Effects of bottom trawling on fish foraging and feeding

The effects of bottom trawling on benthic invertebrates include reductions of biomass, diversity and body size. These changes may negatively affect prey availability for demersal fishes, potentially leading to reduced food intake, body condition and yield of fishes in chronically trawled areas. Here, the effect of trawling on the prey availability and diet of two commercially important flatfish species, plaice (Pleuronectes platessa) and dab (Limanda limanda), was investigated over a trawling intensity gradient in the Irish Sea. Previous work in this area has shown that trawling negatively affects the condition of plaice but not of dab. This study showed that reductions in local prey availability did not result in reduced feeding of fish. As trawling frequency increased, both fish and prey biomass declined, such that the ratio of fish to prey remained unchanged. Consequently, even at frequently trawled sites with low prey biomass, both plaice and dab maintained constant levels of stomach fullness and gut energy contents. However, dietary shifts in plaice towards energy-poor prey items were evident when prey species were analysed individually. This, together with a potential decrease in foraging efficiency due to low prey densities, was seen as the most plausible cause for the reduced body condition observed. Understanding the relationship between trawling, benthic impacts, fish foraging and resultant body condition is an important step in designing successful mitigation measures for future management strategies in bottom trawl fisheries

The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter $Q$ is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low $Q$, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.Comment: 21 pages, 1 figur

Sustaining family forests in rural landscapes: Rationale, challenges, and an illustration from Oregon, USA

Family forests are critical components of rural landscapes, societies and economies. In Oregon, where nonindustrial private forests comprise only 16% of the forestland base, the ecological, social and economic impact of this ownership category is disproportionately large. This is due to the landscape position these lands occupy, the diversification they contribute to forest cover and local economies, and the political and cultural connections they provide to urban populations. The significance of this ownership category is even greater in the United States as a whole, where nonindustrial private forests comprise nearly two-thirds of the commercial forestland base, dominating rural landscapes in many regions of the country. Despite the important role family forests play, their ability to contribute to the wellbeing of rural areas is challenged by several dynamic factors, including industrial consolidation in global wood markets, loss of family forestland to corporate ownership, and parcelization and fragmentation of family forestland at the urban fringe. Moreover, family forestry does not enjoy a strong social contract with the American public, which is largely ignorant of the existence of this ownership class. A foundation of broad social approval and appreciation for family forestry is a prerequisite to development of policies which can sustain family forestland ownerships and the contributions they make. This paper draws from recent research in Oregon to argue that, whereas most research on nonindustrial private forests has focused on economics and management at the individual producer level, these challenges demand greater attention to the role of family forests in the wider context of landscape, culture and rural economy

First-principles Calculation of the Formation Energy in MgO-CaO Solid Solutions

The electronic structure and total energy were calculated for ordered and disordered MgO-CaO solid solutions within the multiple scattering theory in real space and the local density approximation. Based on the dependence of the total energy on the unit cell volume the equilibrium lattice parameter and formation energy were determined for different solution compositions. The formation energy of the solid solutions is found to be positive that is in agreement with the experimental phase diagram, which shows a miscibility gap.Comment: 11 pages, 3 figure

Design of interactive and dynamic anatomical visualizations: The implication of cognitive load theory.

In improving the teaching and learning of anatomical sciences, empirical research is needed to develop a set of guiding principles that facilitate the design and development of effective dynamic visualizations. Based on cognitive load theory (CLT), effective learning from dynamic visualizations requires the alignment of instructional conditions with the cognitive architecture of learners and their levels of expertise. By improving the effectiveness and efficiency of dynamic visualizations, students will be able to be more successful in retaining visual information that mediates their understanding of complex and difficult aspects of anatomy. This theoretical paper presents instructional strategies generated by CLT and provides examples of some instructional implications of CLT on the design of dynamic visualizations for teaching and learning of anatomy

Simulation models for tankless gas water heaters

There is a growing concern about to the scarceness of natural resources and the emissions problematic. Water heating is a relevant part of a household’s energy use, and tankless gas water heaters (TGWH) are widely used. There are design and engineering challenges to develop more efficient devices, with lower emissions of pollutant gases and providing comfort improvements from the user point of view. The main objective of the present work is to provide mathematical models to evaluate and support the development of different TGWH configurations. By simulation, different hardware configurations and advanced control strategies can be tested and optimized regarding energy saving, reducing of harmful environmental emissions and increase of comfort indices by reducing temperature undershoots and overshoots. The TGWH individual components are modelled, laboratory tests are performed and the heat cell is parametrized with experimental data. Configurations with and without bypass function are performed for several water flow rates and setpoint temperature patterns in open loop and with feed-forward control.publishe