This thesis consists of four essays, covering four different topics. The first essay investigates the relationship between inter-firm labor mobility and regional productivity growth. Previous studies have shown that density is positively correlated with growth. I claim that it is not density in itself, but rather the attributes associated with it that drives economic growth. One such attribute is the increased possibility for labor mobility and knowledge diffusion that follows when firms and individuals locate in close proximity to each other. This hypothesis is tested using density as an instrument for labor mobility. The result shows that labor mobility increases regional growth rates. The second essay examines the relationship between agglomeration economies and relative wage costs in influencing location of multinational corporations. An inflow of firms to certain regions and industries is likely to increase demand for labor. If mobility of labor is low increased costs can be expected to deter additional inflows of firms, albeit agglomeration economies may compensate for higher wages. The empirical analysis finds that FDI has become increasingly sensitive to differences in wage costs across industrialized countries, but also that agglomeration economies related to knowledge externalities positively influences higher costs. The third essay looks at the impact of FDI on home country investments. Previous research has been inconclusive as regards the effects on domestic investments. In this article, we show that this inconclusiveness can be explained at a disaggregated level as a function of the way industries are organized. We argue that a complementary relationship can be expected to prevail in vertically integrated industries, whereas a substitutionary relationship can be expected in horizontally organized production. The empirical analysis confirms a significant difference between the two categories of industry as regards the impact of outward FDI on domestic investment. The fourth, and final, essay of this thesis analyses how increased R&D expenditures and market size influence the distribution of comparative advantage. Previous studies report ambiguous results and also refer to periods when markets were much more segmented and production factors less mobile. The empirical analysis comprises 19 OECD-countries and spans the period 1981 to 1999. It is shown how an increase in R&D-expenditures by one percentage point implies a three-percentage point increase in high-technology exports, whereas market size fails to attain significance. In addition, institutional factors influence the dynamics of comparative advantage.

Σκοπός της εργασίας αυτής είναι η τεχνοοικονομική σύγκριση των δυο αρχιτεκτονικών, ADSL και οπτικών δικτύων και η εξαγωγή συμπερασμάτων για τα σχετικά κόστη και δυνατότητες που αφορούν τις αρχιτεκτονικές αυτές. Οι τελευταίες τεχνολογίες καθώς και οι αυξημένες απαιτήσεις σε χωρητικότητα και ταχύτητα, οδήγησαν σε λύσεις που συνδυάζουν διαφορετικά είδη τεχνολογιών, κυρίως υβριδικές τεχνολογίες, που προσφέρουν τεράστιες δυνατότητες με περιορισμένο κόστος ανά bit. Για τις απαιτήσεις της εποχής η τεχνολογία FTTx (Fiber To The x) και οι διάφορες παραλλαγές της, αποτελούν πολύ υποσχόμενες τεχνολογίες πρόσβασης που προσφέρονται ως βάσεις για τη δημιουργία μεγάλων και αξιόπιστων δικτύων που μπορούν να εξυπηρετήσουν μεγάλο αριθμό πελατών. Ωστόσο, οι πλέον υποσχόμενες τεχνολογίες είναι οι τεχνολογίες FTTx, οι οποίες υλοποιούνται αποκλειστικά με οπτικές ίνες. Όπως θα δούμε σε ήδη υπαρκτά δίκτυα, τα δίκτυα αναμορφώνονται και εξελίσσονται από παλαιότερες τεχνολογίες, αναβαθμίζονται σταδιακά, χωρίς να σημαίνει ότι οι παλαιότερη τεχνολογία μένει σε αχρηστία αμέσως μετά τις αναβαθμίσεις. Γίνονται αναφορές σε περιπτωσιολογικές μελέτες που πρέπει να γίνουν ώστε να είναι όσο το δυνατό πιο εύχρηστο και προσπελάσιμο ένα δίκτυο ενός μητροπολιτικού κέντρου. Η εργασία αυτή ολοκληρώνεται με συναρτήσεις κόστους, για την ολοκλήρωση ενός τέτοιου δικτύου, που εξάγονται υλοποιούνται με χρήση του εργαλείου Matlab. / The primary objective of this work is the techno economic comparison between ADSL and optic fiber networks, the export of conclusions on the relative costs and the capabilities that concern these architectures. The secondary objective is understanding the process of constructing an optical fiber nework. The latest technologic improvements as well as the increased requirements in speed and capacity, lead to solutions that combine different technologies types mainly hybrid technologies, which offer enormous possibilities with limited cost per bit. For present day requirements FTTx (Fiber the The x) can serve a large share of customers as base for creating bigger and more reliable networks. However, this promising technology is exclusively for only optical fiber based FTTx. As it will be shown through examples of already founded networks, they can be reformed and evolved from older technologies, can be progressively upgraded to mach the bandwidth and user capacity of future networks Case studies are performed in order to determine the best case of optical network that should satisfy consumers and telecommuters. This thesis is completed with the research of total cost functions which are imported in Matlab. The cost reports are exported and compared in the form of graphic cost charts.