267 research outputs found
Los algoritmos para el cĂĄlculo de la raĂz cuadrada y sus antecedentes en textos escolares antiguos
Estructura i context en una col·lecció de problemes de geometria del segle XVI: les «demandas» de Juan Pérez de Moya
At the paper we explained about the didactic utilization of old geometric
problems in the mathematical education. An example of this question is studied in the
formation of primary education teachers with the geometric «demandas» (problems)
of Juan Pérez de Moya. We show how the structure and the context of these «demandas
» are a reflection of the mathematical interests of the citizens in the 16th century.
The mathematical resources used by PĂ©rez de Moya in the resolution of the problems
that he proposes allow to make a comment of the historical evolution of the
concepts and basicmethods of themathematical science, through a comparison with
the ones current methods. Finally, we point out how some of the problems picked up
in this collection offer suggestions and ideas that they can be from interest for the teacher
of mathematics
El tratamiento elĂ©ctrico de los trastornos del ritmo cardĂaco: resultado en el tratamiento de la fibriolaciĂłn y eo aleteo auriculares mediante contrachoques externos de corriente contĂnua
Variabilité climatique et statistiques. Etude par simulation de la puissance et de la robustesse de quelques tests utilisés pour vérifier l'homogénéité de chroniques
L'analyse statistique de sĂ©ries chronologiques de donnĂ©es hydromĂ©tĂ©orologiques est un des outils d'identification de variations climatiques. Cette analyse consiste le plus souvent Ă la mise en Ćuvre et Ă l'interprĂ©tation de tests statistiques d'homogĂ©nĂ©itĂ© des sĂ©ries. Les sĂ©ries hydrologiques (donnĂ©es de pluie ou de dĂ©bit) se caractĂ©risent frĂ©quemment par des effectifs faibles, et ne rĂ©pondent que rarement aux conditions requises par l'application des tests statistiques dont certains sont paramĂ©triques.Nous avons cherchĂ© Ă Ă©valuer, en terme de puissance et de robustesse, le comportement de quelques mĂ©thodes statistiques largement employĂ©es dans les Ă©tudes de variabilitĂ© climatique. Ce travail a Ă©tĂ© menĂ© dans chaque cas Ă©tudiĂ© au moyen de procĂ©dures de simulations type Monte-Carlo de 100 Ă©chantillons de 50 valeurs conformes aux caractĂ©ristiques souvent rencontrĂ©es dans les sĂ©ries naturelles. La variabilitĂ© simulĂ©e est celle d'un changement brutal de la moyenne. Les procĂ©dures concernĂ©es sont le test de corrĂ©lation sur le rang, le test de Pettitt, le test de Buishand, la procĂ©dure bayĂ©sienne de Lee et Heghinian, et la procĂ©dure de segmentation des sĂ©ries hydromĂ©tĂ©orologiques de Hubert et Carbonnel. Des sĂ©ries artificielles soit stationnaires, soit affectĂ©es par une rupture de la moyenne, normales, non-normales, autocorrĂ©lĂ©es, prĂ©sentant une tendance linĂ©aire ou un changement brutal de la variance ont Ă©tĂ© gĂ©nĂ©rĂ©es.Les conclusions de ce travail doivent ĂȘtre nuancĂ©es selon la mĂ©thode considĂ©rĂ©e. D'une maniĂšre gĂ©nĂ©rale la puissance maximale estimĂ©e se situe autour de 50% pour des taux de rupture de la moyenne de l'ordre de 75% de la valeur de l'Ă©cart-type. Par ailleurs il apparaĂźt que l'autocorrĂ©lation et la prĂ©sence d'une tendance dans les sĂ©ries sont les deux caractĂ©ristiques qui pĂ©nalisent le plus les performances des procĂ©dures.Statistical analysis of hydrometeorological time series is often used to identify climatic variations. Most often this analysis consists of applying and interpreting statistical tests of time series homogeneity. Hydrological time series (rainfall and runoff data) are often short and do not always comply with the hypotheses of the statistical methods. Through simulation we have investigated the power and the robustness of some tests which are widely used in the studies dealing with climatic variability. In each case studied, one hundred samples of fifty elements have been generated based on the main characteristics of natural rainfall series. A shift in the mean has been used to represent a possible climatic variation. The procedures used are the rank correlation test, Pettitt's test, Buishand's test, Lee and Heghinian's bayesian procedure, and Hubert and Carbonnel's segmentation procedure for hydrometeorological series.Each simulation of one hundred samples is used to assess the performances of the methods considering a specific characteristic of the series: normality or non-normality, autocorrelation, trend, shift in the variance. First of all, stationary series have been simulated to evaluate the type I error of the tests. Then the series have been simulated with a break in the mean with different levels of amplitude, from 25% to 100% of the standard deviation value. The rank correlation test, Pettitt's test, Buishand's test and the segmentation procedure with a significance level of 1% (significance level of ScheffĂ©'s test) reject as heterogeneous less than ten series over one hundred homogeneous simulated series. This result is consistent with the type I error of a statistical test. On the other hand, Lee and Heghinian's bayesian method rejects about 40% of the series. This result means that this latter procedure must only be applied under the hypothesis of heterogeneity. The estimated power of the methods exceeds 40% to 50% when the break in the mean is more than 75% of the standard deviation value.Independent series have been simulated from normal, log-normal and Pearson distributions to compare the performances of the methods requiring normality. The results show that normality has no significant impact on the performances of these methods. However, the simulations do show that the condition of independence of the successive elements of the series is essential to keep performances constant. Otherwise a trend in the series makes the tests inefficient, except for the rank correlation test for which the alternative is a trend. No method seems to be robust against both negative and positive autoregressive dependencies. The procedures requiring a constant variance are robust when the series keep a constant mean, but seem more or less slightly influenced by a break both in the mean and in the standard deviation
Solving the Klein-Gordon equation using Fourier spectral methods: A benchmark test for computer performance
The cubic Klein-Gordon equation is a simple but non-trivial partial
differential equation whose numerical solution has the main building blocks
required for the solution of many other partial differential equations. In this
study, the library 2DECOMP&FFT is used in a Fourier spectral scheme to solve
the Klein-Gordon equation and strong scaling of the code is examined on
thirteen different machines for a problem size of 512^3. The results are useful
in assessing likely performance of other parallel fast Fourier transform based
programs for solving partial differential equations. The problem is chosen to
be large enough to solve on a workstation, yet also of interest to solve
quickly on a supercomputer, in particular for parametric studies. Unlike other
high performance computing benchmarks, for this problem size, the time to
solution will not be improved by simply building a bigger supercomputer.Comment: 10 page
De différents aspects de la variabilité de la pluviométrie en Afrique de l'Ouest et Centrale non sahélienne
La sĂ©cheresse observĂ©e depuis plus d'une vingtaine d'annĂ©es dans les pays sahĂ©liens se fait Ă©galement ressentir plus au sud dans des rĂ©gions d'Afrique aux climats plus humides. Cette baisse de la pluviomĂ©trie et la diminution des apports en eau de surface qu'elle entraĂźne y sont de nature Ă pĂ©naliser les diffĂ©rents projets de dĂ©veloppements liĂ©s Ă l'eau. Le programme ICCARE menĂ© par l'ORSTOM a pour objet l'identification et les consĂ©quences de cette variabilitĂ© climatique dans l'ensemble de la zone non sahĂ©lienne d'Afrique de l'Ouest et Centrale, en s'appuyant sur les donnĂ©es de deux cents postes pluviomĂ©triques et sur un ensemble de mĂ©thodes alliant reprĂ©sentations cartographiques et procĂ©dures statistiques de dĂ©tection de ruptures dans les sĂ©ries chronologiques, univariĂ©es et multivariĂ©es. La simple Ă©tude des sĂ©ries chronologiques de hauteurs prĂ©cipitĂ©es annuelles fait apparaĂźtre une nette et brutale fluctuation du rĂ©gime pluviomĂ©trique dans toute la rĂ©gion considĂ©rĂ©e, Ă la fin des annĂ©es 1960 et au dĂ©but des annĂ©es 1970. D'une maniĂšre gĂ©nĂ©rale, il apparaĂźt que ce sont les zones Ă rĂ©gime pluviomĂ©trique extrĂȘme qui ont subi les modifications les plus importantes : les plus arrosĂ©es (de la GuinĂ©e Ă la CĂŽte d'Ivoire) et les plus arides (la bordure sahĂ©lienne au nord de la zone Ă©tudiĂ©e). Entre les deux, le phĂ©nomĂšne est d'intensitĂ© plus nuancĂ©e. Les diffĂ©rentes procĂ©dures statistiques appliquĂ©es aux sĂ©ries de hauteurs annuelles prĂ©cipitĂ©es soulignent l'existence d'une rupture survenue Ă la fin des annĂ©es 1960 ou au dĂ©but des annĂ©es 1970, et donc en phase avec ce qui a Ă©tĂ© observĂ© et Ă©tudiĂ© au Sahel. D'autres variables permettant une caractĂ©risation plus "qualitative" du phĂ©nomĂšne ont Ă©galement Ă©tĂ© Ă©tudiĂ©es. Elles apportent un complĂ©ment d'information quant aux manifestations de cette variabilitĂ© pluviomĂ©trique et montrent que la variabilitĂ© climatique se traduit Ă diffĂ©rents niveaux (durĂ©e des saisons des pluies, quantitĂ©s prĂ©cipitĂ©es hors saisons des pluies, etc.). L'examen des sĂ©ries chronologiques depuis l'origine des stations a permis de resituer l'Ă©vĂ©nement observĂ© dans une perspective historique faite d'alternances de pĂ©riodes sĂšches et de pĂ©riodes humides. Le phĂ©nomĂšne observĂ© Ă la fin des annĂ©es 1960 et au dĂ©but des annĂ©es 1970 apparaĂźt, cependant comme le plus significatif du point de vue statistique. Si les causes premiĂšres d'apparition du phĂ©nomĂšne sont, Ă l'heure actuelle, encore insuffisamment expliquĂ©es, et ce mĂȘme si certaines activitĂ©s humaines y ont, sans aucun doute, contribuĂ©, cette baisse de la pluviomĂ©trie a, bien entendu, des consĂ©quences importantes sur la disponibilitĂ© des ressources en eau dans ces rĂ©gions. Si la carence pure et simple n'est pas Ă craindre dans ces rĂ©gions oĂč les quantitĂ©s prĂ©cipitĂ©es restent importantes dans l'absolu, les effets de cette variabilitĂ© climatique peuvent, malgrĂ© tout, se rĂ©vĂ©ler dĂ©sastreux, en ce sens qu'ils modifient les donnĂ©es d'un Ă©quilibre dĂ©jĂ souvent mis Ă mal par ailleurs (pression anthropique et dĂ©forestation par exemple).The drought observed for more than twenty years in the sahelian countries has also affected those located more to the South with more humid climates (SUTCLIFFE and KNOTT, 1987; NICHOLSON et al, 1988; MAHE and OLIVRY, 1991; OLIVRY et al, 1993 PATUREL et al, 1995). The decrease in rainfall and consequently that in runoff might penalise development projects linked with water supply. The ICCARE programme led by ORSTOM aimed at identifying and measuring the consequences of this climatic variability in the non-sahelian parts of the West and Central African region as a whole. The study was based on rainfall data from more than two hundred stations, break detection methods in the time series as well as cartographic tools were used. This study allowed to highlight the manifestations of the climatic variability observed for nearly 25 years in West and Central Africa. Whereas it had been thought for a long time that the rainfall deficit was restricted to the sahelian region, this study showed that the forest covered regions were also affected and generally speaking the so-called 'humid Africa'. The decrease in rainfall entails that in runoff and thus a change in water resources availability which is the cornerstone of a fairly great number of development projects. Hydrological regimes variability and possible modifications of rainfall-runoff relationship are to be the next stages of the ICCARE programme, partial results were already published (SERVAT et al, 1997). A simple study of the time series showed straightforward fluctuations of the rainfall patterns (figures 2 and 3), which happened during the late sixties or the early seventies over the whole region. The mapping of the time series analysis depicts a clear general trend towards a shift of the isohyets to the south-south-west from the 1950's to the 1980's. This shift reflects a sharp drop in the annual rainfall over the whole of the non-sahelian west and central Africa. Generally speaking it appears that the zones with extreme rainfall patterns underwent the most important modifications, namely : the wettest ones from Guinea to Ivory Coast and the driest ones, bordering the sahelian region to the North of the studied area. Elsewhere changes are less drastic (SERVAT et al, 1996). The different statistical procedures applied to the series of annual rainfall showed breaks taking place during the late 1960's or the early 1970's (figure 4), which was in keeping with what had been observed in the sahelian region. Rainfall deficits were in the order of 20% and they could reach values higher than 25% (table 1), in particular along the Atlantic Coast or in the North, which upholds the fact that 'humid Africa' was also severely affected by the rainfall variability. Other variables which allow a more qualitative characterisation of the phenomenon were also studied (table 2) (figures 5 and 6) ( PATUREL et al, 1997, SERVAT et al, 1997). They brought complementary information about the ways the rainfall variability expresses itself. The pattern of the rainy season was slightly different from what it had been before the 1970's, its length was generally shorter either because it started later than before or because it ended earlier. Likewise, the rainfall distribution was modified, which resulted in a more 'homogeneous' pattern for the zone with only one rainy season and in a sensible change in the ratio of the rainfall heights of the two rainy seasons. Some of the regions of the so-called 'wooded' savannah saw a modification of their climate with a shift from a 'guinean' climate toward a 'sudanese' one. In west Africa some regions saw also a decrease of the amount of precipitation occurring outside the rainy season, which led to a strengthening of the dry season and contributed, if need be, to the perception of the phenomenon by local populations. The decrease in the number of rainy days, where it was possible to study it, was in line with the rainfall deficit. A complementary statistical approach was carried out, it consists of a spatio-temporal study using a multidimensional exploratory analysis (KHODJA et al, 1998). This led to using a multivariate test for detecting a shift in the mean value. This approach confirmed the results obtained with univariate analyses whether it is for the time location of the break (late 1960's, early 1970's) or whether for the heterogeneous character of the phenomenon both from a spatial or temporal point of view. A major characteristic of this persisting rainfall deficit seems to be the existence of two axes of heterogeneity along the north-south and east-west directions (table 3) (figure 7). The survey of the rainfall time series from the origin allowed to place the drought in a historical perspective. So, it appears that, since the beginning of the century, the region underwent a succession of dry and wet periods, although it is difficult to speak of cycles. The phenomenon observed during the late 60's and the early 70's appears, however, as the most significant from a statistical point of view. Besides, the still lasting period of deficit has displayed a length and an intensity quite remarkable, in particular in the north and west sectors of the studied zone where the phenomenon presents an even more exceptional character (figures 8,9,10 and 11). Even though what brought about this diminution in rainfall remains, until now, unexplained, certain human activities undoubtedly contributed to the aggravation of the phenomenon. Although deforestation cannot be held entirely responsible for the drought, the fact remains that overlogging helped to increase the rainfall deficit in numerous regions along the Atlantic coast and the Guinean gulf. Of course, this rainfall deficit has important consequences on the availability of water resources in those regions. Agriculture, the filling of dams and therefore the hydroelectric production, to mention only a few domains, are strongly penalised by this decrease in resources. If a real shortage is not to be feared in those regions where the quantities of precipitation remain high in absolute terms, the effects of that variability can still prove to be disastrous, as they modify the elements of a balance that is already threatened by other factors (anthropic pressure and deforestation, for example). The ICCARE programme, which goes on with the study of the modifications of the river hydrological regimes, will give answers as to the effect of the rainfall deficit upon water resources availability
Importance de la résolution spatiale et temporelle des approches régionales de modélisation du stress hydrique
Les pressions accrues sur les ressources en eau liĂ©es aux changements climatiques et sociĂ©taux sont reconnues comme des enjeux mondiaux. Une approche rĂ©gionale de modĂ©lisation intĂ©grĂ©e, considĂ©rant des scĂ©narios hydrologiques et dâusages de lâeau sous contraintes climatiques et anthropiques, a ainsi Ă©tĂ© dĂ©veloppĂ©e. Celle-ci a dâabord Ă©tĂ© appliquĂ©e Ă lâĂ©chelle du bassin mĂ©diterranĂ©en au pas de temps annuel, puis Ă lâĂ©chelle du canton de Vaud (Suisse) au pas de temps mensuel. Commune aux deux Ă©tudes, cette approche permet dâidentifier les grandes tendances hydro-climatiques et dâusages de lâeau dâici Ă lâhorizon 2050 ainsi que les rĂ©gions les plus vulnĂ©rables au stress hydrique. Ces Ă©tudes soulignent lâimportance de pouvoir reprĂ©senter les variations rĂ©gionales et saisonniĂšres de la disponibilitĂ© des ressources et des demandes en eau. Sâappuyant sur les rĂ©sultats de ces deux travaux, cette communication vise Ă discuter de la question de la rĂ©solution temporelle et spatiale des approches rĂ©gionales de modĂ©lisation intĂ©grĂ©e du stress hydrique
Usefulness of Ultrasound in Assessing the Impact of Bariatric Surgery on Body Composition : a Pilot Study
Bariatric surgery (BS) has a significant impact on body composition. The purpose of the study is to evaluate the usefulness of musculoskeletal ultrasound (MUS) to bioelectrical impedance (BIA) in the follow-up of patients undergoing BS in terms of body composition and quality of life (QoL). This is a prospective pilot study including 32 subjects (75% female, mean age: 49.15 ± 1.9 years) who underwent BS. Fat mass (FM), lean mass (LM), and skeletal muscle index (SMI) were calculated by BIA. MUS measured subcutaneous fat (SF) and thigh muscle thickness (TMT) of the quadriceps. QoL was assessed by the Moorehead-Ardelt questionnaire. All these measurements were performed 1 month prior to BS and at 12-month follow-up. The mean BMI decreased by 6.63 ± 1.25 kg/m 2 (p =0.001). We observed significant reductions in FM (p =0.001) and SF (p =0.007) and in LM (p =0.001) but not in SMI and TMT. We found a correlation between the FM and SF (pre-surgical, r =0.42, p =0.01; post-surgical, r =0.52, p =0.003) and between SMI and TMT (pre-surgical, r =0.35, p =0.04; post-surgical, r =0.38, p =0.03). QoL test showed significant improvement (p =0.001). In addition, a correlation between the QoL questionnaire and TMT post-surgery (r =0.91, p =0.019) was observed. However, we did not find any statistically significant correlation between QoL assessment and SMI or LM. Our results suggest that MUS can be complementary to BIA for the evaluation and the follow-up of body composition after BS. TMT of quadriceps can provide relevant information about regional sarcopenia and has a significant correlation with QoL
Developing Automotive Products Using the EAST-ADL2, an AUTOSAR Compliant Architecture Description Language
International audienceCurrent development trends in automotive software feature increasing standardization of the embedded software structure. But it still remains the critical issue of the overall engineering information management to control the system definition and manage its complexity. System modeling based onan Architecture Description Language (ADL) is a way to keep these assets within one information structure. The original EAST-ADL was developed in the EAST-EEA project (www.east-eea.org) and basic concepts were reused in the AUTOSAR standardization initiative. The original EAST-ADL is currently refined in the ATESST project (www.atesst.org) to EAST-ADL2. This paper presents the results of the language extension provided by the EAST-ADL2 domain model and focuses on its possible extension of the AUTOSAR standard to support decomposition of E/E automotive systems
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