Silver‐doped hydroxyapatite (AgHAp) was prepared by co‐precipitation method at room temperature. The obtained AgHAp was added in different amounts of collagen gel (AgHApC1 and AgHApC2). Afterward, the gel was lyophilized and the final AgHApC1 and AgHApC2 composite was achieved. The purity, crystallinity, and the phase composition of the AgHAp, AgHApC1, and AgHApC2 samples were evaluated by X‐ray diffraction (XRD). The planes corresponding to the 2θ values for hydroxyapatite were found in the three samples analyzed in agreement with the crystalline hydroxyapatite. In the Fourier transform infrared (FT‐IR) spectra of AgHApC1 and AgHApC2 samples the peak characteristic to the presence of ν2 phosphate mode at 472/cm was found. The peaks resulting from the ν4 vibration of the P–O mode, ν1 symmetric P–O stretching vibration and ν3 P–O stretching vibration of PO43− were also evidenced in all the samples. The formation of agglomerated particles with uniform particle size was evidenced by scanning electron microscope (SEM). The uniform distribution of the constituent elements was evidenced by mapping analysis. Furthermore, the strong antibacterial activity of AgHAp, AgHApC1, and AgHApC2 samples against Gram‐negative (Escherichia coli) and Gram‐positive (Staphylococcus aureus) bacterial strains was shown. The inhibition zone increased drastically with the increase of silver concentration. POLYM. ENG. SCI., 57:537–545, 2017. © 2017 Society of Plastics Engineers

Guided waves became in recent years an useful tool in nondestructive testing of pipes used in many industrial applications. The torsional and longitudinal waves in pipes are the main choice for integrity inspection. The first step is the computation of the dispersion curves, for straight pipes. Since most pipes have bends, the problem of guided modes in the toroidal segment remains of interest. Various methods have been applied to solve this problem. The most promising numerical method to obtain the dispersion curves for a torus is based on finite elements (FE), using a standing waves model. Based on these dispersion curves, transmissions of longitudinal and torsional waves through a bend were also investigated. The present paper presents the scattering process produced by geometrical discontinuities such as circumferential welds before and after a pipe bend. Longitudinal L(0,2) mode is sent along the straight pipe in FE simulations, toward the bend. Reflected and transmitted modal amplitudes are determined for frequencies of interest. The capability of detecting a defect close to one of the two welds is thus assessed. The modes transmitted past the bend are also characterized. Comparisons with results obtained by other researchers are used to validate the method.

Guided waves represent promising non-destructive evaluation (NDE) techniques. Their advantage of long distance propagation is however hampered by complex wave scattering at each discontinuity along the investigated structure. These scattered waves can be used to locate and size possible defects. Theoretical investigation is a prerequisite step in the development of a NDE technique. Planar metallic structures with localized thickness variation imposed by design represent possible new industrial structures that could be tested using guided waves. The waves scattered at the region of variable thickness must be theoretically predicted and experimentally measured before any defect could be detected. Very few authors have investigated waveguides with continuous variation of thickness. Our previous numerical and experimental studies have proven the complexity of the scattering phenomenon in such cases. Among other remarks is the curved shape of the wave front. The present work investigates properties of the waves in the linear thickness variation region of the waveguide. A plain strain model is theoretically investigated and numerically tested using specialized finite elements based algorithms. Specific properties such as stress and displacements fields are determined by numerical simulation at several frequencies and slope angles.

Ultrasonic piezoelectric transducers used in classical nondestructive testing are producing in general longitudinal vibrations in the MHz range. A simple mechanical model of these transducers would be very useful for wave propagation numerical simulations, avoiding the existing complicated models in which the real components of the transducer are modeled by finite elements. The classical model for longitudinal vibrations is not adequate because the generated longitudinal wave is not dispersive, the velocity being the same at any frequency. We have adopted the Rayleigh-Bishop model, which avoids these limitations, even if it is not converging to the first but to the second exact longitudinal mode in an elastic rod, as obtained from the complicated Pochhammer-Chree equations. Since real transducers have significant vibrations damping, we have introduced a damping term in the Rayleigh-Bishop model, increasing the imaginary part and keeping almost identical real part of the wavenumber. Common transducers produce amplitude modulated signals, completely attenuated after several periods. This can be modeled by two close frequencies, producing a “beat” phenomenon, superposed on the high damping. For this reason, we introduce a two-rod Rayleigh-Bishop model with damping. Agreement with measured normal velocity on the transducer free surface is encouraging for continuation of the research.

Le problème de l’échec scolaire dynamise l’espace pédagogique réflexif depuis longtemps. Notre étude vise à interpréter les situations à risque scolaire, en construisant un modèle familial de l’échec scolaire. Par modèle familial de l’échec scolaire nous comprenons les expériences négatives de l’école qu’ont connues les parents et qui génèrent chez l’enfant des représentations hostiles envers l’école. Selon cette perspective, l’échec scolaire est un effet transgénérationnel de certains habitus inculqués dans la famille. Pour vérifier l’hypothèse, la méthode principale d’obtention des informations relatives à l’attitude des adultes envers leur propre expérience scolaire est l’enquête, sous ses deux formes : le questionnaire et l’entretien. Nous chercherons à obtenir des informations concernant les performances scolaires des parents, les croyances des parents au sujet de l’école, les messages émis sur l’importance de l’école vers les enfants, le contrôle de l’activité scolaire des enfants, l’image et les croyances que les enfants ont au sujet de l’école. Les résultats sont corrélés avec des indicateurs factuels tels que le sexe, le niveau d’éducation, le nombre des membres de la famille, le revenu. Les recherches seront menées dans les communautés urbaines et rurales du département de Constanţa. L’échantillon est d’une taille de N=140 élèves (des classes V e -VIII e , la moitié d’entre eux se trouvant en situation de risque scolaire) et de N=280 parents.