Visco-hyperelastic model with damage for simulating cyclic thermoplastic elastomers behavior applied to an industrial component

In this work a nonlinear phenomenological visco-hyperelastic model including damage consideration is developed to simulate the behavior of Santoprene 101-73 material. This type of elastomeric material is widely used in the automotive and aeronautic sectors, as it has multiple advantages. However, there are still challenges in properly analyzing the mechanical phenomena that these materials exhibit. To simulate this kind of material a lot of theories have been exposed, but none of them have been endorsed unanimously. In this paper, a new model is presented based on the literature, and on experimental data. The test samples were extracted from an air intake duct component of an automotive engine. Inelastic phenomena such as hyperelasticity, viscoelasticity and damage are considered singularly in this model, thus modifying and improving some relevant models found in the literature. Optimization algorithms were used to find out the model parameter values that lead to the best fit of the experimental curves from the tests. An adequate fitting was obtained for the experimental results of a cyclic uniaxial loading of Santoprene 101-73

A New Multiparameter Model for Multiaxial Fatigue Life Prediction of Rubber Materials

Most of the mechanical components manufactured in rubber materials experience fluctuating loads, which cause material fatigue, significantly reducing their life. Different models have been used to approach this problem. However, most of them just provide life prediction only valid for each of the specific studied material and type of specimen used for the experimental testing. This work focuses on the development of a new generalized model of multiaxial fatigue for rubber materials, introducing a multiparameter variable to improve fatigue life prediction by considering simultaneously relevant information concerning stresses, strains, and strain energies. The model is verified through its correlation with several published fatigue tests for different rubber materials. The proposed model has been compared with more than 20 different parameters used in the specialized literature, calculating the value of the R-2 coefficient by comparing the predicted values of every model, with the experimental ones. The obtained results show a significant improvement in the fatigue life prediction. The proposed model does not aim to be a universal and definitive approach for elastomer fatigue, but it provides a reliable general tool that can be used for processing data obtained from experimental tests carried out under different conditions

Acute mountain sickness susceptibility and basic cognitive function after a brief simulated altitude of 4800 M

Twelve climbers with not been exposed in the last 12 months at high altitude were evaluated using verbal, spatial, reasoning and numerical tasks from Thurstone''s (1969) Primary Mental Abilities (PMA) test. These tasks were undertaken before and immediately after completing the Richalet et al. (1988) Normobaric Hypoxic (NH) test, which evaluates the acute mountain sickness (AMS) risk using a FiO2 of 11.5% during rest and exercise. A control group of eight climbers did not perform the NH test, so as to rule out the possible learning effect of the PMA test. Four participants (33%) from the experimental group were classified as having high-susceptibility to AMS. However, the PMA test performed after the NH test did not significantly differ from the one carried out before the NH test or from the cognitive abilities measured in the control group (p > .05)

Research progress on numerical models for self‐healing cementitious materials

The paper discusses research progress on numerical models for self-healing cementitious materials (SHCMs). The paper considers models developed specifically for SHCMs, as well as other relevant work. This article provides a summary of current self-healing techniques along with descriptions of the processes that govern their behaviour. The paper discusses models for mechanical self-healing, transport processes in materials with embedded healing systems, fully coupled models and other modelling techniques used to simulate SH behaviour. The mechanics models discussed include those based on continuum-damage-healing mechanics (CDHM), micro-mechanics, as well as models that use discrete elements and particle methods. A considerable section is devoted to the simulation of carbonation in concrete since the essential mechanisms that govern this process are applicable to SH systems that employ calcite as a healing material. A number of transport models for simulating early-age self-healing are also considered. The paper highlights the fact that there are currently very few papers that describe fully-coupled models, although a number of approaches that couple some aspects of transport and mechanical healing behaviour are discussed. This article closes with a discussion that highlights the fact that many models have been presented with limited or no experimental validation

Modelado del proceso de angiogénesis en cicatrización de heridas por el Método de los Elementos Finitos

El proceso de angiogénesis consiste en la formación de nuevos vasos sanguíneos a partir devasos preexistentes. Este fenómeno está presente en numerosos procesos biológicos, talescomo la regeneración de tejidos (piel y hueso) y el crecimiento de tumores, y realiza un papelmuy importante en los mismos. En este trabajo se ha estudiado el proceso de angiogénesis enla cicatrización de heridas en la piel ya que la capacidad de las heridas para cicatrizar dependeen gran medida de la capacidad de los nuevos vasos para formarse. El proceso de cicatrizaciónestá formado por tres etapas: inflamación, proliferación y remodelación. Dentro de la segundaetapa se produce el fenómeno de angiogénesis. Este proceso está regulado tanto por factoresbiológicos (células) y químicos (oxígeno, factores de crecimiento) como por estímulosmecánicos. En este trabajo se ha realizado la implementación de un modelo numérico conelementos finitos del proceso de angiogenésis para estudiar su efecto en heridas planas en dosdimensiones. Para ello se han incorpordo diferentes factores bioquímicos y mecánicos demanera desacoplada y se ha estudiado su efecto en el proceso de angiogenesis y en el cambiode geometría de la herida

Leptin and TNF-alpha promoter methylation levels measured by MSP could predict the response to a low-calorie diet

Obesity-associated adipose tissue enlargement is characterized by an enhanced proinflammatory status and an elevated secretion of adipokines such as leptin and cytokines such as TNF-alpha. Among the different mechanisms that could underlie the interindividual differences in obesity, epigenetic regulation of gene expression has emerged as a potentially important determinant. Therefore, twenty-seven obese women (age: 32-50 years; baseline Body Mass Index, BMI: 34.4±4.2 Kg/m2) were prescribed an eight-week Low-Calorie-Diet and epigenetic marks were assessed. Baseline and endpoint anthropometric parameters were measured and blood samples were drawn. Genomic DNA and RNA from adipose tissue biopsies were isolated before and after the dietary intervention. Leptin and TNF-alpha promoter methylation were measured by MSP after bisulfite treatment and gene expression was also analyzed. Obese women with a successful weight loss (≥5% of initial body weight, n=21) improved the lipid profile and fat mass percentage (-12%, p<0.05). Both systolic (-5%, p<0.05) and diastolic (-8%, p<0.01) blood pressures significantly decreased. At baseline women with better response to the dietary intervention showed lower promoter methylation levels of leptin (-47%, p<0.05) and TNF-alpha (-39%, p=0.071) than the non-responder group (n=6), while no differences were found between responder and non-responder group in leptin and TNF-alpha gene expression analysis. These data suggest that leptin and TNF-alpha methylation levels could be used as epigenetic biomarkers concerning the response to a Low-Calorie-Diet. Indeed, methylation profile could help to predict the susceptibility to weight loss as well as some comorbidities such as hypertension or type 2 diabetes

A pilot study of a phenomenological model of adipogenesis in maturing adipocytes using Cahn–Hilliard theory

We consider the accumulation and formation of lipid droplets in an adipocyte cell. The process incorporates adipose nucleation (adipogenesis) and growth. At later stages, there will be merging of droplets and growth of larger droplets at the expense of the smaller droplets, which will essentially undergo lipolysis. The process is modeled by the use of the Cahn–Hilliard equation, which is mass-conserving and allows the formation of secondary phases in the context of spinodal decomposition. The volume of fluid (VOF) method is used to determine the total area that is occupied by the lipids in a given cross section. Further, we present an algorithm, applicable to all kinds of grids (structured or unstructured) in two spatial dimensions, to count the number of lipid droplets and the portion of the domain of computation that is occupied by the lipid droplets as a function of time during the process. The results are preliminary and are validated from a qualitative point using experiments carried out on cell cultures. It turns out that the Cahn–Hilliard theory can model many of the features during adipogenesis qualitatively

Genetic, environmental and stochastic factors in monozygotic twin discordance with a focus on epigenetic differences

PMCID: PMC3566971This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Genome-wide association and HLA fine-mapping studies identify risk loci and genetic pathways underlying allergic rhinitis

Allergic rhinitis is the most common clinical presentation of allergy, affecting 400 million people worldwide, with increasing incidence in westernized countries1,2. To elucidate the genetic architecture and understand the underlying disease mechanisms, we carried out a meta-analysis of allergic rhinitis in 59,762 cases and 152,358 controls of European ancestry and identified a total of 41 risk loci for allergic rhinitis, including 20 loci not previously associated with allergic rhinitis, which were confirmed in a replication phase of 60,720 cases and 618,527 controls. Functional annotation implicated genes involved in various immune pathways, and fine mapping of the HLA region suggested amino acid variants important for antigen binding. We further performed genome-wide association study (GWAS) analyses of allergic sensitization against inhalant allergens and nonallergic rhinitis, which suggested shared genetic mechanisms across rhinitis-related traits. Future studies of the identified loci and genes might identify novel targets for treatment and prevention of allergic rhinitis