62,671 research outputs found
Govaert (Marcel). La langue et le style de Marnix de Sainte- Aldegonde dans son « Tableau des Différens de la Religion ».
No full textDe Grève Marcel. Govaert (Marcel). La langue et le style de Marnix de Sainte- Aldegonde dans son « Tableau des Différens de la Religion ».. In: Revue belge de philologie et d'histoire, tome 33, fasc. 1, 1955. pp. 105-110
Govaert (Marcel). La langue et le style de Marnix de Sainte- Aldegonde dans son « Tableau des Différens de la Religion ».
No full textDe Grève Marcel. Govaert (Marcel). La langue et le style de Marnix de Sainte- Aldegonde dans son « Tableau des Différens de la Religion ».. In: Revue belge de philologie et d'histoire, tome 33, fasc. 1, 1955. pp. 105-110
Modelling the Rate- and Temperature-Dependent Micro-Mechanical Behaviour of Carbon Fiber Reinforced PVDF
No full textThe conditions to which fiber reinforced plastics (FRPs) are exposed in state of the art applications are becoming more extreme, for example in the offshore oil and gas industry. Therefore,
the ability to predict the long-term behaviour, and thereby identifying the failure mechanisms,
of fiber reinforced plastics is of great importance. Especially under these extreme conditions,
the contribution of the matrix plays an important role and a detailed description of its behaviour
is required. In oil and gas applications, polyvinylidene fluoride (PVDF) is used because of
its excellent gas barrier properties. In this work the rate- and temperature-dependent micromechanical behaviour of carbon fiber reinforced polyvinylidene fluoride is studied.
The behaviour of the composite is studied by using a micro-mechanical model that is composed
of individually modelled carbon fibers embedded in a PVDF matrix. The time- and temperature dependent behaviour of PVDF is captured by the Eindhoven Glassy Polymer (EGP) constitutive
model [1]. This model enables the description of the intrinsic behaviour of the semi-crystalline
matrix over a range of applied strain rates and temperatures using a single set of material parameters. The characterization of these material parameters, requires a set of experimental data
obtained from uniaxial compression and tensile tests performed at different temperatures and
applied strain rates. To describe the material behaviour of the individually modelled carbon
fibers, an elastic orthotropic material model is employed. Off-axis tensile tests of the composite
led to the observation that the interface behaviour between matrix and fiber must be incorporated in the micro-mechanical model as well. Subsequently, an interface between the matrix
and fiber is added to the model by using cohesive zone interface elements. The behaviour of
these interface elements is described by an appropriate constitutive relation.
It is demonstrated what influence the rate- and temperature dependence of PVDF, described
by the EGP-model, and the behaviour of the interface elements have on the micro-mechanical
response of the composite
Plastic deformation of glassy polymers: correlation between shear activation volume and entanglement density
No full textThe structural relaxation caused by the plastic deformation of polymer glasses is not yet fully understood. In particular, the size scale of the localized plastic relaxation events is currently unknown. In this work, the effect of molecular entanglement density on the shear activation volume of glassy polymers has been studied. The shear activation volumes of miscible polystyrene?poly(2,6-dimethyl-1,4-phenylene oxide) (PS?PPO) blends at different PS/PPO ratios have been determined experimentally by both plane-strain and uniaxial compression at constant strain rates. We find that the same correlation between the shear activation volume and the entanglement density ?e holds for the blend as well as for various pure glassy polymers:? = C(?e/nm-3)? + V0, with C = 8.2 ± 0.4 nm3, ? = 0.6 ± 0.03, and V0 < 0.1 nm3. The shear activation volume is closely related to the size of the plastic shear zones; therefore, this correlation suggests that the cooperativity of the elementary processes of plastic deformation in glassy polymers scales with ?e
Estimation d'un modèle à blocs latents par l'algorithme SEM
No full textInternational audienceLes modèles de mélanges peuvent être utilisés pour résoudre le problème de la classification non supervisée simultanée d'un ensemble d'objets et d'un ensemble de variables. Le modèle à blocs latents définit une loi pour chaque croisement de classe d'objets et de classe de variables, et les observations sont supposées indépendantes conditionnellement au choix des classes d'objets et de variables. Mais il n'est pas possible de factoriser la loi jointe conditionnelle des labels et l'étape d'estimation de l'algorithme EM n'est pas calculable directement. Govaert et Nadif (2008) en ont proposé une approximation variationnelle qu'ils ont confrontée à un algorithme CEM. Nous présentons ici, dans le cadre de données binaires, l'utilisation d'un algorithme SEM effectuant l'étape d'estimation par échantillonneur de Gibbs, et nous comparons les résultats avec ceux des méthodes précédentes
Estimation d'un modèle à blocs latents par l'algorithme SEM
No full textInternational audienceLes modèles de mélanges peuvent être utilisés pour résoudre le problème de la classification non supervisée simultanée d'un ensemble d'objets et d'un ensemble de variables. Le modèle à blocs latents définit une loi pour chaque croisement de classe d'objets et de classe de variables, et les observations sont supposées indépendantes conditionnellement au choix des classes d'objets et de variables. Mais il n'est pas possible de factoriser la loi jointe conditionnelle des labels et l'étape d'estimation de l'algorithme EM n'est pas calculable directement. Govaert et Nadif (2008) en ont proposé une approximation variationnelle qu'ils ont confrontée à un algorithme CEM. Nous présentons ici, dans le cadre de données binaires, l'utilisation d'un algorithme SEM effectuant l'étape d'estimation par échantillonneur de Gibbs, et nous comparons les résultats avec ceux des méthodes précédentes
Deformation and failure kinetics of polyvinylidene fluoride: Influence of crystallinity
No full textThe present study investigates the effect of processing conditions on the yield kinetics, such as rate dependence of the yield stress and creep rupture, of polyvinilidene fluoride. Samples were compression molded with cooling rates varying from 100°C/s to 0.5°C/min, or isothermally crystallized at temperatures varying from 20 to 120°C. Deformation kinetics were studied over a wide range of strain rates and temperatures. It is shown that for all conditions the yield response is well represented by the Ree–Eyring model. Moreover, the activation volumes and activation energies are independent from the processing conditions. The effect of processing is fully covered by a simple relationship between the rate factors and the degree of crystallinity. Subsequently, the versatility of this relationship is demonstrated by experimental validation
Q&A: Peter Kimani, author of Dance of the Jakaranda, talks with Maëline Le Lay
No full textAfrica in Words. https://africainwords.com/2019/05/23/qa-peter-kimani-author-of-dance-of-the-jakaranda-talks-with-maeline-le-lay
FlexMix Version 2: Finite Mixtures with Concomitant Variables and Varying and Constant Parameters
No full textflexmix provides infrastructure for flexible fitting of finite mixture models in R using the expectation-maximization (EM) algorithm or one of its variants. The functionality of the package was enhanced. Now concomitant variable models as well as varying and constant parameters for the component specific generalized linear regression models can be fitted. The application of the package is demonstrated on several examples, the implementation described and examples given to illustrate how new drivers for the component specific models and the concomitant variable models can be defined.
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