619 research outputs found

    Importance subsampling: improving power system planning under climate-based uncertainty

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    Recent studies indicate that the effects of inter-annual climate-based variability in power system planning are significant and that long samples of demand & weather data (spanning multiple decades) should be considered. At the same time, modelling renewable generation such as solar and wind requires high temporal resolution to capture fluctuations in output levels. In many realistic power system models, using long samples at high temporal resolution is computationally unfeasible. This paper introduces a novel subsampling approach, referred to as importance subsampling, allowing the use of multiple decades of demand & weather data in power system planning models at reduced computational cost. The methodology can be applied in a wide class of optimisation based power system simulations. A test case is performed on a model of the United Kingdom created using the open-source modelling framework Calliope and 36 years of hourly demand and wind data. Standard data reduction approaches such as using individual years or clustering into representative days lead to significant errors in estimates of optimal system design. Furthermore, the resultant power systems lead to supply capacity shortages, raising questions of generation capacity adequacy. In contrast, importance subsampling leads to accurate estimates of optimal system design at greatly reduced computational cost, with resultant power systems able to meet demand across all 36 years of demand & weather scenarios

    Blue light phototherapy for Psoriasis from a systems biology perspective

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    This work analyses the effect of UV-free blue light (BL) irradiation of the skin using mathematical modelling. Prior research has shown that blue light reduces the proliferation of keratinocytes by inducing their differentiation, and causes apoptosis of lymphocytes. The effects of blue light on these cells make it an attractive phototherapy alternative for inflammatory skin conditions, such as psoriasis. Nevertheless, the exact process by which BL affects these cells is not fully understood. A modelling approach may give further insight to understanding how BL irradiation of psoriatic skin leads to the control of the disease. However, no mathematical model is available describing this phenomenon. Two deterministic models were therefore made to describe the epidermal kinetics and interaction between keratinocytes and lymphocytes under the effect of BL irradiation; focusing mainly on the case of psoriasis. We employed a systems biology approach to characterize the effect of BL irradiation of the skin. Since in phototherapy parameters such as fluence and power have a strong impact on the outcome, a parameter sensitivity analysis (PSA) was performed to estimate a range of fluence and power at which BL phototherapy could be successful. The models results suggest that the management of psoriasis is achieved by inducing symmetric differentiation of the keratinocytes in the epidermal proliferative compartment. It is observed that BL irradiation of psoriatic skin decreases the density of keratinocytes and transiently increases the density of lymphocytes, leading to the regulation of the interaction between these two cell types. The PSA of the models predicts that the higher the peak power the better the outcome of the BL phototherapy with a dose of 90J/cm2 per day. This systems biology approach provides additional insight into the use of BL phototherapy for inflammatory skin disorders

    Identifying Citizens' Place Values for Integrated Planning of Road Infrastructure Projects

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    Projects for road infrastructure and spatial development easily meet public resistance because of a lack of local knowledge of place values by (often non-local) planners. The aim of this study is to explore how insights in place values might improve the local knowledge base for planners of integrated road infrastructure projects and spatial development. We developed, tested and analysed the results from a novel online value-mapping tool called the ‘Place Value Identifier’. The developed method allows us to (i) relate to ‘soft’ valuable places identified by Public Participation GIS as a complement to ‘hard’ land use data, (ii) define Valued yet Unprotected places based on combining ‘hard’ and ‘soft’ values and (iii) illustrate how these insights can be used for integrated planning of road infrastructure projects. The findings of this study show the increased potential of value mapping techniques and illustrate possible resistance areas around road infrastructure planning projects. This knowledge may assist planners in creating and selecting acceptable project alternatives that may invoke high public acceptance

    Coarse Grained Molecular Dynamics Simulations of the Fusion of Vesicles Incorporating Water Channels

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    As the dynamics of the cell membrane and the working mechanisms of proteins cannot be readily asserted at a molecular level, many different hypotheses exist that try to predict and explain these processes, for instance vesicle fusion. Therefore, we use coarse grained molecular dynamics simulations to elucidate the fusion mechanism of vesicles. The implementation of this method with hydrophilic and hydrophobic particles is known for its valid representation of bilayers. With a minimalistic approach, using only 3 atom types, 12 atoms per two-tailed phospholipids and incorporating only a bond potential and Lennard-Jones potential, phospholipid bilayers and vesicles can be simulated exhibiting authentic dynamics. We have simulated the spontaneous full fusion of both tiny (6 nm diameter) and larger (13 nm diameter) vesicles. We showed that, without applying constraints to the vesicles, the initial contact between two fusing vesicles, the stalk, is initiated by a bridging lipid tail that extends from the membrane spontaneously. Subsequently it is observed that the evolution of the stalk can proceed via two pathways, anisotropic and radial expansion, which is in accordance with literature. Contrary to the spherical vesicles of in vitro experiments, the fused vesicles remain tubular since the internal volume of these vesicles is too small compared to their membrane area. While the lipid bilayer has some permeability for water, it is not high enough to allow for the large flux required to equilibrate the vesicle content in the time accessible to our simulations. To increase the membrane permeability, we incorporate proteinaceous water channels, by applying the coarse grained technique to aquaporin. Even though incorporating water channels in the vesicles does significantly increase water permeability, the vesicles do not become spherical. Presumably the lipids have to be redistributed as well

    Nanosecond photochromic molecular switching of a biphenyl-bridged imidazole dimer revealed by wide range transient absorption spectroscopy

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    We demonstrate that a biphenyl-bridged imidazole dimer exhibits fast photochromism with a thermal recovery time constant of similar to 100 ns, which is the fastest thermal back reaction in all reported imidazole dimers. Sub-ps transient absorption spectroscopy reveals that the generation process of the colored species occurs within 1 ps

    Lessons learned from computer models on blue light therapy for psoriasis vulgaris

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    Blue light irradiation has been clinically proven to reduce the symptoms of psoriasis vulgaris, a common chronic inflammatory skin disease that affects 2% - 3% of the world’s population. This dermatological condition is characterized by hyperproliferation and disturbed differentiation of keratinocytes, which is evident in lesional areas as thick flaky skin. The lesional areas also exhibit sustained inflammation, induced by immune cells, such as T cells and dendritic cells, infiltrating the affected skin. Blue light reduces the proliferation of keratinocytes and increases their differentiation in a wavelength and fluence dependent manner. Also, it induces apoptosis in T cells and suppresses the activation of dendritic cells. These effects can explain the symptom reduction after treatment. But, the efficacy shown in the clinical studies could be further improved by having a deeper understanding on the underlying mechanism of this therapeutic approach and optimizing the treatment regimens currently used. Diverse findings have been published in different studies of blue light therapy for psoriasis describing large, little or no therapeutic effect. These results may be due to variances in the main treatment parameters of the implemented protocols, i.e. fluence, intensity, and length of treatment. Computational methods can provide a suitable platform to investigate the complex interactions leading to the management of psoriasis by blue light therapy and optimize the treatment protocols. Here, we explore in silico the underlying mechanism of blue light irradiation of psoriatic skin and predict the outcome of a wide range of therapeutic regimens with varying fluence, intensity, and length of treatment. The computational model is defined by a set of ordinary differential equations describing the time evolution of keratinocytes as they move vertically through the layers of the epidermis. The results of our simulations suggest that the temporary decrease in the severity of psoriasis can be explained by the transient decline in the proliferative capacity of keratinocytes. However, it is still unclear how the effects of blue light on the immune system contribute to the reduction of psoriasis symptoms. Simulations implemented for several combinations of treatment parameters predict that high efficacy is achieved by protocols with long duration and high fluence levels, regardless of the chosen intensity. These predictions provide general guidelines for treatment. Our in silico approach constitutes a framework for testing diverse hypotheses on the underlying mechanism of blue light therapy and designing effective strategies for the treatment of psoriasis vulgaris

    Combined effects of land use and hunting on distributions of tropical mammals

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    Land use and hunting are 2 major pressures on biodiversity in the tropics. Yet, their combined impacts have not been systematically quantified at a large scale. We estimated the effects of both pressures on the distributions of 1884 tropical mammal species by integrating species’ range maps, detailed land-use maps (1992 and 2015), species-specific habitat preference data, and a hunting pressure model. We further identified areas where the combined impacts were greatest (hotspots) and least (coolspots) to determine priority areas for mitigation or prevention of the pressures. Land use was the main driver of reduced distribution of all mammal species considered. Yet, hunting pressure caused additional reductions in large-bodied species’ distributions. Together, land use and hunting reduced distributions of species by 41% (SD 30) on average (year 2015). Overlap between impacts was only 2% on average. Land use contributed more to the loss of distribution (39% on average) than hunting (4% on average). However, hunting reduced the distribution of large mammals by 29% on average; hence, large mammals lost a disproportional amount of area due to the combination of both pressures. Gran Chaco, the Atlantic Forest, and Thailand had high levels of impact across the species (hotspots of area loss). In contrast, the Amazon and Congo Basins, the Guianas, and Borneo had relatively low levels of impact (coolspots of area loss). Overall, hunting pressure and human land use increased from 1992 to 2015 and corresponding losses in distribution increased from 38% to 41% on average across the species. To effectively protect tropical mammals, conservation policies should address both pressures simultaneously because their effects are highly complementary. Our spatially detailed and species-specific results may support future national and global conservation agendas, including the design of post-2020 protected area targets and strategies
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