► Wind–photovoltaic systems are used to electrify communities of developing countries. ► Designs that combine individual systems and microgrids are advantageous. ► We develop a MILP model to design ...hybrid wind–photovoltaic systems with microgrids. ► The model is tested with realistic size instances, which are efficiently solved. ► The model is applied to real case studies in Peru; results reduce cost by 20–30%.
Electrification systems based on the use of renewable energy sources are a suitable option for providing electricity to isolated communities autonomously. Wind and hybrid wind–photovoltaic (PV) systems are increasingly getting attention. To electrify scattered communities, designs that combine individual systems and microgrids have recently proven advantageous. In this paper we present a mathematical programming model to optimize the design of hybrid wind–PV systems that solves the location of the wind–PV generators and the design of the microgrids, taking into account the demand of the consumption points and the energy potential. The criterion is the minimization of the initial investment cost required to meet the demand. The proposed hybrid model is tested with realistic size instances and results show the instances are efficiently solved. Moreover, the model is applied to real case studies in Peru; obtained results verify that the hybrid model efficiently finds solutions that significantly reduce costs.
•A mid-term production plan is obtained for a chemical company.•Mathematical programming is used to maximize the company's profit.•Non-constant consumption of materials based on produced quantity is ...considered.•The tool can be used for strategic planning, simulating different scenarios.
Two particular features of a chemical problem with a production planning problem motivate the development of a novel ad-hoc mathematical model for the optimal solution: the consumption of raw materials may not be constant and depend on the quantity to be produce of one reference product, and the demand supplied should be embedded between a minimum (established by contract) and a maximum value. This work aims to plan the production of the company's semi-finished and final products to maximize the profits from the products sales considering resources costs. This mid-term plan is calculated with an optimization tool developed based on a mixed-integer linear programming model. Availability of resources and particular constraints around recipes and processes are considered. An optimal solution is achieved in short time, providing valuable information of the profits expected. Different scenarios are also simulated to study capacity expansions or alternative market positions.
•A new methodology tackles multicriteria decision-making with uncertainty.•A novel procedure based on fuzzy rating scales is presented to model uncertainty.•Possibility pair-wise comparisons are ...calculated to assist decision-making.•A generic example case displays the methodology and argues the effect of confidence.•Lower confidence in an alternative evaluation worsens the final alternative ranking.
Making a decision usually means selecting one from different alternatives to solve a problem according to a set of criteria. Multicriteria analysis usually offers a quantitative approach to ease decision-making by ranking the alternatives. However, uncertainty can arise when rating the importance of criteria and the adequacy of each alternative for each criterion, due to two factors: first, answers are usually expressed in linguistic terms that do not have a unique quantification; and second, there might be a lack of confidence in the response. Most multicriteria procedures combine fuzzy numbers and linguistic scales to deal with the first factor, but underestimate confidence issues. In this context, this work develops a Methodology for Integrated Multicriteria Decision-making with Uncertainty (MIMDU), which considers both factors of uncertainty. MIMDU is structured in three phases: (1) a novel procedure based on fuzzy rating scales to model uncertain opinions; (2) a fuzzy formulation of the compromised ranking method to rank the alternatives; and (3) a systematic procedure for results' interpretation comparing a crisp ranking (without uncertainty) and a fuzzy-based ranking (with uncertainty). The methodology is illustrated with a generic example case, aiming to prove its potential application in any sector. Results show that MIMDU helps decision-makers to choose the most reliable alternative, since significant differences in ranking with and without uncertainty can be addressed. A sensitivity analysis is carried out to bare the effect of confidence in the alternatives evaluation, concluding that worse rankings are obtained for alternatives that are less confidently evaluated. A final comparison with the standard fuzzy VIKOR method shows MIMDU's major preciseness in modelling non-confident opinions and providing more useful and complimentary information to better assist decision-making.
The main goal of this study was to investigate the neural substrates of fluid reasoning and visuospatial working memory in adolescents with precocious mathematical ability. The study population ...comprised two groups of adolescents: 13 math-gifted adolescents and 14 controls with average mathematical skills. Patterns of activation specific to reasoning tasks in math-gifted subjects were examined using functional magnetic resonance images acquired while the subjects were performing Raven's Advanced Progressive Matrices (RAPM) and the Tower of London (TOL) tasks.
During the tasks, both groups showed significant activations in the frontoparietal network. In the math-gifted group, clusters of activation were always bilateral and more regions were recruited, especially in the right hemisphere. In the TOL task, math-gifted adolescents showed significant hyper-activations relative to controls in the precuneus, superior occipital lobe (BA 19), and medial temporal lobe (BA 39). The maximum differences between the groups were detected during RAPM tasks at the highest level of difficulty, where math-gifted subjects showed significant activations relative to controls in the right inferior parietal lobule (BA 40), anterior cingulated gyrus (BA 32), and frontal (BA 9, and BA 6) areas. Our results support the hypothesis that greater ability for complex mathematical reasoning may be related to more bilateral patterns of activation and that increased activation in the parietal and frontal regions of math-gifted adolescents is associated with enhanced skills in visuospatial processing and logical reasoning.
► Math-gifted (MG) subjects show higher recruitment of right hemisphere and more bilateralism. ► Frontoparietal network in MG is used to resolve complex visuospatial and analytical tasks. ► Only during difficult tasks MG show different activation than controls.
The purpose of this study was to elucidate whether cerebral blood flow (CBF) can better characterize perfusion abnormalities in predementia stages of Alzheimer's disease (AD) than cerebral blood ...volume (CBV) and whether cortical atrophy is more associated with decreased CBV or with decreased CBF. We compared measurements of CBV, CBF, and mean cortical thickness obtained from magnetic resonance images in a group of healthy controls, patients with mild cognitive impairment (MCI) who converted to AD after 2 years of clinical follow-up (MCI-c), and patients with mild AD. A significant decrease in perfusion was detected in the parietal lobes of the MCI-c patients with CBF parametric maps but not with CBV maps. In the MCI-c group, a negative correlation between CBF values and cortical thickness in the right parahippocampal gyrus suggests an increase in CBF that depends on cortical atrophy in predementia stages of AD. Our study also suggests that CBF deficits appear before CBV deficits in the progression of AD, as CBV abnormalities were only detected at the AD stage, whereas CBF changes were already detected in the MCI stage. These results confirm the hypothesis that CBF is a more sensitive parameter than CBV for perfusion abnormalities in MCI-c patients.
A framework for visible-light water splitting Navarro, Rufino M; Alvarez-Galván, M. Consuelo; Villoria de la Mano, Jose A ...
Energy & environmental science,
01/2010, Letnik:
3, Številka:
12
Journal Article
Recenzirano
This review article reports the most significant advances made in H
2
production
via
water-splitting and the challenges that need to be addressed over the coming years to verify the feasibility of H
...2
production by both inorganic semiconductors and living microorganisms as a competitive process in the hydrogen economy.
This review presents some progress and projections on sustainable H
2
production through the visible-light water-splitting reaction on both semiconducting materials and microorganisms.
Introduction
Carotid near-occlusion (CNO) is a variant of severe stenosis where there is a distal luminal collapse of the internal carotid artery (ICA) beyond a tight stenosis. This study aimed to ...validate new visual extracranial diagnostic CT angiography (CTA) criteria, for the diagnosis of CNO. The new criteria include distal ICA diameter smaller than contralateral ICA and distal ICA diameter less than or equal to the ipsilateral external carotid artery (ECA). We also assessed the previously described CTA criteria: stenosis ≤ 1.3 mm, ipsilateral distal ICA ≤ 3.5 mm, ipsilateral distal ICA/contralateral distal ICA ratio ≤ 0.87, ipsilateral distal ICA/ipsilateral ECA ≤ 1.27.
Methods
Fifty-eight patients with ICA stenosis (including the near-occlusion variant) or occlusion on digital subtraction angiography (DSA) were included. These patients had DSA and CTA studies completed within 30 days of each other. DSA was considered the reference test. Two neuroradiologists blinded to the DSA results assessed the CTA images and evaluated the new and previously published CNO diagnostic criteria.
Results
Twenty-eight CNO were identified with DSA. The “distal ICA diameter less than or equal to the ipsilateral ECA” criterion had 79% sensitivity and 83% specificity with excellent interobserver agreement (kappa = 0.80), while three or more of the previously published criteria reached 82% sensitivity and 90% specificity, with a good interobserver agreement (kappa = 0.64).
Conclusions
CT angiography may be useful for CNO diagnosis. The new visual diagnostic criteria provide acceptable results of sensitivity and specificity with an excellent interobserver agreement. However, false-negative and positive results persist.
Aliment Pharmacol Ther 2011; 34: 888–900
Summary
Background Determining the risk of rebleeding after endoscopic therapy for peptic ulcer bleeding (PUB) may be useful for establishing additional ...haemostatic measures in very high‐risk patients.
Aim To identify predictors of rebleeding after endoscopic therapy.
Methods Bibliographic database searches were performed to identify studies assessing rebleeding after endoscopic therapy for PUB. All searches and data ion were performed in duplicate. A parameter was considered to be an independent predictor of rebleeding when it was detected as prognostic by multivariate analyses in ≥2 studies. Pooled odds ratios (pOR) were calculated for prognostic variables.
Results Fourteen studies met the prespecified inclusion criteria. Pre‐endoscopic predictors of rebleeding were: (i) Haemodynamic instability: significant in 9 of 13 studies evaluating the variable (pOR: 3.30, 95% CI: 2.57–4.24); (ii) Haemoglobin value: significant in 2 of 10 (pOR: 1.73, 95% CI: 1.14–2.62) and (iii) Transfusion: significant in two of six (pOR not calculable). Endoscopic predictors of rebleeding were: (i) Active bleeding: significant in 6 of 12 studies (pOR: 1.70, 95% CI: 1.31–2.22); (ii) Large ulcer size: significant in 8 of 12 studies (pOR: 2.81, 95% CI: 1.98–4.00); (iii) Posterior duodenal ulcer location: significant in four of eight studies (pOR: 3.83, 95% CI: 1.38–10.66) and (iv) High lesser gastric curvature ulcer location: significant in three of eight studies (pOR: 2.86; 95% CI: 1.69–4.86).
Conclusions Major predictors for rebleeding in patients receiving endoscopic therapy are haemodynamic instability, active bleeding at endoscopy, large ulcer size, ulcer location, haemoglobin value and the need for transfusion. These risk factors may be useful for guiding clinical management in patients with PUB.
PDF
