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:

May 2018


"Bacteria can break down pesticides"

Illustration: Mathilde Jørgensen 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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