The problem of motion detection has received considerable attention due to the explosive growth of its applications in video analysis and surveillance systems. While the previous approaches can... Show moreThe problem of motion detection has received considerable attention due to the explosive growth of its applications in video analysis and surveillance systems. While the previous approaches can produce good results, the accurate detection of motion remains a challenging task due to the difficulties raised by illumination variations, occlusion, camouflage, sudden motions appearing in burst, dynamic texture, and environmental changes such as weather conditions, sunlight changes during a day, and so on. In this paper, a novel per-pixel motion descriptor is proposed for motion detection in video sequences which outperforms the current methods in the literature particularly in severe scenarios. The proposed descriptor is based on two complementary three-dimensional discrete wavelet transforms (3D-DWT) and a 3D wavelet leader. In this approach, a feature vector is extracted for each pixel by applying a novel 3D wavelet-based motion descriptor. Then, the extracted features are clustered by the well-known K-means algorithm. The experimental results demonstrate the effectiveness of the proposed method compared to the state-of-the-art approaches in several public benchmark datasets. The application of the proposed method and additional experimental results for several challenging datasets are available online. Show less
The space between stars is filled with a dilute mixture of atoms, molecules, and dust grains, which we call the interstellar medium (ISM). The physics of the ISM is a crucial part in many areas of... Show moreThe space between stars is filled with a dilute mixture of atoms, molecules, and dust grains, which we call the interstellar medium (ISM). The physics of the ISM is a crucial part in many areas of astronomy, such as the formation and evolution of stars and entire galaxies. It regulates molecule- and dust grain synthesis, which together constitute the very building blocks of planetesimals required to form planetary systems and, ultimately, life itself. Recent observations have revealed that a significant fraction of the ISM is dynamic and filamentary, likely caused by radiation, winds, and supernova explosions from massive stars that constantly stir the material that resides in the ISM. However, the exact mechanisms and contributions of these interactions remain poorly understood. To advance our knowledge of the ISM of galaxies, in first principle, we need to acquire a deep understanding of the interplay between stars and their surroundings. In this thesis, I investigate the interactions between gas, dust, and stars in the ISM, by using the Orion region as a benchmark model. Show less
This thesis is concerned with the transfer of energy from light to matter. Over a century ago it was established that light consists of packets of energy [1], now known as photons. Not much later... Show moreThis thesis is concerned with the transfer of energy from light to matter. Over a century ago it was established that light consists of packets of energy [1], now known as photons. Not much later the energy levels of matter at the atomic scale were found to be discrete [2]. These phenomena required a new physical description that has become the theory of quantum mechanics [3]. Now, this theory of light and matter could contribute to tackling a fundamental socioeconomic and technological challenge: To find a sustainable supply of useful energy that is cheap, abundant and generated on-the-spot Show less
The first massive elliptical galaxies were already in place when the Universe was only 3 billions years old. Surprisingly, they are more compact in comparison to their present-day counterparts. In... Show moreThe first massive elliptical galaxies were already in place when the Universe was only 3 billions years old. Surprisingly, they are more compact in comparison to their present-day counterparts. In this thesis these recent findings are assessed by measuring the stellar kinematics of massive z=2 galaxies from spectra obtained with X-Shooter on the Very Large Telescope. This thesis work shows that high-redshift galaxies are truly very massive and structurally very different from present-day galaxies, yet they follow the same scaling relations. Show less
SUMOylation is a reversible lysine post-translational modification critical for eukaryotic life, and involved in many diseases such as cancer. This thesis describes five years of research into... Show moreSUMOylation is a reversible lysine post-translational modification critical for eukaryotic life, and involved in many diseases such as cancer. This thesis describes five years of research into SUMOylation using cutting edge high-resolution mass spectrometry, at the system-wide level and in an unbiased manner. Various novel and highly efficient methods for purifying SUMOylation from complex samples are described, and validated through mass spectrometry. Overall, we report an unprecedented number of SUMOylation sites, shed light on the dynamic nature of SUMOylation in response to various cellular treatments and stress conditions, and provide an unsurpassed level of depth through extensive bio-informatics analysis. Show less
Imaging subsurface structures with nanometer resolution has been a long-standing desire in science and industry. To obtain subsurface information one usually applies ultrasound, like e.g. in... Show moreImaging subsurface structures with nanometer resolution has been a long-standing desire in science and industry. To obtain subsurface information one usually applies ultrasound, like e.g. in echocardiography. Implementing ultrasound in an Atomic Force Microscope, a setup that is capable of imaging surfaces with atomic resolution, gives access to additional information. In particular, it is possible to image subsurface structures with nanometer resolution. However, it is not known why the subsurface structures become visible when applying ultrasound during the imaging with an Atomic Force Microscope. Based on a special excitation scheme, which makes use of two ultrasound excitations (one through the sample and one through the cantilever), Heterodyne Force Microscopy seems to be the most promising candidate for imaging deeply buried objects or structures with nanometer resolution. This thesis focuses on the poorly understood elements in Heterodyne Force Microscopy. We studied the ultrasound propagation in the sample, the dynamics of an ultrasonically excited cantilever near a sample that is also vibrating at a slightly diff erent frequency, and the generation of the heterodyne signal. The insight we gained in these matters allowed us to determine the contrast mechanism in a very well-de fined model sample, which contains gold nanoparticles buried in a soft polymer matrix. We show that the contrast in this system is determined by “friction at shaking nanoparticles”. Show less
What is the catalytic role played by titanium in the hydrogen storage material NaAlH4? This thesis aims at unraveling the dynamics of an elementary reaction: H2 dissociation on Ti/Al(100) surfaces.... Show moreWhat is the catalytic role played by titanium in the hydrogen storage material NaAlH4? This thesis aims at unraveling the dynamics of an elementary reaction: H2 dissociation on Ti/Al(100) surfaces. Although this reaction is not the rate limiting step in the hydrogen storage of NaAlH4, it is an important reaction to produce atomic hydrogen for the other reaction steps. To achieve the stated goal, we test a large set of possible slab models to represent the Ti/Al(100) surface. After considering the stability of the slab model itself and the barrier height for H2 dissociation, we carefully select two possible slab models: (1) the 1/2 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface with Ti atoms in the second layer, (2) the 1 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface with Ti atoms in the first and third layers. Using these two slab models, potential energy surfaces (PES) are calculated. The H2 dissociation probabilities and rate constants are then calculated. The results suggest that the 1 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface may be the most realistic model for H2 dissociation on Ti/Al(100) surfaces relevant for the hydrogen storage material NaAlH4. In this thesis, time-dependent wave packet, quasi-classical and classical dynamics, and transition state theory have been imployed to calculate the micro-canonical reaction probabilities and canonical reaction rate constants. Show less
In eukaryotic cells, genomic DNA is organized in chromatin fibers composed of nucleosomes as structural units. A nucleosome contains 1.7 turns of DNA wrapped around a histone octamer and is... Show moreIn eukaryotic cells, genomic DNA is organized in chromatin fibers composed of nucleosomes as structural units. A nucleosome contains 1.7 turns of DNA wrapped around a histone octamer and is connected to the adjacent nucleosomes with linker DNA. The folding of chromatin fibers effectively increases the compaction of genomic DNA, but it remains accessible for enzymatic reactions. This apparent paradox motivates a detailed study of the dynamics of chromatin. A structural model at the molecular level will shed light on how cells regulate the compaction and dynamics of genomic DNA. This thesis presents the results of an experimental study on the dynamics of chromatin higher-order folding. Using magnetic tweezers, we observed force-dependent structural changes within chromatin fibers at the single nucleosome level. Show less
Recent studies have provided experimental evidence for the existence of an encounter complex, a transient intermediate in the formation of protein complexes. We have used paramagnetic relaxation... Show moreRecent studies have provided experimental evidence for the existence of an encounter complex, a transient intermediate in the formation of protein complexes. We have used paramagnetic relaxation enhancement NMR spectroscopy in combination with Monte Carlo simulations to characterize and visualize the ensemble of encounter orientations in the short-lived electron transfer complex of yeast Cc and CcP. The complete conformational space sampled by the protein molecules during the dynamic part of the interaction was mapped experimentally. Our results demonstrate that the encounter complex is populated for 30% of the time, where Cc samples only about 15% of the surface area of CcP. We have also shown that the occupancy of the encounter complex can be modulated across a broad range by single point mutations of interfacial residues. Thus, by adjusting the amount of the encounter complex through a judicious choice of point mutations, we can remodel the energy landscape of a protein complex and tune its binding specificity. It has not been well established whether binding hot spots, which are frequently found in strong static complexes, also govern transient protein interactions. To address this issue, we have investigated an electron transfer complex of physiological partners from yeast: yeast Cc and yeast CcP. Using NMR spectroscopy and double mutant cycle, we show that Cc R13 is a hot-spot residue, as R13A mutation has a strong destabilizing effect on binding. Based on our analysis, we propose that binding energy hot spots, which are prevalent in static protein complexes, could also govern transient protein interactions. We have also investigated the effect of interface mutations on the structure and dynamics of the horse Cc __ yeast CcP complex using NMR spectroscopy and X-ray crystallography. The horse Cc forms a more dynamic complex with yeast CcP as compared to the native yeast Cc-CcP complex, and the two Cc molecules acquire different orientations in complex with CcP. Interestingly, a single interface mutation makes the complex more specific, with the horse Cc in an orientation resembling that of the native yeast Cc. Show less
The technique of RSA to determine stent-graft migration and FRSA to study stent-graft dynamics are explained in further detail in CHAPTER 2. CHAPTER 3 and 4 concern the accuracy and feasibility of... Show moreThe technique of RSA to determine stent-graft migration and FRSA to study stent-graft dynamics are explained in further detail in CHAPTER 2. CHAPTER 3 and 4 concern the accuracy and feasibility of RSA to detect stent-graft migration in a static model and in a model with pulsatile motion. The results are compared to CT, the current clinical gold standard. RSA requires an aortic reference marker to detect stent-graft migration. A possible aortic reference marker is studied in CHAPTER 4 and 5. In CHAPTER 5, the feasibility of RSA in vivo is described. Furthermore, the position and the number of aortic reference markers required for accurate analysis needs to be clarified. These issues are discussed in CHAPTERS 5 and 6. Plain abdominal radiography is widely used as a low cost method to determine stent-graft migration. In CHAPTER 7, a study on the accuracy and, therefore, clinical applicability of plain abdominal radiography to detect stent-graft migration is described.In CHAPTER 8 the feasibility of FRSA is studied in a model and the method is validated for accuracy and precision. In CHAPTER 9, the first clinical introduction of this technique is reported. To conclude this thesis, the risk of radiation due to imaging for EVAR is evaluated in CHAPTER 10. Show less
The interactions between proteins are of central importance for virtually every process in a living cell. It has long been a mystery how two proteins associate to form a complex in a complicated... Show moreThe interactions between proteins are of central importance for virtually every process in a living cell. It has long been a mystery how two proteins associate to form a complex in a complicated cellular context. Recently, it was found that an intermediate state called encounter state, of a protein complex, exists briefly before a final protein complex is formed. In the encounter state, one protein is rolling over on the surface of its partner, searching for the optimal orientation. In my PhD thesis, a transient electron transfer complex formed between a heme protein and an iron-sulfur protein was found to be trapped in this intermediate state, existing as a pure encounter complex. Thus, characterization of this dynamic complex by nuclear magnetic resonance spectroscopy advances our understanding of the general mechanism of protein-protein interaction Show less
Microtubules are highly dynamic protein polymers that and are essential for intracellular organization and fundamental processes like transport and cell division. In cells, a wide family of... Show moreMicrotubules are highly dynamic protein polymers that and are essential for intracellular organization and fundamental processes like transport and cell division. In cells, a wide family of microtubule-associated proteins (MAPs) tightly regulates microtubule dynamics. The work presented in this thesis gives a high-resolution perspective on the microtubule assembly process and on the regulation mechanisms employed by representative MAPs. We studied dynamic microtubules outside cells, in a reconstituted minimal system. To follow microtubule growth with near molecular resolution, we developed a high-resolution technique that integrates optical tweezers, micro-fabricated rigid barriers and high-resolution video tracking of microbeads. Using this technique we found, for example, that microtubule assembly does not always occur by addition of single protein subunits, but multiple subunits could be incorporated at once at the growing end. XMAP215, a protein known to dramatically enhance microtubule growth, altered these molecular details. Another intriguing protein studied here is Mal3, a protein that is able to track growing microtubule ends. We found that Mal3 interacts differentially at the growing tip and on the rest of the microtubule, influencing all the parameters describing microtubule dynamics. In conclusion, our results give new insights into the microtubule assembly process in the absence and in the presence of regulators. Show less
The biological processes that are the basis of all life forms are mediated largely by protein-protein interactions. The protein complexes involved in these interactions can be categorised by their... Show moreThe biological processes that are the basis of all life forms are mediated largely by protein-protein interactions. The protein complexes involved in these interactions can be categorised by their affinity, which results in a range from static to transient complexes. Electron transfer complexes, which have to combine high turn-over with specificity are typically transient complexes. The transient complexes under investigation in this work are all part of the photosynthetic redox chain, in which electrons are transferred from membrane bound cytochrome f (cytf) to either plastocyanin (Pc) or cytochrome c6 (cytc6). This work describes the investigation of several aspects of transient protein-protein interactions that are applicable to many other transient complexes. The use of NMR as a tool of choice for these studies has proven it an invaluable technique that provides insight in rules that govern the world of transient complex formation. New approaches such as PRE and the creation of ensembles of structures are investigated. They will hopefully lead to a full understanding of dynamics and the variety of ways that transient complexes use dynamics to perform their function in the cell. Show less
