Category Archives: Seminars

Tuesday 05 November 2019 16:00 – 17:00 A. Payatakes Seminar Room

“Advanced Oxides for Environmental and Energy Applications”

Dr. Vassilios Binas Institute of Electronic Structure and Laser (IESL)

Abstract
The global concerns in the development of human civilization, the scientific and technological issues of energy utilization and environment protection are currently facing challenges. Nowadays, enormous energy demands of the world are mainly met by the non-renewable and environmental unfriendly fossil fuels. The substitution of the conventional energy platform has become extremely urgent, in the pursuit of the renewable and clean energy sources and carriers, including hydrogen storage, CO2 convention, batteries, and supercapacitors. Additionally, long-term industrial and agricultural activities induce serious environmental pollution problems (such as greenhouse and toxic gases, pharmaceuticals and organic micro-polutants) in air and water to deteriorate the ecological balance and the daily human health. The use of solar energy to drive the chemical and energy processes, along with chemical storage of solar energy and air – water cleaning, are imperative for the transition to a low-carbon economy, sustainable and clean society Realizing these challenges requires the development of new ideas, concepts and innovative photocatalytic materials. Advanced oxides (metal oxides and perovskite type nanomaterials) are of great technological importance in energy and environmental applications because if their capability to generate charge carriers when stimulated with a required amount of energy. The promising arrangement of electronic structure, light absorption properties, and charge transport characteristics of most of oxides render them potential candidates particularly for effective environmental and energy applications. Moreover, these materials can be synthesized with low cost, high yield, through easily controlled solution-based techniques. In this presentation, we discuss the use of advanced oxides as photocatalytic materials for the sustainable development in the energy (H2 production etc) and environment (improve air, water and health quality) applications.

Tuesday 22 October 2019 16:00 – 17:00 A. Payatakes Seminar Room

“Neuro-inspired Compression of Images and Videos (NICE2)”

Dr. Effrosyni Doutsi Institute of Computer Science (ICS)

Abstract
In recent years the widespread use of multimedia devices has increased the volume of digital data. Compression algorithms are necessary to store and process this copious amount of data. Unfortunately, these algorithms are developing very slowly while at the same time their complexity is constantly increasing. For this reason, the signal processing community is looking for solutions that will improve the capabilities of compression algorithms in other disciplines, such as neuroscience. Understanding and decrypting the brain has gained scientific interest as it is considered one of the most sophisticated systems yet capable of managing and compressing large volumes of information. In this talk I will introduce our image compression architecture that is based on neuroscience models. We have developed tools that enable to encode the visual information by mimicking the spiking neurons without sacrificing the quality of the reconstruction. In addition, using machine learning-based image quality metrics, we show that the proposed compression system performs much better in terms of perception than the state-of-the-art.

Tuesday 9 October 2018 16:00 – 17:00 A. Payatakes Seminar Room

“How does the brain pay attention?”

Dr. Panos Sapountzis Institute of Applied and Computational Mathematics (IACM)

Abstract
Attention is a cognitive function that allows to prioritise objects or locations that are most relevant to behaviour. The ability to flexibly guide our attention to the most relevant stimuli is critical for normal behaviour and is known to be disrupted in several neuropsychiatric and neurological disorders. Thus, understanding the neural substrates of attention is of significant importance. Invasive electrophysiological studies that aim at understanding the computations that individual neurons and neuronal ensembles carry out during attention have provided most of our knowledge on the role of different brain areas in the mechanisms of attention. These studies have implicated a distributed network of brain regions including area LIP in the parietal and area FEF in the prefrontal cortex. Despite converging evidence about the instrumental role of these regions in the control of attention, the particular contribution of each area in different aspects of attention has not been fully elucidated. Moreover, it is largely unexplored how activities across distant neuronal ensembles are coordinated and how effective communication between distant areas is implemented during attention. By performing simultaneous extracellular recordings in the two areas, we found that the behavioural relevance of stimuli is more robustly encoded in the prefrontal, relative to the parietal cortex. However, information emerges simultaneously in neuronal subpopulations in the two areas. Thus, our results indicate that attentional priority signals are processed in a parallel, distributed manner within the frontoparietal network. Moreover, we found that oscillatory interactions between the two regions have distinct frequency profiles in different task epochs. These data suggest that synchrony at distinct frequency bands reflects communication principles that subserve different cognitive requirements.

Tuesday 24 September 2019 16:00 – 17:00 A. Payatakes Seminar Room

“Sharp weighted Finsler-Kato inequalities for anisotropic Laplacian”

Dr. Konstantinos Tzirakis Institute of Applied and Computational Mathematics (IACM)

Abstract
The talk concerns recent developments in anisotropic weighted Kato type inequalities – with the anisotropy being represented by a generic Finsler metric – which are associated to the so-called Finsler or anisotropic Laplacian. The Finsler Laplacian is one of the most natural and foremost operators in the theory of anisotropic and non-homogeneous media, and in Finsler or Minkowski geometry. Following a unifying approach, we establish first a sharp interpolation between anisotropic weighted Hardy and Kato inequalities, in the half-space, extending the corresponding non-weighted version, being established recently by a different approach. Then, passing to bounded domains, we obtain successive sharp improvements by adding correction terms involving sharp weights and optimal constants, resulting in an infinite series-type improvement. We also discuss the optimality of the weights and the constants of the remainder terms, the results within the special Euclidean context, as well as the application of our method for cones.

Tuesday 23 July 2019 16:00 – 17:00 Seminar Room 1

“Numerical methods and development of Imaging techniques for Structural Health Monitoring applications”

Dr. Christos Panagiotopoulos Institute of Applied and Computational Mathematics (IACM)

Abstract
Research and development issues on material related to Structural Health Monitoring (SHM) worked during the ARCHERS project will be presented through a variety of related topics. First, an Operational Modal Analysis currently developed framework based on Stretching Method is examined and further applied to the case of the old Egyptian lighthouse of Rethymno. Using signal processing results within the Stretching Method framework we set up a minimization problem in order to appropriately define a simple mathematical model of the structure amenable for further numerical processes. Second, Time Reversal for Structural Analysis of frame structures will be covered in order to show whether it fits well as a numerical tool for source and damage localization problems. Another important issue of SHM is the Acoustic Emission that is the phenomenon of radiation of acoustic (elastic) waves in solids that occurs when a material undergoes irreversible changes in its internal structure. A mixed finite element method capable to simulate such problems of elastodynamics has been developed and will be discussed. Finally, Interface Crack Initiation and Growth in Composite Materials is viewed from the viewpoint of a coupled stress-energy failure criterion, and solved as a minimization problem developing appropriate algorithms and utilizing numerical methods such is the Boundary or the Finite Element Methods. Background theory, implementation of algorithms and applications considered will be discussed, while other subsidiary material occurred from the overall research activity will be briefly presented.

Tuesday 16 July 2019 16:00 – 17:00 A. Payatakes Seminar Room

” The role of Setdb1 in intestinal progenitor cells and in colorectal tumorigenesis”

Dr. Ioanna Peraki Institute of Molecular Biology and Biotechnology (IMBB)

Abstract
Setdb1 is a histone-3-lysine-9 methylase, which is highly expressed in embryonic-stem (ES) cells and in a variety of tumors including breast, skin, liver, colon and lung cancer. Setdb1 enzymatic activity contributes to the generation of a condensed, closed chromatin state and transcriptional repression. Previous studies have demonstrated that Setdb1 in ES cells is required for the suppression of a subset of genes encoding developmental regulators. In this way Setdb1 prevents uncontrolled differentiation, contributing to the mechanisms responsible for the maintenance of the pluripotent, stem cell phenotype. Setdb1 function in cancer is less well explored. While in many cases a correlation between Setdb1 expression and cancer phenotype is well established, evidence for a causative relationship is still missing. The current proposal is based on the hypothesis that similar to ES cells, Setdb1 may also repress differentiation specific regulators in adult somatic stem cells, like the intestinal Lgr5+ progenitor cells. The established role of Wnt signaling in both, intestinal progenitor cell maintenance and colorectal cancer, and the putative oncogenic function of Setdb1 in different organs, warrants parallel studies on the role of Setdb1 in progenitor cell maintenance and in colorectal cancer formation. We thus put forward the hypothesis that Setdb1deficiency may induce premature differentiation of Lgr5+ cells and derivative cancer stem cells, which may influence epithelium renewal or the growth characteristics of intestinal tumors.
To address these questions, we will conduct a study, which combines analyses of relevant mouse models with investigations of intestinal progenitor-derived organoid cultures. We expect this effort will not only decipher the role of Setdb1 in colorectal cancer but may also provide broader insights into the epigenetic mechanisms involved in the maintenanc

Tuesday 9 July 2019 16:00 – 17:00 A. Payatakes Seminar Room

“A generalization of Young measures for the Hydrodynamic limit of condensing Zero Range Processes”

Dr. Marios Stamatakis Institute of Applied and Computational Mathematics (IACM)

Abstract
Zero range processes (ZRPs) are stochastic interacting particle systems with zero range interaction. For particular choices of their parameters they exhibit phase separation with the emergence of a condensate. Such ZRPs are referred to as condensing and their hydrodynamic limit is not known, but is expected to be a degenerate non-linear diffusion equation where the diffusivity vanishes above a critical density ρc. In this talk we propose a generalization of the notion of Young-measures which allows to obtain a closed equation as the hydrodynamic limit of condensing ZRPs. We focus on symmetric ZRPs in the discrete torus and prove that the laws of the empirical density of the ZRP in terms of generalized Young-measures are concentrated on generalized Young measure-valued weak solutions π = (πt)t ≥ 0 to the equation θtπ = ΔΦ(π) where Φ(λ) is the mean jump rate of particles under an equilibrium state of mean density λ ≥ 0. Via the barycentric projection of Young measures and partial progress on the replacement lemma we can pass from the description in terms of generalized Young measures to ordinary measures and thus obtain that in the hydrodynamic limit the fluid phase ρ and the condensed phase ρ┴ οf the ZRP satisfy the equation θtρ – ΔΦ (ρ) = – θt ρ┴. Consequently, the fluid phase evolves according to a non-linear diffusion equation with a source term equal to the negative time derivative of the condensed phase.

Tuesday 25 June 2019 16:00 – 17:00 A. Payatakes Seminar Room

” The Plasmodium NF-Y like complex is required for malaria parasite transmission ”

Dr. Chiara Curra Institute of Molecular Biology and Biotechnology (IMBB)

Abstract

Malaria is transmitted by Plasmodium parasites and has a tremendous impact in the world. The sporozoites, transmitted from the mosquito to the vertebrate host during a mosquito bite, are produced in the mosquito inside the oocyst in about 12 days after blood meal uptake. Oocyst rupture is an essential step for the release of the sporozoites, which next travel to the salivary glands where they will be transmitted to the new host. Here, parasites first invade the liver cells and after they reach the blood stream infecting erythrocytes. Little is known about the mechanism of oocyst rupture and liver cells invasion. Recently, three Oocyst Rupture Proteins (ORP1-3) have been identified with a function in sporozoite transmission. Mutants lacking orps are blocked at oocyst stage, and sporozoites mechanically released are not able to establish infection in the vertebrate host. ORP1 and ORP2 play a role in the mechanism of oocyst rupture through the interaction of their histone-fold domains, similar to subunit B and C of the transcription factor NFY. Also ORP3 has a function during oocyst rupture but the mechanism is not known. ORPs represent a new discovery on how the parasite exploits protein domains to provide vital functions such as oocyst rupture and liver cells invasion. ORPs, or their specific domains, could be a possible target for anti-malarial strategies development to stop malaria transmission to the vertebrate host.

Tuesday 18 June 2019 16:00 – 17:00 A. Payatakes Seminar Room

” Liposomes and cellular vesicles: Νovel applications for effective drug targeting”

Dr. Antonia Marazioti Institute of Chemical Engineering Sciences (ICE-HT)

Abstract
Liposomes are well known for their potential applications as efficient carriers for drug delivery, with the most common administration route so far being intravenous administration. Little is known about the potential therapeutic advantages as well as the retention of topically administered liposomal drugs into confined body cavities. In the present study the retention of various types of liposomes in the pleural cavity of healthy mice and mice with malignant pleural effusion (MPE) following their intrapleural administration was monitored by live animal imaging. The experimental results reveal that certain liposome preparative parameters, such as the liposome size/lamellarity and coating with PEG-lipids, significantly affect the local bioavailability of liposomes. Furthermore, no difference was noticed in liposomal retention between tumorinoculated (MPE) and healthy mice, indicating the stability of liposomes in the presence of effusion. Interestingly, when we administered intrapleurally a liposomal formulation of deltarasin, to an experimental mouse model of MPE, fluid accumulation was halted, indicating the high potential of this route of administration as a method to increase the therapeutic potential of liposomal drugs for local diseases. In parallel, we studied the exosome inspired cell derived vesicles (CVs) as alternatives to artificial liposomes for targeted drug delivery. We isolated CVs from different cell lines and characterized their properties, morphology, cytotoxicity, integrity, cellular uptake as well as their brain-targeting potential, in vitro and in vivo. Our results provide new insights in the CVs physiology and potential for effective and targeted drug delivery.

Tuesday 16 April 2019 16:00 – 17:00 A. Payatakes Seminar Room

“Autophagy affects neuronal function via cAMP signalling”

Dr. Thanos Metaxakis Institute of Molecular Biology and Biotechnology (IMBB)

Abstract
Neuronal autophagy is an evolutionarily conserved catabolic process that facilitates recycling of dysfunctional cellular constituents and survival of nerve cells under adverse nutritional conditions. Importance of intact autophagy on neuronal homeostasis preservation is explicitly proven by the severe consequences of its blockage on neuronal survival and functionality: loss of neuronal autophagy causes neuronal pathologies, including neurodegeneration and stroke, while promoting age-related neuronal decline and disease. Apart from the role of basal autophagy on neuronal survival, growing evidence suggests its implication in the development of neuropsychiatric diseases and cognitive impairment in animal experimental models. Relative studies have associated neurodegeneration and certain neuropsychiatric disorders with autophagy impairment, accompanied by extensive protein aggregation. Moreover, autophagy upregulation has been linked to both improvement of neurodegenerative symptoms and mood stabilization in animals. Indeed, evidence suggests that macroautophagy, a specific form of autophagy, plays a major role on presynaptic neurotransmission and neuronal circuits, albeit through unknown mechanisms. Hence, neuronal autophagy is involved in numerous neuronal processes and identification of the relative underlying molecular mechanisms can lead to a better understanding of brain function and neuropsychiatric pathologies in humans. However, the way through which enhancement of neuronal autophagy affects specific brain domains, neuronal circuits, cognition, mood and behaviour is still obscure.
In this study we tested the effects of neuronal autophagic enhancement in flies and zebrafish. Combined behavioral and biochemical analysis revealed that acute and chronic autophagy induction at the brain impaired specific forms of memory and altered behavioral patterns in both species. We identified specific categories of nerve cells at specific brain domains where autophagy exerts its action, serving as coordinators of mood and cognition. We have characterized a neuronal circuit that is affected by autophagy – induced alterations on neurotransmitters transporters’ intracellular localisation, which target activity of specific postsynaptic receptors. Such alterations trigger c-AMP signalling activity, responsible for the autophagic effects on behaviour and cognition. Our results indicate that neuronal autophagy affects neuronal functionality through an evolutionary conserved mechanism, which also regulates developmental phenotypes in Drosophila.