Strike point splitting induced by the application of magnetic perturbations on MAST

Divertor strike point splitting induced by resonant magnetic perturbations (RMPs) has been observed on MAST for a variety of RMP configurations in a plasma scenario with Ip=750kA where those configurations all have similar resonant components. Complementary measurements have been obtained with divertor Langmuir probes and an infrared camera. Clear splitting consistently appears in this scenario only in the even configuration of the perturbation coils, similarly to the density pump-out. These results present a challenge for models of plasma response to RMPs.Comment: 9 pages, 4 figures, submitted to the proceedings of the 20th Conference on Plasma Surface Interactions, to be published in the Journal of Nuclear Material

The genetic control of ovariole number in Sitophilus oryzae L (Coleoptera, Curculionidae) is temperature sensitive

The influence of genetical and epigenetical factors on the determinism of the ovariole number was studied in Sitophilus oryzae. This weevil normally possesses 4 ovarioles with apical bacteriomes harbouring symbiotes. By selecting females with a reduced number of ovarioles, the genetic control of this trait was demonstrated with regard to the easy selection of this character and its similar transmission to the progeny by females and males. Several genes could be implicated and a weak maternal effect cannot be rejected. The character is temperature sensitive: at 30°C, abnormal females with 2 or 3 ovarioles prevail, and conversely, normal females appear at 20°C. The reduction of the number of ovarioles is correlated with a decrease in fitness (reduced progeny and lighter body weight of females). Only ovary formation seems to be affected, because a higher progeny per ovariole in abnormal females can be indicative of a normal yolk production in the fat body. Counting bacteria in ovaries shows that the regulation of symbiote number per female occurs at the ovariole itself and not within the whole insect.L’influence de facteurs génétiques et épigénétiques sur le déterminisme du nombre des ovarioles a été étudiée chez Sitophilus oryzae. Ce charançon possède normalement 4 ovarioles terminés par un bactériome apical hébergeant des symbiotes. En sélectionnant les femelles ayant un nombre réduit d’ovarioles, nous avons pu démontrer le contrôle génétique de ce caractère : sélection aisée et transmission à la descendance aussi bien par les femelles que par les mâles. Plusieurs gènes pourraient être impliqués et un léger effet maternel se manifeste par ailleurs. Le caractère est thermo-sensible : à 30°C, les femelles anormales à 2 ou 3 ovarioles sont majoritaires, alors que, à 20°C, le phénotype normal prédomine. La réduction du nombre des ovarioles est corrélée avec une diminution de la fitness (descendance réduite et poids corporel des femelles plus faible). Seule la formation de l’ovaire semble être affectée, car une fertilité plus grande par ovariole chez les femelles anormales indiquerait une production normale de vitellus dans le corps adipeux. Les dénombrements de bactéries dans les ovaires ont montré que la régulation du nombre de symbiotes par femelle intervient au niveau de l’ovariole lui-même, plutôt qu’au niveau de l’insecte entier

Observation of lobes near the X-point in resonant magnetic perturbation experiments on MAST

The application of non-axisymmetric resonant magnetic perturbations (RMPs) with a toroidal mode number n=6 in the MAST tokamak produces a significant reduction in plasma energy loss associated with type-I Edge Localized Modes (ELMs), the first such observation with n>3. During the ELM mitigated stage clear lobe structures are observed in visible-light imaging of the X-point region. These lobes or manifold structures, that were predicted previously, have been observed for the first time in a range of discharges and their appearance is correlated with the effect of RMPs on the plasma i.e. they only appear above a threshold when a density pump out is observed or when the ELM frequency is increased. They appear to be correlated with the RMPs penetrating the plasma and may be important in explaining why the ELM frequency increases. The number and location of the structures observed can be well described using vacuum modelling. Differences in radial extent and poloidal width from vacuum modelling are likely to be due to a combination of transport effects and plasma screening.Comment: 15 pages, 5 figure

Prospect theory: An application to European option pricing

Empirical studies on quoted options highlight deviations from the theoretical model of Black and Scholes; this is due to different causes, such as assumptions regarding the price dynamics, markets frictions and investors’ attitude toward risk. In this contribution, we focus on this latter issue and study how to value European options within the continuous cumulative prospect theory. According to prospect theory, individuals do not always take their decisions consistently with the maximization of expected utility. Decision makers have biased probability estimates; they tend to underweight high probabilities and overweight low probabilities. Risk attitude, loss aversion and subjective probabilities are described by two functions: a value function and a weighting function, respectively. In our analysis, we use alternative probability weighting functions. We consider the pricing problem both from the writer’s and holder’s perspective, obtaining an interval for the prices of call and put options

An efficient binomial approach to the pricing of options on stocks with cash dividends

In this contribution, we consider options written on stocks which pay cash dividends. Dividend payments have an effect on the value of options: high dividends imply lower call premia and higher put premia. While exact solutions to problems of evaluating both European and American call options and European put options are available in the literature, for American-style put options early exercise may be optimal at any time prior to expiration even in the absence of dividends. In this case numerical techniques, such as lattice approaches, are required. Discrete dividends produce a shift in the tree; as a result, the tree is no longer reconnecting beyond any dividend date. Methods based on non-recombining trees give consistent results, but they are computationally expensive. We analyze binomial algorithms and performed some empirical experiments

Opzioni su titoli che pagano dividendi: proprietà e tecniche di valutazione

Nell'affrontare il problema della valutazione di opzioni emesse su titoli azionari si deve tenere in considerazione la presenza del pagamento di uno o piµu dividendi. Tale problema risulta particolarmente importante anche per le negoziazioni del mercato italiano, soprattutto in seguito all'emissione dei contratti di opzione a lunga scadenza da parte di Borsa Italiana SpA. Solo recentemente µe stata proposta in letteratura una soluzione analitica che puµo essere utilizzata nel caso di opzioni call europee e americane e di opzioni put europee. Per le opzioni put americane si deve ricorrere a metodi di valutazione di tipo numerico, primo fra tutti il metodo degli alberi binomiali che nelle sperimentazioni eseguite ha fornito ottime approssimazioni dei valori analitici. L'impiego del metodo binomiale richiede, peraltro, qualche accorgimento in quanto dopo lo stacco di un dividendo l'albero non ricombina dando luogo a una crescita non lineare nel numero dei nodi nei vari stadi. In questo contributo verranno analizzati alcuni modelli di valutazione di opzioni emesse su attività che pagano dividendi; particolare attenzione sarµa rivolta al modello proposto da Haug et al. (2003) e ad alcuni metodi binomiali. Infine, verranno presentati alcuni esempi numerici

Implied volatilities of American options with cash dividends: an application to Italian Derivatives Market (IDEM)

In this contribution, we study options on assets which pay discrete dividends. We focus on American options, as when dealing with equities, most traded options are of American-type. In particular, we analyze implied volatilities in the model proposed by Haug et al. [12] and in the binomial model, with an application to the Italian Derivatives Market

Electron acceleration in a JET disruption simulation

Runaways are suprathermal electrons having sufficiently high energy to be continuously accelerated up to tens of MeV by a driving electric field [1]. Highly energetic runaway electron (RE) beams capable of damaging the tokamak first wall can be observed after a plasma disruption [2]. Therefore, it is of primary importance to fully understand their generation mechanisms in order to design mitigation systems able to guarantee safe tokamak operations. In a previous work, [3], a test particle tracker was introduced in the JOREK 3D non-linear MHD code and used for studying the electron confinement during a simulated JET-like disruption. It was found in [3] that relativistic electrons are not completely deconfined by the stochastic magnetic field taking place during the disruption thermal quench (TQ). This is due to the reformation of closed magnetic surfaces at the beginning of the current quench (CQ). This result was obtained neglecting the inductive electric field in order to avoid the unrealistic particle acceleration which otherwise would have happened due to the absence of collision effects. The present paper extends [3] analysing test electron dynamics in the same simulated JET-like disruption using the complete electric field. For doing so, a simplified collision model is introduced in the particle tracker guiding center equations. We show that electrons at thermal energies can become RE during or promptly after the TQ due to a combination of three phenomena: a first REs acceleration during the TQ due to the presence of a complex MHD-induced electric field, particle reconfinement caused by the fast reformation of closed magnetic surfaces after the TQ and a secondary acceleration induced by the CQ electric field

Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents

The dynamics of large scale plasma instabilities can strongly be influenced by the mutual interaction with currents flowing in conducting vessel structures. Especially eddy currents caused by time-varying magnetic perturbations and halo currents flowing directly from the plasma into the walls are important. The relevance of a resistive wall model is directly evident for Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However, also the linear and non-linear properties of most other large-scale instabilities may be influenced significantly by the interaction with currents in conducting structures near the plasma. The understanding of halo currents arising during disruptions and VDEs, which are a serious concern for ITER as they may lead to strong asymmetric forces on vessel structures, could also benefit strongly from these non-linear modeling capabilities. Modeling the plasma dynamics and its interaction with wall currents requires solving the magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry consistently coupled with a model for the vacuum region and the resistive conducting structures. With this in mind, the non-linear finite element MHD code JOREK has been coupled with the resistive wall code STARWALL, which allows to include the effects of eddy currents in 3D conducting structures in non-linear MHD simulations. This article summarizes the capabilities of the coupled JOREK-STARWALL system and presents benchmark results as well as first applications to non-linear simulations of RWMs, VDEs, disruptions triggered by massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives for extending the model to halo currents are described.Comment: Proceeding paper for Theory of Fusion Plasmas (Joint Varenna-Lausanne International Workshop), Varenna, Italy (September 1-5, 2014); accepted for publication in: to Journal of Physics: Conference Serie