results from the university. There are many descriptions but still there remains the difficulty of understanding what an incubator is, and what it does. There is a great difference between incubators due to them having been formed in relation to different actors who have varying histories. Based on the appended papers the principal actors in relation to incubators are: the incubator, the NTBFs, the university, the policy actors and the financial actors. Moreover, the part played by the incubator differs depending on the roles in relation to the different actors, and they often have more than one role in relation to the same actor. Hence, the purpose of this thesis is to explore incubation in relation to different actors. The exploration includes five appended papers. Three of the papers focus on the role of the incubators when helping the NTBFs find and utilize resources. The three types of resources are knowledge, financing and relationships. The two remaining papers focus on the incubator as an organization with particular interest in value creation and efficiency. All five appended papers are written using the resource-based view. In the cover paper the findings in the appended papers are reflected upon using the industrial network approach in order to provide another perspective, focusing on relationships as opportunities leading to an understanding of incubators and incubation. In the cover paper principal actors, activities and resources are explored. The NTBFs are developed through the incubation with the help of resources contributed by the other actors. Additional to the development, the cover paper discussed other activities included in the incubation, i.e. mediation, innovation and acceleration. These activities enable actors to access and combine resources, within and across firm boundaries, that they would otherwise have difficulties combining at that point in time, as quickly or in that way. The relationships of the incubator enable mediation of contacts between actors who are otherwise reluctant to collaborate. Through these collaborations new resource combinations may be found. Resource combinations in already existing relationship can be found using experience from other relationships. In other words, the relationships of the incubator contribute to innovation among the actors. Furthermore, the relationships of the incubator contribute to the acceleration of the NTBFs’ development by being a trusted third party actor, and by contributing to the coordination of actors aiming at improving the innovative climate. Hence, relationships are a special kind of resource for the incubators. The importance of the relationships for the incubators implies that the critical issues might not be to pick NTBFs based on criteria for growth potential, but rather on the ability to form and develop relationships for themselves, as well as the NTBF, in order to develop the firm. Furthermore, arguments regarding the increasing homogeneity among Swedish incubators are based on the rather formalized relationships with the policy actors where incubators tend to play rather similar roles. The heterogeneity is likely to be perceived as larger from the perspective of relationships that are more context specific. Moreover, the relationships, activities and combination of resources cross-fertilize each other without a natural or manageable direction that cannot be controlled by one or a few of the actors involved. After the concluding discussion there is a retrospection of the development of the thesis and the empirical material, which is based on qualitative and quantitative data that has been gathered within the Swedish incubator program mainly during 1999, 2005 and 2006.
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| 6. |
- Aagaard, Philip
(författare)
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Cardiovascular assessment in middle-aged male long distance runners
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Endurance events such as long distance running races are increasing in popularity and convey multiple health benefits. However, such exercise forms also represent a major challenge to human cardiovascular physiology and are associated with a momentarily increased risk for adverse cardiac events. Using the world’s largest cross-country running race Lidingöloppet as a model of endurance events, this thesis aims to: 1) investigate male and female participation and performance trends 2) detail the cardiovascular findings of a comprehensive cardiovascular preparticipation evaluation in novice male race participants aged 45 years and older 3) study the impact of race participation on cardiac autonomic tone and 4) assess features of cardiovascular function and vectorcardiography (VCG), and their response to endurance exercise in individuals with early repolarisation (ER). Study I: Participation and performance trends were investigated in >120,000 runners partaking in the Lidingöloppet between 1993 and 2007. In a subgroup of 249 middle-aged males, the association between the cardiac biomarker NT-proBNP and runtime was also studied. Participation increased over the study period, particularly in females and older males, while participants’ fitness deteriorated, as measured by an average increase in runtime of 21 ± 31 min. Longer runtimes were independently associated with higher levels of NT-proBNP. Study II: A preparticipation cardiovascular exam was performed in 153 middle-aged male first-time Lidingöloppet race participants. Runners were assessed by medical history and physical exam, 12-lead ECG, echocardiography, and blood tests. 9 % of runners required further diagnostic work-up and 2 % were discouraged from race participation due to cardiac abnormalities that could increase their risk of exercise- related cardiac events. Study III: Heart rate (HR) and heart rate variability (HRV) was continuously measured from 48 hours before until 96 hours after a Lidingöloppet 30km race. Compared to pre-race values, HR was elevated during the night after the race while HRV remained depressed for 64 [51 - 96] hours after the race. A reduced HR recovery and a greater fall in HRV post race were associated with higher levels of high-sensitivity troponin T (hsTnT). Study IV: The prevalence and associated cardiac features of ER, characterized by ST-segment elevation (STE) and/or J-waves, was investigated in 153 middle-aged males registered for first-time participation in the Lidingöloppet 10, 15 or 30km race. ER was present in 40 % and generally associated with features of better cardiovascular fitness. The cardiovascular effects of participating in the 30km race (n= 94) were also assessed after the race; runners with J-waves, but not with STE alone, showed changes of repolarisation parameters usually considered unfavourable (e.g. prolonged T peak-to-end (Tpe) and QTc). Conclusion: This thesis demonstrated that increased participation in a long distance running event (Lidingöloppet) was paralleled by deteriorating runtimes. In middle-aged men, longer runtimes were associated with higher levels of NT-proBNP. These findings may raise concern regarding the fitness and cardiovascular health of some of today’s race participants. A comprehensive preparticipation evaluation identified 9 % of first- time runners needing additional work-up and 2% who were ultimately discouraged from participating, suggesting that such a protocol is useful to identify individuals requiring further testing prior to vigorous exercise. After the race there was a prolonged depression of HRV. The magnitude and duration of HRV depression correlated with higher levels of hsTnT, suggesting that the degree of troponin (Tn) increase after strenuous exercise may reflect the level of exercise-induced cardiovascular stress. ER was generally associated with a benign cardiovascular profile, although subjects with J-waves showed post-race changes in some parameters of ventricular repolarisation that are usually associated with increased arrhythmia propensity. More research into the mechanisms and potential preventive measures of adverse exercise related effects on cardiac function is warranted.
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| 7. |
- Aagaard, Sunniva Margrethe Due
(författare)
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Reticulate Evolution in Diphasiastrum (Lycopodiaceae)
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis relationships and the occurrence of reticulate evolutionary events in the club moss genus Diphasiastrum are investigated. Diphasiastrum is initially established as a monophyletic group within Lycopodiaceae using non recombinant chloroplast sequence data. Support is obtained for eight distinct parental lineages in Diphasiastrum, and relationships among the putative parent taxa in the hypothesized hybrid complexes; D. alpinum, D. complanatum, D. digitatum, D. multispicatum, D. sitchense, D. tristachyum and D. veitchii are presented. Feulgen DNA image densitometry data and sequence data obtained from three nuclear regions, RPB2, LEAFY and LAMB4, were used to infer the origins of three different taxa confirmed to be allopolyploid; D. zanclophyllum from South Africa, D. wightianum from Malaysia and an undescribed taxon from China. The two Asian polyploids have originated from two different hybrid combinations, D. multispicatum x D. veitchii and D. tristachyum x D. veitchii. Diphasiastrum zanclophyllum originates from a cross between D. digitatum and an unidentified diploid taxon. The occurrence of three homoploid hybrid combinations commonly recognized in Europe, D. alpinum x D. complanatum, D. alpinum x D. tristachyum and D. complanatum x D. tristachyum, are verified using the same three nuclear regions. Two of the three hybrid combinations are also shown to have originated from reciprocal crosses. Admixture analyses performed on an extended, dataset similarly identified predominately F1 hybrids and backcrosses. The observations and common recognition of hybrid species in the included populations are hence most likely due to frequent observations of neohybrids in hybrid zones. Reticulate patterns are, however, prominent in the presented dataset. Hence future studies addressing evolutionary and ecological questions in Diphasiastrum should emphasize the impact of gene flow between parent lineages rather than speciation as the result of hybridization.
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| 8. |
- Aagerup, Ulf, 1969-
(författare)
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It’s Not What You Sell : It’s Whom You Sell it To: How the Customer’s Character Shapes Brands and What Companies Do About it
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this dissertation I investigate the effects of user and usage imagery on brands and how businesses employ user imagery to build brands. Over four articles I present results that suggest that user imagery affects brand personality and that companies under certain conditions adapt their behavior to optimize this effect. Although both mass market fashion and nightclubs are susceptible to the influence of user imagery, out of the two only nightclubs actively reject customers to improve its effect on brand perception. I relate these practices to the practical and financial feasibility of rejecting customers, the character of nightclubs’ brands, and to their inability to differentiate their brands through any other brand personality influencer besides user imagery. In this dissertation, I also discuss the ethical ramifications of user imagery optimization through customer rejection. In one study, the role of conspicuous usage imagery on socially desirable consumer behavior is investigated. It is concluded that conspicuousness increases consumers' propensity to choose environmentally friendly products, and that this tendency is especially pronounced for individuals that are high in attention to social comparison information. The conclusion is that consumers use green products to self-enhance for the purpose of fitting in with the group rather than to stand out from it.
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| 9. |
- Aalaei, Kataneh
(författare)
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Processing and Storage stability of Skim Milk Powder : Monitoring Early and Advanced Stages of the Maillard Reaction
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The non-enzymatic browning known as the Maillard reaction has been the subject of extensive investigation for decades. Studies have focused on areas such as changes in flavour, colour, texture, and the nutritional properties of food materials as a result of this reaction. However, this complex reaction between the amino acids in proteins and reducing sugars in carbohydrates, is still not fully understood, especially the reaction mechanisms and potential impacts on health.Skim milk powder (SMP), is a multi-functional and extremely popular ingredient in the food industry, and is used in infant formulas, reconstituted and fermented dairy products, frozen desserts, bakery products, coffee whiteners, and even processed meat products. Despite the apparent good stability of SMP, it is prone to the Maillard reaction and its consequences, due to its composition, as well as the application of various kinds of thermal processing, and subsequent prolonged shelf life.The aims of this work were thus to improve our understanding of the occurrence of the Maillard reaction in SMP after the application of different drying techniques, and during subsequent storage under realistic conditions, in order to be able to predict and to control the reaction. Previous studies have mainly been conducted on model food systems at the conditions applicable to processing, i.e. at temperatures above 40 ºC. In the present work, changes in two indicators of the early and advanced stages of the Maillard reaction, namely the available lysine and carboxymethyl lysine (CML), respectively, were monitored during storage.To obtain a better understanding of the impact of processing on the progression of the reaction, three different drying techniques were studied and compared on pilot scale: freeze-drying, spray-drying and drum-drying. The extent of the reaction during prolonged storage for 200 days was studied, considering three storage variables: temperature, relative humidity (RH) and time.The kinetics of the available lysine in a commercial, industrially produced SMP was subsequently established over 30 days (the maximum recommended period for the consumption of opened packages) under conditions normally encountered during domestic storage. Furthermore, theearly and advanced stages of the reaction were studied in selected infant formulas available on the Swedish market.The results of these studies showed that the drying technique had a significant impact on the initiation of the Maillard reaction. Furthermore, the storage variables (temperature, RH and time) were also crucial factors in the gradual progression of the reaction during storage. The pattern of the decrease in the available lysine content during 200 days of storage was similar, regardless of the type of SMP. After storage at 52% RH and 30 ºC, a 39.2 – 45.9% decrease in the available lysine content was seen after 200 days. The corresponding value following storage at 52% RH and 20 ºC was 21.2 – 31.8%, indicating the importance of the storage temperature. Storage at 33% RH and 30 ºC caused a 5.2 – 22.4% decrease in the available lysine content, while no significant decrease in the available lysine content was seen after storage at 33% RH and 20 ºC, thus it was considered to be the ideal storage conditions for SMP.Studies of the advanced phase of the Maillard reaction using CML revealed that twice as much CML was formed in the spray-dried powders, than in the freeze-dried samples, after 200 days. The corresponding value in the drum-dried samples was 1.6 times that in the freeze-dried samples.The findings of this work have practical implications for SMP and SMP-based products in the food industry, and can be used to predict and control the Maillard reaction during storage, in order to ensure the safety of these products on the market.
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| 10. |
- Aalberg Haugen, Inger Marie, 1980-
(författare)
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The diapause switch : Evolution of alternative developmental pathways in a butterfly
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diapause decision is a classic example of a threshold switch mechanism with cascading effects on morphology, behaviour and life-history traits. This thesis addresses the downstream effects of the insect diapause switch, with the main focus on pathway-specific regulation of life-history traits, using the speckled wood butterfly (Pararge aegeria) as a study species. The ultimate pathway decision is made towards the end of larval development and allows the larvae to take into account up-to-date information from the environment about future conditions (Paper I, IV). However, already from an early point in development the larvae are sensitive to environmental cues and continuously adjust their growth trajectory in accordance to current information about the environmental conditions to be expected in future (Paper IV). An asymmetry in the ability to change from one developmental pathway to another at a late point in larval development suggests that the diapause and the direct pathway require different physiological preparations (Paper IV). Pathway-specific regulation of traits downstream of the diapause switch is maintained by ongoing selection. When the direct pathway is not regularly expressed, as with a shift from bivoltinism to univoltinism, relaxed selection on the unexpressed pathway leads to genetic drift and loss of protandry (Paper II, III). Natural populations display local adaptations in the diapause switch with an increase in critical daylengths as there is a gradual shift from bivoltinism to univoltinism (Paper III). This thesis highlights two aspects of the diapause decision, the determination of how and when this decision is made as well as the way the resulting pathways are moulded by selection in order to produce adaptive seasonal polyphenism in life-history traits.
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