Leonard Green & Partners

About: Leonard Green & Partners is a based out in . It is known for research contribution in the topics: Cronbach's alpha & Die (integrated circuit). The organization has 9 authors who have published 6 publications receiving 49 citations.

Concentration effect of TEMPO-oxidized nanofibrillated cellulose aqueous suspensions on the flow instabilities and small-angle X-ray scattering structural characterization

Abstract: The rheological behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized nanofibrillated cellulose (NFC) suspensions at different concentrations were examined using Couette with smooth and serrated surfaces and vane-in-cup geometries. A slippage against the walls of rheometer rotor or/and stator (wall-slip) as well as flow localization within a specific volume of the sample (shear banding) took place. These phenomena were visualized using a technique based on introduction of titanium dioxide pigment into the specific volume of NFC suspension and monitoring its deformation. The flow instabilities appeared more pronounced with an increase of the NFC concentration. It was shown that the use of serrated geometry is necessary to compete with the wall-slip but is not sufficient to prevent it completely. Serrated Couette was found to be the most appropriate geometry (among the tested) to measure the rheological properties of NFC suspensions. Small-angle X-ray scattering was used to provide a supplementary information about the structural organization of NFC suspensions. The statistical average diameter of 4.8 nm was determined from the scattering data for the NFC swollen in water.

Validation of the Postnatal Perceived Stress Inventory in a French Speaking Population of Primiparous Women

Abstract: Objective To develop a Postnatal Perceived Stress Inventory (PNPSI) and assess its psychometric properties. Design Cross-sectional quantitative study. Setting One nurse-managed labor and delivery unit in a university hospital in a major metropolitan area. Participants One hundred seventy-nine (179) primiparous French speaking women who gave birth at term. Methods The PNPSI was validated at 6 weeks postpartum. Its predictive validity for depression and anxiety was assessed at the same time. Results The exploratory analysis revealed a 19-item structure divided into six factors. This inventory has good internal consistency (Cronbach's alpha = .815). The predictive validity shows that the PNPSI significantly predicts depression and anxiety at 6 weeks postpartum, and that certain factors are particularly prominent. Conclusion The PNPSI's psychometric properties make it a useful tool for future research to evaluate interventions for perceived stress during the postnatal period. Its predictive power for depression indicates that it is also a promising tool for clinical settings.

Viscoplastic behavior of diamond die attach subjected to high temperature conditions

Abstract: In power electronic applications, diamond based semi-conductors appears to be a new way to widely increase the capabilities of power electronic converters [1, 2]. The main prospective expected is an increasing in system integration and power capabilities. The Diamonix project concerns the elaboration of a single-crystal diamond substrate with electronic quality and its associated packaging. The designed structure has to resist to temperatures varying between −50°C and +300°C. This paper deals with an experimental and numerical study of the diamond die attach solution. The development of a packaging for diamond component relies in particular on a specific choice of solder's alloys for the junction die/substrate. To carry out this junction, AuGe and AlSi eutectic alloys were chosen and characterized; the choice of these two kinds of solders i.e. AuGe and AlSi is motivated by the practical elaboration process and the restrictions of hazardous substances (RoHS). The first solder has a melting temperature of 356°C; the second has a higher melting point of 577°C. In this paper, we present some numerical results obtained from FE simulations of two 2D configurations of simplified electronic packaging. The power electronic packaging is composed of a diamond die and a copper metallized Si 3 N 4 ceramic substrate which are brazed together with either AuGe or AlSi solder alloy. To predict the thermomechanical behavior of the solders, a particular constitutive behavior law was implemented as a User MATerial subroutine which is based on a viscoplastic unified McDowell formulation, coupled with porous damage equations. The mechanical law can describe precisely the viscoplastic damage phenomenon of solder subjected to high thermal cycling and to optimize the thermo-mechanical modeling for advanced package development.

Efficiency and robustness of some behavior laws in the description of viscoplastic deformation and degradation of solder materials

Abstract: Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects. The complexity and interaction of such factors must be considered in suitable way in the mechanical behaviour modelling using the appropriate material behaviour laws. The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material… Following these observations and in order to deal with this critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model. That is the aim of this paper with application to a tin based solder token as the test material.

Dimensionnement d'un fuselage composite réalisé par infusion de résine = Numerical modeling of an aircraft composite fuselage manufactured by Liquid Resin Infusion

Abstract: Le projet FUSCOMP (FUSelage COMPosite) est un programme de Recherche & Developpement qui a recu la labellisation du pole de competitivite de l'Aerospace Valley. Il menera d'ici 2011 au test d'un demonstrateur de fuselage composite realise par le procede d'infusion de resine LRI (Liquid Resin Infusion). Ce procede utilise une resine liquide infusee dans des tissus secs plutot que des tissus preimpregnes, pour mettre en oeuvre des pieces en materiaux composites hautes performances. L'etude de ce demonstrateur technologique est basee sur la cellule du TBM 850, avion d'affaires pressurise monomoteur a turbopropulseur actuellement fabrique par DAHER-SOCATA. Les resultats concerneront les methodes numeriques et l'analyse par elements finis utilisees pour la modelisation de cette structure de fuselage composite. L'integration des structures composites est un sujet d'actualite dans les projets aeronautiques, puisque de plus en plus de structures (raidisseurs,...) sont integrees dans les revetements de fuselage. En effet les principaux avantages du LRI incluent des gains de temps de fabrication lies a l'integration de fonctions. En particulier l'infusion simultanee des elements de structure et de sous-structure doit permettre de s'affranchir du rivetage. Il est cependant necessaire de valider le dimensionnement de cette aerostructure composite etudiee.