Voordrachten 2014

Donderdag 11 december 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door TGM

Onderwerp: From events to quantum theory and not vice versa
Spreker: Kristel Michielsen, Institute for Advanced Simulation, Jülich Supercomputing Centre, and RWTH Aachen University, Germany

Abstract:
From the viewpoint of quantum theory, the central issue is how it can be that experiments yield definite answers. Indeed, it is well-known that quantum theory has nothing to say about individual events, only about their probabilities to occur. On the other hand, it is our brain which decides, based on what it perceives through our senses and cognitive capabilities, what a definite answer is. Therefore, we took up the idea to consider the observed events (clicks of a detector, etc.) as the basic entities for developing a logically consistent, mystery-free description of experimental facts.  The basic premise is that scientific knowledge derives from the discrete events which are observed in laboratory experiments and from relations between those events. The event-based simulation does not require the knowledge of the solution of a wave equation nor does it rely on concepts of quantum theory. The event-based approach reproduces the results of experiments with single photons/neutrons which involve interference, entanglement, and uncertainty [1,2].
Recently, we used techniques of logical inference to provide a rational explanation for the success of quantum theory, building a bridge between the discrete-event simulation methodology and quantum theory [3]. In particular, we demonstrated that (i) logical inference provides a rational explanation for the success of quantum theory, (ii) the Schrödinger equation is obtained through logical inference applied to robust experiments, (iii) the singlet and triplet states follow from logical inference applied to the Einstein-Podolsky-Rosen-Bohm experiment.
1. H. De Raedt and K. Michielsen, “Event-by-event simulation of quantum phenomena”, Ann. Phys. (Berlin) 524, 393–410 (2012)
2. K. Michielsen and H. De Raedt, "Event-based simulation of quantum physics experiments", Int. J. Mod. Phys. C 25, 1430003 (2014))
3. H. De Raedt, M.I. Katsnelson, and K. Michielsen, “Quantum theory as the most robust description of reproducible experiments”, Ann. Phys. 347, 45–73 (2014)

Vrijdag 5 december 2014, 11.30 u., lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: High-Tc Superconducting Tapes: buffer layers and pinning structures
Spreker:  Alexander Medelin, EMAT, University of Antwerp

Abstract:
Since the discovery of the superconducting materials great attention has been paid to incorporate their unique properties into industrial and scientific applications.
The optimization of the buffer layer growth process as well as the consequent superconducting (Y,Gd)BCO layer deposition conditions are extremely important for any commercial production of superconducting wires (>500 meter) with optimized current-carrying capability. The introduction of nanoparticles in the (Y,Gd)BCO layer helps to increase the critical current performance. A wide range of advanced transmission electron microscopy techniques has been applied to investigate the various substrates, buffer layers and superconducting layers. The interfaces, diffusion processes and nanoinclusions have been studied.

Vrijdag 5 december 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Inline Computed Tomography
Spreker: Eline Janssens, Vision Lab, University of Antwerp

Abstract:
Inspection of objects which are moving on a conveyor belt allows differentiation in the quality of the objects. Computed tomography is one of the possible inspection methods. To limit the cost and improve the speed of the inspection system, a design with a fixed source and flat panel detector is preferred compared to a traditional CT scanner. This however leads to artefacts in the reconstruction as the data is acquired in a limited angular range. Due to the limited data, known fast reconstruction algorithms like filtered back projection (FBP) provide inadequate reconstructions. In this talk, improvement of these reconstructions by the use of neural networks and by defining the optimal imaging geometry is discussed.

Donderdag 11 december 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door TGM

Onderwerp: From events to quantum theory and not vice versa
Spreker: Kristel Michielsen, Institute for Advanced Simulation, Jülich Supercomputing Centre, and RWTH Aachen University, Germany

Abstract:
From the viewpoint of quantum theory, the central issue is how it can be that experiments yield definite answers. Indeed, it is well-known that quantum theory has nothing to say about individual events, only about their probabilities to occur. On the other hand, it is our brain which decides, based on what it perceives through our senses and cognitive capabilities, what a definite answer is. Therefore, we took up the idea to consider the observed events (clicks of a detector, etc.) as the basic entities for developing a logically consistent, mystery-free description of experimental facts.  The basic premise is that scientific knowledge derives from the discrete events which are observed in laboratory experiments and from relations between those events. The event-based simulation does not require the knowledge of the solution of a wave equation nor does it rely on concepts of quantum theory. The event-based approach reproduces the results of experiments with single photons/neutrons which involve interference, entanglement, and uncertainty [1,2].
Recently, we used techniques of logical inference to provide a rational explanation for the success of quantum theory, building a bridge between the discrete-event simulation methodology and quantum theory [3]. In particular, we demonstrated that (i) logical inference provides a rational explanation for the success of quantum theory, (ii) the Schrödinger equation is obtained through logical inference applied to robust experiments, (iii) the singlet and triplet states follow from logical inference applied to the Einstein-Podolsky-Rosen-Bohm experiment.
1. H. De Raedt and K. Michielsen, “Event-by-event simulation of quantum phenomena”, Ann. Phys. (Berlin) 524, 393–410 (2012)
2. K. Michielsen and H. De Raedt, "Event-based simulation of quantum physics experiments", Int. J. Mod. Phys. C 25, 1430003 (2014))
3. H. De Raedt, M.I. Katsnelson, and K. Michielsen, “Quantum theory as the most robust description of reproducible experiments”, Ann. Phys. 347, 45–73 (2014)

Vrijdag 28 november 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Making advanced forward and backward projections usable in tomographic reconstruction
Spreker : Holger Kohr, Department of Mathematics, Royal Institute of Technology, Stockholm, Sweden

Abstract:
In many tomographic applications including electron tomography, STEM and X-ray PCT, technical equipment and experimental procedures have been significantly refined in the last years. These improvements include data with higher resolution and the capability of imaging thick or more dense objects. At the same time, however, the established physical models for the image acquisition which are used in reconstruction become more and more imprecise in these regimes. Therefore, advanced models in the form of projections and backprojections become more important. This talk aims at Fourier techniques, a way to make the application of some more complex operators feasible.

Donderdag 27 november 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Departmental Physics Colloquia

Onderwerp: Asteroseismology: the revolution in stellar physics
Spreker: Prof. Conny Aerts, Institute of Astronomy, KULeuven & Department of Astrophysics, Radboud University Nijmegen

Abstract:
The interiors of stars are not directly accessible for scientific experiment. This is problematic, because the life of stars, and by implication of galaxies in the Universe, is directed by the physical processes acting in their core regions.  How do stars rotate internally? How do the products of nucleosynthesis mix inside stars?  Do stars have an internal magnetic field?  Thanks to the recent research domain of asteroseismology we can now start to answer these questions for various types of stars through interpretation of their oscillation frequencies. During the talk, we explain the basic principles of asteroseismology and we illustrate the immense advantage of having long-term uninterrupted high-precision data from space missions.  We review the current status of the probing of stellar physics in general, and of the measurement of internal rotation and angular momentum in particular. We end with future prospects by highlighting the potential of asteroseismology as tool in the study of galactic archeology and of exoplanetary systems.

Maandag 24 november 2014, 11.30 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Using advanced forward and backward projections in tomography
Spreker:  Holger Kohr

Abstract:
In many tomographic applications including electron tomography, STEM and X-ray PCT, technical equipment and experimental procedures have been significantly refined in the last years. These improvements include data with higher resolution and the capability of imaging thick or more dense objects. At the same time, however, established physical models for the image acquisition become more and more imprecise in these regimes.
Therefore, advanced models in the form of projections and backprojections become more important. This talk presents some examples and preliminary results.

Vrijdag  21 november 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Human Body Modeling
Spreker: Femke Danckaers, Vision Lab, University of Antwerp

Abstract:
The human body appears in many shapes and sizes. For ergonomic products, it is important that they have an accurate fit to ensure an optimal comfort. Traditional product development techniques are based on 1D measurements of the body. This is not sufficient because of the wide variety of body shapes. By building a 3D statistical shape model of the body, representing mean shape and the variability inside the population, there is much more information available for the product developer. Such a shape model is built by finding meaningful correspondences between the surfaces and applying PCA to the corresponded surfaces. A shape model can be used to modify features such as length, BMI, gender,... It can also be used to find meaningful clusters in the population, to distinguish different body types. When such a shape model is implemented in a CAD environment, it can be used to validate and optimize designs, which will lead to more ergonomic products and a reduction of the design time.

Vrijdag  21 november 2014, 11.30 u., lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: In-situ SEM observations of thermoelastic martensitic transformation in shape memory alloys
Spreker: Minoru Nishida, Department of Engineering Science for Electronics and Materials, Kyushu University, Japan

Abstract:
The nucleation, growth, forward and reverse transformation processes of thermoelastic martensite in polycrystalline Ti-Ni, Cu-Al-Mn and Ni-Mn-Ga shape memory alloys have been investigated by in-situ SEM cooling and heating observations. Homogeneous nucleation was observed in Ti-Ni alloys. On the other hand, heterogeneous nucleation from grain boundaries was observed in Cu-Al-Mn and Ni-Mn-Ga alloys. There was no microstructure memory of martensitic phase in the three alloys upon thermal cycles. The interaction between habit plane variants clusters of B19’ martensite in Ti-Ni alloys is also presented. The evidence of thin foil effect in in-situ TEM observations will be provided.

Vrijdag 14 november  2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Resolution and precision in quantitative imaging – a survey
Spreker: Arjan den Dekker, Vision Lab, University of Antwerp

Abstract:
Resolution is widely used as a performance measure of imaging systems.  It is usually evaluated in terms of classical criteria, such as Rayleigh’s, which express the possibility to visually distinguish adjacent objects.  However, classical criteria are no longer appropriate if images are interpreted quantitatively instead of qualitatively. In quantitative imaging, alternative criteria are needed. These criteria should reflect the purpose of a quantitative imaging experiment, that is, precise estimation of object parameters. This presentation discusses classical resolution criteria, as well as more recently developed criteria that relate resolution to statistical measurement precision. In addition, it illustrates their use for optimal experiment design in quantitative electron microscopy.

Vrijdag 14 november  2014, 11.30 u., lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Scattering of electron vortex beams on atoms
Spreker: Ruben Van Boxem, EMAT, University of Antwerp

Abstract:
Electron vortex beams provide a prime example of phase tuning in the microscope. They carry curious physical properties such as topological charge and orbital angular momentum. These influence how such an electron probe interacts with matter. In this talk I will attempt to convey the most important properties of this interaction I have discovered, and how they may be combined to potentially extract previously hidden information from a (S)TEM experiment.

Vrijdag  7 november 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Looking for image-based solutions in maxillofacial surgery
Spreker :  Elke Van de Casteele, OMFS-IMPATH, KU Leuven and  Vision Lab, University of Antwerp

Abstract:
Oral and maxillofacial surgery is the speciality that combines surgical training with dental expertise for the treatment of diseases, injuries, tumours, and deformities of the face and jaws. Three-dimensional imaging has become a valuable technology not only for diagnosis but also for surgical planning. A global integration of the digital datasets will enable the creation of a virtual replica of the patient and allows full simulation of the surgery as well as of its expected outcome. In this presentation an overview is given of the research challenges in this discipline where image-processing techniques can make a difference!

Vrijdag 7 november 2014, 11.30 u., lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Surprising Self-Assembly of Hard Spheres and Long-Ranged Repulsive Rods in Confinement
Spreker: Prof. Alfons Van Bladeren, Utrecht University, The Netherlands

Abstract:
In research aimed at making colloidal crystalline ‘supraparticles’ by having monodisperse spherical nanoparticles crystallize in slowly evaporating oil emulsion droplets, we discovered icosahedral symmetry in the resulting dried colloidal crystals [1]. Subsequent work with a different kind of nanoparticles and a similar study using micron-sized silica colloids all confirmed that crystallization of hard spheres in a spherical confinement results in crystals with an icosahedral symmetry up until roughly 100.000 particles. This despite the fact that bulk regular crystals with icosahedral symmetry are known not to be able to regularly pack in 3D space. Computer simulations confirmed the experimental observations and were able to also show that indeed for roughly this number of particles or less the free energy of icosahedral packings is lower than that of an face centere cubic (FCC) crystal. Moreover, the simulations also provide clues to the actual crystallization pathway/mechanism [1]. Preliminary work on achieving binary supraparticles will be shown as well.
Micron-sized and fluorescently labeled rod-like silica colloids [2,3] were recently found in our group to form so-called rotator phases or plastic crystals if the Debye screening length is made sufficiently large (~particle length) [4]. In a plastic crystal positions are long-ranged and ordered on a 3D lattice, while rotations are still free and therefore orientational order is short-ranged or even absent. When such systems are confined between two charged flat walls we find alternating 3D ordinary and plastic crystal phases as function of the plate-plate separation. This surprising sequence was found to originate from subtle differences in the charge repulsions between the rods themselves and a rod with the wall.
1) Entropy-driven formation of icosahedral colloidal clusters by spherical confinement, Bart de Nijs, Simone Dussi, Frank Smallenburg, Laura Filion, Arnout Imhof, Marjolein Dijkstra, Alfons van Blaaderen, Nature Materials 10.1038/nmat4072 (2014).
2) Synthesis of monodisperse, rodlike silica colloids with tunable aspect ratio, A. Kuijk, A. van Blaaderen, and A. Imhof, JACS 133, 2346-2349 (2011)
3) Colloidal Silica Rods: Material Properties and Fluorescent Labeling, A. Kuijk, A. Imhof, M. H. W. Verkuijlen, T. H. Besseling, E. R. H. van Eck, and A. van Blaaderen, Particle 31, 706-713 (2014).
4) Switching plastic crystals of colloidal rods with electric fields,  B. Liu, T. H. Besseling, M. Hermes, A. F. Demirörs, A. Imhof, and A. van Blaaderen, Nature Communications 5: 3092 (2014).

Vrijdag 31 oktober 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp : Beyond DART, when common assumptions face a fearsome reality check
Spreker: Wim Van Aarle, Vision Lab, University of Antwerp

Abstract:
The Discrete Algebraic Reconstruction Technique (DART) has proven its merits in many tomographic applications.  The algorithm exploits prior knowledge about the scanned materials to compute an accurate reconstruction from only a small number of projections.  However, DART makes a few additional assumptions as well.  As an example, it is assumed that each object is completely homogeneous and that there is no partial volume effect (i.e. the object is fully representable on the reconstruction grid).  From experience we know that making these assumptions is usually ok and does not influence the reconstruction quality too much.  However, also from experience, we know that in some cases the made assumptions are not valid with respect to the measure data.  In this lecture, we go on a disaster tourism tour and explore what can go wrong in a scan such that the application of DART will not generate accurate results.  Furthermore, we will propose the use of a stochastic projection and data model that could, in combination with the existing DART framework, improve discrete reconstruction nonetheless.

Donderdag 30 oktober 2014, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Developments of cold field emission source (CFEG) : from higher brightness to ultrafast emission
Spreker: Florent Houdelier - CEMES-CNRS

Abstract:
Cold field emission gun are the brightest electron sources available for transmission and scanning electron microscopes. Due to this very important property in electron microscopy, this technology, which remains almost unchanged since 40 years, could be a suitable choice when using methods which requires a high spatial or  temporal coherence of the electron beam, like for EELS, STEM or electron interferometry. However, some several drawbacks are inherent to CFEG like the stability of the emitted current which, in the most favorable case, decreases by some 10%/hours, the beam noise (rms around 1%), … To tackle these problems, the use of ultra high vacuum, careful high voltage conditioning and flash cleaning of the tip are mandatory. By using a new carbon cone nanotip (CCnT), we have succeeded to improve considerably the stability of the electron beam with almost no decay during 8 hours, and a rms of noise lower than 0.5%, which avoids the use of flash cleaning technology. An increase by a factor of 3 to 5 has been also observed in the reduced brightness. I will present some results obtained both with high voltage TEM and Butler type low voltage SEM gun, combined with « fundamental » investigations of the electric field spatial distribution and strength around these tips, performed in situ inside a TEM by electron holography. Recently, together with Arnaud ARBOUET, we have started a brand new project called FemtoTEM, which aims to build a femtosecond time resolved CFE-TEM. The major challenge of this project concerns the ultrafast CFEG development. I will show how CFEG technology needs to be deeply modify to achieve a femtosecond laser triggered cold field emission of electrons, and present last results obtained with this modify CFE electron source.

Vrijdag 24 oktober 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Four dimensional reconstruction techniques in computed tomography
Spreker: Vincent Van Nieuwenhove, Vision Lab, University of Antwerp

Abstract:
Computed Tomography (CT) is an imaging technique which is able to reconstruct the interior of an object by its (X-ray) projections acquired from different angles. If motion or deformation occurs during the acquisition four dimensional CT (4DCT) techniques are necessary. These 4DCT algorithms image dynamical processes with an as high as possible temporal and spatial resolution and are able to minimize motion artifacts.  Motion artefacts give rise to streaks and blurring in the reconstructed images, compromising further quantitative analysis. This lecture discusses already existing 4DCT methods and a new algorithm which is able to estimate and correct deformations directly on the cone beam projections and their associated projection geometry. This new algorithm results in a fast and reliable motion correction and motion estimation for objects undergoing an approximately affine deformation (combination of rotations, translations, shearing’s and scaling).

Vrijdag 24 oktober 2014, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT / Seminar organised by EMAT

Onderwerp: Linking structures and properties of porous materials by TEM
Spreker: Zhi-Yi Hu, EMAT, University of Antwerp

Abstract:
Over the last decade, tremendous research has been focused on porous materials. Their outstanding properties have led their way into applications in biotechnology, biomedicine, catalysis, energy, optics, and the immobilization of biomolecules and bio-organisms etc. In this talk, we will begin with a brief introduction on synthesis, structures and properties of porous materials. Furthermore, three examples are given in this talk to explore the relationship between structures and properties by TEM investigation: mesoporous single crystal ZnO nanosheets for enhanced photocatalytic selectivity studied by HR-TEM; one particle (PtPd bimetallic nanoparticle)@one cell (SiO2) structure for enhanced oxygen reduction reaction studied by STEM-EDX; and efficient nano-hybrid TiO2/Pt for enhanced water splitting studied by STEM-EELS. It could be concluded that advanced TEM opens up new paths to understand the relationship between structures and properties of porous materials.

Vrijdag 17 oktober 2014, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: An insight into beam sensitive materials
Spreker: Heidari Mezerji Hamed, EMAT, University of Antwerp

Abstract:
The talk is divided into two main subjects; the first part of the talk is dedicated to the use of analytical electron microscopy to visualize material domains in a polymer blend in organic solar cells. Organic solar cells are subject of numerous technological studies due to cost effectiveness, facile manufacturing by printing on flexible substrates and their low environmental footprint. Nevertheless, the power conversion efficiency of organic solar cells is still low. A key factor to improve the performance of such devices is to understand and control the nanomorphology of their photoactive layer. Here we will discuss the steps towards visualization of the morphology of the photoactive layer in organic solar cells using STEM spectral imaging. The second part of the talk will focus on low-dose cryo electron microscopy (cryo-EM) of inorganic materials. With an increasing demand for the study of hybrid systems composed of organic-inorganic materials, electron microscopy is among the few techniques that provide local information about their arrangement. However due to electron beam sensitivity of the organic materials careful considerations are required for the microscopy of these materials. A short introduction will be given about sample preparation for cryo-EM, and it will be shown how the technique can be combined with electron tomography to obtain 3D information about nanomorphology of these nanostructures.

Donderdag 16 oktober 2014, 16.00 u., Lokaal U.203 (Campus Groenenborger)

Voordracht georganiseerd door EDF

Onderwerp: Status of the muon g-2 problem
Spreker: Prof. A. Dorokhov, Dubna

Abstract:
The first part of the seminar contains a brief review on the recent experiments on the electron and muon anomalous magnetic moments and their comparison with the Standard Model predictions. The second part is devoted to the quantitative  estimate of the hadronic corrections to the muon g-2 that dominate the theoretical uncertainties.

Vrijdag 10 oktober 2014, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Study and characterization of Periodic Mesoporous Organosilicas (PMOs) using electron microscopy methods
Spreker: Elena Kukueva, EMAT, University of Antwerp

Abstract:
Mesoporous organic–inorganic hybrid materials are a class of materials with large specific surface areas and pore sizes between 2 and 15 nm. PMOs have been obtained through the coupling of inorganic and organic components by template synthesis and have numerous industrial and scientific applications, including catalysis, adsorption, drug delivery, sensing.  The combination of organic and inorganic properties in one material and the possibility to modify and change the organic part lead to increasing the studies of different types of PMOs.
Transmission electron microscopy (TEM) and  electron tomography are very powerful techniques to characterize the structure of PMOs. Unfortunately, in many cases the PMOs are damaged during the by the electron beam. Therefore, it is not possible to investigate their structure by electron tomography only. Therefore, different PMOs samples synthesized using different templates were investigated using TEM, STEM, STEM-EDX, electron diffraction and tomography. It could be concluded that only using the combination of these methods we can obtain a full characterization of the samples.

Vrijdag 3 oktober 2014, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT / Seminar organised by EMAT

Onderwerp: Evaluation of plasma cleaning on historical photographs
Spreker: Eva Grieten, EMAT, University of Antwerp

Abstract:
The recent development of commercial plasma torches to selectively remove natural grown corrosion has opened up new possibilities to treat historical photographs with silver degradation. Two types of historical photographs were selected – daguerreotypes and gelatin silver glass negatives - to study the efficiency and selectivity of the treatment. By using spectral imaging it is possible to link the chemical composition to the spatial distribution of the nano-particles of the corrosion phenomena. By characterizing both the surface of the photograph and the internal structure the changes in topography and chemical composition due to the plasma treatment can be evaluated. The results show that there is a clear difference in readability of the image after plasma treatment. Whereas the suggested method doesn’t alter the original material it was not possible with the current set-up to remove the corrosion in all cases investigated. We will end the presentation with the viability and limitation of the suggested treatment.

Donderdag 2 oktober 2014, 16.00 u., Lokaal U.247 (Campus Groenenborger)

Voordracht georganiseerd door TGM / Seminar organised by CMT

Onderwerp : Magneto-optical imaging, critical current enhancement, and guidance of flux avalanches in microstructured superconducting films
Spreker: Wilson Ortiz, Federal University of Sao Carlos, Brazil

 

Vrijdag 19 september 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

 

Voordracht georganiseerd door EMAT

Onderwerp / Subject: Conventional Transmission Electron Microscopy Imaging beyond the Diffraction and Information Limits
Spreker / Speaker: Prof. A. Rosenauer, University of Bremen

Abstract:
In this talk I introduce a new TEM imaging mode we called ISTEM (“imaging STEM”) which combines STEM illumination with CTEM imaging. I will present our simulation study that shows that ISTEM generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. It does not contain scan noise caused by “fly-back” errors, is more robust against chromatic aberration, exhibits direct structural imaging with superior precision, and even allows us to overcome the conventional information limit of a microscope. I will also show our experimental data which clearly reveal image resolution beyond the information limit of our low-base TITAN 80/300 microscope.

Vrijdag 19 september 2014, 11.30 u., Lokaal U.408 (Campus Groenenborger)

Voordracht georganiseerd door EMAT / Seminar organised by EMAT

Onderwerp / Subject: Conventional Transmission Electron Microscopy Imaging beyond the Diffraction and Information Limits
Spreker / Speaker: Prof. A. Rosenauer, University of Bremen

Abstract:
In this talk I introduce a new TEM imaging mode we called ISTEM (“imaging STEM”) which combines STEM illumination with CTEM imaging. I will present our simulation study that shows that ISTEM generally allows extending the point resolution of CTEM imaging beyond the diffraction limit. It does not contain scan noise caused by “fly-back” errors, is more robust against chromatic aberration, exhibits direct structural imaging with superior precision, and even allows us to overcome the conventional information limit of a microscope. I will also show our experimental data which clearly reveal image resolution beyond the information limit of our low-base TITAN 80/300 microscope.

Woensdag 17 september 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door ECM

Onderwerp: Nonlinear Spectroscopy: absorption and refraction"
Spreker: Eric Van Stryland, CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, FL USA

Abstract:
The advent of high irradiance, tunable optical sources has allowed the development of new spectroscopic methodologies to determine the spectrum of nonlinear absorption as well as the dispersion of nonlinear refraction.
We will look at several methods including Z-scan and its several variants along with excite-probe methods that also give the temporal response. We will look at several different materials and nonlinear mechanisms.  While bound-electronic nonlinearities are well described by the third-order susceptibility introduced by Bloembergen, several other slow nonlinearities can be better described in other ways.

Vrijdag 12 september 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: On the practical purposes of statistical shape models
Spreker: Daniël Lacko, Vision Lab, University of Antwerp

Abstract:
3D shape models contain detailed statistical information on the shape of the human body. For example, they can be used to accurately predict individual people's head shape and to create design mannequins that better fit the underlying population. However, statistical parameters are difficult to interpret by non-mathematicians such as industrial designers. Therefore, the first part of this lecture discusses a way to extend a shape model of the Western human head with a number of intuitive anthropometric measurements. The resulting shape model is evaluated in terms of prediction error, required sample size and sensitivity to measurement errors. The second part of the lecture gives an overview of the practical applications to individualized and mannequin-based design, with a specific focus on the design of a brain-computer interface headset. The discussion equally applies to other near-body products such as safety helmets or glasses. The results so far show that anthropometric shape models can a valuable tool for design as well as research.

Dinsdag 1 juli 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door TGM

Onderwerp: In Pursuit of the Electronic Ground State and Properties of n-Acenes and Graphene Nanoribbons at the Confines of Non-Relativistic Quantum Mechanics
Spreker: Prof. Dr. Michael S. Deleuze, University of Hasselt

Abstract:
A benchmark theoretical study of the electronic ground state and of the ionization energies [1], electron affinities [2], singlet-triplet (S0-T1) excitation energies [3] and static dipole electric polarizabilities [4] of n-acenes (C4n+2H2n+4) is presented, on the ground of single- and multi-reference calculations based on restricted or unrestricted zero-order wave functions. High-level and large scale treatments of electronic correlation in the ground state are found to be necessary for compensating giant but unphysical symmetry-breaking effects in unrestricted single-reference treatments. The composition of multi-configurational wave functions, the topologies of natural orbitals in symmetry-unrestricted CASSCF calculations, the T1 diagnostics of Coupled Cluster theory and further energy-based criteria demonstrate that all investigated systems exhibit a 1Ag singlet closed-shell electronic ground state. Electronic transition energies can be therefore determined within chemical accuracy (1 kcal/mol, i.e. ~0.04 eV) by applying the principles of a Focal Point Analysis onto the results of a series of single-point and symmetry-restricted single-reference calculations employing correlation consistent cc-pVXZ or aug-cc-pVXZ basis sets (X = D, T, Q, 5) and single-reference methods [HF, MP2, MP3, MP4SDQ, CCSD, CCSD(T)] of improving quality, in order to extrapolate CCSD(T) results to asymptotically complete basis sets (cc-pV¥Z, aug-cc-pV¥Z).
In this talk we will also discuss in some computational and analytical details the issue of half-metallicity in zig-zag graphene nanoribbons and nanoislands of finite width, i.e. the coexistence of metallic nature for electrons with one spin orientation and insulating nature for the electrons of opposite spin, which has been recently predicted [5] from so-called first-principle calculations employing Density Functional Theory. It will be shown that, within the framework of non-relativistic quantum mechanics, like the size-extensive spin-contamination to which it relates, half-metallicity is nothing else than a methodological artefact, due to a too approximate treatment of electron correlation in the ground state [6].

References
[1] M. S. Deleuze, L. Claes, E. S. Kryachko and J.-P. François, J. Chem. Phys., 119, 3106 (2003).
[2] B. Hajgató, M. S. Deleuze, D. J. Tozer, F. De Proft, J. Chem. Phys., 129, 084308 (2008).
[3] (a) B. Hajgató, M. S. Deleuze, D. Szieberth, F. De Proft, P. Geerlings, J. Chem. Phys., 131, 224321 (2009); (b) M. Huzak, B. Hajgató, M. S.
Deleuze, J. Phys Chem. A, 115, 9282 (2011).
[4] M. Huzak and M. S. Deleuze, J. Chem. Phys. 138, 024319 (2013).
[5] Y.-W. Son, M. L. Cohen, S.G. Louie, Nature, 444, 347 (2006).
[6] M. Huzak, B. Hajgató, M. S. Deleuze, J. Chem. Phys., 135, 104704 (2011).

Vrijdag 27 juni 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Spectral unmixing
Spreker: Muhammed Awais Akhter, Vision Lab, University of Antwerp

Abstract:
Spatial pixel sizes for multispectral and hyperspectral sensors are often large enough that numerous disparate substances can contribute to the spectrum measured from a single pixel. Consequently, the desire to extract from a spectrum the constituent materials in the mixture, as well as the proportions in which they appear, is important to numerous tactical scenarios in which subpixel detail is valuable. With this goal in mind, spectral unmixing algorithms have proliferated in a variety of disciplines that exploit hyperspectral data, often duplicating and renaming previous techniques.

 

Donderdag 26 juni 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Dose limited reliability of quantitative ADF STEM for nano-particle atom-counting
Spreker: Annick De Backer, EMAT, University of Antwerp

Abstract:
Many materials which are industrially relevant, such as nanoparticles, are studied using quantitative annular dark field scanning transmission electron microscopy (ADF STEM). One should be particularly aware of the fact that these samples are often beam sensitive. Therefore keeping the incoming electron dose to a minimum is highly advantageous. However, this may reduce the reliability of quantitative ADF STEM which will here be demonstrated for nano-particle atom-counting. We discuss the limits for counting the number of atoms in a projected atomic column with single atom sensitivity based on experimental ADF STEM  images of a real industrial catalyst. We can diagnose these limits by combining a thorough statistical method and detailed image simulations. This indeed shows the requirement for a high enough incoming  electron dose or the collective analysis of multiple images recorded under the same experimental conditions.

Donderdag 19 juni 2014, 16.00 u, Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: An alternative normalization method for quantitative STEM
Spreker: Gerardo T Martinez, EMAT, University of Antwerp

Abstract:
Techniques such as annular bright-field (ABF) or high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) have become widely used in quantitative studies because of the possibility to directly compare experimental and simulated images when the experimental data is expressed in units of ‘fraction of incident probe’. However, since the detector response is spatially inhomogeneous, a ‘detector sensitivity’ profile needs to be included in image simulations in order to account for these irregularities. Unfortunately, the quantification procedure now becomes both experiment and instrument specific, with new simulations needing to be carried out for the specific response of each instrument’s detector. This not only impedes the comparison between different instruments but can also be computationally very time consuming.
In this work, we propose an alternative method for normalizing experimental data in order to compare these with simulations that consider a homogenous detector response. To achieve this, we determine the electron flux distribution reaching the detector by means of a camera length series or PACBED, which is then used to determine the corresponding weighting of the detector response. It will be shown that the proposed method is equivalent to the current used method, giving the possibility to compare experimental data to simulations assuming a homogeneous detector response. The advantages and applications for both methods will be discussed.

Maandag 16 juni 2014, 15.00 u., Lokaal U.203 (Campus Groenenborger)

Voordracht georganiseerd door EDF

Onderwerp: Search for an invisible Higgs boson at LHC
Spreker: Prof Dr. Kajari Mazumdar, Tata Institute of Fundamental Research, Mumbai, India

Abstract:
Current measurements of the properties of 125 GeV Higgs boson based on Run1 data of LHC, have reasonably large uncertainties. This leaves room for accommodating additional decay modes  of the Higgs boson compared to the ones allowed in the standard model. Hence  the search for potentially possible decay of the resonance through experimentally invisible mode is highly interesting. If observed it will also open the door to probe new physics in a more definitive way.
The CMS collaboration has recently published the results of the searches for invisible Higgs. The highlights of the CMS analyses using different production modes of the Higgs boson  will be discussed in this talk.

Vrijdag 13 juni 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: An introduction to audio source separation with NMF
Spreker: Joachim Ganseman, Vision Lab, University of Antwerp

Abstract:
Audio source separation is the problem of unmixing the separate sound signals that constitute an audio mixture. I will present some of the difficulties in this domain with a focus on a limit case: separation of musical instruments in single channel (mono) mixtures of music. Nonnegative Matrix Factorization (NMF) has proven to be an efficient method to tackle the problem, but it has its limitations and results are good but not necessarily optimal. We shortly dive into alternative angles of attack for nonnegative data unmixing, more specifically from probabilistic and geometric viewpoints, and how these perform on audio. Finally we pay some attention to the evaluation of audio source separation, with a discussion on data sets and metrics.

Donderdag 12 juni 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Characterization of microcapsules for self-healing coatings
Spreker: Dhanya Puthenmadom, EMAT, University of Antwerp

Abstract:

Man-made polymeric materials inspired by Nature have become a newly emerging paradigm. One such fascinating area of research is microencapsulation. Biological cells are an example of natural microencapsulation. The same way a cell wall protects the inside cellular matter from undesirable environmental conditions, man-made microcapsules protect encapsulated ingredients. In recent years, microencapsulation technology has gained considerable interest in numerous industrial sectors, such as coatings, food, pharmaceutical, biomedical, agricultural, personal care etc. A typical microcapsule consists of a core material surrounded by a uniform shell. The relative content of core and shell materials in a microcapsule can be expressed as core content. Optimal core content has a substantial commercial importance in terms of storage stability and release behaviour. By controlling the surface morphology, wall thickness, porosity, and mechanical strength of the microcapsule shell, it is possible to release the encapsulated ingredient in a controlled manner. In this presentation, we will discuss the influence of core content on the surface and shell morphology as well as on the wall thickness of the microcapsules.

Dinsdag 10 juni 2014, 16.30 u., Lokaal T.105 (Campus Groenenborger)

Voordracht georganiseerd door TGM

Onderwerp: Atomically thin MoS2: a two dimensional semiconductor beyond graphene
Spreker: Dr. Andres Castellanos-Gomez, Delft University of Technology

In this talk I will introduce and motivate the study of the mechanical, electrical and optical properties of atomically thin crystals different than graphene. I will focus on Molybdenum Disulphide which is considered a case of special interest. Single-layer MoS2 is an attractive two-dimensional material that combines the mechanical flexibility of graphene with a large direct bandgap. While graphene is very interesting as a transparent electrode, its lack of a bandgap limits its usefulness in semiconducting and optoelectronic devices. Atomically thin MoS2, on the other hand, has a large intrinsic bandgap. This attractive feature has been employed to fabricate many devices not possible in graphene, such as field-effect transistors with high mobility and current on/off ratio, logic gates and efficient photo-transistors. Our work on MoS2 has been focused on developing new methods to fabricate single layer MoS2 [1] and to characterize the intrinsic mechanical [2], optical and electrical properties [3-4] of this atomically thin material.
Here, I will show an overview of our last results paying special attention to our studies on the photocurrent generation in single layer MoS2 [4] and the strain engineering in atomically thin MoS2 [5]. New results on the optoelectronic properties of novel 2D semiconducting materials beyond MoS2 (black-phosphorus, TiS3, etc…) will be also discussed.
References
[1] Castellanos-Gomez, A., et al., Laser-Thinning of MoS2: On Demand Generation of a Single-Layer Semiconductor. Nano Letters, 2012, 12(6): p. 3187-3192.
[2] Castellanos-Gomez, A., et al., Elastic Properties of Freely Suspended MoS2 Nanosheets. Advanced Materials, 2012, 24(6): p. 772-775.
[3] Castellanos-Gomez, A., et al., Electric-Field Screening in Atomically Thin Layers of MoS2: the Role of Interlayer Coupling. Advanced Materials, 2013, 25(6): p. 899-903.
[4] Buscema, M., et al., Large and Tunable Photothermoelectric Effect in Single-Layer MoS2. Nano Letters, 2013, 13(2), p. 358–363
[5] Castellanos-Gomez, A., et al., Local strain engineering in atomically thin MoS2. arXiv:1306.3804 (2013)

Vrijdag 6 juni 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Super-resolution reconstruction for MRI
Spreker: Gwendolyn Van Steenkiste, Vision Lab, University of Antwerp

Abstract:
To improve the signal-to-noise ratio (SNR) and shorten the acquisition time, MR images are often acquired with an anisotropic resolution, where the slice thickness is larger than the in-plane resolution. This low through-plane resolution results in larger partial volume effects. Recently, methods have been proposed that improve the trade-off between the SNR, acquisition time and spatial resolution via super-resolution reconstruction. These super-resolution methods acquire multiple low resolution images and combine their information in one image with a high spatial resolution. Next to scalar MRI, these techniques can also be used in diffusion MRI, which suffers from an inherently low SNR and long acquisition times.

Donderdag 5 juni 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Nanoscale plasticity mechanisms in nanocrystalline Pd films under different deformation modes
Spreker: Behnam Amin-Ahmadi, EMAT, University of Antwerp

Abstract:
Nanoscale plasticity mechanisms activated in sputtered nanocrystalline (nc) palladium (Pd) thin films subjected to hydriding cycles to induce both α and β phase transformations have been investigated using advanced TEM techniques. The observation of Pd films hydrated at low hydrogen pressure did not reveal significant changes of the microstructure in comparison with the as-deposited films. In contrast, a loss of the coherency of Σ3 {111} coherent twin boundaries due to dislocation/twin boundary interactions as well as the clear increase of dislocation density after hydriding to β phase have been observed. Surprisingly, a high density of intrinsic/extrinsic stacking faults and an fcc→9R phase transformation at Σ3 {112} incoherent twin boundaries have also been observed after hydriding to β phase indicating a clear effect of hydrogen on the stable and unstable planar fault energies.
Creep/relaxation tests of Pd films were also performed by in-situ HRTEM on electron beam evaporated nc Pd thin films using an original on-chip nanotensile method. Unexpectedly, large creep/relaxation rates have been observed at room temperature. The in-situ HRTEM characterisation of the evolution of the microstructure shows that, despite the small grain size, the creep/relaxation mechanism is mainly mediated by the stress driven nucleation and propagation of dislocations. The formation and the destruction of sessile Lomer-Cottrell dislocations and the clear loss of the coherency of coherent TBs with time confirmed the dislocation based relaxation behaviour of nc Pd films. This fast relaxation constitutes a key issue in the development of a variety of micro- and nanotechnologies such as Pd membranes for hydrogen applications.

Vrijdag 23 mei 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Supervised classification of hyperspectral remote sensing images - an overview
Spreker: Guy Thoonen, Vision Lab, University of Antwerp

Abstract:
Hyperspectral remote sensing images provide a wealth of information about the material that is present on the ground. Often, however, the end user is interested in a limited number of semantically defined classes, depending on the application at hand. This demand is where supervised classification comes in. Throughout the years, many algorithms, originating from the pattern recognition domain, were applied to hyperspectral images. In this lecture, the classification problem will be introduced, together with common ways of solving it. Subsequently, an overview will be given of the open issues related to classification and the research domains that arise from these issues. Additionally, the subject of regression, which is closely related to classification, will be looked at. The final part of the talk will delve into applications that have been studied at the Vision Lab or that will be studied in the near future.

Donderdag 22 mei 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Optimization of electron tomography for the three dimensional study of hybrid nanoparticle assemblies
Spreker: Eva Bladt, EMAT, University of Antwerp

Abstract:
Recently, hybrid materials which contain both organic and inorganic components have gained interest due to a broad range of potential applications, such as catalysis. In order to understand the structure-property relation, a thorough characterization of the 3D nanoparticle organization is crucial, which requires electron tomography. However, the technique has been used in only a few analyses of hybrid systems. This is related to the fact that both compounds of the hybrid structure require different imaging conditions and a specialised approach for TEM sample preparation is needed. Electron tomography for inorganic-organic hybrid systems can therefore be considered as challenging. Here, we discuss a dedicated route towards 3D characterization of hybrid structures consisting of Au nanoparticles suspended in a flexible polymeric matrix.

Vrijdag 16 mei 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: A multiresolution approach to Discrete Algebraic Reconstruction Technique (DART)
Spreker: Andrei Dabravolski, Vision Lab, University of Antwerp

Abstract:
In discrete tomography, a scanned object is assumed to consist of only a few different materials. This prior knowledge can be effectively exploited by a specialized discrete reconstruction algorithm such as Discrete Algebraic Reconstruction Technique (DART), which is capable of providing more accurate reconstructions from limited data compared to conventional reconstruction algorithms. However, like most iterative reconstruction algorithms, DART suffers from long computation times. To increase the computational efficiency as well as the reconstruction quality of DART, a multiresolution version of DART has been proposed, in which the reconstruction starts on a coarse grid with big pixel (voxel) size. The resulting reconstruction is then resampled on a finer grid and used as an initial point for a subsequent DART reconstruction. This process continues until the target pixel size is reached. In this talk, DART and its multiresolution version will be explained in detail and compared with one of the widely used iterative reconstruction algorithms (SIRT) on both simulated and real data.

Donderdag 15 mei 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
 
Onderwerp: Optimal experimental design for the detection of light atoms from high-resolution STEM images
Spreker: Julie Gonnissen, EMAT, University of Antwerp

Abstract:
We report an innovative method to explore the optimal experimental settings to detect light atoms from scanning transmission electron microscopy (STEM) images. Since light elements play a key role in many technologically important materials, such as lithium-battery devices or hydrogen storage applications, much effort has been made to optimize the STEM technique in order to detect light elements. Therefore, classical performance criteria, such as contrast or signal-to-noise ratio (SNR) are often discussed hereby aiming at improvements of the direct visual interpretability. However, when images are interpreted quantitatively, one needs an alternative criterion, which we derive based on statistical detection theory. Using realistic simulations of technologically important materials, we demonstrate the benefits of the proposed method and compare the results with existing approaches.

Vrijdag 9 mei 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
 
Onderwerp: Hyperspectral image processing and analysis research at the Vision Lab
Spreker: Paul Scheunders, Vision Lab, University of Antwerp
 
Abstract:
At the Vision Lab, research on hyperspectral image processing and analysis has been performed since 2000. In this talk, an overview will be given of the actual research topics that are under study in the Vision Lab. Specific topic on hyperspectral image processing (restoration, denoising, compression), classification (spatial-spectral classification, image decision fusion, subpixel mapping, domain adaptation) and spectral unmixing (geometric unmixing, nonlinear unmixing, target detection) will be discussed. Moreover, specific application will be treated (vegetation monitoring, the adjacency effect, water quality monitoring). Finally, some specific research plans for the near future will be given.

Donderdag 8 mei 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
 
Onderwerp: Structure determination of films and bulk materials for electronic applications
Spreker: Robert Paria Sena, EMAT, University of Antwerp
 
Abstract:
The lecture will discuss two different topics: multiferroic multiphase samples and a single phase piezo-electric sample.
Chemical solution deposition is not still exploited enough to manufacture multiferroic magnetoelectric materials, although it is believed to improve the physical properties of the composite materials.  LaAlO3//BaTiO3/CoFe2O4 and LaAlO3//BiFeO3/CoFe2O4 films were fabricated using this technique in order to achieve improved versions of the multiphase multiferroics obtained using other deposition techniques. Using transmission electron microscopy analysis the crystal structures of the perovskite and spinel phases BaTiO3, BiFeO3, and CoFe2O4 were confirmed, the growth and orientation of these phases inside the films was determined as well as the misfit dislocations at the interfaces. Properties measurements are ongoing to be able to link the structure with the differences in the properties of similar films made with other techniques.
The second topic of the lecture is the piezo-electric K2Nb8O21 bulk sample.  The structure of K2Nb8O21 is unknown in the literature. Using a combination of HAADF-STEM images and ED patterns, the cell parameters and atomic coordinates within the structure were determined for the first time.

Vrijdag 25 april 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Automatic Behavior Quantification and Social Network Analysis of Drosophila Melanogaster
Spreker: Tanmay Nath, Vision Lab, University of Antwerp
 
Abstract:
 In order to explain the genetic basis of group level social behavior, there is a need to study the group level interactions rather than between two individuals.  A group level study involves tracking all the flies in a group for the entire video without losing their identity. Flyworld, the dedicated imaging setup records the freely interacting flies. All pairwise fly interactions in a video would lead to the development of a social network.
This lecture presents an overview of study on Drosophila melanogaster and provides a basis on studying their social network.

Donderdag 24 april 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Quantitative measurement of electron orbital angular momentum
Spreker: Laura Clark, EMAT, University of Antwerp
 
Abstract:
The newly developed electron vortex beams are hoped to find applications in a range of electron microscopy fields, including phase contrast imaging, and precise nanomanipulation.  However, the application with the most potential is to produce magnetic state imaging by measuring orbital angular momentum exchange (OAM) between beam and sample.
To achieve this, we need to be able to measure OAM superpositions quantitatively. Here we present the first technique to enable this in a TEM. Our technique calls on a specially designed aperture, called a multi-pinhole interferometer, to sample the wavefront at different angular positions. From the interference pattern of these sampled positions we demonstrate the possibility of reconstructing the input OAM state, by applying a simple algorithm.
We experimentally demonstrate this method with both of ideal, on-axis electron vortices, and off-axis states, measured as complex superpositions of OAM states. The experimental results coincide well with theoretical predictions.

Vrijdag 18 april 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
 
Onderwerp: Water unmixing
Spreker: Dzevdet Burazerovic, Vision Lab, University of Antwerp
 
Abstract:
In this work we study the estimation of water quality from case-II waters, which is a vital part of the all-important hydrological observation. We address the problem by spectral unmixing. This is somewhat atypical, since unmixing in remote sensing is usually considered for unraveling of mixed pixels containing ground covers or solid materials. We start from an analytic model relating the reflectance of water to its masses or constituents,  as specified by their specific inherent optical properties (SIOP) and concentrations. To reformulate the estimation of these concentrations as a spectral unmixing problem, we adopt the classical fully-constrained linear mixing model, while offering a suitable definition of ‘end members’ – the components constituting a mixture. Similar to the practice often used in regression, a ‘substitution trick’ linearizes the problem and in turn enables us to use some prevalent algorithms.
Furthermore, we present a method to automatically extract  the end members from the data. We validate the entire unmixing-based procedure using as reference a method that inverts the water reflectance through a comparisons with the spectra from a look-up table. This validation is done using data simulated from the water-reflectance model and a real airborne hyperspectral image acquired over coastal waters of a shallow sea.

Vrijdag 11 april 2014, 14.00 u., Lokaal N0.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
 
Onderwerp: X-ray phase contrast imaging
Spreker: Dr. Charlotte Hagen, University College London, UK
 
Abstract:
 X-ray phase contrast imaging (XPCi) has become an important tool for the non-destructive visualisation of weakly attenuating samples as often encountered in biomedical applications. The dominant contrast mechanism is the phase shift of as opposed to the attenuation of x-rays which is used in conventional radiography. For biological tissues, the phase effects can be up to three orders of magnitude larger than attenuation effects; hence, it is not surprising that XPCi methods have provided superior contrast for many soft tissue specimen. Among the existing XPCi methods, the Edge Illumination (EI) XPCi method has a potential for a wide spread application as it is based on a simple setup, can be scaled up to large fields of view, is relatively unaffected by environmental vibrations, has a high phase sensitivity and is dose efficient. Moreover, it can be implemented with both synchrotron and standard x-ray sources, which opens up the possibility for lab-based, high throughput imaging. In my talk I will briefly discuss how the method works and will give an overview of its most promising applications in biomedicine. I will explain how we have recently advanced the method from a planar to a tomographic imaging modality, and will highlight the data processing and image reconstruction challenges associated with 3D phase imaging.

Donderdag 10 april 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Microstructural characterization and transformation behavior of a porous Ni50.8Ti49.2 alloy
Spreker: Xiayang Yao, EMAT, University of Antwerp
 
Abstract:
In recent decades near-equiatomic porous Ni-Ti shape memory alloys (SMAs) have drawn increasing attention due to the excellent combination of shape memory effect and unique superelasticity with the porous structure and lightweight. Such materials are now regarded as one of the promising biomaterials for orthopedic implant applications and a candidate of high-strength low-density damping material for mechanical and civil engineering applications. By using powder metallurgy sintering, we obtained a porous Ni50.8Ti49.2 bulk material. Solid solution and aging treatments were applied to improve the phase homogeneity and phase transformation behavior. Scanning and transmission electron microscopy were used for studying the microstructure of the alloys while DSC and EDX were used to investigate the thermal behavior and chemical phase content. The main phase in these porous Ni-Ti alloys is the B2 austenite with dispersed NiTi2 particles while Ni4Ti3 precipitates appear after aging. The pores in the alloy cause strain in surrounding regions, which influences the nucleation and growth of Ni4Ti3. Variants of the latter have a preferential orientation along the strain direction, which is perpendicular to the edges of the pores. Such a preferential growth will also affect the appearance and distribution of the R-phase and possibly the martensite in the porous alloy.

Vrijdag 4 april 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Domain adaptation for hyperspectral remote sensing imagery
Spreker: Jan-Pieter Jacobs, Vision Lab, University of Antwerp
 
Abstract:
Hyperspectral Imagery (HSI) is taking an increasingly important role in remote sensing (RS) for Earth observation.
Many of the analysis techniques applied on RS data are supervised techniques requiring ground reference data for training. Observational parameters like the time of day, angle of observation relative to the sun, meteorological conditions , ... introduce data set shifts traditional supervised classification techniques are unable to cope with. Domain adaptation (DA) is the field in machine learning which aims to resolve this issue. Traditionally this is accomplished adapting the analysis techniques, though recently methods are introduced which directly modify the data itself. This lecture presents the problems encountered in DA and some recently proposed DA methods for solving them.

Donderdag 3 april 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
 
Onderwerp: How to image the atomic structure of Ag-exchanged FAU-Y and FAU-X zeolites by using aberration corrected transmission electron microscopy.
Spreker: Thomas Altantzis, EMAT, University of Antwerp
 
Abstract:
Zeolites are crystalline microporous aluminosilicate minerals with numerous industrial and scientific applications, including catalysis, preparation of advanced materials and nuclear processing. Transmission Electron Microscopy (TEM) is a very powerful technique to characterize the structure and composition of such materials at the atomic scale. For the case of cation exchanged zeolites, it is of crucial importance to determine the atomic positions of the cations in the zeolitic framework.
 Unfortunately, zeolites are extremely sensitive to damage caused by the electron beam, especially in the case of a relatively low Si/Al ratio. The use of aberration corrected TEM at relatively low electron dose, however, does enable one to obtain high resolution images. By combining monochromated, aberration corrected HAADF-STEM with a careful image analysis, the so-called template matching technique, differences in the 3 dimensional positions of Ag cations present in FAU-X and FAU-Y could be determined.

Vrijdag 28 maart 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: An overview of nonlinear hyper spectral unmixing techniques
Spreker: Rob Heylen, Vision Lab, University of Antwerp

Abstract:
An often encountered problem in hyper spectral image processing and spectroscopy is spectral mixing of the different components in the field of view of the sensor. Decomposing the observed spectrum into its constituent components, or end members, allows the estimation of the abundances of each end member, or to detect the presence of certain target spectra. The most popular model in the remote sensing community is the linear mixing model, which assumes that a spectrum is a convex linear combination of end member spectra. However, complex optical interactions are often present in many scenarios, such as between different mineral grains in soils and dust, and in scenes containing layers of vegetation or indirect lighting. This leads to nonlinear mixing effects, and requires more advanced techniques and models for spectral unmixing. In this talk, we first give a short introduction on the spectral mixing problem. Then, we demonstrate several of these nonlinear mixing effects, and present models and techniques that have been developed to cope with them. Some examples that will be treated are secondary reflections, intimate mineral mixtures, vegetation, and more data-driven techniques borrowed from machine learning and differential geometry.


Donderdag 27 maart 2014, 16.00 u., Lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Study and characterization of magnetic nanoparticles and zeolites as carriers of metals
Spreker: Maria Filippousi, EMAT, University of Antwerp
 
Abstract:
A combined morphological and structural characterization of two materials (magnetic nanoparticles and zeolites) was performed for potential use in biomedical applications.
Magnetic nanoparticles are employed as carriers allowing them to be manipulated, tracked, imaged and remotely heated. Although iron oxide nanoparticles are relatively biocompatible, compared to the other magnetic nanoparticles, naked iron oxide nanoparticles have reported to cause in vitro cytotoxicity. Thus, IOs and the anticancer drug (Taxol) were encapsulated inside a biocompatible and biodegradable matrix.  The polymeric matrix used in the present work has a melting point temperature close to the body temperature (Tm=44°C). This is very essential in case these IOs will be used for combinatory cancer treatment with hyperthermia and drug release.
Zeolites as biocompatible materials may be used as a natural mineral, absorbing harmful substances from the body, thus acting as a detoxifier. We characterized the atomic structure of the HEU-type zeolite as well as its interaction with Ag+ and Zn2+.

Vrijdag 21 maart 2014, 16.00 u., Lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB

Onderwerp: Robust parameter estimation in difusion mri
Spreker: Quinten Collier, Visiion Lab, University of Antwerp

Abstract:
Diffusion weighted magnetic resonance imaging (DW-MRI) is used increasingly in clinical research for its ability to depict white matter tracts and for its sensitivity to microstructural and architectural features of brain tissue. Typically, diffusion parameter maps are computed by fitting the signal intensities from the DW-MR images to a diffusion model as a function of their corresponding diffusion weighting strength and direction. Commonly used diffusion models include the diffusion tensor imaging (DTI) model and the diffusion kurtosis imaging (DKI) model. Unfortunately, the performance of most diffusion parameter estimators is often degraded by physiological noise. Spatially and temporally varying artifacts, such as cardiac pulsation, motion or system instabilities, will perturb the DW-MR signals, yet are ignored by conventional estimators. More robust estimators, i.e., estimators that are less sensitive to outliers, are needed to deal with these perturbations.


Donderdag 20 maart 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT

Onderwerp: Organic materials and nanoscale 3D morphology
Spreke: Martin Pfannmöller, EMAT, University of Antwerp
 
Abstract:
The introduction of efficient organic semiconductor materials has influenced our view of the future with flexible and printable electronics.  However, it is still not known how thermodynamic behaviour, structure and electronic processes correlate. Since device efficiencies strongly depend on nanometer sized structural elements, the use of electron microscopy for visualizing the morphology seems inevitable. But how to get contrast? How not to damage beam sensitive materials while creating contrast? The presentation will provide an overview of results from own works using analytical TEM on organic photovoltaic blends of polymers and fullerenes. Furthermore it will be discussed how we can proceed to understand device physics in 3D. Recent observations tell us that it might be very similar to how nature does it.

Vrijdag 7 maart 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
Onderwerp: Prior knowledge based reconstruction techniques in computed tomography
Spreker: Geert Van Eyndhoven, Vision Lab, University of Antwerp

Abstract: Computed tomography (CT) is an advanced non-invasive imaging technique in which a reconstruction of the scanned object’s interior is calculated based on projection data acquired from the scanned object at different angles. If sufficient projection data is available at a sufficiently large angular range, standard reconstruction techniques provide adequate quality of the reconstructed image. However, in many circumstances, this is no longer the case and standard reconstruction techniques result in poor image quality. For instance, in electron tomography, sample restrictions often imply a limited angular range. Another example can be found in dynamic CT, where the object changes during the acquisition process, resulting in only a limited set of available projections per time point. If only limited projection data is available, the reconstruction quality can be improved by incorporating prior knowledge in the reconstruction algorithm. In this lecture, two algorithms incorporating prior knowledge for improving the reconstruction quality will be discussed. The first algorithm is designed specifically for porous samples and utilizes the porosity as prior knowledge during iterative reconstruction. The second approach was designed for objects that undergo structural changes during the acquisition process (e.g., a sample affected locally by beam-damage, pressure tests on material samples, …), where the algorithm exploits the fact that these changes only occur locally, while a large part of the object remains stationary.

Donderdag 6 maart 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Electron microscopy studies on non-stoichiometric layered oxides
Spreker: Nicolas Gauquelin, EMAT, University of Antwerp

Abstract:Layered oxides have been attracting a huge amount of attention in the last decades for their physical properties, such as superconductivity, oxygen diffusion, magnetic resistance ... These are closely related to the stoichiometry in oxygen of these compounds. Over the last few years, the improvements in stability of the instrumentation in electron microscopy (aberration-correctors) and electron energy loss spectroscopy capabilities (with improved energy resolution, high brightness sources and spectrometers) have been tremendous and made it possible to access new information about chemistry and physical properties of these compounds directly at the atomic level. Applications of these, including elemental, valence and hybridization mapping to the study and understanding of the relationship between physical properties, crystallography and electronic structure of high temperature superconductors, and lanthanum nickelates will be presented.

Vrijdag 28 februari 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
Onderwerp: Estimation of white matter fiber orientations under non-white matter partial volume effects in constrained spherical deconvolution
Spreker: Roine Timo, Vision Lab, University of Antwerp

Abstract: Diffusion-weighted (DW) magnetic resonance imaging (MRI) is a noninvasive imaging method, which can be used to investigate neural tracts in the white matter (WM) of the brain. The interpretation of DW-MRI derived indices, however, is often ambiguous due to significant partial volume effects (PVE) caused by the relatively large voxel sizes. These PVEs can be caused by both non-WM tissue, such as gray matter (GM) and cerebrospinal fluid (CSF), and by complex (e.g. crossing) WM fiber configurations.
High angular resolution diffusion imaging (HARDI) methods have been developed to correctly characterize complex WM fiber configurations, but to date, most of the HARDI methods do not account for PVEs caused by isotropic tissue. We investigated the isotropic PVEs caused by non-WM tissue (i.e., CSF and GM) in WM voxels on constrained spherical deconvolution (CSD), and propose a method to take these PVEs into account in the estimation of fiber orientations with CSD.
Results from both simulation and in-vivo bootstrapping experiments demonstrate a significant improvement in the precision of the identified fiber orientations and in the number of false peaks detected especially under GM PVEs. The proposed method significantly improves the fiber orientation estimation at the WM-GM interface, which has an impact in the analysis of connectivity between GM regions.

Donderdag 27 februari 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Correlating Synthesis, Morphology, and Photovoltaic Performance of Poly(3-butylthiophene) Based Polymer Solar Cells
Spreker: Sijun Li, EMAT, University of Antwerp

Abstract: Polymer solar cells (PSCs) has been developed and improved from a fancy concept with less than 1% power conversion efficiency (PCE) to over 9% PCE, particularly through the efforts in the last decade. The high efficiency along with the advantages of low cost, flexibility, ease of manufacture, etc. can represent the broad prospects of commercial applications for PSCs.
Among the novel developed semiconducting polymers using in PSCs, poly(3-alkylthiophene)s (P3ATs), exemplified by poly(3-hexylthiophene) (P3HT), have been extensively studied and have provided a wealth of information that shows how the ultimate performance of cells depends on specific variables involved in the production of the active layers. However, there are still many conflicting experimental results in PSCs even for this well-studied material, which hints that the material-performance relationship in PSCs is still not fully understood.
In this work, we take Poly(3-butylthiophene) (P3BT), another member in P3ATs family, as an example to demonstrate the improvement of the PSCs performance by tuning the macromolecular properties and corresponding self-assembly morphology of the semiconducting polymer.

Vrijdag 21 februari 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
Onderwerp: A flexible algorithm for fully 3D alignment
Spreker: Jan De Beenhouwer, Vision Lab, University of Antwerp

Abstract: Before a reconstruction algorithm can be applied to compute a 3D image from a set of 2D projections, alignment must first be carried out to correct for geometrical changes that may have occurred during the acquisition. The last few years, this has become more and more a bottleneck to the reconstruction quality in electron tomography and nanoCT due to the increasingly higher resolution that can be achieved. In this talk, a markerless alignment algorithm will be presented. Contrary to most alternative methods, which allow only a few geometrical parameters to be varied during the alignment procedure, our algorithm offers full flexibility over the 3D geometry, making it suitable for a wide range of acquisition protocols.

Donderdag 20 februari 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp: Ceria nanocatalysts for chemical looping characterized by transmission electron microscopy
Spreker: Maria Meledina, EMAT, University of Antwerp

Abstract: Mixed FeOx - CeOx materials are promising candidates for use as oxygen carrier material in the process of CO2 reduction to CO by chemical looping.
In close collaboration with the Department of Chemical engineering and technical chemistry of the University of Gent, a series of mixed FeOx-CeOx oxides from different steps of the chemical lopping cycle has been investigated by advanced transmission electron microscopy and spatially resolved spectroscopy, as a first step in the study of the behavior of this type of materials.
The high iron containing samples were shown to consist of two phases: Fe2O3 and CeO2, both present as nanoparticles. In the case of the low iron concentration, the CeO2 is present as nanoparticles, with sizes of approximately 20-60 nm. Electron diffraction and imaging show no evidence for the presence of a separate Fe2O3 (or FeOx) phase in this material. However, nano-voids and nano-inclusions have been found within individual CeO2 nanoparticles and were shown to be Fe-rich. On top of this enrichment of Fe in the ceria nanovoids, single Fe atoms have been found to decorate the ceria surface. After reduction, the samples retain their initial morphology and iron atoms still decorate the voids and the surface. The same situation is observed for a sample after a full reduction/oxidation cycle.

Vrijdag 7 februari 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
Onderwerp / Subject: From planigraphy to digital tomosynthesis: 3D in medical x-ray imaging
Spreker / Speaker: Jeroen Cant, Vision Lab, University of Antwerp

Abstract: Anatomical overlap is a well known problem in 2D imaging of a patient. It obscures possible lung nodules in thorax images and renders other pathologies invisible or hard to position. Ever since the invention of x-rays, physicians therefore have wanted to visualize the insides of a patient in three dimensions. In the era before the CT scanner, radiologists used planigraphy for obtaining pseudo-3D images of a patient using analogue röntgen lms.
In this talk we show how iterative reconstruction and parallel computing hardware have recently lead to the revival of this now forgotten technique into digital tomosynthesis. We outline the algorithmic challenges compared with conventional CT reconstruction and discuss ongoing research for improving mobile 3D x-ray imaging and lung cancer detection.

Donderdag 6 februari 2014, 16.00 u., lokaal U.024 (Campus Groenenborger)

Voordracht georganiseerd door EMAT
Onderwerp / Subject: Measuring the Orbital Angular Momentum of Electron Vortex Beams
Spreker / Speaker: Giulio Guzzinati, EMAT, University of Antwerp

Abstract: The recent demonstration of electron vortex beams has opened up the new possibility of studying orbital angular momentum (OAM) in the interaction between electron beams and matter.
To this aim, methods to analyze the OAM of an electron beam are fundamentally important and a necessary next step.
We demonstrate the measurement of electron beam OAM through a variety of techniques. The use of forked holographic masks, diffraction from geometric apertures, diffraction from a knife-edge and the application of an astigmatic lens are all experimentally demonstrated. The viability and limitations of each are discussed with supporting numerical simulations.

Vrijdag 31 januari 2014, 16.00 u., lokaal N1.08 (Campus Drie Eiken)

Voordracht georganiseerd door VISIELAB
Onderwerp: Novel techniques for compression and denoising of hyperspectral images based on tensor analysis
Spreker: Azam Karami, Vision Lab, University of Antwerp

Abstract: Hyperspectral imagery (HSI) is used in different practical applications such as the detection of earth surface, soil type analysis, agriculture and forest monitoring, environmental studies and military surveillance. Many of these applications require high Signal-to-Noise-Ratio (SNR) for hyperspectral images to achieve good performance. However, despite the advances in hyperspectral sensors, the hyperspectral image sensors are still highly sensitive to noise due to their nonlinear response in different spectral bands. Therefore, the captured data may carry considerable noises which affect the information extraction step and consequently related applications. The presence of the noise significantly decreases the classification accuracy by blurring the boundaries of objects of interest. In addition, these images are usually volumetric and need a great amount of space and time for archiving and transferring. Therefore, in recent years compression and denoising of hyperspectral images have gained particular attention in order to improve the HSI quality and reduce the cost of equipment storage and bandwidth interests.