Polymeric microcapsules with switchable mechanical properties for self-healing concrete: synthesis, characterisation and proof of concept

Microcapsules, with sodium silicate solution as core, were produced using complex coacervation in a double, oil-in-water-in oil, emulsion system. The shell material was a gelatin–acacia gum crosslinked coacervate and the produced microcapsules had diameters ranging from 300 to 700 μm. The shell material designed with switchable mechanical properties. When it is hydrated exhibits soft and ‘rubbery’ behaviour and, when dried, transitions to a stiff and ‘glassy’ material. The microcapsules survived drying and rehydrating cycles and preserved their structural integrity when exposed to highly alkaline solutions that mimic the pH environment of concrete. Microscopy revealed that the shell thickness of the microcapsules varies across their perimeter from 5 to 20 μm. Thermal analysis showed that the produced microcapsules were very stable up to 190 °C. Proof of concept investigation has demonstrated that the microcapsules successfully survive and function when exposed to a cement-based matrix. Observations showed that the microcapsules survive mixing with cement and rupture successfully upon crack formation releasing the encapsulated sodium silicate solution.Financial support from the Engineering and Physical Sciences Research Council (EPSRC—United Kingdom) for this study (Project Ref. EP/K026631/1—‘Materials for Life’) is gratefully acknowledged

A comprehensive approach for the simulation of the Urban Heat Island effect with the WRF/SLUCM modeling system: The case of Athens (Greece)

This study presents a comprehensive modeling approach for simulating the spatiotemporal distribution of urban air temperatures with a modeling system that includes the Weather Research and Forecasting (WRF) model and the Single-Layer Urban Canopy Model (SLUCM) with a modified treatment of the impervious surface temperature. The model was applied to simulate a 3-day summer heat wave event over the city of Athens, Greece. The simulation, using default SLUCM parameters, is capable of capturing the observed diurnal variation of urban temperatures and the Urban Heat Island (UHI) in the greater Athens Area (GAA), albeit with systematic biases that are prominent during nighttime hours. These biases are particularly evident over low-intensity residential areas, and they are associated with the surface and urban canopy properties representing the urban environment. A series of sensitivity simulations unravels the importance of the sub-grid urban fraction parameter, surface albedo, and street canyon geometry in the overall causation and development of the UHI effect. The sensitivities are then used to determine optimal values of the street canyon geometry, which reproduces the observed temperatures throughout the simulation domain. The optimal parameters, apart from considerably improving model performance (reductions in mean temperature bias from 0.30 °C to 1.58 °C), are also consistent with actual city building characteristics - which gives confidence that the model set-up is robust, and can be used to study the UHI in the GAA in the anticipated warmer conditions in the future. © 2017 Elsevier B.V

Comparison of diesel electric with conventional propulsion in a passenger boat with customized models

122 σ.Στη παρούσα διπλωματική εργασία επιχειρήθηκε να συγκριθούν η συμβατική με την υβριδική ντηζελοηλεκτρική πρόωση των πλοίων. Στη σύγχρονη εποχή παρατηρείται μία συνεχώς αυξανόμενη τάση για τον εξηλεκτρισμό των πλοίων. Στην υβριδική ντηζελοηλεκτρική πρόωση εν προκειμένω, οι συμβατικοί κινητήρες Ντήζελ (Diesel) δεν κινούν απ' ευθείας τους έλικες του πλοίου όπως στη συμβατική πρόωση. Αντί αυτού παρέχουν μηχανική ισχύ στις ηλεκτρικές γεννήτριες του πλοίου, οι οποίες τροφοδοτούν με ηλεκτρική ενέργεια το ηλεκτρικό δίκτυο. Η δε πρόωση του πλοίου επιτυγχάνεται μέσω ελεγχόμενων κινητήρων, οι οποίοι τροφοδοτούνται από το ηλεκτρικό δίκτυο του πλοίου, και κινούν τους έλικες, οι οποίοι είναι συνδεδεμένοι στους άξονες των κινητήρων αυτών. Κατά συνέπεια, τόσο η συμβατική όσο και η υβριδική ντηζελοηλεκτρική πρόωση απαιτούν διαφορετικές διαμορφώσεις του ηλεκτρικού δικτύου του πλοίου. Αυτές οι διαφορετικές εναλλακτικές διαμορφώσεις εξετάστηκαν μέσω προσομοιώσεων στην παρούσα διπλωματική εργασία για το επιβατηγό πλοίο “Cumana”. Στόχος ήταν να μελετηθεί η μόνιμη και η μεταβατική κατάσταση του ηλεκτρικού δικτύου του πλοίου καθώς επίσης και η ποιότητα ισχύος των δύο αυτών εναλλακτικών διαμορφώσεων. Συνολικά πραγματοποιήθηκαν τρεις ενότητες προσομοιώσεων σε περιβάλλον MATLAB / Simulink. Στην πρώτη προσομοιώθηκε το ηλεκτρικό δίκτυο του πλοίου με τη λύση της συμβατικής πρόωσης τόσο κατά την πλεύση του πλοίου με σταθερούς κόμβους στη θάλασσα όσο και κατά τη διάρκεια ελιγμών. Στη δεύτερη ενότητα προσομοιώσεων εξετάστηκε το ηλεκτρικό δίκτυο του πλοίου με τη λύση της ντηζελοηλεκτρικής πρόωσης κατά την πλεύση με σταθερή ταχύτητα κόμβων ενώ στην τρίτη ενότητα εξετάστηκε ξανά το δίκτυο της ντηζελοηλεκτρικής πρόωσης, αυτή τη φορά όμως, κατά τη διάρκεια ελιγμών του πλοίου, οπότε τροφοδοτούνται διαφορετικοί κινητήρες. Μπορεί όλες οι προσομοιώσεις που πραγματοποιήθηκαν να αφορούν το πλοίο “Cumana”, παρόλα αυτά έγιναν με παραμετροποιημένα μοντέλα των στοιχείων του δικτύου, δίνοντας έτσι τη δυνατότητα να μπορούν να επεκταθούν με απλο τρόπο στο ηλεκτρικό δίκτυο ενός οποιουδήποτε άλλου πλοίου. Παράλληλα με τη σύγκριση των δύο αυτών εναλλακτικών μορφών πρόωσης σε τεχνικό επίπεδο, επιχειρήθηκε στο πλαίσιο της παρούσας διπλωματικής εργασίας μία σύγκριση της συμβατικής και της υβριδικής ντηζελοηλεκτρικής πρόωσης και σε οικονομικό επίπεδο, εξετάζοντας τις δύο αυτές λύσεις για την πρόωση του πλοίου τεχνικοοικονομικά με βάση την καθαρή παρούσα αξία, τον εσωτερικό βαθμό απόδοσης και την περίοδο αποπληρωμής. Επίσης μελετήθηκαν και οι επιπτώσεις στο περιβάλλον των δύο αυτών μορφών πρόωσης. Σαν κεντρικό συμπέρασμα αυτής της εργασίας αναδείχθηκε ότι η υβριδική ντηζελοηλεκτρική πρόωση του πλοίου “Cumana” αποτελεί μεν ενεργοβόρο και λύση με υψηλό κόστος κατασκευής, εξασφαλίζει όμως αυξημένη σταθερότητα του δικτύου κατά τις μεταβατικές του καταστάσεις και μειωμένες εκπομπές διοξειδίου του άνθρακα, παράλληλα με μειωμένη καθαρή παρούσα αξία σε σχέση με τη συμβατική πρόωση.The objective of the present dissertation is to compare the conventional with the hybrid diesel electric ship propulsion. The trend for ship electrification is growing nowadays. More specifically, in the hybrid propulsion case, the diesel engines provide mechanical power input to the generators, which in turn provide the electricity required by the ship’s grid. In this case, the ship’s propulsion is achieved through convenient motors fed by the ship’s electric grid and attached to the ship’s propellers. Consequently, the conventional and the hybrid propulsion involve different grid topologies. These alternative topologies have been examined through software simulations in the case study of ship “Cumana”. The objective was to study the steady state and transient phenomena of the ship’s electric grid, as well as the power quality in the cases of conventional and hybrid propulsion. In total, three series of simulations have been performed by using MATLAB/Simulink software. In the first one, the ship’s electric grid was simulated in the case of conventional propulsion for both constant speed cruise and during manoeuvres. In the second one, the ship’s electric grid was studied in the case of hybrid propulsion for constant speed cruise, while in the third series of simulations the ship’s grid was studied in the case of hybrid propulsion during manoeuvres, when different motors are implemented. All simulations performed concern the ship “Cumana”, however, the grid models developed are totally customizable, providing the opportunity to study and simulate the electric grid of any ship in MATLAB/Simulink environment. In addition to the technical comparison of the two propulsion modes, in the present dissertation a financial comparison has been equally undertaken. The method adopted included extrapolation of these two propulsion options to potential investments, and considered the net present value, internal rate of efficiency and payback period techniques. Moreover, the environmental impact of these two propulsion options has been assessed. In conclusion, it was found that the hybrid diesel electric propulsion of ship “Cumana” is an energy intensive and costly outset solution, but it guarantees better electric grid stability during its transient conditions, involves reduced carbon dioxide emissions, and presents a better net present value compared with the conventional propulsion.Γεώργιος Δ. Γιάνναρο

An Empirical Analysis of The Effects of Government Spending on Capital Investment: Evidence from O.E.C.D. Countries.

This paper focuses on the possible “direct” effect in increased government size on fixed capital formation. That is, we hypothesize that as government increases its consumption as percentage of GDP, investors modify their investment plans accordingly. It is our contention that the direct effect of government size on fixed capital investment manifest themselves through a downward shift in the investment schedule. To test this hypothesis, we estimate an aggregate investment function for eighteen O.E.C.D. countries for the period 1960-1994. Our findings suggest a negative relationship between government size and fixed capital investment. [ E22, E62]

Development of an operational modeling system for urban heat islands: An application to Athens, Greece

The urban heat island (UHI) effect is one prominent form of localized anthropogenic climate modification. It represents a significant urban climate problem since it occurs in the layer of the atmosphere where almost all daily human activities take place. This paper presents the development of a high-resolution modeling system that could be used for simulating the UHI effect in the context of operational weather forecasting activities. The modeling system is built around a state-of-the-art numerical weather prediction model, properly modified to allow for the better representation of the urban climate. The model performance in terms of simulating the near-surface air temperature and thermal comfort conditions over the complex urban area of Athens, Greece, is evaluated during a 1.5-month operational implementation in the summer of 2010. Results from this case study reveal an overall satisfactory performance of the modeling system. The discussion of the results highlights the important role that, given the necessary modifications, a meteorological model can play as a supporting tool for developing successful heat island mitigation strategies. This is further underlined through the operational character of the presented modeling system. © Author(s) 2014

Development of an operational modeling system for urban heat islands: an application to Athens, Greece

The urban heat island (UHI) effect is one prominent form of localized anthropogenic climate modification. It represents a significant urban climate problem since it occurs in the layer of the atmosphere where almost all daily human activities take place. This paper presents the development of a high-resolution modeling system that could be used for simulating the UHI effect in the context of operational weather forecasting activities. The modeling system is built around a state-of-the-art numerical weather prediction model, properly modified to allow for the better representation of the urban climate. The model performance in terms of simulating the near-surface air temperature and thermal comfort conditions over the complex urban area of Athens, Greece, is evaluated during a 1.5-month operational implementation in the summer of 2010. Results from this case study reveal an overall satisfactory performance of the modeling system. The discussion of the results highlights the important role that, given the necessary modifications, a meteorological model can play as a supporting tool for developing successful heat island mitigation strategies. This is further underlined through the operational character of the presented modeling system

Polymeric microcapsules with switchable mechanical properties for self-healing concrete: synthesis, characterisation and proof of concept

Microcapsules, with sodium silicate solution as core, were produced using complex coacervation in a double, oil-in-water-in oil, emulsion system. The shell material was a gelatin–acacia gum crosslinked coacervate and the produced microcapsules had diameters ranging from 300 to 700 μm. The shell material designed with switchable mechanical properties. When it is hydrated exhibits soft and ‘rubbery’ behaviour and, when dried, transitions to a stiff and ‘glassy’ material. The microcapsules survived drying and rehydrating cycles and preserved their structural integrity when exposed to highly alkaline solutions that mimic the pH environment of concrete. Microscopy revealed that the shell thickness of the microcapsules varies across their perimeter from 5 to 20 μm. Thermal analysis showed that the produced microcapsules were very stable up to 190 °C. Proof of concept investigation has demonstrated that the microcapsules successfully survive and function when exposed to a cement-based matrix. Observations showed that the microcapsules survive mixing with cement and rupture successfully upon crack formation releasing the encapsulated sodium silicate solution

A model for European Biogenic Volatile Organic Compound emissions: Software development and first validation

A grid-oriented Biogenic Emission Model (BEM) has been developed to calculate Non-Methane Volatile Organic Compound (NMVOC) emissions from vegetation in high spatial and temporal resolutions. The model allows the emissions calculation for any modeling domain covering Europe on the basis of: 1) the U.S. Geological Survey 1-km resolution land-use database, 2) a land-use specific, monthly isoprene, monoterpene and Other Volatile Organic Compound (OVOC) emission potentials and foliar biomass densities database, 3) temperature and solar radiation data provided by the mesoscale meteorological model MM5. The model was applied for Europe in 30-km spatial resolution for the year 2003. The European total emissions for 2003 consist of 33.0% isoprene, 25.5% monoterpenes and 41.5% OVOC. BEM results are compared with those from the well-documented global Model of Emissions of Gases and Aerosols from Nature (MEGAN). The BEM total emissions compare well with the MEGAN ones. In July 2003, the results of both models agree within a factor of 1.2 for total isoprene emissions and within a factor of 2 for total monoterpene emissions. The comparison of the spatial distributions of the July 2003 isoprene and monoterpene emissions calculated with BEM and MEGAN shows that, in the greater part of the study area, the differences are below the current uncertainty limit for the estimation of spatially-resolved biogenic VOC emissions in Europe being equal to about ±600 kg km-2 month-1. Differences that are above this limit are found mainly in the eastern European countries for isoprene and in the Mediterranean countries for monoterpenes. © 2010 Elsevier Ltd