Tail approximation for reinsurance portfolios of Gaussian-like risks

We consider two different portfolios of proportional reinsurance of the same pool of risks. This contribution is concerned with Gaussian-like risks, which means that for large values the survival function of such risks is, up to a multiplier, the same as that of a standard Gaussian risk. We establish the tail asymptotic behavior of the total loss of each of the reinsurance portfolios and determine also the relation between randomly scaled Gaussian-like portfolios and unscaled ones. Further we show that jointly two portfolios of Gaussian-like risks exhibit asymptotic independence and their weak tail dependence coefficient is non-negative.Comment: In press, Scandinavian Actuarial Journa

Assessing the Impact of the Iberian Exception on Day-Ahead Prices in Spain : A Difference in Difference and Quantile Regression Approach

The energy crisis of 2021 and 2022 has had severe consequences for Europe. The skyhigh energy prices have reduced economic growth, created inflation, and increased GHG emissions. In an effort to tackle the record high prices, Spain and Portugal have been granted an exception by the EU to implement a cap on the price of gas used for generating electricity. The price cap, best known as the Iberian exception, has sought to limit the impact of volatile gas prices in the electricity market by decoupling the gas price from the electricity price. Within the context of the crisis, it is vital to assess whether the implemented measures have achieved their objectives. This thesis studies the Iberian exception's impact on day-ahead electricity prices in Spain. By estimating a difference in difference model, we find a causal effect of the Iberian exception on day-ahead prices, confirming that the instrument does reduce electricity prices. Furthermore, the results from our quantile regression models show that the gas cap has reduced electricity prices across the price distribution, and reduced price volatility. The results confirm a partial decoupling of the gas price and the electricity price, and the price reducing effect of the instrument is only evident in conjunction with the gas price. While our thesis provides evidence that the Iberian exception has been efficient in reaching its goal, it also highlights multiple adverse effects. The decoupling of gas and electricity prices has led to increased gas generation, alongside increased exports to France, thereby benefitting French consumers. Our analysis show that the Iberian exception can be considered a success in Spain. However, based on our results we do not recommend similar interventions in other European countries, as the adverse effects would exceed the benefits.nhhma

Attachment of APAM to mineral particles in seawater

Polymer injection is used in enhanced oil recovery (EOR) when an oil field ages and the pressure in the reservoir decreases, or for oil fields with heavy oil. By polymer injection, the viscosity of the water injected for pressure support is increased by mixing with a high concentration of a polymer solution. Polymers used in EOR operations are often high molecular weight polyacrylamides, including anionic polyacrylamide (APAM), which may subsequently enter the marine environment with produced water releases. Since seawater (SW) contains mineral particles (MPs) in low concentrations, and polymers like APAM are known to flocculate MPs, we investigated if APAM at different concentrations (0.5–10 mg/L) would attach and flocculate MPs, when these occurred in concentrations relevant for oceanic SW (1 mg/L). Two types of MPs, diatomaceous earth and kaolin, were exposed to fluorescence-tagged APAM (APAM-TAG). A low-energy carousel system with natural seawater (SW) was used for incubation of MPs and APAM-TAG at a temperature relevant for the Norwegian Continental Shelf (13 °C). Attachment to MPs and aggregates of these were analysed by fluorometry and fluorescence microscopy. Particle analyses showed that only minor fractions of the MPs aggregated. When samples were separated in steel filter with a mesh size of 20 μm, APAM-TAG was mainly measured in the flow-through fraction (<20 μm), and the results therefore showed that the polymer mainly remained in the water-phase, or was attached to small particles (<20 μm). For the small fraction of APAM attaching to aggregated MPs, attraction to kaolin was higher than to diatomaceous earth, and fluorescence microscopy analyses confirmed the presence of fluorescent particles at the higher APAM concentrations. MPs at concentrations relevant for oceanic SW are therefore not expected to significantly contribute to sedimentation of APAM dissolved in the water column.publishedVersio

The Intrinsic Fundamental Group of a Linear Category

We provide an intrinsic definition of the fundamental group of a linear category over a ring as the automorphism group of the fibre functor on Galois coverings. If the universal covering exists, we prove that this group is isomorphic to the Galois group of the universal covering. The grading deduced from a Galois covering enables us to describe the canonical monomorphism from its automorphism group to the first Hochschild-Mitchell cohomology vector space.Comment: Final version, to appear in Algebras and Representation Theor

Accumulation and toxicity of monoaromatic petroleum hydrocarbons in early life stages of cod and haddock

A multitude of recent studies have documented the detrimental effects of crude oil exposure on early life stages of fish, including larvae and embryos. While polycyclic aromatic hydrocarbons (PAHs), particularly alkyl PAHs, are often considered the main cause of observed toxic effects, other crude oil derived organic compounds are usually overlooked. In the current study, comprehensive two-dimensional gas chromatography coupled to mass spectrometry was applied to investigate the body burden of a wide range of petrogenic compounds in Atlantic haddock (Melanogrammus aeglefinus) and cod (Gadus morhua) embryos that had been exposed to sublethal doses of dispersed crude oil. Several groups of alkylated monoaromatic compounds (e.g. alkyl tetralins, indanes and alkyl benzenes), as well as highly alkylated PAHs, were found to accumulate in the fish embryos upon crude oil exposure. To investigate the toxicity of the monoaromatic compounds, two models (1-isopropyl-4-methyltetralin and 1-isopropyl-4-methylindane) were synthesized and shown to bioaccumulate and cause delayed hatching in developing embryos. Minor developmental effects, including craniofacial and jaw deformations and pericardial edemas, were also observed at the highest studied concentrations of the alkylindane.acceptedVersio

Dislocations in Grain Boundary Regions: The Origin of Heterogeneous Microstrains in Nanocrystalline Materials

Nanocrystalline materials reveal excellent mechanical properties but the mechanism by which they deform is still debated. X-ray line broadening indicates the presence of large heterogeneous strains even when the average grain size is smaller than 10 nm. Although the primary sources of heterogeneous strains are dislocations, their direct observation in nanocrystalline materials is challenging. In order to identify the source of heterogeneous strains in nanocrystalline materials, we prepared Pd-10 pct Au specimens by inert gas condensation and applied high-pressure torsion (HPT) up to γ ≅ 21. High-resolution transmission electron microscopy (HRTEM) and molecular dynamic (MD) simulations are used to investigate the dislocation structure in the grain interiors and in the grain boundary (GB) regions in the as-prepared and HPT-deformed specimens. Our results show that most of the GBs contain lattice dislocations with high densities. The average dislocation densities determined by HRTEM and MD simulation are in good correlation with the values provided by X-ray line profile analysis. Strain distribution determined by MD simulation is shown to follow the Krivoglaz–Wilkens strain function of dislocations. Experiments, MD simulations, and theoretical analysis all prove that the sources of strain broadening in X-ray diffraction of nanocrystalline materials are lattice dislocations in the GB region. The results are discussed in terms of misfit dislocations emanating in the GB regions reducing elastic strain compatibility. The results provide fundamental new insight for understanding the role of GBs in plastic deformation in both nanograin and coarse grain materials of any grain size