Investment, uncertainty and irreversibility: evidence from belgian accounting data

This paper investigates the effects of uncertainty on the investment behaviour using firm-level data for a sample of Belgian manufacturing firms. In general, the results confirm former analysis at the aggregate level, stating that uncertainty does matter but that the sign of the effect and its magnitude largely depend on which proxies are used and how they are defined. It is shown that uncertainty has mainly an impact on the decision to invest and to a much lesser extent on the amount invested. Furthermore, the difference between reversible and irreversible investment is crucial. The impact of volatility on irreversible investment is far more larger than on reversible investment. In some cases, the amount of reversible investment will increase with higher volatility.investment, uncertainty, irreversibility

Optimization of constant power control of wind turbines to provide power reserves

In several countries, the wind power penetration increased tremendously in the last years. As the current wind turbines do not participate in frequency control nor reserve provision, this may compromise the proper functioning of the primary control and the provision of power reserves. If no actions are taken, increasing levels of wind penetration may result in serious problems concerning the stable operation of the power system. This paper focuses on the provision of power reserves by wind turbines. For this service, the constant power control strategy is chosen as control strategy, as it gives a constant power output and has the ability to provide power reserves. In this way, the wind turbine behaves more like a conventional power plant. The choice of the power reference value is crucial as it determines whether or not a stable operation of the wind turbine is possible and power reserves can be provided. In this paper, an algorithm is proposed to obtain the range of possible reference values. By means of simulations, the optimal reference value to provide power reserves with a single wind turbine is obtained. Also, reserve provision in a wind farm is investigated. It is shown that the provision of power reserves with wind turbines using the constant power strategy is possible, especially in wind farms

Graphs with few Hamiltonian Cycles

We describe an algorithm for the exhaustive generation of non-isomorphic graphs with a given number $k \ge 0$ of hamiltonian cycles, which is especially efficient for small $k$. Our main findings, combining applications of this algorithm and existing algorithms with new theoretical results, revolve around graphs containing exactly one hamiltonian cycle (1H) or exactly three hamiltonian cycles (3H). Motivated by a classic result of Smith and recent work of Royle, we show that there exist nearly cubic 1H graphs of order $n$ iff $n \ge 18$ is even. This gives the strongest form of a theorem of Entringer and Swart, and sheds light on a question of Fleischner originally settled by Seamone. We prove equivalent formulations of the conjecture of Bondy and Jackson that every planar 1H graph contains two vertices of degree 2, verify it up to order 16, and show that its toric analogue does not hold. We treat Thomassen's conjecture that every hamiltonian graph of minimum degree at least $3$ contains an edge such that both its removal and its contraction yield hamiltonian graphs. We also verify up to order 21 the conjecture of Sheehan that there is no 4-regular 1H graph. Extending work of Schwenk, we describe all orders for which cubic 3H triangle-free graphs exist. We verify up to order $48$ Cantoni's conjecture that every planar cubic 3H graph contains a triangle, and show that there exist infinitely many planar cyclically 4-edge-connected cubic graphs with exactly four hamiltonian cycles, thereby answering a question of Chia and Thomassen. Finally, complementing work of Sheehan on 1H graphs of maximum size, we determine the maximum size of graphs containing exactly one hamiltonian path and give, for every order $n$, the exact number of such graphs on $n$ vertices and of maximum size.Comment: 29 pages; to appear in Mathematics of Computatio

Provision of Ancillary Services with Variable Speed Wind Turbines

In recent years, the amount of wind turbines in the power system has increased tremendously. As the current wind turbines do not participate in the provision of ancillary services such as frequency control and voltage control, this may compromise the proper functioning of the electric power system. However, since the modern wind turbines are equipped with a power-electronic converter, they can assist in the provision of ancillary services. To achieve this, additional control loops have to be added to the wind turbine controller. In this paper, an overview of the different ancillary services is given. The ability to provide them with wind turbines is discussed. Since frequency and voltage control are the most important, these two services are further elaborated. It can be concluded that wind turbines are suited to provide frequency control, especially when they are operated slightly below their maximum power point. They can also assist in voltage control, while operation in the maximum power point is usually possible, so few energy is lost. These are important outcomes, since wind turbines which provide ancillary services can contribute in allowing a higher penetration of renewable energy in the power system without compromising its proper functioning

Impact of speed ripple on the back-Emf waveform of permanent magnet synchronous machines

Permanent Magnet Synchronous Machines (PMSMs) are frequently used in industry due to their high efficiency and favorable dynamic properties. Mechanical limitations and design considerations cause several harmonics in the flux and back-emf of these machines. The back-emf harmonics can be measured on the machine terminals if no stator current is present and the neutral point is accessible. The measured harmonics can then be included in a mathematical model of the machine. This measurement is often done for a constant speed. However, when a speed ripple is present, several new harmonics are introduced in the flux and back-emf. Although the existence of this phenomenon is intuitively clear, it has not yet been investigated in detail and no method exists to calculate these additional harmonics. Nevertheless, the impact of a speed ripple on the back-emf can become significant in some applications. Therefore, in this paper, a mathematical model is presented which allows to accurately calculate the additional back-emf harmonics in the presence of speed ripples. Also, it provides more insight in the interaction between speed ripples and harmonics. The mathematical model is extensively validated by means of simulations and experiments

Municipal driven fiber access network rollout

A citywide fiber to the home network would certainly bring about a lot of advantages for the municipality. Still the operators tend to hold off, partly because of the very high deployment costs and often also because there is a medium high bandwidth network available. This is also the case for the city of Ghent in which an FTTH network is not available and does not seem to be planned in the near future. In this paper we investigate to which degree the municipality can play a role in triggering the rollout of FTTH or less extensive a fiber to the business rollout by initiating the first steps in the deployment. If a city plans to connect its own public buildings first, such as governmental offices and city services and in extension hospitals, schools, museums and other public care or recreational centers, it could already open up some of the advantages of an FTTH network to its citizens. One step further, the city could take a more foresighted deployment scenario into account, in which more ducts and feeders are deployed and some detours are allowed, to enable a faster and cheaper rollout towards businesses and/or residential customers. In this paper we investigate three rollout scenarios with varying focus and amount of foresight: sequential (noncoupled) rollouts; optimized for municipal, public and business areas; fully optimized network for all buildings in the city. The final scenario targets thus a future proof network topology for the whole city. The results of this study shows a much lower final cost when considering a full optimal rollout plan from the start for all buildings in your city. The potential value will also be higher, as the cost for furthermore rolling out towards a business and full FTTH network for inhabitants will be much lower. In addition a geomarketing methodology should be used selecting the most optimal areas focusing first on connecting municipal and other public buildings

M & L Jaargang 24/1

Hilbrand De Vuyst, Jo De Schepper en Kathy Stevens Herbestemmen van Industrieel Erfgoed. [New destinations for industrial heritage.]De slagzin waarmee in 1975 de tentoonstelling werd aangekondigd beloofde een Ontmoeting met de Industriële -Archeologie, toen een primeur voor België en voor de monumentenzorgers-van-het-eerste-uur een ware revelatie. Een duizend industrieel-archeologische monumenten later, nu erfgoed de oude waarden heeft vervangen en herbestemming herontdekt wordt, kijken Jo De Schepper, Hilbrand De Vuyst en Kathy Stevens terug op drie decennia omgaan met aanleg-steigers tot zinkfabrieken. Een discipline waar dynamisme en geduld als moer en bout onherroepelijk op elkaar zijn aangewezen.Bernard Lambert De brouwerij Rodenbach in Roeselare. [The Rodenbach Brewery in Roeselare.]Einde 19de eeuw wellicht diende het traditioneel donker bier uit Roeselare te wijken voor het gelagerd bier met zurige smaak waar Rodenbach nog steeds voor staat. Aanvankelijk een familiebedrijf, nadien vennootschap en heden deel van een groep, bleef de brouwerij onverdroten functioneren in een nauwelijks gewijzigd gebouwenbestand. Maar wat een last leek blijkt nu een troef: selectieve sloping, reconstructie en een nieuw dienstengebouw leidden, aldus Bernard Lambert, tegelijk tot een optimaliseren van de productie en een optimaal onthaal van de bezoekers.Ignace Onraet Een nieuwe functie voor een oude kaasmakerij. [A new Role for an old Cheese Factory in Passendale.]Zoveel is zeker: Passendale staat heden voor méér dan één der meest moorddadige slagvelden van Wereldoorlog I.Opgestart in een wederopgebouwde hoeve, diende het familiale kaasbedrijf nog tijdens het interbellum uit te wijken naar een heus bedrijfsgebouw.Een nieuwe verhuizing en vele jaren later blikt Ignace Onraet terug op de Oude Kaasmakerij, voortaan een museum met hedendaagse ontsluitingsinfrastructuur.Jan Strynckx en Jan Meersman De vuurtorens Hoog Licht en Laag Licht in Knokke-Heist (Heist) en Brugge (Zeebrugge). [The Lighthouses Hoog Licht and Laag Licht (high light and low light) in Knokke-Heist (Heist) and Bruges (Zeebrugge).]Sinds de vroegste 14de-eeuwse vierboete in de duinen bij Heist, bestendigden het Hoog Licht en bijbehorend Laag Licht vanaf 1907 een niet aflatende zorg om veilige scheepvaartroutes langs de Noordzeekust.Een 70 jaar later op hun beurt onaangepast bevonden, deden beide torens nauwelijks nog moeite om de littekens te verhullen van het barre zeeklimaat. Hun jongste rehabilitatie bood Jan Strynckx en Jan Meersman tegelijk de gelegenheid om met enig ontzag op te kijken naar één der allereerste betonconstructies in Vlaanderen.Frank Philippart De Duitse commandopost in het park Den Brandt in Antwerpen. [The German command post in park De Brand in Antwerp.]Op veilige afstand van het krijgsgewoel had het hoofdkwartier van het Duitse 89ste Korps zich vanaf 1942 ingegraven in het Antwerpse park Den Brandt. Her en der verspreide commandobunkers, schuilplaatsen voor manschappen, een lazaret e.a., bleven zomer 1944 als stille maar veelzeggende getuigen achter.Frank Philippart verklaart hun reden van bestaan, organisatie en belang, doch niet zonder aandacht voor initiatieven tot ontsluiting door verknochte vrijwilligers.Summar