Microtubule organization and cell geometry

We present a systematic study of the influence of cell geometry on the orientational distribution of microtubules (MTs) nucleated from a single microtubule organizing center (MTOC). For simplicity we consider an elliptical cell geometry, a setting appropriate to a generic non-spherical animal cell. Within this context we introduce four models of increasing complexity, in each case introducing additional mechanisms that govern the interaction of the MTs with the cell boundary. In order, we consider the cases: MTs that can bind to the boundary with a fixed mean residence time (M0), force-producing MTs that can slide on the boundary towards the cell poles (MS), MTs that interact with a generic polarity factor that is transported and deposited at the boundary, and which in turn stabilizes the MTs at the boundary (MP), and a final model in which both sliding and stabilization by polarity factors is taken into account (MSP). In the baseline model (M0), the exponential length distribution of MTs causes most of the interactions at the cell boundary to occur along the shorter transverse direction in the cell, leading to transverse biaxial order. MT sliding (MS) is able to reorient the main axis of this biaxial order along the longitudinal axis. The polarization mechanism introduced in MP and MSP overrules the geometric bias towards bipolar order observed in M0 and MS, and allows the establishment of unipolar order either along the short- (MP) or the long cell axis (MSP). The behavior of the latter two models can be qualitatively reproduced by a very simple toy model with discrete MT orientations.Comment: 38 pages, 13 figure

Models for spatial organization of microtubules and cell polarization

The main actors in this PhD thesis are microtubules, dynamic polymers built from protein subunits that play many important roles in cells of all higher organisms. We study a number of their functions using mathematical modelling and computer simulations. First, we consider the role of microtubules in establishing the ordered cortical array, a structure that plays a key role in the plant cell elongation. We show theoretically that the observed effect that new microtubules are nucleated from pre-existing microtubules strongly enhances the order of the array and makes it more robust against variations in the conditions. Next, we turn to the role the shape of the cell plays in the spatial organization of microtubules. We show that depending on how the microtubules interact with the cell boundary, either the long or the short axis of the cell determines the majority direction of the microtubules. Additionally, we formulate a model that predicts the positioning of the mitotic spindle, which is the cellular structure that segregates the duplicated chromosomes during eukaryotic cell division. We analyze how the speed, precision and final direction of the spindle orientation process depends on cell shape and the parameters that describe the microtubules. Finally, we turn to the potential role of microtubules in establishing cell polarity, the non-uniform distribution of cellular constituents, which is crucial for many developmental processes. Based solely on the propensity of microtubules to bind and transport proteins to the cell membrane, we set up a feasible and robust cell polarization mechanism, which could potentially be used to set up polarity in a minimal cell-like environment using a biochemical reconstitution approach. We study this model in its pure form in a perfectly spherical cell, in order to establish proof-of-principle, but also show that the effect remains in a more realistic non-spherical cell.</p

OLIVE MILL WASTE MANAGEMENT-THE CASE OF MESSENIA AREA

Η ελαιουργία είναι η κυριότερη αγροτοβιομηχανική δραστηριότητα στο νομό Μεσσηνίας και προκαλεί διάφορα περιβαλλοντικά προβλήματα. Τα περισσότερα ελαιοτριβεία είναι μικρά ως μεσαία που αδυνατούν να καταβάλουν το κόστος επεξεργασίας των αποβλήτων, καταλήγοντας στην ανεξέλεγκτη διάθεση σε φυσικούς αποδέκτες. Η νέα τεχνολογία των διφασικών ελαιοτριβείων δεν παράγει σημαντική ποσότητα υγρών αποβλήτων και λύνει εν μέρει μόνο το πρόβλημα καθώς είναι ακριβή για τα μικρά ελαιοτριβεία. Το μεγάλο κόστος των συμβατικών μεθόδων επεξεργασίας και η χωρική διασπορά των ελαιοτριβείων καθιστά αδύνατη την επεξεργασία σε κεντρικές μονάδες συμβατικής τεχνολογίας. Διερευνώνται εναλλακτικοί τρόποι διαχείρισης των αποβλήτων με μεθόδους επεξεργασίας χαμηλού κόστους και προσαρμοσμένοι στα χαρακτηριστικά του ελαιουργικού κλάδου της Μεσσηνίας. Olive oil industry is the main agro-industrial activity in the area of Messenia, causing various environmental problems. Most olive mills are small to medium sized and unable to pay the costs for the treatment of their wastewater, so, they end up in the uncontrolled disposal or their wastewater in natural sites. The new two-phase technology of olive mills does not produce big amounts of wastewater and it only partially solves the problem as it is too expensive for small sized olive mills. The implementation of big central treatment plants is practically impossible because of the high costs of the treatment methods and the high spatial dispersion of olive mills. Alternative ways for the management of olive mill wastewater are investigated, adopting low cost treatment methods and adapted to the characteristics of olive oil industry in the area of Messenia

Modelling of additive manufacturing processes: a review and classification

Additive manufacturing (AM) is a very promising technology; however, there are a number of open issues related to the different AM processes. The literature on modelling the existing AM processes is reviewed and classified. A categorization of the different AM processes in process groups, according to the process mechanism, has been conducted and the most important issues are stated. Suggestions are made as to which approach is more appropriate according to the key performance indicator desired to be modelled and a discussion is included as to the way that future modelling work can better contribute to improving today's AM process understanding

sus4 CASP Marketing Video

&lt;p&gt;In the sus4 CASP Platform Marketing Video, the GUI of the CASP sus4 platform is displayed, as well as a demonstration of its most important capabilities based on the two case studies of the project's end-users:&nbsp;&lt;/p&gt;&lt;ul&gt;&lt;li&gt;Welding optimization in terms of electricity consumption and productivity for I-FEVS.&lt;/li&gt;&lt;li&gt;HVAC systems optimization in terms of electricity consumption and temperature requirements for SELTEKA.&lt;/li&gt;&lt;/ul&gt

Dam design optimization

In the present doctoral thesis a new algorithm and computer software are developed, which produce the layout of water reservoirs and dams, and calculate their surface areas and their volumes at different elevations. Moreover, the new algorithm calculates the contour lines with high accuracy, using cubic spline interpolation. The main problem of the research is the minimization of volume of an earth dam and it’s solved by using computational methods of optimization. The new software’s ability of designing dams with different geometry and minimizing earth dam volume, allows the environmental positioning of dams, reinforcing in that way the environmental dimension of the design.Στην παρούσα διατριβή αναπτύσσονται αλγόριθμος και λογισμικό που παρέχουν ακρίβεια στη σχεδίαση και τους υπολογισμούς επιφανειών και όγκων ταμιευτήρα και φράγματος σε διαδοχικά υψόμετρα. Επιπλέον, ο αλγόριθμος με κυβικές splines που αναπτύχθηκε, οδηγεί στον υπολογισμό των ισοϋψών καμπυλών του εδάφους με μεγάλη ακρίβεια. Ο ακριβής προσδιορισμός της θέσης χωμάτινου φράγματος με το μικρότερο όγκο αποτελεί το κύριο πρόβλημα της διατριβής και επιτυγχάνεται με την εφαρμογή υπολογιστικών μεθόδων βελτιστοποίησης. Η δυνατότητα σχεδιασμού φραγμάτων διαφορετικής γεωμετρίας χάρη στο νέο λογισμικό και η δυνατότητα ελαχιστοποίησης του όγκου χωμάτινων φραγμάτων, οδηγούν στην εναρμονισμένη με το περιβάλλον χωροθέτηση φραγμάτων, ενισχύοντας την περιβαλλοντική διάσταση του σχεδιασμού

Modelling of additive manufacturing processes: a review and classification

Additive manufacturing (AM) is a very promising technology; however, there are a number of open issues related to the different AM processes. The literature on modelling the existing AM processes is reviewed and classified. A categorization of the different AM processes in process groups, according to the process mechanism, has been conducted and the most important issues are stated. Suggestions are made as to which approach is more appropriate according to the key performance indicator desired to be modelled and a discussion is included as to the way that future modelling work can better contribute to improving today's AM process understanding