This article considers a continuous-time variant of the stochastic inventory routing problem. In most of the articles present in the literature related to inventory routing, customers reveal their ...demands at the end of each period, which is when the inventory level is calculated. In the variant of the problem at hand, the demand that each customer experiences on each period, results in a continuous decrease of the inventory for the customer during the period. This characteristic strongly affects the quantities that can be delivered to each customer and, if the deliveries are not sufficient or arrive too late, they can cause some stock-out situations within the periods. In the inventory routing problem, the vendor manages all the replenishment decisions of the vendees and, therefore, creates delivery plans for a planning horizon, aiming to reduce the routing, consistency, inventory and lost-sales costs. We formulate the problem as a two-stage mathematical program. Customers experience a continuous stochastic demand within each period and present information about inventory level and capacity at each period, as well as the time windows in which deliveries can take place. To solve this problem, we develop a matheuristic solution approach based on an adaptive large neighborhood search algorithm. In addition, we evaluate the impact of applying recourse actions to deal with expected lost sales during the planning horizon. We compare the performance of the algorithm with adapted variants of the multiple scenario approach and the branch and regret algorithms from the literature. Samples based on the stochastic demands are considered in the algorithms, to find robust solutions that can minimize the objective function. We evaluate the solutions by means of a sample average estimator procedure, and we compare the efficiency of the algorithms as well as the impact of different levels of stochasticity.
•Stochastic inventory routing problem with continuous time commodity consumption.•Customers require consistency in the delivery times and might experience stock outs.•We present different solution approaches to solve the problem.•A computational analysis is presented to evaluate the effectiveness of the algorithms.
► We study the efficiency and spatial equity impacts of HSR in urban areas. ► Accessibility measures are capable of addressing efficiency and equity impacts of HSR extensions. ► HSR stations cause ...the existence of “islands” with enhanced levels of accessibility. ► The territorial homogeneously Spanish HSR extension causes a global rise in spatial equity.
Urban areas benefit from significant improvements in accessibility when a new high speed rail (HSR) project is built. These improvements, which are due mainly to a rise in efficiency, produce locational advantages and increase the attractiveness of these cities, thereby possibly enhancing their competitiveness and economic growth. However, there may be equity issues at stake, as the main accessibility benefits are primarily concentrated in urban areas with a HSR station, whereas other locations obtain only limited benefits.
HSR extensions may contribute to an increase in spatial imbalance and lead to more polarized patterns of spatial development. Procedures for assessing the spatial impacts of HSR must therefore follow a twofold approach which addresses issues of both efficiency and equity. This analysis can be made by jointly assessing both the magnitude and distribution of the accessibility improvements deriving from a HSR project.
This paper describes an assessment methodology for HSR projects which follows this twofold approach. The procedure uses spatial impact analysis techniques and is based on the computation of accessibility indicators, supported by a Geographical Information System (GIS). Efficiency impacts are assessed in terms of the improvements in accessibility resulting from the HSR project, with a focus on major urban areas; and spatial equity implications are derived from changes in the distribution of accessibility values among these urban agglomerations.
► We study the territorial cohesion impacts of a HSR extension at different planning levels. ► We use accessibility measures to address territorial cohesion impacts. ► The direction and intensity of ...cohesion impacts are different depending on the planning level considered. ► Cohesion results are explained mainly by the combination of population density distribution and location of HSR stations. ► Accessibility relative starting situation and quality of the access to the HSR network also drive the cohesion results.
The assessment of the impacts of high-speed rail (HSR) projects on territorial cohesion has recently emerged as an important issue for transport planners. HSR networks are usually designed to interconnect strong economic centers efficiently. Hence, the greatest improvements in accessibility concentrate near HSR stations, whereas intermediate locations suffer from comparatively lower accessibility benefits. Negative territorial cohesion impacts appear if HSR ultimately results in a more polarized spatial distribution of accessibility levels.
There has so far been little research aimed at exploring the implications of the definition of the geographical limits of study area in the measurement of HSR territorial cohesion impacts. In this context, this paper presents a Geographical Information System (GIS)-based methodology which analyzes changes in the territorial distribution of accessibility resulting from HSR investments. These changes are analyzed at different planning levels, in order to assess the sensitivity of territorial cohesion results to scale definition.
The methodology is tested by its application to the development of the 670km of the Galician (north-western) HSR corridor included in the Spanish PEIT (Strategic Transport and Infrastructure Plan) 2005–2020. Cohesion impacts are assessed at different direct planning levels: regional, corridor and national levels, as well from the perspective of spillover effects. In all cases, the construction of the HSR corridor increases the accessibility values, and results show positive cohesion effects at the national and corridor levels, whereas at the regional level both balancing and polarization effects appear. These differences are mainly due to the location of HSR stations or to the quality of the transport network from the surrounding cities to the station, which determines the territorial distribution of accessibility improvements. Similar results are found from the spillover perspective.
High Speed Rail (HSR) in Spain began in 1992 and currently has a network of some 3200 km. In this 25-year period, accessibility has progressively increased, changing its spatial distribution ...throughout the country. However, improvements in the HSR network may or may not have contributed to a more balanced territorial distribution of accessibility levels. These distributional effects of HSR have important implications for territorial cohesion, which is a strategic planning goal for transport infrastructures in the European Union. This paper presents a methodology for evaluating 'accessibility-based' territorial cohesion effects of HSR corridors. Accessibility values are calculated for successive five-year periods. Territorial cohesion effects are assessed based on changes in accessibility patterns and their spatial distribution. The results show that new HSR lines have significantly increased the accessibility levels of the Spanish population to most destinations. On average accessibility values have improved in the 1990-2015 period by 48.6% due to HSR, with differences among locations depending if they are or not nodes of the HSR network. The study's findings show also a more balanced distribution of accessibility, with 15% reduction in the dispersion of accessibility values between 1990 and 2015, implying a positive contribution to territorial cohesion goals.
Hyperglycemia and hypoglycemia currently are considered risk factors for cardiovascular disease in type 1 diabetes. Both acute hyperglycemia and hypoglycemia induce endothelial dysfunction and ...inflammation, raising the oxidative stress. Glucagon-like peptide 1 (GLP-1) has antioxidant properties, and evidence suggests that it protects endothelial function.
The effect of both acute hyperglycemia and acute hypoglycemia in type 1 diabetes, with or without the simultaneous infusion of GLP-1, on oxidative stress (plasma nitrotyrosine and plasma 8-iso prostaglandin F2alpha), inflammation (soluble intercellular adhesion molecule-1 and interleukin-6), and endothelial dysfunction has been evaluated.
Both hyperglycemia and hypoglycemia acutely induced oxidative stress, inflammation, and endothelial dysfunction. GLP-1 significantly counterbalanced these effects.
These results suggest a protective effect of GLP-1 during both hypoglycemia and hyperglycemia in type 1 diabetes.
Habitat fragmentation is a process that may impair the "habitat provision" ecosystem service provided by forests. Thus, it is relevant to quantify the degree of forest fragmentation, since higher ...levels are expected to have greater effects on forest species. Our goal was to deploy the Forest Area Density (FAD) metric as a tool to derive maps localizing potential priority areas for species requiring large, relatively undisturbed blocks of forest. The Spanish Forest Map (1:50,000) provided comprehensive data on forestland in the country. We defined forest types considering the ten most abundant species in Spain and pure and mixed stands. Then, we calculated FAD by forest type and produced a set of maps showing the results by general management scenario, namely habitat conservation and restoration. To develop forest planning, specific actions can be implemented within these areas in later steps, fostering biodiversity at national or smaller scales.
•We characterize the relationship between forest amount and configuration.•We study real-world landscapes: forests in the Iberian Peninsula,•We provide: thresholds that discriminate among forest ...fragmentation levels,•Novel references valuable to identify priority areas for management in the region,•Foundation for further research on ecological responses to forest fragmentation.
Understanding the role of habitat loss and fragmentation per se is crucial to generate relevant knowledge for habitat management. In the case of forest species, this can be achieved by measuring forest amount and configuration metrics at the landscape scale, including their relationship. We aimed to characterize the relationship between forest amount and configuration metrics in real-world landscapes of an extensive area, identifying forest amount thresholds that discriminate among forest fragmentation levels. We also investigated whether ecological and political contexts could affect the strength of the relationship. We comprehensively analyzed forest cover in the Iberian Peninsula (20.56 million ha, year 2,018). We calculated Forest Area Density (FAD) and three configuration metrics by employing a moving-window procedure. From metrics’ surfaces we derived bivariate probability-density scatterplots, a synoptic Fragmentation Level indicator (FL) and subsequent classification and correlation analyses. For Number of Patches and Edge Density (ED) maximum values and variability appeared at FAD 20% and 50%, respectively. The extreme FAD thresholds relative to FL were 89% and 55%, potentially representing fragmentation and extinction thresholds for a generic forest species. Major differences between Portugal and Spain were found in ED in the Mediterranean Ecoregions, being wildfire regimes and ownership patterns plausible explanations. We provide insights into the patterns of forest cover and metrics’ references valuable to identify areas of concern for management and conservation in the region, as well as a foundation for further research on the ecological responses to forest fragmentation.
This article introduces a new variant of the inventory routing problem related to real-world businesses. Specifically, in the beverage industry, business customers such as restaurants and bars, ...demand consistent delivery times, have different opening times and delivery time windows, and occasionally, due to special events, exhibit demands that exceed single-vehicle capacity leading to the need of splitting demands between several vehicles. We present two variants of a mathematical formulation that include all the characteristics of this inventory routing problem. In the first, we apply the maximum level policy, whereas in the second variant, we apply an order-up-to-level policy. As a solution technique, we propose a matheuristic based on an adaptive large neighborhood search algorithm for which we developed several destroy and repair operators specifically designed to address the special problem features. Extensive computational tests based on artificial and real-world instances affirm the efficiency of the solution approach. Furthermore, we analyze the solution quality, the impact of the characteristics and policies applied, and the practicability for the real world.
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