The dual variational principle and equilibria for a beam resting on a discontinuous nonlinear elastic foundation

In this paper we study the existence of solutions of the nonlinear fourth-order equation [1] under the asymmetric nonlinear boundary conditions [2], [3] where g is a strictly monotonous function that may have some “one-sided” discontinuities and f and h exhibit some singularities.info:eu-repo/semantics/publishedVersio

Extremal solutions for third-order nonlinear problems with upper and lower solutions in reversed order

This paper deals with the existence of extremal solutions for the third-order nonlinear boundary value problem ....info:eu-repo/semantics/publishedVersio

Homoclinic and periodic solutions for a class of second order differential equations

In this paper we are concerned with the existence of positive homoclinic solutions of the second order equation …info:eu-repo/semantics/publishedVersio

On the solvability of a boundary value problem for a fourth-order ordinary differential equation

We study the existence and multiplicity of nontrivial periodic solutions for a semilinear fourth-order ordinary differential equation arising in the study of spatial patterns for bistable systems. Variational tools such as the Brezis–Nirenberg theorem and Clark theorem are used in the proofs of the main results.info:eu-repo/semantics/publishedVersio

SOLVABILITY OF HIGHER-ORDER BVPS IN THE HALF-LINE WITH UNBOUNDED NONLINEARITIES

This work presents suficient conditions for the existence of unbounded solutions of a Sturm-Liouville type boundary value problem on the half-line. One-sided Nagumo condition plays a special role because it allows an asymmetric unbounded behavior on the nonlinearity. The arguments are based on fixed point theory and lower and upper solutions method. An example is given to show the applicability of our results

Occurrence of polycyclic aromatic hydrocarbons, microplastics and biofilms in Alqueva surface water at touristic spots

Freshwater pollution is a huge concern. A study aiming to evaluate physico chemical characteristics, microbiota, occurrence of two groups of persistent environmental pollutants with similar chemical properties polycyclic aromatic hydrocarbons PAHs and microplastics MPs in Alqueva s surface water was performed during 2021. Water samples were collected at three spots related to touristic activities two beaches and one marina during the Winter, Spring, Summer and Autumn seasons. In addition, the presence of biofilms on plastic and natural materials stone, wood vegetal materials were assessed and compared. Water quality based on physicochemical parameters was acceptable with a low eutrophication level. PAHs concentration levels were lower than the standard limits established for surface waters by international organizations. However, carcinogenic compounds were detected in two sampling locations, which can pose a problem for aquatic ecosystems. PAHs profiles showed significant differences when comparing the dry seasons with the rainy seasons, with a higher number of different compounds detected in Spring. Low molecular weigh compounds, usually associated with the atmospheric deposition and petroleum contamination, were more prevalent. MPs were detected in all samples except one during the Winter season. The polymers detected were poly methyl 2 methylpropenoate , polystyrene, polyethylene terephthalate, polyamide, polypropylene, styrene butadiene, polyvinyl chloride and low high density polyethylene with the last being the most frequent. Biofilms were more often detected on plastics than on natural materials. In addition, biofilms detected on plastics were more complex with higher microbial diversity e.g., bacteria, fungi yeast and phytoplancton organisms and richer in extrapolymeric material. Based on morphological analysis a good agreement between microbiota and microorganism present in the biofilms was found. Among microbiota were identified microorganisms previously linked to plastic and PAHs detoxification suggesting the need for further studies to evaluate the viability of using biofilms as part of a green bioremediation strategy to mitigate water pollutio

Issues of Scale in Nested Integrated Assessment Models

Integrated assessment models have been used to explore cost effective abatement strategies in connection with negotiations on the Gothenburg protocol under the UN/ECE Convention on Long Range Transboundary Air Pollution (CLRTAP). A variety of spatial and temporal issues must be addressed in order to model the multi-scalar processes involved and develop nested Integrated Assessment Models (n-IAM) useful both for further protocol negotiations and to address inter-relationships between local air quality, transboundary air pollution and climate change. We summarise the generic framework, highlighting the spatial characteristics of its' application to UK and European contexts, and identify the specific variations of the constituent models and data at each resolution. Encompassing NH 3 , SO 2 , NO X , particulates, O 3 and VOCs, it is clear a n-IAM must capture dynamics both beyond and through the current scales implemented by the UKIAM and ASAM. Ammonia abatement becomes significant at the micro scale using non-technical measures and buffer zones, roadside NO 2 is important at the urban scale, and the dynamics of O 3 stretch from the urban scale to the hemispheric level, affecting the fates of VOCs and NO X . Timescales implicit in dispersion models and empirical data, together with multi-scalar effects and policy scenarios must be mapped, and methodological approaches to critical loads and ecosystem recovery must be captured. At the UK National Focal Centre for Integrated Assessment Modelling work is ongoing linking the European scale ASAM and the national scale UKIAM, and progress is being made in linking these to global and urban scale integrated assessment models