Extracts from recent PhD theses

At DTU you can get a research education equal to the world’s very best in fields such as mathematics, physics, informatics, chemistry, biotechnology, chemical and biochemical engineering, electrical engineering, communications technology, space science, mechanical engineering, nanotechnology, energy, civil engineering, transport, environmental engineering, food science, veterinary science, and life science.

Below are extract from a selection of recent PhD theses:

Oktober 2018


"Satellite monitoring of water reservoirs"

Illustration: Liguang JiangSurface water is an important global resource, but reservoir water levels can often be difficult to monitor  - e.g. in remote regions. Here, satellite monitoring provides a  viable solution. Thanks to its orbit around the Earth, the ESA CryoSat-2 mission is able to monitor a very high number of water bodies. Liguang Jiang from DTU Environment used six years of data from CryoSat-2 to investigate more than 1,000 Chinese Lakes and reservoirs. 

The dynamics of these water bodies varies according to region. Lakes in the Northern Tibetan Plateau are rising - e.g. noticeably in populated areas presumably due to human intervention. The satellite has also managed to map the surface of six rivers over long distances. The results for Songhua River in Northeast China were compared with data from a modelling which showed a strong correlation between simulated and measured river levels.

The assumption, therefore, is that measurements of surface water with modelling can be used to project the risk of flooding - crucial for poorly studied rivers.

Illustration: Liguang Jiang



"Better CT scan models"

Photo: ColourboxX-ray computed tomography - better known as CT scanning - has become an indispensable technology  with many applications ranging from medical imaging to materials science. In some applications, high-quality CT images are crucial in order to avoid misinterpretations or false conclusions. For example, it can be difficult for a doctor to make a correct diagnosis on the basis of a CT image polluted by noise and artefacts (man-made phenomena, ed.). And within the field of materials science, serious artefacts can be confused with cracks in an object - or vice versa.

Hari Om Aggrawal from DTU Compute has studied the factors affecting the quality of CT images and has - among other things, devised a new mathematical model that can reduce certain types of noise. He has also developed a model that can better accommodate movement from e.g. a beating heart - or a pill that has been dissolved.

The models can lead to significant improvements in picture quality and pave the way for improved methods that can help researchers to study dynamic processes using a CT scan.



"Modelling of cities’ future energy consumption"

Photo: ColourboxModern cities account for the majority of the world’s energy consumption, and as cities generally continue to grow, energy systems must undergo radical change in order to be sustainable. Using, among other things, nine case studies, Dominik F. Dominkovic from DTU Energy has focused on the roles that can be taken by different technologies in the urban energy mix of the future - and on different technologies that can increase energy system flexibility.

Among other things, he found that 72 per cent of the demand in the transport sector could be electrified immediately using available technology. In addition, both district heating and cooling can exploit thermal energy storage, which is much cheaper than storage in batteries.

Finally, he concluded that air pollution increased significantly through the use of biomass despite a reduction in CO2 emissions. Including air pollution - rather than simply focusing on CO2 emissions - is therefore an important part of future modelling of urban energy systems.

Illustration: COLOURBOX



August 2018


"MRSA infections in almost every pig herd and about every third mink farm tested"


Mink The rising incidence of MRSA multidrug-resistant bacteria has received considerable attention in recent years, particularly due to an increase in the number of people carrying the bacteria.

MRSA is primarily associated with pig herds, but Julie Elvekjær Hansen from DTU Vet shows in her thesis that new reservoirs of MRSA have arisen, and these have most likely arisen as a result of carry-over from pigs via routes which are still relatively unknown. These include dairy cow and veal calf herds (in which the number of carriers is low, however), while 33 per cent of the screened mink farms tested positive for MRSA.

An increasing number of people in contact with mink have also tested positive for MRSA since 2011. This is a worrying trend, as the emergence of new reservoirs increases the number of people who are exposed to the bacteria and in danger of getting an infection or unintentionally adding to the spread of the bacteria in society.

The thesis emphasizes the importance of lowering the levels of MRSA in pig production and illustrates that it is vitally important to identify potential new MRSA reservoirs and continue to screen MRSA-positive herds with low incidence.



"New radioactive sources to fight cancer"

Cancer - colourbox

A challenge in cancer treatment is that a high percentage of patients find that their cancer or metastases return, even though the treatment had a positive effect. Effective and safe treatments are therefore needed which improve the therapeutic effect and minimize side effects on healthy tissue.

Radiation is one of the most effective treatments for cancer. This includes brachytherapy, where the radioactive source is inserted into the tumour tissue - a very successful form of treatment. But even state-of-the-art brachytherapy depends on solid physical sources and design principles that were developed over 50 years ago.

In collaboration with DTU Nutech and DTU Nanotech, Gocke Engudar from DTU Chemistry has developed new brachytherapy sources which are biocompatible and biodegradable, and distribute the therapeutic dose uniformly in the tumour tissue. The new radioactive sources are showing potential for improving the effectiveness of brachytherapy.



"Genomic diversity in Aspergillus fungi"

Thorkild Amdi Christensen vandkandeskimmel

Aspergillus is a genus of mould which is very commonly found, for example as black mould on onions. Some species can make us ill, even very ill. Others are used in enzyme and chemical production and in the food industry. These differences within the same genus are extraordinary, and identification of the genes behind the diversity is therefore of great significance to both the industrial and academic world.

The genomic era for moulds actually began in 2005 with the sequencing of three Aspergillus species. Jane Lind Nybo Rasmussen has now sequenced and developed bioinformatics tools to compare the 350 Aspergillus species. She has also helped to release and analyse more than 40 genomes in cooperation with the Aspergillus whole genus sequencing project.

Within a few years the project will have published all known Aspergillus genomes, giving researchers and industry a resource which permits research at a level not previously possible in fungi.

Photo: Thorkild Amdi Christensen



June 2018


"Surface scanning of breast cancer patients can improve radiation treatment"

Patients with breast cancer are often treated with radiotherapy where it is important that the patient lies in the same position for each treatment. Susanne Nørring Bekke from DTU Nutech  has therefore developed a system that can optically scan the surface of the  patient’s skin and automatically (and in real time) make small adjustments to the patient’s position. The system can also detect breathing movements which are necessary in some treatments where the patient needs to hold their breath.

Two different patient studies showed that the surface scanning system can improve radiotherapy for breast cancer patients.
However, the studies also showed that the patient set-up cannot be based on the surface scanning system alone, and thus X-ray-imaging will continue to be an essential part of the clinical workflow.

Photo: Colourbox


"Gel therapy offers targeted and less toxic cancer treatment"

Globally, cancer is the leading cause of death after heart disease. Current cancer treatments are often based on an approach where several therapeutic agents or therapies are combined. However, it is difficult to target the treatment so that it is active in the tumours, and in most cases it unfortunately results in poisoning of the patient. 

Trine Bjørnbo Larsen from DTU Nanotech has therefore developed a gel therapy — a jelly containing drugs — that can be injected directly into the tumour tissue to release the active ingredients. This increases the concentration of drug in the tumour, which is much less toxic to the patient, as fewer healthy areas are affected by the drugs.

Alone and in combination with radiation therapy, preclinical trials of gel therapy with both chemo and immune therapeutic agents showed that it was superior to current treatment methods. This suggests that gel technology has the potential to become an essential part of future cancer treatment.

Photo: Jesper Scheel



"Cheaper maintenance of offshore wind turbines"

Welds in constructions at sea — e.g. offshore wind turbines — are subject to strong loads and corrosion, which can result in structural faults. The structures must therefore be regularly inspected and if necessary repaired. However, this is a costly business: frequent inspections in the service life of a wind turbine will result in high maintenance costs. On the other hand, a lack of inspection may result in the risk of high costs should the construction fail.

Gustavo-Adolfo Ruiz-Muñoz from DTU wind Energy has therefore developed techniques based on, among other things, how cracks are propagated in wind turbines, to identify the optimal inspection interval for a welded component. The techniques can be helpful in developing  cost-effective solutions for maintaining offshore constructions.

Photo: Colourbox


May 2018


"Bacteria can break down pesticides"

Illustration: Mathilde Jøgensen Hedegaard

Waterworks use sand filters to remove particles and undesirable substances such as ammonium from the water. These sand filters may also be able to remove pesticides. Mathilde Jørgensen Hedegaard from DTU Environment has investigated which biological processes in sand filters control pesticide degradation and how these can be used to treat polluted groundwater. She has shown that naturally occurring methane-oxidizing bacteria can break down e.g. the herbicide Bentazone—one of the most commonly found pesticides at Danish water plants.

Bentazone is therefore biodegradable, especially in filter sand from waterworks treating groundwater with high methane concentrations. This process is probably already underway at these water plants, but at waterworks without methane in the groundwater it may be possible to stimulate the growth of methane-oxidizing bacteria to increase Bentazone degradation.

The ability to remove pesticides using biological sand filters, for example, is of great commercial interest, as it offers simple, sustainable water treatment.

Illustration: Mathilde Jørgensen Hedegaard


"Small measurements give bigger blades"


Illustration: Monica Jane Emerson

The longer the wings of a wind turbine, the more energy they can produce. However, longer blades mean that the materials must be able to withstand higher stress loads. It is therefore important to know the mechanical properties, which to a large extent depend on the internal structure of the material all the way down to the micro- and nanoscale.

Using X-ray computed tomography (CT), it is possible to observe microstructures in fibre composites and determine how they adapt under stress. Monica Jane Emerson from DTU Compute has demonstrated that when X-ray CT is combined with the automatic image analysis she has developed, it is possible to measure the fibre geometry automatically and in a very high resolution.

For example, she was able to precisely monitor how each fibre flexes under stress and discovered that fibres already start bending at relatively low stress loads—and in a similar direction to the resulting fault. In other words, using this method it is possible to predict with great precision the mechanisms that cause damage to the turbine blade.

Illustration: Monica Jane Emerson


"Promising design advances in thermal systems" 

Illustration: Jan Hendrik Klaas Haertel

Thermal systems such as heating elements and heat exchangers are used in various technical systems to transfer heat—from power stations and cars—to laptops and smartphones. Designing them is a complex task which is highly dependent on the engineer’s knowledge—and experiments.

However, using topology optimization—a mathematical method for calculating the optimal material consumption in a structure—it is possible to automate and optimize the shape of the thermal systems. 

Jan Hendrik Klaas Haertel from DTU Energy has, among other things, applied topology optimization to design refrigeration structures that can cool computer processors, and shown that these structures provide better cooling performance than even ultramodern conventional refrigeration appliances. With the help of a 3D printer, he has used metal casting, among other things, to show that topology optimization is ideal for exploiting the flexibility offered by 3D print technology.

Illustration: Jan Hendrik Klaas Haertel




"Buildings bound together stronger"

Photo: Jesper Harrild SørensenIn Denmark, new buildings are often composed of precast concrete elements. The immediate advantage is that the building can be erected faster. The precast concrete elements are bound together by cast-in-situ joints, ensuring structural context and overall stability. However, large loads in multi-storey or unconventionally designed buildings, for example, pose a challenge to the traditional joint system—both in terms of strength and deformation capacity.

In his thesis, Jesper Harrild Sørensen from DTU Civil Engineering www.byg.dtu.dk/english has examined a new design of shear connectors between the wall elements which have been developed and tested. His findings revealed huge potential, as the new connectors offer greater strength per assembly and, in particular, greater overall stability. An improvement of current best practice can lead to better and more economic design.

Photo: Jesper Harrild Sørensen

"Less noise for the hearing impaired"

Photo: ColourboxFor many people—especially those with hearing aids or cochlear implants—understanding speech in noisy surroundings can be a real challenge. Researchers are therefore working to develop noise-reduction strategies that can improve speech understanding in these devices. The effectiveness of these strategies is dependent on how well the speech and noise characteristics are known.

To achieve this, automatic methods for separating speech from ambient noise as precisely as possible are therefore required. These methods often use sophisticated software to calculate a time-frequency mask containing speech information.

In his thesis, Thomas Bentsen from DTU Electrical Engineering www.elektro.dtu.dk/english has investigated three of these methods and evaluated them with a view to improving, in particular, speech intelligibility for hearing aid and cochlear implant users in noisy environments.

Photo: Colourbox

"Alternative energy via cells"

Photo: ColourboxSociety’s strong dependency on fossil fuels and their impact on the environment is driving researchers to find sustainable alternatives. One of the alternatives may very well be microorganisms when they are converted into so-called microbial cell factories. Instead of crude oil, for example, cell factories use renewable resources or waste to generate energy.

The challenge, however, is that the formation of new cell factories causes congestion in protein production.
With her thesis, Maja Simone Rennig from DTU Biosustain www.biosustain.dtu.dk/english is contributing towards a basic knowledge of protein biosynthesis.

Photo: Colourbox



"Brain essential for obesity treatment"

Photo: Colourbox The mean body mass index (BMI) is steadily increasing all over the world—in the USA, obesity affected more than 35 per cent of the population in 2009 to 2010. Obesity is a major health problem, as it often involves consequential illnesses. The brain, which is crucial for appetite regulation and body weight, is therefore an important organ when it comes to developing treatment options. But brain access for medicine is limited by the blood-brain barrier—just as a better understanding of how drugs enter the brain is needed.
Casper Jensen from DTU Compute has developed algorithms that can automatically quantify microscope images of the brain and provide valuable data on brain access, mapping of receptors, and brain activity. The analysis tools were used to study the peptides that affect appetite regulation, and it was found that peptides injected under the skin were able to gain access to the brain and be active in brain groups related to decreased food consumption. Together with future experiments, these findings may provide new knowledge about how to improve the treatment of people suffering from obesity.

Illustration: Colourbox

"Live 3D degradation of fuel cells"

Illustration: Salvatore Angelis Solid Oxide Fuel Cells (SOC) can play a key role in an energy system based on renewable energy, as they can effectively convert chemical energy into electrical energy. However, they have a limited lifetime, as they are degraded by changes in the microstructures. In order to understand the complex phenomena in the cell, it is crucial to be able to track this development during operation.
With the help of X-rays, Salvatore Angelis from DTU Energy has investigated these changes in 3D high resolution, enabling him to see phenomena approximately 800 times smaller than a human hair. By means of ptychographic tomography, he has observed the effect of—among other things—oxidation and how nickel particles in the cell become coarser over time. The time-consuming technique, however, cannot follow the entire oxidation process, for example. He has therefore turned to X-ray holotomography, which in exchange for a few minutes’ lower resolution can create 3D images of the missing steps. Among other things, the experiments enabled him for the first time to follow the oxidation of nickel particles live in 3D—something which increases our understanding of the degrading of SOCs.

Illustration: Salvatore Angelis

"Antimicrobial agents alone cannot explain resistance in Danish pigs"

Photo: Colourbox As part of a larger project aimed at providing new knowledge about antimicrobial resistance in Danish pig herds, Anna Camilla Birkegård from DTU Vet has used a cross-sectional study of collected samples from 681 Danish pig herds. Five pigs were tested from each herd and examined for seven genes for antimicrobial resistance. Among other things, she investigated whether the herd’s geographical location and the pigs’ lifetime exposure to antimicrobial agents affected antimicrobial resistance levels in the herds.
The geographical location had a limited impact on the levels of antimicrobial resistance, while lifetime exposure to antimicrobial agents had a clear effect on these levels. However, antibiotic consumption can only explain up to approximately 40 per cent of the variation in the resistance level—so it is clear that other—as yet unknown—factors are involved.

Photo: Colourbox


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