Identification of viscoplastic parameters and characterization of Lüders behaviour using digital image correlation and the virtual fields method

In this study, tensile loading experiments are performed on notched steel bars at an average applied strain rate of 1s-1. Displacement fields are measured across the specimen by coupling digital image correlation (DIC) with imaging using high speed CCD cameras (4796 fps). Results from the experiments indicate the presence of local strain rates ranging from 0.1 to 10s-1 in the notched specimens. The heterogeneity of the strain rate fields provides suitable conditions for determining simultaneously all the elasto-visco-plastic constitutive parameters governing the material behavior. For that, the whole stress fields are reconstructed in the specimen using the full-field deformation measurements. This reconstruction is repeated with different constitutive parameters until the average stress in the specimen matches the one measured with the load cell response. Perzyna’s model is firstly considered for the reconstruction of stresses but it is shown to be unsuited for providing the drop in the average stress that is systematically detected at the onset of plasticity by the load cell. This drop is attributed to the sudden occurrence of plasticity in the material due to Lüders effect. A modified model for elasto-visco-plasticity taking account of Lüders behavior in the material is considered afterwards. It yields a better agreement between the reconstructed stresses and the load cell response, and a more accurate identification of the parameters driving the visco-plastic model. Eventually, it is shown how to use DIC measurements for replacing the load cell measurements when the transient effects in the test reach the resonance frequency of the load cel

No evidence for social immunity in co-founding queen associations.

Ant queens often associate to found new colonies, yet the benefits of this behaviour remain unclear. A major hypothesis is that queens founding in groups are protected by social immunity and can better resist disease than solitary queens, due to mutual grooming, sharing of antimicrobials, or higher genetic diversity among their workers. We tested this hypothesis by manipulating the number of queens in incipient colonies of Lasius niger and measuring their resistance to the fungal entomopathogen Metarhizium brunneum. We found no evidence for social immunity in associations of founding queens. First, co-founding queens engaged in self-grooming, but performed very little allo-grooming or trophallaxis. Second, co-founding queens did not exhibit higher pathogen resistance than solitary queens, and their respective workers did not differ in disease resistance. Finally, queens founding in groups increased their investment in a component of individual immunity, as expected if they do not benefit from social immunity but respond to a higher risk of disease. Overall, our results provide no evidence that joint colony founding by L. niger queens increases their ability to resist fungal pathogens

Male production by workers in the polygynous ant Prolasius advenus

The ability of workers to produce male individuals is reported here for the first time in a species of the formicine ant genus Prolasius. We show that Prolasius advenus workers possess ovaries and demonstrate that they are able to produce adult males in queenless colonies. We also experimentally tested the influence of queen volatiles on the level of worker reproduction. Workers produced fewer eggs in treatments where they could perceive odors from queens. Some volatile compounds emitted by queens may thus have a signaling or inhibitory effect on worker reproduction. This effect of queen presence did not entirely stop worker reproduction, however, as adult males still emerged under these conditions. Worker-produced males were absent only in treatments with the physical presence of queens. Dissections of workers collected from queenright nests in the field revealed signs of egg-laying activity in more than half of individuals. Together, these results suggest that in nature P. advenus workers produce males at least in orphaned colonies or in situations where the physical presence of queens is limited

Mechanical identification of layer-specific properties of mouse carotid arteries using 3D-DIC and a hyperelastic anisotropic constitutive model

The role of mechanics is known to be of primary order in many arterial diseases; however, determining mechanical properties of arteries remains a challenge. This paper discusses the identifiability of the passive mechanical properties of a mouse carotid artery, taking into account the orientation of collagen fibres in the medial and adventitial layers. On the basis of 3D digital image correlation measurements of the surface strain during an inflation/extension test, an inverse identification method is set up. It involves a 3D finite element mechanical model of the mechanical test and an optimisation algorithm. A two-layer constitutive model derived from the Holzapfel model is used, with five and then seven parameters. The five-parameter model is successfully identified providing layer-specific fibre angles. The seven-parameter model is over parameterised, yet it is shown that additional data from a simple tension test make the identification of refined layer-specific data reliable.Comment: PB-CMBBE-15.pd

L?mites y alcances para la evaluaci?n de la pol?tica p?blica de deserci?n escolar caso: Pol?tica p?blica de educaci?n 2010-2014 en Ibagu? (Tolima)

107 p. Recurso Electr?nicoEntre los a?os 2010-2014 en Colombia se da el proceso de implementaci?n y ejecuci?n de la Pol?tica P?blica de Educaci?n Nacional implementado y desarrollado bajo el gobierno de Juan Manuel Santos Calder?n. Esta pol?tica educativa se enfoca en aspectos como: la deserci?n escolar, cobertura, calidad educativa, acceso y permanencia de los estudiantes en el sistema educativo entre otros. As?, la presente investigaci?n se propone proporcionar al lector una mirada sobre los l?mites y alcances que tuvo dicha pol?tica p?blica educativa en lo que corresponde al municipio de Ibagu?, usando como herramienta principal algunos enfoques de evaluaci?n del campo de la pol?tica p?blica. El ejercicio se realiz? desde una perspectiva cualitativa y cuantitativa de an?lisis descriptivo y documental, en la que se propuso relacionar la informaci?n obtenida en funci?n de los enfoques de la investigaci?n. Palabras Clave: Pol?tica- Pol?tica P?blica - Educaci?n- Deserci?n EscolarBetween 2010-2014 in Colombia the process of implementation and execution of the Public Policy of National Education is implemented and developed under Juan Manuel Santos Calder?n government. This educational policy focuses on aspects such as: School dropout, coverage, educational quality, access and permanence of students in the education system among others. The aims of this investigation are to provide the reader both a look to the limits and the significance especially in Ibague and highlighting some assessment process of Public Educational Policy. This exercise attempts to demonstrate a quantitative and qualitative perspective with a descriptive analysis documentary in order to focus the data obtained into the research approaches. Keywords: Politics- Public Policy- Education- School Dropou

Identification of plastic constitutive parameters at large deformations from three dimensional displacement fields

The aim of this paper is to provide a general procedure to extract the constitutive parameters of a plasticity model starting from displacement measurements and using the Virtual Fields Method. This is a classical inverse problem which has been already investigated in the literature, however several new features are developed here. First of all the procedure applies to a general three-dimensional displacement field which leads to large plastic deformations, no assumptions are made such as plane stress or plane strain although only pressure-independent plasticity is considered. Moreover the equilibrium equation is written in terms of the deviatoric stress tensor that can be directly computed from the strain field without iterations. Thanks to this, the identification routine is much faster compared to other inverse methods such as finite element updating. The proposed method can be a valid tool to study complex phenomena which involve severe plastic deformation and where the state of stress is completely triaxial, e.g. strain localization or necking occurrence. The procedure has been validated using a three dimensional displacement field obtained from a simulated experiment. The main potentialities as well as a first sensitivity study on the influence of measurement errors are illustrated

Electrochemistry and application of a novel monosubstituted squarate electron-transfer mediator in a glucose oxidase-doped poly(phenol) sensor

Electrosynthetic poly(phenol) nanofilms were deposited in situ on platinum electrodes in the presence and absence of glucose oxidase. The synthesis charges and currents of the nonconducting polymer films were recorded at various applied potentials for films grown from 25–100 mM phenol concentrations. Film parameters such as the standard rate constant for film deposition, film thickness, and surface concentration of the poly(phenol) films were evaluated from the cyclic and step voltammograms of the polymerization process. A novel electron-transfer mediator consisting of monosubstituted 4-hydroxycyclobut-3-ene-1,2-dione (squarate) was used as a mediator for Pt/poly(phenol) nano-film/GOx amperometric glucose biosensors. Amperometric responses for 3-diphenylamino-4-hydroxycyclobut-3-ene-1,2- dione (diphenylaminosquarate: E°′ = of +328 mV/Ag-AgCl at pH 7.0)-mediated systems were measured by both steady-state amperometric and cyclic voltammetry. The sensor sensitivity was calculated to be 558 nA cm –2 (µM) –1

Discovery-dominance trade-off among widespread invasive ant species.

Ants are among the most problematic invasive species. They displace numerous native species, alter ecosystem processes, and can have negative impacts on agriculture and human health. In part, their success might stem from a departure from the discovery-dominance trade-off that can promote co-existence in native ant communities, that is, invasive ants are thought to be at the same time behaviorally dominant and faster discoverers of resources, compared to native species. However, it has not yet been tested whether similar asymmetries in behavioral dominance, exploration, and recruitment abilities also exist among invasive species. Here, we establish a dominance hierarchy among four of the most problematic invasive ants (Linepithema humile, Lasius neglectus, Wasmannia auropunctata, Pheidole megacephala) that may be able to arrive and establish in the same areas in the future. To assess behavioral dominance, we used confrontation experiments, testing the aggressiveness in individual and group interactions between all species pairs. In addition, to compare discovery efficiency, we tested the species' capacity to locate a food resource in a maze, and the capacity to recruit nestmates to exploit a food resource. The four species differed greatly in their capacity to discover resources and to recruit nestmates and to dominate the other species. Our results are consistent with a discovery-dominance trade-off. The species that showed the highest level of interspecific aggressiveness and dominance during dyadic interactions

Excess androgen production in subcutaneous adipose tissue of women with polycystic ovarian syndrome

© 2019 Society for Endocrinology Published by Bioscientifica Ltd. The purpose of this study was to investigate androgen production and the role of insulin and LH in its regulation in subcutaneous adipose tissue (SAT) of women with polycystic ovarian syndrome (PCOS). Protein and mRNA expression of androgen synthesis enzymes (cytochrome P450 17A1 (CYP17A1) and aldo-keto reductase 1C3 (AKR1C3)) were measured in SAT biopsies from women with PCOS, diagnosed according to the Rotterdam criteria (n = 15) and healthy controls (n = 15). Cultured mature adipocytes (differentiated from SAT biopsies) were treated with insulin ± phosphoinositol-3-kinase inhibitor (LY294002) or LH ± insulin. CYP17A1 and AKR1C3 mRNA expression and testosterone concentrations were measured in treated and untreated adipocyte cultures. AKR1C3 mRNA was significantly (P < 0.001) greater in PCOS vs non-PCOS SAT, but CYP17A1 was not significantly different between the two groups. AKR1C3 and CYP17A1 protein expression was not significantly different in PCOS vs non-PCOS SAT. In untreated adipocyte cultures, CYP17A1, AKR1C3 and testosterone levels were significantly higher in the PCOS vs the non-PCOS groups. Addition of insulin increased AKR1C3 mRNA and testosterone levels, but not CYP17A1 mRNA in non-PCOS with no effect on PCOS adipocytes. The stimulatory effects of insulin were not inhibited by LY294002. Addition of LH increased CYP17A1, AKR1C3 and testosterone in non-PCOS adipocytes with no effect in PCOS adipocytes. In conclusion, SAT of women with PCOS produces excess androgen, which may contribute to PCOS-related hyperandrogenaemia. This SAT androgen excess is independent of obesity and is not directly stimulated by inulin or LH