Preparation and characterization of graphene/metal composites

Since the isolation of graphene in 2004, much research has been conducted to understand this novel material and how its properties can be utilized in different applications. One type of venture involves graphene as a reinforcing filler in metal matrix composites (MMC) which is becoming increasingly prevalent in the automotive and aerospace industries. Such composites combine the machinability and processing flexibility of metals with the unique properties of graphene. In fact, copper-graphene composites have demonstrated ameliorated mechanical strength with thermal conductivities elevated beyond pristine copper. However, the challenges that remain to commercialize copper-graphene composites are numerous. The most challengeable one is that graphene must be uniformly dispersed in the matrix and adhere to copper through an industrially scalable and affordable process. Moreover, the volume fraction of graphene must be efficiently controlled, lest superfluous amounts lead to structural detriment. In this regard, the emphasis of this study was to investigate a scalable and simple method to obtain such MMC via powder metallurgy. Specifically, gas atomized copper powder was functionalized with 3-aminopropyl-triethoxysilane (APTES) in toluene (APTES-Cu), resulting in a positively charged surface; then aqueously dispersed and negatively charged graphene oxide (GO) could then be self-assembled on the surface APTES@Cu via electrostatic interaction (Cu@APTES-Cu). The thickness of GO layers and morphology on the powder was controlled by modulating APTES grafting duration and APTES concentration in toluene. Cu@APTES-Cu powders were thermally annealed before compaction and sintering in inert atmosphere.The results show that surface modification of metal powders serves as a scalable and versatile approach to coat graphene on metal particles for the preparation of graphene/metal composites. Surface modification of copper with 0.2 vol% APTES in toluene for 30 minutes was sufficient to obtain composite powders with incomplete GO coating, which nonetheless demonstrated improved hardness. However, cold working of sintered composites was essential to densify the porous structure created by reduced GO during sintering. On the other hand, sintered composite samples that exhibited higher thermal conductivity than copper was obtained with higher APTES and GO loading. After thermal annealing, these thicker GO coatings were found to improve thermal conductivity in sintered composites by acting as thermal bridges between individual composite particles. Despite incomplete sintering of these composites, a 20% increase in thermal conductivity was attainable. Finally, both polarization scans and etching measurements in concentrated HCl and ammonium persulfate (APS) indicate that the GO coating decomposes on the outer surface during sintering. However, the reduced GO coating can retard corrosion of the internal composite structure by diffusion inhibition

High temperature mechanical properties of a zirconium-modified, precipitation- strengthened nickel, 30 percent copper alloy

A precipitation-strengthened Monel-type alloy has been developed through minor alloying additions of zirconium to a base Ni-30Cu alloy. The results of this exploratory study indicate that thermomechanical processing of a solution-treated Ni-30Cu-0.2Zr alloy produced a dispersion of precipitates. The precipitates have been tentatively identified as a Ni5Zr compound. A comparison of the mechanical properties, as determined by testing in air, of the zirconium-modified alloy to those of a Ni-30Cu alloy reveals that the precipitation-strengthened alloy has improved tensile properties to 1200 K and improved stress-rupture properties to 1100 K. The oxidation characteristics of the modified alloy appeared to be equivalent to those of the base Ni-30Cu alloy

Diagnostic des lésions étiologiques de l’infertilité secondaire à Cotonou : rôle de l’hystérosalpingographie et de l’échographie pelvienne

Objectif : L’infertilité est une préoccupation du couple et de la famille en milieu africain. Le but de cette étude est d’améliorer la prise en charge des femmes présentant une infertilité secondaire au Bénin.Méthodologie et résultats : Il s’est agi d’une étude descriptive de type transversal. Elle a porté sur 110 femmes béninoises venues au Centre National Hospitalier et Universitaire et au Centre Autonome de Radiologie pour la réalisation des examens d’hystérosalpingographie et/ou d’échographie pelvienne, dans le cadre de l’exploration d’une infertilité secondaire. La collecte des données a nécessité des fiches d’enquête qui ont permis de recueillir les renseignements concernant les caractéristiques sociodémographiques et épidémiologiques de ces femmes d’une part, et les résultats des différentes explorations effectuées d’autre part. L’âge moyen des femmes est de 33,7 ± 5,6 ans. Les primigestes et secondigestes (58,2%), ainsi que les nullipares et primipares (76,4%) sont les plus représentées. A l’hystérosalpingographie, les lésions utérines les plus décelées sont les myomes utérins dans 71,4 % des cas suivis des synéchies dans 22,8%, tandis que les lésions tubaires les plus représentées sont les obstructions tubaires bilatérales avec un pourcentage de 45,9%. A l’échographie pelvienne, les myomes sont les plus représentés avec un pourcentage de 94,6%, et une prédominance des myomes interstitiels dans 54,1% des cas. Avec un pourcentage de 63,3%, les dystrophies ovariennes micropolykystiques sont les lésions ovariennes les plus décelées.Conclusion et application : Si l’hystérosalpingographie et l’échographie pelvienne permettent toutes de poser le diagnostic du myome utérin, l’échographie pelvienne en précise le siège par rapport aux tuniques de l’utérus, ainsi que les mesures. Par ailleurs, lors de l’exploration de l’infertilité secondaire, l’HSG permet de déceler les lésions tubaires tandis que l’échographie pelvienne dépiste les lésions ovariennes. Il en ressort donc que ces deux explorations apportent de façon complémentaire, le diagnostic des lésions étiologiques dans la prise en charge de l’infertilité secondaire féminine.Mots-clés : Infertilité secondaire, étiologie, hystérosalpingographie, échographie pelvienne

Circumstances of occurrence of uterine ruptures treated in a national reference maternity department in Benin from 2015 to 2019

Background: Uterine rupture is an obstetric disaster and a major concern for the obstetrician in an African environment because of the insufficient technical support. Objective of current study was to study the circumstances of occurrence of uterine ruptures.Methods: The study was carried out at the university clinic of obstetrics and gynecology of CNHU-HKM in Cotonou. This was a descriptive and cross-sectional study with retrospective collection from January 1, 2015 to December 31, 2019. We made an exhaustive recruitment of all the patients treated in the department for uterine rupture during the study period. The study variables were socio-demographic and clinical characteristics. Data confidentiality and the anonymity of women were respected.Results: The study involved 85 cases of uterine rupture. Patients were relatively young with a mean age of 30±15.02 years. Women profile was that of populations with unfavorable socio-economic conditions. The circumstances of discovery were multiparity equal to or greater than 4 (43.5%), scarred uterus (32.9%), non-use of partogram (97.6%), osseous dystocia (10.9%) and fetal dystocia with fetal macrosomia (21.2%) and dystocic presentation (15.3%).Conclusions: This study identified epidemiological and clinical characteristics related to the circumstances of known uterine ruptures occurrence. A preventive and anticipatory oriented approach can reduce the frequency of that obstetric tragedy, the adequate management of which is often uncertain in Benin

X-ray pelvimetry: prognosis of delivery by cephalous-pelvic confrontation in Cotonou

Background: The mechanical dystocia constitutes one of the causes of maternal death during labour. Reducing the incidence of complications of dystocia means recognize the factors induce dystocia. That justifies X-ray pelvimetry and cephalic fetal ultrasonography to predict the outcome of labour. This survey aims at establishing the prognosis of labour by a cephalous-pelvic confrontation.Methods: This study was realised at CUGO and HOMEL, reference maternity hospitals in Cotonou from 28th March to 4th August 2006. That was a prospective study. During prenatal visit, pregnant women who had pelvis abnormality were recruited after their consent after counselling about exploration of their pelvis and fetal cephalic diameters. Pregnant women in their ninth month underwent to X-ray pelvimetry and fetal biometric ultrasonography.Results: During that study, 122 pregnant women in their ninth month were recruited. Favourable prognosis (36.89%): natural delivery 31.15%; (concordance rate is 84.44%). Uncertain prognosis (18.85%): caesarean section (10.66%), natural delivery (7.37%). Unfavourable prognosis (44.26%): 40.16% deliveries by caesarean section. Concordance rate is 90.74%.Conclusions: The cephalous-pelvic confrontation is a reliable prognosis method. It is recommendable in our maternity hospitals to prevent complications of dystocia, a cause of maternal death

Acts of Requesting in Dynamic Logic of Knowledge and Obligation

Although it seems intuitively clear that acts of requesting are different from acts of commanding, it is not very easy to sate their differences precisely in dynamic terms. In this paper we show that it becomes possible to characterize, at least partially, the effects of acts of requesting and compare them with the effects of acts of commanding by combining dynamified deontic logic with epistemic logic. One in- teresting result is the following: each act of requesting is appropriately differenti- ated from an act of commanding with the same content, but for each act of request- ing, there is another act of commanding with much more complex content which updates models in exactly the same way as it does. We will also consider an application of our characterization of acts of requesting to acts of asking yes-no questions. It yields a straightforward formalization of the view of acts of asking questions as requests for information