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Specialization can become detrimental to a discipline if it fosters intellectual isolation. A bibliographic analysis of several research areas in plant ecology (invasion biology, succession ecology, gap/patch dynamics, and global change effects on plants) revealed that plant ecologists do not regularly make use of the findings and insights of very similar studies being conducted in other research subdisciplines, nor do they try to make their findings and insights easily accessible to researchers in other areas. Invasion papers were least likely to be cross-linked (6%) with other fields, whereas gap/patch dynamics papers were most likely to be cross-linked (15%). This tendency toward intellectual isolation may be impeding efforts to achieve more powerful generalizations in ecology by reducing the number of potentially productive exchanges among researchers. In this paper, we illustrate this problem using the example of several speciality areas that study vegetation change. We argue that, rather than characterizing studies of vegetation change on the basis of what distinguishes them from one another, plant ecologists would benefit from concentrating on what such studies have in common. As an example, we propose that several speciality areas of plant ecology could be reunified under the term ecology of vegetation change. Individual researchers, journals, and ecological societies all can take specific steps to increase the useful exchange of ideas and information among research areas. Promoting rapid and more effective communication among diverse researchers may reduce the proliferation of narrow theories, concepts, and terminologies associated with particular research areas. In this way, we can expedite our understanding of the ecological mechanisms and consequences associated with plant communities. (c) 2004 Elsevier GmbH. All rights reserved.

We have recently shown, in studies with patients with Type 1 (insulin dependent) diabetes, that alcohol intake at 21:00 h significantly reduced blood glucose values after 10-12 h, compared with control studies with no alcohol.We hypothesised that this was due to the following effects of alcohol: (1) alcohol metabolism increases NADH, leading to a reduction in hepatic gluconeogenesis; (2) increased glycogen phosphorylase activity depletes hepatic glycogen stores; (3) after the alcohol is metabolised, hepatic insulin sensitivity is increased, leading to the restoration of glycogen stores and reduction in blood glucose levels; and (4) consequently, after several hours, glycogen stores and insulin sensitivity return to normal.A model describing these changes (DiasNet-Alcohol) was implemented into the DiasNet model of human glucose metabolism. Our study suggests that the DiasNet-Alcohol model gives a reasonable approximation of these effects of alcohol on blood glucose concentration observed in our study and supports our hypothesis for the mechanism behind these effects in Type 1 diabetes.

This paper discusses the modeling, design and operation of a PV powered stand-alone system, which includes a PV array, a battery bank, power electronic converters and the associated control system. The design considerations are analyzed and a design platform is presented. Furthermore the operation modes of the system are described. A power electronic system with the associated control scheme has been proposed and simulation models have been developed. Simulation studies have been conducted on an example system; the results have demonstrated the effectiveness of the presented methods.

A comprehensive, three-dimensional analysis of a polymer electrolyte membrane (PEM) fuel cell has been developed to study the performance of this device under different operational conditions. This steady-state analysis is single-phase and non-isothermal. A commercial computational fluid dynamics (CFD) program provided a numerical platform for solving the conservation equations for species, energy, charge, mass and momentum. Different boundary conditions were added to a computational domain to simulate single channel PEM fuel cell. The electrochemistry involved in this model was added by a set of user-defined subroutines that feature: electrochemical reactions, electric and ionic charge and heat generation. The calculations were then solved by an iterative method following an adapted computational procedure. The results were validated with other computational models and experimental data. These show a noticeable non-uniform distribution of the current density across the catalyst layer (CL) at different operational conditions. The results emphasize on the differences of anodic and cathodic activation overpotentials, the oxygen transport limitations and the ohmic losses distributions of both proton and electric overpotentials.

A comparison between two numerical models describing the thermo-chemical conversion process of a solid fuel bed in a grate-fired boiler is presented. Both models consider the incoming biomass as subjected to drying, pyrolysis, gasification and combustion. In the first approach the biomass bed is treated as a 0D system, where the thermo-chemical processes are divided in two successive sections: drying and conversion. Phenomenological laws are written to characterize the syngas release as a function of the main governing parameters. The second model is an empirical 1D approach. Temperature, species concentrations and velocity of the syngas provided by the two models are compared. Sensitivity analyses with respect to the drying agent mass flow rate, the initial moisture content and the composition of the biomass are performed. The relative error between the mean values of the temperature and velocity of the syngas predicted by the two models is equal to about 7%. The application to different types of biomass shows that the difference in the predictions increases as the carbon content grows. The phenomenological model, in fact, generally considers higher conversion rates of this element to volatiles with respect to the analogy model.

More "green" power provided by Distributed Generation will enter into the European electricity network in the near future. hi order to control the powerflow and to ensure proper and secure operation of this future grid, with an increased level of the renewable power, new power electronic converters for grid connection of renewable sources are needed. These power converters must be able to provide intelligent power management as well as ancillary services. This paper presents an overview of an advanced power converter for universal and flexible power management that can enable the large scale-integration of dispersed generation into these future networks. The overall structure and the control requirements that are to be placed upon this converter are given. Furthermore, some possible applications as well as the bene,fits of using this converter are presented.

Abstract In this paper, the ability of a micro combined heat and power (mCHP) system to cover the heat and electricity demand of a single-family residence is investigated. A solid oxide fuel cell based mCHP system coupled with a hot water storage tank is analyzed. The energy profiles of single-family households in different European countries are evaluated. The range of Heat-to-Power Ratio for the SOFC-based mCHP System of 0.5–1.5 shows good agreement with the hot water, space heating and electricity demand during the warm seasons across Europe. This suggests that the fuel cell system should be sized according to the summer energy demand. The winter energy demand shows a Heat-to-Power Ratio which cannot be covered by the mCHP unit alone. To ensure that the mCHP system meets both the thermal and electrical energy demand over the entire year, an auxiliary boiler and a hot water storage tank need to be coupled with the mCHP unit. It is further noted that the size of the auxiliary boiler should match the larger winter space heating demand. In contrast, the hot water tank volume should be sized according to the warm season space heating requirement, when space heating is not required but electricity and hot water are still in demand. This maximizes the running time of the fuel cell, and thus the economic and environmental benefit of the system, without wasting produced heat.

Changing environmental conditions may substantially interact with site quality and forest stand characteristics, and impact forest growth and carbon sequestration. Understanding the impact of the various drivers of forest growth is therefore critical to predict how forest ecosystems can respond to climate change. We conducted a continental-scale analysis of recent (1995–2010) forest volume increment data (ΔVol, m3 ha−1 yr−1), obtained from ca. 100,000 coniferous and broadleaved trees in 442 even-aged, single-species stands across 23 European countries. We used multivariate statistical approaches, such as mixed effects models and structural equation modelling to investigate how European forest growth respond to changes in 11 predictors, including stand characteristics, climate conditions, air and site quality, as well as their interactions. We found that, despite the large environmental gradients encompassed by the forests examined, stand density and age were key drivers of forest growth. We further detected a positive, in some cases non-linear effect of N deposition, most pronounced for beech forests, with a tipping point at ca. 30 kg N ha−1 yr−1. With the exception of a consistent temperature signal on Norway spruce, climate-related predictors and ground-level ozone showed much less generalized relationships with ΔVol. Our results show that, together with the driving forces exerted by stand density and age, N deposition is at least as important as climate to modulate forest growth at continental scale in Europe, with a potential negative effect at sites with high N deposition.