Universidad de Valladolid
  • Valladolid, Spain
Recent publications
Model-based approaches to cluster analysis and mixture modelling often involve maximizing classification and mixture likelihoods. Robust clustering and mixture modelling procedures, that can resist certain amount of contaminating data, can be introduced by considering trimmed versions of those classification and mixture likelihoods. Without appropriate constrains on the scatter matrices of the components, these trimmed likelihood maximizations result in ill-posed problems. Moreover, non-interesting or “spurious” clusters are often detected by unconstrained algorithms aimed at maximizing these trimmed likelihood criteria.A useful approach to avoid spurious solutions is to restrict relative components scatter by prespecified tuning constants. Recently new methodologies for constrained parsimonious model-based clustering have been introduced which include, in the untrimmed case, the 14 parsimonious models that are often applied in model-based clustering when assuming normal components as limit cases. In this paper we extend this approach to cope with the presence of atypical observations and discuss two viable strategies for automatically estimating the restriction parameters.
This paper is focused on the problem of inferring a circular order to solve two different issues arising in the analysis of real data in genomics: the development of a human atlas of circadian gene expressions and a taxonomy of neuronal mouse brain cells. The solutions are derived using different approaches to ordering in a circle the sampling points, the cells or the genes.
Robust inference for the Cluster Weighted Model requires the specification of a few hyper-parameters. Their role is crucial for increasing the quality of the estimators, while arbitrary decisions about their value could severely hamper inferential results. To guide the user in the delicate choice of such parameters, a monitoring approach has been introduced in the recent literature, yielding an adaptive method. The approach is here exemplified, via the analysis of a dataset on the effect of punishment regimes on crime rates.
Background Clinical management in orthogeriatric units and outcome indicators are similar for extracapsular fragility hip fractures, without discriminating between subtrochanteric and pertrochanteric fractures. Hypothesis Geriatric patients, 75 years or older, with subtrochanteric fractures have worse clinical and functional outcomes than those with pertrochanteric fractures. Materials and methods Retrospective observational study of data prospectively collected by the Spanish Hip Fracture Registry including patients 75 years or older, admitted for extracapsular hip fractures from January 2017 to June 2019. Demographic and baseline status, pre-operative, post-operative and 30-day follow-up data were included. Results A total of 13,939 patients with extracapsular hip fractures were registered: 12,199 (87.5%) pertrochanteric and 1740 (12.5%) subtrochanteric. At admission, patients with subtrochanteric fractures were younger (86.5 ± 5.8 versus 87.1 ± 5.6 years old), had better pre-fracture mobility (3.7 ± 2.7 versus 3.9 ± 2.8) (1-to-10 scale, 1 being independent) and were more likely to be living at home; those with pertrochanteric fractures had worse cognitive function (Pfeiffer 3.3 ± 3.3 versus 3.8 ± 3.5). The subtrochanteric fracture group showed worse post-fracture mobility (7.3 ± 2.7 versus 6.7 ± 2.7) and greater deterioration of mobility (3.7 ± 3.0 versus 2.9 ± 2.7). Among individuals living at home at baseline, those with subtrochanteric fractures were more likely to remain in an assisted facility at 30-day follow-up. In-hospital mortality during acute admission was higher for the subtrochanteric group (5.6% versus 4.5%) ( p = 0.028). To our knowledge, this is the first paper highlighting the differences between these two fracture groups in the geriatric population. Conclusions Subtrochanteric fractures in the older population are a different and worse entity, with greater morbimortality and functional decline than pertrochanteric fractures. Despite being younger and fitter at admission, older patients with subtrochanteric fractures have a higher risk of remaining non-weight bearing and undergoing re-operation and institutionalization. Orthogeriatric units should be aware of this and manage subtrochanteric fractures accordingly. Level of evidence: IV.
Background The diagnosis of migraine is mainly clinical and self-reported, which makes additional examinations unnecessary in most cases. Migraine can be subtyped into chronic (CM) and episodic (EM). Despite the very high prevalence of migraine, there are no evidence-based guidelines for differentiating between these subtypes other than the number of days of migraine headache per month. Thus, we consider it timely to perform a systematic review to search for physiological evidence from functional activity (as opposed to anatomical structure) for the differentiation between CM and EM, as well as potential functional biomarkers. For this purpose, Web of Science (WoS), Scopus, and PubMed databases were screened. Findings Among the 24 studies included in this review, most of them (22) reported statistically significant differences between the groups of CM and EM. This finding is consistent regardless of brain activity acquisition modality, ictal stage, and recording condition for a wide variety of analyses. That speaks for a supramodal and domain-general differences between CM and EM that goes beyond a differentiation based on the days of migraine per month. Together, the reviewed studies demonstrates that electro- and magneto-physiological brain activity (M/EEG), as well as neurovascular and metabolic recordings from functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), show characteristic patterns that allow to differentiate between CM and EM groups. Conclusions Although a clear brain activity-based biomarker has not yet been identified to distinguish these subtypes of migraine, research is approaching headache specialists to a migraine diagnosis based not only on symptoms and signs reported by patients. Future studies based on M/EEG should pay special attention to the brain activity in medium and fast frequency bands, mainly the beta band. On the other hand, fMRI and PET studies should focus on neural circuits and regions related to pain and emotional processing.
The choice of age as a physiological parameter to structure a population and to describe its dynamics involves the election of the life-span. The analysis of an unbounded life-span age-structured population model is motivated because, not only new models continue to appear in this framework, but also it is required by the study of the asymptotic behaviour of its dynamics. The numerical integration of the corresponding model is usually performed in bounded domains through the truncation of the age life-span. Here, we propose a new numerical method that avoids the truncation of the unbounded age domain. It is completely analyzed and second order of convergence is established. We report some experiments to exhibit numerically the theoretical results and the behaviour of the problem in the simulation of the evolution of the Nicholson’s blowflies model.
Farmland ecosystems are seasonally dynamic habitats shaped by meteorological fluctuations and anthropogenic land-use changes. Farmland birds may be seasonally constrained with limited foraging and breeding resources (so-called “resource bottlenecks”), especially when there is a loss of natural and semi-natural habitats. During spring, the growth of cereal crops makes a large proportion of arable land unsuitable for specialist steppe birds with narrow vegetation structure requirements. We investigated the existence of a seasonal bottleneck of suitable habitats for steppe birds using the endangered Pin-tailed sandgrouse (Pterocles alchata) as a model species. We used for first time lightweight GPS tags to study habitat selection and movement patterns throughout the cereal crop cycle during three years in north-eastern Spain. We also evaluated if conservation measures promoting suitable vegetation structures for steppe birds (Targeted Fallow Management, TFM) influenced habitat selection. Sandgrouse avoided cereal crops when cereal vegetation was high, resulting in a 30% reduction of suitable habitat area at the start of the breeding season. This proved the existence of a spring habitat bottleneck when sandgrouse only selected open natural habitats and fallows. Sandgrouse similarly selected TFM and conventionally managed fallows during and after the bottleneck, possibly because of their similar vegetation structure and the scarcity of alternative suitable habitats. Halting the ongoing loss of fallow land is paramount for the conservation of steppe birds like sandgrouse because they constitute a key refuge to buffer the impacts of seasonal habitat bottlenecks.
Water leakages and unplanned water supply interruptions are relevant variables in the provision of drinking water since they directly impact customers and the economic and environmental performance of water companies. For the first time, in this study, we estimated specific efficiency scores for these two quality-of-service variables using the multi-directional data envelopment analysis technique for a sample of 21 Chilean water companies over the 2007–2018 period. Unlike previous studies, this methodological approach allowed us to estimate potential savings for both quality-of-service variables. The results indicate that the Chilean water industry could improve its efficiency over water leakage and unplanned water supply interruption by 28.6% and 52.5%, respectively, while supplying the same volume of drinking water. It is estimated that water companies could save around 48 million cubic metres of drinking water per year. Savings on unplanned water supply interruptions for the Chilean water industry are estimated to be at the level of 62,419 h per year.
Pressure retarded osmosis (PRO) is a process that is able to convert a salinity gradient into electrical energy through a turbine. This process has gained attention as a possible renewable energy technology for integration into desalination plants to improve their energy efficiency. Despite recent efforts, PRO is not yet commercially available due to drawbacks related to, among others, PRO membrane and module development. The aim of this study is to provide a simulation tool for full-scale PRO systems that allows accurate estimates of PRO-related energy generation to be made. The proposed tool enables analysis of single-stage systems with PRO modules in series and the setting of boundary conditions per module in terms of maximum flux recovery, and maximum and minimum feed/draw flow. The HTI OsMem™ 2521 spiral wound membrane module (SWMM) was evaluated considering an 8 in. diameter (high active area). Increasing the number of SWMMs in series was found to increase permeate flow and the energy that can be generated, even when considering the pressure drop on both draw and feed side and the effect of the dilution and concentration of the draw and feed solutions. The proposed tool allows to determine the safe operating windows and operating points for maximization of energy generation for fixed and variable operating conditions.
Entrepreneurial intention plays a key role in entrepreneurship. Over the years, scholars have explained it using personality traits, cognitive models and, to a lesser extent, the role of social environment. Since this role has been underestimated, we build on trait activation theory to explore how social networks are especially relevant and can trigger the activation of individuals’ need for achievement to predict entrepreneurial intention. We test our hypotheses on a sample of 597 university students from Spain using partial least squares (PLS). Our results confirm that social network size positively influences the entrepreneurial information obtained in social networks, which in turn, positively impacts entrepreneurial intention. Additionally, we found that need for achievement is activated in the context of social networks, enhancing the influence of this information on entrepreneurial intention. Through fuzzy-set qualitative comparative analysis (fsQCA), we also identify alternative configurations of the previous variables that lead to greater entrepreneurial intention.
Different agri-food wastes (brewer´s spent grain (BSG), spent coffee ground (SCG) and kale stems) have been proposed as excellent sources of protein-enriched extracts with an antioxidant capacity. The optimization of the microwave-assisted hydrothermal and alkali extraction has been compared in this study. From a technical and economic point of view, the extraction of BSG under optimal conditions (110 ºC, 10 min and 0.5 M NaOH) provided the best extract with a content of 14.6 kg protein/100 kg BSG (dry matter), 13.8 g/L of total sugars and an antioxidant activity (DPPH method) of 17.1 mg trolox equivalents (TE)/g BSG. This extract had the lowest production cost (29.9 €/kg) and a minimum selling price of 51.7 €/kg, estimated for an extraction pilot plant of 15 kg/h of BSG. The microwave-assisted hydrothermal extraction of kale stems, a novel waste in the biorefinery context, also provides bioactive and green extracts of commercial interest. There is a need for specific research studies related to biorefining of agri-food wastes to produce proteins for food, contributing to the development of a future sustainable and climate-neutral agriculture. The proposed techno-economic assessment represents an important advance in research and scaling-up of microwave-assisted extraction processes for protein recovery from agri-food wastes.
The waste formed during sugar- and wine-making activities has attracted our attention given its ability to inhibit corrosion in the presence of brine in a de-icing formulation. Herein the addition of amines to de-sugared beet molasses and winery lees is found to improve their anti-corrosive properties. Thus, weight-loss experiments clearly show that the addition of a small amount of amines to molasses or lees results in marked corrosion inhibition on carbon and galvanized steel. Subsequent electrochemical experiments and microscopy studies supported this finding. In addition, microscopy images indicated that triethanolamine was the best candidate amongst the amines tested for use in the final de-icing formulation. Ice-melting experiments demonstrated that the presence of molasses/lees together with triethanolamine does not alter the properties of the de-icing agent. When corrosion on galvanized and carbon steel probes was measured under environmental conditions, a decrease of 88% for galvanized steel and 65% for carbon steel was achieved due to the inhibiting action of the molasses/triethanolamine mixture. These results suggest that the addition of molasses/lees and triethanolamine to brine-based de-icing agents is recommended.
Background The hydrothermal reduction of CO2 using organic molecules such as alcohols can produce renewable fuels and platform chemicals, such as formic acid (FA). If the process is performed using glucose as reductant, the yield is especially high, because FA is selectively produced both by reduction of CO2 and by degradation of glucose degradation in alkaline hydrothermal media. Methods This article analyzes the origin of formic acid using NaH¹³CO3 as CO2 source, assisted by HPLC and ¹³C-NMR to study the origin of FA. Significant findings Results show that two reactions pathways take place: the first one, at short reaction times, consists on the decomposition of glucose into formic acid and other by-products, achieving low yield to FA-¹³C, whereas longer reaction times lead to a higher yield to FA-¹³C. Similarly, temperature plays an important role, being 300°C the optimal. Further reactions were performed using the main by-products of previous reactions (acetic acid, lactic acid, glycolaldehyde and glyceraldehyde) as reductants to understand the reaction mechanisms. Results indicate that the reduction pathway of NaHCO3 take place by oxidation of the by-products rather than by the oxidation of glucose itself, needing long reaction times to achieve significant high ratios of FA-¹³C/ total FA.
Key message Tree-ring growth of pollarded narrow-leaved ash trees in Central Spain reveals traditional management cessation in 1970 and property-specific management patterns. Abstract Tree pollarding was a dominant management strategy of European forests for centuries creating open agroforestry landscapes with important cultural and environmental values. This traditional practice has been widely abandoned in last decades with a subsequent impact in terms of biodiversity and cultural loss. Central Spain hosts the largest and best-preserved area of pollarded narrow-leaved ash (Fraxinus angustifolia Vahl.) woodlands in Europe. The main aim of this research is to obtain rigorous historical records of pollarding frequency to get adequate information for traditional ash management. We used dendrochronological techniques to evaluate temporal changes of pollarding frequency and rotation length. We analysed the stand level synchrony and the effect of land property on pollarding activity from 322 trees growing in eight pollard stands in Central Spain. Pollarding events were unequivocally identified at tree level by a characteristic change in growth pattern. We identified 2426 tree-level pruning events with the first event dated in 1777. Historical pruning recurrence ranged between 5 and 10 years with higher pollarding frequency on private lands. Pruning events within each site were synchronous, suggesting the existence of a rotational schema within each stand. Pruning frequency decreased drastically in the 1970s matching with the depopulation of rural areas and the general abandonment of traditional practices. Pollarding practices have recovered in recent decades although with lower intensity and lacking the synchronic historical patterns. Providing technical and economic support to make this traditional activity profitably would have strong environmental revenue due the multiple ecosystem services provided by pollarded ashes.
Background Orthokeratology (ortho-k) is an overnight clinical contact lens wear technique to correct myopia and to reduce myopia progression wearing reverse-geometry rigid gas-permeable lenses. The lens fitting procedure in clinical practice usually requires subjective assessment of fluorescein pattern (fluorescein “bull’s eye” pattern). The aim of this study was to develop a novel tool for fluorescein pattern measurements to reduce subjective practitioner dependency, especially in inexperienced practitioners, in ortho-k practice. Methods A new MATLAB customized algorithm to measure the horizontal width of the four main zones of ortho-k fluorescein patterns (central bearing, tear reservoir, mid-peripheral bearing and edge lift) was designed. The algorithm was tested on a small image database consisting of 26 ortho-k fluorescein pattern images of 13 volunteers fitted with reverse geometry lenses (Seefree, Conoptica-Hecht Contactlinsen). The agreement between two independent observers and the ImageJ measurements was determined. Results The new clinical tool provided similar measurements to ImageJ software for the central bearing (4.20 ± 0.74 and 4.27 ± 0.69 mm; P = 0.21), tear reservoir (1.69 ± 0.41 and 1.69 ± 0.45 mm; P = 0.69), mid-peripheral bearing (1.17 ± 0.11 and 1.13 ± 0.10 mm; P < 0.01) and edge lift (0.48 ± 0.06 and 0.48 ± 0.06 mm; P = 0.81) zones. Good agreement between the software (limits of agreement lower than ±0.55 mm) and inter-observer measurements (limits of agreement lower than ±0.66 mm) was found. Conclusions The proposed clinical tool for semiautomatic fluorescein pattern measurements in ortho-k could help to reduce practitioner dependency in fluorescein pattern assessment with future potential to introduce prediction algorithms or artificial intelligence methods in myopia control management.
We propose a modification of a method based on Fourier analysis to obtain the Floquet characteristic exponents for periodic homogeneous linear systems, which shows a high precision. This modification uses a variational principle to find the correct Floquet exponents among the solutions of an algebraic equation. Once we have these Floquet exponents, we determine explicit approximated solutions. We test our results on systems for which exact solutions are known to verify the accuracy of our method including one dimensional periodic potentials of interest in quantum physics. Using the equivalent linear system, we also study approximate solutions for homogeneous linear equations with periodic coefficients.
Water deficit is the main cause of abiotic stress to which plants are susceptible, whether cultivated or those that are underexploited, such as Physalis peruviana L. Searching for tools that contribute to the management of water deficit in plants is fundamental for the maintenance of agriculture, especially in arid and semi-arid areas around the world. Thus, the objective of this study was to evaluate the effect of chemical priming with proline and sodium nitroprusside as promoters of increased tolerance to water deficit in P. peruviana plants. Plants grown under well hydrated conditions (FC of 70±5%) were sprayed with proline (10 and 20 mM) or sodium nitroprusside (25 and 50 μM) and evaluated after exposure to water deficit (FC of 20±5%). Plants cultivated under water deficit without pretreatment showed reductions in the variables of water relations, gas exchange and growth. Proline and sodium nitroprusside were effective in maintaining less negative water potential, contributing to improvements in gas exchange, such as CO2 assimilation, stomatal conductance and transpiration. Thus, it was possible to measure greater tolerance to water deficit in pretreated plants and, consequently, greater biomass accumulation. It appeard that pretreatment of proline and sodium nitroprusside can have a priming effect against water deficit in P. peruviana plants. Index terms: Abiotic stress; water deficit mitigation; goldenberry.
Context: Design smell Prioritization is a significant activity that tunes the process of software quality enhancement and raises its life cycle. Objective: A multi-criteria merge strategy for Design Smell prioritization is described. The strategy is exemplified with the case of God Class Design Smell. Method: An empirical adjustment of the strategy is performed using a dataset of 24 open source projects. Empirical evaluation was conducted in order to check how is the top ranked God Classes obtained by the proposed technique compared against the top ranked God class according to the opinion of developers involved in each of the projects in the dataset. Results: Results of the evaluation show the strategy should be improved. Analysis of the differences between projects where respondents answer correlates with the strategy and those projects where
European green agricultural policies have been relaxed to allow cultivation of fallow land to produce animal feed and meet shortfalls in exports from Ukraine and Russia. However, conversion of semi-natural habitats will disproportionately impact long term biodiversity and food security. In their Comment in @CommsEarth, Manuel Morales and colleagues argue that we must act now to protect green agricultural policies in the EU to ensure food security in the future.
Institution pages aggregate content on ResearchGate related to an institution. The members listed on this page have self-identified as being affiliated with this institution. Publications listed on this page were identified by our algorithms as relating to this institution. This page was not created or approved by the institution. If you represent an institution and have questions about these pages or wish to report inaccurate content, you can contact us here.
4,461 members
Javier Finat
  • Department of Algebra, Geometry and Topology
Cesareo Hernandez Iglesias
  • Grupo de Ingeniería de los Sistemas Sociales
Javier Pajares
  • Grupo de Ingeniería de los Sistemas Sociales
Segismundo Izquierdo
  • Department of Business Organization and Marketing and Market Research
Information
Address
Pza. del Campus Universitario, s/n, 47011, Valladolid, Spain
Head of institution
Prof. Antonio Largo
Website
http://www.uva.es