Nouvelles méthodes d’intégration pour traiter la plasticité en X-FEM

La méthode d’intégration utilisée classiquement en X-FEM fait dépendre la position des points d’intégration de la position de la fissure, ce qui convient difficilement à l’étude de la propagation d’une fissure dans un milieu plastifié. En effet, des étapes de projection de champs sont alors nécessaires. Afin de s’en affranchir, cette contribution propose deux approches alternatives. La première s’appuie sur les schémas d’intégration standards tandis que la seconde propose de différencier les points d’intégration des points où le comportement est évalué. Les méthodes proposées se limitent aux cas des interfaces

Two-stage reconstruction of post-traumatic segmental tibia bone loss with nailing

Introduction Treatment of lower extremity segmental bone loss is difficult. Masquelet et al. proposed a two-stage technique: first, debridement and filling of bone loss with an acrylic spacer; second, bone reconstruction by filling with cancellous bone in the space left free (following cement removal) inside the so-called self-induced periosteal membrane. In the originally described technique, the fracture site is stabilized by an external fixator, which remains in place throughout the bone healing process, i.e., often longer than 9 months with all the known disadvantages of this type of assembly. Following the principle of two-stage reconstruction, we modified the technique by reconstructing around an intramedullary-locking nail placed in the first stage. Hypothesis This technique prevents the mechanical complications related to external fixator use and provides faster resumption of weight-bearing. Patients and methods Twelve patients were operated for segmental tibial bone loss greater than 6 cm resulting from injury (four cases) or aseptic necrosis (one case) or septic necrosis (seven cases). All the patients were operated on in an emergency setting and the first stage was performed before the 2nd week. A free muscle flap (ten patients) or a pediculated fasciocutaneous flap (two patients) was necessary during this first step to cover the site and provide good conditions for secondary bone growth. The follow-up was 39.5 months (range, 12–94 months). Results Complete weight-bearing was resumed at a mean 4 months. After the second step, all the patients except one had apparently healed (complete weight-bearing with no pain). Five septic complications occurred after the second step, in one case leading to reconstruction failure. Four other patients had infectious complications successfully treated (as of the last follow-up) either by changing the nail in two cases or by prolonged antibiotic therapy in two other cases, with no graft loss. Discussion The use of the intramedullary nail facilitates the Masquelet technique by allowing the patient to resume weight-bearing more quickly and avoiding secondary fractures. However, the risk of sepsis remains high but can be controlled without compromising the final bone union in four cases out of five. Level of evidence Level IV. Retrospective study

Stability of a frictional, cohesive layer on a viscous substratum: validity of asymptotic solution and influence of material properties

This study deals with the stability of a stratified structure composed of a cohesive and frictional overburden, a viscous substratum, and a rigid basement. That structure should be seen as a prototype for various salt tectonics and lithospheric plates stability analyses. The destabilizing factors are the density contrast, the tectonic compressive stress, and the possible erosion and deposition at the top surface. The overburden stiffness, a nonlinear function of in situ stress, has a stabilizing role. Two solutions are extracted from the variational formulation of the stability problem previously proposed [Leroy and Triantafyllidis, 1996]: the first is analytical and is obtained by disregarding gravity, and the second is numerical and is based on the finite element method. The latter is used to assess the validity of the previously presented asymptotic solution. It is shown that the asymptotic solution is accurate even for values of the small parameter, defined as the perturbation wavenumber times the overburden thickness, as large as 0.4. Furthermore, the possibility for the cohesive material in the overburden to accommodate part of the deformation by slip along a population of small pervasive faults is accounted for by the introduction of a deformation theory of plasticity. Stability predictions based on this theory indicate that structural modes, such as folding, and localized faulting modes are triggered for similar stress magnitudes. The parametric study presented includes the previously undetected influences of the stress gradient with depth and of the work hardening properties of the competent overburden. The role of erosion and deposition in destabilizing shallow overburdens, regardless of the magnitude of the tectonic stress, is also established. The stability predictions are then applied to a folded section through the Campos basin, offshore Brazil, revealing that the deformation theory of plasticity is necessary to explain the buckling that occurred during the Albian

On Component Forces in Physics: A Pragmatic View

Do component forces exist? I argue that the answer lies in the affirmative, on historical and operational grounds

Unexpected Course of Nonlinear Cardiac Interbeat Interval Dynamics during Childhood and Adolescence

The fluctuations of the cardiac interbeat series contain rich information because they reflect variations of other functions on different time scales (e.g., respiration or blood pressure control). Nonlinear measures such as complexity and fractal scaling properties derived from 24 h heart rate dynamics of healthy subjects vary from childhood to old age. In this study, the age-related variations during childhood and adolescence were addressed. In particular, the cardiac interbeat interval series was quantified with respect to complexity and fractal scaling properties. The R-R interval series of 409 healthy children and adolescents (age range: 1 to 22 years, 220 females) was analyzed with respect to complexity (Approximate Entropy, ApEn) and fractal scaling properties on three time scales: long-term (slope β of the power spectrum, log power vs. log frequency, in the frequency range 10−4 to 10−2 Hz) intermediate-term (DFA, detrended fluctuation analysis, α2) and short-term (DFA α1). Unexpectedly, during age 7 to 13 years β and ApEn were higher compared to the age <7 years and age >13 years (β: −1.06 vs. −1.21; ApEn: 0.88 vs. 0.74). Hence, the heart rate dynamics were closer to a 1/f power law and most complex between 7 and 13 years. However, DFA α1 and α2 increased with progressing age similar to measures reflecting linear properties. In conclusion, the course of long-term fractal scaling properties and complexity of heart rate dynamics during childhood and adolescence indicates that these measures reflect complex changes possibly linked to hormonal changes during pre-puberty and puberty

Finite element analysis of the effect of cementing concepts on implant stability and cement fatigue failure

Background and purpose Two contradictory cementing techniques (using an undersized stem versus a canal-filling stem) can both lead to excellent survival rates, a phenomenon known as the “French paradox”. Furthermore, previous studies have indicated that the type of bone supporting the cement mantle may affect implant survival. To further evaluate the mechanical consequences of variations in cementing technique, we studied the effect of implant size and type of bone supporting the cement mantle on the mechanical performance of cemented total hip arthroplasty, using finite element analysis

Updating known distribution models for forecasting climate change impact on endangered species

To plan endangered species conservation and to design adequate management programmes, it is necessary to predict their distributional response to climate change, especially under the current situation of rapid change. However, these predictions are customarily done by relating de novo the distribution of the species with climatic conditions with no regard of previously available knowledge about the factors affecting the species distribution. We propose to take advantage of known species distribution models, but proceeding to update them with the variables yielded by climatic models before projecting them to the future. To exemplify our proposal, the availability of suitable habitat across Spain for the endangered Bonelli’s Eagle (Aquila fasciata) was modelled by updating a pre-existing model based on current climate and topography to a combination of different general circulation models and Special Report on Emissions Scenarios. Our results suggested that the main threat for this endangered species would not be climate change, since all forecasting models show that its distribution will be maintained and increased in mainland Spain for all the XXI century. We remark on the importance of linking conservation biology with distribution modelling by updating existing models, frequently available for endangered species, considering all the known factors conditioning the species’ distribution, instead of building new models that are based on climate change variables only.Ministerio de Ciencia e Innovación and FEDER (project CGL2009-11316/BOS

Back from a Predicted Climatic Extinction of an Island Endemic: A Future for the Corsican Nuthatch

The Corsican Nuthatch (Sitta whiteheadi) is red-listed as vulnerable to extinction by the IUCN because of its endemism, reduced population size, and recent decline. A further cause is the fragmentation and loss of its spatially-restricted favourite habitat, the Corsican pine (Pinus nigra laricio) forest. In this study, we aimed at estimating the potential impact of climate change on the distribution of the Corsican Nuthatch using species distribution models. Because this species has a strong trophic association with the Corsican and Maritime pines (P. nigra laricio and P. pinaster), we first modelled the current and future potential distribution of both pine species in order to use them as habitat variables when modelling the nuthatch distribution. However, the Corsican pine has suffered large distribution losses in the past centuries due to the development of anthropogenic activities, and is now restricted to mountainous woodland. As a consequence, its realized niche is likely significantly smaller than its fundamental niche, so that a projection of the current distribution under future climatic conditions would produce misleading results. To obtain a predicted pine distribution at closest to the geographic projection of the fundamental niche, we used available information on the current pine distribution associated to information on the persistence of isolated natural pine coppices. While common thresholds (maximizing the sum of sensitivity and specificity) predicted a potential large loss of the Corsican Nuthatch distribution by 2100, the use of more appropriate thresholds aiming at getting closer to the fundamental distribution of the Corsican pine predicted that 98% of the current presence points should remain potentially suitable for the nuthatch and its range could be 10% larger in the future. The habitat of the endemic Corsican Nuthatch is therefore more likely threatened by an increasing frequency and intensity of wildfires or anthropogenic activities than by climate change

Mitochondrial Diabetes in Children: Seek and You Will Find It

Maternally Inherited Diabetes and Deafness (MIDD) is a rare form of diabetes due to defects in mitochondrial DNA (mtDNA). 3243 A>G is the mutation most frequently associated with this condition, but other mtDNA variants have been linked with a diabetic phenotype suggestive of MIDD. From 1989 to 2009, we clinically diagnosed mitochondrial diabetes in 11 diabetic children. Diagnosis was based on the presence of one or more of the following criteria: 1) maculopathy; 2) hearing impairment; 3) maternal heritability of diabetes/impaired fasting glucose and/or hearing impairment and/or maculopathy in three consecutive generations (or in two generations if 2 or 3 members of a family were affected). We sequenced the mtDNA in the 11 probands, in their mothers and in 80 controls. We identified 33 diabetes-suspected mutations, 1/33 was 3243A>G. Most patients (91%) and their mothers had mutations in complex I and/or IV of the respiratory chain. We measured the activity of these two enzymes and found that they were less active in mutated patients and their mothers than in the healthy control pool. The prevalence of hearing loss (36% vs 75–98%) and macular dystrophy (54% vs 86%) was lower in our mitochondrial diabetic adolescents than reported in adults. Moreover, we found a hitherto unknown association between mitochondrial diabetes and celiac disease. In conclusion, mitochondrial diabetes should be considered a complex syndrome with several phenotypic variants. Moreover, deafness is not an essential component of the disease in children. The whole mtDNA should be screened because the 3243A>G variant is not as frequent in children as in adults. In fact, 91% of our patients were mutated in the complex I and/or IV genes. The enzymatic assay may be a useful tool with which to confirm the pathogenic significance of detected variants