292 research outputs found

    Phytosociological study of Hirschfeldia incana (L.) Lagraze-Fossat (Cruciferae) communities in mainland Greece

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    Using numerical analysis, the phytosociological study of Hirschfeldia incana communities in mainland Greece allowed their classification into the Rapistro rugosi-Hirschfeldietum incanae ass. nov., a new subnitrophilous association of the Hordeion leporini alliance. Three subassociations were distinguished (anthemidetosum incrassatae, hedypnoidetosum creticae and cardarietosum drabae), the distribution of which seems to depend on latitudinal alteration of rainfall. The new association has its optimum growth in habitats with moderate human influence, specifically in abandoned cultivations and wastelands. With respect to its floristic composition, the Rapistro rugosi-Hirschfeldietum incanae is close to anthropogenic vegetation with a high degree of naturalness, particularly to the therophytic, subnitrophilous vegetation of the Thero-Brometalia (Stellarietea mediae) and the perennial, subnitrophilous vegetation of Carthametalia lanati (Artemisietea vulgaris)

    Investment decision making under uncertainty: the impact of risk aversion, operational flexibility, and competition

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    Traditional real options analysis addresses investment under uncertainty assuming a risk-neutral decision maker and complete markets. In reality, however, decision makers are often risk averse and markets are incomplete. Additionally, capital projects are seldom now-or-never investments and can be abandoned, suspended, and resumed at any time. In this thesis, we develop a utility-based framework in order to examine the impact of operational flexibility, via suspension and resumption options, on optimal investment policies and option values. Assuming a risk-averse decision maker with perpetual options to suspend and resume a project costlessly, we confirm that risk aversion lowers the probability of investment and demonstrate how this effect can be mitigated by incorporating operational flexibility. Also, we illustrate how increased risk aversion may facilitate the abandonment of a project while delaying its temporary suspension prior to permanent resumption. Besides timing, a firm may have the freedom to scale the investment’s installed capacity. We extend the traditional real options approach to investment under uncertainty with discretion over capacity by allowing for a constant relative risk aversion utility function and operational flexibility in the form of suspension and resumption options. We find that, with the option to delay investment, increased risk aversion facilitates investment and decreases the required investment threshold price by reducing the amount of installed capacity. We explore strategic aspects of decision making under uncertainty by examining how duopolistic competition affects the entry decisions of risk-averse investors. Depending on the discrepancy between the market share of the leader and the follower, greater uncertainty may increase or decrease the discrepancy in the non-pre-emptive leader’s relative value. Furthermore, risk aversion does not affect the loss in the value of the leader for the pre-emptive duopoly setting, but it makes the loss in value relatively less for the leader in a non-preemptive duopoly setting

    The impact of temperature on wave interaction with damage in composite structures

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    The increased use of composite materials in modern aerospace and automotive structures, and the broad range of launch vehicles’ operating temperature imply a great temperature range for which the structures has to be frequently and thoroughly inspected. A thermal mechanical analysis is used to experimentally measure the temperature-dependent mechanical properties of a composite layered panel in the range of −100 ℃ to 150 ℃. A hybrid wave finite element/finite element computational scheme is developed to calculate the temperature-dependent wave propagation and interaction properties of a system of two structural waveguides connected through a coupling joint. Calculations are made using the measured thermomechanical properties. Temperature-dependent wave propagation constants of each structural waveguide are obtained by the wave finite element approach and then coupled to the fully finite element described coupling joint, on which damage is modelled, in order to calculate the scattering magnitudes of the waves interaction with damage across the coupling joint. The significance of the panel’s glass transition range on the measured and calculated properties is emphasised. Numerical results are presented as illustration of the work
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