Operational research and simulation methods for autonomous ride-sourcing

Ride-sourcing platforms provide on-demand shared transport services by solving decision problems related to ride-matching and pricing. The anticipated commercialisation of autonomous vehicles could transform these platforms to fleet operators and broaden their decision-making by introducing problems such as fleet sizing and empty vehicle redistribution. These problems have been frequently represented in research using aggregated mathematical programs, and alternative practises such as agent-based models. In this context, this study is set at the intersection between operational research and simulation methods to solve the multitude of autonomous ride-sourcing problems. The study begins by providing a framework for building bespoke agent-based models for ride-sourcing fleets, derived from the principles of agent-based modelling theory, which is used to tackle the non-linear problem of minimum fleet size. The minimum fleet size problem is tackled by investigating the relationship of system parameters based on queuing theory principles and by deriving and validating a novel model for pickup wait times. Simulating the fleet function in different urban areas shows that ride-sourcing fleets operate queues with zero assignment times above the critical fleet size. The results also highlight that pickup wait times have a pivotal role in estimating the minimum fleet size in ride-sourcing operations, with agent-based modelling being a more reliable estimation method. The focus is then shifted to empty vehicle redistribution, where the omission of market structure and underlying customer acumen, compromises the effectiveness of existing models. As a solution, the vehicle redistribution problem is formulated as a non-linear convex minimum cost flow problem that accounts for the relationship of supply and demand of rides by assuming a customer discrete choice model and a market structure. An edge splitting algorithm is then introduced to solve a transformed convex minimum cost flow problem for vehicle redistribution. Results of simulated tests show that the redistribution algorithm can significantly decrease wait times and increase profits with a moderate increase in vehicle mileage. The study is concluded by considering the operational time-horizon decision problems of ride-matching and pricing at periods of peak travel demand. Combinatorial double auctions have been identified as a suitable alternative to surge pricing in research, as they maximise social welfare by relying on stated customer and driver valuations. However, a shortcoming of current models is the exclusion of trip detour effects in pricing estimates. The study formulates a shared-ride assignment and pricing algorithm using combinatorial double auctions to resolve the above problem. The model is reduced to the maximum weighted independent set problem, which is APX-hard. Therefore, a fast local search heuristic is proposed, producing solutions within 10\% of the exact approach for practical implementations.Open Acces

Stochastic dynamic programming methods for the portfolio selection problem

In this thesis, we study the portfolio selection problem with multiple risky assets, linear transaction costs and a risk measure in a multi-period setting. In particular, we formulate the multi-period portfolio selection problem as a dynamic program and to solve it we construct approximate dynamic programming (ADP) algorithms, where we include Conditional-Value-at-Risk (CVaR) as a measure of risk, for different separable functional approximations of the value functions. We begin with the simple linear approximation which does not capture the nature of the portfolio selection problem since it ignores risk and leads to portfolios of only one asset. To improve it, we impose upper bound constraints on the holdings of the assets and we notice that we have more diversified portfolios. Then, we implement a piecewise linear approximation, for which we construct an update rule for the slopes of the approximate value functions that preserves concavity as well as the number of slopes. Unlike the simple linear approximation, in the piecewise linear approximation we notice that risk affects the composition of the selected portfolios. Further, unlike the linear approximation with upper bounds, here wealth flows naturally from one asset to another leading to diversified portfolios without us needing to impose any additional constraints on how much we can hold in each asset. For comparison, we consider existing portfolio selection methods, both myopic ones such as the equally weighted and a single-period portfolio models, and multi-period ones such as multistage stochastic programming. We perform extensive simulations using real-world equity data to evaluate the performance of all methods and compare all methods to a market Index. Computational results show that the piecewise linear ADP algorithm significantly outperforms the other methods as well as the market and runs in reasonable computational times. Comparative results of all methods are provided and some interesting conclusions are drawn especially when it comes to comparing the piecewise linear ADP algorithms with multistage stochastic programming

The role of the creative industries in regional development during the economic cycle: case of the Region of Epirus, Greece

In the era of extraordinary changes and globalisation, many researchers acknowledge that creativity and innovation are now driving the new economy. Countries and regions that embrace creativity generate higher revenue, more jobs and provide greater stability. The objective of this paper is to analyse the role of cultural and creative industries in regional development during the economic cycle. In this context, we map the current situation and needs for development of the cultural and creative industries using the case of the Region of Epirus in Greece. This research is based on literature reviews, interviews, statistical data and commercial register’s data. The data was collected between September 2014 and March 2015. The database is built according to the NACE codes used to describe the cultural and creative industries. In the paper, we analyse the trend in the development of cultural and creative industries during the last decades with emphasis on the years of the last economic crisis. We identify main opportunities and challenges for its development, necessary conditions, main constraints and we try to outline main directions for future sector’s growth taking into consideration the assumption that the development of this sector maybe the engine of the future region’s growth

Decision making using multicriteria analysis: A case study of decision modeling career in education

The aim of this paper is to offer an applicable evaluation framework relating to the right choice of one’s profession via his/her studies. The first part of the paper consists of the basic principles of Multicriteria Decision Making. To begin with, the paper initially focuses on the Macbeth Method. This helps to provide a perspective for procedural types of decisions in which various qualitative and quantitative aspects are incorporated. In the second part of the paper, the above-mentioned multicriteria method is applied to a “real-world” case concerning a specific case of a student, Eva. For this specific study, it is concluded that the factors of greatest importance that lead to choosing the University Eva finally chose, were four: the cost of undergraduate studies, the reputation-status of the University, its logistics and infrastructure and its interconnections with other Universities and other Academic Institutions

Minimum wage and unemployment in greek labour market: A descriptive analysis

The purpose of this paper is to investigate the relationship between the minimum wage level and the rates of unemployment and employment in the Greek labour market. More specifically, this study analyses the evolution of the minimum wage during the period 2000-2013 and also whether these changes have really affected the unemployment and employment rates or not. The main conclusion of our study supports several other studies conclusions suggesting that the level of minimum wage in Greece did not really affect the unemployment and employment rates. The views of economists on effect of the establishing of minimum wages are quite contradictory. The evaluation of relationship between labour market and minimum wage rate is either positive or negative or even not related at all, depending on the assumptions about characteristics of labour market

The evolution of alternative forms of tourism: a theoretical background

Between the 1970s and early 1980s new forms of tourism emerged in developing countries as an alternative solution to the “undesired” type of tourism “the mass tourism” or “the conventional/commercial tourism” or “the traditional tourism”. These forms of tourism appearing in different names and various models, served a more sensitive approach giving priority to natural and cultural resources at the front line of planning and development. The purpose of this paper is to describe the theoretical background of alternative tourism in which origins and main definitions are presented followed by an analysis of the complexity of classifying the alternative forms of tourism. Three of the many forms, seemed to be the core of alternative tourism, are distinguished and analyzed. The ecotourism, the cultural tourism and the creative tourism. Ecotourism in recent years, encloses many tourist forms focused on natural environment. Although these forms are closely related to ecotourism need to be distinguished from it as ecotourism presents many dimensions. In the concept of alternative tourism, the dynamic growth of cultural tourism can be explained by the fast growth of demand for trips to various cultural attractions and amenities. A rise in interest of tourists both to distant cultures and to the local heritage occurred through the increase of educated people around the world and the globalization. Moreover, technology supported this growth. The cultural tourist, from consumer is transforming to producer of the cultural products and experiences. As culture tourist become more interactive and creative, the cultural tourism need to be repositioned and to become more “creative”. In “creative tourism” there is a co-creation of creative experiences between visitors and hosts, usually expressed through the creation of networks, itineraries, courses and events. Finally, the paper ends with a brief mention on the current trends in alternative tourism and the concluding remarks

Evaluating Centering for Information Ordering Using Corpora

In this article we discuss several metrics of coherence defined using centering theory and investigate the usefulness of such metrics for information ordering in automatic text generation. We estimate empirically which is the most promising metric and how useful this metric is using a general methodology applied on several corpora. Our main result is that the simplest metric (which relies exclusively on NOCB transitions) sets a robust baseline that cannot be outperformed by other metrics which make use of additional centering-based features. This baseline can be used for the development of both text-to-text and concept-to-text generation systems. </jats:p

Evaluation of leasing as a method of funding Investments in greek agribusiness sector

Funding for acquiring assets in Greek agribusiness sector is very common and supports Greek agribusiness SME's production. Purpose of this study is evaluation of leasing as a method of financing in order to acquire assets used directly in the production process of a business of secondary Greek agribusiness sector or even vertically integrated business. Thus, research was held in December of 2012, collecting proper data from Greek banking sector and considering Tax Legislation. Selection decision of practices financing in the event of such an investment should be made after taking into consideration several factors. Proper financial evaluation of future investment is necessary, while it's too necessary to be compared the financing choices that are given in Greece. Considering Tax Legislation, Banking Practices, and Law on Leasing, financing methods were compared in reference period. Avoiding generalizations, typical examples are given, showing that leasing preceded against borrowing, considering conditions prevailing in Greece at the time. But decision making for selection of financing method is affected by factors, which may lead to either correct or incorrect conclusions for firm's interests, if evaluation is not correct or there are personal interests of decision-makers in the administration. Consequently, incentives to use leasing for financing a business can be a lot, but quite important are ownership structure, nature of investment opportunities, business risk and tax status.(original abstract

Market liberalization in a Small Open Economy and Its Impact on employment characteristics

Market liberalization affects overall employment. The institutional liberalization of specific industry took place quickly at European and global level, aimed at upgrading the role of the market and establishing a competitive environment. Two opposing trends were noted in the area of employment: job losses in public enterprises and employment Growth in new private enterprises operating in new subsectors. A change in ownership relations, via privatization and the entry of private undertakings in the market, causes important differentiations in size and characteristics of employment