On extended chebyshev systems with positive accuracy

Agraïments: The first author is supported by a FAPESP-BRAZIL grant 2013/16492-0. The second author is supported by UNAB13-4E-1604 grant.A classical necessary condition for an ordered set of n+1 functions F to be an ECT-system in a closed interval is that all the Wronskians do not vanish. With this condition all the elements of Span(F) have at most n zeros taking into account the multiplicity. Here the problem of bounding the number of zeros of Span(F) is considered as well as the effectiveness of the upper bound when some Wronskians vanish. For this case we also study the possible configurations of zeros that can be realized by elements of Span(F). An application to count the number of isolated periodic orbits for a family of nonsmooth systems is performed

Los exámenes de Física en la enseñanza por transmisión y en la enseñanza por investigación

In this paper we show the results of a comparative ancilysis between ordinary tests of Physics and Chemistry and the ones used from a constructivist view. The study is focused in two aspects: firstly, it aims to show that the constructivist conception of leaming imposes considerable modifications in the tests content; secondly it highlights the deficiencies found in the tests designed after constructivist teaching. These deficiencies will just be solved by an investigation mainly aimed to assessment transformation

Bone Mineral Disease After Kidney Transplantation

Chronic kidney disease-mineral bone disorder (CKD-MBD) after kidney transplantation is a mix of pre-existing disorders and new alterations. The final consequences are reflected fundamentally as abnormal mineral metabolism (hypercalcemia, hypophosphatemia) and bone alterations [high or low bone turnover disease (as fibrous osteitis or adynamic bone disease), an eventual compromise of bone mineralization, decrease bone mineral density and bone fractures]. The major cause of post-transplantation hypercalcemia is the persistence of severe secondary hyperparathyroidism, and treatment options include calcimimetics or parathyroidectomy. On turn, hypophosphatemia is caused by both the persistence of high blood levels of PTH and/or high blood levels of FGF23, with its correction being very difficult to achieve. The most frequent bone morphology alteration is low bone turnover disease, while high-turnover osteopathy decreases in frequency after transplantation. Although the pathogenic mechanisms of these abnormalities have not been fully clarified, the available evidence suggests that there are a number of factors that play a very important role, such as immunosuppressive treatment, persistently high levels of PTH, vitamin D deficiency and hypophosphatemia. Fracture risk is four-fold higher in transplanted patients compared to general population. The most relevant risk factors for fracture in the kidney transplant population are diabetes mellitus, female sex, advanced age (especially > 65 years), dialysis vintage, high PTH levels and low phosphate levels, osteoporosis, pre-transplant stress fracture and high doses or prolonged steroids therapy. Treatment alternatives for CKD-MBD after transplantation include minimization of corticosteroids, use of calcium and vitamin D supplements, antiresorptives (bisphosphonates or Denosumab) and osteoformers (synthetic parathyroid hormone). As both mineral metabolism and bone disorders lead to increased morbidity and mortality, the presence of these changes after transplantation has to be prevented (if possible), minimized, diagnosed, and treated as soon as possible.info:eu-repo/semantics/publishedVersio

25(OH)D3-enriched or fortified foods are more efficient at tackling inadequate vitamin D status than vitamin D3

The ability to synthesise sufficient vitamin D through sunlight in human subjects can be limited. Thus, diet has become an important contributor to vitamin D intake and status; however, there are only a few foods (e.g. egg yolk, oily fish) naturally rich in vitamin D. Therefore, vitamin D-enriched foods via supplementing the animals’ diet with vitamin D or vitamin D fortification of foods have been proposed as strategies to increase vitamin D intake. Evidence that cholecalciferol (vitamin D3) and calcifediol (25(OH)D3) content of eggs, fish and milk increased in response to vitamin D3 supplementation of hens, fish or cows’ diets was identified when vitamin D-enrichment studies were reviewed. However, evidence from supplementation studies with hens showed only dietary 25(OH)D3, not vitamin D3 supplementation, resulted in a pronounced increase of 25(OH)D3 in the eggs. Furthermore, evidence from randomised controlled trials indicated that a 25(OH)D3 oral supplement could be absorbed faster and more efficiently raise serum 25(OH)D concentration compared with vitamin D3 supplementation. Moreover, evidence showed the relative effectiveness of increasing vitamin D status using 25(OH)D3 varied between 3·13 and 7·14 times that of vitamin D3, probably due to the different characteristics of the investigated subjects or study design. Therefore, vitamin D-enrichment or fortified foods using 25(OH)D3 would appear to have advantages over vitamin D3. Further wellcontrolled studies are needed to assess the effects of 25(OH)D3 enriched or fortified foods in the general population and clinical patients

Prediction of the transmission loss in a flexible chamber

[EN] Acoustic components have been extensively studied supposing perfectly rigid behavior. Although some works have been performed for the radiated sound in the case of a flexible element, an important lack of information exists concerning transmission loss analysis. The current investigation proposes the study for a generic flexible expansion chamber. The analysis has been performed using two different methods: a resolution in the time domain, using a Finite Volume discretization for the fluid domain and a Finite Element discretization for the solid domain, and an approach in the frequency domain, using a Finite Element discretization for both fluid and solid. After studying the rigid case in order to tune up the simulation, the study of the flexible case shows a good agreement among both methods. The comparison of rigid and flexible expansion chambers shows the importance of accounting for these phenomena when the frequency content of the acoustic signal excites the natural modes of the structure.This work has been partially supported by the Spanish Ministerio de Economia y Competitividad through Grant No. DPI2015-70464-R and Generalitat Valenciana by means of project Prometeo/2016/007.Torregrosa, AJ.; Gil, A.; García-Cuevas González, LM.; Quintero-Igeño, P.; Denia, FD. (2018). Prediction of the transmission loss in a flexible chamber. Journal of Fluids and Structures. 82:134-153. https://doi.org/10.1016/j.jfluidstructs.2018.07.003S1341538

Self-Description Questionnaire II (short version): evidence of reliability and validity in a sample of chilean adolescents

El objetivo de este estudio fue analizar la fiabilidad y validez de las puntuaciones de la versión breve del Self-Description Questionnaire II (SDQ-II-S) en población chilena. La muestra se compuso de 1255 adolescentes chilenos, con un rango de edad de 13 a 17 años (M = 15.10; DT = 1.30). El análisis factorial confirmatorio corroboró la estructura original de 11 factores correlacionados del SDQ-II-S. La multidimensionalidad del cuestionario también fue avalada por la pequeña magnitud de las correlaciones entre los 11 factores (M = 0.26). Los coeficientes alfa de Cronbach variaron desde 0.70 hasta 0.84, y se destacó una adecuada fiabilidad. Para profundizar en el análisis de la validez de constructo del SDQ-II-S, se relacionaron las puntuaciones de las diferentes escalas con puntuaciones en medidas de ansiedad (Inventario de Ansiedad Estado-Rasgo) y autoeficacia (Escala de Autoeficacia Percibida Específica de Situaciones Académicas). Los resultados pusieron de manifiesto que estos cuestionarios permiten analizar constructos diferenciados aunque relacionados. Los datos de este trabajo destacan que el SDQ-II-S presenta adecuadas propiedades psicométricas en población chilena, contrarrestando las carencias existentes en lo que respecta a la evaluación del autoconcepto, y resaltan interesantes aplicaciones tanto en el ámbito aplicado como en el de la investigación.This study sought to analyse the reliability and validity of the scores from the Short Version of the Self-Description Questionnaire II (SDQ-II-S). The sample consisted of 1255 Chilean adolescents with an age range of 13–17 years (M = 15.10; SD = 1.30). Confirmatory factor analyses verified the original correlated 11-factor structure of the SDQ-II-S. The multidimensionality of the questionnaire was also supported by small magnitude of correlations among factors (M = 0.26). Cronbach's alpha coefficients ranged from 0.70 to 0.84, showing adequate reliability. For further analyses of the construct validity of SDQ-II-S, scores of the different scales were related to scores on anxiety (State Anxiety Inventory-Trait) and self-efficacy measurements (Academic Situations Specific Perceived Self-Efficacy Scale). The results revealed that those questionnaires assess different –yet related– constructs. The data presented indicate that the SDQ-II-S shows adequate psychometric properties in the Chilean population, thereby countering the current scarcity of appropriate self-concept assessment measurements, and displaying interesting applications both in the applied and research areas

A tool for predicting the thermal performance of a diesel engine

This paper presents a thermal network model for the simulation of the transient response of diesel engines. The model was adjusted by using experimental data from a completely instrumented engine run under steady-state and transient conditions. Comparisons between measured and predicted material temperatures over a wide range of engine running conditions show a mean error of 7◦C. The model was then used to predict the thermal behavior of a different engine. Model results were checked against oil and coolant temperatures measured during engine warm-up at constant speed and load, and on a New European Driving Cycle. Results show that the model predicts these temperatures with a maximum error of 3◦C.Torregrosa, AJ.; Olmeda González, PC.; Martín Díaz, J.; Romero Piedrahita, CA. (2011). A tool for predicting the thermal performance of a diesel engine. Heat Transfer Engineering. 32(10):891-904. doi:10.1080/01457632.2011.548639S891904321

New lower bound for the Hilbert number in piecewise quadratic differential systems

We study the number of limit cycles bifurcating from a piecewise quadratic system. All the differential systems considered are piecewise in two zones separated by a straight line. We prove the existence of 16 crossing limit cycles in this class of systems. If we denote by H (n) the extension of the Hilbert number to degree n piecewise polynomial differential systems, then H (2)≥16. As fas as we are concerned, this is the best lower bound for the quadratic class. Moreover, in the studied cases, all limit cycles appear nested bifurcating from a period annulus of a isochronous quadratic center