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  • Aalaei, Kataneh (författare)
  • Processing and Storage stability of Skim Milk Powder : Monitoring Early and Advanced Stages of the Maillard Reaction
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt)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.
  • Aaltonen, Emil (författare)
  • Prokaryotic Arsenic Resistance - Studies in Bacillus subtilis
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Arsenic is a toxic metalloid which is found all over the globe. Due to its toxicity and wide abundance, all living organisms have evolved intrinsic arsenic resistance systems. In this study, three proteins that provide arsenic resistance in the Gram-positive bacterium Bacillus subtilis have been investigated. Acr3 is a trans-membrane protein that extrudes arsenite to the cell exterior. It belongs to the ACR family of arsenite transporters. Experimental data on the topology of Acr3, the first ever for a member of the ACR family, is provided and show that Acr3 has 10 trans-membrane helices. Both the N- and C-terminal ends of Acr3 are located to the cytoplasm and the protein has unusually short loops connecting its helices. ArsR is an arsenite sensitive transcription regulator that controls the expression of genes encoding arsenic resistance proteins. Experiments show that the operator site for ArsR from B. subtilis consists of a 6-6-6 inverted repeat and that DNA binding by ArsR involves formation of higher order multimers of the protein. The ArsK (former YqcK) protein has an unknown function. The present study shows that the arsK gene contributes to resistance towards both arsenite and arsenate. The results indicate that the function of ArsK is important in an aerobic environment and that it decreases the inhibitory effect that arsenite has on the sporulation efficiency of B. subtilis. A function of ArsK that involves an enzymatic addition of low molecular weight thiols to arsenic is proposed.
  • Aaltonen, Kristina (författare)
  • Mating system evolution and self-incompatibility in the wild plant species Brassica cretica
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Compared to animals like ourselves, plants have a very flexible sexual life. Most plants are, for example, hermaphrodites with the potential capacity for reproduction by self-fertilization (or selfing). While selfing can provide several definite advantages for the individual plant, there is a downside; mainly the severe reduction in fitness due to inbreeding depression. To avoid the negative consequences of selfing, many hermaphrodite plant species have evolved an intricate self-recognition – or self-incompatibility (SI) – system that prevents fertilization by cognate pollen. SI is in the majority of cases genetically controlled by a narrowly delimited region of the genome, called the S locus. The S locus contains several tightly linked genes, two of which – SRK and SCR – determine the pistil (female) and pollen (male) SI recognition type. One of the best-characterized SI systems is found in the Brassicaceae family, which includes the model plant Arabidopsis thaliana and a number of economically important crop species of the Brassica genus, e.g. rape seed, cabbage, and turnip. For evolutionary biologists, SI have long been a prominent and fascinating example of Darwinian natural selection acting in a frequency-dependent manner, i.e. the rarer a genetic variant becomes, the more favoured by natural selection it is. For the S locus, this means that a very large number of variants – or haplotypes – are expected to be maintained in a population and that the DNA sequences of different haplotypes will be very divergent. However, until recently there has been a shortage of empirical studies from natural plant populations to test these, and other, theoretical predictions of S locus evolutionary dynamics. In this thesis, I have produced the largest SRK and SCR DNA sequence data set from a wild Brassica species available to date. These data have allowed me to explore, in more detail than previously possible, the population genetic properties and the evolutionary history of the Brassica S locus. Moreover, accompanying studies of the pattern of inheritance of S locus variants and the occurrence of self-fertilization in natural B. cretica population have added novel information of great value to the understanding of how plants produce offspring in nature.
  • Aardal Lönnerfors, Celine (författare)
  • Robot-assisted laparoscopy for benign uterine disease. Feasibility, outcome and hospital cost.
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The introduction of the laparoscope was a milestone within gynecologic surgery. Despite evidence of better perioperative outcome compared to laparotomy, laparoscopy is mostly performed for less advanced surgical procedures and the uptake of laparoscopic hysterectomy has been slow. An effort to preserve the clinical benefits of laparoscopic surgery and facilitate the performance of more advanced surgery has led to the development of robot-assisted laparoscopic surgery. Technical progress has been advantageous for the patient from a historical point of view, but this cannot be assumed without proper evaluation. As for all surgical approaches, it is important to recognize the possible applications of robotic surgery as well as proper patient selection both from a clinical and economical point of view. The overall aim of this thesis was to investigate the possible applications, clinical outcome and hospital cost of robot-assisted laparoscopic surgery for benign uterine disease at a single institution following the introduction of robotic surgery. Study I: Evaluating the first 1000 robotic surgeries performed showed that a surgical robot provides the possibility to offer minimally invasive surgery to a larger patient population with low rates of conversions and intraoperative complications. Study II: 31 women with symptomatic, deep intramural myomas and either otherwise unexplained infertility or myomas with a possible effect on conception had a pregnancy rate following robotic myomectomy of 68%. Study III: All women (n=114) with a BMI ≥ 30 kg/m2 who underwent a simple hysterectomy by robotics or laparotomy during the study period were included. Robot-assisted laparoscopic hysterectomy in obese women was associated with shorter hospital stay, less bleeding, and fewer complications and longer operative time compared to laparotomy although the operative times for morbidly obese women were similar between robotics and laparotomy. Study IV: 122 women planned for minimally invasive hysterectomy for benign disease were randomly allocated to either robot-assisted- or traditional, minimally invasive hysterectomy in a 1:1 proportion with vaginal hysterectomy as a primary choice in the latter. From the perspective of hospital costs, robotic-assisted hysterectomy is not advantageous for treating non-complex benign conditions when a vaginal approach is feasible in a high proportion of patients. A similar hospital cost is attainable for laparoscopy and robotics when the robot is a preexisting investment. Study V: Complication rates in 949 women planned for robotic hysterectomy for malignant (75%) and benign (25%) gynecological disease over an 8-year period with special awareness of complications possibly related to robot specific risk factors. Intraoperative- and postoperative complications and complications possibly related to the robotic approach diminish with training, experience and refinement of practice. Study VI: All women (n=483) undergoing hysterectomy for benign disease during 2013 and 2014. Vaginal hysterectomy was associated with the lowest hospital cost and robotic hysterectomy with the lowest rate of perioperative complications. Procedure-specific proficiency influences outcome. Robotic hysterectomy for benign disease is clinically advantageous and economically feasible in complex cases, when performed by high volume surgeons.
  • Abaravicius, Juozas (författare)
  • Demand Side Activities for Electric Load Reduction
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The research described in this thesis, focuses on some activities on the demand side that could reduce peak load in electricity system by using consumer flexibility i.e. by increasing the demand side response to signals coming from the energy market. The major objective is to test and analyse different strategies to reduce peak load at the demand side considering their techno-economic, environmental and behavioural aspects. Both quantitative and qualitative research methods were used, including the detailed energy use data evaluation, direct and indirect load control experiments and interviews with residential and commercial consumers and utilities. One general conclusion of this research process is that there's a lack of knowledge and information on load demand variation and its consequences both on the consumer side and the utility side. New automated interval metering technologies enable 'visibility' of electricity use, however this potentially valuable information is rarely analysed and used. Modern metering and communication systems enable utilities to perform direct load control measures and to automate demand response. As the experiments with direct load control at residential consumers show, these measures could be implemented without significant comfort losses for the consumers. However, the value of this kind of demand side actions needs to be clearly expressed or quantified both for consumers and the supplier. Indirect load control with the help of various types of pricing is possible, but needs to have more significant financial motivation for the consumers than the present offers give. The results of the analysed examples of a tariff with a load demand component indicate that consumers' electrical expenses have to be more considerably reduced if they are to significantly 'improve' the consumption patterns. Utilities, for example one of those analysed in our case studies, may not assess indirect load control as a reliable resource. Therefore the integration of direct and indirect load control measures could be an attractive solution for them. Load reduction strategies at the demand side could influence the environmental performance of an energy system by decreasing emissions and preventing the distortion of territories. Nevertheless, it should be emphasized that the environmental effects depend on the prevalent generation and transmission system and could be different on different levels - regional, national and local - as the analysis example of the Swedish case, described in this thesis, shows. Load management and demand response could be considered as a socially responsible behaviour rather than only a solution to techno-economic problems of an energy market. The results of this research showed interesting examples proving that certain residential and commercial consumers are willing to participate in demand response programs from a corporate social responsibility point of view.
  • Abbas, Taimoor (författare)
  • Measurement Based Channel Characterization and Modeling for Vehicle-to-Vehicle Communications
  • 2014
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Vehicle-to-Vehicle (V2V) communication is a challenging but fast growing technology that has potential to enhance traffic safety and efficiency. It can also provide environmental benefits in terms of reduced fuel consumption. The effectiveness and reliability of these applications highly depends on the quality of the V2V communication link, which rely upon the properties of the propagation channel. Therefore, understanding the properties of the propagation channel becomes extremely important. This thesis aims to fill some gaps of knowledge in V2V channel research by addressing four different topics. The first topic is channel characterization of some important safety critical scenarios (papers I and II). Second, is the accuracy or validation study of existing channel models for these safety critical scenarios (papers III and IV). Third, is about channel modeling (paper V) and, the fourth topic is the impact of antenna placement on vehicles and the possible diversity gains. This thesis consists of an introduction and six papers: Paper I presents a double directional analysis of vehicular channels based on channel measurement data. Using SAGE, a high-resolution algorithm for parameter estimation, we estimate channel parameters to identify underlying propagation mechanisms. It is found that, single-bounce reflections from static objects are dominating propagation mechanisms in the absence of line-of-sight (LOS). Directional spread is observed to be high, which encourages the use of diversity-based methods. Paper II presents results for V2V channel characterization based on channel measurements conducted for merging lanes on highway, and four-way street intersection scenarios. It is found that the merging lane scenario has the worst propagation condition due to lack of scatterers. Signal reception is possible only with the present LOS component given that the antenna has a good gain in the direction of LOS. Thus designing an antenna that has an omni-directional gain, or using multiple antennas that radiate towards different directions become more important for such safety critical scenarios. Paper III presents the results of an accuracy study of a deterministic ray tracing channel model for vehicle-to-vehicle (V2V) communication, that is compared against channel measurement data. It is found that the results from measurement and simulation show a good agreement especially in LOS situations where as in NLOS situations the simulations are accurate as far as existing physical phenomena of wave propagation are captured by the implemented algorithm. Paper IV presents the results of a validation study of a stochastic NLOS pathloss and fading model named VirtualSource11p for V2V communication in urban street intersections. The reference model is validated with the help of independent channel measurement data. It is found that the model is flexible and fits well to most of the measurements with a few exceptions, and we propose minor modifications to the model for increased accuracy. Paper V presents a shadow fading model targeting system simulations based on channel measurements. The model parameters are extracted from measurement data, which is separated into three categories; line-of-sight (LOS), LOS obstructed by vehicles (OLOS), and LOS blocked by buildings (NLOS), with the help of video information recorded during the measurements. It is found that vehicles obstructing the LOS induce an additional attenuation in the received signal power. The results from system level vehicular ad hoc network (VANET) simulations are also presented, showing that the LOS obstruction affects the packet reception probability and this can not be ignored. Paper VI investigates the impact of antenna placement based on channel measurements performed with four omni-directional antennas mounted on the roof, bumper, windscreen and left-side mirror of the transmitter and receiver cars. We use diversity combining methods to evaluate the performance differences for all possible single-input single-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) link combinations. This investigation suggests that a pair of antennas with complementary properties, e.g., a roof mounted antenna together with a bumper antenna is a good solution for obtaining the best reception performance, in most of the propagation environments. In summary, this thesis describes the channel behavior for safety-critical scenarios by statistical means and models it so that the system performance can be assessed in a realistic manner. In addition to that the influence of different antenna arrangements has also been studied to exploit the spatial diversity and to mitigate the shadowing effects. The presented work can thus enable more efficient design of future V2V communication systems.
  • Abbasi, Maisam (författare)
  • Exploring Themes and Challenges in Developing Sustainable Supply Chains - A Complexity Theory Perspective
  • 2014
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Popular Abstract in English If you wonder about the journey of goods and services before they reach you and the effects that journey has on the natural environment and the society, this dissertation is for you. In order to deliver goods and services from raw materials to you, the customer/consumer, several organizations and individuals interact with each other. They source the materials, manufacture or produce the products, pack and handle them, transport and distribute them, and ultimately sell them. These interactions and activities make up the supply chain (SC). Supply chain management (SCM) involves the management and integration of these interactions and activities. Numerous evidence-based studies show that SCM can increase your satisfaction as a customer and consumer, meet your demands, and reduce costs and conflicts for the organizations, businesses and individuals involved. Businesses are beginning to realize that SCs have several negative effects on their surrounding natural environment and societies that should be minimized. Examples of these are that SCs are still dependent on fossil fuels and nonrenewable natural resources. They give rise to atmospheric, land, water, noise, air pollution; lead to waste, congestion, injuries, and accidents; produce/manufacture and trade goods and services according to unethical laws and standards; and abuse human as well as employees’ rights. If remedies for mitigating the negative effects are not found soon, the costs will be too high for future generations to cope with the effects. It might also be too late for them to find and implement long-term solutions to keep our planet a sustainable place to live and our businesses sustainable to operate. The purpose of this research was to explore themes (topics, activities) in developing sustainable SCs so that the negative effects can be minimized. It also explored challenges (difficulties, obstacles, or dilemmas) that can hinder sustainable development of SCs. In-depth studies of logistical services and activities were carried out because they have not been well examined with a sustainability lens. The results revealed a pattern of themes in developing sustainable SCs. The first theme originated from the direct characteristics of sustainable goods and services. Goods and services can be sustainable if they are effective and efficient with minimized pollution, if they are sourced from renewable raw materials and natural resources, and are recyclable, safe, healthy, secure, and transparently traceable. This means that appropriate steps should be taken to generate goods and services sustainably so that all sorts of waste, emissions, toxicants, noise and air pollution are minimized. The second theme was related to sustainability in the resources necessary for generating goods and services, including the physical, financial, human, and intangible ones. Among the aspects discussed are: effectiveness and efficiency (appropriate resources, rightly utilized) with minimized pollution; recyclability; safety; security; respecting the rights of employees; developing a learning context; exploring and exploiting innovation; fostering diversity; employee development; protecting trust, brand, and reputation; maintaining and continuing business relationships; dealing with risks; as well as resistance and resilience. Sustainability does not emerge in just the goods, services, and resources of SCs, though. The third theme sheds light on inter-processes and interrelationships in sustainable SCs including the flows of goods and services from suppliers to consumers and vice versa that should be integrated. All the businesses involved should take and share responsibilities in following the ethical norms and minimum standards and requirements. They should also be responsible and collaborative in their relationships with others. Businesses also have responsibilities in developing their societies such as social investment, supporting public services, and vi philanthropy. Finally, the fourth theme underlined managerial and governmental activities in developing SCs. The results also revealed the pattern of the challenges in developing sustainable SCs. The first challenge was to shift the values in the supply chains in a way that the two non-economic pillars of sustainable development (environmental and social friendliness) are equally weighted with the economic pillar. This can hinder sustainable development of SCs when short-term costs are in focus or when customers prioritize financial criteria such as delivery time, price, functionality, and service-rate ahead of environmental and social criteria such as recyclability, emissions, and working conditions or rights of employees. The second challenge was related to the difficulties of operationalization due to asymmetric knowledge in the interpretation of criteria for sustainable development in different parts of SCs; difficulties in changing the resistant, reluctant, disregarding, or short-term mind-sets and behaviors; and uncertainties about short- and long-term changes that might affect SCs. The third challenge was dealing with the increasing complexity associated with the sustainable development of SCs. The first dimension that contributes to this complexity is the difficulty in evaluating SC sustainability. This is due to the subjectivity in defining the changing SC boundaries, the organizations and individuals involved, as well as the multiple ways that SC activities affect or are affected by their surrounding societies and environments. The second dimension relates to leakage/spillovers in open SCs because of the shift of emissions from one sector to another (from transport to production of electricity, for example) or from one country to another. Leakage may also occur when a stakeholder evades its responsibilities or externalizes its social and environmental degradation costs by transferring to or sourcing from places or stakeholders with looser regulations and standards. The third dimension involves several trade-offs that exist in the sustainable development of SCs, where making one part sustainable leads to unsustainability in another. There are also several conflicts of a paradoxical character that simultaneously exist in the managing and governing of sustainable SCs. The fourth challenge was related to the difficulties in corporate governance of sustainable SCs due to the large scale of interactions and activities. There are several contexts where supply chains operate, ranging from local to urban areas, regions, and different countries. Different rules, laws, standards, certificates, labels, norms, bureaucracies, and administration processes exist. There is considerable heterogeneity regarding sustainability practices between and within industries, and a reluctance of businesses to accept legislation or to participate in initiatives. There are also concerns over transparency, accountability, and the credibility of standards, norms, and third party or external auditors and certifiers. Finally, the fifth challenge was related to the difficulties of small and medium sized enterprises, as they may be uncertain about the benefits of upgrading to new sustainability standards and codes of conduct. They may also lack the knowledge, skills, time, money and human resources to respond to the social and environmental requirements of global buyers and SCs. The conclusion is that taking a complexity theory perspective (CTP) on sustainable SCs is beneficial to better understand, manage, and govern gradual and radical changes in them. A CTP takes into account changes in the themes and challenges and is helpful in dealings with the challenges, such as changing customers’ priorities; changing short-term mind-sets and behaviors; uncertainties; subjectivity in embodying SCs; dealing with leakage/spillovers, trade-offs, and paradoxes; and heterogeneity regarding sustainability practices between and within industries.
  • Abbott, Jessica (författare)
  • Ontogeny and Population Biology of a Sex-Limited Colour Polymorphism
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Popular Abstract in Swedish Hur man undviker att bli trakasserad på flicksländornas vis Tidigare forskningsresultat har visat att hos honor i de flesta djurarter begränsas fortplantningkapacitet av hur mycket tid och energi de kan lägga på sina avkommor. Hos hanar, å andra sidan, begränsas fortplantningskapacitet av hur många honor de kan para sig med. Då kan man dra slutsatsen att hanar ska försöka para sig så ofta som möjligt med så många honor som möjligt. Honor, däremot, ska enbart para sig när de behöver befruktas. Eftersom honor behöver förmodligen befruktas ganska sällan jämfört med hanars parningskapacitet leder det till en konflikt mellan könen över hur ofta parning sker. Honor kan därför bli ?trakasserade? av hanar i ett försök att få dem att gå med på parning, och att stå emot dessa trakasserier kan utgöra en betydande kostand i tid och energi för honorna. Så hur kan honorna undvika trakasserier och deras medföljande kostnader? Ett sätt är att förklä sig som en hane så att man inte känns igen som en hona. Ett annat är att honorna kan finnas i olika varianter, eller morfer, så att hanarna har svårt att sikta in sig på en enda variant. Eller varför inte göra både och? Det verkar som honorna av flicksländearten Ischnura elegans (mångfärgad flickslända) har tagit det sista alternativet. I. elegans är Sveriges minsta flickslända, och honorna finns i tre olika färgvarianter som kallas för morfer. Morferna heter Androkrom, Infuscans, och Infuscans-obsoleta, och Androkromerna verkar efterlikna hanarna eftersom de har samma färg som hanarna (hanarna har inga morfer). I min avhandling har jag observerat flera olika populationer av I. elegans runt om i Skåne, och tittat på hur morffrekvenser har ändrats med tiden, hur kroppsstorlek och kroppsform skiljer sig mellan könen och mellan morfer, skillnader i tillväxttid och tillväxthastiget, skillnader i äggläggningsförmåga mellan morfer, och genetisk differentiering mellan populationer. Det visade sig att Androkromerna hade minskat i frekvens över 4 år medan Infuscans ökade i frekvens, men förändringsmönstret skiljde sig mellan gamla och nya populationer. Hanar och honor hade olika kroppsstorlek och kroppsform, och Androkroma honor hade mest hanlik kroppsform av alla morfer. Det stämmer bra överens med hypotensen att Androkromer efterliknar hanar för att slippa bli trakasserade. Skillnader i laboratoriet i tillväxttid och tillväxthastighet samspelar för att öka storleksskillnaden mellan könen, men för morferna tar skillnader i tillväxttid och tillväxthastighet ut varandra så att morferna är lika stora som vuxna. Infuscans honor hade störst äggläggningsföråga men äggläggningsförmågan minskade med ökat frekvens för alla morfer, och en datamodell fick fram samma resultat. Genetiska data visar att detta system är väldigt dynamisk, och befinner sig inte i jämvikt. Vindriktning kan ha en viktig effekt på genetiska skillnader mellan populationer genom dess påverkan på flicksländornas sprindning. Dessa resultat tyder på att det finns negativ frekvens-beroende selektion i detta system. Negativ frekvens-beroende selektion är när en variant klara sig bäst när den är ovanlig i populationen, och kan till exempel hända när en predator utvecklar en sökbild av den vanligaste bytesvariant. Men hos I. elegans är det förmodligen hanarnas sökbild för den vanligaste honmorf som leder till negativ frekvens-beroende selektion. Eftersom morferna skiljer sig på så många sätt kan de betraktas som alternativa strategier, med en morf (Androkrom) som unviker trakasserier genom att efterlikna hanar, och en morf (Infuscans-obsoleta) som undviker trakasserier genom att skilja sig så mycket från de övriga honorna att den är kanske svårt att kanna igen som samma art.
  • Abdalkhalik, Mostafa (författare)
  • Oligomerization of human and bacterial frataxin : Structural and functional studies
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Iron is a one of the critical elements in our life, being the most common element on earth, forming most of the inner and outer earth’s core. In our bodies iron is required in small amounts for biological processes to be performed. It is recommended to eat food containing iron to avoid common health problems such as anemia. A slight increase or decrease in iron levels above or below normal in living cells leads to various health problems. Iron can also be highly toxic if it is accumulated in cells in a free form. As such it may easily interact with different cellular components, including proteins and DNA. Iron accumulation may occur in our bodies if iron is not properly treated physiologically. It may lead to many disorders and diseases such as thalassemia, Parkinson’s disease, and Friedreich’s ataxia (FRDA). FRDA is a hereditary neurodegenerative disease that causes progressive damage to the nervous system. Many symptoms and problems were observed for FRDA patients, such as heart problems, skeletal deformation, speech problems, diabetes and sensory loss. No cure is known for FRDA till now. The cause of FRDA is linked to deficiency in FRDA patients of a protein called frataxin. This protein is found inside the mitochondria (the factories of energy our body uses). When frataxin is present in our cells at lower levels than normal, increase of iron levels takes place. This increase leads to the formation of highly toxic molecules called radicals. These radicals may destroy mitochondrial DNA and proteins. The disturbance in the balance of iron within the cells when frataxin is present at low levels is related to frataxin function. Frataxin is responsible for iron delivery to other proteins within the mitochondria. Frataxin has been suggested to be involved in iron storage by forming large complex within which iron is stored. These complexes of different sizes are called oligomers, which are built up by varied number of frataxin monomers. Therefore, low levels of frataxin in FRDA patients lead to imbalance of iron within cells. Two things happen when frataxin levels are low; first, the binding and transporting of iron to its target proteins will decrease. Second, the cell will translate this as an iron deficiency and will import more iron to the mitochondria. This will result in iron accumulation. This iron accumulation inside the mitochondria will increase the free iron content, leading to the formation of toxic radicals. If the mitochondria cannot deal with these radicals, the cell will die.Towards finding a cure for FRDA, we need to have a clear picture of the exact role of frataxin. A main problem is that the full structures of frataxin oligomers are still unknown. Since protein function is always related to its structure, without clear knowledge of the structure of different oligomers it would be difficult to understand the exact role of frataxin. Since frataxin from different organisms has similar structures, in this work we compare oligomerization of frataxin from human and Escherichia coli. Different experiments have been performed to characterize these two proteins in absence and presence of iron, to try to understand how those oligomers are formed and to describe the structures of the oligomers. Iron chelators have been suggested for use as drugs for decreasing the symptoms of FRDA. These molecules have the ability to bind iron with strong affinity. They are introduced into the body to bind excess iron and to reduce the severe symptoms associated with iron accumulation. The effect of these chelators on frataxin oligomers was also studied during this work trying to understand how they work in vivo. We have found that the increase of iron concentration increases the formation of human and bacterial frataxin oligomers. Some oligomers were formed of two, three or four frataxin monomers. Higher oligomers could be observed but their order and percentage could not be determined. The structure of dimeric bacterial frataxin was determined. The iron chelators showed an opposite effect on both human and bacterial frataxin. For human frataxin they help in the building up of larger oligomers, while in bacterial frataxin they dissociate large oligomers into smaller ones. The stability of these oligomers was found to be low in general suggesting that they are formed in the cells for temporary functions then dissociate to single units to perform their main function in delivering iron to other proteins.The effect of these iron chelators, which are used in chelation therapy, needs further studies. Even other chelators need to be studied in the future. We believe that having a clear picture of how these chelators work will help to identify more suitable drugs for patients suffering from FRDA.
  • Abdelhady, Dalia (författare)
  • Immigrant identities, communities and forms of cultural expression : The Lebanese diaspora in New York, Montreal, and Paris
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This dissertation draws on postcolonial understandings in order to offer a sociological analysis of Lebanese immigrants in Montreal, New York City and Paris. I argue that the concept of diaspora provides a framework for understanding Lebanese immigrant experiences, as some immigrants may undergo a process of assimilation while others continue to hold on to their ethnic identities. Proposing that “diaspora” is a more comprehensive framework for understanding migration and incorporation, this dissertation provides an understanding of international immigration that transcends traditional analyses of population movements. Traditionally, globalization and immigration have been understood as resulting in either the homogenization (or assimilation) or localization of communities, identities, and cultures. Instead of focusing on one aspect of globalization, this project investigates the contradictory elements of immigrant identities and communities by highlighting their diasporic features. Diaspora refers to the multiple loyalties that migrants have to places and societies: their connections to the space they currently occupy, or host country; their continuing involvement with the homeland; and their involvement with the larger diaspora community. These multiple loyalties allow for the flourishing of communal life, and the increasing involvement with global issues and cosmopolitan identification. Thus, the framework of diaspora promises significant contributions to the understanding of the complex dynamics involved in migration and globalization. Utilizing in-depth interviews with seventy-seven first-generation Lebanese immigrants in Montreal, New York City and Paris, the analysis explores three main areas of inquiry: (1) the manner in which members of diasporic communities make sense of their identities; (2) the types of networks and alliances that structure diaspora communities; and (3) the kinds of cultural expression members of these communities generate. As three manifestations of diasporic experiences, immigrants’ forms of identification, community attachments and cultural expression point to the ways Lebanese immigrants are moving beyond nationality, ethnicity and religion and giving rise to cosmopolitan solidarities and forms of identification.
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